Effect of rock phosphate and triple superphosphate for rice-mungbean cropping system in Rangsit series, very acid phase

Effect of lime and phosphate fertilization on the chemical properties of the soil, growth and yield of rice-mungbean cropping system on Rangsit series, very acid phase was studied. The phosphate fertilizer used were rock phosphate in combination with triple superphosphate. The investigation comprises two pot experiments and two field experiments. Experiment 1. Lime was added as marl at the rate of 75 g/8 kg soil in the pot. Phosphate fertilizer was applied at the rate of 75 ppm P. Nitrogen and potassium were also added at the rate of 75 ppm N and K to every treatment. The phosphate treatments were RP 100 percent, RP 75 percent+TSP25 percent, RP 50 percent+TSP 50 percent, RP 25 percent+TSP 75 percent and TSP 100 percent. The experiment was factorial in completely randomized designed with 3 replications. Two three week old seedings of Suphanburi 90 rice variety were transplanted to each pot. The results showed that liming had no beneficial effect. The growth and yield of rice were higher in the unlimed and triple superphosphate treatment. The chemical analysis of soil solution revealed the low water soluble iron in the liming treatment. This could be attributed to deficiency of iron in the plant. The higher percentage of unfilled grain in the liming treatments supported this result. Experiment 2. Mungbean was grown after harvesting the rice plants. Kampangsaen 1 mungbean variety was used in this experiment. The seed was inoculated with Rhizobium and coated with marl. No phosphate and potassium fertilizer was added, but 0.33 gm/pot of urea was added as the recommendation rate with Rhizobium. Three seeds were planted to each pot. The results showed that the yield of mungbean was higher in the liming treatment except the unlime+rock phosphate treatment, the higher seed weight of mungbean was observed. The plant analysis showed that N, P, and K uptake were higher in the liming treatment. Experiment 3. Lime was added at the rate of 1 ton/rai. Phosphate fertilizer was added at the rate of 12 kg P2O5/rai. The combination of rock phosphate and triple superphosphate were the same as the experiment 1. Nitrogen and potassium were applied as urea and muriate of potash at the rate of 6 kg N/rai and 6 kg K2O/rai as basal dressing respectively. Urea was applied at 6 kg N/rai as top dressing at 30 days after transplanting. Three twenty five day old seedlings of Suphanburi 90 rice variety were transplanted in the 4x6 square m/plot. The experiment was factorial in randomized complete block design with 4 replications. The results showed that when lime was applied, triple superphosphate gave higher grain yield compared to rock phosphate. The soil analysis showed that pH of unlimed soils were between 4.4-4.5, while the pH of the limed treatments were between 4.6-4.9. Experiment 4. Mungbean was grown after rice crop in the dry season. Kamphangsaen 1 mungbean variety was used in the study. The seed was inoculated with Rhizobium and coated with marl. The spacing of the plants was 25x50 square cm. No phosphate and potassium feritlizer were added, except nitrogen was added as urea at the rate of 3 kg N/rai. The result showed that all of the liming treatments regardless of phosphate fertilizer gave significantly higher in seed weight of mungbean. The plant analysis showed the higher uptake of N, P, and K in those treatments.