Group Title: investigation of the potential for the use of organic fertilizer on small, mixed farms in Costa Rica /
Title: An investigation of the potential for the use of organic fertilizer on small, mixed farms in Costa Rica /
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 Material Information
Title: An investigation of the potential for the use of organic fertilizer on small, mixed farms in Costa Rica /
Physical Description: vi, 262 leaves : map ; 28 cm.
Language: English
Creator: Swisher, Marilyn E., 1948-
Publication Date: 1982
Copyright Date: 1982
Subject: Compost   ( lcsh )
Organic fertilizers -- Costa Rica   ( lcsh )
Farms, Small -- Costa Rica   ( lcsh )
Geography thesis Ph. D   ( lcsh )
Dissertations, Academic -- Geography -- UF   ( lcsh )
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
Thesis: Thesis (Ph. D.)--University of Florida, 1982.
Bibliography: Bibliography: leaves 158-174.
Statement of Responsibility: by Marilyn E. Swisher.
General Note: Typescript.
General Note: Vita.
 Record Information
Bibliographic ID: UF00098273
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: alephbibnum - 000318105
oclc - 08919339
notis - ABU4936


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Space permits that only a few of the many individuals who en-

couraged and aided me in this study can be mentioned here, but I

wish to express my sincere appreciation to all those who were so

kind to me during the course of my Ph.D. program and field work in

Costa Rica. Dr. Hugh Popenoe not only provided me with the guidance

I needed during my program at the University of Florida, but also

created the environment of curiosity and confidence needed to make

it possible to learn. Without his help, and that of his staff

assistant, Ms. Arlene Remington, the study would not have been


The entire staff at the Centro Agrondmico Tropical de Investi-

gacion y Ensenanza was supportive of my efforts, and special thanks

go to Dr. Manuel Ruiz, who helped direct my field work, and to Mr.

Fran Romero and Mr. Arnoldo Ruiz, whose logistical support aided

me greatly. I also wish to thank those farmers, Mr. Jesus Arce,

Mr. Luis Mejia, Mr. Angel Chavarria, and Mr. Bernal Haugenhauer,

who kindly allowed me to carry out experiments on their land and

who taught me how to grow a corn crop in Costa Rica.

Inter-American Foundation provided a large portion of the

funding for this study, and the Fulbright-Hays Scholarship Fund

also funded portions of the study. My appreciation for their

confidence in my ability is great. I especially want to thank

Ms. Liz Veatch of the Inter-American Foundation for her attention

to all the details that made it so enjoyable to work in Costa Rica.



ACKNOWLEDGMENT ..................................... ii

ABSTRACT ......................... .... ..... ........ V


I INTRODUCTION....................................... 1

Cost and Availability of Needed Inputs........... 2
Alternatives for Improving Fertilizer Use
and Efficiency............................... 7

SELECTION....................................... 11

Fertilizer Production in Costa Rica............. 12
Fertilizer Use and Cost in Costa Rica........... 14
Study Site Selection............................ 22

III LITERATURE REVIEW .................................. 36

The Composting Process.......................... 36
Plant and Soil Response to Organic Fertilizers.. 41
Potential Problems in Using Organic Fertilizers. 42

IV MATERIALS AND METHODS............................... 50

Compost Production.............................. 50
Field Trials................................... 61
Labor and Survey Information.................... 68

V RESULTS AND DISCUSSION............................. 69

The Composting Process.......................... 69
Yield Response.................................. 97
Effects on Soil Chemical Characteristics........ 108
Labor Demand................................... 145

VI CONCLUSIONS....................................... 153

LITERATURE CITED.................................. 158


A COMPOST.. .................................. ........ 176

B YIELD RESPONSE...................................... 244

C SOILS DATA........................................... 249

D QUESTIONNAIRE...................................... 257

BIOGRAPHICAL SKETCH.................................. 262

Abstract of Dissertation Presented to the Graduate Council
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy



Marilyn E. Swisher

May, 1982

Chairman: Hugh Popenoe, Professor
Major Department: Geography

Two types of aerobic, thermophilic compost were produced in

Costa Rica, one enriched in superphosphate and one unenriched.

Three study sites, ranging from a seasonally very dry to a very

humid climatic regime, were selected for the study in order to

examine the feasibility of producing compost under this range of

tropical environmental conditions. Zones where cattle, especially

dairy cattle, are important or apt to become important were selected

because of the need to minimize labor costs for collecting manure.

Only manure from corrals or milking parlors was used. A very

simple composting technique was employed, incorporating manure

and crop residues in an overground heap.

Results show that the simple overground heap is not adequate

for compost production under the very humid conditions encountered.

High levels of nutrient loss, especially nitrogen loss, occurred,

and near anaerobic conditions prevailed in the heaps on occasion.

Where soils are high in heavy metals, these elements accumulated

at high levels in the compost as well. At less humid sites, the

technology proved adequate.

The compost was used as a fertilizer for corn production at

all three sites. Five fertilizer treatments were employed: unen-

riched organic, enriched organic, combined chemical and organic,

chemical, and a control receiving no fertilization. Organically

treated plots received only one fertilizer application while the

chemically treated plots received two. Corn grain yields at two

of the three sites did not differ significantly (0.05 significance

level) on the chemically and organically treated plots, indicating

that the organic fertilizer is as effective as chemical or combined

chemical and organic fertilizer for corn production.

Labor costs were calculated for producing the compost and

show that the cost of 1 kg of plant nutrients (n, P205, K20) is

comparable in chemical and organic fertilizer as of January, 1981.

A survey of farms in three zones showed that the overall feasibility

of using compost varies greatly from zone to zone, depending on

such factors as the number of cattle maintained on the farm, the

frequency of milking, availability of easily collected vegetative

material, availability of a mechanical chopper, and the presence

of high value crops on the same farm.


Concern over an imbalance between food production capability

and the world's growing human population has been voiced for many

years. In the post-World War II period, and particularly in the

1960's and 1970's, predictions of coming disastrous food shortages

were widely expressed (Borgstrom, 1965; Erhlich, 1968; Meadows et al.,

1972; Mesarovic and Pestel, 1974). Others (Cole et al., 1973;

Poleman, 1975; Wortman, 1976) argued just as vehemently that world

food production could keep pace with population growth.

Whatever the validity of the opposing viewpoints, the entire

post-war debate has served to focus the attention of the international

scientific community on the need to increase agricultural productivity,

particularly in developing nations. As a result, as early as 1960

the International Rice Research Institute (IRRI) was established in

the Philippines (Jennings, 1976). Its success and that of the

International Center for the Improvement of Maize and Wheat (CIMMYT),

established in Mexico in 1966 (Jennings, 1976), in breeding and

introducing the use of improved grain varieties have led to the

establishment of an extensive international network of agricultural

centers (Wade, 1975).

While the success of these centers in reaching their stated

goals has not been uniform, real gains have been made. The Food and

Agricultural Organization of the United Nations (FAO) shows that

total food production in all developing countries increased an

average of 3.0% per year for the period 1961-70, and 2.8% per year

for the period 1970-77 (FAO, 1978). Such growth rates are excellent,

but their impact on alleviating hunger is often limited by simultane-

ous population growth. Thus, in the period 1961-70, the average

annual increase in per capital food production was only 0.6% for all

developing countries, and was only 0.5% in the period 1970-77 (FAO,


It is not possible to assess the degree to which increases in

food production have been due to the efforts of the international

research centers in particular, and to the concerted efforts of the

international scientific community in general, to address the problem

of raising food production in developing countries, and especially in

the humid tropics. Nonetheless, it is clear that intensification of

agricultural practices is a key to increasing world food supplies,

although, of course, expansion of agricultural land is possible in

some areas.

Cost and Availability of Needed Inputs

As Hopper (1976) correctly notes, success in intensifying

agricultural production through the use of high-yielding varieties

requires access to supplies of fertilizer and abundant water. Due

to loss of native soil fertility, and to maintain soil resources

for the future, fertilizer should be used even where traditional

varieties are planted. It is essential that farmers, especially

the millions of small farmers who make up the bulk of the farming

population in most countries, be assured access to abundant, timely,

and low-cost supplies of fertilizer if they are to continue the

progress that they have been making in raising yields. In fact,

since small farmers have often benefitted less from the introduction

of new technology than larger farmers (Chambers and Farmer, 1977;

Perelman, 1976), even greater efforts must be made to make sure that

small farmers have access to needed inputs. Otherwise, the net out-

come of introducing more intensive agricultural technology may be to

increase food production at the cost of social imbalance resulting

from displacement of small farmers who cannot compete successfully

for the needed inputs.

The high dependence of intensive agriculture on these inputs,

such as herbicide, pesticide, diesel, and particularly fertilizer,

is cause for alarm. Both the cost and the availability of these

materials are now bringing into question the feasibility of increas-

ing, or perhaps even maintaining, current levels of use on the world's

small farms. In addition, as Hopper (1976) mentions, the risk to the

family on small farms when cash indebtedness in incurred is so great

that many small farmers are reluctant to use purchased inputs even

when they are available at relatively low cost.

The major problem in the foreseeable future is not so much that

of absolute scarcity of fertilizer as it is the rising cost and

relative scarcity of fertilizers in developing countries. All ferti-

lizer production, and particularly industrial nitrogen fixation, is

tied to the cost of energy. Within the United States, and not taking

into account any transportation costs for either raw materials or

finished products, production of ammonium nitrate prills requires

about 50 million BTU per ton of nitrogen (Davis and Blouin, 1977).

Although energy costs are lower for phosphorus and potassium, 8

million BTU per ton of phosphate (P205) in triple superphosphate

and 4 million BTU per ton of potash (K20) to mine and process

fertilizer grade potassium chloride (Davis and Blouin, 1977),

rising energy costs are still strongly reflected in their market

price.1 In 1975, fuels and electric power constituted only about

12% of the cost of fertilizer manufacture in the United States

(Sherff, 1975). However, the relative contribution of energy costs

to total fertilizer production costs has been high and will increase

greatly. This occurs both because energy costs are rising rapidly

in proportion to other costs and because of the dependence of indus-

trial nitrogen fixation on a single energy source, natural gas, that

is in absolute shortage both in the United States and worldwide

(Sherff, 1975).

In the developing countries the cost of fertilizers is even

more adversely affected by rising energy costs. Many developing

nations must import all the raw materials to make fertilizers, or

import fertilizer itself. Not only does the cost of the raw mater-

ials themselves rise, but so do costs associated with transportation

of raw materials. Internally, the cost of distributing the finishes

product also rises in direct proportion to rising petroleum costs,

especially in those nations that must import their gasoline and

diesel fuel. For developing countries, then, the impact of rising

'Other authors indicate much higher energy costs. Sherff (1975)
estimates 62 million BTU per ton nitrogen in prilled ammonium nitrate,
19 million BTU per ton P205 in superphosphate, and 6 million BTU per
ton K20 in potassium chloride, for example.

energy costs on fertilizer prices is both more complex and greater

than it is in developed nations which have their own raw materials

and energy sources, especially natural gas.

Agriculture accounts for a small percentage of total commercial

energy use in both developing and developed countries, 4.0% in the

former and 3.4% in the latter (Mudahar and Hignett, 1981). Although

a relatively large portion of this energy use is in the form of

fertilizer in developed countries, about 33% (Price, 1981), fuel and

materials for machinery far outweight fertilizer in energy inputs in

agriculture. In developing countries, where fewer energy inputs are

used, fertilizer accounts for a much higher percentage of agricultur-

al energy inputs, projected at 70.3% by 1985-86 (Stout et al., 1979).

The impact of rising energy costs on fertilizer prices is therefore

relatively much more important in overall increasing costs of produc-

tion in developing than in developed countries.

All of these factors came into play during the 1973-74 energy

crisis. Anjos and Noronha (1974) have analyzed the effects of the

energy crisis and an accompanying cyclical shortage of all major

fertilizers that occurred in 1973-74 on fertilizer costs and supplies

in Brazil. Using 1967 as a base year with fertilizer prices in both

North America and Brazil at 100%, prices of fertilizer for North

American farmers reached slightly over 160% of their 1967 value in

June, 1974. In Brazil, prices reached 200% of the 1967 value (Anjos

and Noronha, 1974). This reflects the absolutely higher cost of

fertilizer in Brazil and also indicates that supplying nations.give

preferential treatment to their own internal markets in time of

crisis, which provokes both speculative price increases in importing

countries and relatively more severe shortages.

Harriss (1977) also discusses the problems that developing

nations, which are heavily dependent on imported fertilizers, face

in times of crisis. In North Arcot District, India, in 1974, a

black market in fertilizer developed as a response to government

controls on price and distribution. Black market prices, which are

normally some 30 to 50% higher than controlled prices, rose to 150%

of controlled prices during the oil crisis (Harriss, 1977). In

addition, the shortages caused severe misallocation of the resource

and resulting losses in yields in undersupplied areas.

