Nitrogen Balance in a Poorly Draining Intensively Cultivated Soil

Abstract

The increasing use of nitrogen in fertilizers has not only increased the productivity of agricultural crops but also the concern for the effects of high N inputs on the natural environment. Economic, agronomic and environmental concerns have led to greater efforts towards more effective utilization of nitrogenous fertilizers, which can be achieved through a better quantitative understanding of the fate of nitrogen when applied to the soil. So Nitrogen balance was investigated in a poorly draining intensively cultivated soil. Nitrogen inputs and outputs, such as additions by precipitation (N_atm), irrigation water (N_irr), commercial fertilizers (N_fert), mineralization (N_min), denitrification (N_denitr), volatilization (N_gas), capillary rise (N_cap), uptake (N_upt), residual (N_res) and leaching (N_leac) were studied and quantified during a period of 72 weeks for two growing crops (maize and wheat). Nitrogen excess or deficit at time ‘t’ (Nt) was calculated from the following balance equation: Nt = N_res + N_atm + N_irr + N_min + N_fert + N_cap − N_upt − N_denitr – N_gas − N_leac. Existing models were used after proper adjustments to calculate these fluxes. Only a single model, based on soil temperature at 60 cm and NO₃^--N concentration in ground water was developed for the estimation of denitrification at the ground water boundary. The calculated values satisfactorily matched the respective experimental data. The results shown that the greater part of the applied nitrogen fertilizer was lost to ground water during the winter causing considerable environmental concern. For sustainable land use, inputs and outputs of nutrients must be balanced in order to avoid negative impacts on the environment, especially in intensively exploited agricultural ecosystems.