Effects of drip irrigation system uniformity and nitrogen applied on deep percolation and nitrate leaching during growing seasons of spring maize in semi-humid region

Abstract

Abstract. Deep percolation and nitrate leaching are important considerations in the design and management of drip irrigation systems. Field experiments were conducted during two growing seasons of spring maize (Zea may L.) in 2011 and 2012 on a silt loam soil to evaluate the influence of drip irrigation system uniformity on deep percolation and nitrate leaching under semi-humid conditions. In the experiments, three Christiansen uniformity coefficients (CU) of 59%, 80%, and 97% and three levels of nitrogen applied at 0, 120 and 210 kg ha -1 were tested using a completely randomized design with three replications. Tensiometers were installed at 60- and 80-cm depth in the soil and the daily readings were used to estimate the water flux at the bottom of the root zone (70 cm depth). Nitrate concentration of soil solution at the bottom of the root zone was monitored from the extraction of a ceramic suction cup installed at 70 cm depth. Nitrate leaching from the root zone was determined from the estimated daily deep percolation rate and NO 3 -N concentration of the soil solution. Deep percolation most likely occurred following a heavy precipitation event although slight deep percolation was observed following an irrigation event of any drip irrigation system uniformity tested. Almost 80% of the seasonal deep percolation was caused by the intensive rainfall events that occurred at the later growing seasons of maize for both seasons. A significant effect of system uniformity on deep percolation was observed at a significance level of 0.05 in 2012. The seasonal deep percolation averaged over all the three levels of nitrogen applied increased from 80 to 94 mm in 2011 and increased from 89 to 105 mm in 2012 as system uniformity decreased from 97% to 59%. Nitrate leaching was most importantly affected by the nitrogen applied, followed by the initial nitrogen content in the soil and the drip irrigation system uniformity. An increasing nitrogen applied and initial nitrogen content increased the seasonal nitrate leaching significantly, while an improving system uniformity decreased the nitrate leaching. The results of the study showed that the conventional nitrogen application rate of 210 kg ha -1 could be reduced and an extremely low drip uniformity of less than 60% is not recommended to reduce the risk of deep percolation and nitrate leaching in the semi-humid region of North China Plain.