These, and other similar cases that could be cited, illustrate

the need for developing countries to achieve some degree of self-

sufficiency in fertilizer supplies. Clearly, the problems associated

with dependence on imported fertilizers manifest themselves most

acutely in times of crisis, such as occurred in the 1973-74 oil

embargo. There are, however, more general long-term problems asso-

ciated with over-dependence on external sources of agricultural

inputs as well. As Dahlberg (1979) points out, developing nations

can easily become so reliant on externally supplied sources of

inputs that their food producing capacity meets severe constraints

that are imposed by institutions and events beyond their own control.

Since these countries, with weakened economies, will be least able

to compete in the international marketplace for scarce resources, it

is important that long-term trends be carefully evaluated so that

appropriate strategies for the future can be developed.

One important aspect of a viable strategy is to augment the

capacity of developing nations to produce their own chemical ferti-

lizer. Many countries have constructed production facilities in

recent years, and Food and Agriculture Organization analyses indicate

that developing countries will reach the target figure of 25% of

world chemical fertilizer production by the year 2000 (FAO, 1978).

Still, most developing nations will not have the necessary resource

capability to develop an adequate national fertilizer industry.

Nonetheless, substantial imports will still be necessary to meet

projected demand, and where raw materials are not available locally,

dependence on external sources of fertilizer will continue. Further,

several authors (Shapley, 1977; Tanner, 1968; White-Stevens, 1977)

have made estimates of total fertilizer demand in the year 2000 and

beyond, based on both desired levels of use and extrapolation of

past trends in fertilizer use. Whatever method used, it is clear

that, at some point, total demand will outstrip world production

capacity of chemical fertilizer.

Alternatives for Improving Fertilizer Use and Efficiency

From both short-term and long term points of view, it is impor-

tant that developing nations, and in fact, all nations, increase

efficiency of fertilizer use and begin to search for sources of

fertilizer other than chemical fertilizer. Research that can provide

farmers with more efficient methods of fertilizer use are important,

as are efforts to breed better nitrogen-fixing strains of plants and

encourage their use. Yet, even readily available sources of fertili-

zer have often been ignored, both in developing and industrialized

nations, in the post-World War II period as chemical fertilizers

became abundantly available and relatively inexpensive.

Human and animal wastes are supplementary sources of fertilizer

that all too frequently go unused. These sources have the advantages

of being available on the farm at little or no cost to the farmer,

and without the added cost of transportation either to the country

or to the farm, with perhaps the exception of some transportation

on the farm itself. While their use could almost certainly not

completely replace the use of chemical fertilizers, they could pro-

vide an important supplementary source of fertilizer. Failure to

utilize these resources is unfortunate from another point of view as

well, since the accumulation of such materials pose increasing health

and pollution hazards in both industrialized and developing nations.

The fertilizer value of these materials is great. Using produc-

tion figures based on an extrapolation of Indian findings, van Voor-

hoeve estimates that human wastes, cattle wastes, and farm compost

produced 12.25 million metric tons of nitrogen, 2.87 million metric

tons of phosphorus, and 2.61 million metric tons of potassium in

developing nations in 1971, for a total of 17.73 million metric tons

(Duncan, 1975).2 In the same year, 13.2 million metric tons of ni-

togen, phosphorus, and potassium from chemical fertilizer sources

were used in those countries (Singh, 1975).3 While these figures

2Van Voorhoeve's data are reproduced in Duncan's article. The
original source is J. J. C. van Voorhoeve, "Organic Fertilizers: Prob-
lems and Potential for Developing Countries," World Bank Fertilizer
Study, Background Paper No. 4, I. F. C. Office of the Economic Adviser,
1974. Van Voorhoeve's calculations exclude Central America and Oceania.
3Singh draws his figures from the 1971 FAO Production Yearbook.

are only estimates, they do show that the nutrients available in

human and animal wastes in 1971 exceeded those applied in chemical

fertilizers in developing nations.

Makhijani and Poole (1975) estimate that in September, 1974,

fertilizer dollar values were $400 per ton of nitrogen content, based

on the price of urea with 46% nitrogen content; $240 per ton of

phosphorus, based on superphosphate with 56% P205 content; and $150

per ton of potassium, based on potash with 60% K20 content. At these

prices, the dollar value of the nitrogen, phosphorus, and potassium

contained in the human and animal wastes produced in developing na-

tions in 1971 was $4,900 million for nitrogen, $718 million for

phosphorus, and $392 million for potassium. Further, these values

are probably underestimates since farmers in the United States, the

source of Makhijani and Poole's base prices, typically pay less for

fertilizer than those in developing nations.

Organic fertilizers have played an important role in agriculture

in many parts of the world, but despite the importance of such ferti-

lizers in many agricultural systems, little attention has been devoted

to their use in recent years. In some areas animal wastes are simply

not readily available. Such is the case in large areas of Africa

where the tsetse fly prevents much animal husbandry. In other areas,

animals are an important element in agriculture, but are not integra-

ted into the farming system in such a way that their wastes are re-

claimed. Effective utilization of animal manures requires penning

or tethering and may therefore require change in agricultural customs;

but several writers comment on the failure to utilize cattle manure


in Uganda, for example, even though the animals are tethered (Cleave

and Jones, 1970; Parsons, 1970). The use of human excreta poses

additional problems both in the evolution of an appropriate system

of collection and re-distribution, as well as the development of

socio-cultural attitudes that endorse its effective utilization.


This research was undertaken to examine the socio-economic and

environmental constraints on the use of composted animal manure on

small farms in Costa Rica. The study was integrative in nature,

that is, all facets of manure utilization, including the problems

associated with compost production, yield response of corn upon appli-

cation, effects on selected soil chemical properties, and integration

into overall farm labor availability, were considered. The full re-

search program, described below, was completed at three study sites,

offering a variety of socio-economic, physical, and biological settings

for comparison.

Specifically, the project objectives were

(1) To determine the quality of compost that can be produced

using the simplest possible technology under thelvariety of environ-

ments encountered;

(2) to compare the quality of two types of!aerobic, thermophilic

compost, one enriched in phosphorus and the other not;

(3) to compare the yield of corn using a single application of

compost or compost combined with chemical fertilizer to yields ob-

tained where no fertilizer was used, or where two applications of

chemical fertilizer were made;

(4) to determine the labor and material requirements for making

and applying compost;

(5) to examine the effects of compost on selected soil chemical

properties; and

(5) to determine the possibilities for using compost in the

three zones in Costa Rica in terms of both laborirequirements and

availability of needed resources.

The study was integrative in two senses. The research sought

a method for combining animal and crop productioA so that the small

farmer could reap the greatest benefits from hisimixed farming system,
where both components are generally present. Further, both the physico-

biological and socio-economic environments of the small farmer were

taken into consideration. Overall, it is the combination of all pro-

ject objectives, rather than any single facet of the study, which

yields insights into the possibility of putting this technological

innovation into practice.

It is useful to examine current trends in fertilizer use in

Costa Rica in order to put the objectives of the project in proper

perspective. The following brief discussion describes the fertilizer

industry in Costa Rica and examines current trends in fertilizer use

and costs in the country.

Fertilizer Production in Costa Rica

Like many developing nations, Costa Rica has developed a ferti-

lizer industry, and both the government as a whole and the Ministry

of Agriculture strongly encourage the use of fertilizer. The first

fertilizer plant in Costa Rica was established in Puntarenas by

Fertilizantes de Centroamerica S.A. (FERTICA) in 1963 (Organization

of American States, 1970). While FERTICA was originally privately

owned, it is now a public corporation. The Refinadora Costarricense

de Petroleo (RECOPE) bought 10% interest in FERTICA in January,

1978, and the Corporaci6n para el Desarrollo S.A. (CODESA) bought

90% interest in March, 1980. Both organizations are funded by the

Costa Rican government (Ortiz, 1981). FERTICA imports, processes,

and mixes fertilizer raw materials and distributes and sells

fertilizer in Costa Rica. Part of its production is re-exported

to other Central American nations as well.

While FERTICA accounts for about 70% of all fertilizer sales

in Costa Rica (Ortiz, 1981), six other private companies also market

fertilizer products in the country. They are Distribuidora Superior

S.A., Holterman and Petchel Ltda., Abonos Agro S.A., Rainbow Ltda.,

Casa del Agricultor Ltda., and J. H. Baker and Bro., Inc. Some of

them own mixing plants in Costa Rica as well (Organization of Ameri-

can States, 1970). In addition, banana growers import some fertili-

zer directly, especially urea, although they buy most of their ferti-

lizer on contract from FERTICA.

Fertilizer sales and distribution are not government controlled

in Costa Rica. Both individuals and intermediaries may buy fertili-

zer from FERTICA at any of its three warehouses in Puntarenas,

Alajuela, or Liberia. Cost of transportation from the Puntarenas

plant, averaging $US 0.54 per 100-lb bag, to the other two ware-

houses is split evenly between FERTICA and the customer.4 Further

4All conversions from the Colon to the U.S. dollar will be made
on the basis of C8.54 per $US 1.00. This exchange rate is no longer
applicable, but the current rate changes frequently. The old rate
was effective until November, 1980, and local prices, especially
labor costs, did not yet reflect, for the most part, the new, higher
rates when this research was completed.

transportation costs are the client's responsibility (Ortiz, 1981).

FERTICA imports all raw materials for its fertilizer production.

These include sulfur, ammonia, urea, potassium sulfate, potassium

chloride, diphosphate, triple superphosphate, phorphoric rock, and

minor elements. Canada is the chief supplier of potassium chloride,

but Mexico and the United States supply most other materials. These

materials, most importantly triple superphosphate, are not resold as

single element fertilizer except in very small quantities because

there exists a tax on all primary materials which are not processed

within the country (Ortiz, 1981). Almost all fertilizers,with the

exception of some forms of nitrogen fertilizer, are available only

in complete mix formulas. It is difficult and expensive to procure

superphosphate, except in complete mixes, of particular importance

because of phosphorus deficiency in many Costa Rican soils.

Fertilizer Use and Cost in Costa Rica

As Pritchett and Blue (1966) point out, although certain Costa

Rican export crops, such as coffee and bananas, have been fertilized

for many years, use of chemical fertilizers in Costa Rica is rela-

tively recent for most farmers and for most crops. As Table 1 shows,

imports of fertilizer materials have increased greatly for the

period of record, with extremely rapid increases occurring since

1950. Since 1963, when FERTICA began to export fertilizer,5 all of

these materials have not been consumed in Costa Rica. Nonetheless,

the growth in demand does indicate that fertilizer use has increased

5FERTICA exported 42,467 metric tons of fertilizer in 1965,
32,438 tons in 1970, and 70,200 tons in 1974 (Ministerio de Agricul-
tura, 1974).

Table 1. Fertilizer imports and costs in Costa Rica, 1920-74.

r Total Imports Total Cost Cost/Ton
(Metric Tons) (Thousands, SUS) ($US)

1920 272 24 88
1925 1,409 152 108
1930 1,591 195 123

1935 2,462 340 138
1940 5,808 284 49
1945 3,508 193 55

1950 15,802 1,454 92
1955 24,208 2,413 100
1960 57,780 4,866 84

1965 169,528 11,745 69
1970 139,217 7,497 54
1974 168,900 31,900 189

Source: Ministerio de Agricultura, Consejo Agropecuario Nacional,
Comisi6n de Fertilizantes. 1974. Informe Sobre el
Consumo de Fertilizantes en Costa Rica. Preliminar.
San Jose: Ministerio de Acricultura.

greatly in the post-World War II period. The Ministry of Agricul-

ture (1974) reports, for example, that fertilizer use grew by 7.7%

per year for the period 1963-73. Table 1 also gives some indication

of the cost of these materials to Costa Rica.

Table 2 indicates fertilizer use on basic grains, pasture, the

most important export crops, and vegetables. With the exception of

vegetables, a high value crop grown for sale in San Jose, fertilizer

use on export crops greatly exceeds that on crops grown for domestic

consumption and pasture. Two crops alone, coffee and bananas, ac-

counted for 60% of all fertilizer use in 1980, whereas the basic

grains accounted for only 12% of all fertilizer consumption. Simi-

larly, the table shows that application rates on corn, rice, beans,

and pasture remain low, especially in comparison to use on export


Despite the imbalance suggested by these data, fertilizer use

on basic food crops has grown in the past. In 1963, only 33% of

all land planted in rice and virtually none of the land planted in

corn and beans were fertilized (Pritchett and Blue, 1966).6 At

roughly the same time, in 1965, corn, rice, and beans accounted for

only 4% of all fertilizer consumed, whereas coffee, bananas, and

sugar cane accounted for 85% of all fertilizer use. By only 1970,

some 12% of all fertilizer consumed in Costa Rica went to corn,

beans, and rice, and use on the three export crops had dropped to

71% (Ministerio de Agricultura, 1974), and by 1973, 63% of all land

6Based on 1963 census data.

