Effect of high salinity and SAR waters on salinization, sodication and yields of pearl-millet and wheat

A characteristic feature of saline ground waters is an increase in their sodium adsorption ratio, SAR with salinity. Besides salinity, irrigation with such waters leads to sodium saturation of soils which may lead to reduced infiltration. A field experiment was conducted from 1983 to 1989 to study the effects of irrigation with saline waters having combinations of electrical conductivity, ECiw (6 and 12 dS/m) and SARiw (5, 10, 20, 30 and 40 (mmol/l)12) on properties of a sandy loam soil and yields of pearl-millet and wheat grown in rotation. Production functions fitted to predict relative yields (RY) could be represented for pearl-millet as: RY (%) = 133.1−ECiw (5.58−0.0026 R)−SARiw (0.0025 R + 0.43T)−0.03 (SARiw)2; R2 = 0.79∗∗ and for Wheat as: RY (%) = 98.14−0.54 ECiw−SARiw (0.10 ECiw + 0.09T)−0.01 (SARiw)2; R2 = 0.95∗∗ where R and T denote rainfall (mm) and time period after initiation of irrigation (years). Adverse effect of increased SARiw was greater on pearl-millet grown during monsoon rains. Increase in SAR of waters lead to increased build up of sodicity and salinity in soils, effects being more pronounced at ECiw 12 than 6 dS/m. Irrigation with waters having SAR of 20 and 40 (mmol/l)12 reduced infiltration rates to 12 and 7% of the original soil, respectively. Monsoon rains leached a major portion of the salts added with irrigations to wheat, but the soils being irrigated with higher SAR (> 20) waters retained more salts. A leaching test confirmed reduced leaching efficiency of soils irrigated with high SAR waters as the depth of water required per unit depth of soil (DwDs) for displacing 75% of the salts averaged to 0.64, 0.82 and 0.89 m/m in soils irrigated with SARiw = 5, 20, 40 (mmol/l)12, respectively. Amending the soil with gypsum @ 2 tha before leaching increased the infiltration rate and salt displacement in soils irrigated with high SAR waters.