#08-013

Complete

Date Full Report Received

03/17/2010

Date Abstract Report Received

03/17/2010

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 Webster clay loam soil at the Southern Research and Outreach Center at Waseca. Swine manure from a pit under a finishing barn was sweep-injected on August 8, September 2, October 1, October 31 and April 14 at a target available N rate of 120 lb N/A. The available N rate applied averaged 110 lb N/acre across the five application dates. An oat cover crop (ForagePlus) was established on August 8 and September 4 and harvested on October 20. The dry matter yield was 0.73 and 0.23 tons/acre while N uptake totaled 47 and 16 lb N/acre for the two planting dates, respectively. Soil samples taken to a 3-foot depth in early November indicated 88 to 90% of nitrate-N was located in the top foot of the profile from the 8/8, 9/2, and 10/1 manure application dates in this dry fall. The oat cover crop had removed 77 and 41% of the nitrate-N from the soil profile by 11/3 for the 8/8 and 9/4 cover crop planting dates. Soil samples taken to a 3-foot depth in mid-May and mid-June provided evidence of greater amounts of nitrate in the profile for the April application of manure compared to the fall application. However, more than 75% of the nitrate in the 3-foot profile was found in the top 2’ for all application dates. Less than 15% was found in the 2-3’ depth for the October and April manure application treatments while 18% and 25% were found for the September and August applications, respectively. Thus, only slight amounts of nitrate leached below the 2-foot depth in this dry year. Grain yields were not statistically different among the four manure application dates when the rate of manure N was not yield limiting. Yields ranged from 210 to 223 bu/A when the oat cover crop was absent. The zero-manure control plot yielded 158 bu/acre. The oat cover crop reduced corn yield for the August 8 and September 2 application by 71 bu/acre and 30 bu/acre respectively. Nitrogen uptake by the corn was reduced slightly by the August and September manure applications and substantially by the oat cover crop. Considering the dry conditions from August 1-October 31, 2008, the results from this 1-year study indicate that producers could apply hog manure anytime between August 8 and April 14 the following spring without affecting grain yields. However, nitrate in the soil profile in June and N uptake by the corn plant was slightly greater for the manure applications made in October and April compared to those made in August or September. Corn yields were reduced significantly when an oat cover crop was planted in August and early September.