Evaluation of Water and Nitrogen Distribution and Redistribution in Subsurface Drip Irrigation Systems

ABSTRACT Determination of the distribution and redistribution of water and nitrogen in the soil is critical for the design and management of subsurface drip irrigation (SSDI). Laboratory experiments were conducted to investigate the effects of the emitter discharge rate (2 and 5.5 L h −1 ) and lateral depth (0 to 20 cm) on water and nitrogen distributions and redistributions under SSDI. The wetted soil area clearly decreased with the emitter discharge rate and increased dramatically with lateral depth following fertigation while an opposing trend was observed in the average soil moisture and nitrate content. Ammonium accumulated near the emitter and the nitrate concentration dropped at the emitter and accumulated at the wetting front edge for both surface drip irrigation (SDI) and SSDI. The wetted soil area exhibited a trend of initial increase followed by a decrease during the redistribution process. A gradual decline and increase were respectively found in the maximum ammonium and nitrate concentrations. An SSDI with an emitter discharge rate of 2 L h −1 produced superior spatial uniformity of water and nitrate according to the lower coefficients of variation. The outcomes recommend that low emitter discharge rates in SSDI can enhance water and nitrogen use efficiency and reduce leaching losses.