Effects of longterm applications of ammonium sulfate to paddy soils of the central plain on some soil chemical properties, growth, yield and chemical composition of rice

The effects of longterm application of ammonium sulfate on some soil chemical properties, growth and chemical composition of rice were studied on brackish water alluvial at Khlongluang rice experiment station (KRES) and on fresh water alluvial at Supanburi rice experiment station (SRES). Results of the study are summarized as follows: 1. Long term effect of ammonium sulfate influence some soil properties, that is increased rate of ammonium sulfate decreases pH of the soils, and the residual phosphorus added but significantly increases soil organic matter content at KRES but tended to increase only at SRES. Soil analysis before and after cropping did not give good evidence of plant nutrient removals. 2. Plant height, tiller numberrs and dry matter of roots were not clearly affected by long term application of ammonium sulfate but the effect was highly significant on the top dry matter at 6 and 8 weeks after transplanting (WAT) at SRES and at 8 WAT at KRES. The yield and yield components were affected by the long term application of ammonium sulfate but there was no statistical difference on the yield and filled grains per panicle of rice grown at KRES. 3. The N content of the rice plant is increased when the N rates applied is increased. Nitrogen content was decreased at the rice plant became older. The concentration of phosphorus and potassium in rice plant was reduced as heavy rates of nitrogen were applied. 4. Dry matter, yield components and N uptake before flowering reflexed grain yield of each variety differently, depending on soil properties. a. In normal infertile soil (SRES), numberr of panicles/hill was the best yield indicator of each variety. Number of good grain/panicle, dry matter at 6 wat and N uptake at 4 and 6 WAT were among good yield indicators of the RD9. For RD7, numberr of panicles/hill, N uptake at 6 WAT was another good yield indicator. The yield of RD5 could be estimated only by the number of panicles/hill. b. In acid sulfate soil (KRES), only the numberr of panicles/hill could predict yield of all varieties except RD9. Data suggested that variety RD9 is less resistant to adverse factors of the acid sulfate soils