Author : Inciong, Nora B.

Summary : Investigation on the effects of soil pH, varying concentrations of calcium, phosphorus and aluminum on the growth, nodulation and nitrogenase activity of ipil-ipil in potted soil and culture solutions were conducted using Luisiana clay and modified Hoagland nutrient solution. Luisiana clay was obtained from the municipalities of Cavinti and Siniloan. The experimental design for both acid soils included five concentrations of Ca as CaCl2 and CaCO3 (at 25% and 50% of soil CEC) in factorial combination with four P concentrations (0, 60, 180 and 540 kg P 2O5/ha) replicated three times. The toxic effects of aluminum and the modifying effects of CaCl2 and CaCO 3 were determined in a potted soil experiment with soils from Cavinti. The sand culture studies were of two sets : the first set which determined the effects of concentrations of Ca and P in nutrient solutions included five Ca concentrations (0,0.10,0.25,0.50 and 1.0 mmol L-1) and five P concentrations (0,1,10,100 and 500 umol L-1) adjusted at three pH levels : pH 5.0,7.0 and 8.0. The investigations revealed that given similar concentrations of essential nutrients in sand culture, growth of ipil-ipil at pH 5 was similar to growth obtained at pH 7 and remarkably better than growth observed at pH 8.0. Liming of acid soils showed remarkably improved growth of plants when the acid soil was applied CaCO3 which provided calcium at the rate of 25% of the soil CEC, raising the pH of the soil to pH 5.4-pH 5.6, than when soils was applied with more CaCO3 which resulted to pH higher than pH 6.