ARS/SCA: Are Water Soluble P Losses Within Pastures Spatially Coincident with Reduced C Storage?

Towards project hypotheses, we will monitor grazing beef cow behavior (Agouridis, et al., 2004) in at least 2 representative (established) pastures, and impose a spatial sampling design for soil P and surface soil hydrology that fulfils the following needs: captures any impact of animal behavior; is a functional representation of the main geographical, soil type, and management units; is a local representation of functional properties, transport coefficients, and surrogate or indicator variables; captures spatial variability structure of measured information as a basis for co-regionalization; and is a quantitative basis for transferring findings from intensively sampled areas to less intensively sampled areas. To accomplish that, the initial spatial sampling protocol for these established pastures will require a minimum of two transects are to be laid out across each pasture. Pastures greater than 20 acres will likely require an additional transect for each 10 acres increase in size. Pre-sampling will be used to establish the distance between sample locations along the transect, but there will be a minimum of 40 locations per transect. At each of the 40 locations soil surface hydraulic and physical properties; soil test P (0 to 2.5 cm); and soil C storage (0 to 10 cm) will be measured. In-situ measurements will include water infiltration at saturation and dry bulk density. Grove will direct field sampling. D'Angelo will determine how soil P is partitioned into water soluble/runoff P for the pasture soils. The final sampling will be by "zone", done after cow GPS collar monitoring (5 cows per pasture, including the "lead" cow, with position query every 15 min, 24 hr day-1, every third day, for one year) has allowed determination of areas with different animal traffic intensity. The pasture area would then be 'binned' according to the temporal density of animal use. Soil hydraulic, physical and chemical (P and C) properties would be taken as outlined above. Ambient temperature and relative humidity, as potential co-variate drivers of animal behavior, would be determined from the nearest weather station for the duration of GPS monitoring (allows coverage of seasonal impacts). Grove will be responsible for GPS data download. Aiken will assist with GPS data interpretation and animal handling protocols.