Study On Evaluation Methods On Quality Of Cultivated Land And Application In Arid Oasis Based On GIS And RS

With the cultivated land reducing and the quality dropping, enhancing research on the quality of cropland evaluation has important significance. This is necessary for ensuring the national food security, quality of agricultural products and social and economic sustainable development. It is meaningful for mproving the quality of cultivated land and production capacity in oasis.The 81st,89th,90th corps in the Fifth Agricultural Construction Division has been selected as study area. The goal of this study is constructing the evaluation indexes system of cultivated land for its quality based on GIS and RS methods. Through the application of the two evaluating indexes system in arid oasis, the differences of evaluation indexes, evaluation methods and evaluation results can be analyzed. A new way of investigating the quality of cultivated land can be found, which is mainly based on RS technology and the high spatial resolution image—CBERS. This method would be applied to the typical oasis—the Seventh and Eighth Agricultural Construction Division for revealing the change characteristic of the quality of cultivated land. The result could provide a new method and establish foundation for dynamic monitoring, rational using and right managing farm land.Each block of land was taken as an evaluation unit of quality of cultivated land based on GIS technology. The index system includes site condition, physical and chemical properties and soil nutrient status in topsoil, soil management, climatic conditions and barrier factors. They can be divided into six kinds of 19 indexes. The index system for evaluating the quality of cultivated land in the Fifth Agricultural Construction Division has been put forward. The weight and membership function of the indexes were calculated using Delphi method and AHP. Then evaluation of single factor has been made. The quality of cultivated land was evaluated comprehensively using fuzzy classification method, which were classified into five grades. The results shows that the first class and the second class land mainly distributed near the 89th corps, in the middle of the 81st corps and the 90th corps, while the fourth and the fifth class land mainly distributes on the edge of the region. Most of the lands are the third class land which occupied 76.08%. On the other hand, the first class land and the fourth land are almost equivalent, and they are 1.66% and 1.13% respectively. The quantity of the second class land is close to the fifth class, they are 10.70% and 10.42%. On the whole, the quality of cultivated land in the study area is very ordinary, the fist class and the second class land only occupy 11.03%, while the fourth and the fifth class land are 26.58%. This shows the farmland need to be improved.When evaluating the quality of cultivated land with CBERS image, the grid cell can be regarded as evaluation unit. Under "P-S-R" framework, evaluation index system include production press Index (PPI), land status index (LSI) and social action index (SAI), they can be divided into slope, soil degradation index, fertility index, soil moisture index and land use degree index. Based on these indexes, land quality index model was put forward. Depending on the model and ENVI software, cultivated land information and special themes were picked up, and land quality was evaluated. The result shows that the first class land occupies 1.87%, which mainly distribute in the middle of the 89th corps. Most of lands are high-quality vegetable and grain crop fields. The soil texture is light loam. They have strong performance of water and fertilizer supply, with no threat of drought and salinization. The land quality is very good. The second class land occupies 9.86%, which exist scattered in space. Their irrigation guarantee rate and nutrient storage are very high. The soil texture is middle loam. They have no threat of drought and salinization and little producing pressure. The highest proportion of the land is the third class, which occupies 81.86% and distributes surrounding regiment. Most of the soil is middle loam, and the topsoil is light loam. Sand and clay are well situated. Their irrigation guarantee rate and nutrient storage are good. They have good performance of water and fertilizer supply. The land quality is very good. The fourth class land occupies 1.07%, which mainly distribute in the edge zone. Most are used for vegetable and grain crop fields. The soil has barrier layer, and the performance of water and fertilizer supply are poor. The fifth class land occupies 5.35%, which mainly distribute in the edge zone. The phreatic water level is very low. Being scare of water, the irrigation guarantee rate and nutrient storage are very poor. In all, the quality of cultivated land is normal in the study area. The first and the second class land only occupy 11.73%, and the fourth and the fifth class land occupy 6.42%. This indicates the land needs to be modified. The classified result using RS is consistent with that using GIS.Comparing the evaluating result from area and location difference using above two methods respectively, the results indicate that the relative error of each class evaluating land is no more than 10%, that is to say, concordance rate is more than 90%. Among the five classes of spatial change, no difference, little difference, moderate difference, big difference and large difference occupy 70.39%,17.23%,10.14%,1.88% and 0.36%, respectively. This indicates RS method has certain feasibility in the evaluating the quality of cultivated land. The evaluation errors between the two methods mainly come from the differences of evaluation unit, evaluation indexes, evaluation model and collecting time. It proved the advantages of RS, such as fast, accurate.The calculation method for the quality of cultivated farmland based on RS was used to the typical oasis—the Seventh and Eighth Agricultural Construction Division. The results show that the farmland quality is good in this region. The first and the second grade farmland occupied 95.66%, and the fourth and the fifth grade farmland only occupied 0.19%. According to the indexes, we know that there is little farmland pressure in this area. Although there are good conditions, the soil is confined by water resource and it is very fragile in the transition zone between oasis and desert. The cultivated land would still be protected and reformed.The two methods based on GIS and RS has been compared, the result shows that there is a good consistency between them. This indicated that RS image could be seen as a reliable data. If all works about extracting indexes, constructing evaluation model and evaluating the quality of farmland are based on RS data, it would be more fast, accurate, and dynamic. Because GIS is excellent in spatial analysis, integrating GIS technology is very necessary when evaluating the quality of farmland using RS technology. This would get a more accurate result.In this paper, CBERS image has been used for constructing indexes system of evaluating farmland quality. Few researches about this method have been done in evaluating the quality of cultivated land, especially in the arid area. This study is helpful for seek an quantitative and rapid evaluation method which could be suit for arid oasis farmland.