Table 2. Fertilizer use by crop, in Costa Rica, 1980a

% of All
Crop kg/ha Fertilizer Used

Banana 1,150 20

Coffee 779 40

Sugar Cane 320 10

Beans 120 2

Corn 202 3

Rice 200 7

Pasture 158 2

Vegetables 1,207 2

aThese preliminary data were compiled in early 1981 and some
minor changes may appear in final data.
Source: Fertilizantes de Centroame'rica S.A. 1981a.
Consumo Nacional de Fertilizantes y Area
Fertilizada (por Cultivo). Mimeo Sheet.
San Jose: FERTICA.

in rice, 20% of all land in corn, and a small percent of all land

in beans were fertilized (Ministerio de Economica, 1974).

Since 1970, however, relatively little progress has been made.

As Table 2 indicates, in 1980, the export crops still accounted

for 70% of all fertilizer use, and rice, beans, and corn for only

12%. The increase in fertilizer consumption, from 65.2 metric tons

in 1965, to 114.1 metric tons in 1970, to 162.5 metric tons in 1980,

has not changed the basic trends in fertilizer use (FERTICA, 1981b;

Ministerio de Agricultura, 1974). These data illustrate that far-

mers can best afford to fertilize the low risk, high value crops,

especially those grown for export. Fertilizing basic food crops

grown for domestic consumption remains problematic. These tendencies

will be exaggerated as fertilizer prices rise, and show the need for

developing a low-cost, readily available source of fertilizer.

Table 3 illustrates the use of fertilizer on small (20 ha or

less) versus large farms. The willingness of farmers with small

acreages to use fertilizer when a high value crop can be grown is

demonstrated by the data for fertilizer use on vegetables, a very

high value crop. The vast majority of vegetables are grown on small

farms near the capital, in the provinces of San Jose, Alajuela, and

Cartago. As the data in Table 3 show, these small farms account for

a similarly high percentage of the fertilized land planted in vege-

tables, with fertilizer application rates exceeding those on large

farms. Small farms also have a higher fertilizer application rate

on pasture than do large farms. Again, this is explained by the

high fertilizer use on small dairy farms near the Central Valley

producing milk for sale in San Jose.


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In general, however, small farms account for a smaller percent-

age of the fertilized acreage than they do of the total acreage

planted in a given crop, and they generally exhibit lower application

rates. These data show that small farmers are well aware of the

advantages that are gained when fertilizer is applied and are willing

to use fertilizer when risk is low and it is cost effective to do so.

The problem now confronting Costa Rican farmers is that of rapid-

ly rising fertilizer costs. In Costa Rica, as elsewhere, fertilizer

prices fell and stabilized after the severe increases in 1973-74.

This occurred both because the oil embargo ended and because the

worldwide shortfall in fertilizer production that took place at the

same time was eliminated as new production facilities were built.

In the last two and one-half years, however, fertilizer prices have

begun to rise once again.

Figure 1 shows the cost of three commonly used fertilizers in

Costa Rica for the period 1977-80. The graph illustrates the average

price in the entire country, although there are regional variations

due to transportation costs. The trend toward higher prices that

began in 1979 shows no sign of abatement. In fact, between December,

1980, and January, 1981, the cost of these three fertilizers rose

another 7.7% (Ministerio de Agricultura, 1981a),and again, between

January, 1981, and March, 1981, another 8% increase occurred (FERTICA,

1981b). Further price increases can be expected as a result of both

generally increasing worldwide fertilizer prices and because of the

inflation currently plaguing the Costa Rican economy.


/ 15-15-15 -~


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1 -

sjS spN~

II r
S /

c- -
s -

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6/77 12/77 6/78 12/78 6/79 12/79 6/80 12/80

Fig. 1. Cost of three commonly used fertilizers in Costa Rica.

These trends clearly demonstrate the need to seek alternative

sources of fertilizer in Costa Rica. Even discounting short-term

price fluctuations that may occur, no fertilizer raw material is

produced within the country. Thus, the long-term prospect is one

of continued dependence on external sources.

Study Site Selection

The study was conducted in Costa Rica for a number of reasons.

First, the country offers a wide variety of climatic zones in rela-

tively close proximity. Given the well developed transportation

system in most of the country, this makes it possible to conduct

research under a variety of environmental conditions simultaneously.

Second, the Centro Agronomico Tropical de Investigaci6n y Ensefanza

(CATIE) expressed interest in the project and offered the use of

their facilities in the Department of Animal Production. Two projects

under investigation were of particular interest: one concerned with

the use of crop residues, a possible use being raw material for com-

posting; and another designed to increase milk production on small

farms, where fertilizer could be a key element (CATIE, 1978; 1980a).

Finally, the project was undertaken in Costa Rica because the

use of organic as fertilizers is not traditional and has received

little attention. Large animals are a post-Columbian introduction

in Latin America and it is not surprising that pre-Columbian use of

animal manure was very limited. Winterhalder, Larsen, and Thomas

(1979) report that use of manure, traditionally llama dung and more

recently cattle and sheep manure as well, is practiced in highland

Peru. Similarly, Vargas (1942) describes manure use bypre-Columbian

peoples in Mexico. There is no strong tradition of integrated animal

and plant production in Latin America such as characterizes much of

Southeast Asia.

Some interest in using organic fertilizer prior to the widespread

availability of chemical fertilizers after World War II had been

expressed. In Puerto Rico, projects were undertaken to promote the

utilization of organic, for example (Perez-Garcia, 1948). In the

post-World War II period, interest was minimal, but recently has

come to the fore again in some areas. Brazil has begun to compost

municipal wastes in Sao Paulo (Burnett, 1975), and Peace Corps

volunteers in San Carlos, Costa Rica, worked with the use of municipal

wastes (Sullivan, 1975). In total, however, very little research has

been undertaken. The recent series of publications by the Food and

Agricultural Organization (1975, 1976, 1977, 1978a)does not describe

the use of organic wastes in Latin America although its coverage for

Africa and Asia is excellent. Given the rising cost of fertilizer

not only in Costa Rica but throughout Latin America, the ongoing

dependence on foreign sources of chemical fertilizer for Costa Rica,

and the ready availability of animal manure, especially cow manure,

on many small farms in the country, the use of organic deserves


Within Costa Rica, the full research program was completed at

three study sites: Cariari in the Province of Limon; Turrialba in

the Province of Cartago; and Caias in the Province of Guanacaste.

Compost was also made and applied in Santa Elena in the Province of

Puntarenas. However, by the time interest in using compost devel-

oped there it was not possible to carry out the full research

program. Farmers in Santa Elena were interviewed, and these data

are included here, but compost trials and field test plots were

not established. The study sites were chosen on the basis of the

differences they display both in environment and farming systems,

and to accompany other CATIE research projects. A brief descrip-

tion of each follows.

Although manure is a carefully husbanded resource in some

places, such as India and China (King, 1911; Makhijani and Poole,

1975), and is carefully collected even from unpenned animals, this

is not the case in Costa Rica. Further, labor is often in short

supply on small farms and it is always relatively expensive to hire

off-farm workers. As a result of these factors, it is most feasible

to use the manure of penned or tethered animals, which is easily

collected. One major source of manure, therefore, is that left in

milking parlors or corrals while cows are milked, and for this

reason research was conducted on dairy farms.


Turrialba is situated 639 m above sea level in a valley on the

eastern flank of Costa Rica's Cordillera Central (see Fig. 2). For

the period of record 1961-78, the mean annual temperature was 21.60C,

with a mean low temperature of 17.7C and a mean high of 26.7C

(Instituto Meterol6gico Nacional, 1979c). The coolest month is

January, with a mean temperature of 20.4"C, and the warmest is May,

with 22.4C mean temperature (Table 4). Precipitation averages




1 Cariari


La Pacifica

Fig. 2. Study Sites in Costa Rica

Based on: Ministerio de Economla, Industria y Comercio, Direccion General
de Estadistica y Censos, Censos Nacionales de 1973, Agropecuario,
Regiones Agrfcolas, Vol. 7, San Jose: Ministerio de Economla, In-
dustria y Comercio, DirecciLn General de Estad'stica y Censos, 1975.

Table 4. Temperature and precipitation, Turrialba, Costa Rica.

Maximum Minimum Median
Month Temperature Temperature Temperature Precipitation
(C() (0C (C) (mm)

January 25.4 16.3 20.4 173.4
February 25.8 16.2 20.6 135.9
March 26.6 16.9 21.3 77.9
April 27.1 17.6 21.8 212.9

May 27.6 18.4 22.4 221.7
June 27.4 18.6 22.3 285.3
July 26.9 18.5 22.2 283.9
August 27.2 18.3 22.1 239.3

September 27.5 18.4 22.3 245.0
October 27.3 18.3 22.0 247.7
November 26.2 18.1 21.6 281.4
December 25.6 17.1 20.8 338.4

Annual 26.7 17.7 21.6 2,651.7

Source: Instituto Meterolde'ico Nacional. 1979c. Weather

Records for Turrialba,
Institute Meterologico

Costa Rica. San Jose:

2651.7 mm per year, based on a period of record from 1942 to 1978.

There is a dry season, from January to April, but it is not nearly

as pronounced as the severe dry season experienced on Costa Rica's

Pacific side, and it is possible to raise two crops per year without


The research in Turrialba was carried out at the CATIE Depart-

ment of Animal Production's field station. A milk production module

that reproduces conditions common to small farms in Costa Rica, and

particularly around Turrialba, has been established on the experimen-

tal farm. It is operated by a CATIE employee with the same limited

resources, by and large, that are typical for small dairy producers.

The unit is specialized for milk production, but some cash crops are

grown, such as corn, cassava, and plantains. While conditions on

the module are not an exact replica of a small dairy farm in the area,

they do reproduce the small producer's situation fairly well. In

addition, working at the research station offered benefits in terms

of needed control over experimental conditions.

Dairying is very important in the Turrialba area. Avila's

(1979) study provides a good description of the small dairy farm in

the zone. Since milk and cheese production are very important ele-

ments in the farming system, most of the area of the farm is typically

devoted to pasture. Nonetheless, some portion of the farm is also

usually devoted to cash crop production. In Turrialba, coffee and

sugar cane are the most important cash crops. Other crops may be

grown, both for sale and for home consumption,and small animals,

especially chickens, are very important. From the point of view of

organic fertilizer use, the role of cane and coffee on dairy farms

here is very important. Coffee often receives fertilizer, currently

a cash input, and sugar cane can provide a good source of raw green

material for composting, a severe constraint in some locales.


Cariari, lying 50 m above sea level, is an agricultural colony

on Costa Rica's Atlantic Lowlands (see Fig. 2). No meteorological

station is maintained by the National Meteorological Institute in

Cariari. Data are available from nearby Guapiles and, for selected

years, from private banana plantations around Cariari. For descrip-

tive purposes the data from Guapiles are sufficiently representative

of the climate. For the 1961-78 period of record, rainfall averaged

4,421.6 mm annually (Instituto Meterologico Nacional, 1979a). There

is no true dry season, but rainfall does decline to 200 to 300 mm

per month in January, February, and March (see Table 5). The mean

annual temperature is 24.60C, and monthly means vary little from

the annual mean. The diurnal fluctuation is similar to that in

Turrialba, about 10C, with a mean maximum temperature of 29.5C

and a mean minimum temperature of 19.8*C. The period of record for

temperature data extends from 1942 to 1978.

Cariari was established by Costa Rica's Institute of Land and

Colonization (ITCO) eighteen years ago as part of the country's

agrarian reform program. The country has invested heavily in the

colony. Schools, medical facilities, and roads have all been con-

structed, and various government agencies maintain personnel and/or

offices in the colony. A highway connecting the capital to Guapiles,

Table 5. Temperature and precipitation, Guapiles, Costa Rica.

Maximum Minimum Median
Month Temperature Temperature Temperature Precipitation
(C) (C) (*C) (mm)

January 28.5 18.9 23.7 300.1
February 28.7 18.3 23.3 215.5
March 29.4 18.8 24.3 207.4
April 29.5 19.5 24.6 247.6

May 30.3 20.4 25.3 413.5
June 30.1 20.4 25.3 434.5
July 29.2 20.6 24.9 493.5
August 30.0 20.5 25.1 403.5

September 30.3 20.3 25.2 344.5
October 29.9 20.2 25.0 436.6
November 29.1 20.3 24.4 495.6
December 28.5 19.4 23.7 516.0

Annual 29.5 19.8 24.6 4,421.6

Source: Institutio Meterologico Nacional. 1979a. Weather
Records for Guapiles, Costa Rica. San Jose: Instituto
Meterologico Nacional.

the local regional center, is currently under construction. It is

hoped that the agricultural potential of the area, given its high

rainfall and relatively fertile soils, especially in Cariari, will

provide a good return on this investment.

Each settler in Cariari received 20 ha of land. Large areas

of the farms are in unimproved pasture, and cow-calf operations are

a very important enterprise on most farms. Pasture occupies an

average of 9 ha on the farms and cattle production accounts for

roughly half the farm income. Only 28% of the farms surveyed in

1979 were involved in dairying (CATIE, 1980b). The cow-calf enter-

prise is a low management enterprise and one that represents an

unintensive form of land use. Today, marketing is a major drawback

to dairying, and it is hoped that access to the San Jose milk market

provided by the new highway will encourage farmers to turn to milk

production. Many farmers in the area do express interest. Because

of the importance of the area to Costa Rica, the emphasis on intro-

ducing milk production, and its climatic characteristics, the research

was completed in the area.

