Comparison of the yield, response of groundnuts to single and triple superphosphate in Uganda

Abstract

Since 1963 more than a thousand fertilizer trials on small private farms in Uganda have been carried out to test the effect of single superphosphate on groundnuts. Many significant yield responses have been recorded [1, 2] and recommendations for the application of single superphosphate to groundnuts have been made for specific areas in Uganda [3]. It was generally assumed that the yield response was almost entirely due to the phosphate content of the fertilizer. However, analysis of soils from responsive trials in Ankole district revealed that some contained a high level of extractable phosphate, suggesting that yield response in these trials may infact have been due to the calcium or sulphur content of the fertilizer. To obtain a quick indication of which constituents of single superphosphate were indeed responsible for crop response in Ankole and also other districts of Uganda, pot tests on soil collected from different response areas were carried out. The results, which have been published [4], indicated that crop response to single superphosphate in all districts was mainly or entirely due to the phosphate content of the fertilizer. However, on very acid soils or low organic matter soils, calcium probably produced an extra response. The pot test results indicated that the sulphur content of single superphosphate had little or no effect on crop yields.