No abstract

Ammonia (NH 3 ) volatilization is an important N loss pathway in intensive agriculture of the North China Plain (NCP). Simulation models can help to assess complex N and water processes of agricultural soil-crop systems. Four variations (Var) of a sub-module for the deterministic, process-based HERMES model were implemented ranging from simple empirical functions (Var 3 and 4) to process-oriented approaches (Var 1 and 2) including the main processes of NH 3 volatilization, urea hydrolysis, nitrification from ammonium-based N fertilizer, and changes in soil solution pH. Ammonia volatilization, plant growth, and changes in ammonium and nitrate pools in the soil over several winter wheat-summer maize double-crop rotations at three locations in the NCP were simulated. Results were calibrated with two data sets (Dongbeiwang 1, Shunyi) and validated using two data sets (Dongbeiwang 2, Quzhou). They showed that the ammonia volatilization sub-module of the HERMES model worked well under the climatic and soil conditions of N China. Although the simpler equations, Var 3 and 4, showed lower deviations to observed volatilization across all sites and treatments with a mean absolute error (MAE) of 1.8 and 1.4 in % of applied N, respectively, compared to process-oriented approaches, Var 1 and 2, with a MAE of 2.2 and 1.9 in % of applied N, respectively. Environmental conditions were reflected better by the process-oriented approaches. Generally, simulation results were satisfying but simulated changes in topsoil pH need further verification with measurements.

Background: Intensive winter wheat–summer maize (Triticum aestivum L.–Zea mays L.) double‐cropping systems in the North China Plain often show high nitrogen (N) losses and water use causing harmful threats to the environment. Methods: Continuous multiple‐year simulations (31 years) with the HERMES model were used to spatially quantify N and water losses at county scale in order to identify best‐practice management applications. Results: Results show simulated annual long‐term N losses for the investigated Quzhou County, Hebei Province of 297 kg N ha−1 under common farmers practice treatment (FP) and 102 kg N ha−1 under optimized treatment including model derived N fertilizer recommendation and automated irrigation (OPTai). Total losses by N leaching, volatilization and denitrification were 57% (FP) and 40% (OPTai) of the applied fertilizer N, respectively. Spatial differences in N losses were found due to survey‐specific differences of average N inputs among the townships. More than 260 kg N ha−1 y−1 of fertilizer input, N losses of 190 kg N ha−1 y−1, and around 116 mm y−1 of irrigation water could be saved on average by optimized treatments compared to farmers practice. Conclusion: On clay loam soil only OPTai could maintain crop yield without drought stress. The optimized treatments had the lowest N inputs and N losses but they did not seem to be able to sustain the organic N pools.