Skip to main content
ARS Home » Plains Area » Mandan, North Dakota » Northern Great Plains Research Laboratory » Research » Publications at this Location » Publication #142541
Title: EVAPOTRANSPIRATION FROM NORTHERN SEMIARID GRASSLANDS.

Author
item Frank, Albert

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/21/2003
Publication Date: 11/20/2003
Citation: FRANK, A.B. EVAPOTRANSPIRATION FROM NORTHERN SEMIARID GRASSLANDS. AGRONOMY JOURNAL 95:1504-1509. 2003.

Interpretive Summary: Water is the single most limiting factor to forage production on semiarid grasslands. Proper grazing management can affect soil water needed for forage production. The Bowen ratio/energy balance method was used to measure evapotranspiration (ET) on three grasslands at Mandan, North Dakota in 1996, 1997, and 1998: a nongrazed mixed-grass prairie, a grazed mixed-grass prairie, and a grazed western wheatgrass site. Leaf area, above ground biomass, soil water extraction, and micro-climatic measurements were made during the period. Peak ET rates generally coincided with periods of peak biomass production and occurred between early-July and early-August. Peak biomass averaged 1097 kg ha-1 and LAI 0.38 for the prairie;1227 kg ha-1 and LAI 0.44 for grazed prairie; and 1725 kg ha-1 and LAI 0.59 for western wheatgrass. Averaged ET was 489 mm for the prairie, 455 mm for the grazed prairie, and 497 mm for the western wheatgrass over the three year period. Rates of ET for the grazed prairie was 7% less than the nongrazed prairie and 8% less than the western wheatgrass, but ET for the nongrazed prairie and the grazed western wheatgrass were not different. These results should be of interest to modelers, and hydrologist interested in the water balance of grasslands, and to land managers who desire a better understanding of the relationship between water supply and grazing practices.

Technical Abstract: Management of forage production for livestock grazing on semiarid grasslands depends on water availability. Evapotranspiration (ET) was measured using the Bowen ratio/energy balance (BREB) method on three grasslands at Mandan, North Dakota: a nongrazed mixed-grass prairie (prairie), a grazed mixed-grass prairie (grazed prairie), and a grazed western wheatgrass site (western wheatgrass). Measurements were made from 24 April to 17 October (the growing period) in 1996, 1997, and 1998. Leaf area, above ground biomass, and soil water extraction were measured about every 21 d during the ET measurement period. Peak ET rates generally coincided with periods of peak biomass production and occurred between early-July and early-August. Peak biomass averaged 1097 kg ha-1 for the prairie, 1227 kg ha-1 for grazed prairie, and 1725 kg ha-1 for western wheatgrass and peak LAI averaged 0.38 for the prairie, 0.44 for grazed prairie, and 0.59 for western wheatgrass. Growing period ET averaged 489 mm for the prairie, 455 mm for the grazed prairie, and 497 mm for the western wheatgrass. Grazing reduced ET of the grazed prairie by 7% from the nongrazed prairie and 8% from the western wheatgrass, but ET for the nongrazed prairie and the grazed western wheatgrass were not different. The ratio of the latent heat of ET to net radiation averaged 0.25 for grazed prairie and 0.28 for prairie suggesting that grazing changed the canopy structure and energy budget components that affected ET. These results should be of interest to modelers, hydrologist, and managers who have interest in managing the limited water supply common on semiarid grasslands.