Evaluation Of The Farmland Productivity In The Central Shaanxi Plain At County Level

Taking Huxian, which is a county located in the Guanzhong plain, Shaanxi province, as an example, Analysis of the 1985 and 2009 land use cover change and the study has explored the spatial distribution of land use and analysed the land utilization degree of different terrain gradients within Huxian with data from the Second Soil Survey (SSS), Terrain Bits Index (TBI) and Integrated Land Utilization Degree Index (ILUDI). Besides, based on several Geographical Information System sofewares, for example ArGIS, and Geostatistics, the spatial distribution of soil nutrition in Huxian has been studied. Also the production potential evaluation has been done by using Cultivated Land Resource Evaluation Information System (CLREIS) and Cumulative curve classification method was used to determine the cultivated land fertility level.Results are shown as follows:1) Terrain index was able to comprehensively reflect the spatial distribution and differences of terrain conditions. Distribution index was developed to describe the discrepancy between actual and standard distribution of one component, overcoming the disturbance caused by area. It was concluded that Huxian cultivated lands and construction lands tend to have more advantages on lowlands.2) The combination of land-use types were various in areas of different elevations and gradient grades. Areas of all land-use types were dominant at regions of low altitude and gentle slope. However, the land-use diversity decreased with the increasing altitude and slope followed by the reduced impact of anthropogenic effects.3) Land use type converted amongst one another frequently in areas of low altitude and gentle slope. Nevertheless, land use pattern appeared to become relatively more stable when altitude and slope increased. Some cultivated lands still existed on slopes above 25 degrees, which provided the implication for reforestation. The 3D landscape diagrams, which were established using Digital Elevation Models (DEM) and land use maps, offered an effective way to display the links between land use spatial pattern and environmental factors, and this proved that as the base of land use distribution, natural factors restricted the general land use pattern in some degree. TBI could reflect more detailed information of terrain spatial differentiation compared to traditional altitude-slope description methods.4) Soil organic matter content in Huxian was in the medium level. Average soil organic content of cultivated lands was 16.93g/kg, 3236.581hm~2 of cultivated lands, which equalled 56.45% of the total area, contained organic content between 16.0g/kg and 18.0g/kg. Meanwhile, the soil alkali-hydro nitrogen content was 65.71g/kg and also lied in medium level, having a good correction with soil organic matter. That is to say, high soil organic content places had high alkali-hydro nitrogen content as well. For rapidly-available phosphorus, 33789.62hm~2 of cultivated lands, which equalled 81.99% of the total area, held less than 25mg/kg with more concentrated between 16 and 18mg/kg accounting for 53.16% of total land areas. Content of soil rapidly-available potassium was relatively higher, with concentration on 120-150mg/kg occupying 26556.99hm~2, which was equivalent to 64.44% of the total cultivated areas. The average, top and bottom content were 137.48mg/kg, 186.18mg/kg and 80.32mg/kg, respectively.5) The assessment of production potential of Huxian cultivated areas has been completed using hierarchical analysis supported by Geographic Information System (GIS) and CLREIS. It was concluded that Huxian cultivated lands had relatively high production potential, and could be divided into five levels. Level one, 2530.39hm~2 accounting for 6.4% of total arable areas; Level two, 19407.49hm~2, 47.09%; Level 3, 12426.87hm~2 equivalent to 30.15% of the total; Level 4, 4464.56hm~2 covering 10.83% of the total ; Level 5, 2385.13hm~2 standing for 5.79% of the total.6) The soil fertility level of Huxian cultivated, landform lands was closely related to terrain, soil type and slop etc., showing markedly regional distribution. In response to soil fertility rises, physiognomy types transferred from flood lands and sloping lands to some well-irrigated flat grounds such as loess tablelands and flood accumulate fans etc.