Response of soil nutrients to different cropping systems in the oasis of arid land

In the process of transformation of tropic rain forest and semi-arid grassland to farmland, the soil degradation usually occurs. But the transformation of arid desert to oasis is likely to differ from that of tropic rain forest and semi-arid grassland. Taking an alluvial plain oasis as a study case, the oasis soil properties during the process of the transformation of different cropping systems have been investigated and evaluated. Selected cropping systems consist of saline tolerance crop (STC), food crop (FC), melon and vegetables (MV), Economic plants-cotton (EP-C), economic plants-grape (EP-G), Economic plants-Hop (EP-H). Surface soil (0–20 cm) samples were collected in 1982, 1999 and 2003. Soil organic matter (OM), and available N (AN), available P (AP) and available K (AK) were determined for each soil sample. SPSS statistical software was used to analyze the soil property data. The transformation of cropping systems in the Sangong River watershed was affected directly by the policy, law and market. The soil OM contents experienced a decline during 1982–1999, then a rise during 1999–2003. AN, AP and AK contents increased significantly with cultivated time. Soil OM tends to decrease during the conversion from STC and FC to cotton but increase during the conversion from the cotton to the grape. The soil OM was increased gradually with the cultivation time, so the oasis soil presented carbon sink, which indicates that human activities was reasonable and favorable for improvement of the oasis-ecosystem.