Calcium and Salt‐Tolerance of Rice

Abstract

The impact of calcium (Ca) supply on the growth and yield of rice was studied in nutrient and soil culture experiments. In solution culture experiment, the effect of external‐Ca supply (0.5, 1.0, 1.5, 2.0, 3.0, 4.0 mM Ca) on the growth and shoot composition of two rice cultivars, varying in salt‐tolerance, in the presence and absence of 100 mol m− 3 NaCl was measured in a four week trial. In soil culture experiment, Ca (as gypsum; CaSO4 · 2H2O) was applied at the rates of 0, 10, 25, 50 and 100% of gypsum requirement (GR) of the saline‐sodic soil (after determining its GR). A positive, improving and stimulative effect of Ca was noted in growth characteristics (shoot and root weight and tillering capacity) in both the cultivars at 1.0 to 1.5 mM Ca; above this concentration, Ca had inhibitory effect. Although increasing supply of Ca tended to decrease sodium (Na) and chloride (Cl) concentration in the shoots of both rice cultivars, shoot‐concentrations of Na and Cl were much lower in NIAB‐6 (salt tolerant) than IR 1561 (salt sensitive). An increase in potassium(K):Na ratio, an indication of salt tolerance, was observed at 1.0 mM Ca and above in both rice cultivars under saline environment. Result, confirmed in salt affected soils of two different types (saline and saline sodic), showed an improvement in the paddy yield of both salt tolerant and salt sensitive rice cultivars due to Ca application as gypsum at the rate of 25% of GR of soil. Excessive rates of Ca either in solution culture or soil were detrimental for plant growth and paddy yield. The ameliorative effect of Ca was because of increased Ca:Na ratio of the growth medium.