TROPSOILS
Field Research Brief# 1

TITLE: P Fertilization and Mainenance

RESEARCHERS: Mike Wade and Al-Jabri

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 -maintenance
applications.

SOIL: Inceptisol (?with amorphous material or volcanic ash)
cropped for 7 years after bulldozer clearing without
lime or fertilizer inputs.

TREATMENTS: Factorial design, ROB, 4-replications, 4.5X7m plots


Initial Rates

1. 0 kg P/ha
2. 20
3. 40 "
4. 80
5. 160
6. 320


Per-crop Rates (2X per year)

1. none
2. 20 kg P banded/ha
3. 20 Kg P broadcast/ha


CROP: First planting, corn (cv. C-l, hyarid by Cargill)
Spacing 25X75X1
Planted 29 Sept 84
Harvested 7 Jan 85 (100 days)
Pesticides Furadan with seec at planting (30kg 3G/ha)
Base Fertilizer and Lime 3.5 T/ha lime, 300 kg urea (triple
solit), 200 kg KC1, and 100 Mg S04/ha.

RESULTS:
The par-crop applications significantly increased yields for
the 0 and 20 kg P/ha initial rates, but did not on the higher
rates (Table 1.). Both banding and broadcasting were equally
effective in causing the increase.

Since the banding and broadcast applications showed no
consistence differential response, the effect of total applied P
(irregardless of method) on corn yield is shown in Figure 1.
A very good fit of a 2-slop linear plateau model, is obtained,
with an R2 = 0.88. Table 2 show the rate of corn yield increase
and rate of return (in Rupiah) for each segment of the model.

Figure 2 shows the effect of added P fertilizer on
extractable P (by modified Olsen) soil analysis. The inceptisol







of this experiment shows a drastically different relationship
than an ultisol of Sitiung Vc. The inceptisol appears to have
much higher P fixation. However Figure 3 shows a relatively low
critical level (8 ppm), which corresponds to the rate (40 kg
P/ha) that was required to get good yields (Figure 1).


Table 1. Corn Grain yields as affected by Initial P
Applications and Per-crop (at planting) P Applications.

Per-crop

Initial P 20 kg P 20 kg P
Rate none banded broadcast X

kg/ha ............... T/ha.............................

0 2.1 3.3 4.3 3.2
20 3.2 4.3 4.2 3.9
40 4.4 4.9 4.1 4.5
80 4.5 4.7 4.6 4.6
160 5.2 5.7 5.1 5.3
320 5.3 -

X 4.1 4.6 4.5

LSD. 05 for interaction 0.8



Table 2. Rate of Corn Grain Increase and Rate of Return
for each Linear Segment of the Linear Plateau Model.


P kg corn Rp. gain
rate per kg TSP per Rp. spent

0-40 11 12
40-160 1.7 1.8
+160 0 0















/6o /80


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320


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