Interactive effects of pH, EC and nitrogen on yields and nutrient absorption of rice (Oryza sativa L.)

Soil salinity and sodicity can not only directly restrain crop growth by osmotic and specific ion stresses, it also may reduce grain yield indirectly by impacting plant absorption of essential nutrients. Ensuring adequate nitrogen is an important management aspect of rice production in saline-sodic soils. The objective of this study was to investigate the interaction of soil pH, salinity and nitrogen application on rice yield and nutrient absorption. We conducted a rice experiment in containers in a greenhouse. The soils were first leached with 9 target salt solutions of pH 7, 8 and 9 and electrical conductivity (EC) of 2, 6 and 10 dS m−1. Nitrogen application rates were 100, 200 and 300 kg N ha−1. Rice grain yield and shoot weight significantly decreased with increasing soil pH and increasing soil EC, and significantly increased with increasing nitrogen application (P < 0.001). However, at high EC and/or high pH yield was not significantly increased by increased N. High pH and high EC in soil significantly influenced the mineral nutrient content of rice shoots (P < 0.05). High soil pH and soil EC stresses were superimposed on each other, the negative effects on rice were compounded. The results by stepwise regression analysis showed that soil pH very significantly and adversely impacts grain yield and was the major factor impacting rice grain yield (R2 = 0.565, P < 0.001). Nitrogen application provided a positive response under control and pH 7 at all salinity values, and at pH 8 under low salinity only. There was no significant response to additional N under pH 8 and elevated EC and no significant response at pH 9 for all EC values. Thus, adequate nitrogen application is an important technical measure for improving rice yield and promoting nutrient absorption in rice of high EC soils but not of high pH soils where pH is the major limiting factor for rice production in saline-sodic soils.