Effects of drip irrigation quota on yield and water productivity in watermelon-cotton intercropping system

Abstract: The intercropping system, which contains combination and collocation of different crops, is a traditional and productive planting of agricultural production. Field intercropping system has been widely proved to be able to improve the productivity of agroecosystem effectively. Compared to monoculture, intercropping can increase the interception of light energy, grain yield and water productivity of croplands. Nowadays, water shortage becomes more severe in the face of the projecting population growth and food demands. Therefore, a more efficient intercropping pattern, including highly efficient utilization of resources and water saving, is urgently needed. Currently, the research and application of drip irrigation in intercropping system are gradually increasing, but the principles of irrigation index and water productivity are relatively inadequate. Therefore, field experiments with 4 treatments were carried out during 2013 in this study in order to reveal the appropriate magnitude of drip irrigation index in a watermelon-cotton intercropping system. Drip irrigation with mulch was integrated into the watermelon-cotton intercropping system and different drip irrigation quotas: i.e., 15 mm (T1), 22.5 mm (T2), 37.5 mm (T3) and 30 mm (CK) were conducted to investigate the impacts of drip irrigation quota on crop growth, yield, water production efficiency and economic benefit in watermelon-cotton intercropping system. The results showed that the main vine length of watermelon was larger in T3 treatment during the early growing stage, but shorter in T2 treatment during the middle and late growing stage, and T1 was the smallest during the whole growing stage. The cotton height of T3 was the largest, and T1 was the smallest; leaf area index of intercropping population showed a double-peak curve and increased with the irrigation quota in symbiotic period, and no significant differences of leaf area index were found among all treatments in non-symbiotic period; the eventual shedding rate of buds and bolls was the minimal in T2, only 59.6%, the second for T1 treatment, and T3 treatment was up to 62.3%. Among all treatments, T2 significantly improved the watermelon-cotton intercropping production, water production efficiency and economic benefits. For T2, the yield of watermelon was 59 697.0 kg/hm2, the yield of cotton was 4 851.2 kg/hm2, the water productivity was 28.20 yuan/m3, and the total economic output value was as high as 163 054.8 yuan/hm2. The irrigation water amount of T1 treatment was the smallest, and the output was the lowest. The main reason was that the water supply of T1 was less than other treatments, and the enhancement of water competition led to the smallest main vine length of watermelon and the lowest plant height of cotton and population LAI in the intercropping system, limiting the exertion of the advantages. The vegetative growth of T3 treatment was over vigorous as a result of the largest irrigation water amount. Accordingly, the WP (water productivity) and comprehensive profit of T3 treatment was the smallest. In conclusion, the suitable drip irrigation quota of watermelon-cotton intercropping was 22.5 mm, and the total irrigation time was 7 in the whole growing stage. Using this irrigation mode to carry out scientific water management can realize the unity of high yield and water productivity and provide reference for scientific utilization of drip irrigation technology in watermelon-cotton intercropping system in this region.