Distribution of Plant Available Nitrogen in Beef Pastures: As Affected By Management and Landscape.

Conventionally managed beef-pastures are prone to non-uniform spatial distribution of nitrogen in soil. Nitrogen distribution is likely influenced by cattle position, which is affected by management activities and landscape. This study aims to determine the spatial distribution of plant available nitrogen (NH₄⁺ and NO₃^-) and factors responsible for such distribution. In 2014/2015, an extensive soil sampling was conducted in 10 pastures (9.31-21.62 hectares) of Georgia Southern Piedmont. The soil samples were taken at 0-5-cm, 5-10-cm and 10-20-cm depths in a 50-m grid (“Matrix”) as well as specific areas with high cattle activity (“Area of Interest”/” AOI”). Plant available nitrogen was measured in air-dried samples using cold KCL extraction procedure. Different pasture management factors (distance to nearest hay, water and tree/shade) and landscape parameters (elevation, slope, aspect, flow direction) were measured using GIS technology. Cow locations were measured using LOTEK GPS collars every 5 minutes. Results suggested significant spatial autocorrelation (p=0.05) in the distribution of plant available nitrogen, at all three soil depths, suggesting uneven spatial distribution. Stepwise variable selection was conducted to identify the parameters responsible for the uneven distribution of plant available nitrogen. Plant available nitrogen decreased significantly with distance from either water and trees. Elevation and slope also had significant effect on plant available nitrogen. As expected, cattle density and plant available nitrogen were both significantly higher within 20-m of the hay feeding areas suggesting the important role of hay placement in nitrogen distribution. These results put light on the importance of management factors for uniform distribution of nitrogen in beef-pastures. Although landscape parameters cannot be manipulated easily, strategic placement of hay, shades, and waterers can be useful tools for achieving optimum land use for sustainable productivity.