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Field Research Brief No. 2
TITLE: Effect of Green Manuring on Food Crop Response to Lime
and P Fertilization.
RiESEARCHERS: Heryadi and Mike Wade
OBJECTiVES: 1. Study the effect of green manure on active Al
and the subsequent lime requirement.
2. Study the effect of green manure and lime on
the availability of soil P.
3. Determine if green manuring can be cost
effective in reducing or eliminating the need for
lime and P fertilizer.
SOIL: Haplorthox, located in Sitiung lie, cleared by bulldozer
six years ago, with annual cropping of upland rice since
clearing. pH=4.1, A1+H=2.6 meq, Ca+Mg=0.5 meq, Al sat=82%,
P=5 ppm (Olsen).
TREATMENTS: Partial Factorial design, RCB, 3 replications, 5X5m plots
Lime Rates P Rates
0 10 kg P/Fha
-1 T/ha 25
2 50 "
3 "10 "+ 20 T/ha (fresh
Trt No. 1-16 all combinations of above
17 np lime, P or green manure
-18 2 T/ha lime, no P or green manure.
CROP: First planting, upland rice (cv. Sentani), October, 1984
Spacing, 25 X 25cm
Base fertilizer, 100kg urea, 100 kg KC1, 50 kg MgSO4/ha
Harvested February, 1985.
RESULTS: First of all, a three week drought at grain fill and
a serious infestation of neck blast caused grain yields to be
very erratic and low. Therefore rice straw yields are used to
represent the influence or-effects of the various treatments.
Figure 1 illustrates the most striking response of the
trial. The no-lime plots showed consistent and strong Al
toxicity (or Ca deficiency) symptoms throughout the growing
cycle. Early the rice was quite stunted and showed yellowing and
drooping of the older leaves. During times of moisture stress,
the unlimed plots exhibited plants with rolled and placid
leaves several days before the other treatments. All of these
symptoms however were absent in the plots that had received green
manure, regardless of the lime rate. The non-manured plots
responded well to lime and were not significantly different from
the green manured plots when lime was applied. The first
increment (1 T/ha) was sufficient to overcome the soil acidity
problem. So it appears that the green manure was comparable to
lime aleviating soil acidity as a limiting factor for rice
The non-manured rice also responded well to applied P (Figure
2). However the green manured plots, which all had a constant 10
kg P/ha, are noticeably far above the response line of the non-
manured treatments. Since the green manured plots did not have a
P variable, a response curve can not be drawn, and we can only
conjecture what such a curve might look like. However it seems
likely that F was not limiting in the green manured plots despite
the fact that only 10 kg P/ha was added as inorganic fertilizer,
whereas that amount was definitely limiting in the non-manured
There was no significant correlation between dry matter
yield and either Al saturation or extractable P. However a
multiple linear regression, (based on the non-manured plots only)
Y = 1.51 0.012 Al sat. + 0.075 ext. P,
has a significant R2 = 0.54. While that is not exceptionally
high, it is quite reasonable considering the water and pest
problems as well as the inherent high soil microvariability that
exists in this area. The manured plots do not fit this regres-
sion; as all green manure treatments did relatively well regar-
dless of the soil analysis for Al or P.
It seems apparent that the green manure has seriously al-
tered the influence of soil acidity and possibly available P on
the growth of upland rice. However in Table 1 we see that the
green manure has not affected the Al saturation (KCI extractable)
nor available P (Olsen extractable). It is consistent with
current knowledge of Al-organic matter relationships that the
green manure is releasing some compound that complexes soil Al
and renders it unavailable or non-toxic to plant roots. However
if this is the case the standard KC1 extract appears to still
measure the completed Al. This matter should be further investi-
gated to clarify our knowledge and understanding of the useful-
ness of green manure as a potential lime substitute.
Table 1. Extractable P (Olsen) and Al saturation as affected by
lime rates, P rates, and green manure.
P Rates (-k P/ha)
10 25 50 1 o)m X
Sppm P -
6 12 7
8 17 8
4 14 11
6 8 6
---------- ----*.--- ------
X 54 53 46 50
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