| As a fundamental element contributing to overall grain production capability, the precious farmland is the basis of assuring national food security. Northeast China is the main crop production base and commodity grain supply area, which plays an essential role in future national food security. To discuss the capability to ensure national grain security from the perspective of farmland productivity in Northeast China is of practical significance for ecological security and agricultural sustainable development. The study was carried in the four areas in Northeast China, namely Liaoning Province, Jilin Province, Heilongjiang Province and four eastern league cities of Inner Mongolia. Based on numerous related literature, combining characteristics in Northeast China and using the technology of GIS, knowledge of pedology, soil fertility, etc., the paper presented the description and statistical analysis of farmland fertility evaluation during the period of 2003-2013, analyzed the temporal and spatial changes of soil, evaluated the farmland fertility, estimated the grain production potential, analyzed the increased potential and the capability of ensuring national food security. The main results and conclusions were as follows:(1) GIS combined with geostatistics was applied to analyze the spatial-temporal variation of soil fertility in Northeast China, in the past 30 years. The results indicated that the average contents of soil organic matter (SOM), total nitrogen (TN), available nitrogen (AN), available phosphorus (AP), and available potassium (AK) reached grade 3 or more. The spatial correlation of SOM and AN was strongly dependent, and the spatial pattern gradually increased from the south to the north, form southwest to the northeast, and the spatial correlation among TN, AP and AK were moderately dependent. The distribution pattern of TN and AK were similar to that of SOM, and the spatial pattern of AP was higher in northeast and southwest and lower in the center of Northeast China. From 1980-2010, the content of SOM, TN, and AN in Northeast China dropped, while the content of AP increased greatly, and AK content in different area showed different trend after the application of different kinds and history of fertilization.(2) The evaluating units of farmland fertility were established by overlapping soil maps, land use maps and administrative maps with GIS. Index system was set up according to the total of 13 factors from 6 aspects of climate, site conditions, profile situation, soil physical and chemical condition, soil nutrient, and soil management, and the farmland fertility grade was comprehensively evaluated based on AHP, Delphi and fuzzy methods. The result showed that the integrated fertility index of farmland in Northeast China was 0.5-0.93, and cultivated land was divided into ten grades. The area of high-yield farmland (grade one to three) was 0.9275 million hm2, accounting for 27.71% of the total cultivated area; that of middle-yield farmland (grade four to seven) was 21.6188 million hm2, accounting for 60.32%, and that of low-yield farmland (grade eight to ten) was 4.2906 million hm2, accounting for 11.97%.(3) The spatial characteristics of climate, farmland and grain production potential at county level in 2013 were estimated based on soil fertility factors gathered from county-level soil fertility evaluation database (in 2013) and detailed observed data (in 1980-2013) from 107 national meteorological stations. The Miami model, combined with integrated fertility index and yield increase effect of chemical fertilizers, was used to predict production potential, and then the surplus productivity for analyzing the capability of ensuring grain security. The estimated production potential of climate, farmland and grain in 2013 were approximately 4.65-13.06 t/hm2 (an average of 8.67t/hm2),2.77-9.38 t/hm2 (an average of 6.63t/hm2), and 2.97-12.1 t/hm2 (an average of 7.64t/hm2), respectively. Combined the grain sown area in Northeast China, 400kg per capita was taken as the standard of grain share, and the surplus productivity was 136.56 miHion tons, which could feed 341.4 million people in the other areas of China.(4) In this paper, the increase potential was calculated by the differences between climatic production potential and actual yield potential, and then the limiting factors of farmland fertility were clustered into 8 categories using the K-means clustering method. The result revealed that the increase potential of average yield in Northeast China was 0.90-8.82t/hm2, with an average of 3.44t/hm2. Moreover, there was 2.04 t/hm2 increase potential were caused by the factors of environmental conditions and infrastructure,1.40t/hm2 by socioeconomic factors (such as technologies, input usage, and agronomic factors). From the provincial scale, the increase potential decreased following the order of Liaoning (3.99t/hm2)>Jilin (3.59t/hm2)> Heilongjiang (3.34t/hm2)>Inner Mongolia (2.60t/hm2). In accordance with the 8 categories of limiting factors, the cultivated land was classified into three different types of thoroughly rearrangement, selected rearrangement and improved rearrangement, which aim to improve farmland quality. As a conclusion, the high yield could be optimized by making full use of climatic resources and the future production potential in Northeast China could be promoted through adapting effective strategies of remediation measures, enhancing farmland productivity and eliminating farmland obstructive factors. |
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