Modelling Depth Distribution, Leaching and Balance of Nitrate under Irrigation with Nitrate-rich Water in Pearl Millet-Wheat Cropping Conditions

A field experiment was conducted to study depth distribution, leaching and balance of nitrate under irrigation with nitrate rich water in pearl millet-wheat cropping sequence. Pearl millet was grown as summer rainfed crop (July-September) and wheat as winter crop receiving 5–6 irrigations as required (November-April). Depth distribution of NO₃–N in the soil profile, leaching and balance of NO₃ from the profile was predicted using LEACHM model considering water flow, uptake, transformation of different forms of nitrogen, rate constants, other exchange processes and weather parameters. The yields were not affected significantly by reducing N application when nitrate content of the tubewell water was taken into account. Simulated N uptake was almost similar for recommended and reduced N levels for both the crops. Deviation between experimental and simulated mean NO₃–N balance of the profile after the harvest of the two crops varied from ±2.03% (pearl millet 2004, reduced N) to ± 13.32% (pearl millet 2004, recommended N). The magnitude and the trend of the experimental and the simulated NO₃-N concentration of the soil profile after harvest of different crop showed a reasonably good agreement (R² =0.2999). This study suggests that nitrate-N to the tune of 12–25 kg ha⁻¹ from both the crops was lost beyond the rooting zone under these crops and management practices.