Topics : Hay & Silage : Harvest Management
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Plant Factors Affecting Legume Harvest Management
The goal of most forage programs is to maximize economic yield of nutrients while ensuring stand persistence. Frequent cutting produces high-quality forage while less frequent cutting generally results in increased stand longevity. Therefore, harvest management of perennial legumes such as alfalfa, red clover, and birdsfoot trefoil requires a compromise between quality and persistence. The intensity at which these forage legumes are harvested should depend on the nutrient needs of the livestock that will be consuming the forage as well as the life expectancy of the stand. Because of sudden changes in weather and year-to-year variation in growing seasons, there is no simple rule to follow when making a decision to cut. Decisions on when to cut have to be made based on a sound understanding of how a plant grows and survives.
The stage of maturity at which forages are cut can certainly influence the quality of that forage. Most forage crops decline in nutritive value as they mature. A short delay in harvest can result in forage of much lower quality. However, cutting when the plants are immature in order to improve quality often causes a reduction in yield. In addition, continuous early harvests can reduce stand longevity. If a forage stand is to be kept for only a couple years, forages may be harvested for higher quality than if a long-lived stand is desired.
The initial growth of perennial forage legumes in the spring and after every harvest depends on energy (food) reserves stored in the taproots and crowns of the plants. High energy reserves are important for fast regrowth, which results in higher yields. Substantial energy reserves are also needed for the development of cold hardiness, which allows the plant to persist during the winter and still have enough energy to provide for good spring growth. Research has shown that energy reserves are usually highest when the plant is in the full-bloom stage and usually lowest a short time after cutting, when the plant is growing rapidly.
Indicators on Which to Base Cutting
The stage of plant development is generally a reliable predictor of energy reserve status and when the plants should be harvested. However, when the weather is extremely cool and cloudy for an extended period and flowering is delayed, energy reserves nevertheless continue to increase. Under these conditions, which often occur in May, the development of new shoots from the crown indicates that it is time to cut. A delay in harvesting after the new crown shoots begin to grow can delay regrowth and reduce yield of the next harvest. Under normal growing conditions, particularly in the summer, the development of new crown shoots may not occur until well after full bloom or even after seed set. Therefore, relying on the appearance of crown shoots to begin harvesting is not always advisable.
Relying on the calendar alone to make a decision to harvest is unwise. Light, temperature, and moisture vary from year-to- year and have a direct effect on maturation. The most consistent method to determine when to harvest is the stage of plant development in conjunction with calendar date, since seasonal weather variations can alter the relationship between stage of development and energy reserve.
Descriptions of legume development stages
It is important to use terms such as half-bloom or mid-bud stage accurately, since recommendations are often based on stages of maturity. The description of a stage of maturity refers to the whole field, not to an individual plant. The most accurate method to determine the stage of development is to count 100 stems randomly selected from the field and determine the average stage of development.