Study On Soil Enzymological Characteristics Of Cotton Field In Xinjiang

As a major factor, soil enzymes not only influence soil quality and crop yield, but also reflect the function and effect of soil management. In this study,the relationship between the activities of five soil enzymes (viz. urease, alkaline phosphatase, invertase,catalase, and dehydrogenase) and the fertilities of soils sampled from the cotton fields under different planting years, different irrigation methods, different growth period in the main cotton planting area in Xinjiang was explored. The conclusions are drawn below:In general, the activities of the five soil enzymes in the cotton farmland were all higher than that in the unclaimed wildland as control. The activities of urease, alkaline phosphatase and invertase enzymes were changed from increase to decrease along with the continuous cropping years of cotton in the southern and northern Xinjiang. The activities of catalase enzyme were at the same level compared that with the southern and northern of Xinjiang. The activities of dehydrogenase enzyme with the increase in number of years even for fluctuating change in the northern Xinjiang; the activities of dehydrogenase enzyme were increased along with the years of continuous cotton cropping in the southern Xinjiang. In the soil profile, the activities of urease, alkaline phosphatase and invertase enzymes decreased with the depth of soil. The activity of catalase showed irregular changes with the depth of soil in the northern Xinjiang, whereas decreased gradually with the depth of soil in the southern Xinjiang. The activity of dehydrogenase decreased gradually with the depth of soil. The activities of urease and alkaline phosphatase, invertase, dehydrogenase were significantly or very significantly correlated between each other. The activities of urease, alkaline phosphatase, invertase, catalase and dehydrogenase were significantly or very significantly correlated with the total nitrogen, organic matter, alkali-hydrolyzed nitrogen, and available phosphorus in the soil.In drip irrigation the activities of soil urease, alkaline phosphatase and invertase were slightly higher than the surface irrigation methods, whereas the activity of catalase was at the same level between drip irrigation and the surface irrigation methods, and the activity of dehydrogenase was slightly less than that under the surface irrigation methods. Soil profiles of urease, alkaline phosphatase, invertase, and dehydrogenase activities were decreased with the depth of soil, and the activity of urease under drip irrigation was higher than that of surface irrigation, the activities of alkaline phosphatase and invertase under drip irrigation and surface irrigation methods were basically at the same lever. The activity of dehydrogenase under surface irrigation was higher than under drip irrigation, and the catalase activity from the surface layer to underlying layers was changed with complexity and inconsistency.The geo-statistical methods were applied for the corresponding contour maps were plotted by using kriging analysis. The results showed that: in the seedling stage the activities of five soil enzymes were relatively even in basically zonal distribution, compared to the former two stages they all increased generally in different magnitudes in the boll opening stage. The soil enzyme activities in five soil profiles during three different stages mostly showed zonal distribution. Not only being different horizontally but also vertically the soil enzymatic activities showed difference at the different depths and decreased with the depth,however, a few did not change significantly.The conclusion of the above experimental analysis on the spatial variability of soil enzymatic activities in the cotton field of Xinjiang may provide better understanding of the spatial distribution of soil enzymatic activities in the study area, which may further be used as the basis for spatial interpolation and mapping for formulation of reasonable fertilization and provides a theoretical basis for research on precision agriculture and its implementation in the future.