| At present, due to the continuous development of economy and society, urban land is getting tighter in supply and demand, the rural residential land intensive utilization degree is low, the lack of reasonable planning and layout, the number is "not less", the rural homestead idle phenomenon is serious, rural residential land consolidation is potential. Chongqing city approved for urban and rural construction land linked areas, vigorously carry out the work of rural construction land reclamation, the urban and rural comprehensive reform work is smooth. However, rural residential land reclamation emphasizing quantity over quanlity, accounted for much less, compensation of inferior and so many problems, therefore the Ministry of land and resources must emphasize the evaluation of cultivated land fertility of rural residential land reclamation supplement farmland, to meet the relevant requirements in order to pass the acceptance, to ensure that the balance of arable land, quantity and quality can reach the standard. The evaluation of the reclamation of farmland productivity, to find out the limiting factors of soil fertility, improve the quality of cultivated land after reclamation and comprehensive production capacity, provide important support for the check and acceptance work of supplementary cultivated land in the future, it is a very necessary research work.This paper takes Fuling District of Chongqing city as the research object, considering the topography of Fuling district, soil parent material, with the distribution of land reclamation project of rural construction, a total of 665 pieces of reclamation soil samples were randomly collected in riversides, level ground areas, mountain areas, selected 16 indexes, construct the evaluation index system, the overall analysis of the fertility status of land reclamation, evaluated farmland productivity based on agricultural land classification, method of GIS and fuzzy comprehensive evaluation, SOFM neural network model, analysised and comparised the distribution of farmland productivity grades in different soil types and different areas, accounted for reclamation of farmland productivity, analysised the restriction factors the reclamation of farmland productivity and improving measures, the spatial distribution of different grades of farmland productivity, the comparison of different methods of the reclamation of cultivated land, clarified the reclamation of farmland productivity grades in Chongqing city, in order to supplement the cultivated land for future land after reclamation of arable land evaluation, supply the scientific basis for reasonable and efficient use of the fertilizer. The main conclusions were as follows:(1) The study area of 665 samples of the analysis showed that reclamation of cultivated soil surface was smooth, the soil thickness was in 25-60 cm, the average was 43 cm, but there were still 7% of the sample pieces of the reclamation soil thickness did not reach 40 cm, the gravel content was in 1%～12%, the bulk density was between 0.930～1.73 g/cm3, the average was 4% and 1.36 g/cm3 respectively, on the whole, the soil acidity, organic matter and available phosphorus content was not high, available nitrogen content was between in 4.00～320 mg/kg, the average was 85.8 mg/kg, the content is moderate, the average content of available K was 296 mg/kg, the content was generally high. The average gravel content of calcareous soil maximum up to 6%, the pH value of yellow soil was 5.26, and 80.87% of the soil samples was less than 6, the soil was acidic, low organic matter content in purple soil, yellow soil, calcareous soil, the average is 9.15 g/kg, the average available nitrogen of calcareous soil was slightly higher than that of yellow soil, purple soil was the lowest, the average available phosphorus content in purple soil was 12.8 mg/kg, higher than that of yellow soil and calcareous soil 1.3 times, the available phosphorus content was general not high, calcareous soil available K content was significantly higher than that of purple soil and yellow soil.(2) The evaluation results for the cultivated land fertility nature index in 1700～2200 based on agricultural land classification, between grade 4～8, grade 4 was the best, grade 6 was the most, followed by grade 5,7,4 and 8, the grade of soil fertility showed normal distribution, the overall level was in the upper; from the point of view of regional distribution of different soil fertility levels, riversides, level ground areas, mountain areas weighted average fertility of cultivated land grade were 5.61,5.9,6.66, the overall level of the cultivated land fertility is riversides, level ground areas, mountain areas was declined in trend, from the point of view of the distribution of different soil types, the purple soil> yellow soil>calcareous soil, the average grade were 5.64, 6.46,6.71, the purple soil was better than yellow soil and calcareous soil.(3) The total production capacity of the homestead reclamation of cultivated land reached to 534.278 t, the average yield was 9003 kg/hm, grade 4-8 were in decreasing trend, the difference between each grade was about 500 kg/hm2; the soil thickness was the most limiting factor of cultivated land fertility, restricted by terrain altitude was also the limiting factor, irrigation and road and ditch, gravel content, organic matter, available nitrogen, available phosphorus in the overall score was not high, but also were the limiting factors.(4) The average grade of farmlands was 3.03 based on the evaluation method of GIS and fuzzy comprehensive evaluation, grade 3 was the most, accounted for 52.18%, followed by grade 4,2,1 and 5, the average grade of the purple soil, yellow soil and calcareous soil was 2.96,3.32 and 3.04 respectively, the average grade of the riversides, level ground areas and mountain areas were 2.82,3.15 and 3.19.(5) The spatial distribution, grade 1 only in the riversides and level ground areas, in the reclamation of rural homestead can be preferred selecting the vicinity of the reclamation area; grade 2 in the riversides, level ground areas, mountain areas were respectively accounted for 24%, 14.99%,12.77%, should be as the focus of the future reclamation areas, grade 3 in the regional distribution were the most, can be used as the future implementation of the internal potential and moderate reclamation areas; grade 4 and 5 subject to geographical constraints, can suit one’s measures to local conditions reclamation for other agricultural land or woodland; in the future the riversides should be combined with industrial development focused on improving the irrigation conditions and road ditch supporting to enhance soil fertility, organic matter and available N content was low; level ground areas can improve the pH and available P content by fertilization; mountain areas can increase the soil thickness, the utilization house site demolition, improve the soil available N and available P content to improve the productivity of cultivated land.(6) Homestead reclamation soil quality grade evaluation model was builded based on SOFM neural network, the grades of cultivated land fertility evaluation for automation provided a good method for reclamation of cultivated land, grade 3 was the most, grade 1,2,3 accounting for the total sample number 84.51%, grade 5 accounting for only 3.61%, overall level was higher; the grades of cultivated land fertility the riversides were slightly higher than the level ground areas, mountain areas were the lowest, followed by 2.52,2.56,2.88; according to the soil types, results showed that the average grades of cultivated land fertility of yellow soil, purple soil, calcareous soil was in declined trend,,2.35,2.6,2.92 etc respectively.(7) The evaluation results of the three assessment methods have a certain consistency, especially between agricultural land classification and fuzzy comprehensive evaluation method of evaluation results. The distribution was the same trend, high consistency, because the understanding of the quality of cultivated land was different, different theories, focus was not the same, there were some differences between the evaluation results, they were all have the advantages and disadvantages, it was difficult to form a unified and effective evaluation method of farmland, according to the main application range for each evaluation method, combined with the technical route and asked to actual needs to select the suitable evaluation method of farmland; through fitting analysis of the linear regression equation, connection and inspection were implemented between the results of fuzzy comprehensive evaluation method and agricultural land classification in the same index area, also according to the grain output, to achieve unity between the comparability of evaluation results. |
