Field evaluation of drip fertigation uniformity effects on distributions of water and nitrogen in soil

The effects of drip fertigation uniformity and nitrogen applied on the distributions of water and nitrate in soil were investigated in a solar heated greenhouse in the growing season of Chinese cabbage to determine the design and evaluation standards of drip irrigation uniformity. Three Christiansen uniformity coefficients of 0.62, 0.80 and 0.96 and two levels of nitrogen applied at 150 and 300 kg/hm2 were used. The distributions of soil water content and bulk electrical conductivity were monitored continuously by equally spaced TDR sensors (Hydra Probe) along a dripline. Gravimetric samples of soil around each TDR sensor were collected regularly to determine the distributions of nitrate and ammonium nitrogen contents. A substantially high uniformity coefficient of soil water content was observed during the whole growing season for all three fertigation uniformity tests. The effects of fertigation uniformity and nitrogen applied on the mean and the uniformity of water in soil were insignificant at a significance level of 0.05. The uniformity coefficient of soil bulk electrical conductivity and nitrate in soil was substantially lower than that of soil water content, being greatly dependent upon the nonuniformity of initial nitrogen contents in the soil. An insignificant influence of fertigation uniformity on the uniformity of soil bulk electrical conductivity and nitrate content in soil was also observed. It was supported by this study that lower uniformity values of drip irrigation system than those recommended by the current standards could be used if the system mainly aimed at producing a uniform distributions of water and nitrogen in the soil.