• TABLE OF CONTENTS
HIDE
 Copyright
 Introduction
 The orchard and techniques
 Chemicals and materials used
 Results
 The need for phosphorus
 Sources of nitrogen and potass...
 Liquid fertilizers
 Summary and conclusions














Group Title: Homestead AREC research report - University of Florida Agricultural Research and Education Center ; SB76-1
Title: Fertilizing avocado orchards through trickle irrigation
CITATION PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00067824/00001
 Material Information
Title: Fertilizing avocado orchards through trickle irrigation
Series Title: Homestead AREC research report
Physical Description: 4 leaves : ; 28 cm.
Language: English
Creator: Malo, Simâon E
Agricultural Research and Education Center, Homestead
Publisher: University of Florida, Agricultural Research and Education Center
Place of Publication: Homestead Fla
Publication Date: 1976
 Subjects
Subject: Avocado -- Irrigation -- Florida   ( lcsh )
Microirrigation -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: S.E. Malo.
General Note: "May 3, 1976."
 Record Information
Bibliographic ID: UF00067824
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 72469510

Table of Contents
    Copyright
        Copyright
    Introduction
        Page 1
    The orchard and techniques
        Page 1
    Chemicals and materials used
        Page 1
    Results
        Page 2
    The need for phosphorus
        Page 3
    Sources of nitrogen and potassium
        Page 3
    Liquid fertilizers
        Page 3
    Summary and conclusions
        Page 4
Full Text





HISTORIC NOTE


The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source
(EDIS)

site maintained by the Florida
Cooperative Extension Service.






Copyright 2005, Board of Trustees, University
of Florida





2+i bAUHomestead AREC Research Report SB76-1 May 3, 1976

/ Fertilizing Avocado Orchards Through Trickle Irrigation

S. E. Malol

Introduction

One of the advantages of trickle irrigation is that soluble'fertilizers can be added
to the irrigation water, distributed throughout the orchar,d;'ah' appp -"dfted"tQaepch
tree in precalculated amounts. This report summarizes, 5 years of e. AM yiA
fertilizing avocado trees through trickle irrigation systems. It is inteded o
bring to your attention initial findings and relevant infornuiipn which can be used
to lower costs of fruit production. Many growers are beginning t pircice erti-
gation" (fertilizing through irrigation) and need information on several relevant
aspects as they apply to our own unique conditions offgrow;ng fruit trees in he
oolitic limestone of Homestead. ... Li f i -! .
:" *--.," "' on'.^ .
The Orchard and Techniques -

A trickle irrigation system was installed in 1971 in an experimental avocado orchard
consisting of 390 trees, planted in 1969 as a cultivar collection (with 3 trees of
each cultivar), at a spacing of 20 x 20 feet. A h.p. self-priming electric pump
was used to obtain water from a 30-foot deep, 9-in well with a water level about 9
feet from the surface. Water pressure was approximately 15 psi at the ends of the
300 ft. laterals (18 psi at the pump) and the system worked automatically with a
24-hour time clock to turn the pump on and off.

Black polyethylene laterals lying on the soil with emitters (rated at 1 gal. (4
liters)/hour) were used to distribute water throughout the orchard. One emitter was
S placed near the trunk of the tree and the other midway between trees. Periods of
irrigation and amounts of water applied were coordinated very closely through the
reading of tensiometers located in the planting trench at varying distances from the
emitters. The rate of irrigation was increased gradually as the dry season pro-
gressed and decreased to lower levels after the onset of the rainy season; thus irri-
gation proceeded continuously throughout the year regardless of intensity of rain-
fall. The amount of irrigation water was calculated to wet the entire trench during
periods of normal evapotranspiration (approximately 0.15-inch a day). However, now
that the trees are approaching their 8th year we consider that a third emitter is
probably needed.

