Fertilization levels, 15N labeling and N flow separation
2 Labor fuer Isotopenbiogeochemie
3 Pflanzenoekologie
4 Bodenphysik
5 Agraroekosysteme
P 1.21 in Ecosystem Function
Nitrogen is one of the most important nutrients for plant growth and the application of fertilizer nitrogen is playing an important role in agricultural production. Yet, the efficiency of fertilizer nitrogen is low and losses are large. We hypothesize that nitrate leaching is the main N loss pathway in Haean catchment due to excessive rainfalls during monsoon season, poor water and nutrient storage characteristics of the top soil as well as high fertilization rates, and low N uptake efficiency by plants. In this experiment, nitrogen dynamics and budgets in a typical agricultural soil of Haean basin are investigated in a summer radish cropping system comparing the effects of three different fertilizer N rates (100, 200 and 400 kg N ha-1). The fertilizer will be mostly applied before seed and then a second time during the growing season. Crop management including inputs of pesticides and herbicides is conducted according to local conventional agricultural practices. The main focus of this approach is to investigate (1) the biomass response to different N application rates; (2) the retention of inorganic N in the soil profile; (3) the specific N use efficiency of plants for the various treatments; (4) and the N loss pathways as related to the different fertilizer rates. Therefore, we use 15N labelled potassium nitrate (K15NO3) to follow the fate of fertilizer in the ecosystem and to document its major loss pathways. Observed pools in 2010 will be soil, plants, seepage and the atmosphere. Rates will be determined as following: · Recovery rate (percentage of applied 15N fertilizer taken up by aboveground plants) · Retention rate (percentage of applied 15N fertilizer recovered in the top 100 cm of the soil profile) · Loss rate (subtracting the recovery rate and retention rate from 100) Furthermore, we coupled the 15N dilution method with exchange resins to identify the atmospheric N deposition into the system. Atmospheric N deposition is a key parameter in the N cycle of ecosystems and should therefore be taken into account for N fertilizer recommendations. Measurements of the total atmospheric N deposition will be conducted from Mai to August 2010 at three representative locations in Haean basin.