Comparative effects of green manure and lime on the growth of sweet corn and chemical properties of an acid oxisol in Western Samoa

Liming values of calcium carbonate (CaCO3) and cowpea green manure were evaluated on an acid Oxisol (Typic Acrorthox, Togitogiga series), based on seed yield and tissue composition of sweet corn (Zea mays), and soil chemical properties. Application rates were 0, 5, and 10 Mg/ha for CaCO3 and 0, 7.5, and 15 Mg/ha for the green manure, factorially arranged. Treatments with commercial NPK fertilizers were included for comparison. Growth and yield of sweet corn showed that soil acidity can be corrected by either lime or green manure additions. Both lime and manure raised soil pH and (modified Truog) extractable phosphorus (P), which were partially responsible for yield increases. Green manuring significantly increased plant P and potassium (K) concentrations, which explain why the manure was more effective than lime in increasing corn yield. Ear leaves sampled at tasseling required at least 0.25% P and 2.4% K to attain >90% of the maximum seed yield.