By Shelby Gruss
Alfalfa hay harvest this fall was significantly delayed, and in many cases canceled, due to the unusually high number of rainy days throughout September. Excessive rainfall prevented many producers from taking a final cutting before winter. As temperatures cool and alfalfa begins to go dormant, some may be considering grazing those fields.
Before turning cattle onto dormant alfalfa, the first question should be: Do we need to? Pastures currently have abundant growth in many areas, and hay inventories may be adequate to meet winter feeding needs. If forage supplies are sufficient, grazing dormant alfalfa may not be worth the risk this year.
First, the same wet conditions that delayed harvest have also resulted in many yellowing alfalfa stands heading into winter. As discussed in “Yellow alfalfa and wet soils: What to do now?”, yellowing can indicate stress caused by several factors, including nodulation damage and nitrogen deficiency, crown and root injury, and disease pressure from pathogens such as Aphanomyces. Regardless of the specific cause, yellowing is a clear signal that the stand has been under stress.
Second, grazing dormant alfalfa can add additional stress to plants that are already compromised. While grazing after dormancy does not necessarily reduce root carbohydrate reserves, removing top growth can increase the risk of winter injury. Residual stubble helps trap snow, which provides insulation during cold weather. Stubble may also remain above ice layers that form after winter precipitation events, allowing plant tissues to continue exchanging gases under otherwise stressful conditions.
Source : iastate.edu