ASSESSMENT AND ANALYSIS OF SOIL QUALITY CHANGES AFTER 11 YEARS OF RECLAMATION IN SUBTROPICAL CHINA

Soil quality is one of the most important factors in sustaining the gl obal biosphere and developing sustainable agricultural practices. It h as been defined in several different ways in recent years from view po ints of bioproductivity, sustainability, environmental protection, and human and animal health. In this paper, soil quality refers to its ca pacity to meet the need of plant growth. Land use and management pract ices greatly impact the direction and degree of soil quality changes i n time and space. Understanding the effects of land use and management practices on soil quality and its indicators has been identified as o ne of the most important goals for modern soil science. This paper pre sents a method for assessing and mapping soil quality changes in time and space in small watersheds. It was developed and used to evaluate t he changes in soil quality after 11 years of reclamation at Qian-Yan-Z hou experimental station (QYZES), which is located in subtropical Chin a. Changes in soil quality was assessed and analyzed for cropland, cit rus orchards, pastureland, grassland, sparse weed land, artificial for ests, natural forests, bare land and other land uses. The Qian-Yan-Zho u Soil Quality Information System (QYZSQIS) has been developed using A RC/INFO and FOXBASE software. Two concepts of Relative Soil Quality In dex (RSQI) and its difference (Delta RSQI) are introduced and used in the evaluation and analyses. By combining the QYZSQIS with databases o f soil properties for different time periods, the system provides an e ffective method for evaluating soil quality changes in time and space in small watersheds. The RSQI provides a standard for comparing region al soil quality and the Delta RSQI a standard for evaluating soil qual ity changes over time. After 11 years of reclamation, there was a decr ease in the area of both low quality and high quality soils, while med ium quality soils increased. In terms of land use systems, the soil qu ality in paddy fields, vegetable fields and citrus orchards was domina ted by improvement, whereas fuel woods, sparse weed land, and bare lan d were mainly degraded. Annual grass played an important role in the c onservation and improvement of soil quality in the area. Except for la nd uses and management practices, original soil quality level also pla ys a major role in soil quality changes. Soils with higher quality wer e degraded more rapidly, because they usually need more nutrient input to maintain their quality status than those with lower quality. These analyses show that it is of equal importance to improve soil quality in degraded locations and to sustain it in high-quality areas. (C) 199 8 Elsevier Science B.V.