华北两熟区农田磷流失风险预警研究

轮作是长期以来在各地形成的相对固定的作物组合模式，同时也是农田养分平衡状况计算的基本单元，多年累积形成的养分盈亏则直接影响环境。在植物必需的3种大量营养元素中，对环境影响最大的营养元素是磷和氮，与氮素相比，磷素循环途径则相对稳定，没有气态损失，磷的表观养分平衡与环境污染的相关性高，且计算方便，因而本文选择磷素作为环境风险预警指示元素。为探究简易、有效的轮作环境效应预警方法，从筛选适宜预警的关键元素和环境风险产生的关键环节入手，提出适合我国小农户现实国情的、基于农田地块级别的预警指标体系，并以华北两熟区5种轮作类型、38个地块的调查数据为例进行了验证。该预警体系包括3级评价指标（周年磷平衡、耕层土壤质地、周年磷肥运筹）共6种预警级别并用3种色系进行标识（深绿、浅绿、浅黄、深黄、浅红、深红）。该预警方法的特点为：研究对象为整个轮作周期而非单茬作物；磷平衡既考虑周年的总量均衡（即整个轮作周期磷素投入、产出平衡状况），又考虑不同茬次间的科学分配（即磷素统筹），且二者均采用相对平衡值而非绝对平衡值，从而使得不同轮作类型之间的磷平衡可以进行统一量化和比较；土壤质地简化为沙土、壤土、黏土3种。验证结果表明，磷肥用量、运筹合理、环境友好（深绿）的地块仅占10.53%；而高环境风险（深红、浅红）的轮作地块达57.89%，即一半以上的地块目前的轮作方式存在高或极高的环境风险。该预警方法具有科学、实用、简便，所需数据容易获得的特点，可用于农户对自己地块磷流失风险进行判断，也可用于国家、区域或地方农业主管部门进行种植业结构调整时参考。

Early warning system of field phosphorus loss risk for double cropping area in North China

Rotation is a relatively fixed crop combination pattern that forms in various places over a long period. It is also the basic unit for the calculation of farmland nutrient balance. The accumulation of nutrient surplus or deficiency over the years directly affects the environment. Among the three essential nutrients for plants, the most important for the environment are phosphorus and nitrogen. Compared with nitrogen, the phosphorus cycle is relatively stable, has no gas loss, and reveals a high correlation between apparent nutrient balance and environmental pollution of phosphorus, and the calculation for which is convenient. Therefore, phosphorus was selected as the indicator for environment risk in this study. In order to establish a simple and effective method to detect early warnings of environmental effects, starting with the screening of key elements suitable for early warning and key links to phosphorus loss in farmland, this article proposed an early warning indicator system based on farmland plots suitable for small-holder farmers in China. The study also performed trial calculations with survey data from 38 plots, including five typical rotation systems in North China. The early warning system included three evaluation indicators-annual phosphorus balance, plough layer soil texture, and annual phosphate fertilizer operation. A total of six early warning levels of phosphorus loss was set in the early warning system-dark green, light green, light yellow, deep yellow, light red, and deep red, in which the red meant high phosphorus loss risk, the green meant low phosphorus loss risk, the yellow meant medium phosphorus loss risk, deep and light mean degree of the level. The characteristics of the early warning system were 1) measuring the entire rotation cycle rather than a single crop; and 2) the phosphorus balance considered the total balance of the anniversary (i.e., the phosphorus input and output balance of the entire rotation cycle) and considered the difference between different crops. Scientific allocation (i.e., phosphorus co-ordination) used relative equilibrium values rather than absolute equilibrium values so that the phosphorus balance between different rotation types could be uniformly quantified and compared. Soil texture was simplified to sand, loam, and clay species. The trial results showed that a low early warning level (dark green) which was rational in application of phosphate fertilizer with reasonable application rate and co-ordination between rotation crops only occupied 10.53% of all plots analyzed, while the high environmental risk (dark red, light red) rotation plots accounted for 57.89%, i.e., more than half of the plots using the current rotation methods had high or extremely high environmental risks. The early warning system was scientific, practical, and simple, and the required data were easy to be obtained. It can be used for farmers to judge the risk of phosphorus loss in their own plots and for national, regional, or local agricultural authorities to reference when adjusting planting structures.