Modelling Nutrient Leaching Below Crop Root Zone of Onion under Drip Fertigation

An experiment was conducted during the year 2008 and 2009 to study nutrient distribution (phosphorus, P; potassium, K and sulphur, S) under different fertigation strategies and to quantify the leaching of nutrients in onion crop. The study involved field experiment, laboratory analysis and modelling of P, K and S leaching and scenario generation for different types of soil and emitter discharge rates. Field data were used to calibrate and validate HYDRUS-2D model for solute transport. From the model performance parameters, HYDRUS-2D model was found to be good for predicting the P, K and S distribution in soil. The validated model was used for the simulations which were carried out on different soil types as well as with different fertigation and irrigation strategies. The results revealed that leaching of these nutrients was negligible in fine textured silty clay loam soil, whereas highest leaching occurred in coarse textured sandy loam soil. While considering discharge rate, more leaching was observed in case of emitter with higher discharge rate. Fertigation strategy also played an important role in leaching of P, K and S. Maximum leaching was observed in fertigation during first half of irrigation duration, whereas minimum leaching of P, K and S was observed with fertigation during second half of irrigation duration with two-day irrigation interval. It was concluded that 2.5 l.h-1 emitter discharge rate is suitable to reduce the leaching of nutrients, as well as minimize the free drainage of water with two-day irrigation interval in onion field.