Still Looking For A Way To Make Cover Crops Pay

Fall seeded cover crops can increase soil cover and perhaps add some organic matter to the soil. In some cases, they can also reduce nitrogen (N) losses from the soil profile, either by reducing leaching or gaseous losses. However, for a cover crop to be cost effective, there must be an efficient transfer of cover crop nitrogen to the succeeding corn crop.

Corn response to cover crops and manure applications was evaluated in 2004 on three sites within the OSCIA sponsored Greenhouse Gas Mitigations project. The plots were split so that multiple rates of fertilizer N could be applied. This allowed better evaluation of the N contribution of the various cover crops and manure treatments to the following corn crop.

Table 1 outlines some of the findings from one of these sites near Embro. The farm co-operator applied 0, 4,000, and 8,000 gallons of liquid dairy manure to the fall seeded cover crops of oats, oilseed radish and peas. Cover crop growth was reasonable but not outstanding during the fall of 2003.

Generally, higher corn yields were observed where manure was applied during the previous year, even when relatively high rates of fertilizer (150 lbs N/ac) were applied. Corn planted following a cover crop generally responded much less to adding fertilizer N compared to the plots that had no cover crops.

At this site, there was a need for 87 to 106 lbs per acre of fertilizer N to optimize yields where a cover crop had not been established. However, cover crops reduced fertilizer N requirements to optimize corn yields by 50 to 100%, provided that the cover crop was established in conjunction with manure application.

The 2004 results showed that establishment of a cover crop can result in improved manure N use efficiency of corn planted the next year. This study also clearly demonstrates the need to make the appropriate reductions in fertilizer nitrogen application following manure application/cover crop combinations.

Did the cover crops pay?

If you look at the 4,000 gallon data, it appears you are able to give about a 30 lb/acre N credit to the role of cover crops. At $0.42/lb that is $12.60/ac. This pays for the cost of the cover crop seed, but not the pass of the no-till drill to plant them. In the 8,000 gallon data it appears that the N credit is 87 lbs/acre which would represent $36/acre. This would cover most costs and maybe leave you some net returns for your effort.

Further data will be forthcoming from this project over the coming months. However, it appears that the use of cover crops either planted prior to or immediately after manure applications may improve manure N use efficiency enough to pay their own way!

Table 1. Summary of previous fall cover crop biomass and cover crop nitrogen content, subsequent corn yields and the estimate of fertilizer N required to economically optimize corn yield (Embro Site).