ALL THINGS ORGANIC - Sweet clover for green manure

by Ian Cushon
February 19, 1998

In prairie organic crop production, green manure fallows are the foundation of successful crop rotations. Certified organic farmers cannot use commercial inorganic fertilizers to meet the nutrient needs of crops. Instead, organic farmers use crop rotations that include perennial legumes such as alfalfa, biennial legumes like yellow blossom sweet clover and annual legumes such as lentils and peas. The most popular of these is yellow blossom sweet clover. It is used extensively by organic farmers across the Prairies as a reliable source of nitrogen-rich organic matter.

Research shows that clover plowdowns can produce good yields in at least two following crops. Yellow blossom sweet clover is a biennial. It is underseeded with wheat and oats. In year one, the clover usually does not grow a lot, unless there is extensive moisture, in which case it can sometimes be competitive with the crop.

Yield loss and harvesting problems can result if the crop is overly productive in the first year. Harvesting a heavy green growth of clover in a mature crop can cause straight combiners a lot of frustration. Patience and header height control skills are sharpened when trying to cut above all that green growth to avoid plugging and return problems while still getting all those heads. An obvious solution is to swath. This eliminates most of the plugging and return problems. But leaving a large amount of clover in the swath with high quality cereals can leave a clover taste and smell in the resulting cereal products. You are undoubtedly familiar with that nice smell of fresh cut clover. That taste, however, while appetizing to ruminants, is a flavor some buyers do not want, so make sure you check. You might want to blend it with some other wheat to diminish its influence.

Plowing down clover requires appropriate equipment. A heavy disc is the first choice of most farmers. In a heavy stand, two passes may be required. Some farmers also use rotary mowers to cut the clover and leave the residue on the surface for later incorporation. This can reduce fuel costs and make subsequent tillage easier. However, there is some evidence of nitrogen loss through volatization of unincorporated decomposing green manure.

But enough of the downside. Clover is really a wonderful plowdown. It is relatively inexpensive to seed, has a deep taproot that draws nutrients from lower soil depths. It adds substantial nitrogen and organic matter to reduce soil erosion, increases water infiltration and soil biological activity and releases nitrogen and other nutrients for two or more crops. It will help produce high protein that attracts higher prices from wheat buyers. It does use moisture in the second-year growth, but with timely, early plowdown at about 10 percent bloom, water use is minimal, and soil water recharge can take place during the rest of the summerfallow season. Some farmers leave barrier strips of clover to catch snow to offset this moisture use. While clover has long been recommended as a plow down only for moister regions, farmers in all regions are using it successfully.

I recently talked to a farmer who cuts it for hay, chemical fallows, then direct seeds the next year into the clover stubble. He reports high protein levels and competitive yields with reduced fertilizer application. This was not an organic farmer, but a producer in southwest Saskatchewan who has found a way to make clover a valuable addition to his crop rotation.

Sweet clover weevil is an insect that can damage yellow blossom sweet clover. We have used clover on our farm for more than 20 years and sometimes see significant damage. Clover is especially vulnerable in year two, early in the spring, when temperatures are increasing and the shoots are just starting to grow. The weevil chews holes in the leaves and in some cases eats the whole plant. This can cause complete crop failures, but often the damage is minimal and the plants outgrow the insect damage.

Crop rotation and planting away from previous clover crops help reduce the damage. The other option is to switch to other clovers that are not prone to weevil damage. You can also consider some of those annual legume options, or even a perennial legume. As with most farming decisions, having a back-up plan is always a good strategy.

Ian Cushon
Moose Creek Organic Farm Inc.
P.O. Box 85
Oxbow, Saskatchewan
Canada, S0C 2B0

Tel. 306-483-5034
FAX 306-483-2799
Cell 306-483-8257
E-mail: coldridge@sasktel.net