Capturing the Potential of Alfalfa

By Matthew Wiens, M.Sc.

Matthew Wiens, from the University of Manitoba, has just completed a study of the benefits of "strip farming" with alfalfa. Strip farming allows producers who chose not to take years out of grain production to gain some of the advantages of alfalfa production.

Including alfalfa in a crop rotation offers substantial benefits. Alfalfa can suppress weeds such as wild oats, Canada thistle and green foxtail. Alfalfa forms partnerships with bacteria that fix nitrogen. Tapping this source of nitrogen does not require the use of large amounts of economically, environmentally and socially expensive fossil fuels. The nitrogen is then available for the crops that follow.

So why do so few producers include alfalfa in their rotations? The benefits of alfalfa are balanced against liabilities. Alfalfa can deplete moisture. Long-term alfalfa stands can reduce phosphorus and sulfur availability in the soil. The main limitation, though, for many organic producers who do not have livestock is that an alfalfa field produces no cash crop unless large amounts of valuable nutrients are exported from the field.

Strip farming uses alfalfa as an organic nitrogen fertilizer in grain crops. Alfalfa is grown in strips across the field. Annual crops are grown between the alfalfa strips. The alfalfa is harvested and applied directly to the annual crop strips. Eventually, the alfalfa strips are moved. A three year alfalfa strip is suggested for greatest benefit.

Photo 1. Centre plot received 1.9 tons/acre of alfalfa (dry weight) (4300 kg/ha), bearing 105 lb N/ac (118 kg/ha). Plot is noticeably darker green than pathways, indicating N response from mulch. Mulch was applied June 13, 2003 at three-leaf stage of wheat and photo was taken on July 9, 2003. The dark green plot behind and to the left received 54 lbs N/ac (60 kg/ha) as broadcast ammonium nitrate.

In the University of Manitoba study, Matthew paid particular attention to the effect of alfalfa mulch on AC Barrie wheat. He harvested the alfalfa strips with a flail mower and applied the mulch to the wheat crop at different times and at different rates. He repeated his study at 4 sites, over 2 years.

The mulch was applied to the wheat plots either before the wheat emerged, or at the three-leaf stage. Three different amounts of alfalfa mulch were tested: the amount that would be generated 1) if alfalfa and wheat were in equal sized strips, 2) if the alfalfa strips were twice as wide as the annual crop, or 3) if the alfalfa strips were half as wide as the annual crop.

Alfalfa did not smother the wheat crop even when the amount applied was over 2.5 tons per acre of dry matter (5700 kg/ha). Wheat received a nitrogen boost from the alfalfa; treated plots were a darker green. Both nitrogen uptake and wheat yield increased as the amount of alfalfa was increased. Wheat that received the most alfalfa mulch yielded nearly twice as much as wheat that received no mulch.

Alfalfa mulch suppressed weeds when applied at higher rates. At low rates, weed numbers were higher than in plots without alfalfa mulch. It appears that small amounts of alfalfa improve the conditions for weed establishment, perhaps by reducing moisture loss at the surface. Higher rates discourage weeds, perhaps by shading or by creating a physical barrier between the soil and the surface.

Matthew has shown that alfalfa can be used as mulch on spring wheat to get value from alfalfa hay. This opens the door for broader thinking about rotations. Organic producers may find additional benefits from such diversification, including reduced erosion potential and greater habitat for beneficial organisms.

This study also has important implications for reducing tillage in organic systems. Tillage to incorporate the alfalfa green matter was not necessary to gain substantial nitrogen and weed control benefits. Green manure crops balance the benefits of nitrogen and organic matter build up, and of weed suppression with the risks of tillage. This study may help shift this balance, and be another step forward on the path to healthy soils.

Matthew Wiens recently completed a Masters of Science at the University of Manitoba, under the supervision of Martin Entz. The research on the potential for alfalfa mulch was conducted in collaboration with Ralph Martin and Andy Hammermeister of the Organic Agriculture Centre of Canada. Matthew may be reached at umwiensm@cc.umanitoba.ca

Brenda Frick, Ph.D., P.Ag., is the Prairie Coordinator for the Organic Agriculture Centre of Canada at the College of Agriculture, University of Saskatchewan. She welcomes your comments at 306-966-4975 or via email at brenda.frick@usask.ca .

This article first appeared in The Western Producer, and is published here on the OACC website with permission.