Don't Let Spring Pastures Win Race

By Jane Fyksen, Crops Editor
Wednesday, April 25, 2007 6:12 PM CDT

Pasture managers are in a race with Mother Nature in the spring.

It's the time of year when keeping pasture grasses in a vegetative state can be the hardest. But managing pasture growth early in the growing season is important for maintaining high quality and high quantity forage production throughout spring, summer and fall, says Mark Landefeld, Ohio State University Extension Educator in Monroe County, Ohio.

"Spring flush" occurs in cool-season grasses because temperatures are optimum for growth and the most important "nutrient" - water - is readily available.

Graziers should start moving animals through the first paddocks when soil condition permits and pasture plants are a few inches tall. Rotate livestock through paddocks at a pace that gives them just enough time to graze the tops off the forage. This will help stagger forage growth, keep more plants in a vegetative state and reduce seed head formation as the season progresses.

While this is a good strategy, keeping ahead of grass growth when temperatures are warm and the growth explosion occurs is easier said than done, Landefeld admits.

"In the first rotation each spring livestock preferences are not very noticeable, but as grasses and legumes grow, livestock preferences for certain forages begin to show and uneven grazing patterns appear. Problems arise in many paddocks because fescue is mixed with orchardgrass, bluegrass, ryegrass and clover. If allowed, cattle will eat other grasses and clovers to the ground and leave the fescue standing," he says.

"Using heavy stocking density on small paddocks at this time may help, but moving livestock frequently will be necessary to make this approach work," he notes.

After the early spring grazing period, if you fescue has been refused to this point, it will not likely be grazed in the next rotation or in the remainder of the summer rotations, Landefeld maintains. If large amounts of ungrazed fescue persist in paddocks, clipping should be considered to stop seed-head production, reduce shading of other plants in the pasture and allow more favorable grass/legume growth.

Soil that's too wet can complicate grazing management, too. "Pugging" the soil occurs when livestock walk on water-soaked ground. Care should be taken so pugging doesn't occur over large portions of the grazing area. Severe pugging can decrease pasture growth for weeks, maybe months. Fencing livestock onto a heavy-use pad or using a sacrifice area to feed the hay in, if conditions like this exist, may be the best option, even though you might be anxious to reduce the chore of feeding harvested feed.

Landefeld says paddocks that are well drained or those that are predominantly fescue are good choices to use early, too. If minor pugging occurs, plant production will not decline very much. "It may even boost production of clovers because opening the soil can stimulate new plant growth if viable clover seeds are present," he notes.

Forages in early-spring pastures are extremely lush. Plant material is only about 15 percent dry matter, while crude protein is generally high, possibly 25 to 30 percent. Hay or supplemental feed should still be provided during early rotations to be sure adequate dry matter is in animals' diet.

He cautions cattle producers to be sure to supply free-choice mineral mixes with adequate amounts of magnesium (12 to 14 percent Mg in the mix) at this time of year and be conscientious about moving the minerals along to each new paddock, too. This reduces the chance of grass tetany in livestock grazing grass-dominate paddocks.

Cool-season grasses attempt to reproduce in the spring by shooting seed heads. If plants are allowed to flower and set seed, the quality of forage and production may be greatly decreased the remainder of the growing season, Landefeld warns. Again, regulating the frequency and time livestock spend in each paddock will keep grass in a vegetative state; that's the pasture manager's objective.

If legumes are the predominant species in a paddock, don't turn livestock in while plants are wet. Bloat may occur. Wait until the surface moisture dries and feed hay before turning livestock in those paddocks to reduce chances of bloat.

"It is important look ahead and monitor growth in your paddocks," he stresses. "Selected paddocks could be made into hay and brought back into the rotation later, but the grass should really be cut no later than the boot stage to keep the plants in a vegetative growing stage." He admits there's a problem with that strategy; if you mow paddocks when you should to keep maximum vegetative production in May, it's difficult to get the grass dry to make hay. Many graziers leave paddocks grow until haymaking weather arrives, usually June, and make hay from the forage that couldn't be grazed at the proper time.

"Be careful not to set aside too many paddocks where you make hay because you may find yourself in a deficit situation for forage the correct height for grazing in late June," he remarks. Regrowth in those set-aside fields may not be ready to graze again until mid-July depending on temperatures and moisture availability.

Clipping some paddocks a few days apart in May could be advantageous, even if hay can't be made. This will keep plants vegetative and highly productive so uninterrupted rotations can continue the next time around.

Wise use of fertilizer in the spring, says Landefeld, is an important part of pasture management. He warns against heavily fertilizing pastures early in the spring and says late May or early June is a better time. "This will have several benefits," he lists. "First, you are not adding to the excess growth problem most managers have in the spring. Second, you will be feeding the forage plants at a time before warmer and drier weather is about to begin. The plants can use the nutrients at this time to maximize productivity before the 'summer slump' occurs in July and August. This provides additional growth at a time when it will be needed by the livestock, and quality of this forage should still be very high."

