Cyclic Use of Sodic and Non-Sodic Canal Waters for Irrigation in Cotton-Wheat Cropping System in a Semi-Arid Region

Abstract

ABSTRACT A 6-year field study (1996 to 2002) was conducted on a sandy loam soil to investigate the effect of different irrigation cycles involving sodic water (SW) and good-quality canal water (CW) on soil properties and crop yields in a cotton-wheat rotation. The treatments were: irrigation with CW, irrigation with SW (residual sodium carbonate 10 mmolc L−1) and different combinations of CW and SW applied in a cyclic mode starting with CW or SW. Irrigation with SW increased soil pH, sodium adsorption ratio (SAR), exchangeable sodium percentage (ESP) and bulk density (BD), and decreased final infiltration rate (FIR). From the third year onward, wheat and seed-cotton yields in the SW treatment declined by 5.9% and 16.5% yr−1, respectively. Compared with SW alone, alternating irrigation between CW and SW helped maintain significantly lower pH, SAR, and ESP levels, improve FIR and BD of the soil, and achieve higher crop yields. Exchangeable sodium percentage of the soil (0 to 0.30 m layer) measured 6 years after initiation of the experiment explained 94% and 83% variation in wheat and seed-cotton yields, respectively. Compared with SW, significantly higher wheat and seed-cotton yields were obtained in irrigation cycles starting with CW involving one SW (2CW:SW, CW:SW) or SW followed by two CW irrigations (SW:2CW). Decline in seed-cotton yield was relatively greater (18% to 23%) than that in wheat (9% to 10%) in irrigation cycles starting with SW (SW:CW, 2SW:CW) and involving only one CW.