[Changes of soil chemical properties in sheep urine patches in Inner Mongolia steppe]

Sheep play an important role in the nutrient cycling in extensively grazed grasslands, mainly through their annual return of around 5-25 kg N in the shape of urine. This return changes the temporal distribution of nutrients in soil and alters their bioavailability. Urine patches are the most important areas of the transformation and cycling of nutrients in the grazed grasslands. In order to make known the changes of soil chemical properties in sheep urine patches, an experiment was set up in the typical steppe area of central Inner Mongolia. The results indicated that soil pH value reached the maximum on the second day after urine excretion, and then declined. It maintained at around 6.5 from the 58th day, which was under the level of the control. Soil dissolved organic carbon (DOC) in urine patches exhibited the identical changing characteristics with soil pH, and had a significantly (P < 0.01) positive correlation with it. Soil total dissolved phosphorus (TDP) increased significantly (P < 0.05) after urine excretion, and reached the maximum at the 2nd day. The percentage of molybdate reactive phosphorus (MRP), dissolved organic phosphorus (DOP) and dissolved condensed phosphorus (DCP) showed significantly two changing phases, and there existed significantly (P < 0.05) negative correlations between MRP, DOP and DCP. Soil NH4+-N reached the maximum on the 2nd day after urine excretion and then declined, while soil NO3(-)-N increased significantly after 14 days and reached the maximum on the 21st day, showing significant "double peaks" characteristics. Soil dissolved organic nitrogen (DON) also increased significantly after urine excretion.