Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 26, 2005
Publication Date: May 1, 2006
Citation: Bell, J.M., Robinson, C.A., Schwartz, R.C. 2006. Changes in soil properties and enzymatic activities following manure applications to a rangeland. Rangeland Ecology and Management. 59(3):314-320. Interpretive Summary: Land application of manures to rangelands is oftentimes employed to increase the land base available for nutrient assimilation. However, manure amendments to rangelands may alter soil properties and functions related to nutrient recycling. We studied the effects of stockpiled beef cattle manure amendments and cattle grazing on enzyme activities, biomass production, soil organic C, nitrogen, and phosphorus in a short-grass native rangeland. Seasonal plant biomass production increased with manure and synthetic fertilizer applications. Mechlich 3 extractable P was greatest on manure amended plots, although increases in soil test P as a function of total P applied were similar for manure and a synthetic potassium phosphate fertilizer. Soil enzymatic activities were strongly influenced by sampling date and soil depth. There were no consistent grazing effects on soil enzymatic activities. Although alkaline phosphatase activities in the soil increased following manure applications, extractable P was the most reliable indicator of manure loading.
Technical Abstract: Manure amendments to rangelands may alter soil properties and functions related to nutrient recycling. We investigated the short-term influence of grazing and cattle manure on total soil carbon and nitrogen, Mehlich 3 phosphorus, and the enzyme activities of alkaline phosphatase and dehydrogenase. Fertility treatments (manure and urea + KH2PO4 fertilizer) were imposed under grazed and nongrazed conditions in a short-grass native rangeland. Manure was applied in March of each year at 150 kg N ha-1, and Urea + KH2PO4 was applied at 75 kg N ha-1 and 20 kg P ha-1, respectively. Total aboveground biomass and soil samples at four depths (0-25, 25-50, 50-100, and 100-200 mm) were collected throughout two growing seasons of this study. A controlled environment study was used to further examine fertilizer source effects on enzymatic activities at five P rates (0, 20, 40, 80, and 120 mg Kg-1 P applied as manure or urea + KH2PO4). Aboveground biomass exhibited a positive response to amendments. However, biomass was not significantly correlated with soil carbon, NO3-N, and NH4-N. Fertility treatments significantly (P'0.04) influenced extractable P following the second fertilizer application for the three uppermost depth increments. Extractable P levels were greatest on manure amended plots, increasing 44% from February 1999 to July 2000 at the surface. However, increases in P extractability as a function of total P applied were similar for manure and KH2PO4. Dehydrogenase and alkaline phosphatase activities were significantly (P<0.001) influenced by sampling date and soil depth. There were no consistent grazing effects on enzyme activities. Amendments did not influence dehydrogenase activities in the field; however, in the controlled environment, dehydrogenase activities increased 16% with manure amendments (P=0.0248). Phosphatase activities increased significantly following manure applications under both field (P=0.0065) and controlled environment (P=0.0034) conditions. Extractable P was the most reliable indicator of manure loading.