Responses of Medicago sativa and M. falcata type alfalfas to different defoliation times and grass competition

Incorporating alfalfa into rangelands can enhance the quantity and quality of forage production. We evaluated the impact of clipping timing and selective clipping on two M. falcata (Anik and Yellowhead) and one M. sativa type alfalfas (Vernal) near Mandan, North Dakota, USA. Cultivars were space-planted into an existing mixed grass prairie and clipped at the mid-bud, flower or flower and subsequent vegetative stages. In each clipping treatment, half of the plots had only the alfalfa clipped and half had both the alfalfa and the associated native vegetation clipped. Plots without alfalfa were also included to evaluate the impact of alfalfa on grass and forb biomass. Including Yellowhead increased total productivity by 38 to 185% without lowering the productivity of the grass or forb biomass components. Plots with Yellowhead produced 17 to 26% more total biomass than the next highest entry every year. In 2003 and 2005, alfalfa biomass was increased 1.5 to 2.7 times by clipping only alfalfa in the flower and regrowth stages compared with a mid-bud clipping of only alfalfa. Vernal and Yellowhead generally produced more total biomass when clipping was deferred to the flower stage, but clipping Anik in the mid-bud stage produced as much or more total biomass than did the later clipping treatments. Selective clipping of the alfalfa did not have a consistent impact on yield. Yellowhead appeared to be a good choice for incorporating into rangelands. Producers with Yellowhead or Vernal should consider delaying defoliation until flowering to maximize productivity. Key words: Grazing-type alfalfa, hay-type alfalfa, defoliation timing, biomass productivity