干旱区生态环境知识资源中心

Conversion of native desert to irrigation cropland often results in the changes of soil processes and properties. The objective of this study was to investigate the changes of soil nutrients and their spatial distribution characteristics of a newly reclaimed cropland at the initial stage of the conversion using statistical and geo-statistical methods. Soil samples were collected at regular intervals from a cropland of 0.24 ha, and their nutrient indicators determined. The mean contents of soil organic carbon (SOC), total nitrogen (TN), available nitrogen (AN), available phosphorus (AP), available potassium (AK), and pH value in this newly reclaimed sandy cropland were averaged at 4.45 g kg(-1), 0.49 g kg(-1), 19.99 mg kg(-1), 21.08 mg kg(-1), 121.60 mg kg(-1), and 8.98, respectively. The ranges were less than 20 m for the semivariogram of SOC, TN, and pH, but exceeded 20 m for AN, AP, and AK. The ratios of nugget-to-sill were less than 10 % for the semivariogram of SOC, TN, and pH, but exceeded 25 % for AN, AP, and AK. There were similar distribution characteristics for SOC, AN, and pH, with different sizes of patches present; such distribution patterns were related to the regular planting of orchard and the interval application of manures. There were big-sized patches in the distributions of AN, AP, and AK. Topography was the main factor causing the spatial heterogeneity of available N, P, K, and the 4 years (2001-2004) of cropping affected the distribution patterns of these nutrient variables. The conversion of native desert to irrigation cropland caused significant increases in soil nutrients, but their spatial distributions had large variations. This study identified the main factors affecting the spatial distribution of each soil nutrient variable, including the environment factors and anthropogenic management practices. There is a great potential to improve the productivity and soil fertility for the newly reclaimed sandy cropland, only if the appropriate and sustainable soil management practices are adopted.