A preliminary study on the relationship between soil urease activity and soil fertility in the grazing grasslands of Yongchang county, Gansu province.

The relationship between soil urease activity and soil fertility in the grazing grasslands of Yongchang county of Gansu province was studied from 2007 to 2008.There were significant differences in the urease activities of different grazing grasslands,and these activities were more intense in the surface layer than in the deeper layers.The soil urease activities showed significant positive correlations with organic matter content,total nitrogen,available nitrogen,and available potassium,but a significant negative correlation with soil pH value.Path analysis showed that the sequence of soil fertilities based on their direct acting coefficients to soil urease activity was: Total nitrogenavailable potassiumavailable nitrogenavailable phosphorussoil pH valueorganic matter.The organic matter does not affect urease activities directly,but acts indirectly through its effect on total nitrogen.Total nitrogen directly affects urease activity.Other factors like soil available nitrogen,available phosphorus,and available potassium do not directly affect urease activity,but indirectly affect ti through total nitrogen.Both direct and indirect effects of soil pH value are limited and soil pH value is not a major factor affecting urease activity.