The vigorous growth of most trees has required selective pruning almost every year.
In addition to "fertigation" the orchard has received normal management practices,
such as 2 annual applications of paraquat for weed control and a minimum of 6 fungi-
cidal sprays for disease prevention.

Chemicals and Materials Used

The orchard has been fertilized every two weeks exclusively with soluble forms of
fertilizer from the time the irrigation was installed in 1971. From the beginning
we have applied ammonium nitrate and potassium nitrate as sources of nitrogen (N)
and potassium (K). The amount of these elements has gradually increased from 0.25
Ibs (115 gms) for both N and K per tree/year (calculated as actual N and K) to the
latest increment (Jan. 1976) of 1.5 lb (690 gms) of N and 1.75 Ibs (805 gms) of K
per tree/year. However, for the 2 years previous to Jan. 1976 the levels of N and K

0

1 Associate Horticulturist, University of Florida Agricultural Research and Education
Center, Homestead 33030.





2+i bAUHomestead AREC Research Report SB76-1 May 3, 1976

/ Fertilizing Avocado Orchards Through Trickle Irrigation

S. E. Malol

Introduction

One of the advantages of trickle irrigation is that soluble'fertilizers can be added
to the irrigation water, distributed throughout the orchar,d;'ah' appp -"dfted"tQaepch
tree in precalculated amounts. This report summarizes, 5 years of e. AM yiA
fertilizing avocado trees through trickle irrigation systems. It is inteded o
bring to your attention initial findings and relevant infornuiipn which can be used
to lower costs of fruit production. Many growers are beginning t pircice erti-
gation" (fertilizing through irrigation) and need information on several relevant
aspects as they apply to our own unique conditions offgrow;ng fruit trees in he
oolitic limestone of Homestead. ... Li f i -! .
:" *--.," "' on'.^ .
The Orchard and Techniques -

A trickle irrigation system was installed in 1971 in an experimental avocado orchard
consisting of 390 trees, planted in 1969 as a cultivar collection (with 3 trees of
each cultivar), at a spacing of 20 x 20 feet. A h.p. self-priming electric pump
was used to obtain water from a 30-foot deep, 9-in well with a water level about 9
feet from the surface. Water pressure was approximately 15 psi at the ends of the
300 ft. laterals (18 psi at the pump) and the system worked automatically with a
24-hour time clock to turn the pump on and off.

Black polyethylene laterals lying on the soil with emitters (rated at 1 gal. (4
liters)/hour) were used to distribute water throughout the orchard. One emitter was
S placed near the trunk of the tree and the other midway between trees. Periods of
irrigation and amounts of water applied were coordinated very closely through the
reading of tensiometers located in the planting trench at varying distances from the
emitters. The rate of irrigation was increased gradually as the dry season pro-
gressed and decreased to lower levels after the onset of the rainy season; thus irri-
gation proceeded continuously throughout the year regardless of intensity of rain-
fall. The amount of irrigation water was calculated to wet the entire trench during
periods of normal evapotranspiration (approximately 0.15-inch a day). However, now
that the trees are approaching their 8th year we consider that a third emitter is
probably needed.

The vigorous growth of most trees has required selective pruning almost every year.
In addition to "fertigation" the orchard has received normal management practices,
such as 2 annual applications of paraquat for weed control and a minimum of 6 fungi-
cidal sprays for disease prevention.

Chemicals and Materials Used

The orchard has been fertilized every two weeks exclusively with soluble forms of
fertilizer from the time the irrigation was installed in 1971. From the beginning
we have applied ammonium nitrate and potassium nitrate as sources of nitrogen (N)
and potassium (K). The amount of these elements has gradually increased from 0.25
Ibs (115 gms) for both N and K per tree/year (calculated as actual N and K) to the
latest increment (Jan. 1976) of 1.5 lb (690 gms) of N and 1.75 Ibs (805 gms) of K
per tree/year. However, for the 2 years previous to Jan. 1976 the levels of N and K

