Impacts of farmland transfer on rice yield and nitrogen pollution in Dongting Lake district

Abstract: With the rapid development of urbanization, farmland transfer has become a more and more common phenomenon to improve farmland use efficiency, alleviate small farmland fragmentation, and release the farm labor force in China. To assess the comprehensive effect of land transfer on rice cropping and nitrogen use for policy-maker, an agent-based (ABM) and substance flow analysis (SFA) coupled models were constructed. In this paper, farmland transfer was assumed that it was only related with the internal factors of households which mainly included those linked to the ability and the willingness. According to the analysis of households' ability and willingness, farmers' decision behaviors included expand, shrink, stable or stop farming/inheritance, which directly influenced the transfers of farmland and the change of cropping system in study area. The rice yield and nitrogen flow of a region was calculated by SFA model which regarded the cropping system changes as an important input data. Thus those results as an important input data were adopted in the ABM model. As mentions above, we built an integrated SFA and ABM model. Daligang Township, located in a typical subtropical hilly region and mainly planted double-cropping rice in the past, was taken as a case study area. Land use data, agricultural productivity data, household survey data and statistical data were used to feed the coupled model. This model was initialized from 1997 to 1999 and simulated from 2000 to 2014. The data of sown area of double rice cropping system and total rice product yield were used to test the reliability of the simulated results. The results indicated that: 1) Along with the transfer of farmland, the farmland was gradually controlled by farmers with balanced household, farming-oriented household or large-scale households, which improving the ratio of planting double-rice and rice yield; 2) Because of the changes of cropping system, the amount of nitrogen lost from farm field through ammonia volatilization, denitrification, runoff and leaching decreased at the beginning, then increased; 3) As a result of the expansion of farmland transferring and the rural management area, poor productivity farmland was also transferred to high intensive utilization, however, these region were most likely to cause environmental problems due to congenital nature conditions. Owing to the complexity and uncertainty of human decision-making behaviors and environment, we didn't consider some factors, such as, the effect of climate change and farmers' irrational behaviors, to simplify the coupled model. These factors would affect the accuracy of simulated results. Although the coupled model had these limitations, the coupled model offered a useful tool to model the process of farmland transfer, analyze the effect of farmland transfer on cropping and environment, and provide advice for policy-maker to make a trade-off between food security and environmental risk. Hence, coupling the ABM and SFA model can be used to evaluate land transfer and their potential risk in agricultural land use system in the future.