Response of Rice-Wheat to Sodic Water Irrigation and Gypsum Application

Response of rice-wheat system to sodic water irrigation (EC_w = 3.1 dS m⁻¹, SAR = 17 (mmol L⁻¹)^½, RSC=10.5 me L⁻¹, Ca = 2.0 me L⁻¹, Mg = 4.6 me L⁻¹) and gypsum applications was evaluated for 7 years in a field experiment at the Bhaini Majra farm of CSSRI, Karnal. During study period, the water table remained below 4 m and amount of rainfall was between 50 to 90 cm. Overall build-up of pH_s, (8.5), SAR_e, (20.7) and EC_e, (2.5) in the soil remained lower than the threshold salinity/sodicity limits of both these crops. The rainfall dilution coupled with greater dissolution of Ca from CaCO₃, owing to high leaching fraction and high pCO₂, attained during rice growth appear to be the dominant processes leading to the development of low pH_s, and sodicity level in the irrigated soil. Gypsum application, however brought about 3–12 per cent enhancement in crop yields and 5–8 per cent increase in its sustainability index. Data revealed that a minimum yield of 60 per cent both in rice and wheat of their respective maximum (6, 5 t ha⁻¹) could be sustained with the use of sodic (RSC=10 me L⁻¹) water when 1.25 t ha⁻¹ gypsum was applied each year in a relatively high rainfall (50–90) semi-arid region.