喀斯特地貌区耕地地力评价与分级

Evaluation and gradations of cultivated land fertility in Karst area

为了解喀斯特地貌区耕地地力详情并掌握土壤肥力演变规律,该文以广西壮族自治区德保县为研究区域,借助GPS(global positioning system)、RS(remote sensing)技术,通过野外调查采样、实验室化验等方法获得耕地地力评价相关信息,包括N、P、K、有机质、pH值、成土母质、排灌能力、障碍因素、耕层厚度、质地等74项基本信息。以GIS(geographic information system)技术为核心基础支撑,综合运用模糊评价、专家意见法、层次分析等方法和模型对耕地地力进行自动化、定量化评价。结果表明:德保县1～6级的耕地面积分别占总耕地面积的8.80%、13.84%、20.29%、39.63%、16.83%、0.61%。在量化分级的基础之上,将此次评价数据与1980年进行的土壤第二次土壤普查数据进行深入比较,比较发现:德保县的耕地地力总体水平上升;有机质、有效磷的含量水平明显上升;同时pH值趋于中性;速效钾呈下降趋势。该结果为喀斯特地貌区的个性化施肥、土壤改良、农业生产决策、绿色农产品的生产等提供了基础信息和科学依据。

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.