Thursday, November 27, 2014

Managing Drought Risk on the Ranch

Setting Critical Dates and Target Conditions

Midpoints of rapid-growth windows for dominant cool-season and dominant warm-season grasses are excellent critical dates for implementing different phases of drought management plans.

Many semiarid rangelands are composed of mixtures of cool and warm-season species. Consequently, it is often helpful to select two or more critical dates when most species of each growth-season category have headed to evaluate the contribution of each component to total herbage production.

Northern/Central Great Plains - Sample Critical Dates

End of June + Periodic throughout Season

In the northern and central Great Plains, annual herbage production  - on good condition loamy and silty sites dominated by mixtures of shortgrasses (buffalograss and blue grama) and mid-grasses (western wheatgrass, needle-and-thread, and junegrass) -  is correlated with total precipitation during May and June (r = 0.68 to 0.86). 

Average or better precipitation during May and June indicates enough herbage is likely to be produced to sustain moderate stocking rates 68% to 86% of the time. Periodic monitoring will still be necessary.

Central Great Plains - Sample Critical Dates

January 1

On good condition semiarid sandhills rangelands in the central Great Plains, annual precipitation for the two preceding years is a good indicator (r = 0.83) of herbage production during May and June (Dahl 1963).  One or two below-average precipitation years should lead managers to predict forage deficits at this time.


Depth of soil moisture in mid April in these ecosystems correlates highly (r=0.80) with peak standing herbage in early August. 

Depth of moist sand is readily discernable when replacing fence posts in the spring. When there are 3 feet or more of wet soil in mid April, there will be enough herbage to support moderate stocking through the grazing season in at least 8 out of 10 years. This would be a great way to start the year.

Late June &
Late July

Near average or better precipitation during June and July would remove all concern of forage deficits.

Southern Great Plains - Sample Critical Dates




Livestock are often on Southern Great Plains rangeland all year long. In addtition, the lenght of the frost-free period and the bimodal precipitation patterns make it difficult to predict annual forage production early in the year. Forage resources must be monitored throughout the year.

Grazing management often has a greater effect on herbage production than year-to-year changes in precipitation in the southern Great Plains.  

Ranchers should have reasonable monthly estimates of the total forage demand of their herd(s) and know how many pounds of nongrazed herbage to leave for hydrological condition.


Critical Dates Appropriate for Your Ranch

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Critical Date Target Point or Condition


Drought Plan Worksheet

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