Seeded Legume Cover Crops
Late Season Production
|Location||Heat (GDD)||Rain (mm)|
Legume cover crops are low-growing plants that are grown in association with grain and vegetable crops. Benefits of cover crops include adding N to soils, weed suppression, reduced soil erosion, and reduced N leaching. Cover crops are used all over the world.
Cover crops can be grown after crop harvest to take advantage of heat and moisture before killing frost. Normally the benefits of this heat and moisture is lost to weeds.
This table (at right) shows the number of growing degree days (GDD) and precipitation available after winter wheat harvest at various locations in Manitoba. 400 GDD are considered necessary to grow a late-season cover crop.
There are two main classes of cover crops:
- Seeded cover crops
- Self-seeding cover crops
Seeded Cover Crops
Seeded cover crops can be grown during the cropping year in two ways: as relay crops or double crops.
- In relay cropping, a legume crop, or relay crop, is seeded directly into the established first crop.
- E.g. alfalfa and red clover can be sown as relay crops into winter wheat and fall rye in the spring after they are established.
- In double cropping, a grain crop and legume are grown in succession in the same field without overlapping.
- E.g. chickling vetch and black lentil can be double cropped after winter wheat and fall rye are harvested.
In Ontario and Quebec, farmers have long used red clover cover crops in winter wheat production. The system involves seeding red clover in early spring, just as the winter wheat is regrowing after winter. After winter wheat harvest, red clover grows for 4 to 6 weeks and adds significant amounts of N to soils.
Trials in Manitoba have shown that this systems can be effective here, especially in the Red River Valley where moisture shortages are typically not a limitation.
Double-cropping, where legumes are seeded after winter wheat harvest can also provide significant N benefits to following crops.
For more information on seeded cover crops, see http://www.sarep.ucdavis.edu/ccrop/
A research trial was conducted at two locations to determine the feasibility of cover cropping in Manitoba. In this experiment, red clover and alfalfa were relay cropped with winter wheat and fall rye. Chickling vetch and black lentil were double cropped with winter wheat and fall rye. Management was as follows:
|Winter wheat seeding rate||1.5 bu/ac|
|Fall rye seeding rate||1.5 bu/ac|
|Red clover seeding rate||11 lb/ac|
|Alfalfa seeding rate||9 lb/ac|
|Chickling vetch seeding rate||83 lb/ac|
|Black lentil seeding rate||38 lb/ac|
|Fertilizer||20 lb/ac P with seed, 80-100 lb/ac N broadcast as 34-0-0 after cereal emergence in spring|
|Inoculant||proper strain of inoculant used with all legumes|
The presence of cover crops reduced winter wheat and fall rye grain yield by 3.4 to 3.8% when compared to these cereals grown without the cover crops (data not shown). This yield reduction was not significant and was similar to that found by other researchers. The potential for reduction in grain yield is greater where soil moisture is limiting. Cover crop yield potential is also greater when moisture is not limiting. In this experiment red clover produced the most forage and had the fastest daily growth rate (data not shown). Black lentil produced the least forage although this difference was not significant. Forage yield was similar for alfalfa and chickling vetch, however, chickling vetch had a faster growth rate. For information on the N fertilizer value of the cover crops see The Fertilizer Replacement Value of Legume Cover Crops.
|Crop||Grain Yield||Forage Yield|
|Winter wheat||60 bu/ac||-|
|Fall rye||79 bu/ac||-|
|Red clover||-||1031 lb/ac|
|Chickling vetch||-||664 lb/ac|
|Black lentil||-||565 lb/ac|
- If moisture and heat are not limiting in your area try a cover crop after cereal harvest.
- Cereal and cover crops can be planted at 100% recommended rates.
- Legume cover crops must be inoculated with proper bacteria to achieve N benefits.
Further Reading: J.R. Thiessen Martens, J.W. Hoeppner, and M.H. Entz. 2001. Legume cover crops with winter cereals in southern Manitoba: Establishment, productivity, and microclimate effects. Agronomy Journal 93: 1086-1096.
This page created August 2004.