More Payback from Cover Crops
Cover crops. One of the “holy grails” of crop production!! Cover crops have been touted to increase soil cover, reduce erosion, fix nitrogen, add organic matter, improve soil structure, break up “hard pan”, and reduce nitrogen losses. All these potentials are real.
However, for a cover crop to be truly cost effective there must be an efficient transfer of cover crop nitrogen to the succeeding corn crop.
Red Clover Credits Revisited
The cover crop standard in Ontario has been red clover underseeded into a cereal crop such as winter wheat. We have recently done a comprehensive review of the nitrogen credits that can be applied to red clover for the subsequent corn crop. It turns out that these credits are affected by the tillage practice employed for the corn crop. If tillage is performed (this is generally considered to be fall moldboard or fall chisel plow) the credit is, on average, 73 lbs N per acre. In no-till situations the credit is 60 lbs N acre. These are slightly higher than traditional recommendations. Some situations will be higher or lower than these values, but there is a good set of Ontario data that supports these recommended credits, for an average, uniform stand of red clover.
Filling In Uneven Red Clover Stands
Of course using the words uniform and red clover immediately gets us into trouble. If a grower has a good catch on 60% of his field, but on 40% of the field there is little or no red clover, it becomes difficult to give the appropriate reduction in N application to the field. Preliminary results from a series of research trials suggest that patching uneven red clover stands with peas may provide an opportunity to reliably apply an N credit to the entire field.
These field trials were started in the fall of 2003 where various cover crops were seeded following the application of liquid manure applied in wheat stubble fields in late August. Corn was planted on these sites in 2004 with multiple rates of sidedress fertilizer nitrogen applied in order to better evaluate the N contribution of the various cover crop and manure treatments to the following corn crop.
At one of these sites located near Mitchell, Ontario, peas clearly demonstrated an ability to reduce N requirements for the corn crop. The farmer co-operator applied liquid finishing hog manure on the manured treatments at 4000 gal/ac just prior to the seeding of the cover crops. Optimum corn yields where cover crops were not used needed 57 to 68 lbs-N/ac of sidedress fertilizer N. The pea cover crop reduced N requirements 40 lbs/ac where manure was not applied and by at least 70 lbs N/ac where manure was applied (Table 1).
So the option (yet unproven) exists to drill peas into those parts of the field where red clover is absent to help to equalize the cover crop N credit. The peas would need to be drilled in mid to late August. They may not provide the full 73 lbs of N per acre credit like the clover, but a partial credit across the entire field is still a step ahead of no credit, and significantly ahead of over-applying N on the parts of the field were the red clover was good.
Using Cover Crops to Boost Manure N Credits
We have suggested peas in a non-manure situation in order to balance out N credits. Where manure is applied, other non-legume cover crops have potential as well. Table 2 outlines the results of a second study located near Embro, Ontario where use of fall seeded cover crops of oats, oilseed radish and peas clearly reduced the need for fertilizer N to optimize corn yields where manure was applied. At this site, the farm co-operator applied liquid dairy manure at 8000 gal/acre to the manured treatments. Cover crop growth could be described as reasonable, but not outstanding.
Fertilizer N requirements to optimize corn yields at the Embro site ranged from 89 to 107 lbs-N/ac where cover crops were not seeded. Where manure was not applied, oats and oilseed radish reduced N requirements by 15 to 32 lbs-N/ac. Peas apparently did not reduce N requirements where manure was not applied, but yields were increased by 14 bu/ac which may explain why N requirements were not reduced. However, where manure was applied all three cover crops effectively reduced fertilizer N requirement to 0, which suggests a N credit for each of the cover crops of at least 89 lbs-N/ac when manure was applied. The value of the N credit (N valued at $0.42 per lb of N)) for the cover crops where manure was applied was $37.40/ac, this would pay for the cover crop seed and drilling in most cases, and perhaps leave some net returns for your effort.
In our quest to improve cover crop cost effectiveness a few short term challenges lie ahead:
Remember you can get updates and a timely exchange of information on these and other topics by calling the OMAF CROPLINEat 1 (888) 449-0937.
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 (Mitchell, Ontario).
Manure Amount (gal/acre) |
Cover Crop |
2003 |
2003 |
2004 Corn Yield |
2004 Corn Yield |
Additional Fertilizer N Required to Optimize Corn Yield |
0 |
No Cover |
- |
- |
125 |
138 |
57 |
0 |
Peas |
594 |
29 |
137 |
140 |
17 |
4000 |
No Cover |
- |
- |
121 |
140 |
68 |
4000 |
Peas |
893 |
45 |
146 |
146 |
0 |
Table 2. 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, Ontario).
Manure Amount (gal/acre) |
Cover Crop |
2003 |
2003 |
2004 Corn Yield |
2004 Corn Yield |
Additional Fertilizer N Required to Optimize Corn Yield |
0 |
No Cover |
- |
- |
105 |
145 |
107 |
0 |
Oats |
2131 |
42 |
125 |
150 |
92 |
0 |
Oilseed Radish |
1723 |
47 |
119 |
133 |
75 |
0 |
Peas |
1122 |
41 |
110 |
159 |
114 |
8000 |
No Cover |
- |
- |
150 |
172 |
89 |
8000 |
Oats |
2696 |
72 |
171 |
171 |
0 |
8000 |
Oilseed Radish |
2821 |
90 |
166 |
166 |
0 |
8000 |
Peas |
1389 |
59 |
175 |
175 |
0 |
Acknowledgement: Evaluations and demonstration plots made possible by the Greenhouse Gas Mitigation project sponsored by Agriculture and Agri-Food Canada, Soil Conservation Council of Canada, and the Ontario Soil and Crop Improvement Association