Saturday, October 25, 2014

Managing Drought Risk on the Ranch

Herbage Production at Three Latitudes

Under good grazing management, native grasslands on similar soils in similar precipitation zones are co-dominated by similar plant species. Consequently, exchange of ranch drought experiences and management practices can be helpful over relatively large geographic areas, especially in the semiarid climate zone. 

From North Dakota to northern Texas, sand bluestem (Andropogon hallii) and prairie sandreed (Calamovilfa longifolia) or big sandreed (Calamovilfa gigantea) co-dominate upland sites in high ecological condition on loamy fine sands. 

This example looks at three sites with similar soil types and plant communities, located near Dickinson, North Dakota (N 46o 53'), Crescent Lake Wildlife Refuge (WLR), Nebraska (N 41o 43'), and Dumas, Texas (N 35o 52').

 

Length of growing season, average monthly air temperatures, and evaporation rates increase from north to south.

Growing season day length increases from south to north. Summer-solstice day length is about 14½ hr at Dumas, 15¼ hr at Crescent Lake, and 16 hr at Dickinson.

Monthly average maximum temperatures (F)

Day length (hours)
The percentage of frost-free precipitation occurring during the first half of the growing season increases northward over the 700 miles from Dumas to Dickinson.

The integrated effect of these environmental variables is a moderate northward increase in total herbage production, about 2,065 lb/ac near Dumas, 2,300 lb/ac near Crescent Lake, and about 2,500 lb/ac near Dickinson.

Average monthly precipitation (inches) - Dickinson, ND Average monthly herbage production (lb/ac) - Dickinson, ND
Average monthly precipitation (inches) - Crescent Lake WLF, NE Average monthly herbage production - Crescent Lake WLF, NE
Average monthly precipitation (inches) - Dumas, TX

Average monthly herbage production (lbs/ac) - Dumas, TX

 

This pattern corresponds to an average yield response of 116 lb, 133 lb, and 150 lb of herbage per inch of average annual precipitation in Texas, Nebraska, and North Dakota, respectively.

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