Despite the importance of cattle operations, farms in Cariari

almost always have mixed farming systems. Small animals, hogs and

chickens, are very common, although they are usually not penned.

Most farmers also plant corn, both for cash sale and for home consump-

tion, and a wide variety of other crops, such as beans, cassava,

tiquisque, banana, pejibaye palm, black pepper, and plantains, may

all be found on the same farm. Thus, opportunities for the use of

fertilizer are many, although most farmers do not fertilize most of

their crops or their pasture. The research program was carried

out on three farms in the colony.


Finca La Pacifica, the farm where the research was completed on

Costa Rica's Pacific side, is located just north of Cafas at 50 m

elevation (see Fig. 2). Total annual rainfall at La Pacifica for

the period of record 1920-79 averaged 1,639 mm (Hagenhauer, 1981).

However, the region experiences a strong seasonality in rainfall.

During the dry season, from November to March, rainfall averages

less than 100 mm per month. Further, a strong, desiccating wind

accompanies the low rainfall period. Unlike Turrialba or Cariari,

it is not possible to grow two crops per year without irrigation,

and planting must be timed carefully to take advantage of the onset

of the rains. For the period 1961-75, the mean annual temperature

was 27.40C, with very little monthly fluctuation (Table 6).

Because of the difficulties with transportation and in finding

cooperators on small farms, the research was carried out on a large,

commercial farm. At the time the study was started, there were no

ongoing CATIE projects in the area. It was felt, nonetheless, that

it was important to test the production of compost under the climatic

conditions prevalent on the dry Pacific side of Costa Rica, and it

was possible that CATIE projects would be started in nearby Nicoya,

with its similar climate.

Later, CATIE projects were undertaken in La Sierra (Santa Elena).

This area differs from La Pacifica in that it has a higher elevation

Table 6. Temperature and precipitation, Finca La
Costa Rica.

Pacifica, Cafas,

Maximum Minimum Median
Month Temperature Temperature Temperature Precipitation
(C) ("C) ("C) (mm)

January 31.9 23.2 27.3 3.7
February 32.5 25.2 27.7 15.0
March 33.4 23.7 28.2 8.0
April 34.3 24.2 28.6 44.0

May 33.7 23.7 28.2 141.9
June 31.8 22.8 27.0 264.8
July 31.7 23.2 27.2 114.4
August 32.1 22.8 27.3 155.6

September 31.9 21.9 26.8 294.6
October 31.4 22.0 26.6 297.5
November 30.9 22.1 26.5 98.8
December 31.0 22.6 26.8 20.1

Annual 32.2 23.1 27.4 1,639.0

Source: B. Hagenhauer. 1981. Unpublished Weather Data for
Finca La Pacifica, Caiias, Costa Rica.

(900 to 1,500 m), and correspondingly cooler temperatures, but it

shares the strong seasonal precipitation pattern and wind, and

pulsed crop production, with the lowlands. La Sierra itself can be

divided into two zones, the lower (900 to 1,100 m) and the upper

(1,100 to 1,500 m). When the CATIE projects were undertaken in La

Sierra, compost was made and applied there and farmers were inter-

viewed, even though the complete research program could not be


Farms in the upper zone are strongly specialized in milk produc-

tion. With an average farm size of 19 ha, 15.5 ha are occupied by

pasture and 95% of the family income comes from milk production. In

the lower zone, farther from the cheese plant which is the market for

milk, 15.5 ha of an average farm size of 29 ha are devoted to pasture

and only 36% of the family income comes from dairying. Production

from coffee accounts for an almost equal share of family income in

the lower zone, 32% (CATIE, 1980b). Farmers in the upper zone

expressed interest in using compost to fertilize vegetable plots,

part of which may go for sale, and to apply to tall grass pasture

(which is cut during the dry season). In the lower zone, coffee

needs fertilizer, but, unfortunately, farms there are less well

equipped to collect and utilize manure. They have fewer cows,

generally milk only once per day, and are less apt to milk under


Figure 3 shows the rainfall pattern at the three study sites.

Precipitation distribution was an important parameter for this

research for two reasons. First, different problems are encountered

m 1

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in producing compost under high rainfall and low rainfall conditions.

Second, periods of peak demand for fertilizer vary with rainfall

distribution. When there is only a single growing season, as at La

Paciffca, for example, the farmer will need to produce large amounts

of organic fertilizer for use at one time. In a site like Cariari,

demand for fertilizer is much less pulsed. Temperature was a rela-

tively unimportant factor here because none of the study sites has

an elevation sufficiently high to produce night temperatures low

enough to affect the composting process significantly. Temperature

would, however, be an important variable in higher elevation loca-



The use of animal manure and other organic materials as a soil

amendment is an ancient practice. No literature review could ade-

quately cover the volumes of material that have been written on this

subject. Further, much of the detailed information regarding com-

posting is described below in the discussion of the results obtained

by the author in Costa Rica. This brief review will familiarize

the reader with the major sources of information that are available.

The Composting Process

The compost heap is an ecosystem in which optimal growing condi-

tions for a wide range of bacteria, fungi, and actinomycetes are

provided (Allen, 1949-50; Cooney and Emerson, 1964; Waksman, Umbreit,

and Cordon, 1939). By providing optimum growing conditions for these

organisms, the rate of decomposition is increased so that a stable

organic complex can be produced rapidly (Grossman and Thygeson, 1974).

Achieving stability is important because the addition of only

slightly decomposed material to the soil results in increased

growth and activity of soil microbiota. Since these organisms can

more readily extract plant nutrients, especially nitrogen, from the

soil than most higher plants, enhanced levels of microbiological

activity are not desirable for crop production. The main factors

which must be controlled to achieve high decomposition rates are

moisture content, aeration, carbon to nitrogen (C:N) ratio, pH,

phosphorus and potassium content, temperature, and micronutrient

supply (Gotaas, 1956; Taiganides, 1977; Toth, 1973).

Many techniques for composting have been developed. Krishna-

murthy (1966) reviews the major techniques that have been developed

in India, one of the nations where ongoing research has been con-

ducted for many years. McGarry and Stainforth (1978) and the 1977

FAO report on the use of organic wastes provide a good discussion

of composting techniques in the People's Republic of China, where

compost is a very important source of fertilizer. For a general

review of the basic methods of composting, Gotaas (1956) is excel-

lent, and Golueke (1972) and Poincelot (1974) also discuss the

critical parameters in composting.

High temperature, aerobic composting is generally preferable

to anaerobic and/or mesophilic composting. The latter are possible,

however, and are often intentionally included as stages in composting.

High temperature composting is rapid and maintenance of aerobic con-

ditions eliminates foul odors, minimizes fly problems, and leads to

less nutrient loss by leaching than other methods. Barring extreme

external environmental conditions, the process is self-regulatory.

An initial population of mesophilic microorganisms is replaced by a

thermophilic population as the temperature of the compost rises, a

result of the microbial activity itself (Bagstam, 1979). There is

no distinct temperature at which the microbiotic population can be

said to be thermophilic as opposed to mesophilic, although many

authors (Golueke, 1972; Poincelot, 1974; Taiganides, 1977) define

the mesophilic range of activity as 20 to 40C and the thermophilic

range as 40 to 70C. This definition of thermophily is accepted for

purposes of this discussion.

The number and type of organisms in compost heaps change greatly

over time. Early efforts to identify the organisms responsible for

decomposition in compost, especially the thermophiles involved, and

to determine the nature of their activity, include Allen's (1944-

50) work, that of James, Rettger, and Thom (1941), the work of

Carlyle and Norman (1941), and Gaskill and Gilman's (1939) work on

nitrogen transformations. Poincelot (1974) gives a list of those

organisms believed to be most important in composting.

Waksman, Unbriet, and Cordon (1939) described the basic nature

of the populations involved. They found that fungi are initially

more prevalent, but that as temperatures rise to 50C or more bacteria

and actinomycetes (which are usually treated separately because of

their importance in composting) predominate. Bagstam (1978, 1979)

studied population changes in a spruce bark compost and also found

that the importance of bacteria increases as temperature rises. He

found that fungi were least tolerant of high temperatures, followed

by the actinomycetes species, and that bacteria accounted for 90 to

100% of the microorganism population during the thermophilic stage.

Polprasert, Wangsuphachart, and Muttamara (1980) found, however, that

both thermophilic bacteria and cellulytic fungi were active at the

40 to 60C temperature range and that mesophilic bacteria and actino-

mycetes became more prevalent as temperatures fell to 35 to 40*C.

The role of the fungi is particularly important because some species

are able to degrade lignin (Cooney and Emerson, 1964; Jain, Kapoor,

and Mishra, 1979), and because of their efficiency in attacking

cellulose (Cooke, 1977). Actinomycetes and bacteria are more

limited in the range of substances they easily attack (Waksman,

Cordon, and Hulpoi, 1939).

Prior to World War II, when organic materials were the primary

sources of plant nutrients, a great deal of literature dealing with

the properties and utilization of manure in general, and compost in

particular, was produced (Heck, 1931; Murray, 1925; Richardson and

Wang, 1942; Salter and Schollenberger, 1939; Thorne, 1913; VanVuren,

1948). As chemical fertilizer became inexpensive, little research

in the use of compost was completed in most regions of the world.

China and India were exceptions, and in the United States the ongoing

support of a group interested in organic gardening was an exception

as well (Fukuoka, 1978; Rodale, 1945; Wolf, 1977). In addition,

some researchers in Europe (Garner, 1966; Hemingway, 1961; Richardson,

1946) continued to investigate the use of organic, as did researchers

in countries where chemical fertilizers continued to be relatively

expensive and difficult to procure (Bache and Heathcote, 1969; Grimes

and Clark, 1962; Jameson and Kerkham, 1960; Wood, 1963). Interest

in Latin America was apparently very restricted.

In recent years interest has grown again, partly because of

rising fertilizer costs and partly because of renewed interest in

"organically" grown food. Perhaps even more important in the United

States, disposal of sewage sludge, solid waste, and animal feedlot

wastes has become an increasingly severe problem. Land application

of these wastes is one alternative and has become an area of great


Much of this research, however, is not of great utility from

the point of view of achieving maximum utility of organic materials

as a fertilizer because the central research problems are defined

differently. When composting is seen as a method of disposing of

large amounts of waste, rapidity of the process and reduction in

bulk are stressed; nutrient retention is not necessarily a goal.

The systems designed by such researchers are highly technical and

are not appropriate to small farm conditions, nor are they, of

course, intended for such use (Satriana, 1974; Sikora et al., 1979;

Sikora et al., 1981; Willson et al., 1980). Even where disposing

of animal wastes is the object of the system design, scale and tech-

nology are inappropriate for farms in developing nations (Demmel, 1980;

Taiganides, 1977; Willson, 1971).

Further, when these organic materials are seen as wastes, the

question of maximum loading rates and problems associated with exces-

sively high application rates are critical research priorities

(Adriano, Pratt, and Bishop, 1971; Clapp et al., 1978; Concannon and

Genetelli, 1971; Hileman, 1971; Stewart and Meek, 1977). These are

less apt to be critical questions where disposal of large amounts of

material is not a problem.

Nonetheless, as the discussion of the results obtained in Costa

Rica shows, this most recent research has improved greatly out under-

standing of the nature of composting. Recent findings on the effects

of C:N ratios and temperature, for example, have design implications

even for very low-technology systems. Similarly, the recent findings

regarding effects of organic materials on soils are often very useful.

Plant and Soil Response to Organic Fertilizers

Use of fresh manures and composts has resulted in both the

improvement of the physical properties of soils and an increased

crop production. Manuring adds organic matter as well as plant

nutrients to the soil, which is believed to increase the soil's

nutrient retention capacity. If applied on the surface, it prevents

crusting, whereas mixing manure into the soil by tillage improves

the soil structure and physical conditions (North Carolina Agricul-

tural Extension Service, 1973b). In addition, compost increases

the moisture retention capacity of the soil and conserves soil water

(North Carolina Agricultural Extension Service, 1973a; Rodale, 1945).

Organic fertilizers also reduce erosion through the interaction of

three interconnected factors. If manure is on the soil surface, or

only slightly tilled, it protects the soil from the force of falling

raindrops. It also helps hold water and thus prevent runoff, and

it promotes soil aggregation, all of which help reduce erosion.

Many authors (Bache and Heathcote, 1969; Djokoto and Stevens,

1961a, 1961b; Jameson and Kerkham, 1960) have commented on the value

of manure in maintaining soil fertility. As Guinard (1967) points

out, unlike chemical fertilizers, the effects of applying manure are

prolonged, providing an ongoing release of plant nutrients. Crop

yields are increased by manure application, and several experiments

have dealt specifically with improved yields in tropical areas

(Agboola et al., 1975; Grimes and Clarke, 1962; Hartley, 1937;

Hartley and Greenwood, 1933).

