Effects of Phosphorus on Seed Oil and Protein Contents and Phosphorus Use Efficiency in Some Soybean Varieties

Phosphorus (P) uptake and utilization by soybean (Glycine max (L.) Merrill) is essential for plant growth. Therefore, this experiment was conducted to evaluate the P effects on selected soybean varieties based on the seed oil content (SOC) and the seed protein content (SPC) and to assess the physiological responses associated with changes in shoot P-utilization efficiency (SPUE). The experiment was carried out during 2008 and 2009 with a split-plot design at the Agronomy Department, Kasetsart University, Bangkok, Thailand. The main plots were for tested three P levels in a nutrient solution (0.5, 1.0 and 2.0 mM P), with subplots for the three soybean cultivars, CKB1, SJ5 and CM60. The results indicated that at maturity, the P levels of 2.0 mM P decreased SPUE by 27% compared to that of 0.5 mM P (the control). SOC was not significantly affected by the P level. Relative to the control, the P nutrition levels of 1.0 and 2.0 mM P significantly decreased SPC by 4% and 5%, respectively. There were no significant differences in SOC between varieties. The SPC of CKB1 was 8% greater than that of SJ5 but showed no significant difference to that of CM60.