Modelling of nitrogen leaching from experimental onion field under drip fertigation

Instances of groundwater pollution from use of nitrogenous fertilizer are at increase in recent years. With increase in area under cultivation and regular use of fertilizer in irrigated agriculture, groundwater pollution from agricultural activities is becoming a major concern in India. This requires appropriate water and nutrient management to minimize groundwater pollution and, maximize the nutrient use efficiency and production. Drip fertigation is an alternative, which improves water and nutrient use efficiency with higher production and minimum effect on groundwater quality. Appropriate design of drip fertigation system requires detailed knowledge of water and nutrient distribution pattern and nutrient availability in root zone and, nutrient leaching below root zone in different types of soils under varying emitter discharge rates and fertigation strategies. Design and operation of drip fertigation system requires more understanding of nutrient leaching behaviour in case of shallow rooted crops like onion, which cannot extract nutrient from lower soil profile leaving more scope for nitrogen leaching. Present study was undertaken to asses the nitrogen leaching from onion field under drip fertigation system. The study involved field experimentation for 2 years on onion crop under drip fertigation. Field data were collected on spatial and temporal distribution of water and available nitrogen in the growing season to calibrate and validate the solute transport model. A two-dimensional solute transport model HYDRUS-2D was applied to simulate the nitrogen leaching from various soils for varying emitter discharge rates and fertigation strategies. It was found that more permeable soils like sandy loam is prone to nitrogen leaching compared to less permeable soils. Nitrogen leaching from loam and sandy loam soils was negligible. Effect of soil type on nitrogen leaching was more than the emitter discharge rates. Fertigation strategies did not affect the nitrogen leaching as commonly perceived. Increased emitter discharge rates did not affect the nitrogen leaching except in coarse textured soils like sandy loam. Outward spreading of nitrogen was more in fine textured silt clay loam and silt soils. In all the scenarios, adequate nitrogen availability was maintained in the root zone. Based on the results, it is reported that with selection of appropriate emitter discharge, irrigation duration and irrigation interval, and nitrogen leaching even from fields under shallow rooted crops can be minimized.