Using EMI, Geospatial Statistics and Multi-Linear Regression for Identifying Areas of Manure Accumulation on Feedlot Surfaces.

Accumulated feedlot manure negatively affects the environment.  The objective was to test the validity of using EMI mapping methods combined with predictive-based sampling and ordinary linear regression for measuring spatially variable manure accumulation.  A Dualem-1S EMI meter also recording GPS coordinates was pulled across the feedlot surface on 2 m intervals to collect horizontal dipole EC_a data.  A stratified random sampling (SRS) design was determined by ranking pen EC_a data from highest to lowest value, segmented into 4 equal ranges.  Five values from each range (N=20) were randomly selected.  Another 20 sites were selected using the response surface sampling design (RSSD) program contained in the ESAP program suite.  The associated site GPS coordinates were used to navigate for sample collection.  Samples were analyzed for volatile solids (VS), total nitrogen (TN), total phosphorus (TP), and chloride.  This sampling approach enables evaluations of the prediction-based ESAP sampling design with the SRS design by employing three different model validation tests.  Correlation coefficients between EC_a and VS, TN, TP and Cl^-, data were 0.95, 0.95, 0.93 and 0.95, respectively, for the RSSD based model and 0.94, 0.88, 0.88 and 0.92, respectively, for the SRS based model.  Composite F-tests showed the two sampling methods to be equivalent for each soil constituent.  Additionally, joint predictive F-tests indicated that the regression models for the soil constituents were able to make unbiased predictions of average values at the SRS sites using the RSSD models.  The mean predictive t-tests indicated no bias in average value predictions across the SRS sites that were predicted using the RSSD sites.  The combination of geo-referencing EC_a, directed soil sampling data and regression modeling provides a tool for accessing manure accumulation on feedlot surfaces. This knowledge will aid in the development of BMP for mitigating environmental contamination.