Validation of best management practices on eight Kansas farms

Abstract

Changes in field-scale agricultural nonpoint source pollution levels were assessed relative to changes in land management practices over a five-year period. The primary objective was to quantify edge-of-field nutrient and herbicide concentrations in first flush runoff, shallow groundwater (i.e. soilwater) and surface water for various Kansas agricultural practices under existing weather conditions on working farms. Additionally, attempts were made to relate the observed changes water quality to causative factors (e.g. weather patterns, natural conditions, adoption of best management practices) associated with the study areas and farms. Eight farms in central and northeast Kansas were chosen for study from thirty-five farms selected to participate in the Kansas Rural Center’s Clean Water Farms Project. The management practices on the selected farms were (1) green manure cover crops in a stripped-crop rotation, (2) no-till procedures on rowcrops and small grains, (3) ongoing wheat field conversion to a grazing pasture, (4) rotational grazing systems on pasture already converted from cropland, and (5) limiting livestock access to watering ponds. Unforeseen changes in management plans or delays in implementation of management practices required alterations to study objectives for two of the monitoring programs to make them relevant to the actual management activities occurring on the farm. Runoff and groundwater samples were collected from 1996 to 2000 and analyzed for a number of constituents, most notably the major nutrients nitrogen and phosphorus and the herbicides atrazine and metolachlor. Scatter plots and box plots were used to organize and interpret the water quality data. A case study was developed for each farm in which potential causes of the observed changes in water quality were identified and related to the specific combination of weather, topography, land use and land cover on each farm. Variations in nutrient and herbicide concentrations in runoff and groundwater from study fields were related to weather patterns, the timing or elimination of fertilizer applications, off-site contributions of nutrients and herbicides, and the presence or absence of groundcover during larger runoff events. The runoff and groundwater data collected during this project serves as baseline data to characterize edge-of-field nutrient and herbicide concentrations on Kansas farms managed with practices intuitively beneficial to water quality.