Management of summer grazed alfalfa

Alfalfa (Medicago sativa, L. cv. Arc) productivity, regrowth, and quality as affected by summer grazing management and K fertilization (560 kg K/ha) was investigated with sheep. Sheep grazed alfalfa for 2-, 4-, or 6-weeks following a 2 July hay cut when regrowth was 450 kg/ha dry matter; beginning in early bud for 10 days (delayed); at early bloom for 7 days (conventional); and non-grazed (hay removed at 1/10 bloom).

Forage yields, leaf area index (LAI), tiller numbers, crude protein (CP), and in vitro dry matter digestibility ( IVDMD) generally declined during grazing. Neutral detergent fiber (NDF), lignin, and cellulose content generally increased on all grazing systems. Forage at the end of grazing was nigher in percent leaf, CP, Mg, P, Kand IVDMD and lower in cellulose, lignin and NDF on 2-, 4-, and 6-week systems than forage remaining on the other systems.

A late summer hay cut at 1/10 bloom was made on 2-week, delayed and non-grazed systems. Grazing by the 2-week system decreased yield, LAI, and plant height but forage quality as measured by percent leaf, NDF, lignin, and cellulose was increased, compared to the non-grazed system. Grazing by the delayed system resulted in similar results as the 2-week system but differences were not as great. There were no differences in IVDMD.

On 1 Oct., 4-week and conventional grazing systems had reduced yields, plant height, tiller number, and root total nonstructural, but had no significant effect on forage quality. Conventional grazing resulted in the least damage to yield and productivity measurements. Percent weed increased in 2-, 4-, and 5-week systems in fall but no differences were measured in percent weed, yield, or tiller number in regrowth the following spring.