Nutrient Management Behavior on Wisconsin Dairy Farms

Nutrient management plans for livestock operations should account for rates and timing of manure application to cropland, as well as how manure is integrated with other nutrient sources. Little is known, however, about actual nutrient management behavior of farmers, and what changes may be needed for farmers to adhere to nutrient management regulations. Detailed records were kept on fertilizer, manure, and legume N and P applications on 33 representative Wisconsin dairy farms during the period October 2003 through September 2004. Average available N applications ranged from 118 to 200 kg ha⁻¹ of which 40% was derived from fertilizer, 30% from manure and 30% from previous legume. On a regional basis, the following percentages of corn (Zea mays L.) area fell within available N application categories of 0, 1 to 80, 81 to 160, 161 to 240 and >240 kg ha⁻¹, respectively: in the Northeast (NE) region, <1, 26, 33, 21, and 19% of the total corn area surveyed (504 ha); in the South–Central (SC) region, <1, 39, 41, 14, and 5% of the corn area (576 ha); and in the Southwest (SW) region, 0, 31, 45, 14, and 10% of the corn area (180 ha). Average available P applications ranged from 16 to 18 kg ha⁻¹, of which 65% came from manure and 35% from fertilizer. On a regional basis, the following percentages of surveyed cropland area fell within available P application categories of 0, 1 to 24, 25 to 48, 49 to 72 and >72 kg ha⁻¹, respectively: in the NE region, 30, 50, 15, 4, and 1% of the cropland area (1340 ha); in the SC region, 23, 54, 17, 5, and 1% of the cropland area (1168 ha); and in the SW region, 41, 48, 8, 1, and 2% of the cropland area (542 ha). Of the total cropland area (ha) across all regions that received manure during winter, 7 to 25% were within regulated surface water buffer zones. In the NE, SC, and SW regions, 100, 83, and 63% of winter-spread cropland area received available P application rates <24 kg ha⁻¹, the 1-yr crop P replacement ceiling set by State regulations. Regional differences in nutrient management behavior due to topography, soils and other factors should be used to better target efforts aimed at improving fertilizer-manure-legume management on Wisconsin dairy farms.