Managing for variation in forage production with trigger dates and stocking rates
March 30, 2015
A warm, dry March has left the topsoil dry in many parts of central and western Nebraska.
While subsoil moisture is still adequate in many locations, the pattern of above-normal temperatures with below-normal precipitation is concerning. In addition, below-average snow pack conditions are an ominous sign looking toward potential precipitation as spring continues.
Forage production from pasture and native range can vary significantly from year to year, based on precipitation, temperatures, available nutrients and plant health. The primary limiting factor for grass production in the Sandhills and Nebraska panhandle is spring and early summer precipitation.
Planning to adjust stocking rates by critical trigger dates can help producers take a proactive approach to manage for an expected deficit of forage production when precipitation and available soil moisture is below the long-term average.
From a rangeland and pasture-production standpoint, it is good to remember how critical available soil moisture is to plant growth. Cool- and warm-season grass species have "rapid-growth windows" when air temperature, day length and soil moisture all need to be present to allow plants to fully express their growth potential. Once the window of opportunity has passed for a particular grass species, even if it does rain, it is too late to get significant growth from those plants.
From a grassland manager standpoint, lack of precipitation means limited forage growth and less grass available for grazing, reducing the expected stocking rate for the grazing season.
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Precipitation during May, June and July are strongly correlated with forage production on warm-season dominated range sites in the Nebraska Sandhills. In the panhandle where many range sites are dominated by cool-season grass plants, the major influencer is precipitation in April, May and June.
Trigger dates to reduce stocking rates will vary depending upon the grass species present and available grazing resources. Here are some key trigger dates to consider for western Nebraska cool- and warm- season dominated range sites.
Available soil moisture on April 1. Look at dormant season precipitation from October – March and dig some post holes to see how much moisture is in the soil profile. A lack of soil moisture in early April will impact growth from cool season grass species such as Threadleaf sedge (blackroot) and Needlegrasses. Exceptionally dry conditions at this time can trigger the need to plan for a 10-20% reduction in stocking rates on cool season dominated rangeland.
Moisture available from the middle of April to early May. By this time forecasts can be pretty accurate as to what is expected for the next 30-45 days in terms of precipitation. If expectations are for above average temperatures with average to below average precipitation, additional reductions in stocking rates on pastures should be planned for.
Late May into early June precipitation. Needlegrasses will be completing their forage production by this time and western wheatgrass is in its rapid growth window. If March-May precipitation was only 50-75 percent of the long term average for precipitation, a stocking rate reduction of up to 30-40 percent or greater should be planned for depending upon grass species and plant health. Warm season grasses such as prairie sandreed and little bluestem are just getting started.
Precipitation and soil moisture available from mid to late June. Approximately 75 to 90 percent of grass growth on cool-season-dominated range sites will have happened by mid- to late June, and 50 percent of grass growth on warm-season-dominated range sites. Rainfall after late June will result in limited benefit to cool-season grasses in terms of forage production but could still result in some benefit to warm-season grasses.
Precipitation and available soil moisture from the middle of June to the middle of July is important for warm-season grass growth. Precipitation after July 15 will have limited benefit to forage production from warm-season tallgrass species, but can still result in some forage growth from shortgrass warm-season species such as buffalograss and blue grama. However, buffalo grass and blue grama produce limited amounts of forage for grazing.
For additional information see the following two resources:
Skillful Grazing Management on Semiarid Rangelands: This NebGuide describes the growth pattern of grass species and provides information on good grazing management practices.
The Nebraska Drought Resources website http://droughtresources.unl.edu/ provides a wide range of information related to drought including 'Managing Drought Risk on the Ranch' which provides additional information on trigger dates and a planning guide.