EFFECTS OF PHOSPHORUS RATE AND FORM IN COMBINATION WITH LIME AND GYPSUM ON YIELDS AND COMPOSITIONS OF GERMAN MILLET AND ALFALFA FROM HIGHLY WEATHERED SOILS

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Abstract
Effects of P rate and form (degree of acidulation of rock phosphate) in combination with liming (pH levels) and gypsum additions on yields and composition of German millet (Setaria italica, "German") and alfalfa (Medicago sativa L. Vernal) were evaluated. The study was conducted in a growth chamber on 3 relatively highly weathered soils, i.e., 2 Oxisols from Uganda and 1 oxidic Ultisol from Tennesse, USA.) German millet yields increased significantly when P was applied at all pH levels on all soils. On the relatively more weathered Kabanyolo and Alcoa soils yields were not significantly different from P1(TSP = triple superphosphate) and P2(PARP = partially acidulated rock phosphate), but those from P2(TSP) were superior to both P1(TSP) and P2(PARP) [subscripts denote year of study]. On relatively less weathered Serere soil yields of German millet were not significantly different from P1(TSP) and P2(TSP), but both were significantly higher than that from P2(PARP). For all soils German millet yields were highest at lowest pH level and decreased with increasing pH. Alfalfa yields were significantly increased by P on Serere and Alcoa soils, but they were not significantly different from P1(TSP), P2(TSP), or P2(PARP). Alfalfa yields were significantly depressed by P on Kabanyolo soil which had relatively high levels of Al-P and native available P. Alfalfa yields markedly increased with initial increase in pH and generally continued to increase at high Ca and pH levels. Plant analysis and visual symptoms suggested that Mn was the main adverse factor depressing alfalfa growth at lower pH levels. The reason for somewhat different results from those reported previously for Ohio and Virginia [USA] soils may be a consequence of a lower level of exchangeable Al in more highly weathered soils used in this study.
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