A Long Term Experiment on Soil Fertility and Cotton Yield in Tanzania

SUMMARY Compost or ammonium sulphate improved and maintained cotton yield for 6 years but both, together with triple superphosphate, were needed to maintain it for 9 years, after which yield declined and lime was necessary. Compost supplied necessary but insufficient phosphorus, potassium, calcium and nitrogen. Manganese toxicity was severe when potassium chloride was used on very acid soil. At suitable soil pH and with adequate phosphorus and cations, response to nitrogen was large, but for it to be most effective, calcium seemed necessary to maintain the cation: anion ratio. Without lime, yields declined with heavy rain; with it they were largest in the wettest seasons.