Abstract 2013: Process-based biogeochemical models can be used to predict the impact of various agricultural management practices on plant nitrogen use efficiency and nitrogen losses to the environment, such as greenhouse gas emissions and nitrate leaching, by analyzing the interactions between management practices, primary drivers such as climate, soil properties, crop types and biogeochemical reactions. In this study we applied the Landscape-DNDC model, which combines functions from Agricultural-DNDC and Forest-DNDC, for simulation of C and N turnover, GHG emissions, nitrate leaching, and plant growth for Korean arable fields cultivated with radish (Raphanus sativus L.) and soybean (Glycine max) in Haean Catchment.
The annual average temperature in Haean is ca. 8.5°C and the annual precipitation is ca. 1,500 mm. According to farmers practice, the radish field received a basal fertilizer application of ca. 190 kg N ha-1 before setting up four fertilizer treatments, i.e., additional 50, 150, 250 and 350 kg N ha-1. All N treatment plots were tilled a week after application of specific N fertilizer in order to make rows and interrows. Just before radish seeding, rows were covered with black plastic mulch which was removed after harvest. In spite of the widespread usage of black mulch in Korea or even Asia, so far biogeochemical models do not consider impacts of mulch on soil environmental conditions and soil biogeochemistry. Thus, based on field measurements, we adjusted our input data and used only half of the annual precipitation and 90% of the maximum temperature as drivers for simulation of soil environmental conditions of rows with foil coverage, whereas the actual weather data was used for interrow simulations. Simulated soil moisture and temperature as well as N2O emissions and soil nitrate concentrations agreed well with field measurements. However, peak emissions after fertilization were slightly underestimated in row and interrow. Annual N2O emissions of the fertilizer treatments increased with increasing fertilization rates from around 2.1 to 2.4 kg N ha-1 in rows and 2.4 to 3.2 kg N ha-1 in interrows. Due to the sandy soil conditions and the monsoon character of rainfall, major N loss of the agricultural systems was in form of nitrate leaching. Nitrate leaching rates were as high as 290 - 450 kg N ha-1 for the different fertilizer treatments and rows and interrows. Only slight increase of measured and simulated yields (4.4 to 5.6 t DW ha-1) with higher rates of N fertilization indicate that actual farmer practices can be improved. Optimizing agricultural management considering the specific climatic and soil conditions has a high potential to reduce environmental impacts of crop cultivations in the study area.
Model simulations for a soybean field without fertilization and one tillage before seeding were also in good agreement with field observations. However, simulated N2O emissions (0.85 kg N ha-1) and nitrate leaching (54.7 kg N ha-1) were much lower than for the radish field.
Key words: Landscape-DNDC, N fertilizer, plastic mulch, N2O emissions, nitrate leaching, biomass
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