No-till alfalfa stand termination strategies: Alfalfa control and wheat and barley production

Crop rotations involving perennial alfalfa (Medicago saliva L.) present the unique problem of terminating the alfalfa stand. Intensive tillage current ly used to terminate alfalfa increases the risk of soil erosion and reduces many of the rotational benefits from alfalfa. Inadequate alfalfa terminati on results in severe competition to the following crop by surviving alfalfa plants. Field experiments were conducted in Manitoba between 1991 and 1993 with the following objectives: I) to investigate no-till vs. tillage manag ement systems for successful alfalfa termination, 2) to compare fall vs. sp ring alfalfa termination, 3) to compare the performance of barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.) seeded into alfalfa residue, a nd 4) to determine the relationship between alfalfa escapes and grain yield . Fall termination produced higher grain yields than spring termination, ho wever this advantage was only achieved with the better termination treatmen ts capable of lowering alfalfa regrowth below a critical level. The best he rbicide treatment tested here was glyphosate at 1.78 kg a.i. ha(-1) Success ful treatments would have to reduce residual alfalfa basal crown area (a me asure of alfalfa regrowth potential) after cereal grain harvest to below 2% . Alfalfa escapes reduced yield of following wheat and barley crops similar ly (P > 0.05). When alfalfa termination treatment method allowed some regro wth, in-crop herbicide treatments significantly reduced alfalfa basal crown area. Results of this study indicate that it is feasible to terminate alfa lfa with herbicides in the absence of tillage, however an overall cropping strategy, including adequate consideration of weeds present in alfalfa fiel ds at time of termination, must be considered.