Modelling Nitrogen Losses From Maize Production in Denmark and North China Plain: Current Condition and Opportunities for Mitigation.

Nitrogen (N) losses from the intensive agriculture in both Denmark and China pose a challenge to the water environment. The ability of the DAISY model to satisfactorily simulate maize production and water and N dynamics, including infiltration and leaching, was tested in Denmark and in the North China Plain. The main objectives were to (i) assess the importance of different crop and soil parameters under the studied climates and (ii) their interactions in the Soil-Vegetation-Atmosphere Transfer (SVAT) system, (iii) assess alternatives to the current agro- management systems aiming to reduce N input while retaining yields, thereby reducing N loss. Data collected from field experiments in Denmark (loamy sand and coarse sand) involving maize monoculture and intercropped with catch crops, and in the North China Plain (silty loam) with maize- wheat rotation, were used to calibrate and evaluate the DAISY modules for soil hydrology, crop growth and soil organic matter turnover.

In Denmark, the model performed well at both sites, though simulated residual soil mineral N in loamy sand was in better agreement with the field data than that in coarse sand. The high maize N uptake principally underestimated residual soil mineral N on coarse sand. Higher simulated mineralization during maize growth may thus be necessary. The successfully established catch crops decreased N leaching, especially from coarse sand, but also reduced yields at low fertilizer rates.

After thorough crop calibration for the local climate and soil conditions in North China Plain, DAISY was able to simulate aboveground biomass and N, soil nitrate levels and N leaching. The model responded well on different N fertilization rates, though overestimated nitrate levels in the deeper soil, compared to the measurements. Field and model results also demonstrated options for reducing the current high N inputs used in the North China Plain without affecting grain yield.