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Effects of Soil pH, Calcium, Phosphorus, and Aluminum on the Growth and Nodulation of Leucaena Leucocephala (Lam.) de Wit
Dissertation Abstract:
Investigation on the effects of soil pH; varying concentrations of calcium (Ca), phosphorus (P), and aluminum (Al) on the growth; and 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, Laguna, Philippines. The experimental design for both acid soils included five concentrations of Ca as calcium chloride (CaCl2) and calcium carbonate (CaCO3) [at 25% and 50% soil cation exchange capacity (CEC)] in factorial combination, with four P concentrations (0, 60, 180, and 540 kg P2O5/ha) replicated three times. The toxic effects of Al and the modifying effects of CaCl2 and CaCO3 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) adjusted at three pH levels (5, 7, and 8). The second set of culture solution had Ca concentrations of 0, 0.10, 0.25, 0.50, 1.0, and 2.0 mmol L-1, adjusted to pH 4.8 + 0.1.
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.
Liming of acid soils was applied with CaCo3, which provided calcium at the rate of 25 percent of the soil CEC. This raised the pH of the soil from pH 5.4 to pH 5.6. When CaCO3 was applied to soils, it resulted in pH higher than pH 6. The addition of CaCl2 which provided a similar concentration of Ca as CaCO3, did not improve the growth of ipil-ipil in acid soil. This indicated that the restricted growth at acid condition was not due to lack of Ca supply but the effect of low pH on the availability of essential elements such as phosphorus.
The application of 180 kg P2O5/ha alone significantly improved growth, nodulation, and nitrogenase activity of plants grown in soils from Cavinti, which had less than 2 ppm P. Plants grown in soils from Siniloan, which had more than 7 ppm P, did not respond to P fertilization. Liming combined with P fertilization enhanced growth of plants in both acid soils.
The culture solution experiment showed that growth at pH 5 was comparable to growth at pH 7 when the Ca was at 0.1-0.5 mmol L-1 and P at 100-500 mmol L-1, was was significantly better than growth observed at pH 8. Treatment with 3 mc Al/100 g soil adversely affecte growth, nodulation, and nitrogenase activity. However, the sand culture showed enhanced growth of ipil-ipil when the culture solution had 20 mmol L-1 of Al.
Root elongation was most adversely affected by higher Al concentration. Liming with CaCo3 neutralized the adverse effects of Al, while addition of CaCl2 aggravated its effects. Treatment of soils with CaCo3 increased the Ca:Mg (magnesiium) ratio in shoots to approximately 2.45:1.00 and higher, while plants treated with CaCl2 showed Ca:Mg ratio of approximately 1.50:1.00. Treatment of soils with Al resulted in lower Ca:Mg ratio in shoots.