Group Title: TropSoils field research brief ;, 22
Title: P fertilization and maintenance, Sitiung Ia
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 Material Information
Title: P fertilization and maintenance, Sitiung Ia
Series Title: TropSoils field research brief ;, 22
Physical Description: 2, 1 leaves : ill. ; 28 cm.
Language: English
Creator: Wade, M. K.
Wade, M. K. (Michael Karl)
Widjaja-Adhi, I. P. G.
Soil Management Collaborative Research Support Program.
Publisher: Soil Management Collaborative Research Support Program, North Carolina State University,
Publication Date: 1986
Subject: Soil management -- Indonesia.
Soil chemistry -- Indonesia.
Spatial Coverage: Indonesia.
General Note: Caption title.
General Note: "January, 1986."
General Note: At head of title: TropSoils-Indonesia.
 Record Information
Bibliographic ID: UF00080599
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 156945697

Full Text

Field Research Brief No. 22
January, 1986

TITLE: P Fertilization and Maintenance, Sitiung la'

RESEARCHERS: Mike Wade and I P. G. Widjaja-Adhi

OBJECTIVES: 1. Determine initial P rates necessary to reach a
critical soil test value and optimum crop yield,
2. Determine per crop rates necessary to maintain
established soil levels,
3. Compare banding vs. broadcasting of mainentance

SOIL: Inceptisol, Cak, cropped for 7 years after bulldozer
clearing without lime or fertilizer inputs

TREATMENTS: Factorial, RCB, 4 replications, 4.5 X 7m plots

Initial Rates Per Crop Rates
(2X per year)

1. 0 kg P/ha 1. none
2. 20 2. 20 kg P/ha band
3. 40 3. 20 kg P/ha broad-
4. 80 cast
5. 160
6. 320

CROP: (4th) Corn-variety C-l, spacing 25x75cm, pesticides
carbofuran 0.5kg a.i./ha at planting and Ridomil
5g/kg seed, one hand weeding at 4 weeks after
emergence, base fertilizer 150 kg KC1, 100 kg
kieserite, and 300 kg urea (100 each at planting,
3 weeks and 6 weeks) per ha.

RESULTS: The corn crop of this second season grew and produced
well by tropical standards. The treatment means, as affected by
initial P rates (x-axis) and maintenance applications, are plot-
ted in Figure 1. Trend analysis of this factorial experimental
design showed that only the linear portion of the response sig-
nificantly influenced the regression. Thus, we compare only the
linear slopes of the response to initial P rates of the mainten-
ance treatments. The coefficients of the two maintenance
methods, banding and broadcasting, are not significantly differ-
ent from each nor from zero. Therefore, apparently the two
methods are (1) equally effective and, (2) have eliminated a
response to the initial rates of P, which were applied at the
beginning of the experiment in September, 1984. This suggests
that the maintenance rate of 20 kg P/ha must be building soil P
rather than merely maintaining it.

The residual effect of the initial applications in fact is
rather remarkable. Figure 2 shows the corn yield response of
both year 1 and year 2 to the initial rates (without maintenance
applications). Clearly there has been little change between the
two seasons. So if the residual-of the initial rates is not
declining over time, then any "maintenance" applications would
logically be building soil P rather than maintaining it. Indeed,
Figure 3 shows that total P applied, whether initial or mainten-
ance, or combination thereof, correlates extremely well with corn
yield of year 2. Again the indication is that residual P is just
as effective as fresh (maintenance) applications.

Soil analysis has so far been inconclusive in detecting the
apparent changes (or lack thereof) in the available soil P.
Initially we extracted the soil with mod Olsen but were dissatis-
fied as the range of values was quite-narrow. From year 1 data
the minimum value was 3 ppm and the critical value was only 8
ppm. Figure 4 shows the relationship of year 2 yield data with
Mehlich I extractable P. There. is good correlation and defini-
tion of a critical level (23 ppm). With a minimum value of 11
ppm, a much wider range in the response portion of the regression
exists than with the mod Olsen of year 1. Therefore we are
currently re-analyzing previous soil samples with-the Mehlich I.
Hopefully this will produce sound correlation data, but it re-
mains to be seen if it will correlate over time as well.

The-strength of the residual effect of the P fertilizer in
this trial is unusual. Normally we would expect a decrease in P
availability over time. The reason for lack of such here may not
be readily apparent. However our hypothesis is that the answer
may well be in the organic activity of the soil. Other trials in
Sitiung have shown impressive responses to organic additions,
whether as green manure or crop residues. Yet the soils are
surprisingly high in OM, usually 4-5% by Wackley-Black. This
suggests that, like the clay, the organic matter may have a low
activity quality. Thus fresh additions of organic material cause
considerable and positive changes in the soil dynamics. Although
crop residues are removed at harvest time in this experiment,
root and stubble from the high yielding crops would be substan-
tial. Enhanced nutrient availability by organic additions has
been observed in other trials here, and even though this experi-
ment has no specific organic treatments the same processes may
well enter into the nature of the P response. Prior to experi-
mentation, the field for this trial had been in low input (and
low yielding) production. Initiation of our trial has brought
about many changes that could radically alter the organic complex
of the soil. As mentioned, indirect applications of crop resi-
dues (roots and stubble), liming and macronutrient fertilization
would all favor a more active microbial population and increase
the quantity (and.quality?) of the organic fraction of the soil.
This may in turn result in more favorable root growth and P
availability, thereby offsetting the expected decline in P over
time. This of course is conjecture time but raises some import-
ant, if not critical, research issues for optimizing long-term
economic crop production.

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