Seed phosphorus fertilizer effect on the early growth of soybean under low phosphorus supply

One approach to obtain a crop response under limited P supply is to use genotypes that are more efficient in extracting soil P. Further, better early establishment of the crop is expected to positively benefit subsequent growth and P uptake. A high seed P content is likely to improve early crop establishment. In hydroponics and pot experiments using soybean as a test crop, the hypothesis that high seed P content ensures better early crop establihment was tested under low P conditions. Two seed P contents (0.5 percent and 0.7 percent P) and four solution levels (0, 0.05, 0.5 and 5.0 ug/ml) were the treatments used in the hydroponics experiment. The same two seed P contents as the hydroponics experiment and four P fertilizer levels (0, 25, 50, and 200 kg P/ha) were used in the pot experiment. The high and low P content seeds used were selected for similar size. A highly P-fixing soil from Cavinti, Laguna, Philippines, was used in the pot experiment. High seed P content significantly increased leaf area and shoot dry weight measured at 7 and 14 d of growth in the hydroponics: however, the effect disappeared when measured at 21 d of growth. High-seed P plants average between 15 and 26 percent higher leaf area and shoot dry weight than the low-seed P plants across P levels and the 7 and 14 d sampling times. In the pot experiment, significant high seed P effects on leaf area and shoot dry weight (21-26 percent higher) were measured at the first sampling at 21 d but not at 36 d after seeding. Plants from high seed P sustained increased root length until the last sampling at 21 d of growth in the hydroponics. This effect was more pronounced at the low solution P concentrations. At 21 d, the root length of high-seed P plants were 70 percent higher than the low-seed P ones at the 0.05 ug P/ml level. In both hydroponics and pot experiments, increasing P levels significantly increased leaf area, shoot dry weight and root dry weight, but decreased root-shoot ratio. Results indicate that high seed P favorably influences early growth but only root length effects are maintained beyond the first 2 week growth. Increased early root length development by plants from seeds with high P content could benefit from increased P uptake in low-P supply soils