The debate over the nutritive value of "organically" versus

"chemically" grown foods is an ongoing one, but of little relevance

here. Long-term experiments have been undertaken to determine, for

example, the effects of organically versus chemically fertilized

feedstuffs on animal health (Bruin, 1969), but no conclusions have

been drawn. More recently, concern over pollution effects of chemi-

cal fertilizer use has also been expressed (Molen, 1974). While

these may be critical issues, the point of this study is to look at

the feasibility of supplementing or replacing chemical fertilizer

use by organic from an economic viewpoint. The preferability of

doing so, from other points of view, is not considered.

Potential Problems in Using Organic Fertilizers

Despite the highly beneficial aspects of organic fertilizers,

problems with their use may still arise, a few of which are discussed

here. Problems of a soil chemical nature are dealt with only briefly

because they are much more likely to arise where very large quantities

of material are being applied to the soil. While these problems

could come to the fore with continued application of compost over

many years, they are not likely to be a serious drawback to the use

of compost in developing nations. Health hazards are dealt with at

more length.

Human and animal wastes are quite high in salt content, and

problems of salt accumulation in soils have arisen when they are

applied in large quantities. Salt toxicity to plants is a problem

when conductivity (EC) exceeds 0.05 mmho in a 1:2 soil-water slurry,

and is a very serious problem at values greater than 1.0 mmho (Hileman,

1971). Excessive salinity can also cause soil structure deteriora-

tion. Some salt cations, mainly sodium, cause soil particles to

disperse, which will eventually greatly retard water movement

through the soil (Travis et al., 1971). While such problems have

largely resulted from very high rates of slurry application, the

same results can come about from high, prolonged levels of manure,

sludge, and compost use.

The use of poultry litter in northwestern Arkansas, practiced

for over 30 years, has caused soil chemical imbalances. Hileman

(1971) applied broiler litter at rates of 5, 10, 15, and 20 tons per

acre and found that soil pH rose in all cases. It is believed that

ammonia released during decomposition of the litter may affect the

soil exchange complex, affecting calcium, potassium, and magnesium

ionic replacement and resulting in high levels of these salts in the

soil and high pH values. The rise in soluble salts was found to vary

with soil texture. Hegg and Skipper (1977) found that yields were

lower when poultry effluent was applied to soils than when synthetic

fertilizers containing equivalent amounts of nitrogen were used, and

conclude that salt toxicity could be one reason for the decline.

Although the salt content of poultry manure is considerably higher

than that of cattle manure, salt accumulation has also been high

when beef feedlot manure and lagoon water were applied to soils

(Wallingford et al., 1975, 1976).

Heavy metal contamination may also be a problem, although it is

one that is much more apt to arise where sewage sludge from urban

sources is applied to the land. Of most concern are lead, zinc,

copper, nickel, and cadmium (United States Department of Agriculture,

1978). This problem is complicated by the fact that differences in

soil chemical and physical properties affect retention in the soil

of these metals, and subsequent uptake by plants. Chubin (1981)

found, for example, that cadmium uptake was influenced by soil pH

and CEC, and that, in some cases, zinc and cadmium uptake were

related as well. Further, as Willson et al. (1980) note, plant

species, and even varieties within species, differ in uptake and

translocation of heavy metals. While heavy metal contamination is

not likely to be a problem using compost made of animal manure, this

possible source of hazard should be kept in mind.

Finally, problems can also result from the high biological oxygen

demand (BOD) or organic wastes, which can result in anaerobic soil

conditions. Such problems have been reported in Europe and North

America, but will probably be much less serious in developing nations

where manure or compost is more likely to be used than lagoon water.

One advantage of compost is that its BOD is low because decomposition

has already occurred. Nonetheless, soils can become anaerobic from

the high BOD of manure, especially very wet soils. Such conditions

cause denitrification, and many of the products of anaerobic decompo-

sition, such as organic acids, are harmful to plants (McCalla et al.,


Because of the possibility of transmitting disease causing organ-

isms, the use of organic wastes, especially manure, as a fertilizer

has caused concern. In addition, dung heaps and compost piles can

become attractants for flies, both a nuisance factor and a health

hazard to the degree that the enhanced fly population itself promotes

the spread of disease (Anderson, 1967). Over 100 diseases that can

be passed from animals to man are known and could be a problem where

manure is used as a fertilizer (Decker and Steele, 1967). It night-

soil is used, especially in areas with high levels of infection in

the population, health problems are particularly important.

The health hazard associated with the use of organic fertilizers

will depend on the incidence of viable pathogens in the fecal waste

material, the survival rate of these organisms in the compost, and

the epidemiology or mode of transmission of the organism. Table 7

lists some of the organisms and diseases that are of special impor-

tance to the discussion here because of their prevalence in tropical

regions and their ease of transmission to man (see Faust, Beaver, and

Jung, 1975; Metcalf, 1976; National Academy of Sciences, 1977;

Swellengrebel and Sterman, 1961). Pathogens which cannot pass more

or less directly from human or animal feces to the soil or crop, and

then to the human vector, are relatively unimportant. For example,

Schistomata japonicum (the blood fluke) is a relatively common

pathogen, causing schistosomiasis, in the tropics. It is not very

important, however, to this discussion because an intermediate host,

a snail, is required to complete its lifecycle (Faust, Beaver, and

Jung, 1975).

Composting has proven effective in destroying these pathogens.

Gotaas (1956) reports that virtually all of the bacterial, protozoan,

and helminthic organisms in Table 7 have been shown to be destroyed

in properly prepared compost. Maintenance of high temperatures and

Table 7. Pathogens of special concern when using manure as a

Type Organism Disease

Bacterial Salmonella typhosa
Salmonella spp.
Shigella spp.
Vibrio cholera
Mycobacterium tuberculosis

Protozoan Endamoeba histolytica

Helminthic Ascaris lumbricoides
Oxyaris vermicularis
Thichuris trichuria
Taenia saginata
Taenia solium
Strongyloides stercoralis
Hymenolapis nana
Andyostoma duodenale
Necator americanus

Viral Adenoviruses

Coxsackievirus A



Infectious hepatitis virus



Typhoid fever
Bacillary dysentery

Amebic dysentery



Eye, respiratory infections

Aseptic meningitis, congeni-
tal heart anomalies, dia-
betes (?), fever, herpangina,
myocarditis and pleurodynia

Aseptic meningitis, diarrhea,
rash and respiratory infec-

Aseptic meningitis, polio-

Infectious hepatitis

Acure infections non-bacter-
ial gastroenteritis

Diarrhea, respiratory infec-

adequate mixing of the compost are important in ensuring complete

destruction. Ascaris lumbricoides is particularly important because

it is extremely prevalent in man and in animals in developing areas,

and because it is difficult to destroy. Gotaas (1956), for example,

indicates the Ascaris eggs survived longer (22 days or more) than

those of most pathogens during composting. He states that anaerobic

composting may not completely destroy Ascaris eggs even in six

months. McGarry and Stainforth (1978), however, found that Ascarid

egg mortality was 100% in 30 days in properly managed self-composting

toilets. Less is known regarding virus mortality during composting,

but research findings in some cases do indicate that survival is

decreased by high temperatures and prolonged storage (Sigel et al.,


Control of the fly population around compost piles can be a

serious problem. Scott (1952) studied this problem in China and

makes several suggestions regarding fly control. Ensuring uniform

exposure of the entire heap to prolonged high temperatures is

crucial (Gotaas, 1956). Turning is important because the fly lar-

vae migrate to the cooler, outer layers of the heap. Shredding

may help as well. Fly control is particularly important where

large amounts of fecal waste are used in the compost.

Some general comments are in order here as well. First, as

Menzies (1976) points out, reclaiming wastes really involves striking

an acceptable balance between the benefits derived from using the

wastes and the resultant potential health risks to man and animals.

In developed nations, particularly in North America, the general view

is that the health risk must be very low to make the use of organic

fertilizers worthwhile. Spread of disease among animals is often

cited as a major drawback to use of organic wastes, for example

(Bell, Wilson, and Dew, 1976; Hojovec, 1977; Taylor, 1973; Taylor

and Burrows, 1971).

In developing nations this question must be viewed somewhat

differently. Failure to use organic fertilizers may mean failure

to use fertlilizers at all. Even assuming that the health risk is,

by North American standards, high, this risk must be balanced against

the general improvement in public health that results from higher

sustained yields and resultant improvements in dietary standards.

Second, where infection is endemic in the population, and espec-

ially where wastes are not treated, individuals are exposed to preva-

lent pathogens at an early age. Nnochiri (1975) points out, for

example, that 90% of preschool children are exposed to and develop

antibodies against at least one of the three types of polio in many

tropical areas. While use of raw wastes as a fertilizer may be

partly responsible for this exposure (Beaver and Deschamps, 1949),

the problem lies with the method of application of the manure, not

the use of manure as a fertilizer. Infection from manure use was

once considered a serious problem in China (Faust, 1924; Lane, 1934).

By stressing hygienically acceptable practices, this problem has

largely been overcome (Department of Environmental Health, 1977).

Finally, composting represents an improvement of sanitary stan-

dards in many cases. Because of the high concern over health hazards

in developed countries, and because of the low cost of chemical

fertilizers, wastes have been systematically destroyed, for the most

part, and agriculture has been supported by an energy subsidy in the

form of fossil fuels. Yet, even in those wealthy nations, it has

become obvious that the substitution of nonrenewable energy and

chemical resources for lost nutrients cannot go on forever. Further,

the cost of destroying wastes, itself a pollution hazard and energy

consumptive process, is rising. Sewage treatment is limited or non-

existent in many parts of the world, and the energy-intensive and

technologically sophisticated systems in use in the United States

and Europe will probably remain unavailable to much of the world's

population. Composting can provide a practicable method of sanitary

waste disposal (Rybczynski, 1977), and help reduce dependence on

expensive fertilizer materials.


The study was essentially a three-stage process, and Fig. 4

provides a schematic overview of the entire experimental design.

The first stage involved the actual manufacture of compost. The

second stage involved utilization of the compost in field trials,

using a variety of treatments on the plots, and the third stage was

a survey, designed to gauge the number of farms in each zone where

the technology that was developed could be utilized. In order to

facilitate the discussion here, each of these stages is described


Compost Production

Two types of compost were made at each study site, unenriched

and enriched. The unenriched compost consisted of a simple mixture

of cow manure and corn or sorghum stover. The enriched contained a

few kilograms of a complete mix fertilizer as well, 15-15-15.

The fertilizer was added to increase the phosphate content of

the compost, although, of course, use of complete mix fertilizer

means that nitrogen and potassium content should be increased as

well. Cattle manure is very low in phosphorus, and as Lauer (1975)

point out, the most serious constraint in replacing chemical ferti-

lizer use by use of organic fertilizer made from manure is that of

meeting the phosphorus requirements for plant growth. Others (Mathur,

Sarkar, and Mishra, 1980; Rastogi, Mishra, and Ghildyal, 1976;

CATIE I, Wet Season Trial

Fig. 4. Overview of Project

La Pacifica


Sadaphal and Singh, 1979; Walunjkar and Acharya, 1955) have also

attempted to overcome this problem by the addition of phosphate in

some chemical form to compost. Since it is difficult and expensive

to acquire superphosphate singly in Costa Rica, the phosphate was

applied in a readily available and commonly used complete mix.

The manure and corn stover were placed in layers, always starting

and ending with a layer of stover. It is best that the uppermost

layer be one of vegetative materials, not manure, in order to avoid

attracting flies and other pests. At CATIE, where large concrete

pits were available, one group of replicates was constructed in

those pits. In the second trial at CATIE and at the trials in

Canas and Cariari, the compost was made as overground heaps. A

shallow pit (30 to 50 cm deep) was dug and lined with clear plastic

both to provide support and to serve as a trap for the nutrient-rich

liquid that is produced during composting. In all cases, the original

heap was at least 2 m long by 1.5 m wide by 1 m deep. These are the

minimal dimensions that can be used because smaller heaps do not

provide the mass and insulation that is needed to support the thermo-

philic population during the composting process. Wider heaps are

apt to suffer from inadequate aeration and deeper heaps from compac-

tion, but almost any length heap can be constructed (Gotaas, 1956).

Aeration was provided by bamboo poles. The centers were removed from

the bamboo shoots and holes were cut in each side to make a chimney.

These were placed in the center of the heap at intervals of about

50 cm. The heaps were covered with plastic as well to provide some

protection from rain and excessive desiccation. The compost was

turned at 4 and 8 weeks after construction of the heaps. Tables

8 through 11 show the materials used in the compost heaps.

The carbon, nitrogen, phosphorus, potassium and microelement

content of the manure and stover, and of the finished compost were

determined. In addition, all compost was sampled at 2, 4, 8, and

12 weeks after construction of the heaps and pH, humidity, and

nitrogen and carbon content were determined. In the case of the

first trial at CATIE, the compose was sampled at 1, 5, 6, 9, and

10 weeks after construction as well. Only pH, humidity, and nitro-

gen content were determined for these samples. These samples were

extracted with a soil probe.

