EFFECTS OF GYPSUM AND ZN ON UPTAKE RATIOS OF NA, K AND GROWTH-YIELD OF RICE GROWN ON A COASTAL SALINE SOIL

Salinity reduced (reduction below control = RBC) grain yield of rice b y 80 and 98% at 8 and 16 mS/cm levels of saline irrigation, respective ly, below tap water (0.6 mS/cm). The adverse effect of salinity was mo re pronounced on grain yield (98% RBC at 16 mS/cm) than on straw yield (84% RBC). The combined application of gypsum and Zn at the rates of 160 and 5 kg/ha produced 49, 45, and 41% more grain yield above contro ls at 0.6, 8, and 16 mS/cm levels of salinity, respectively. The lengt h of panicles, percentage of filled grains, and 1000-grain weight, pro tein concentrations of the rice grains, sum of Ca, Mg and K concentrat ions were reduced due to imposition of saline irrigation, but gypsum a nd Zn treatments significantly improved these parameters even at the h ighest (16 mS/cm) salinity stress. The combined application of gypsum and Zn was found to be effective to increase the protein concentration s in rice grains by 2-4% and to increase total concentrations of Ca, M g and K, but reduced the Na/K ratios in plant tissues by 29, 13, and 1 2% at 0.6, 8, and 16 mS/cm salinity, respectively, suggesting that the application of gypsum and Zn in parallel with irrigation of saline so ils, would be effective to reduce the adverse effects of high Na/K rat ios as well as to improve growth, yield, and nutritional balance in ri ce.