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United States Department of Agriculture

Agricultural Research Service

Title: Predicting Nitrogen Content in the Northern Mixed-Grass Prairie

Authors
item Haferkamp, Marshall
item Macneil, Michael
item Grings, Elaine

Submitted to: Journal of Range Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 21, 2004
Publication Date: March 1, 2005
Citation: Haferkamp, M.R., MacNeil, M.D., and Grings, E.E. 2005. Predicting Nitrogen Content in the Northern Mixed-Grass Prairie Rangeland Ecology & Management 58:155-160.

Interpretive Summary: Forage quality and quantity are important factors affecting livestock production from grazinglands. Greenness of herbage has been proposed as an indicator of forage quality, particularly N content. Forage samples collected April through October over 3 years from 3 grazing regimes on a silty range site in eastern Montana, were sorted into live and dead components, then dried, ground, and analyzed for N content. Growing degree days (GDD) (base 45ºF) were calculated from NOAA reported monthly average temperatures for Miles City. An equation to predict percent N in the total forage from percent dead forage and cumulative GDD was developed using multiple linear regression. The equation accounted for 75.9% of variation in percent N. The equation was validated using data from an independent study conducted during July 1991 to April 1993 at Fort Keogh LARRL. Samples from 8 areas on silty and clay-pan range sites were treated and analyzed similarly to those in the base-line study. When the developed equation was used to predict percent N in the validation data, the resulting correlation between predicted and actual values was 0.79. The regression coefficient for actual values on predicted values was 0.995±0.125. The prediction equation has promise for rapid estimation of forage quality on Northern Great Plains Rangelands. Such a tool might allow livestock producers to make more efficient use of forage and manage the nutritional status of their livestock without incurring the cost of chemical analysis of forage samples.

Technical Abstract: Forage quality and quantity are important factors affecting livestock production from grazinglands. 'Greenness' has been proposed as an indicator of herbage quality, particularly N content. Standing crop samples were collected April through October over 3 years from each of 3 replicated grazing regimes on a silty range site in eastern Montana. Samples were sorted into live, current dead, and old dead components, then dried, ground, and analyzed for N content. Growing degree days (GDD) (base 45ºF or 7.2oC) were calculated from NOAA reported monthly average temperatures for Miles City. An equation to predict percent N in the total standing crop from percent dead forage and cumulative GDD was developed using multiple linear regression. This equation accounted for 75.9% of variation in percent N, and prediction error variance was 0.026. To validate this equation, data were obtained from samples collected from April through September in an independent study of 8 areas on silty and clay-pan range sites grazed during autumn and winter. Samples from these sites were treated and analyzed similarly. When the developed equation was used to predict percent N in the validation data, the resulting correlation between predicted and actual values was 0.79. The regression coefficient for actual values on predicted values was 0.995±0.125. The intercept did not differ from 0.0 (P=0.22), and prediction error variance was 0.042. This equation may have utility for predicting quality of forage from Northern Great Plains rangelands.

Last Modified: 7/28/2014
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