农牧交错带农牧系统氮素流动与环境效应——以山西省为例

【目的】探明山西省农牧交错带农牧生产系统的氮素流动特征及其环境效应,进一步为山西实施区域养分资源管理、加快农牧交错带产业结构调整提供科学依据。【方法】在整理统计资料、文献数据和实地调研的基础上,使用食物链养分流动模型(nutrient flows in food chains,environment and resources use,NUFER)和GIS,估算山西省农牧交错带(主要涉及大同、朔州、忻州、吕梁、临汾和太原等6个地市)42个县区农牧生产系统的氮素账户平衡、流动路径及损失途径。【结果】不同县区农田化学氮肥投入存在"两极分化"的现象,投入水平范围在6.7—253 kg·hm~(-2),极值间相差38倍;各县区农田氮素的投入结构也表现出较大差异,主要跟当地化学氮肥施用习惯及农业种植结构有很大的关系;单位农田面积农作物主产品的氮素携出量范围在19.11—96.75kg·hm~(-2),空间上整体呈现南北高、中部低的变化趋势;不同县区农田氮素盈余量在-16—202 kg·hm~(-2),氮素亏缺与盈余情况并存;区内畜牧生产系统中外源饲料氮素投入差异较大,朔州市的山阴县外源饲料氮素投入高达0.94×104 t,而忻州的五寨、临汾的隰县、大宁和蒲县,则可以通过作物生产系统来满足畜牧生产系统的饲料需求,也充分反映了各县区畜牧业养殖规模和农牧产业结构存在较大差异;区内单位面积农田动物主产品氮素携出量范围在1.51—27.50 kg·hm~(-2),极差25.99 kg·hm~(-2),说明各县区畜牧生产系统的生产力水平差异较大,单位农田面积动物主产品的氮素携出量13 kg·hm~(-2)的分布在区域北部朔州市的山阴、怀仁、大同等县区,表明这些县区畜牧生产系统中的氮素利用率较高;单位耕地面积畜禽粪尿氮素负荷较高(50 kg·hm~(-2))的县区主要分布在区域北部;农牧生产系统氮素损失的空间分布格局明显:一级区(200 kg·hm~(-2))分布在区域北部,二级区(120—200 kg·hm~(-2))分布在区域南部和北部,三级区(120 kg·hm~(-2))主要分布在区域中部,今后应重点关注区域北部农牧业生产过程中的氮素损失及环境问题。【结论】农业生产结构不合理、"农牧分离"是造成农牧生产系统氮素利用率低下的主要原因,今后农田养分资源综合管理要在空间上合理配置氮素资源,在养分投入上既要考虑化学氮肥和粪尿氮素的投入,还要兼顾来源于环境投入部分的氮素,更要注重和畜牧生产系统的耦合,以最小的环境代价生产更多的农牧产品。

Nutrient Flow and Environmental Effects on Crop-Livestock System in Farming-Pastoral Transition Zone - A Case Study in Shanxi Province

【Objective】The objective of this study is to explore the characteristics of nitrogen (N) flow of crop-livestock systems and its environmental effects on farming-pastoral transition zone in northwestern Shanxi Province, further to give scientific suggestions on the nutrient management and to speed up the adjustment progress of industrial structure in farming-pastoral transition zone in Shanxi Province.【Method】a systematic and quantitative analysis on the nutrient balance, nutrient losses of crop-livestock production in farming-pastoral transition zone (42 counties in total, mainly involving Datong, Shuozhou, Xinzhou, Lüliang, Linfen and Taiyuan) in Shanxi Province was reported using a coupled NUFER model (nutrient flows in food chains, environment and resources use) with GIS after collecting and sorting of data from statistical yearbooks data, literature, and field investigation.【Result】 In different counties, the N fertilizer application showed a great disparity, ranging from 6.7 to 253 kg·hm^-2, which means a 38 times difference between the maxima and the minima. The N input structure of different counties also varied, due to the different N application habits and cropping systems. Crop N uptake ranged from 19.11 to 96.75 kg·hm^-2, and the high amounts of crop N uptake were found in North and South regions, and low values in the middle regions. Crop N surplus ranged from -16 to 202 kg·hm^-2, showing a coexistence of N sufficient and N surplus. There was a great difference in external N input by feed in livestock production system in the zone. In Shanyin county of Shuozhou City, the external N input by feed reached up to 9 400 t, whereas in Wuzhai of Xinzhou City and Xixian, Daning and Puxian of Linfen City, the demand of feed by livestock production system was met by local cropping system. This shows a great variation in the livestock production scale and farming-pastoral industrial structure among those counties. N uptake of animal main product per unit area of farming land was 1.51-27.50 kg·hm^-2, with a range of 25.99 kg·hm^-2, indicating a great disparity in the livestock productivity level among different counties. In the northern counties of Shanyin, Huairen and Datong, N uptake of animal main products was ＞13 kg·hm^-2, showing a high N use efficiency of livestock production system in these counties. In the northern regions, the N load by manure was high (＞50 kg·hm^-2). There was an obvious spatial trend of N loss in crop-livestock production system. Grade I area (＞200 kg·hm^-2) was found in the north of the zone, Grade II area (120-200 kg·hm^-2) was found in the north and south of the zone, and Grade III area (＜120 kg·hm^-2) mainly distributed in the middle of the zone. Therefore, N loss and environmental issues occur in the crop-livestock production process in the northern part of the zone should be paid close attention in the future. 【Conclusion】 Unreasonable agricultural production structure and the segregation of agricultural and animal husbandry systems were the main reasons for the low N use efficiency in the farming-pastoral transition zone in northwestern Shanxi Province. In the future management of farmland nutrient resources, apart from rational spatial allocation of N resources, not only N input by both chemical fertilizers and livestock excrement/urine should be taken into account, but also N input from the environment. Also, the coupling of farmland production system and animal husbandry production system should be emphasized. By these means the production of crop and animal products at the minimum environmental costs can be achieved.