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Nov 12, 2015Keywords:
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Main Article Content
Cassava response to natural and simulated erosion on the ultisols of Owerri, southeastern Nigeria
Abstract
The impact of erosion on soil productivity is soil, crop and environment specific. It is therefore important that erosion-soil-productivity relationships be established for each soil type and ecological zone. The results reported here are a part of an elaborate series of studies to quantify the relationship between natural and simulated erosion on the yield of major crops on the ultisols of Owerri, southeastern Nigeria. Two crops of cassava were grown between 1998 – 2000 on non-eroded (NE), slightly (S), moderately (M) and severely (Sv) eroded phases of ultisols within the Otamiri watershed of Owerri. Simultaneously, desurphased experiments with three levels of topsoil depth removals (2.5, 5.0, 7.5, cm) were conducted on the non- eroded reference plateau terrain. Natural erosion had no adverse effect on plant establishment and tuber numbers, but led to significant reductions of total dry matter, stem and storage root yields. For instance, the relative yield performance of fresh tubers in the 1998/1999 planting (40 WAP) was in the order 100:52:59:36 for NE:S:M:Sv and the corresponding yield values were 29.6, 15.4, 17.4 and 10.7 t/ha respectively. Desurphasing led to drastic reductions on all yield parameters and tuber yield declines of 91% were recorded when 7.5 cm of topsoil was removed. Linear functions of storage root yield decline per cm of topsoil eroded naturally was 1.74 t/ha, and 10.34 t/ha for mechanical topsoil removal. The best-fit indicators for predicting tuber yields were soil organic matter (SOM), aluminium saturation, (Ca + Mg)/ (Al + H) ratio, available water capacity (AWC), bulk density (BD) and A-horizon depth, accounting for 68.9 % of the variability in tuber yields. The simulation of erosion through mechanical topsoil removal exaggerated the impact of erosion on cassava yield by factor of 6, therefore the results from such experiments should be used with caution.
Keywords: Erosion, Desurphsed, Cassava, Yield decline and Soil productivity.
