Conservation tillage and irrigation methods effect on the water use efficiency in the wheat-cotton rotation

In this research, effect of tillage and irrigation methods on the soil properties, crop yield, and water use efficiency (WUE) was evaluated in wheat-cotton rotation. The study was conducted in the form of a split plot experimental design with nine treatments and three replications in Darab Agricultural Research Station (Bakhtajerd). Main plots were irrigation methods including surface irrigation (gated pipe), tape irrigation, and sprinkle irrigation. Tillage methods including zero tillage (direct drilling), reduced tillage, and conventional tillage (control treatment) were considered as sub plots in this research. Treatments were applied in plots with dimensions of 20 by 6 m and local cotton and wheat varieties (Bakhtegan and Chamran) were planted in the plots. Soil bulk density, soil infiltration rate, water consumption, crop yield, and water use efficiency were measured in different tillage and irrigation treatments. Collected data were analyzed using SAS software and Duncan's multiple range tests were used to compare the treatments means. Results showed that tillage and irrigation methods had a significant effect on the soil bulk density so that tape irrigatin had the higher soil bulk density compared to the other irrigation methods. Soil bulk density was also higher in the conservation tillage methods compared to that of conventional tillage. The maximum water accumulated infiltration occurred in the tape irrigation and the minimum water accumulated infiltration was related to the surface irrigation. Conventional tillage had the highest water accumulated infiltration and the reduced tillage had the lowest one. Tillage methods had no significant effect on the wheat and cotton yield; while, crop yield was affected by irrigation methods. In both crops (wheat and cotton), pressurized irrigation methods had the higher yield compared to the surface irrigation. Wheat and cotton consumed the largest water volume in the surface irrigation method and the least water consumption in these two crops was related to the tape irrigation. Tape and sprinkle irrigation saved water in cotton growing compared to the surface irrigation for 51 and 28%, respectively. These water saving in wheat growing were 59 and 40%, respectively. Irrigation methods had a significant effect on the water use efficiency of wheat and cotton; whereas, water use efficiency was not affected by tillage methods. The maximum water use efficiency was obtained from tape irrigation in both crops and the minimum water use efficiency was related to the surface irrigation.