Element cycles in mountain regions in Korea under different land use J. Kettering1 & Y. Kuzyakov1 1 University of Bayreuth Dept. of Agroecosystem Research, Universitätsstraße 30, D-95440 Bayreuth Janine.kettering@uni-bayreuth.de Introduction and Research Aims While crop production is considered desirable, negative effects include high inputs of nutrients, greater erosion rates, removal of nutrients and carbon in harvests and decreases in the quality of SOM. The strongest impacts occur in mountainous landscapes. The International Research Group TERRECO examines the way to carry out land management in mountain regions, in order to ensure sustainable yield of ecosystem services. The higher goal of this project (T-8) within TERRECO is to examine the influence of forest conversion to agriculture on nutrient cycles at the farm level as well as to reconstruct the history of previous erosion and nutrient losses, and attempt to define best agricultural management practices. Study Area The sites of the project are located in the Haean Catchment in the central part of Korea, just south of the demilitarised zone (see Fig.2+3). The landscape of Haean Catchment consists of three zones including deciduous forest, dry land farming, and rice paddies (see Fig.1). Intensive land use due to the low percentage of flat land in Korea, high levels of fertilisation together with extreme precipitation during the summer monsoon can be found on-site. Korean chemical fertilizer applications for intensive agriculture are extremely high on a worldwide scale, increasing from 230 kg/ha/yr in 1980 to 450 kg/ha/yr in 1994. Annual erosion of topsoil may reach 40 cm year-1 (see Fig.6+7). Therefore, the impacts on this mountainous terrain are considered to be profound. North Korea South Korea Lake Soyang Haean Catchment Seoul Lake Soyang Fig.1: Panoramic view of the study area, the Haean Catchment, Yanggu Gun, South Korea Picture: Dr. Jan Fleckenstein, University of Bayreuth. Fig.2: Map indicating the location of Haean Catchment within the Lake Soyang Watershed Fig.3: Satellite image of Korean Peninsula indicating locations of Seoul and the Soyang Lake Reservoir; Red = Mixed Forest; Green = Croplands Fig.4: Satellite (left) and terrain (right) image of Haean Basin Sources: left: Google Earth 2009 ; right: Google Maps 2009 Fig.5: Cultivated area at slopes in Korea (right), soil erosion during the summer monsoon in Korea (left) Pictures: Professor Jae E. Yang, KNU, Chuncheon Methods – Research Plans for the 1st phase Field Work In the initial phase of the study, the focus of the field work will be put on estimation of fertiliser budgets and on estimation of fertilizer losses by runoff or leaching and their outflow in aquatic systems. Calculations will be based on specific crop areas, NPK input and NPK withdraw by harvest. Another aspect of investigation will be soil carbon dynamics in soils under maize, using 13C natural abundance. The approach is based on the discrimination of 13C isotopes during CO2 assimilation by plants with different photosynthesis types. Therefore, by growing a C4 plant on soils with former C3 vegetation, the amount of C4 plant derived C can be estimated on the basis of the changing δ13C values of SOC. Laboratory work The methods of our research are based on application of isotopes: 14C and 13C labelling. Goals of the laboratory work focus on the analysis of organic polymers locally used for soil stabilisation against erosion by Prof. Yong Sik Ok. Experiments include analysing the degradation of these polymers as well as their effects on microbial mass, SOM decomposition and C sequestration. Afterwards, 3-5 polymers will be chosen and in following experiments tested both for their effect on decomposition of plant residues and for their incorporation into SOM and microbial mass. Finally, another experiment will deal with the question of the effect of polymers on DOM leaching and aggregate stability. Experiment (1) – Decomposition rates of organic polymers Layout: Incubation experiment under controlled conditions Aims: Evaluation of period for which organic polymers have direct and indirect effect on soil stabilisation; Effects of polymers on microbial mass, SOM decomposition and C sequestration Prerequisite: δ13C of polymers should be for at least 10‰ different from δ13C of the soils Analyses: - total CO2 efflux from soil (effect of polymers on SOM decomposition and C sequestration) - δ13C of CO2 (decomposition rate of the polymers) - Microbial biomass by fumigation/extraction method (FEM) - Aggregate size, composition and stability (effect of polymers on aggregate stabilization) Outlook: 3-5 “best” polymers will be chosen for the following experiments Collaboration: - Prof. Yong Sik Ok, Dept. of Biological Environ., KNU: polymers, soil aggregates, erodibility, C sequestration - Prof. Taeseok Ahn, Dept. of Environ. Science, KNU: enzymes, DGGE of microorganisms Experiment (2)+(3) – Effect of polymers on decomposition of plant residues Layout: Incubation experiment under controlled conditions Aims: Effect of these 3-5 “best” polymers on decomposition of plant residues and their incorporation into SOM and microbial biomass Prerequisite: 14C labelled plant residues will be produced (maize and rice) Analyses: - Total CO2 efflux from soil (effect of polymers on SOM decomposition and on plant residue decomposition) - 14C of CO2 (decomposition rate of plant residues) - Microbial biomass by fumigation/extraction approach - 14C in microbial biomass (incorporation of plant residues into microbial biomass) - Enzyme activities Collaboration: - Prof. Yong Sik Ok (see Experiment 1) - Prof. John Tenhunen, Dept. Of Plant Ecology, UBT: C budgeting in rice Experiment (4) – Effect of polymers on DOM leaching and aggregate stability Layout: Column experiment Aims: Effect of 2-3 polymers on soil aggregation; Effects of polymers on DOM leaching Prerequisite: Presence of DOM added on soil surface (DOM will be labelled by 14C) Collaboration: - Prof. Bernd Huwe, Dept. of Soil Physics, UTB: erosion experiments Fig.6: Overview illustration of the integration of Project 8 within TERRECO; red = DFG projects, blue = Korean projects Source: Proposal for an International Training Group 2009, available at: www.bayceer.uni-bayreuth.de/terreco/en/forschung/43708/65489/proposal.pdf International Research and Training Group TERRECO - Complex Terrain and Ecological Heterogeneity http://www.bayceer.uni-bayreuth.de/terreco/