Abstract
Crop production in maize-based smallholder farming systems of Southern Africa is hampered by lack of options for efficiently managing limited and different quality organic nutrient resources. This study examined impacts of farmers’ short- and long-term organic resource allocation patterns on sizes and quality of soil organic matter (SOM) fractions. Farmers’ most- (rich) and least- (poor) productive fields were studied for two seasons under low (450–650 mm yr−1) to high (>750 mm yr−1) rainfall areas in Zimbabwe, on Lixisols with ∼6% clay and 88% sand. Rich fields received 0.5–14 Mg C ha−1 compared with <4 Mg C ha−1 for poor fields, and the differences were reflected in soil particulate organic matter (POM) fractions. Organic inputs were consistent with resource endowments, with well-endowed farmers applying at least five times the amounts used by resource-constrained farmers. Rich fields had 100% more macro-POM (250–2,000 μm diameter) and three times more meso-POM (53–250 μm) than poor fields. Application of high quality (>25 mg N kg−1) materials increased labile C (KMnO4 oxidizable) in top 60 cm of soil profile, with 1.6 Mg C ha−1 of Crotalaria juncea yielding labile C amounts similar to 6 Mg C ha−1 of manure. Labile C was significantly related to mineralizable N in POM fractions, and apparently to maize yields (P < 0.01). Farmers’ preferential allocation of nutrient resources to already productive fields helps to maintain critical levels of labile SOM necessary to sustain high maize yields.
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Acknowledgements
The study is an output of the Soil Organic Matter Dynamics for Sustainable Cropping and Environmental Management in Tropical Ecosystems (NUESOM) project (Grant 2002 FS 189) funded by the Rockefeller Foundation. The authors also gratefully acknowledge the high level of cooperation received from farmers in Chikwaka, Chinyika and Zimuto smallholder areas, and officers from the Department of Research and Extension (AREX) of the Ministry of Agriculture, Zimbabwe who were key facilitators in the study sites.
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Mtambanengwe, F., Mapfumo, P. Smallholder farmer management impacts on particulate and labile carbon fractions of granitic sandy soils in Zimbabwe. Nutr Cycl Agroecosyst 81, 1–15 (2008). https://doi.org/10.1007/s10705-007-9136-0
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DOI: https://doi.org/10.1007/s10705-007-9136-0