Irrigation and soil management strategies for using saline-sodic water in a cotton–wheat rotation

Consequent to population growth and high living standards in several arid and semi-arid regions, competition for freshwater among different water-use sectors is expected to increase vis-à-vis its decreased allocation to irrigation. Non-conventional water resources, such as saline and/or sodic drainage and groundwater represent complementary supply to narrow the gap between freshwater availability and demand. We carried out a 3-year field study in the Indus Plains of Pakistan to evaluate different irrigation and soil management strategies for using saline-sodic water to grow cotton (Gossypium hirsutum L.) and wheat (Triticum aestivum L.) on a sandy loam soil (ECe=1.31–1.76dSm−1, pHs=8.47–8.61, SAR=5.50–7.41, infiltration rate=0.6–0.8cmh−1, ρb=1.56–1.61Mgm−3). The treatments were: (1) irrigation with freshwater from a nearby canal (FW); (2) irrigation with saline-sodic water (EC=3.32dSm−1, SAR=16.29, SARadj=18.24, RSC=5.25mmolcL−1) (SSW); (3) cyclic use of fresh and saline-sodic water through alternate irrigations (FW−SSW); (4) Soil application of farm manure at 25Mgha−1year−1 and irrigation with saline-sodic water (FM+SSW); and (5) soil application of gypsum equivalent to gypsum requirement of saline-sodic water and irrigation with the same water (G+SSW). The seed yield of first cotton crop was not significantly affected by different treatments. The yields of subsequent wheat and cotton crops were lower in the SSW than other treatments, indicating negative impacts of saline-sodic water when used in the absence of a soil or irrigation management approach. The treatments using saline-sodic water did increase soil ECe and SAR levels, but this increase was only significant in SSW treatment. Irrigation with saline-sodic water together with amendments significantly increased infiltration rate than SSW alone, where bulk density was increased. The net benefit was the maximum from FW−SSW treatment followed by FW, G+SSW, FM+SSW and SSW.