Simulated nitrogen dynamics and losses in a layered agricultural soil

Abstract

A soil nitrogen model emphasizing mineral nitrogen dynamics and losses is presented. The model has a one-dimensional layered structure and considers plant uptake, mineralization, immobilization, leaching and denitrification processes. Fertilization and manure additions are included as management inputs. A physically based soil-water and heat model provides daily values of temperature, unfrozen water content, water flow and drainage, at different depths in the profile. Input data requirements include standard meteorological variables, basic soil physical and biological properties and crop management characteristics. Soil nitrogen dynamics were simulated for a 3-year period in N-fertilized and unfertilized barley. Model predictions were compared with measurements of nitrate leaching and mineral N content of the soil. Simulation of mineral N levels and leaching generally agreed with field data. Prediction of mineral N dynamics in both N-fertilized and unfertilized barley was better for surface layers than for deeper layers in the profile. Discrepancies between simulated and measured mineral N content in the topsoil were mainly related to mineralization and plant uptake. In deeper soil layers, differences between measured and predicted values were primarily related to the water flow and the drainage pathway. Simulated amounts of nitrate leached were close to measured values. Discrepancies in the temporal distribution of nitrate leached were mainly attributable to the simulated water flow. The model predicted that nitrate leaching to drainage tiles occurred mainly from the upper layers. Prediction of leaching depended as much on the simulation of drainage flow pathways and the vertical distribution of nitrate in the profile as on the simulation of water flow rates.