县域尺度耕地生产能力的空间变异

研究河北省雄县耕地生产能力空间变异性特征及其主控因素，为黑龙港典型区耕地质量等级与生产能力提升及可持续利用提供指导。该文在分析县域和景观尺度耕地生产能力变异性特征的基础上，引用分类回归树模型探讨耕地自然属性因素和耕地管理因素对不同尺度耕地生产能力的影响。结果表明：县域尺度上耕地生产能力差异显著，呈现出西南部和东部高，东南部和中西部低的空间分布格局。5种景观尺度上耕地生产能力由高到低依次为：轻壤蒙金型小二坡地＞轻壤均质型小二坡地>黏壤均质型小低平地>砂壤蒙金型准缓岗>砂壤均质型准缓岗；耕地管理因素较耕地自然属性因素更能解释县域耕地生产能力空间变异性，主控因素依次是灌溉保证率、氮肥施用量、耕地速效氮和耕地有机质，贡献率总计51%。耕地自然属性因素是不同景观尺度间的主控因素，依次为阳离子交换量、有机质、速效钾和速效氮含量，贡献率总计55%；不同景观尺度上耕地生产能力主要受耕地管理因素所主控。因此，要想维持区域高水平耕地生产能力应注意调整耕地管理措施，包括节约集约用水，控制氮肥施用量（不宜超过240.34 kg/hm2）和加强耕地培肥管理。

Spatial variability of cultivated land productivity in county territory

Heilonggang basin is one of the major grain production areas in Hebei Province, but its cultivated land production was strongly constrained by poor nutrients supply and limited water resources. In this study, a method of classification and regression trees model (CART) proposed by Breiman in 1984 was used to study the variation characteristics of cultivated land productivity of Xiong County at landscape and county scales. This nonparametric statistical model belonging to the classification data excavation algorithms is widely used in many fields because of its simplicity and high precision in comparison with conventional analysis methods. Meanwhile, the evaluation of the impacts of natural and management factors on the variability of cultivated land productivity to reveal its major controlling factors can enrich the study contents of cultivated land productivity and the methods for quantitative research on influence factors. Results showed that: 1) at county scale, the cultivated land productivity in Xiong County varied from 4.75 to 6.95 t/hm2, where the southwest and east region had high productivity and the southeast and middle west had low productivity. At landscape scale, the productivity rank of the cultivated lands was: the loam above and clay below slope (6.25 t/hm2)>the light loam homogeneous slope (6.02 t/hm2)>the clay loamy homogeneous bottom land (5.89 t/hm2)>the sandy above and loam below hillock (5.67 t/hm2)>the sandy loam homogeneous sustained hillock (5.39 t/hm2). 2) Management factors had a greater impact on the spatial variation of the cultivated land productivity than natural attributes of cultivated land factors at the county level, where the main controlling factors in an order of irrigation, nitrogen application amount, rapidly-available nitrogen and organic matter contributed 51% of the productivity. Among different landscapes, natural attributes of the cultivated land were the main controlling factors, where the total contribution of cation exchange capacity, content of organic matter, and rapidly-available potassium and nitrogen accounted for 55% of the productivity. It was found that limiting factors for the light loam homogeneous slope were irrigation assurance rate and nitrogen application amount; for the loam above and clay below slope they were cation exchange capacity and nitrogen application amount; for the sandy loam homogeneous sustained hillock with poor water retention capacity it was irrigation; for the sandy above and loam below hillock and the clay loamy homogeneous bottom land they were fertilization rates of potassium and nitrogen. Overall, the cultivated land productivity was significantly correlated with the factors of cultivated land management and natural attributes, especially cultivated land management factors. Cultivated land management factors including the economic water use, rational N fertilization (< 240.34 kg/hm2), and strengthening fertility management of cultivated land should be adjusted to maintain the high cultivated land productivity. This study is very useful in improving the quality and productivity and ensuring the sustainable utilization of cultivated land.