0

1 Associate Horticulturist, University of Florida Agricultural Research and Education
Center, Homestead 33030.





2+i bAUHomestead AREC Research Report SB76-1 May 3, 1976

/ Fertilizing Avocado Orchards Through Trickle Irrigation

S. E. Malol

Introduction

One of the advantages of trickle irrigation is that soluble'fertilizers can be added
to the irrigation water, distributed throughout the orchar,d;'ah' appp -"dfted"tQaepch
tree in precalculated amounts. This report summarizes, 5 years of e. AM yiA
fertilizing avocado trees through trickle irrigation systems. It is inteded o
bring to your attention initial findings and relevant infornuiipn which can be used
to lower costs of fruit production. Many growers are beginning t pircice erti-
gation" (fertilizing through irrigation) and need information on several relevant
aspects as they apply to our own unique conditions offgrow;ng fruit trees in he
oolitic limestone of Homestead. ... Li f i -! .
:" *--.," "' on'.^ .
The Orchard and Techniques -

A trickle irrigation system was installed in 1971 in an experimental avocado orchard
consisting of 390 trees, planted in 1969 as a cultivar collection (with 3 trees of
each cultivar), at a spacing of 20 x 20 feet. A h.p. self-priming electric pump
was used to obtain water from a 30-foot deep, 9-in well with a water level about 9
feet from the surface. Water pressure was approximately 15 psi at the ends of the
300 ft. laterals (18 psi at the pump) and the system worked automatically with a
24-hour time clock to turn the pump on and off.

Black polyethylene laterals lying on the soil with emitters (rated at 1 gal. (4
liters)/hour) were used to distribute water throughout the orchard. One emitter was
S placed near the trunk of the tree and the other midway between trees. Periods of
irrigation and amounts of water applied were coordinated very closely through the
reading of tensiometers located in the planting trench at varying distances from the
emitters. The rate of irrigation was increased gradually as the dry season pro-
gressed and decreased to lower levels after the onset of the rainy season; thus irri-
gation proceeded continuously throughout the year regardless of intensity of rain-
fall. The amount of irrigation water was calculated to wet the entire trench during
periods of normal evapotranspiration (approximately 0.15-inch a day). However, now
that the trees are approaching their 8th year we consider that a third emitter is
probably needed.

The vigorous growth of most trees has required selective pruning almost every year.
In addition to "fertigation" the orchard has received normal management practices,
such as 2 annual applications of paraquat for weed control and a minimum of 6 fungi-
cidal sprays for disease prevention.

Chemicals and Materials Used

The orchard has been fertilized every two weeks exclusively with soluble forms of
fertilizer from the time the irrigation was installed in 1971. From the beginning
we have applied ammonium nitrate and potassium nitrate as sources of nitrogen (N)
and potassium (K). The amount of these elements has gradually increased from 0.25
Ibs (115 gms) for both N and K per tree/year (calculated as actual N and K) to the
latest increment (Jan. 1976) of 1.5 lb (690 gms) of N and 1.75 Ibs (805 gms) of K
per tree/year. However, for the 2 years previous to Jan. 1976 the levels of N and K

0

1 Associate Horticulturist, University of Florida Agricultural Research and Education
Center, Homestead 33030.







have remained uniform at 0.84 lbs (387 gms) of N and 0.81 lbs (373 gms) of K per
tree/year. Iron as "Sequestrene 138" has been applied monthly at 5 lbs for 390 trees
* or approximately 72.5 gms per tree/year (2.52 oz) (which at current prices of $3.45/
Ib, is the equivalent of 57 cents per tree/year). Liquid chelates of zinc and man-
ganse (Ciba Geigy) 200 ml (one cupful) of each, are also applied twice a month.

Magnesium as magnesium sulfate has been added to the fertilizer mixture only occa-
sionally; however, no phosphorus has been used at all for the last 5 years.

