Agronomic benefits of alfalfa mulch applied to organically managed spring wheat

M. J. Wiens¹, M. H. Entz¹, R. C. Martin², and A. M. Hammermeister²

Field experiments were established at two locations in Manitoba in 2002 and 2003 to determine N contribution, moisture conservation, and weed suppression by alfalfa mulch applied to spring wheat (Triticum aestivum L).

Mulch treatments included mulch rate (amount harvested from an area 0.5´, 1´ and 2´ the wheat plot area), and mulch application timing (at wheat emergence or at three-leaf stage).

Positive relationships were observed between mulch rate and wheat N uptake, grain yield, and grain protein concentration. At Winnipeg, the 2´ mulch rates (3.9 to 5.2 t ha-1) produced grain yields equivalent to where 20 and 60 kg ha-1 of ammonium nitrate-N was applied in 2002 and 2003, respectively.

Where mulch and ammonium nitrate produced equivalent grain yield, grain protein in mulch treatments was often higher than where chemical fertilizer was used. N uptake was also observed in the following oat (Avena sativa L.) crop. The highest mulch rate (2´) produced higher N uptake and grain yield of second-year oat compared with ammonium nitrate treatments. N use efficiency of mulch-supplied N by two crops over 2 yr [calculated as (treatment N uptake - control N uptake)/total N added] was between 11 and 68%.

Mulch usually suppressed annual weeds, with greater suppression with late- than early-applied mulch. Increased soil moisture conservation was observed with high mulch rates (= 4.3 t ha-1) at three sites. Alfalfa mulch holds promise for low-input cropping systems when used on wheat at the 2´ rates.

¹ Department of Plant Science, University of Manitoba, Winnipeg, Manitoba, Canada, R3T 2N2;
² Organic Agriculture Centre of Canada, Nova Scotia Agricultural College, P.O. Box 550, Truro, Nova Scotia, Canada B2N 5E3

Can. J. Plant Sci. 86: 121-131