Alleviation of sodicity stress on rice genotypes by Phosphorus fertilization

Abstract

Rice seedlings transplanted into sodic soil are exposed to an excess of potentially toxic ions as well as nutritional imbalance, both of which adversely affect their growth and yield. The present study was aimed to investigate the beneficial effects of fertilization with phosphorus and potassium on the plants at varying sodicity levels and also the response of genotypes with known variability in their tolerance to sodicity. In pot-house experiments during two seasons, the alleviating effects of P and K fertilization on three rice genotypes were examined at four sodicity levels. Seedlings of CSR13 and Jaya (both moderately tolerant to sodicity), died by 25–35 days after transplanting in sodic soils of pH 9.7–9.9 where Olsen's P was 12.5 and 14.8 kg/ha, respectively. However, there was no problem of survival or growth in these soils when Olsen's P was 17.6 and 20.8 kg/ha. Depletion in P from 12.0 kg to 10 kg resulted in some mortality of the seedlings even at pH 9.1. Sodicity tolerant genotype CSR10, did show some survival and growth even at pH 9.9 with Olsen's P at 14.8 kg/ha (without P fertilization) which suggests that differences in tolerance to sodicity which exist at genotypic level are not masked by low P. None of the three genotypes showed any survival problem at pH 8.0 and 8.1 with Olsen's P at 8.5 and 8.7 kg/ha, respectively. Seedlings in P fertilized sodic soils not only produced significantly more new roots but also higher root biomass than those in unfertilized sodic soils and these roots seem to have some control on Na uptake as reflected by low Na concentration in the shoots. Thus, P fertilization not only improved P and K status of plants but also reduced the concentration of potentially toxic Na ions in shoots, resulting in better survival, growth and yield. Although fertilization with K alone did improve shoot K content, it had no significant effect on reducing Na. So the mortality of the seedlings or grain yield in K fertilized sodic soils was as good as in control and this could be explained on the basis of lack of any significant difference in Na concentrations in shoots between these two treatments.