All chemicals except Sequestrene 138 are dissolved simultaneously in a 30 gal plastic
container. Seq. 138 is applied separately because it dissolves more slowly than the
others. A wetting agent -- one cupful (200 ml.) of F-239* -- is added to the mix-
ture to help speed up the dissolution of the chemicals in water. This is particu-
larly helpful with Seq. 138 which is a fine powder, difficult to wet. In addition
to helping maintain salts flowing, F-239 has kept the system clean preventing the
accumulation of iron and calcium compounds in the emitters.

The dissolved fertilizers are incorporated into the irrigation water by opening a
valve located at the suction end of the pump which is connected to the fertilizer
tank by clear polyethylene tubing to make sure the solution is flowing. This method
has proven simple and inexpensive, and has given uniform distribution of the ferti-
lizer when absorbed slowly, at an approximate rate of no more than 15 gal. of solu-
tion per hour.

Results

This work indicates that avocado trees can produce good crops with fertilizer applied
solely through the trickle irrigation. Furthermore, -- as evidenced by production
* records -- adequate yields have been obtained even when the levels of these ferti-
lizers are much lower than those generally recommended for conventional fertilizer
application (0.84 and 0.81 lbs of N and K per tree/year as compared to the usual
recommended amount of 3.5-4.0 Ib of N and K respectively). This high degree of
efficiency of soluble fertilizer is at least partially explained on the basis that
there is a considerable concentration of roots in the areas directly wetted by the
emitters. Thus root uptake of dissolved salts apparently takes place very rapidly
with a minimum of leaching, nitrogen volatilization and other forms of fertilizer
loss which presumably occur when fertilizers are broadcasted around orchards in the
conventional manner.

In addition to normal production, spot sampling for leaf analysis has shown no dras-
tic departures from the normal levels of major elements encountered in comparable
orchards giving satisfactory yields.

If the conventional handling and application of fertilizers can be eliminated in the
orchard it is obvious that other savings such as labor and equipment costs will
automatically follow.

Chelates: Another aspect of this work of much interest to the grower is that the
application of iron chelates through trickle irrigation systems is more economical
and efficient than either manual application or mechanical injection. This is par-
ticularly important for expensive materials such as Sequestrene 138 which is some-
times difficult to dissolve and to obtain good distribution in the soil. The pre-
sent condition of our trees is excellent and even 'Mexican' cultivars which were
* frequently chlorotic before trickle irrigation was installed have remained normally
green and healthy. No symptoms of zinc and manganese deficiency have been observed.


Described by the manufacturer as a blend of ionic and non-ionic biodegradable
phosphate free surfactants.







3
The frequent application of chelates (Fe, Zn and Mn) has allowed us to prevent defi-
ciencies from appearing. This is very important since our research in the past has
shown that the productive capacity of the tree is impaired before the symptoms of the
deficiency become visible. The maintenance application of 2.5 oz (72.5 gms) of
Seq. 138 per tree/year is also considerably less than the amount required to control
the chlorosis of a tree once it has occurred (anywhere between 3 1.0 Ib (230-460
gms) of Seq. 138). Although 3-4 annual foliar applications of Zn and Mn are enough
to prevent deficiency problems, the twice a month injection of Zn and Mn liquid
chelates costs much less and appears to give good results.

The Need for Phosphorus

With the exception of some initial applications to young trees, in order to build up
the level in the soil, it is not necessary to apply phosphorus (P) fertilizers con-
tinuously to orchards in the Homestead area. This applies particularly to orchards
planted on old tomato or vegetable land which as a rule receive large amounts of
phosphorus. Our calcareous soils usually fix and accumulate sufficient amount of
this element to last for many years in the life of an orchard. Our research has
shown that trees which have not received phosphorus for as many as 15 years show low
but still adequate amounts of P in their leaves.