There is no commonly accepted method for determining carbon

content in compost. Suzuki, Harada, and Kumada (1975) used a wet

digestion procedure, whereas Abd-El-Malek et al. (1976) estimated

carbon by loss on ignition in a muffle oven at 700C for one hour,

for example. Several factors may interfere with determination of

oxidizable carbon using wet combustion procedures. Most important,

these procedures are subject to incomplete carbon oxidation, neces-

sitating the use of a correction factor. This factor must be

determined by using some other accurate measure of oxidizable carbon.

Since the relative digestibility of the remaining organic complexes

in compost changes over time, the factor determined at any given

time may not be correct for other samples, and a new factor should

be determined for each set of samples. Similarly, a factor must

be determined for each type of fresh organic material that is ana-


Table 8. Materials included in compost heaps, CATIE, Trial I.

Unenriched Enriched

Replicate Materiala Wet Weight Dry Weight Materiala Wet Weight Dry Weight
(kg) (kg) (kg) (kg)

1 Manure 2 797 136 Manure 3 and 4 1,080 189
Corn Stover 1 596 312 Corn Stover 4 214 165
Fertilizer 20 20

Total 1,393 448 Total 1,314 374

2 Manure 2 730 124 Manure 3 and 4 1,080 189
Corn Stover 2 603 456 Corn Stover 4 212 164
Fertilizer 20 20

Total 1,333 580 Total 1,312 373

3 Manure 2 730 124
Corn Stover 2 618 467

Total 1,348 591

aSee Table 44, Appendix A, for details of the chemical characteristics of the materials used.

Table 9. Materials included in compost heaps, CATIE, Trial II.

Unenriched Enriched
a Wet Weight Dry Weight a Wet Weight Dry Weight
Replicate Material Weight Dry Weight Material (kg) (kig
(kg) (kg) (kg) (kg)

1 Manure 251 30 Manure 150 18
Corn Stover 72 56 Corn Stover 99 77
Fertilizer 3 3

Total 323 86 Total 252 98

2 Manure 252 30 Manure 152 18
Corn Stover 72 56 Corn Stover 102 79
Fertilizer 3 3

Total 324 86 Total 257 100

3 Manure 253 30 Manure 150 18
Corn Stover 72 56 Corn Stover 100 77
Fertilizer 3 3

Total 325 86 Total 253 98

aSee Table 45, Appendix A, for details of the chemical characteristics of the materials used.

Table 10. Materials included in compost heaps, Cariari.

Unenriched Enriched

Replicate Materiala Wet Weight Dry Weight Materiala Wet Weight Dry Weight
(kg) (kg) (kg) (kg)

1 Manure 2 and 3 162 39 Manure 2 70 23
Corn Stover 39 34 Corn Stover 42 32
Fertilizer 3 3

Total 301 102 Total 115 58

2 Manure 1, 2 & 3 470 112 Manure 2 and 3 77 18
Corn Stover 41 31 Corn Stover 60 45
Fertilizer 4 4

Total 511 143 Total 141 67

3 Manure 2 and 3 179 35 Manure 2 70 23
Corn Stover 39 29 Corn Stover 60 45
Fertilizer 4 4

Total 218 64 Total 134 71

aSee Table 46, Appendix A, for details of the chemical characteristics of the materials used.

Table 11. Materials included in compost heaps, La Pacifica.

Unenriched Enriched

Replicate Materiala Wet Weight Dry Weight Materiala Wet Weight Dry Weight
(kg) (kg) (kg) (kg)

1 Manure 435 159 Manure 275 100
Sorghum Stover 94 55 Sorghum Stover 96 56
Fertilizer 4 4

Total 529 214 Total 375 160

2 Manure 475 173 Manure 275 100
Sorghum Stover 106 62 Sorghum Stover 96 56
Fertilizer 4 4

Total 581 235 Total 375 160

3 Manure 475 173 Manure 275 100
Sorghum Stover 104 61 Sorghum Stover 96 56
Fertilizer 4 4

Total 579 234 Total 375 160

aSee Table 47, Appendix A, for details of the chemical characteristics of the materials used.

Gotaas (1956) suggests that ashing in a muffle oven is ade-

quate. He reports that results within 2 to 10% of more accurate

determinations were found using this method. Schulze (1960) gives

the formula:

%C = (100 % Ash)

for determining carbon by ashing.

No muffle oven was available and, given the inherent problems

with wet digestion procedures, the best alternative was to use a

carbon-hydrogen analyzer. This is a very accurate, but time-consuming

and expensive method for determining carbon. Dried, finely ground

(80 mesh sieve) samples were used. A 0.01 g sample was combusted

at approximately 850C for six minutes.

Total nitrogen was determined using the micro-Kjeldahl method

(Bremmer, 1965; Hesse, 1971). Samples were digested for one hour.

Comparison of findings when the same samples were also digested for

2, 3, and 4 hours showed no differences from the results obtained

with one hour of digestion. Samples were oven dried at 80C and

ground (40 mesh sieve) prior to analysis.

The solution for determination of phosphorus, potassium, and

microelement content was extracted with a heated mixture of perchloric

and nitric acid, and total phosphorus was determined volumetrically.

Calcium, magnesium, copper, iron, manganese, zinc, and aluminum were

determined by atomic absorption spectrometry (Willard, Merritt, and

Dean, 1974).

Determining the pH of the compost sample presented some diffi-

culties. Although pH is a frequently measured characteristic of

compost, most authors fail to indicate how they determine pH (Galler

and Davey, 1971; Golueke, Card, and McGaukley,1954; James, Rettger,

and Thom, 1941; Poincelot, 1974; Willson and Hummel, 1975). Schulze

(1962) measured pH by placing a 20 g sample of compost in a beaker

and adding enough distilled water to completely cover the sample.

The sample was stirred prior to determining pH.

The literature discussing pH testing in soils indicates the

range of problems that are encountered in making this determination.

These same problems can be expected to occur in the case of organic

materials such as compost. Use of CaC12 or KC1 in the solution gives

a lower pH reading because of the replacement of H and Al cations on

the exchange sites by Ca or K cations (Pearson and Adams, 1965). The

magnitude of this effect in compost samples is not discussed in the

literature. Using distilled water avoids these problems, but even

where distilled water is used, increasing the dilution factor in the

sample decreases the salt concentration and increases the pH value

(Heese, 1971; Peech, 1965). No standard dilution factors for compost

samples have been established. Finally, in diluted samples, measur-

ing pH in the sediment gives a different, and usually lower, value

than measuring pH in the supernatant liquid (Pearson and Adams, 1965).

Since high cation-exchange capacity (CEC) favors a large suspension

effect, this difference could be expected to be rather large in

compost samples. Further, practical difficulties were encountered.

Dried samples, which can be ground, do not rewet well, and may

therefore give inaccurate results. Wet samples were mixed in a

blender with distilled water, but this required a high degree of


Because of these problems another method was used. A wet

sample was placed in a metal sleeve with small holes in the sides.

The sleeve was placed on a platform and elevated so that a metal core,

nearly the same diameter as the sleeve, was gradually inserted,

compressing the sample. The sample was compressed until it refused

to yield further liquid, and the liquid exuded under pressure was

collected. The pH of the liquid, which was murky but clear of

sediment, was measured with glass electrodes. This method has been

successfully used at CATIE to measure pH of ensilage, a material

similar to compost in its physical properties.

The temperature of the compost, especially the first trial

heaps at CATIE, was monitored. A special thermometer, over one

meter long, was made for this purpose by inserting a glass submer-

sion thermometer in a metal tube so that the tip of the glass thermo-

meter fit into a tip formed on the tube. A window in the tubing

permitted the user to read the temperature. Comparing the tempera-

ture reading on this thermometer with that on an unenclosed glass

submersion thermometer showed that there was no appreciable differ-

ence if the metal apparatus was left for at least four minutes in

the medium. The inside of the metal tube was also stuffed with

aluminum foil to increase conductivity.

The temperature of the heaps at CATIE was measured regularly

and frequently, daily for one week after turning and every third

day otherwise, but this was not possible at Cafas and Cariari.

Even though thermometers were left at those sites with the coopera-

tors,. there was a tendency for the individuals concerned not to

record the temperature. Periodic readings showed that the tempera-

ture was adequately high, but the scanty data make it impossible to

compare temperature curves at the three sites.

Obtaining representative samples from a compost heap is difficult

because it is not a uniform medium. This is especially true prior to

the first turning of the heap, when the manure and vegetative mater-

ial are still layered, and when the material is still largely decom-

posed. Even after turning, the heap may still not be very uniform.

Suzuki and Kumada (1976) found, for example, that six distinct layers

formed over a one-year period of time in a heap formed of manure and

sawdust. Such distinct strata are not visible in heaps that are

turned more frequently. In order to overcome this problem, each

sample consisted of three subsamples, extracted from various depths,

and each heap was sampled at several spots on each sampling date.

The samples were either analyzed individually to obtain an average

value, or were dried, ground, and mixed together to form one sample

in the case of the use of the carbon-hydrogen analyzer.

Field Trials

Corn (Zea mays) was planted at all study sites. Five fertili-

zation treatments were used: (1) unenriched organic fertilizer;

(2) enriched organic fertilizer; (3) a mixture of chemical and

unenriched organic fertilizer; (4) chemical fertilizer; and (5)

zero fertilization. The equivalent of 100 kg nitrogen per ha was

applied on all fertilized plots. Due to the deficiency of phosphate

in the organic fertilizers, a chemical source of phosphorus was

needed for those plots receiving compost. It was applied in the form

of triple superphosphate, at such a level as to bring the total phos-

phate applied on all plots, except the controls, up to the total

phosphate level received by the plot with the highest phosphate

fertilization rate, the plot receiving both chemical and organic

fertilizer. In order that all plots receive the same amount of

potassium, a small amount of potassium was also applied to the plots

receiving chemical fertilizer alone. The organic fertilizer was

extremely rich in potassium and therefore additional potash (as KC1)

was usually needed on the plots receiving chemical and mixed chemi-

cal and organic fertilizer. Tables 12 through 14 show the materials

applied to the plots.

The test plots were 20 m2 and the corn was planted at a row

spacing of 75 cm, with 50 cm between hills. Four to five seeds per

hill were planted, using a corn variety appropriate to local condi-

tions (Tuxpeno in Cafas, Tico VI in Turrialba, and a local white corn

in Cariari). The seed was treated with fungicide prior to planting.

A randomized complete block design was employed.

The chemically fertilized plots received two applications of

fertilizer. Forty percent of the total nitrogen requirement was

applied at planting, as 10-30-10, along the rows. About 45 days

Table 12. Materials applied to field plots, CATIE.

Dry Weight Wet Weight
Treatment Source Amount Amount N P205 K20
(kg/ha) (kg/ha) (kg/ha) (kg/ha) (kg/ha)

Chemical 10-30-10 400 40 120 40
NH4NO3 179 60
Triple Superphosphate 146 67
KC1 1,587 1,000

Unenriched Unenriched Compost 10,870 29,698 100 110 1,040
Organic Triple Superphosphate 167 77

Enriched Enriched Compost 7,407 11,538 100 82 524
Organic Triple Superphosphate 228 105
KC1 819 516

Mixed 10-30-10 400 40 120 40
Unenriched Compost 6,521 17,819 60 67 624
KC1 597 376

Table 13. Materials applied to field plots, La Pacffica.

Dry Weight Wet Weight
Treatment Source Amount Amount N P205 K20
(kg/ha) (kg/ha) (kg/ha) (kg/ha) (kg/ha)

Chemical 10-30-10 400 40 120 40
NH4NO3 179 60
Triple Superphosphate 49 23
KC1 150 94

Unenriched Unenriched Compost 6,757 13,514 100 38 128
Organic Triple Superphosphate 228 105
KC1 10 6

Enriched Enriched Compost 6,250 12,026 100 98 134
Organic Triple Superphosphate 210 97

Mixed 10-30-10 400 40 120 40
Unenriched Compost 4,054 8,108 60 23 77
KC1 28 17

Table 14. Materials applied to field plots, Cariari, Farms I, II, and III.

Dry Weight Wet Weight
Treatment Source Amount Amount N P205 K20
(kg/ha) (kg/ha) (kg/ha) (kg/ha) (kg/ha)

Farm I

Chemical 10-30-10
Triple Superphosphate

Unenriched Unenriched Compost
Organic Triple Superphosphate

Enriched Enriched Compost
Organic Triple Superphosphate


Unenriched Compost

120 40







100 78 91

100 76 66

40 120 40
60 47 54

Farm II

Chemical 10-30-10
Triple Superphosphate

120 40

Table 14.--Continued.

