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

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

1,2,* , 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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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) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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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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