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 by 80 and 98% at 8 and 16 mS/cm levels of saline irrigation, respectively, below tap water (0.6 mS/cm). The adverse effect of salinity was more 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 controls at 0.6, 8, and 16 mS/cm levels of salinity, respectively. The length of panicles, percentage of filled grains, and 1000-grain weight, protein concentrations of the rice grains, sum of Ca, Mg and K concentrations were reduced due to imposition of saline irrigation, but gypsum and Zn treatments significantly improved these parameters even at the highest (16 mS/cm) salinity stress. The combined application of gypsum and Zn was found to be effective to increase the protein concentrations in rice grains by 2–4% and to increase total concentrations of Ca, Mg and K, but reduced the Na/K ratios in plant tissues by 29.13, and 12% at 0.6, 8, and 16 mS/cm salinity, respectively, suggesting that the application of gypsum and Zn in parallel with irrigation of saline soils, would be effective to reduce the adverse effects of high Na/K ratios as well as to improve growth, yield, and nutritional balance in rice.