Dry Weight Wet Weight
Treatment Source Amount Amount N P205 K20
(kg/ha) (kg/ha) (kg/ha) (kg/ha) (kg/ha)

Unenriched Unenriched Compost
Organic Triple Superphosphate

Enriched Enriched Compost
Organic Triple Superphosphate


Unenriched Compost

Chemical 10-30-10
Triple Superphosphate

Unenriched Unenriched Compost
Organic Triple Superphosphate

Enriched Enriched Compost
Organic Triple Superphosphate


Unenriched Compost



Farm III









100 67

100 91

40 120
60 40

40 120

40 120 40
60 51 58

later a post-emergence application of ammonium nitrate, accounting

for 60% of the nitrogen requirement was made. The compost was

applied in narrow trenches, which were covered over with soil.

The seed was planted directly into the compost, using a planting

stick in the same manner as on all other plots. Neither the organi-

cally fertilized plots, not those receiving a mixture of organic and

chemical fertilizers, received two fertilizer applications. The

entire fertilizer requirement was applied at planting.

Yield of both grain and biomass was measured. After taking

field weights, a sample of the grain and stover from each plot was

dried at 80C to obtain the dry weight yield.

Soil samples from each test plot were collected. The soil was

sampled on four occasions: prior to planting, at planting, at about

45 days, and at harvest. Each sample consisted of three subsamples,

taken at 0-25 cm. Samples were taken from within the rows, but the

two outside rows in each plot were excluded from the sampling area.

These samples were analyzed for pH, organic matter content, and

macroelement and microelement content. The pH was determined using

a 2:1 dilution with distilled water, The Walkley-Black wet digestion

method was used to analyze organic matter content, and nitrogen con-

tent was determined by the semi-micro-Kjeldahl procedure (Bremmer,

1965). Double acid extraction in 0.05N HC1 and 0.025N H2S04 was

used to prepare the solution for determining available phosphorus,

potassium, and microelement content (Olsen and Dean, 1965). Avail-

able phosphorus was determined colorimetrically with a molybdate-

venadate solution, and potassium and microelement content by atomic

absorption spectrometry.

Labor and Survey Information

Labor was recorded for all tasks involved in the production and

application of compost. The labor values are reported in man-hours

per task. Although the exact kcal expenditure for each type of

activity was not measured, the general value of 191.2 kcal per hour

provided by Leach (1976) for agricultural work can be used in energy


Farmers in Cariari, Turrialba, and La Sierra were interviewed

to determine availability of manure and vegetative materials for

composting on those farms to find out current fertilizer usage, and

to determine the potential for and interest in the use of compost in

the three zones. A copy of the questionnaire is included in Appendix

C. The farms visited were selected because further data about these

farms are available at CATIE (Avila, 1979; CATIE, 1980b). A copy of

the CATIE questionnaire is also included in Appendix C. Manure

samples, analyzed for nitrogen content, were taken at various farms

in each zone to determine whether there is wide variability in the

nitrogen content of manure from one zone to another.


In order to facilitate reading, the results and discussion of

them will be presented in four parts. First, the results of the

composting process itself are discussed; then yield data are pre-

sented. Finally, changes in selected soil chemical characteristics

are described, and labor investment is detailed.

The Composting Process

Fairly complex technologies have been developed to maintain

optimum conditions for thermophilic composting (Finstein, 1980;

Singley et al., 1975; Schulze, 1962; Willson, 1971). Controlling

the necessary factors under field conditions and at the same time

using an appropriately inexpensive and simple technology is difficult

and, as the discussion below shows, achieving optimal conditions is

not always possible. Nonetheless, despite the imperfect environmental

control that could be achieved, the data indicate that the composting

process proceeded adequately in most cases. Measure of humidity,

pH, C:N ratio, nitrogen content, temperature, and macro and micro-

element retention are discussed here.

Figure 5 shows the C:N ratio over time in the 24 heaps that

were built. As the graph shows, stability was achieved very rapidly,

that is, the C:N ratio changed very little after 8 weeks, and may in

fact have been stable even sooner, after about 6 weeks.

C:N Ratio

35.0 1




5 .0 1, ....... ............... I

0 2 4 6 8 10 12

Age of heaps, in weeks

Fig. 5. C:N ratio of compost heaps.


S-.- P Cariari
La Pacifica

4-*-4. CATIE I
--4--+. Cariari
6 6 & La Pacifica

Several methods for determining when compost is stable have

been suggested. These include measures of phytotoxin production,

laboratory tests utilizing rapidly growing plants or fungi as

indicators, sulfide tests, nitrate tests, determination of redox

potential, and detection of starch (Lossin, 1970; Spohn, 1969;

Zucconi et al., 1981). Stabilization of the C:N ratio at low values

(less than 20:1) is considered an adequate test of compost maturity,

although perhaps not as ideal as determination of redox potential.

An unchanging or very slowly changing C:N ratio indicates that

further decomposition will occur only very slowly (Gotaas, 1956;

Taiganides, 1977). The C:N ratios of the test heaps stabilized at

values of 10:1 to 17.5:1, well within the accepted range.

The rapid stabilization of the compost is somewhat surprising

given the technology used. Using highly sophisticated systems where

temperature and oxygen supply are completely controlled, and where

the compost is continually turned in a bench-scale drum, composting

time has been reduced to as little as 7 to 10 days (Galler and Davey,

1971; Schulze, 1962; Willson, 1971). The test heaps, however, were

turned only twice and the only source of aeration was bamboo chimneys.

Thus, the more normal four to six months usually required to reach

stability under such conditions would be expected.

Polprasert, Wangsuphachart, and Marramara (1980), in their dis-

cussion of composting nightsoil and water hyacinth in the tropics,

also noted a very high rate of decomposition during the first 16 days

of the process, followed by a more prolonged period of lower activity,

and apparent stability of the product at 60 to 72 days, using a

similar composting procedure to that utilized here. Strom, Morris,

and Finstein (1980), on the other hand, found that up to 10 months

were needed to stabilize leaf compost, using a similar technology

in a mid-latitude setting. Similarly, Duthie (1937) found that

maize straw composted under tropical conditions for 107 days reached

the same degree of decomposition as rye straw composted 290 days in

a mid-latitude setting, as measured by content of hydrolyzable cellu-

lose and hemicellulose and lignin. These divergent results suggest

that the process may be much more rapid in the tropical setting.

However, no definitive conclusions can be drawn because of the wide

variety of materials and methods used, and the scarcity of informa-

tion on composting under tropical conditions.

The extreme rapidity of the process reported here suggests that

there is indeed a pronounced difference in the process between mid-

latitude and tropical situations. If so, this probably is due to the

relatively high mean daily temperature and the low daily or periodic

fluctuation in temperature typical of the tropical setting, rather

than differences in microbial populations. Even where innoculums

(Golueke, Card, and McGauhley, 1954; Greenstreet, 1928; Obrist, 1966)

or cultures of pure and mixed microorganisms (Waksman and Cordon,

1939) have been purposely introduced into compost, no significant

differences in composting rate have been reported. Under cold condi-

tions, however, the process is greatly slowed, and even under cool

conditions some portion of the outer layer of the heap will be rela-

tively inactive (Lambert, 1934).

Temperature was carefully monitored in the first group of heaps

constructed at CATIE, and Fig. 6 shows the temperature curves of

these heaps during the process. Although the data are incomplete,

temperatures at La Pacifica are also shown to provide a point of

comparison (Fig. 6). These curves also suggest that microbial acti-

vity was greatly reduced after 60 days. As the graph shows, the

temperature increased after turning at 30 days, and the average temp-

erature (although not the maximum temperature in the unenriched heaps)

then dropped below the generally accepted thermophilic boundary of

37.50C at roughly 45 days. The second turning, at 60 days, produced

a slight temperature increase, but generally failed to raise biologi-

cal activity to the thermophilic level again. Although temperature

could not be monitored as thoroughly at other sites, the temperature

readings that were taken suggest a similar pattern at all three loca-

tions, and later in the Santa Elena site as well, although maximum

temperatures recorded at Cariari and Santa Elena were never as high

as those recorded at CATIE and La Pacifica.

Obtaining representative temperature readings from a compost

heap is difficult because the temperature is not uniform throughout.

Suzuki and Kumada (1976) found that temperature differences in the

various zones of a compost heap persisted even when it was left un-

turned for a period of one year, and Strom, Morris and Finstein (1980)

found similar zonal differences in recently constructed heaps. The

values reported in Fig. 6 are averages of readings extracted at eight

predetermined locations and at two to four depths at each location

(depending on the-degree to which the height of the heap had decreased)

turned T turned
20 40 60
Fig. 6. Temperature in compost heaps, CATIE I



/ I \


50 r

4 //

turned turned
0 20 40 60


Fig. 7. Temperature in compost heaps, La Pacifica




for each of the three replicates. The individual readings varied

with the depth and distance from the side of the heap as well,

generally being highest in the center of the heaps and lowest in

the corners and near the bottom. Similarly, as Atchley and Clark

(1979) report, mesophilic sites or pockets were encountered even

when overall temperature was high, and some spots consistently main-

tained higher than average temperatures. As they currently point

out, this shows that there are not distinct mesophilic and thermophi-

lic phases in composting. Rather, a mix of the two types of activity

is always present, with one or the other predominating.

Temperatures in the compost heaps did not reach the high mean

values of 60-70C reported by others (Singley, Decker, and Toth,

1975; Galler and Davey, 1971). While several factors could prevent

the temperature from reaching such high levels, aeration is probably

the most critical in this case. Schulze (1960) found that a 100C

increase in temperature nearly doubles oxygen uptake, and Willson

(1971) showed oxygen consumption rates as high as 1.12 ft3 per minute

per ton compost at temperatures of 35-62*C. Given the limited aera-

tion provided by the technique used in Costa Rica, temperature is

almost undoubtedly limited by oxygen uptake.

The relatively low temperature may be less indicative of the

efficiency of the process than was once assumed, however. Finstein

(1980) suggests, contrary to the popular belief that the compost heap

should be maintained at as high temperature as possible, that even at

55C excess metabolic heat begins to accumulate in the heap to a

degree sufficient to inhibit growth of thermophiles. Similarly,

Bagstam (1978) found that the most rapid decomposition in a compost

containing spruce bark occurred at 450C, and that fungal and actino-

mycete populations declined at higher temperatures. Waksman, Cordon,

and Hulpoi (1939) found that ammonia, which is easily lost, increased

at 65C and remained very high at 750C, but reached trace amounts

within only 19 days of composting at temperatures of 50*C, minimizing

this loss. Thus, the temperatures maintained in Costa Rica may be

near the optimum.

Where higher temperatures are desired, some improved method for

ventilation would be required. This could be the case, for example,

where farmers wish to apply the compost to vegetable crops and where,

therefore, assuring maximum pathogen extinction is critical. Placing

more vertical bamboo chimneys and adding one or more layers of hori-

zontally placed chimneys could, perhpas, alleviate this problem.

Overall, however, temperatures were sufficiently high to produce a

stable product quickly. No pathogen counts were made.

A comparison of Fig. 8, showing nitrogen content (dry weight

basis) over time in the heaps, and the graph of C:N ratios (Fig. 6)

explains the apparent increase in carbon at about two weeks in six

of the eight curves. There is, in fact, no way that significant

additional carbon can enter the heaps unless fresh carbonaceous mater-

ial is added, which did not occur. The apparent increase in carbon

actually is due to a high loss of nitrogen during the first two weeks

of composting.

Nitrogen can be lost easily from compost when it is present in

either the nitrate (NO3) or ammonia (NH3) form, the former through

%N (dry weight basis)

0 2 4 6 8

Age of heaps, in weeks

Fig. 8. N content of compost heaps.


S-c--- CAT'IE II
-'U -*- Cariari
a- L Pacific&

a a-e CATIE Ic
-4-4-4 Cariari
,b 6 La Pacific&

10 12


leaching and the latter through escape into the atmosphere. In

addition, Elliott, Schuman, and Viets (1971) have reported that

organic nitrogen compounds enter the atmosphere from beef feedlot

surfaces, and nitrites and nitrates can be reduced under anaerobic

conditions and enter the atmosphere as nitrogen gas (Vanderholm,

1975). Several factors can cause such losses.

One possible cause of loss in this case was the low initial

C:N ratios of the heaps. There is considerable disagreement over

the optimal initial C:N ration for a compost heap. Golueke (1972)

states that the optimum is 20:1 or 25:1, whereas Poincelot (1974)

gives 26:1 to 35:1 as the optimum. In fact, the optimum initial

C:N ratio will vary, depending on the types of materials being

composted. The problem is to achieve a balance between nitrogen

supply and available carbon. If the carbon is in a form that is

very resistant to attack, a much higher C:N ratio is needed because

only a portion of the total carbon is available as an energy source

for the microorganisms (Regan and Jeris, 1970). A much lower C:N

ratio is possible where more easily extractable forms of carbon are

available. The problem is complicated even further by the differences

in availability of nitrogen in various organic materials (Rubins and

Bear, 1942; Toth, 1973).

