Linking Wisconsin dairy and grain farms via manure transfer for corn production
One relatively under-used 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 an effort to link grain and livestock farms in southern Wisconsin, 20 on-farm trials were conducted to study the agronomic and environmental effects of including manure in cash-grain rotations. Manure was applied at a rate of approximately 107 m3 ha–1 as slurry (11,000 gal acre–1) or 54 Mg ha–1 (24 ton acre–1) as a solid. Across-site analysis indicated that the manured treatment increased corn (Zea mays L.) yields significantly (alpha = 0.05), by 0.5 Mg ha–1 (11.5 vs. 11.0 Mg ha–1), with 67 kg ha–1 less purchased fertilizer N during the 3 yr of this study. However, there were environmental concerns: (i) Early fall manure spreading significantly increased fall nitrate (NO3) levels in the manured plots (175 vs. 87 kg NO3–N ha–1); (ii) Following corn harvest, fall NO3 levels were fairly low and equivalent between treatments with the exception of three sites where manuring resulted in significantly higher NO3–N; and (iii) Soil tests following corn harvest indicated a significant increase in soil test phosphorus (STP) on the manured plots. These results indicate that dairy manure can reduce fertilizer inputs although there is a risk of NO3–N leaching and P accumulation. Informal interviews were conducted with farmer-participants following this study to asses current manure use.