The availability of trace elements in an oasis soil under different utilization intensity in an arid area in China

Trace elements are important components of soil and their characterization is necessary for determining soil quality.Farming practices can change soil properties,thereby altering the effectiveness of the soil trace elements present.Soil trace element research in extremely arid regions,aiming at the determining effects of different land uses,has received little attention until now.The Cele Oasis(80°03′24″-82°10′34″E,35°17′55″-39°30′00″N) located on the southern margin of the Tarim Basin,Xinjiang,China,was selected as a study area.Agriculture is the main land use here;however,management intensities differ across the oasis and as the oasis area has grown.In 2005,four experimental fields were selected,representing typical land use types according to local tillage practices.These were newly cultivated,fertilized land(NEF),a field receiving a normal manure application rate(NMF),a field receiving a high manure application rate(HMF) and a field in the Oasis interior(OIF). A single index(Ei) and integral index(Ec) were calculated to evaluate the effects of these land use types on soil trace element availability over 20cm depths.The relationship between soil organic matter and available trace elements was determined by correlation analysis.Our results showed that:(1) There were statistically significant differences in the amounts of available Fe,Cu,Mn,Zn present in the different land uses at a depth of 0—20 cm.Cultivation management can improve the accumulation of soil organic matter and soil particle size distribution,which in turn can increase the availability of soil trace elements to pasture and crops.The application of manure and fertilizer being the main source of available trace elements in these soils was the probable reason for the differences. (2) The farmland(OIF) situated in the oasis interior showed the highest level of trace element availability of all the fields.The main reason for this result would likely be that long-term irrigation has played an important role in altering the availability of soil trace elements,while more than one hundred years' of careful cultivation management had led to the soil becoming more fertile. (3) A comparison of the unfertilized treatments(i.e.NEF,situated in the edge of the oasis and CTP) showed that the lowest concentrations of available Fe,Cu,Zn,were found in the NEF treatment,which was probably due to the removal of these micronutrients from the soil through crop uptake and harvest. (4) Fertilization of the NMF and the HMF fields(which are also situated in the desert-oasis ecotone) resulted in a positive effect on soil trace element concentrations;the available indices of Fe,Cu,Mn and Zn in the HMF were higher than in the NMF,because of the higher input of manure(see earlier). (5) The results of a correlation analysis indicated that soil organic matter was highly positively correlated with the availability of the soil trace elements,the soil organic matter exerting a significant and direct effect on the availability of Zn,Mn,Fe and Cu in the process of oasis growth.These results indicate that refining agricultural management practices in the process of oasis growth could be beneficial.