Effect of foliar spray of nutrient solutions on photosynthesis, dry matter accumulation and yield in seawater-stressed rice

The effects of seawater salinity and foliar application of nutrient solutions on rice in the early tillering stage and early reproductive phase of growth were investigated in a glasshouse. During early tillering stage, from 10 to 35 days after transplanting (DAT) and the early reproductive phase, from 75 to 100 DAT, potted rice plants were irrigated with Japan seawater of 0, 8.8, 17.5 and 35% (equivalent to an EC of 0.9, 5.7, 11.5 and 21.5 ms cm(-1), respectively). The nutrient solution of 1 mM Ca(NO3)2, MnSO4 or K2HPO4 was sprayed twice a week until the solution ran off the leaves. Photosynthesis and its related parameters were measured at 30 and 95 DAT in the early tillering stage and in the reproductive growth phase, respectively. Seawater salinity diminished photosynthesis rate and photosynthesis related parameters, such as stomatal conductance, intercellular CO2 concentration, leaf water and osmotic potential and relative leaf water content in both growth stages and have reduced tiller number, leaf area and top dry matter content in tillering stage. We have also studied the effect of salt-stress on the mineral content at 35 DAT. Na+ concentration increased, whereas Ca2+, Mn2+ and K+ concentration were decreased with increasing stress. Seawater decreased fertile spikelets in the panicle, decreased accumulation of dry matter in the grain and concomitantly decreased grain yield. Foliar spray of Ca(NO3)2, MnSO4 or K2HPO4 partially minimized the salt-induced nutrient deficiency, increased photosynthesis, dry matter accumulation, number of fertile spikelet in the panicle and grain yield. Among the nutrient solutions, Ca(NO3)2 seemed to be the most effective, followed by MnSO4 and K2HPO4. These results suggested that foliar application of nutrient solutions partially alleviates the adverse effects of salinity on photosynthesis and photosynthesis-related parameters, yield and yield components through mitigating the nutrient demands of salt-stressed plants.