A field study was initiated towards the end of the 1973 rain season to assess some residual effects of lime, N and P applications to a moderately acid Oxisol (initial pH 5.6; LR 10 tons/ha) on grain yield in navy beans, Phaseolus vulgaris L., grown soon following maize silage. The Oxisol was a sandy clay loam (35:13:52). The design was a split-plot, confounded factorial with 4 levels of lime at 0, 7.5, 10.0 and 12.5 tons agricultural lime/ha; N at 0, 100, 200 and 300 kg N/ha as ammonium sulphate; and P at 0, 40, 80 and 120 kg P/ha as triple superphosphate. Lime was applied in November, 1970 and N and P rates repeated annually during 1971-73 with previous maize crops. Grain yield increased linearly and significantly with lime up to mean pH of 6.7 along with increases in residual Ca2+, electrolyte, base content, AI-P, Fe-P, and with reduction in extractable Mn and exchangeable Al. Yields at low N and P fertility were, however, drastically reduced as the optimum mean pH was exceeded. Yield increased linearly and highly significantly with N and P fertilization. Yields were low where lime, N and P were not applied together. The data indicate that for the Oxisol, which had less than 0.2 me/100 g of exchangeable Al in the absence of applied lime and N, liming to reduce exchangeable Al cannot be taken as a criterion for liming but that optimum pH, adequate balance of ion ratios and adequate conservation of soil nutrients would be appropriate.
Mongi et al. (Thu,) studied this question.