Soil Properties and Yields of Upland Crops as Influenced by the Long-term Use of Waters having Variable Residual Alkalinity, Salinity and Sodicity

Long term effects of irrigation with waters varying in residual alkalinity (RSC 5 and 10 me L⁻¹), salinity (ECiw 2 and 4 dS m⁻¹), sodicity (SARiw 10,20 and 30 mmol L^−1/2) and anionic composition (HCO₃ vs Cl-SO₄) were evaluated in lysimeters filled with a silt loam soil (Typic Haplustalf). The crop rotation was cotton-wheat for initial 4 years (1991–95), followed by pearl-millet (fodder)-wheat for another 7 years (1995–2002). The rainfall varied from 7–23 and 39–107 em during rabi and kharif seasons, respectively. Build-up of sodicity (SARe) in soil in general was more where waters of higher salinity but of similar SAR were used. Similarly, for the same adj. RNa of water, sodication was more with HCO₃-type water as compared with Cl-SO₄ ones. Increase in soil pH was related to RSC rather than to SAR. Progressive build-up in salts (ECe 1.2–5.8 dS m⁻¹), sodicity (SARe 5.6–38.5) and soil pHs (8.10–8.66) monitored during cotton-wheat rotation were either curtailed or even got reduced as a consequence of shifting to pearl millet-wheat rotation. Sodicity build-up was also related to duration of irrigation both in cotton (R² = 0.64*) and wheat (R² = 0.81**) but was negated by the quantum of rainfall received during kharif (R² = 0.67*). Similarly, increase in leaching fraction (LF) and rainfall during kharif reduced SARe build-up during wheat (R² = 0.68). Decline in yield of kharif crops (cotton/pearl millet) ranged from 9 to 36% when referenced to good quality water. Reductions in yields of pearl millet were comparatively more than those of cotton while no effect was observed in case of wheat. In general, the yields of wheat could be sustained (> 90%) with waters of ECiw ≤ 4 dS m⁻¹, SAR ≤ 30 and RSC ≤ 10 and of cottonl pearl millet (>80%) with water of ECiw ≤ 4 dS m⁻¹, SAR ≤ 20 and RSC ≤ 5.