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Agriculture 2011, 1(1), 22-37; doi:10.3390/agriculture1010022
Article

Effects of Tillage and Crop Residue Application on Soybean Nitrogen Fixation in a Tropical Ferralsol

1,2,* , 2
,
3
 and
2
1 Tropical Soil Biology and Fertility (TSBF) Institute of CIAT, Box 30677, Nairobi 00100, Kenya 2 Zentrum für Entwicklungsforschung (ZEF), Walter-Flex Str. 3, Bonn 53113, Germany 3 Alliance for Green Revolution in Africa (AGRA-Alliance), CSIR Office Complex, #6 Agostino Neto Road, Airport Residential Area, PMP KIA 114, Airport-Accra, Ghana
* Author to whom correspondence should be addressed.
Received: 25 October 2011 / Revised: 6 December 2011 / Accepted: 8 December 2011 / Published: 20 December 2011
(This article belongs to the Special Issue Soil Biology and Its Importance in Soil Fertility)
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Abstract

This study was aimed at quantifying soybean (Glycine max) nitrogen fixation under reduced tillage (RT) and conventional tillage (CT) in a tropical Ferralsol of the sub-humid zone of western Kenya, using the isotope 15N dilution method. Crop residue (CR) management was a superimposed treatment in soybean-maize rotation and intercropping systems. This study quantified N in abscised soybean leaves. Soybean-N derived from the atmosphere (%NDfA) ranged between 41–65%; it was higher (P < 0.05) in RT (55.6%) than in CT (46.6%). Total fixed-N under ‘RT + CR’ was more than in the other treatments by at least 55% in intercropping and 34% in rotation system. Nitrogen fixed in soybean aboveground parts was 26–48 kg N ha−1 with intercropping and 53–82 kg N ha−1 with rotation. Seasonal litter fall contained about 15 kg N ha−1, with 54% NDfA. Annual nitrogen balances with soybean and maize grain removed were better in RT (−9 to −32 kg N ha−1) than in CT (−40 to −60 kg N ha−1). Application of P increased nodule weight (P < 0.05) by 3 to 16 times over the control. Soybean residues should be returned to the field after harvest to reduce soil N mining. We conclude that ‘RT + CR’ increases biological nitrogen fixation in soybean, over CT, and that phosphorus application is needed for better soybean nodulation in western Kenya.
Keywords: intercropping; litter fall; N balance; %NDFA; 15N dilution intercropping; litter fall; N balance; %NDFA; 15N dilution
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

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Kihara, J.; Martius, C.; Bationo, A.; Vlek, P.L.G. Effects of Tillage and Crop Residue Application on Soybean Nitrogen Fixation in a Tropical Ferralsol. Agriculture 2011, 1, 22-37.

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