Planning for earlier grazing
March 29, 2010
Warmer air temperatures are always welcome this time of year. Returning robins, warming soils and emerging green grass can’t be far behind! When many grazingland managers consider extending the grazing season, they often are considering plans at the conclusion of the growing season. Strategies like stockpiling standing vegetation, swath grazing or bale grazing may come to mind. With careful planning, there may also be opportunities to extend grazing at the beginning of the growing season.
Recall that perennial vegetation emerging in the spring is entirely dependent on stored reserves to initiate new growth. Photosynthesis provides an energy source as new green leaves are formed. But most grass plants require the development of three leaves before they are no longer dependent on reserves. Removal of tissue before this point requires the mobilization of additional storage reserves. If grazing is initiated too early, production for the balance of the growing season can be reduced. Research in North Dakota suggests the reduction can be as severe as 50 percent.
Climatic information can help estimate when grass plants can achieve given growth stages. For example, introduced grasses generally produce three leaves following the accumulation of about 500 growing degree days (GDD, base 32 degrees after March 1). For many native cool-season grasses, about 1,200 GDD are required to reach the three-leaf stage.
The calendar date when these growing conditions occur varies considerably from one location to another and from year to year. In southwest South Dakota, the average date at which 500 GDD accumulate is April 28 at Oral and May 3 at Nisland. The normal date for 1,200 GDD is May 28 at Oral and June 1 at Nisland. This has occurred recently as early as May 11, 2004 at Oral and May 21, 2004 at Nisland. Growing degree day data for South Dakota weather stations can be accessed using the SDSU Climate web site. A “Growing degree days querying module” is available at: http://climate.sdstate.edu/awdn/archive/degreedays.asp. This site allows users to specify parameters for the calculation of growing degree days. Similar climate data can be accessed for adjoining states. Using climate information can provide an estimate, but evaluating your own pasture by counting the number of leaves on a particular key grass species and taking an average provides the same information.
But what about planning for earlier grazing? If pastures are grazed season long, total production is likely to be compromised by premature turn out. However, in a planned rotation, growth suppression may be restricted to the first few pastures grazed. By planning sufficient recovery periods before grazing in repeated, reductions may be minimized. With experience and careful planning, retarding the growth pastures grazed early may even overcome of the imbalance often encountered during rapid growth of the “spring flush” which occurs most years. The period of highest nutritive value can sometimes be extended for the earliest grazed pastures. Risk of further reduction in vigor of pasture vegetation may be further minimized by avoiding the use of the same pastures for earliest grazing each year.
A second opportunity to extend the grazing season earlier in the growing season could result from the careful use of particular species which exhibit the earliest growth. Cheatgrass, crested wheatgrass and several sedge species are among the first to exhibit active growth in the spring. Livestock will selectively graze this earliest growth because it is tender and palatable. In healthy rangeland, with a wide diversity of plants, actively growing green tissue will be much preferred to standing dead from the previous growing season. Careful estimation of the quantity of “green feed” actually available will be important to properly using this early growth. This most often requires very brief periods of occupation in any one pasture, “skimming” only the early growth of targeted plants. As the spring continues, it is equally important to avoid excessive grazing of plants developing later, such as native cool-season grasses.
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Because moisture is often more abundant in the spring, and evaporates more slowly during cool temperatures, excessive mud may result with premature initiation of grazing. This may also be minimized by very short periods of occupation in pastures. In making plans to use early grazing, it makes sense to have a contingency plan for a “sacrifice area” where livestock can be confined and fed in order to limit damage to a larger area.
Finally, it only makes sense to consider early grazing if it fits with your feed resources and calving dates. Enjoy the sunshine and marvel at the miracles of new life that surround us this time of year.