Choosing The Right Cutting Height For Alfalfa Stands

FAYETTEVILLE, ARK.
   Alfalfa growth morphology is different from grass morphology, which features protected growing points and a fibrous root system. Likemost leguminous plants, alfalfa develops a deep taproot that serves as carbohydrate reserve for regrowth after defoliation. Regrowth is initiated from buds that are lined around the crown and from axillary buds that are located further up on tillers. Unlike grasses, forage legumes can be cut relatively low in height but, in turn, not very frequently to preserve root carbohydrate necessary for regrowth. Specific cutting heights can be achieved with modern equipment, and it is a good idea to review some principles of harvesting alfalfa.
   Regrowth of alfalfa tillers early in the growing season comes mostly from crown buds. Growth from the axillary buds is also generated, but this growth is less vigorous than that coming from the crown buds. Since axillary buds are located higher up in the canopy, there are questions related to cutting heights and effects on yield and quality. Research has indicated that leaves emerging from axillary buds contribute less to overall yield than tillers stemming from crown buds. In addition, these leaves contribute much less to photosynthesis and may even shade lower portions of the stem. It is, therefore, recommended to cut at 1-2 inches throughoutmost of the growing season to achieve a good compromise of yield and quality. However, a short cutting height is not always the recommended practice. If alfalfa stands emerge weakened from the winter months, cutting height has to be somewhat increased to account for the necessity of stand recovery.
   During the course of the growing season, stress factors should be kept to a minimum to achieve high yields and quality. It is mandatory to keep soil fertility and weeds in check as much as possible. Abiotic stresses which may occur during the growing season, such as drought or lack of sunlight, also have to be considered for making crop management decisions. Good overall forage management will ensure stands remain healthy over the years. This includes monitoring of soil fertility (macro- and micro-nutrients), lime requirements, insect control and weed control where necessary. Stand longevity will likely not be compromised through short cutting heights if these general management guidelines are taken into account. It has been shown that cutting height affects milk yield for example, but the increase in forage quality resulting from a higher cutting height does not offset enough to justify lower yields. Therefore, a low cutting height is still recommended. This will also help in reducing weed incidence, which would otherwise compromise dry matter production and forage quality.
   Cutting regimens in fall before the first frost occurs require a different approach. As a reminder, alfalfa stands need to accumulate carbohydrates in their taproot to have enough reserves for the winter months and first regrowth the following spring. Killing frosts may occur sometime in the middle of October in northern Arkansas. Alfalfa stands should not be harvested within 4-6 weeks leading up to that date, because root reserves would be depleted due to the ensuing, albeit reduced, regrowth. Harvests during the year should be scheduled so that the final fall harvest can take place no later than September 1. After the killing frost occurs, stands can be harvested, but a stubble height of 4-6 inches should be maintained for protection during longer periods of snow, albeit those rarely happen in Arkansas. While the harvested material at that point may be hard to cure for hay, silage or baleage are good options to make use of post-freezing cuts. ∆
DR. DIRK PHILIPP: Assistant Professor/Department of Animal Science, University of Arkansas