Effects of saline irrigation at various reproductive stages on rice yield

The objective of this study was to examine whether the difference in the effects of saline irrigation conducted at various reproductive stages on the yield of rice (Oryza sativa L.) depends on the sodium and potassium contents in plant organs. Two rice cultivars, Kala-Rata 1-24 (KR1) and IR28 were subjected to saline irrigation (100 mM sodium chloride) at six different reproductive stages for one week. Saline irrigation at the booting stage reduced the winnowed paddy weight. The decrease was due to the decrease in one-grain weight in both cultivars, and also to the decrease in grain number in KR1 and that in the percentage of ripened grain in IR28. One-grain weight decreased as a result of the decrease in hull size. Decrease in winnowed paddy weight and hull size was related to low potassium content in leaves and stems, but was unrelated to sodium content and potassium : sodium ratio. The low potassium content in leaves and stems did not correspond to the low potassium : sodium ratio, indicating that it was not the result of the competition with sodium ion, but was caused by the inhibition of potassium uptake by roots.