Simulation Of Soil Carbon Cycle In Agro-ecosystem In The Different Tillage Systems By DNDC Model

During the past century decreases in soil organic carbon content and soil fertility have been widely observed in many agricultural regions. Maintaining farmland soil organic carbon content is essential for the sustainable development of Chinese agriculture. Dingxi county with typical inland agro-ecosystems was selected as a geographic domain for a modeling study reported in this paper. A process-based biogeochemical model DNDC was linked to a Geographic Information System (GIS) database holding spatially differentiated information of climate, soil, vegetation and management for Dingxi to quantify impacts of farming management alternatives on C sequestration in farmland of this region.(1) DNDC (Denitrification Decomposition) was first validated against a long-term SOC dataset observed in Dingxi County in Gansu Province. Based on the feasibility of DNDC (denitrification decomposition) model in the hilly areas of the Loess Plateau, which was validated using database of a long-term experiments on different tillage practices in Dingxi experimental station of Gansu Agricultural University, continuous SOC changes and carbon cycle features under different tillage patterns were studied by using DNDC model. DNDC (Denitrification Decomposition) model was validated using database of a long-term experiments on different tillage practices in Dingxi experimental station of Gansu Agricultural University. There was a high similarity between the simulated data and measured data, the DNDC model could be used to study spatio-temporal variation of soil organic carbon (SOC) storage at both farm land and county scales.(2) Sensitivity tests indicated that soil property especially initial SOC content was the major source of uncertainty generated from up scale modeling. The simulation of soil organic carbon content under different tillage mode showed that SOC can be increased depending on higher manure , higher proportions of straw returning. Results from the sensitivity tests have a dual implication,which indicate that SOC dynamics is sensitive to some input factors (e.g.,initial SOC content, crop residue incorporation, manure amendment) more than others. It also revealed there are potentials for enhancing SOC sequestration through improved farming management practices.(3) The results derived from four tested simulations for long - term periods (100 years) showed that SOC increased greatly in the treatments of no-tillage with straw cover and conventional tillage with straw incorporated, by 74.76% and 71.13% respectively; but increased gently in the treatments of no tillage with no strew cover and conventional tillage with no straw, by 39.18% and 43.09% respectively. According to the simulating results of DNDC model on the hilly areas of the Loess Plateau, straw addition, fertilizer application or no-tillage will be an effective measure for maintaining improved soil fertility, increasing the amount of storage of the organic carbon pools in soil.(4) The simulation of carbon cycling in different treatments indicated that stubble retention or mulching could increase exogenous carbon input, which was brought into soil as crop residues and root exudates, it also could increase endogenous carbon consuming by soil heterotrophic respiration. No-tillage could reduce the organic carbon consumption by soil respiration.(5) Total SOC storage in the surface layer (0～10 cm) of farm land in Anding district was predicted at 2.8×109kg, 22710.51kgCï¹'hm^-2 in 2008, lower than the national average (40990 kgC hm^-2). The overall level of SOC is not high, also is put in apparent dimensional difference. Each region's SOC content per hectare may differ from each other generally in the range of 18963.98 kg hm^-2 to 26943.03 kg hm^-2.(6) Scenario analysis from 2008 to 2037 showed that SOC storage could be significantly improved by applying manure, and by no-tillage with increasing stubble retention rate by 50%. However, SOC accumulated slowly under the practice of no-tillage without straw cover, and conventional tillage with straw incorporated. According to the simulating results of DNDC model on the hilly areas of the Loess Plateau, straw addition, fertilizer application or no-tillage will be an effective measure for maintaining improved soil fertility, increasing the amount of storage of the organic carbon pools in soil.