Landefeld stresses that the type of forage and amount of forage produced in paddocks is directly related to management practices. "Look at your paddocks and project in your mind what you think they will look like two to three weeks in the future based on the growing conditions. Then match your projections with what you observe. Doing this on a regular basis throughout different stages of the growing season helps one become a better grass manager," he says.

Rory Lewandowski, Landefeld's counterpart in Athens County, Ohio, says before pasture growth explodes, now is the time to review some basic plant morphology (external changes) and physiology (internal/chemical changes).

To properly manage pasture, producers must understand tillers, which Lewandowski says are composed of a growing point, leaves, roots, stems, nodes (joints) and dormant buds. "Individual tillers and individual leaves on a tiller both have a limited life span. Depending upon when in the growing season a tiller is developed, the life span could be up to a year, but frequently is measured in terms of months or even weeks," he notes.

"A tiller population in a pasture is maintained by continuous replacement and development of tillers. The story is similar for leaves on an individual tiller," he points out.

Looking at the physiology behind reproductive growth, Lewandowski says that while reproductive tillers become visible in the grass plant during the spring, those tillers were actually induced to reproductive growth the preceding fall. Cool-season grasses, which make up the bulk of most graziers' pastures, require a period of cold temperatures - four weeks or longer of 40 degrees and lower - together with long nights, to initiate flower buds on the crowns of the plants. This process is called floral induction, he says.

"In the spring of the year new growth begins by drawing upon the carbohydrate reserves stored in the plant roots. New tillers develop and produce leafy material, remaining in the vegetative stage in early spring. However, at some point, the decreasing night length (i.e. longer days) acts as a trigger to send a message to induce tillers that it is now time for reproductive growth," Lewandowski describes. "The tiller responds by entering the jointing stage where internodes (the area between nodes) are elongated and stem formation begins. The priority now shifts to seed development and further leaf production on the tiller ceases."

A seed head develops and pushes out of the tiller. At boot stage, the seed head is just about ready to emerge from the last elongated node area and is still wrapped in a leaf sheath, he details. Once the seed head emerges, the reproductive stage continues with flowering and seed development and maturation.

"Once reproductive growth is initiated, it may seem that all the grass plants' tillers are coming into head at the same time," says Lewandowski. "The realty is that there is a range of maturity among tillers and not every tiller is a reproductive tiller." Only those tillers induced the preceding fall have the capacity to produce a stem and seed head; new tillers developed in the early spring don't have this capacity.

"However, reproductive tillers dominate the grass plant because they shade out the vegetative tillers, and in addition, hormones produced in reproductive tillers as seeds mature, retard or inhibit the development of other vegetative tillers," he explains. The grass plant will not return to vegetative growth until the seed head is mature, or the process is interrupted by the removal of the reproductive tiller."

"Remember, the plant's priority is to put its resources into the development of a mature seed - not to produce high quality vegetative material," he tells producers.

Lewandowski notes that the apical meristem or growing point of the grass plant is at or near soil level and thus is protected from grazing livestock. "A vegetative tiller will continue to develop new leaves as long as growing conditions are favorable due to this protected position of the growing point," he states. "Once a tiller enters reproductive growth, marked by stem elongation, the growing point is no longer protected and moves up the plant as the stem elongates. The growing point in a reproductive tiller is generally found just below the last completed node."

"This elevated growing point is vulnerable to being eaten off by livestock. If the growing point has been eaten off, regrowth has to come from development of a new tiller," he says.

Tiller growth from buds is dependent upon defoliation and the resulting light penetration to the base of the plant. If all of the tillers induced into reproductive growth the preceding fall can be clipped off once they begin seed head formation, the remaining plant growth will stay vegetative through the rest of the growing season, because reproductive tillers are only initiated under fall conditions.

Seed heads must be avoided through grazing or clipping to keep plants in vegetative growth and keep them from developing tillers. "The wrinkle in this is that since not all reproductive tillers on a grass plant are of the same maturity and expressing themselves at the same time, it will take several clippings throughout the spring and early summer season to get all the reproductive tillers clipped," says Lewandowski.

"While some graziers may prefer to wait until most of the reproductive tillers have developed seed heads before clipping later in the grazing season, the trade-off is a sacrifice of some yield and quality as some vegetative tillers die-off due to shading," he remarks.

Echoing Landefeld, Lewandowski says that trying to avoid seed heads by grazing is best accomplished by quickly moving livestock from one paddock to the next. "Essentially the goal is to use the livestock to just graze the top couple of inches of the grass," he notes. "The principle here is to match paddock rotation speed to pasture growth. When pasture grass is growing fast, rotate fast, when growth slows, slow the rotation."

He, too, admits this is easier said than done. "In reality, unless there is a heavy stocking rate and small paddock size, it is unlikely that grass will be grazed uniformly enough to avoid seed head formation, and some mechanical clipping will still need to be done after the grazing pass," Lewandowski points out.

"Enjoy the early spring vegetative growth, because once the reproductive 'trigger' is pulled, the management challenge begins," he concludes.

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