Most authors also agree that a higher initial C:N ratio increases

composting time (Waksman and Gerretson, 1931). However, the reported

data do not clearly support the view of many authors (Golueke, 1972;

Knuth, 1970; Poincelot, 1974; Taiganides, 1977) that a low initial

C:N ratio necessarily or typically leads to higher levels of nitrogen

loss. Polprasert, Wangsuphachart, and Muttamara (1980) composted

mixtures of leaves, water hyacinth, and nightsoil at initial C:N

ratios of 20:1, 30:1, and 40:1. While those heaps with an initial

C:N ratio of 30:1 or 40:1 showed a greater gain in total nitrogen

(a 46% increase in total nitrogen) than the heaps with an initial

ratio of 20:1 (a 10% increase in total nitrogen), the authors do not

report any significant nitrogen losses. Similarly, Galler and Davey

(1971) failed to find that nitrogen loss was greater in material with

an initial C:N ratio of 21:1 than in that with a ratio of 43:1 com-

posting poultry manure and sawdust.

The results found here are contradictory. The coincidence of

high initial decreases in nitrogen content with low initial C:N

ratio generally supports the view that this first episode of nitrogen

loss was related to the original C:N ratio. Those heaps with the

highest initial C:N ratios illustrated the least nitrogen loss in

weeks one and two (Fig. 8) and do not illustrate the increase in

C:N ratio at two weeks typical of the heaps with lower initial C:N

ratios (Fig. 5). Nonetheless, as Table 15 shows, total nitrogen

loss or gain, over the full process, was not necessarily related to

initial C:N ratio.

Referring again to the graph of nitrogen content over time (Fig.

8), it will be seen that several heaps, especially those in the first

trial at Turrialba (CATIE I) and those at Cariari, lost nitrogen well

beyond the first two weeks. Table 15 shows that their total nitrogen

loss was also high, and that it was lowest at La Pacifica. These

data suggest that other mechanisms than the initial C:N ratio played

Table 15. Loss or gain of nitrogen in compost heaps.

Initial N Loss or Gain
Location Treatment C:N Ratio (%)
C:N Ratio M

CATIE I Unenriched 34:1 -27
CATIE I Enriched 20:1 -35

CATIE II Unenriched 30:1 +14
CATIE II Enriched 20:1 0

Cariari Unenriched 20:1 -22
Cariari Enriched 17:1 -54

La Pacifica Unenriched 22:1 +57
La Pacifica Enriched 19:1 +59

a role in nitrogen loss. Even in the first two weeks, it was prob-

ably a combination of several factors rather than any single mechanism

which produced the high nitrogen loss.

Inadequate aeration, already discussed above, was one problem.

Poor aeration, in and of itself, limits biological activity. This is

reflected in temperature, as described above, but the low level of

microbiological activity also means that inorganic nitrogen begins to

accumulate. As Knuth (1970) points out, inorganic nitrogen is subject

to loss be several mechanisms. Nitrates, in particular, are apt to

be lost by leaching.

Further, inadequate aeration is often accompanied by the onset of

anaerobic conditions, or generally excessively high humidity, both of

which occurred at Cariari and ar the first CATIE trial. Under these

conditions, problems of nitrogen loss are exacerbated since nitrates

are denitrified to nitrogen gas and lost. The high humidity further

inhibits aeration, producing even more easily lost inorganic nitrogen.

Optimum moisture content for composting is generally considered

to be 40 to 60% (Taiganides, 1977). Table 16 shows the moisture

content of the compost heaps for the four trials. The heaps at both

Cariari and those in the first trial at CATIE (I) maintained an aver-

age moisture content above the upper limit of 60% during composting,

while those as La Pacifica and in the second trial at CATIE main-

tained acceptable humidity.

Willson and Hummel (1975) note that at moisture contents above

55% some anaerobic activity occurs. Further, at high moisture contents

water replaces air, especially in the large pore spaces. Schulze's (1962)

Table 16. Average moisture content of compost heaps.

Location Average Humidity

CATIE I 70.4

Cariari 61.9


La Pacifica 50.2

data show that a minimum of 30% free air space should be maintained

for aerobic composting. Free air space is affected both by bulk

density, and by moisture content. Thus, at a bulk density of 400 g/l

and moisture content of 60%, free air space remains adequate at 34%.

But at the same bulk density and 70% moisture content, free air space

drops to 27%. In compost heaps bulk density increases over time, so

that moisture content becomes even more critical as the material

approaches maturity. Schulze (1960) has also shown that oxygen uptake

decreases slightly at a moisture content of 70%, even at low (20C)

temperatures. At higher temperatures with higher oxygen demand, this

effect should be more pronounced. Anaerobic conditions were also

noted at the CATIE I and Cariari trials. Poor aeration and excessive

humidity were probably also important in nitrogen loss, then, in

these two trials.

Another factor that can affect nitrogen loss is pH. Values of

6.0 to 8.0 are considered optimum for composting because most micro-

organisms exhibit greatest growth in that range (Willson et al., 1980).

At lower pH values, bacteria, in particular, cannot survive well, but

nitrogen loss due to ammonia volitalization increases with pH (Willson

and Hummel, 1975), and the acceptable pH range is therefore limited.

As Fig. 9 shows, the mean pH values in the four trials staued well

within the accepted limits and should not have produced any negative

effects. Even where pH was initially low (CATIE II), values rose

very soon to near neutrality.

The pH values varied from heap to heap and did not conform to

any of the general "patterns" of behavior that have been described.





0 2 4 6 8
Age of heaps, in weeks

Fig. 9. Mean pH of compost heaps.


4 -.-. Cariari
L la Pacdfica

8 --ee CATI 11
-4---4. Cariari
A, La P-aifica

10 12

Regan and Jeris (1970) and Taiganides (1977), for example, state

that pH values generally drop to about 5.0 in the early stages of

composting, and then rise to 8.0 or 9.0 as the process terminates.

Poincelot (1974) describes a similar sequence of values, but notes

that finished compost is near neutral. These authors attribute the

early acidity they noted to acid formation by bacteria. Willson

(1971) and Willson and Hummel (1975), on the other hand, report

contradictory trends, i.e., an initial increase in pH followed by

a decline to near neutrality, while Suzuki, Harada, and Kumada

(1975) and Schulze (1962) all report only very slight changes over

time. As is generally true, pH samples must be taken from several

points in a heap because pH, like temperature, is not uniform

(Atchley and Clark, 1979) and failure to sample uniformly could

explain some of these contradictory findings. All pH values are

included in Appendix C, but no obvious trends are discernible from

the individual values either.

In summary, the data indicate that nitrogen loss was related to

initial C:N values, poor aeration, and excessive humidity. Total

nitrogen loss was highest at high rainfall sites (CATIE I and Cariari)

and initial C:N ratio varied strongly with nitrogen loss at these

same sites. At lower rainfall sites, initial C:N ratio was less

critical. Overall pH values fell within accepted norms at all sites.

In addition to nitrogen, retention of phosphorus and potassium

are important in composting. Tables 47 through 54 (Appendix A) show

the initial and final phosphate and potash contents for the heaps at

the four trials and the concentration factor for each.7 Analysis of

variance shows a significant difference in the concentration of

phosphate for site but not for treatment (Table 17). In the case

of potash, site, treatment, and the interaction effect were all

significant (Table 18). Duncan's multiple range test shows that

the concentration factor for phosphate at the second CATIE trial

(2.67) was significantly higher than that at La Pacifica (1.55), the

first CATIE trial (1.43), or the Cariari trial (0.88). The latter

three sites did not differ significantly. In the case of potash,

analysis of least significant difference between means reveals that

for both unenriched and enriched compost, the first trial at CATIE

resulted in significantly higher concentration factors than those at

all other sites, and that at CATIE the concentration factor was signi-

ficantly higher for unenriched than for enriched compost (See Tables

59 and 60, Appendix A). No other site exhibited differences in potash


The interpretation of these findings is somewhat unclear. The

very high concentration factor for potash for the first trial at

Turrialba (CATIE I) is repeated for other elements as well. Reference

7The concentration factor refers essentially to the percent
concentration of a given element over time. It is derived by dividing
the final concentration (in percent) of a given element by the initial
concentration (in percent) of that same element. This factor was
used for analysis because the heaps varied greatly in actual content
of a given element both initially and at termination. This occurs
because the manure, and vegetative material as well, differ in their
elemental composition from one site to another. Thus, for example,
final phosphate content varied significantly by site and treatment.
However, this analysis does not reveal much information since initial
phosphate content also varied by treatment and site. Concentration
factors of less than one indicate overall loss of the given element.

Table 17. Analysis of variance,
in compost.

change in phosphate concentration

Source df Mean Square F Value

Treatment 1 0.86 2.40
Site 3 3.41 9.51**
Interaction 3 0.85 0.11
Error 15 0.36

Table 18. Analysis of variance, change in potash concentration in

Source df Mean Square F Value

Treatment 1 4.70 22.67**
Site 3 19.60 94.57**
Interaction 3 2.06 9.94**
Error 15 0.21

to Tables 19 through 22 will show that the results of analysis of

variance produced almost exactly the same results for aluminum, iron,

zinc, and manganese. Tables 61 through 68 (Appendix A) show similar

patterns for these elements when the least significant difference

between means are examined as well. Further, as the partial table

of correlation shows (Table 23), concentration of these elements

was strongly correlated at the first CATIE trial, but not at other


Few authors report microelement content of compost, so that it

is difficult to compare these findings to others. Singley, Decker,

and Toth (1975) do report the final content of some microelements in

compost made of swine waste and urban garbage. They report final iron

contents of 0.66% to 1.07%, compared to the 15.94% and 12.18% for

unenriched and enriched heaps at CATIE (Group I, Table 47, Appendix

A). At the other trials, the findings in Costa Rica are in line with

theirs (see Tables 49, 51, and 53; Appendix A). Similarly, manganese

contents in their compost ranged from 130 to 240 ppm, compared to

2,287 ppm for unenriched and 1.942 ppm for enriched heaps at CATIE.

At CATIE, final copper content averaged 976 ppm for unenriched and

853 ppm for enriched heaps, whereas their values ranged from 8 ppm

to 118 ppm. Average zinc content at CATIE was 4,713 ppm in unenriched

heaps and 942 ppm in the enriched heaps--again compared to only 350

to 500 ppm for Singley, Decker, and Toth. These differences are

even more surprising considering that the compost at CATIE did not

incorporate urban wastes, which are normally higher than crop residues

and animal manure in these elements.

Table 19. Analysis of variance, change in aluminum concentration
in compost

Source df Mean Square F Value

Treatment 1 1277.04 183.31**
Location 3 3187.47 457.55**
Interaction 3 1086.14 155.91**
Error 15 6.97

Table 20. Analysis of variance, change in zinc concentration in

Source df Mean Square F Value

Treatment 1 363.21 6.21*
Location 3 950.15 16.24**
Interaction 3 247.33 4.23*
Error 15 58.49

Table 21. Analysis of variance,
in compost.

change in iron concentration

Source df Mean Square F Value

Treatment 1 2,496.10 80.59**
Location 3 12,591.14 406.53**
Interaction 3 1,532.63 49.48**
Error 15 30.97

Table 22. Analysis of variance, change in manganese concentration
in compost.

Source df Mean Square F Value

Treatment 1 500.42 22.46**
Location 3 4,454.02 199.91**
Interaction 3 152.97 6.87*
Error 15

Table 23. Partial correlation matrix, selected elements.

Fe Al Zn Mn

CATIE I K20 .97 .92 .63 .90

CATIE II K20 -.59 -.85 -.24 -.15

La Pacifica K20 -.91 -.82 .41 .54

Cariari K20 -.72 -.47 .13 -.03

Willson et al. (1980) report that composting both raw and

digested sewage sludge reduced copper and zinc content. Copper

content fell from 420 ppm in raw sludge and 725 ppm in digested

sludge to 300 ppm in composts made from raw sludge and to only

250 ppm in that made from digested sludge. Zinc behaved similarly.

This is difficult to explain since composting normally increases

the concentration of non-volatile elements.

It is possible that potash, aluminum, iron, zinc, and manganese

eneterd the first compost heaps at CATIE from outside sources. It is

a commonly recommended practice to cover compost heaps with soil at

the initiation of composting and after each turning. This practice

was followed at the first CATIE trial until early analyses revealed

a tendency toward high accumulations of aluminum and iron. At that

time the practice was discontinued and it was not used at any other


The soil at the CATIE test site is classified as a Typic

Dystropept (Aste, 1971). It is high in iron, aluminum, and potash,

as well as certain other microelements. The incorporation of this

soil into the compost heaps could have resulted in the extremely

high concentration of some of these elements in the final product.

This hypothesis is supported by the extremely high concentration

factor for iron and aluminum in the first CATIE trials, and by the

very high total content of these elements in the finished heaps.

Aluminum content reached 21.69% in the unenriched and 15.76% in the

enriched heaps (dry weight basis) and iron content was 15.94% in the

unenriched and 12.18% in the enriched heaps at maturity. Biological

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