– Jeff McCutcheon, Knox County Extension Educator, Ag & NR
Forage producers understand that the stage of growth determines when to harvest. For example, to optimize both yield and quality, grasses should be harvested in the boot to early seed head emergence time period and legumes should be harvested in the bud stage. But is this also important in the seeding year? Since we spent so much time and money to plant the forage shouldn’t we treat it carefully, take fewer grazings/cuttings, to give it a chance to establish? To answer these questions let’s review grass and legume growth.
There are three basic growth stages in grasses that producers should be able to recognize, they are: 1) vegetative; 2) elongation; and 3) reproductive.
The vegetative stage is leaf growth. The growing point is compact and near the soil surface. Grazing/cutting at this time typically only removes older parts of the leaves. Each tiller will sustain a critical number of leaves. Newer leaves shade older leaves. Generally older and lower leaves die at the same rate as new leaf growth. Shading by growing leaves at this stage can cause small, non-flowering tillers to die.
Elongation, as its name implies, is the stage where the stem lengthens. Some call it jointing. Stems elongate in response to changing day length and temperature. The growing point is elevated and can be removed by grazing/clipping. If the active growing point is removed, then leafy growth will develop from dormant basal buds as new tillers. Most cool season grasses produce reproductive stems only in the spring after a period of short days/long nights and cold weather, which means after removing the seed stems; only leafy vegetative growth will be present for the remainder of the growing season.
When the developing seed head is in the uppermost leaf sheath, the plant has reached boot stage. This is the start of the reproductive stage. This stage is when the seed head develops, pollination occurs, and seed develops. As the seed heads develop, they produce plant hormones which retard the development of basal buds. This “apical dominance” reduces forage re-growth. Removing seed heads soon after they emerge will reduce tiller death due to shading and reduce the length of time that new tillers are suppressed by dominant reproductive tiller.
Legume growth is classified a little differently 1) vegetative, 2) bud, and 3) flowering. These stages are controlled by day length and temperature. Reproductive development will occur during each growth cycle. Legumes have many potential growth points. These are located at the stem tip, leaf-stem junction and most legume species also have dormant buds at the crown. These crown buds will produce new, leafy growth when growing stems are grazed or clipped.
The location of the growing points determines the legume’s response to grazing/clipping. The growing points on alfalfa, red clover, and birdsfoot trefoil are susceptible to removal by grazing/clipping. Re-growth will come from dormant crown buds and lower stem branches when the growing stems are grazed or cut. White clover’s growing points are on stolons and are too low to be removed by grazing, but can be damaged by trampling.
Principles that apply to established stands also apply to new seedings. Most cool season grasses need a cold period to induce flowering. New seedings will not show reproductive development during the seeding year. These could be harvested when leaves are fully elongated but before leaf death occurs. To encourage tillering, grazing or clipping when grasses reach 6-8 inches would be beneficial. Grazing should be done on firm soils and with a high stocking density and short duration. In other words, use enough livestock to reach your target residual in 3-5 days. Over grazing should be avoided.
Won’t grazing/cutting early effect root development? Remember the “take half, leave half” rule? Everyone who has attended a grazing school has seen the data from the classic study by F.J. Crider that was published in 1955. This data showed that in grasses if you removed 40% of the leaf volume you would not stop root growth. Removing 50% of the leaf volume only stopped 2% of the roots growing. At 60% leaf removal 50% of the roots stopped growing. All of the roots stopped growing at 80% leaf removal. If anything, err on the side of leaving just over half of the leaf area as residual with a new seeding.
Spring seeding of alfalfa should be harvested in the bud stage to optimize both yield and quality. Depending on the weather this could happen 60-70 days after emergence. If seeded with a companion crop then it should be harvested as hay when the companion crop is in the boot stage. After the first cutting follow a normal cutting schedule. Lots of data suggest that with a new alfalfa seeding you should avoid a late cutting after the first week of September in Ohio.
Photo above taken 6/7/06: Alfalfa field seeded with a companion nurse crop of oats in late March, harvested the first time while the oats were in boot stage on May 30, 2006.