Effect of Long-Term Continuous Cotton Mono-Cropping on Depletion of Soil NPK and Changes in Some Selected Soil Chemical Characters on Vertisols and Fluvisols

摘要

A long-term cotton exhaustion trial was conducted on lowland Vertisols and Fluvisols at Werer Agricultural Research Center during the 1968-2002 in Ethiopia to investigate nutrient depletion rate and changes in selected soil chemical properties. Treatments used include cultivated fallow, control, 80kgN ha~(-1), 80-80 kgNP ha~(-1), 80-80kgNK ha~(-1) and 80-80-80kgNPK ha~(-1) arranged in RCBD with four and six replications in Vertisols and Fluvisols, respectively. The cotton was grown as a test crop and the status of soil N, P, K, OC, pHe and ECe were periodically monitored every seasons. Seed cotton yield had shown significant response to treatments imposed after 10 and 3 years of continuous cotton mono-cropping, respectively, on Vertisols and Fluvisols, and consistently continued for further 3 consecutive periodical checking years. Then onwards, until the end of the experiment, seed cotton yield didn't showed consistent yield response. Combined analysis revealed highly significant (p < 0.01) yield response to N applications. Despite the long-term continuous mining of soil nutrients through seed cotton harvest and crop residue removal, soil analytical result revealed no indication of depletion in total nitrogen, available K and P. Soil pHe (in both soil types) and ECe only in Fluvisols tend show gradual increase.