Jiusheng Li, Weixia Zhao, Hang Zhang, Hongjie Guan, Yanfeng Li
China Institute of Water Resources and Hydropower Research

Uniformity is an important parameter in the design and operation of microirrigation systems. The redistribution of water and nutrients non-uniformly applied through microirrigation system in the soil and their effects on crop growth and yield have not been adequately and quantitatively considered in establishing the current standards. The effects of microirrigation uniformity on the spatial and temporal dynamics of water and nitrogen in soil and on the crop growth, yield and quality were evaluated by field experiments on typical crops in different regions from 2009 to 2012. The experiments included vegetable crops (Chinese cabbage) grown in a greenhouse and field row crop (maize) in a semi-humid region of North China Plain and cotton in an arid region of Xinjiang Autonomous Region. In the experiments, the CUs were varied from a value substantially below the current design criteria to fully uniform (60-98%) with an emitter spacing of either 30 or 40 cm and the irrigation amounts were varied from 50 to 100% of crop water requirement (ET). An approximately uniform distribution of water in the soil, resulted from the lateral and vertical redistribution, was obtained in either arid or semi-humid regions, even under a quite nonuniform water application of CU around 60%. The uniformity of nitrogen in the soil was highly variable, being mainly dependent on the distribution of initial nitrogen in the soil. In the semi-humid region, microirrigation uniformity produced an insignificant influence on the mean value of crop yield and the variation of yield along the dripline as uniform precipitation could compensate for the negative influence of non-uniformly applied water and fertilizers on crop growth to some extent. However, a lower uniformity resulted in a significant lower crop yield and nonuniform yield distribution in the arid region. The results of these studies recommended that different design criteria of microirrigation uniformity can be used in different environmental regions.