Comparative shortterm effects of different qualit

Authors: Florence Mtambanengwe Paul Mapfumo Bernard Vanlauwe

Publish Date: 2006/10/03

Volume: 76, Issue: 2-3, Pages: 271-284

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Abstract

Major challenges for combined use of organic and mineral nutrient sources in smallholder agriculture include variable type and quality of the resources their limited availability timing of their relative application and the proportions at which the two should be combined Shortterm nutrient supply capacity of five different quality organic resources ranging from high to low quality namely Crotalaria  juncea Calliandra  calothyrsus cattle manure maize stover and Pinus  patula sawdust were tested in the field using maize as a test crop The study was conducted on two contrasting soil types at Makoholi and Domboshawa which fall under different agroecological regions of Zimbabwe Makoholi is a semiarid area 650 mm yr−1 with predominantly coarse sandy soils containing approximately 90 g kg−1 clay while Domboshawa 750 mm yr−1 soils are sandyclay loams with 220 g kg−1 clay Each organic resource treatment was applied at low 25 t C ha−1 and high 75 t C ha−1 biomass rates at each site Each plot was subdivided into two with one half receiving 120 kg N ha−1 against zero in the other At Makoholi there was a ninefold increase in maize grain yield under high application rates of C juncea over the unfertilized control which yielded only 04 t ha−1 Combinations of mineral N fertilizer with the leguminous resources and manure resulted in between 24 and 104 increase in grain yield against sole fertilizer implying an increased nutrient recovery by maize under organic–mineral combinations Maize biomass measured at 2 weeks after crop emergence already showed treatment differences with biomass yields increasing linearly with soil mineral N availability R 2 = 075 This 2week maize biomass in turn gave a positive linear relationship R 2 = 082 with grain yield suggesting that early season soil mineral N availability largely determined final yield For low quality resources of maize stover and sawdust application of mineral N fertilizer resulted in at least a sevenfold grain yield increase compared with sole application of the organic resources Such nutrient combinations resulted in grain harvest indices of between 44 and 48 up from a mean of 35 for sole application suggesting the potential of increasing maize productivity from combinations of low quality resources with mineral fertilizer under depleted sandy soils At Domboshawa grain yields averaged 7 t ha−1 and did not show any significant treatment differences This was attributed to relatively high levels of fertility under the sandyclay loams during this first year of the trial implementation Differences in N supply by different resources were only revealed in grain and stover uptake Grain N concentration from the high quality leguminous resources averaged 2 against 15 from sawdust treatments We conclude that early season soil mineral N availability is the primary regulatory factor for maize productivity obtainable under poor sandy soils Maize biomass at 2 weeks is a potential tool for early season assessment of potential yields under constrained environments However the likely impact on system productivity following repeated application of high Ncontaining organic materials on different soil types remains poorly understood

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