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Yield and Regrowth Characteristics of Alfalfa Grazed by Steers during Spring and Summer

Dep. of Crop & Soil Environ. Sci., Virginia Polytechnic Inst. and State Univ.

^* Corresponding author.

Current recommendations for grazing alfalfa (Medicago sativa L.) include grazing for a few hours or days when plants are near a haycut stage. This study investigated the influence of continuous grazing of ‘Arc’ alfalfa by steers (Bos taurus L.) during spring (38 d), summer (26 d), or both on plant growth, potato leafhopper (Empoasca fabae Harris) population, and subsequent hay yields. Three grazing and one nongrazed treatments were imposed during 1986 and 1987 on Groseclose silt loam (clayey, mixed, mesic Typic Hapludults). Treatments included: (i) spring grazing started when alfalfa height was approximately 10 cm, followed by three hay harvests; (ii) hay harvested twice, followed by summer grazing that started when alfalfa height was approximately IS cm, followed by one hay harvest; (iii) both spring and summer grazing as described above with hay harvested after the second and fourth growth cycles; and (iv) nongrazed with hay harvested four times. No grazing was imposed during 1988 when hay was harvested four times to measure the influence of previous grazing. In 1986 and 1987, hay yields following spring grazing (6.61 Mg ha^–1) were not different than those for nongrazed (6.47 Mg ha^–1). Fall hay yields following summer grazing (1.39 Mg ha^–1) and spring plus summer grazing (1.34 Mg ha^–1) treatments were lower than for spring grazing (1.85 Mg ha^–1) or nongrazed treatments (1.80 Mg ha^–1). Grazing had no influence on root total nonstructural carbohydrates at the end of Year 2. Grazing for 2 yr by any treatment had no effect on yields during Year 3 when alfalfa was harvested four times for hay. Potato leafhopper density increased during regrowth following summer grazing to a level of 11.5 insects per sweep that required insect control, whereas little buildup occurred following hay harvest during the same growth period. Our data show that grazing, begun in spring or summer at a young vegetative stage, can continue for a time equal to a growth cycle in either or both seasons of at least 2 yr with no detrimental effect on alfalfa hay yield in Year 3.

Received for publication February 5, 1990.