农地流转对洞庭湖区水稻产量与氮素污染的影响

该文通过构建ABM（agent-based model）与SFA（substance flow analysis）的耦合模型，模拟农地流转对水稻种植与氮素环境效应的影响，为决策者权衡粮食生产与环境风险两者之间的关系，制定合理的调控政策提供参考依据，并以洞庭湖双季水稻种植区大栗港镇为案例，对该耦合模型进行了实证研究。结果表明：1）随着农地的流转，耕地逐渐向规模种植农户转移，提高了双季稻种植比例和区域水稻总产量；2）因农地流转所致的作物种植制度的变化，导致氮素通过挥发、反硝化、径流以及淋失方式损失的环境输出量呈现先减少后增加的变化趋势，分别从2000年的286.5、77.3、46.4和100.0 t减少到2003年的252.2、67.0、40.4和86.5 t，再增加到2014年的324.03、82.6、49.4和107.2 t，此外，氨挥发是此区域氮素损失最主要的途径，而氮淋失是南方水稻田氮素进入水体中最主要的方式；3）随农地流转，农村土地规模化经营面积的扩大，在耕地地力等级较好的区域，其氮淋失量与氮盈余增长放缓，反而在耕地地力等级较差的区域，其氮淋失量与氮盈余量增加明显。

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.