Feigin, A., Agric. Res. Org., The Volcani Center, Bet Dagan, Israel
Vaisman, I., Agric. Res. Org., The Volcani Center, Bet Dagan, Israel
Bierlorai, H., Agric. Res. Org., The Volcani Center, Bet Dagan, Israel

The suitability of sewage effluent for drip irrigation of cotton (Gossypium hirsutum) growing on a deep calcareous clay soil (Typic Chromoxererts) was studied during three seasons. Secondary effluent was compared with freshwater at three application rates, the average of which for the three seasons were: low (350 mm yr-1), standard (440 mm yr-1, and high (515 mm yr-1). Fertilizer was applied with the fresh water in order to deliver amounts of nutrients (average for the 3 years) equivalent to those in the effluent that contained 150, 180, and 230 kg N; 32, 37, and 46 kg P; and 80, 100, and 120 kg K ha-1 yr-1 for the three rates, respectively. In addition, the standard amount of fresh water was given with half the quantity of fertilizer, and without fertilizer. The concentration of available N and P in soil was increased greatly in all effluent and fertilizer-amended freshwater treatments, while available K in the soil was increased to a lesser extent. In general, at equivalent application levels, no significant differences in the level of available N, P, and K in the soil or in their uptake by plants, were detected between effluent and fertilizer-amended fresh water, although dry matter yield as well as N, P, and K accumulation were greater in the high-application-rate effluent treatment. The distribution of NO3-N in the soil profile was controlled by drip irrigation and practically no build-up of NO3- was detected below the 0- to 0.6-m depth layer during the irrigation period (in summer). However, during the rainy, winter season, heavy losses of residual NO3-N occurred, probably mainly through leaching.The suitability of sewage effluent for drip irrigation of cotton (Gossypium hirsutum) growing on a deep calcareous clay soil was studied during three seasons. Secondary effluent was compared with freshwater at three application rates. Fertilizer was applied with the fresh water in order to deliver amounts of nutrients (average for the 3 years) equivalent to those in the effluent. The concentration of available N and P in soil was increased greatly in all effluent and fertilizer-amended freshwater treatments, while available K in the soil was increased to a lesser extent. In general, at equivalent application levels, no significant differences in the level of available N, P, and K in the soil or in their uptake by plants, were detected between effluent and fertilizer-amended fresh water, although dry matter yield as well as N, P, and K accumulation were greater in the high-application-rate effluent treatment. Additional results are discussed in the paper.