Linking Dairy and Cash-Grain Farms in Wisconsin via Manure Transfer for Use in Grain Production: Corn (Zea Mays L.) Yield, Environmental Effects, and Implementation Constraints

ABSTRACT: One relatively under-utilized manure management strategy employed by dairy farmers is to transport and apply manure onto the fields of nearby grain farmers. While this system offers advantages to both parties, little of the existing research on manure management has been conducted on grain farms. As part of a larger effort to link grain and livestock farms in southern Wisconsin, 20 on-farm trials, located around 6 cooperating dairies, were conducted to study the agronomic and environmental effects of including manure in cash-grain rotations. The variables studied included manure nutrient variability, corn yields, grain protein, and potential nitrate-nitrogen (NO3¯ -N) leaching and phosphorus (P) accumulation. Manure was applied at the rate of approximately 107 m3 ha-1 of slurry (11,000 gal ac-1) or 54 Mg ha-1 (24 ton ac-1) as a solid. Across-site analysis of the on-farm trials indicated that the manured treatment increased corn yields significantly, by 0.5 Mg ha-1 (11.5 vs. 11.0 Mg ha-1). Manured corn received an average of 67 kg ha-1 less purchased fertilizer N during the three years of this study. However, there were environmental concerns: 1) At the sites where manure was spread in the early fall (following wheat harvest), fall soil nitrate levels (0-91 cm depth) were significantly higher than in the non-manured plots (175 vs. 87 kg NO3¯ -N ha-1); 2) Following corn harvest, fall soil nitrates in the soil profile were fairly low and equivalent between manured and non-manured plots, except in three of the analyzed sites where manuring resulted in significantly higher fall nitrates; and, 3) Soil testing in the late fall after corn harvest showed a significant increase in soil test phosphorus and potassium on the manured plots. These results indicate that spreading dairy manure on neighboring grain farms can result in fertilizer savings while maintaining crop yields, although there is an increased risk of NO3¯ -N leaching and P accumulations. Interviews conducted a year after the project was completed indicated that most of the participants were continuing to utilize manure from nearby livestock operation primarily because of its fertilizer replacement value. In addition, the majority of participants paid in some way for this manure and felt that it provided an important economic edge at a time of rapidly rising fertilizer and corn grain prices. Those that were not continuing to use manure cited sourcing problems as their main constraint.

Published in Agron. J. 101:167–174 (2009).