THE EFFECT OF LONG-TERM WATER TREATMENT RESIDUALS – BIOSOLIDS CO-APPLICATIONS ON NATIVE RANGELAND SOIL

The city of Fort Collins, Colorado owns 10,390 ha of semi-arid rangeland for the recycling of municipal wastes via land application. In 1991, a study was initiated to determine the potential short-term impacts of water treatment residuals-biosolids co-application on soils and vegetation. Treatments consisted of 10 Mg biosolids ha−1 co-applied with 5, 10, and 21 Mg water treatment residuals (WTR) ha−1 to 15 × 15 m plots. All treatments were replicated four times. In October 2002, the plots were divided in half with one half of each plot receiving rates identical to the 1991 application. Soils data was collected in June 2004 and June 2005, from the 0–8, 8–15, and 15–30-cm depths, to access the short-term impacts of a repeated co-application and the long-term impacts of a single application. Soil pH and electrical conductivity (EC) were relatively unaffected by co-application. Soil NO3-N increased with both increasing WTR and with the repeated application, while soil NH4-N only increased in the soil surface. Total soil C and N increased in the soil surface with increasing co-application rate. Total surface-soil Cu, Cr, and Zn increased with increasing co-application and with repeated co-application. Total surface soil Ni increased with repeated co-application. Downward transport of both Mo and P indicated that these materials are translocated most likely as a WTR-particulate-bound phase.