Trickle Irrigation of Cotton with Treated Sewage Effluent

The objectives of this field study, conducted in 1984 through 1986, were to assess the long‐term effects of applying treated municipal effluent (EC w = 2.6 dS m −1 ; SAR = 12.0) by trickle irrigation on soil N fertility, soil salinity, and yield of cotton ( Gossypium hirsutum L. cv. Sindos 1980) under semiarid conditions. Secondary treated effluent was compared with borehole water. Both waters were supplemented with 0, 30, 60, and 90 mg N L −1 . The N concentration in the effluent was about 30 mg L −1 during the 3 yr of experimentation. The residual soil NO 3 ‐N and the NO 3 ‐N concentrations in laminae and petioles were in general greater in the effluent‐irrigated crops. With both waters, excessive salt buildup occurred at the periphery of the wetting front. Sodium adsorption ratio (SAR) was reduced beneath the dripper in the surface 15 and 30 cm depth with borehole water and effluent, respectively, but below this depth the reverse occurred. Under the conditions of soil type, climate, and borehole water and effluent qualities used during this experiment, effluent was generally superior to borehole water, particularly at the lower N levels in increasing yields. The seedcotton yield obtained in the first season was significantly greater in the effluent irrigated treatments supplemented with N up to 60 mg L −1 ; in 1985 and 1986 seasons, yield with treated effluent was significantly higher in comparison with borehole water when additional N of 30 mg L −1 was applied. It can be concluded that municipal‐treated effluent containing 30 mg N L −1 can be used effectively by trickle irrigation systems as a source of irrigation water and N, and with appropriate N and water management, ecological hazards due to NO 3 ‐N are minimized, and salinity and sodicity are maintained at acceptable levels for cotton.