Response of wheat to irrigation with saline water varying in anionic constituents and phosphorus application

Abstract

Most underground saline water is characterized by the predominance of either the SO 2− 4 or Cl − ions. Toxicity of chloride has been reported but how the ionic constituents effect the crop response to added phosphatic fertilizers is not known. This field study investigated the interactive effects of: salinity (80 and 120 meq/1), anionic constituents (Cl : SO 4 ratios of 3 : 1, 1 : 1 and 1 : 3) and phosphatic fertilization (0, 26 and 39 kg P/ha) on salinization and sodication of soil and response of wheat. Average yields of wheat grown for 3 y in wheat-fallow rotation showed reductions of 4.7 and 12.5% at irrigation water electrolyte content (EC iw) of 6.1-6.7 and 8.8-9.9 dS/m, respectively. Increasing Cl : SO 4 ratio in saline water to 1 : 1 and 3 : 1 reduced the grain yield by 5.9 and 11.6 percent, respectively when compared with yield obtained at Cl : SO 4 ratio of 1 : 3. Phosphorus application (26 and 39 kg/ha) improved yield by 39 and 55 percent, respectively. A regression model used to describe the production function revealed that wheat yields could be sustained with higher salinity water if the Cl : SO 4 ratio is lowered and/or with the application of additional phosphorus. Salt leaching due to monsoon rains was reduced in soils irrigated with SO 4-dominant water. The SO 2− 4 associated cations were Na + and Ca 2+ + Mg 2+ and higher SARe was maintained in lower soil layers. The amount of rain during monsoons influenced the patterns of sodication in soils irrigated with saline water varying in Cl : SO 4 ratio.