Sources of Nitrogen and Potassium

Until we learn more about the whole subject of fertilizing with soluble salts of
nitrogen and potassium in our oolitic limestone soils we recommend ammonium nitrate
and potassium nitrate as the best sources of N and K. Sources of nitrogen containing
* all of this element in the ammoniacal form tend to fix their nitrogen and immobilize
it at the soil surface where it subsequently becomes vulnerable to volatilization.

Urea is a highly soluble chemical and is comparatively inexpensive as a source of
nitrogen; however, only the expensive low-biuret (L.B.) form should be used. The
regular form contains varying amounts of the contaminant biuret which is milding
toxic to plants, particularly citrus. For this reason and because urea first de-
grades in the soil to ammonium compounds with the attendant problems explained be-
fore, we do not recommend its long, continued use.

There are several good sources of soluble potassium; however, few if any are as
practical and effective as potassium nitrate since it also contains nitrogen as
nitrate which is readily available to the plant.

Liquid Fertilizers

Most of the commercial preparations are solutions of ammonium nitrate and potassium
nitrate but may also contain urea unless the grower specifically asks that it not be
included in the mixture. Liquid forms come in tanks in readily injectable form and
are quite easy to use. They save the grower the chore of dissolving the chemicals
which can be quite tedious. Liquid fertilizer is usually more expensive per unit of
nutrient than dissolvable forms, but their convenience can be very practical to the
grower who wants to keep labor costs at a minimum.


k .- 4







3
The frequent application of chelates (Fe, Zn and Mn) has allowed us to prevent defi-
ciencies from appearing. This is very important since our research in the past has
shown that the productive capacity of the tree is impaired before the symptoms of the
deficiency become visible. The maintenance application of 2.5 oz (72.5 gms) of
Seq. 138 per tree/year is also considerably less than the amount required to control
the chlorosis of a tree once it has occurred (anywhere between 3 1.0 Ib (230-460
gms) of Seq. 138). Although 3-4 annual foliar applications of Zn and Mn are enough
to prevent deficiency problems, the twice a month injection of Zn and Mn liquid
chelates costs much less and appears to give good results.

The Need for Phosphorus

With the exception of some initial applications to young trees, in order to build up
the level in the soil, it is not necessary to apply phosphorus (P) fertilizers con-
tinuously to orchards in the Homestead area. This applies particularly to orchards
planted on old tomato or vegetable land which as a rule receive large amounts of
phosphorus. Our calcareous soils usually fix and accumulate sufficient amount of
this element to last for many years in the life of an orchard. Our research has
shown that trees which have not received phosphorus for as many as 15 years show low
but still adequate amounts of P in their leaves.

Sources of Nitrogen and Potassium

Until we learn more about the whole subject of fertilizing with soluble salts of
nitrogen and potassium in our oolitic limestone soils we recommend ammonium nitrate
and potassium nitrate as the best sources of N and K. Sources of nitrogen containing
* all of this element in the ammoniacal form tend to fix their nitrogen and immobilize
it at the soil surface where it subsequently becomes vulnerable to volatilization.

Urea is a highly soluble chemical and is comparatively inexpensive as a source of
nitrogen; however, only the expensive low-biuret (L.B.) form should be used. The
regular form contains varying amounts of the contaminant biuret which is milding
toxic to plants, particularly citrus. For this reason and because urea first de-
grades in the soil to ammonium compounds with the attendant problems explained be-
fore, we do not recommend its long, continued use.

There are several good sources of soluble potassium; however, few if any are as
practical and effective as potassium nitrate since it also contains nitrogen as
nitrate which is readily available to the plant.

