Ranchers in the United States have experienced through the years the highly sporadic year of exceptional sweet clover (SC) production with varying degrees of increased forage production and wonderment in its wide-ranging establishment. There are two general types of sweet clover; white and yellow sweet clover. White SC is found more often in "run-in" range sites and tends to produce much more biomass, but becomes less desirable as a forage source when mature, as palatability and digestibility are greatly reduced. On the other hand, yellow SC can be found in all locations of the prairie landscape and can be managed to provide a more desirable livestock forage. During these "sweet clover years," rangeland forage production can increase three- to four-fold, providing opportunities for ranchers to capitalize on this added biomass with increased stocking rates, longer grazing duration and more hay production. Ranchers who consistently monitor their rangeland and develop grazing plans position themselves to take advantage of the forage "boom" that this introduced biennial can provide. A well-developed grazing plan will include locating water and fencing to allow for flexibility as grass production varies from year to year as in "sweet clover" or drought years.

Forage profile

Sweet clover's forage production, nutritive value and soil enhancement properties are quite similar to alfalfa and the methods employed in determining alfalfa yields can be used to predict the second year's growth potential for SC. The second year's growth will develop a crown, much like alfalfa, from which the stems originate and counting the number of stems per square foot can estimate a production expectation. With as few as 6 stems/square foot, SC has potential to yield 1960 pounds of dry matter/acre using the formula: Yield = (0.10 x # stems/square foot) + 0.38) (University of Wisconsin's extension publication (A3620) Alfalfa stand assessment: Is this stand good enough to keep? by Dan Undersander, Craig Grau, Dennis Cosgrove, Jerry Doll, Neal Martin).

While SC is an introduced invader of the North American prairie, it does possess unique qualities that will benefit the rangeland. As a legume, SC has the ability to become a fertility source for the grass community by fixing 60-100 pounds of nitrogen per acre in the top soil horizon. Additionally, the tap root draws into the grass root growth zone other nutrients such as phosphorus and potassium necessary for grass production. At the end of its growth cycle these roots decompose and serve as moisture-holding wicks of organic matter that continue to support rangeland vegetation.

Establishing a grazing plan

Timing is everything when utilizing the potential forage that SC can provide for grazing animals. SC is a cool season, fast maturing forage plant that will sharply decrease in nutritive value, palatability and digestibility as it begins to blossom and produce seed from mid-June through early-July. Ignoring the signs indicating an abundance of sweet clover can pose a host of problems that could impact a producer's bottom line. SC stands can potentially be as dense as to reduce grass production by competing for moisture and reducing sunlight reaching the grasses. Hardening of the plant structure occurs as SC matures, creating a degree of grazing restraint that inhibits livestock foraging to the nutritious plants that may lie below the SC canopy. If livestock persist in grazing through the hardened canopy, eye infections may increase due to irritation of the eye lens from scratches and pollen dust exposure.

Establishing an annual grazing plan, developed from pasture forage inventory and monitoring, use of precipitation records, USDA-NRCS Web Soil Survey information and the USDA-NRCS SD Drought tool, will allow ranchers to predict, plan and stock for the current year's growing season and, in the case of a "sweet clover year", take advantage of increased forage production, adding to the bottom line and improving the rangeland resource.

The 2014 forage production season is a case in point. Ranchers who monitored their rangeland and utilized precipitation records in 2013 discovered that conditions were right for the germination and development of the vegetative stage of SC. As producers evaluated their rangeland health in fall 2013 it became apparent that there is an inordinate level of SC in regions of Western South Dakota rangeland. Using the USDA-NRCS SD Drought Tool and inputting precipitation records from ranch/pasture precipitation records or the nearest weather station, it is evident that if the weather conditions remain near or above normal we can expect rangeland forage production to be above 100 percent. Referencing the USDA NRCS Web Soil Survey provides forage production estimates for rangeland soils and ecological sites. Accounting for the potential yield from SC using alfalfa yield models, a multi-fold forage production prediction can be anticipated.

Ranchers that became aware of this opportunity in the fall 2013 or in the spring 2014 will develop a grazing plan that can take advantage of this increase in forage production through grazing and haying by:

Increasing stocking rates and/or duration of grazing period in pastures with high densities of SC to utilize the added forage production and open SC's dense canopy to allow for greater grass production from the available nitrogen.

Deferring grazing pastures and rangelands that are recovering from the effects of the 2012 drought and are still sensitive to normal grazing pressure.

Haying sweetclover in highly productive, accessible areas will remove excess forage to be used for winter feed, open the area for grass production and reduce the threat of prairie fires in critical areas of the ranch near the headquarters, livestock facilities and hay storage areas.

Grazing Plans: Things to consider during a cool spring

The cool spring of 2014 has placed rangeland plant development behind a normal year and this allows time for producers to implement some different scenarios into their current grazing plans. There are a number of options producers can develop to increase stocking rates or the duration of the grazing period. These scenarios could include the following; individually or in combination to meet the forage harvesting goals of the producer.

Targeted grazing. Identify and graze pastures with heavy concentrations of SC early in the growing season using the current levels of livestock on the ranch. Temporary fencing can be installed to concentrate grazing in heavily infested SC areas. Lengthen the duration of the grazing period in pastures with dense SC, while deferring other pastures.

Bring in additional livestock to temporarily match the forage supply for the current production year. Cow/calf pairs, yearling cattle, ewes/lambs or lambs and certainly combinations of these grazing animals could be used to better balance grazing pressure. Sheep will focus on the broadleaf plants when abundant, allowing more grass for cattle. Throughout the growing season continual monitoring needs to occur to make certain the rangeland vegetation is providing necessary nutrients to sustain livestock performance while guarding against overgrazing. Livestock use of SC forage will decrease considerably when the plant matures. Producers will need to monitor pastures to recognize when livestock begin to decrease SC consumption and increase the use of grasses. Establishing trigger points based on the goals of the grazing plan and current range conditions will indicate when and what livestock should be destocked from the ranch.

Haying SC in the early bud to bud stage will provide for the highest level of forage quality and also allowing an opportunity for some SC and grass regrowth that could be grazed later in the season. Approaching harvesting of SC for hay with consideration of other prairie improvement goals could include leaving patches in areas low in surface cover to increase residue, leaving standing strips to catch snow and provide wildlife habitat as well as planning and establishing fire breaks.

The grazing plan should consider wildlife development and habitat goals. A "sweet clover" year can provide excellent cover and food habitat for nesting upland game birds. In this case the grazing plan may defer grazing of some pastures with dense patches of SC until the end of the nesting period.

While ranchers may consider using a grazing plan only during drought years, it can be a very profitable and useful management tool every year, positioning producers to make appropriate use of rangeland forage in years of above average production. Ranchers who experienced the breaking of the 2000-2008 drought with above average precipitation in 2009 witnessed an extraordinary "sweet clover" year in 2010, resulting in two-fold grass production in 2011 due to the added nitrogen availability from the SC residue and above average rainfall in May of that year. When the next drought began in late 2011 and persisted into the growing season of 2012, many producers subsisted on the over-abundant grass production from 2011 and what little grew in 2012. Learning from the past and developing a grazing plan each year will help manage risk and help to insure a future for the rancher.

See more at: http://igrow.org/livestock/sheep/develop-a-grazing-plan-for-a-sweet-clover-year/#sthash.yxznXnof.dpuf

–SDSU Extension