#07-031

Complete

Date Full Report Received

03/03/2009

Date Abstract Report Received

03/03/2009

Investigation

Institution:
Primary Investigator:

The overall objective of this field study was to determine the effect of late summer and fall applications of liquid swine manure with and without an oat cover crop on the nitrate distribution in the soil profile, uptake of nitrogen (N) by the oat cover crop, corn yield and N utilization by corn. An experiment was conducted on a Clarion-Nicollet soil complex at the Southern Research and Outreach Center at Waseca. Swine manure from a pit under a finishing barn was sweep-injected on August 2, August 31, October 12, October 31 and April 15 at a rate of 3500 gal/A. The available N rate applied averaged 139 lb N/acre across the five application dates. An oat cover crop (ForagePlus) was established on August 2 and 31 and harvested on October 25. The dry matter yield was 1.80 and 0.76 tons/acre while N uptake totaled 113 and 60 lb N/acre for the two planting dates, respectively. Soil samples taken to a 2-foot depth in late August, mid-October, and mid-November indicated significantly lower nitrate concentrations in the soil for the August manure applications in this wet year, especially when the oat cover crop was present. Soil samples taken to a 3-foot in mid-May and mid-June provided further evidence of N loss with the late summer manure applications; whereas, manure applied October 12, October 31, and April 15 provided highest soil nitrate levels. Furthermore, soil nitrate levels were not different between the August 2 manure application/cover crop treatment and the zero-manure control treatment. Grain yields were not statistically different and ranged from 207 to 223 bu/acre for the five manure application dates when a cover crop was not planted. This was surprising considering some of the early-season visual differences, but the zero-manure control plot yielded 179 bu/acre. The oat cover crop reduced corn yield for the August 2 and 31 application by 34 bu/acre and 8 bu/acre respectively. Nitrogen uptake by the corn was reduced by the early manure application and the oat cover crop. Considering the wet conditions from August 1-October 31, 2007, the results from this 1-year study indicate that producers should apply hog manure in October or in the spring to achieve greatest yield and N uptake. Applying manure in early August to early September, presents a significant risk of lower yield and N loss, especially when a oat cover crop is planted in August.