Effect of Time of Manure Application and a Cover Crop On Nitrogen Availability and Corn Yield.

Cover crops are being considered by some producers to minimize nitrate losses from the soil, enhance N availability, and increase corn (Zea mays L.) yield from fall-applied manure. A two-year study was conducted on clay loam mollisols at the University of Minnesota Southern Research and Outreach Center to determine the role of time of manure application and an oat (Avena sativa) cover crop on nitrate concentration in the soil profile, corn yield, and N uptake. Target dates for swine (Sus scrofa domesticus) manure application were 1 Aug., 1 Sep., 1 Oct., and 15 April. Available manure-N averaged 146 kg N ha^-1 across the four application times. Oats was established immediately after the 1 Aug. and 1 Sep. manure applications and on a set of zero-N control plots. Across the 2-yr period, oat growth and N uptake were 2.6 and 2.1 times greater, respectively, for August establishment. Oat growth and N uptake were 1.4 times greater when manure was applied. Corn yields, ranging from 13.1 to 14.0 Mg ha^-1, were not different among the four application dates when the cover crop was absent. Corn yields and N uptake were reduced 3.3 Mg ha^-1 and 56 kg ha^-1, respectively, when oats were established 1 Aug. and 1.0 Mg ha^-1 and 26 kg ha^-1 with 1 Sep. establishment. These data plus the soil nitrate data indicate that substantial N was sequestered by the oat cover crop, which substantially reduced corn yield and N uptake. Foregoing an oat cover crop and applying manure later in the fall or early spring appears to be a better management practice for corn producers.