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Abstract
This study compared the effect of a weedy fallow (5.2 t/ha biomass), a velvet bean (Mucuna pruriens) cut for hay (7.2 t/ha biomass) and a green-manured M. pruriens (6.49 t/ha biomass) on the dynamics of soil N and C in a maize crop. An on-farm, farmer participatory experiment was established on a farmer’s field in Wedza District, Zimbabwe. Soil mineral N and labile carbon were determined at intervals upto 120 cm depth, at maize planting and at 1 and 2 weeks after planting. Before planting, the soil mineral N content ranged from 28 kg N/ha after weed fallow to 107 kgN/ha following M. pruriens. Total nitrate concentration was highest in the 0-15 cm depth of the M. pruriens treatments in the pre-planting sampling, but following rainfall and maize planting, nitrate concentration declined rapidly. By 2 weeks after planting, 7.5 and 13.5 kg N/ha remained in the 0-120 cm soil depth of the weedy fallow and green-manured M. pruriens, respectively. Improving synchrony of nutrient release and uptake is critical when applying high quality residues which breakdown relatively slowly. This could result in significant inputs of C, release nutrients more slowly and reduce soil nutrient losses.
Highlights
Soil organic matter (SOM) is considered to be a key factor in maintaining soil quality and is crucial in determining long-term soil fertility (Bationo, 2007)
Total biomass measured at the end of the 1999/2000 wet season (reported in detail in the thesis of Jiri (2003)) was 5.22t/ha on the weed fallow, 7.15 t/ha on the M. pruriens treatment cut for hay and 6.49 t/ha on the green manured M. pruriens treatment
Soil organic carbon was determined on samples collected from the weed fallow and M. pruriens cut for hay treatments at pre-planting (Table 2) and at 2 week after planting (WAP)
Summary
Soil organic matter (SOM) is considered to be a key factor in maintaining soil quality and is crucial in determining long-term soil fertility (Bationo, 2007). Soil management to increase SOM and supply nitrogen for crop production has generally been approached via the use of green manuring and crop residue retention. The application of green manures often results in increases in crop yield. There is no evidence of long-term improvement of SOM and soil fertility (Rurinda et al, 2014). The application of high quality residues, which breakdown relatively rapidly due to their chemical and/or physical attributes and improved mineralisation of nutrients, could result in significant increases in soil C, provide plant nutrients for longer periods and reduce soil nutrient losses
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