SIMULATION OF NITROGEN BALANCE UNDER SUB-SURFACE DRAINAGE CONDITIONS AT THEHRI MUKTSAR PUNJAB, USING THE DNDC MODEL V. 9.5

Aim of the study: The aim of the study is DNDC model simulation for nitrogen balance in rice-wheat cropping system. Material and methods: The DeNitrification-DeComposition (DNDC) model is a computer simulation model for the biogeochemistry of carbon and nitrogen in agro ecosystems that takes a process-oriented approach. The DNDC model version 9.5 (http:// www.dndc.sr.unh.edu) was selected for estimating nitrogen balance. The model consists of two modules. The first component simulates moisture, soil temperature, pH, and substrate concentration, which are determined by ecological parameters such as soil, climate, anthropogenic activities, and vegetation. It consists of sub-models for plant growth, decomposition, and soil climate. The second module predicts the emission of gasses from plant-soil systems such as methane (CH4), nitrous oxide (N2O), nitrogen oxide (NO), dinitrogen (N2), ammonia (NH3), and carbon dioxide (CO2). The model includes empirical equations developed from laboratory studies and is based on the classical laws of chemistry, physics, and biology. The empirical equations included parameterizing specific biochemical or geochemical reactions. The entire model bridges the primary ecological drivers with the biogeochemical cycles of C and N (see: Figures 1 and 2). Results and conclusions: This study used the DNDC model to estimate nitrogen balance in the study area. A calibrated and validated DNDC model was used to simulate NO3-N loss in runoff and leachate from a rice–wheat cropping system from 2018 to 2020. The total nitrogen balance estimated by the DNDC model was negative (–99.44 kg N ha–1 yr–1) and positive (69.1 kg N ha–1 yr–1) for rice and wheat cropping systems, respectively, in the study area.