The Effects of Drip Irrigation System Uniformity on Soil Water and Nitrogen Distributions

Abstract

The effects of drip irrigation system uniformity and nitrogen application rate on the distribution of water and nitrate in the soil were investigated through field experiments to modify the current design and evaluation standards for drip irrigation uniformity. The experiments were conducted in a solar-heated greenhouse in the 2009 and 2010 growing seasons of Chinese cabbage. Three statistical uniformity coefficients (Us = 55%, 73%, and 95%) and two nitrogen application rates (150 and 300 kg ha-1) were evaluated in 2009. In 2010, three Us values (53%, 65%, and 94%) and one nitrogen application rate (225 kg ha-1) were tested. The distribution of the soil water content and bulk electrical conductivity was monitored continuously with equally spaced frequency domain reflectometry (FDR) sensors located along a dripline. Gravimetric samples of soil for each plot were collected regularly to determine the distribution of nitrate. For all of the tested system uniformities, the soil water content displayed high uniformity coefficients throughout the entire growing season. The effects of system uniformity and nitrogen application rate on the seasonal mean water content and bulk electrical conductivity (ECb) and on the seasonal mean uniformity of water content and bulk electrical conductivity were insignificant at a significance level of 0.05. The uniformity coefficient of the soil bulk electrical conductivity and nitrate content was substantially lower than that of the soil water content and was dependent on the uniformity of the initial salt and nutrient constituents in the soil. Moreover, the system uniformity and nitrogen application rate had an insignificant effect on the uniformity of the nitrate content. The results of this study showed that uniformity values that are lower than those recommended by the current standards can be used in drip irrigation systems if sufficient irrigation and fertigation events are conducted to approach a uniform distribution of water and nutrients in the soil.