Effect of Agricultural Land Use Changes on Soil Nutrient Use Efficiency in an Agricultural Area,Beijing,China

Agricultural land use and management practices may affect soil properties,which play a critical role in sustaining crop production.Since the late 1970s,several new agricultural land use types had been introduced in the rural areas of China.The purpose of this study is to evaluate the effect of these land use changes on the soil properties,nu-trient absorption rate,and nutrient use economic efficiency ratio in an agricultural area of Beijing.Specifically,the cropland,the orchard and the vegetable field were examined.Results of this study suggest that land use and farming management practices significantly affect the content of soil organic carbon (SOC),total nitrogen (TN),total phos-phorus (TP),and available phosphorus in the surface layer of 0-25 cm (p<0.05) in the Yanqing Basin,northwestern Beijing.Soil nutrients in each agricultural land use type decrease rapidly with the increasing soil depth.Orchard and vegetable field tend to have higher soil nutrients than the cropland does.However,the soil nutrient-absorption rate (NAR) of the orchard and vegetable field is lower than that of the cropland,even though orchard and vegetable field may provide much higher economic benefit.While increasing SOC,TN,and TP in the orchard and vegetable field by intensive farming may be a valuable option to improve soil quality,potential increase in the risk of nutrient loss,or agricultural non-point source pollution can be a tradeoff if the intensive practices are not managed appropriately.

The Effect of Land Use on Soil Organic Carbon Stocks in Lake Victoria Crescent Agro-Ecological Zone, Uganda

The effect of land use on soil organic carbon （SOC） stocks and depth distribution of SOC was investigated in the Lake Victoria Crescent ago-ecological zone of Uganda. Soil samples were collected from six land use types at 0-30, 30-60 and 60-90 cm from profile pits dug in similar soils and slopes. Results indicated that SOC stocks significantly differed across the various land use systems. SOC also varied significantly by depth. The highest SOC and pH were recorded under natural forest-strict nature. Grassland had the lowest SOC but the highest bulk density （BD）. Phosphorous （P） was the highest in banana-coffee systems and the lowest under tea plantations. The lowest values of pH and BD were found in highly disturbed natural forest. The upper layers of the soil （0-30 cm） stored higher amounts of SOC compared to other depths （30-60 cm and 60-90 cm）. Land use therefore has a significant effect on SOC and other soil physical and chemical properties.

Effect of Land Use on Soil Phosphorus Sorption-Desorption Under Intensive Agricultural Practices in Plastic-Film Greenhouses

With rapid urbanization and economic growth, Chinese traditional rice-legume production is increasingly replaced by vegetable and horticultural flower production, which could affect soil properties. This study was conducted near Kunming City, Yunnan Province, Southwest China to investigate how soil phosphorus （P） sorption and desorption processes respond to land use changes and to relate P sorption and desorption parameters to soil properties. Soil samples （0-20, 20-40, 40-60, 60-80 and 80-100 cm） were collected from five sites representing four land use types： rice-legume production in a two-crop, one-year rotation （Rice）, vegetable production in open fields （Vegetable）, recent （〈 3 years） conversion from open fields to plastic-film greenhouse vegetable and flower production at two sites （VFCS1 and VFCS2）, and longer-term （〉 10 years） plastic-film greenhouse vegetable and flower production （VFCL）. The changes in land use affected soil pH, electrical conductivity, available N and P and organic carbon content in topsoil and subsoil. In turn, these changes of soil properties influenced soil P sorption capacity. The P sorption maximum （Smax） was affected by land use types, soil sampling depth and their interactions （P 〈 0.0001）. For surface soil, Smax was in the order of Rice （1 380 mg kg-1） 〉 VFCL （1 154 mg kg-1） 〉 VFCS2 （897 mg kg-1） 〉 VFCS1 （845 mg kg-1） 〉 Vegetable （747 mg kg-1）. The lowest Sm^x generally occurred at the surface （except for Rice at 80-100 cm） and increased with depth. The amount of P desorbed during the 8 successive extractions was in the range 23%-44% of sorbed P, and was not affected by land use types or sampling depths. The decreases in Smax suggested that soil P sorption capacity decreased when rice-legume production converted to more intensive vegetation and flower production and caution should be exercised when applying P fertilizer to minimize potential leaching and runoff P loss to the environment.