Winter Cereal Cover Crop Removal Strategy Affects Spring Soil Nitrate Levels

The use of winter cereal cover crops in no-till row crop systems has increased in the North Central Corn Belt. Timing of the cover crop removal can be managed to improve nitrogen availability for subsequently grown crops. Growers utilizing cover crop systems have several alternatives regarding the removal strategy for the winter cereal cover crop prior to seeding rotational corn (Zea mays L.) or soybean [Glycine max (L.) Merr.]. These alternatives include: herbicide burndown; harvest of the winter annual cover crop as an early spring forage; or, allowing the winter cereal cover crop to mature as grain. The objective of this study was to evaluate the affect of winter cereal wheat (Triticum aestivum L.) and rye (Secale cereale L.) cover crop burndown or harvest strategies on spring soil nitrate levels. Experiments were established in 1999 through 2001 in East Lansing, Michigan. Each cover crop strategy evaluated had significantly lower or tended to have lower spring soil nitrate levels compared with a no-cover check treatment at all depths, especially in the mid (30-60 cm) and deep (60-90 cm) soil profile. The lower quantity of soil nitrate following the winter annual cereals can be attributed to the winter cereals scavenging soil nitrate over the fall and winter. The herbicide burndown strategies for terminating the winter cereals resulted in significantly greater spring soil nitrate levels in the upper soil profile than the forage or grain harvest removal strategies in 2001. The higher soil nitrate levels near the soil surface following the herbicide burndown strategies indicate the release of N from desiccation of plant material in the upper soil profile. The grain harvest removal strategy resulted in a tendency for less soil nitrate in the upper soil profile, probably due to the fact that the cover was still viable at the time of the spring soil sampling, preempting mineralization of N from plant residue and providing a longer residency time for the winter cereal to scavenge residual soil nitrates.