| Along with the progress of the society and the growth of population, demanding for agricultural products is constantly increasing. Therefore the issue about cultivated land and food has become a focal point. In China, the issue about food security is more serious due to lack of reserve cultivated land resource, increasing of land for construction, and degradation of soil. Cultivated land resource has become a main limiting factor for agricultural production and even sustainable development of the national economy. Reasonable land use practices are urgently needed. Besides, significant changes have been in soil fertility during the past 30 years. Therefore, reevaluation of the soil fertility is necessary.With the help of local experts,12 evaluation indicators, including slope degree, effective soil layer thickness, slope position, pH, available P, available K, organic matter, total N, irrigation assurance, texture, parent materials and cropping system were selected. Then Analytic Hierarchy Process (AHP) and Fuzzy Comprehensive Evaluation (FCE) were applied to evaluate the soil fertility. The results obtained are as follows:(1) On the basis of understand the soil nutrients status, we try to use the analytic hierarchy process (AHP) to do a scientific and effective farmland productivity evaluation research in Lu county. And use the fuzzy comprehensive evaluation model to determine the cultivated land fertility level. Then use GIS software produce to make the soil nutrient and geography rating thematic maps. Thus we can clearly understand the soil nutrient and the spatial distribution of the in study area.According to the cultivated land's fertility composite index of each evaluation units, we divided Lu county's cultivated land fertility into three levels which are first-class land, second-class land and third-class land. Among them, the largest one in area is second-class land, which area is 378793.70mu, Proportion is 57.64%. The second largest one is first-class land, which area is 260942.OOmu, Proportion is 39.71%.The smallest one is third-class land, which area is 17381.30mu, Proportion is 2.65%.(2)We had use 12 factors about soil nutrient status, physical and chemical properties of soil,site conditions and land management.etc to make Series of special analysis, then obtained their corresponding area maps, and use these maps to build a project atlas. Among them, organic matter content is distributed in level 3 and 4, and give priority to with content level 3. Total nitrogen content is distributed in level 3 and 4, and give priority to with content level 3. Effective phosphorus content is distributed in level 3,4 and 5, most effective phosphorus were focused on level 4, followed by level 5, a minimum of distribution area is level 3. In first-class and second-class, Rapidly-available potassium content is distributed in level 3 and 4, and give priority to with content level 4, third-class land is all level 4 in rapidly-available potassium content. Lu county's farmland is common acidic, there are level 2,3 and 4 in Potential Of Hydrogen. Soil in Lu county have six texture types, loam, sandy soil, sand loam, clay, light loam soil and heavy loam soil, mainly loam, clay and sand soil in first-class land, and mainly clay, sand loam, loam and sand soil in second-class land, and mainly sand soil, clay and sand loam in third-class land. The terrain in Lu county is gentle overall, each grade of slope for farmland is small. After research the cropping systems of Lu county, we know that mostly onecrop a year(rice) in first-class and second-class land, and by large to small for one crop a year (rice), two crops a year(wheat-corn), three crops a year(wheat-cole-potato) and two crops a year(rice-cole). Effective soil layer thickness is divided into four levels,60-75,75-80,80-90 and 90-100 cm in first-class and second-class land, there are five levels in third-class land, and the largest one is 90-100cm level.(3)This study use the cultivated land fertility soil grade figure, and serial project grade figures about The soil nutrient, physical and chemical properties of soil, site conditions and farming system to go alone superposition analysis, combined with the "national in low yield farmland type partition and improvement specification" (NY/T309-1996),we divided Lu county'low yield farmland into four genus:sloping ladder retrofit, irrigation improved type, barren fertilizer type and obstacles hierarchical, the area respectively is 4207.60,13430.43,2821.77 and 172.57 mu, and the proportion respectively is 0.64%,2.04%,0.43% and 0.03%.(4) Scientific advices are given to agricultural production in Lu county in the future, separately from the aspects of soil improvement, resources rationally, scientific fertilization and quality of arable land management. In this Paper, we developed an effective method and technical processes to carry out the investigation and evaluation of soil fertility of arable land, and this is positive for the scientific management of cultivated land resources and sustainable use.
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