SPATIAL VARIATION OF PLANT-AVAILABLE PHOSPHORUS IN PASTURES WITH CONTRASTING MANAGEMENT

Authors: Sauer, Thomas; Meek, David

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2002
Publication Date: 5/1/2003
Citation: SAUER, T.J., MEEK, D.W. SPATIAL VARIATION OF plant-available PHOSPHORUS IN PASTURES WITH CONTRASTING MANAGEMENT. SOIL SCIENCE SOCIETY OF AMERICA JOURNAL. 2003. V. 67(3). P. 826-836.

Interpretive Summary: There is growing concern that applying too much animal manure to fields leads to pollution of lakes and streams. It is possible to apply fertilizers at different rates in different parts of the same field based on the amount of nutrients in the soil at each location. The same approach could be used to apply animal manures based on the nutrient content of the manure and the amount of nutrients in the soil. A study was completed to measure how soil phosphorus content changed within two pastures, one with and one without poultry manure applications. The pasture receiving poultry manure was also grazed by more cattle. The pasture receiving poultry manure had very high levels of soil phosphorus and didn't need any more manure to grow enough grass for the grazing animals. The pasture without manure applications needed more phosphorus for better grass growth. This study is important to growers because it shows that when manure is over applied the nutrients are wasted but, if the right amount of manure is applied better grass growth will result and less water pollution may occur.

Technical Abstract: Land application of animal manure using site-specific techniques has potential to optimize nutrient recycling and minimize offsite environmental impacts. The objective of this research was to characterize the spatial variation of soil phosphorus (P) and other chemical properties (carbon (C), nitrogen (N), and pH) in two pastures having contrasting grazing and poultry litter management. One site (Cellar Ridge) was a lightly grazed, 6-ha tall fescue (Festuca arundinacea Schreb.) pasture with a history of limited poultry litter application and the other (Haxton) was a 9.5-ha tall fescue pasture under intensive rotational grazing with poultry litter application for 10 y. Soil cores (0-0.15 m) were collected on a 30-m grid at both sites and analyzed for plant available P (Mehlich 3 extract), total C and N (combustion method), and pH (1:1 water and 0.01 M CaCl2). A second grid (10 x 10 at 3-m spacing) was sampled for all parameters at the Haxton site and 0-0.05 m cores were collected on both grids at this location for measurement of H2O extractable P. Cellar Ridge had significantly lower Mehlich 3 extractable P (32 vs. 315 mg kg**-1) and pH (5.25 vs. 5.77) and significantly higher C (23.3 vs. 16.3 g C kg**-1) and N (1.76 vs. 1.53 g N kg**-1). Rotational grazing and litter application reduced variation in soil properties but the scale and orientation of the spatial variation were not consistent. Variable rate litter application in pastures having low plant available P could improve forage production, grazing animal performance, and environmental protection.