Preliminary Estimates of Nitrogen Availability from Liquid Dairy Manure to Potato

Abstract

Within Wisconsin, there is a distinct movement toward dairy herd expansion and consolidation of small farms. These large dairies are considering various land and manure management arrangements with non-livestock farmers, such as potato (Solanum tuberosum) producers to increase their manure management options. This study used a fertilizer equivalence approach to evaluate the availability of nitrogen from dairy manure to potatoes. Nitrogen (N) availability was evaluated in field experiments in 2000 and 2001, conducted in northeast Wisconsin using a moderate and a high liquid dairy manure rate [10,000 and 20,000 gal/acre (93,536 and 187,072 L·ha-1)] compared with results obtained from N fertilizer applied at five rates [0 to 240 lb/acre (269.0 kg·ha-1)]. Availability estimates using the fertilizer equivalence method based on tuber yield, harvested tuber N concentration and uptake, petiole nitrate concentration, and soil nitrate levels resulted in apparent availability of manurial N from 10% to 40%, with an overall average across both years of 29.2%. This level is only slightly less than values typically measured where corn has been used as the test crop. In spite of being more shallow-rooted and perhaps somewhat less efficient in N use it does not appear that adjustments to manurial N availability estimates are warranted when potatoes are grown.