Weed Encroachment in Established Alfalfa as Affected by Cutting Frequency

Abstract

Crazing‐tolerant alfalfa (Medicago sativa L.) cultivars are more persistent than hay‐type cultivars under severe grazing pressure but the influence of defoliation on weed encroachment is not well defined. Our objective was to determine the effect of rest interval between cuttings on encroachment of large crabgrass [Digitaria sanguinatis (L.) Scop.1 or common bermudagrass [Cynodon dactylon (L.) Pers.] into a grazing‐tolerant alfalfa cultivar. We used small‐plot field experiments with four replications of ‘Alfagraze’ alfalfa to evaluate nine treatment combinations of (i) harvesting at 2‐, 4‐, and 6‐wk intervals, and (ii) overseeding with common bermudagrass, large crabgrass, or nothing. Experiments were conducted for 3 yr at Eatonton, CA, on Davidson loam (clayey, kaolinitic, thermic, Humic Paleudult) and at Athens, CA, on Cecil sandy clay loam (clayey, thermic, kaolinitic, %pic Hapudult). Alfalfa yields were similar at both locations when harvested at 4‐ or 6‐wk intervals. Crass invasion was virtually nil with the 4‐ and 6‐wk treatments at Eatonton but at Athens there was some grass encroachment, probably a result of soil compaction,which adversely affected overall alfalfa growth. Cutting at 2‐wk intervals reduced alfalfa yields to 50% of the 4‐ or 6‐wk cut treatments and resulted in heavy bermudagrass encroachment during the third year. Alfalfa cut every 4 or 6 wk persisted well but stands were reduced when cut every 2 wk Results suggest that frequent defoliation will not only reduce alfalfa yield but also favors grass encroachment. Thus, defoliation methods that keep alfalfa canopies at a high level would appear to be desirable in resisting bermudagrass and crabgrass invasion and increasing yield of grazed alfalfa. Research Question Recommended management for alfalfa pasture is rotational stocking to graze off the forage in a few days followed by a 5 to 6 wk rest period. Unfortunately, in actual farm practice, this recommendation is often modified with shorter rest periods or continuous stocking, which may result in grass invasion and alfalfa stand loss. The present study evaluated the effect of rest interval between cutting on encroachment of large crabgrass and common bermudagrass in a sward of a grazing‐tolerant alfalfa cultivar at two locations in north and central Georgia. Literature Summary Alfagraze is much more tolerant of continuous stocking at high grazing pressure than hay‐type alfalfa cultivars. However, under these conditions in the southeastern USA, invasion of the sward by large crabgrass and common bermudagrass is a serious problem. In contrast, under a hay‐cut system, rapid regrowth by alfalfa provides the sward with enough shade to reduce grass establishment competition. Information is lacking in the southeastern USA on the effect of rest interval between cuttings or grazings on encroachment of warm season grass weeds in alfalfa. Study Description Alfalfa yield, persistence, and weed invasion were determined for Alfagraze alfalfa grown alone or overseeded with large crabgrass or bermudagrass an...

Yield, Quality, and Persistence of Grazing‐ and Hay‐Type Alfalfa under Three Harvest Frequencies

“…These data are similar to those reported by Kust and Smith (1961), who found that harvesting alfalfa four times per year in Wisconsin led to lower yields than when harvested three times. Hoveland et al (1996) in Georgia and Sheaffer et al (2000) in Minnesota showed that the optimum harvest interval for alfalfa is about 35 d.…”

“…Subsequent research with Alfagraze showed that it tolerated weekly harvests in the greenhouse better than ‘Florida 77’ (Brummer and Bouton, 1992). An extension of this work in the field by Hoveland et al (1996) showed that Alfagraze had equal yields when harvested every 4 wk vs. every 6 wk during the growing season. Based in part on the research of Hoveland et al (1996), farmers in the lower Midwest often plant Alfagraze and other grazing‐type alfalfas, expecting that more frequent harvests (and in turn better quality forage) are possible with these cultivars without decreasing yields or stand persistence.…”

Allelopathic Effects of Cereal Rye on Weed Suppression and Forage Yield in Alfalfa

“…Weeds compete with alfalfa for light, water, and nutrients [4] [5] and consequently reduce yield and forage quality [6]. Newly established stands are especially more vulnerable [7], but older stands [8] and frequently cut stands [9] [10] are also affected. Therefore, the first year of planting is very crucial in terms of crop establishment, biomass yield, and stand persistence of alfalfa.…”

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

“…For instance, alfalfa survival was lower in treatments with a single yearly defoliation of alfalfa in Conservation Reserve Program than in treatments that had three to four cuttings per year (Sheaffer et al 1997). A lower frequency of defoliation in mixed alfalfa-grass stands improved yield (Bittman et al 1991;Hoveland et al 1996) and decreased grass encroachment (Comstock and Law 1948;Bates et al 1996;Hoveland et al 1996).…”