Saturday, 15 July 2006
168-6

Influence of land use change on soil nutrients in southern Beijing Municipality following land reform.

xiangbin Kong, China Agricultural University, Yuan ming yuan west road 2, beijing, 100094, China

The pressures of development and major shifts in land use have increased the need to assess the impact of land use change on soil nutrients.Following land reform in China in the early 1980s,farm management practices, such as the type of land use, intensity of cropping and fertilizer and pesticide use,underwent drastic changes. To assess effects of land use change on soil organic matter (SOM),total nitrogen (TN),available phosphorus (AP) and available potassium (AK).A case study was conducted in Daxing County (southern Beijing Municipality).Soil in the Daxing area was sampled from rainfed land, irrigated land, rice land, virgin grassland, forest land and vegetable land in 1982 at the onset of land reform and again in 2000. Surface soil (020 cm) samples were collected and analyzed for organic matter (OM), total nitrogen (TN), and available N (AN), P (AP) and K (AK) contents. The soil OM, TN, AN, and AP all increased significantly while AK decreased slightly. The soil OM, TN,AN, AP increased by 31.02%,50%, 37.89% and 177% respectively, but the AK decreased from 1982 to 2000. The variation of soil OM, TN, AN,AP contents changes were different between different land use types in 1982 and 2000. Soil OM content was increased in different land uses in 1982 as follows:orchard land> rainfed land> rice land> irrigated land> forest land> vegetable land; but soil OM was increased in 2000 as follows: rainfed land> orchard land>Riceland> forest land> irrigated land>vegetable land;Soil TN content was increased in different land uses in 1982: rice land> rainfed land>orchard land> irrigated land> vegetable land > forest land; but soil TN was increased in 2000: orchard land>rainfed land and forest land> rice land >irrigated land>vegetable land;Soil AN content was increased in different land uses in 1982 : rice land> rainfed land> irrigated land>orchard land> vegetable land > forest land; but was increased in 2000: rainfed land> riceland> orchard land> forest land> irrigated land>vegetable land;Soil AP content was increased in different land uses in 1982 : forest land > irrigated land> orchard land> rainfed land>rice land> vegetable land ; but was increased in 2000: forest land>rainfed land> vegetable land> irrigated land>riceland>orchard land>;Soil AK content was increased in different land uses in 1982 : orchard land> rice land>forest land > rainfed land> vegetable land>irrigated land; but was increased in 2000: rainfed land> orchard land> riceland> irrigated land>forest land> vegetable land> . The increased order of content of soil OM, TN and AN was rainfed land>orchard land>irrigated land>vegetable land, and the increased order of content of AP was orchard land >irrigated land> vegetable land >rainfed land, due to the transition of rice land into irrigated land, vegetable land and orchard land. With the rainfed land transiting into irrigated land and orchard land. the content of AP increased in orchard land and rainfed land,the order of extent change of OM and AP was orchard land >irrigated land> rainfed land, the order of extent change of TN was rainfed land> orchard land>irrigated land, The order of extent change of AN was irrigated land > orchard land> rainfed land, the extent of AK decreased, But the other nutrient of soil increase at the same time, when the virgin grassland was transited into such land types as irrigated land, orchard land, rainfed land, forest land and vegetable land. Increased crop yield (higher biomass production) with increasing fertilizer application combined with soil conservation measures that have retained more crop residue on land, are responsible for the increases in soil OM, N and P concentrations. However, the slight decreases in AK reflect the increased cropping intensity and low AK supplying power of these coarse textured soils as well as the low K fertilizer input. With the crop yield meeting the demand of the farms and the economic developing following the land reform in China, they have the cash to use much more fossil-energy inputs, agricultural yields are primarily raised through fossil-energy inputs, also permitting fantastic increases in output and the more crop residue on land. Driven by economic benefits, farmers converted irrigated land to vegetable land and increased fertilizer inputs in vegetable land, resulting in overall increase in soil nutrients. The N and P fertilizer inputs in irrigated land were much higher than in rainfed land, largely due to the higher reliability for grain production in irrigated land as compared with rainfed land. The observations show that different benefits led to the different levels of input, resulting in changes in soil nutrient contents in different land use types. Key words: land use type; soil nutrients; land reform; Beijing Municipality


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