Liquid Fertilizers

Most of the commercial preparations are solutions of ammonium nitrate and potassium
nitrate but may also contain urea unless the grower specifically asks that it not be
included in the mixture. Liquid forms come in tanks in readily injectable form and
are quite easy to use. They save the grower the chore of dissolving the chemicals
which can be quite tedious. Liquid fertilizer is usually more expensive per unit of
nutrient than dissolvable forms, but their convenience can be very practical to the
grower who wants to keep labor costs at a minimum.


k .- 4







3
The frequent application of chelates (Fe, Zn and Mn) has allowed us to prevent defi-
ciencies from appearing. This is very important since our research in the past has
shown that the productive capacity of the tree is impaired before the symptoms of the
deficiency become visible. The maintenance application of 2.5 oz (72.5 gms) of
Seq. 138 per tree/year is also considerably less than the amount required to control
the chlorosis of a tree once it has occurred (anywhere between 3 1.0 Ib (230-460
gms) of Seq. 138). Although 3-4 annual foliar applications of Zn and Mn are enough
to prevent deficiency problems, the twice a month injection of Zn and Mn liquid
chelates costs much less and appears to give good results.

The Need for Phosphorus

With the exception of some initial applications to young trees, in order to build up
the level in the soil, it is not necessary to apply phosphorus (P) fertilizers con-
tinuously to orchards in the Homestead area. This applies particularly to orchards
planted on old tomato or vegetable land which as a rule receive large amounts of
phosphorus. Our calcareous soils usually fix and accumulate sufficient amount of
this element to last for many years in the life of an orchard. Our research has
shown that trees which have not received phosphorus for as many as 15 years show low
but still adequate amounts of P in their leaves.

Sources of Nitrogen and Potassium

Until we learn more about the whole subject of fertilizing with soluble salts of
nitrogen and potassium in our oolitic limestone soils we recommend ammonium nitrate
and potassium nitrate as the best sources of N and K. Sources of nitrogen containing
* all of this element in the ammoniacal form tend to fix their nitrogen and immobilize
it at the soil surface where it subsequently becomes vulnerable to volatilization.

Urea is a highly soluble chemical and is comparatively inexpensive as a source of
nitrogen; however, only the expensive low-biuret (L.B.) form should be used. The
regular form contains varying amounts of the contaminant biuret which is milding
toxic to plants, particularly citrus. For this reason and because urea first de-
grades in the soil to ammonium compounds with the attendant problems explained be-
fore, we do not recommend its long, continued use.

There are several good sources of soluble potassium; however, few if any are as
practical and effective as potassium nitrate since it also contains nitrogen as
nitrate which is readily available to the plant.

Liquid Fertilizers

Most of the commercial preparations are solutions of ammonium nitrate and potassium
nitrate but may also contain urea unless the grower specifically asks that it not be
included in the mixture. Liquid forms come in tanks in readily injectable form and
are quite easy to use. They save the grower the chore of dissolving the chemicals
which can be quite tedious. Liquid fertilizer is usually more expensive per unit of
nutrient than dissolvable forms, but their convenience can be very practical to the
grower who wants to keep labor costs at a minimum.


k .- 4




%. ,- 0


4


Summary and Conclusions

1. The work reported here indicates that avocado orchards can produce adequate
yields when fertilized with soluble forms of nitrogen and potassium, even when
the amounts used are much lower than those recommended for conventional mixed
fertilizers. Experiments are being initiated to determine with more precision
the lowest possible levels of N and K necessary to obtain optimum yields at a
minimum cost. The price of fertilizer has recently become an even more important
item than before in the cost of agricultural production.

2. The work presented also shows that trickle irrigation is a very efficient tool
for applying chelates to fruit trees. This is particularly important for expen-
sive iron chelate -- such as Sequestrene 138 -- which has repeatedly been shown
to be the most efficacious material to prevent and control iron chlorosis under
our soil conditions. Trickle irrigation eliminates the need for manual appli-
cation or mechanical soil injection of Seq. 138 which at best are not the most
efficient ways of putting the chemical in contact with the roots.

3. In addition to the savings associated with the lower amounts of chemicals neces-
sary to give the same results, "fertigation" can lower the total cost of labor
since there is much less handling and work involved in applying the chemicals
from a central point and letting the irrigation water distribute them to the
trees.




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