Evaluation and gradations of cultivated land fertility in Karst area

Abstract: Cultivated land is necessary for agricultural production. It is also the most fundamental requirement for humans' survival and development. In recent decades, along with the increase of population, stress on the environment, and diminishment of cultivated land area, the conflicts between humans and cultivated land are getting more and more obvious. As the thorough utilization of cultivated land is getting extremely urgent, the evaluation of cultivated land fertility, which supports basic information and a scientific foundation for thorough utilization of cultivated land, is becoming necessary.Debao County was here taken as our study case. Cultivated land within its areas possesses several classic KARST topographic features: 1) There are many mountains and rocks, but little farmland. At the same time, there is limited land for agriculture, but abundant land for forestry and grazing. 2) Carbonate geology is widely distributed, farmland has been developed in KARST topography, rocky mountains take a large percentage of county land, and stony desertification is heavy. 3) There are 7 groups of soil, 20 sub-groups of soil, and 71 soil types, and these types of soil intermingle in complex patterns. Paddy soil and lime soil take 80% of the county's cultivated land. 4) The fertility of cultivated land is relatively sterile; medium- & low-fertility farmland takes a large priority percentage of county farmland. 5) The vertical utilization discrepancy of the land resource is notable, and three-dimensional agriculture is prominent.The informational value of a Farmland-Resource-Information-Management-System (FRIMS) is very important for agricultural productivity. We use Remote Sensing (RS) and Global Positioning System (GPS) technology for on-site field-surveys to collect local cultivated land information, such as: obstacle factors, slope strike, latitude and longitude, irrigation conditions, drainage conditions, parent materials, terrain, basic farming equipment, and so on. We further use laboratory analysis to acquire basic data including: the glass-electrode method to measure pH; Kjeldahl determination to measure available N; NaHCO-extraction and ammonium molybdate-tartaric emetic-ascorbic acid colorimetry to measure available P; atomic absorption spectrophotometry and ammonium acetate extraction to measure available K; atomic absorption spectrophotometry and nitric acid extraction to measure slowly available K; atomic absorption spectrophotometry and DTPA extraction to measure available Cu, available Fe, available Mn, and available Zn; azomethine-H colorimetry to measure available B; dichromate potassium oxidation to measure organic matter, as well as other organic nutrition values from 3,938 soil samples 0-40cm underneath farmland.Based on geographic information system (GIS) technology, an evaluation unit was determined from overlapping a soil distribution map with a utilization map. Ten index factors were selected based on local KASRT topography combined with plant growth trends from 64 national index factors to evaluate the cultivated land of Debao County. These index factor were as follows: available P, available K, organic matter, pH, soil texture, drainage capacity, irrigation capacity, obstacle factors, plough layer thickness, and parent material. Furthermore, we used an analytic hierarchy process to determine the weights associated with each factor, the Delphi method to acquire data membership degree of each factor; and fuzzy math to calculate the membership function of each numerical factor. Finally, the automatic and quantitative evaluation of local cultivated land was conducted successfully by computer analysis of information.The results showed that the fertility grades from first to sixth of the local farm land account for 8.8%, 13.84%, 20.29%, 36.63%, 16.83%, and 0.61%, respectively, and the overall farmland fertility is increasing in comparison with the second cultivated land survey. The availability of P and enrichment of organic nutrients are increasing, in contrast to a small decrease in pH and K of Grade-3 and upward. This study provides some basic information and scientific insights into specifically practical fertilization and recovery of degenerated and contaminated soil, for adjustment of agricultural structure and production of natural agriculture products. The methodology used in this study could also be adapted to other, similar Karst areas in our country.