iTROPS3OLS j
PUSLUTTAN ;
WEST SUMATrERA4
TROPSOILS INDONESIA
Field Research Brief #13
June. 19SS

Title: Response of Soybeans and Soil K Levels to K Fertilization
ana Green Manure Applications at Sitiung 5

Experiment #: 3501

Researchers: Dan Gill, Antonius Kasno ana J. Sri Adiningsih

Objectives: 1. To examine the effects of K rates and residue
management/green manure treatments on soyoean
yields and soil K levels.
2. To observe the effect of green manuring on K, Ca
and Mg retention within the profile of a udult
in Sitiung 5.

Soil: Uduit, probably an orthoxic tropudult (to be positively
identified when complete lab data become available). FCC: Ceak.

Treatments: This experiment was an incomplete factorial set out
in a randomized complete block design with 3 replications. Seven
rates of K were applied: 0, 10, 20, 40, 80, 120, and 240 kg K/ha.
Three residue/green manure treatments were installed on both a 0
and a 90 kg K/ha plot. These treatments were: rice straw
removed, rice straw incorporated and rice straw + Calopogonium
so. .3.4 t/ha dry weight) incorporated.

Crop History: Soybean cultivar "Orba" was planted using
commercial inoculum .on 7 March at a 20 X 40 cm spacing. A
blanket application of 100 kg/ha TSF and 125 kg kieserite (MgSG4)
was incorporated before planting, while rice straw from the
previous crop was removed except as indicated above for the
stover and green manure treatments. Pest problems were minimal.
Harvest of 2/3 of the plots occurred on 4 June (89 days) and the
remainder was harvested 8 June (93 days).

Results: This crop grew well, being fortunate to have good
rainfall distribution and low pest pressures. The crop responded
strongly to K, more than doubling yields with only 10 kg K/ha
-(Figure i), whilee pl-ateau yields were achieved at 120 kg/ha.
Results of the different residue management treatments are shown
in Table 1, clearly demonstrating the importance of residue
management in developing any cropping systems package for this
area. Incorporated straw from the previous rice crop more than
doubledd yields at the 0 K rate and at 30 kg K/ha, it increased
yields to almost 2.5 t/ha, extremely good yields for this area.
Bean yields as high as those on the K response plateau were
obtained at the 0 K level by adding both rice straw and
Calopogonium.











Table 1. Soybean vield with several residue management treatments
and at 2 K application rates.


Residue

Management


1.Rice straw removed

2.Rice straw incorporated

3.Rice straw + Caloponium


Sovbean Yield (t/ha)
--ppiied K
(g / ha) 30

-~7

1.22 a.43

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