How Do Long-Term, Low-Emission Applications of Dairy Slurry and Fertilizer on Perennial Grass Affect Growth and N Recovery of a Subsequent Corn Crop?.

Previous work showed that low-emission applications of dairy slurry on perennial grass over multiple years built up soil nitrogen (N) and carbon. The objective of this project was to examine the response of corn planted after grass which had received applications of dairy slurry or mineral fertilizer for many years in a humid maritime climate.  Dairy slurry had been applied with a sliding shoe at 400 and 800 kg total N ha^-1 yr^-1 (about 50% ammonium-N), ammonium nitrate was applied at 200 and 400 kg N ha^-1 yr^-1, and there was a treatment (ALT) with alternating high rates of manure and fertilizer. All treatments were split into 4 equal doses annually and applied for 14-16 years. All corn received starter P and ammonium nitrate treatments also received lime, K and S. Averaged over three years, historical manure applications increased corn dry matter yield by 4 and 6.8 t ha^-1 at the 400 and 800 kg N ha^-1 rates, respectively, but there was little effect of historical mineral fertilizer applications compared to the control. Similar corn yields were observed for the 400 kg total N ha^-1 manure treatment and the ALT treatment, despite much higher historical grass yields from the latter. Hence, there was little effect of historical mineral fertilizer N on corn yield. Historical manure increased N uptake by 44 and 89 kg N ha^-1 for the 400 and 800 kg N ha^-1 treatments, respectively, and the ALT treatment increased N uptake by 52 kg ha^-1 compared to control, but there was little effect of the historical mineral fertilizer.  Apparent N recovery rate was about 10% of the manure N applied in the previous year and less than 1% of the combined manure N applications, suggesting that most of the accumulated soil N is resistant to mineralization.