Abstract
Forage quality and quantity are important factors affecting livestock production from grazing lands. ‘‘Greenness’’ has been proposed as an indicator of herbage quality in semiarid environments, particularly nitrogen (N) content. The objective of this study was to assess the potential of estimating N content of forage using dead:green ratios and accumulated growing-degree- days (AGDD). 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. The AGDD for base temperature 45 degreesF (7.2 degreesC) was calculated from National Oceanic and Atmospheric Administration (NOAA) reported monthly average temperatures for Miles City. An equation to predict percent N in the total standing crop from percent dead forage and AGDD 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 in the same manner as those used to develop the equation. The developed equation was used to predict percent N for 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 has utility for predicting N level of forage from Northern Great Plains rangelands.
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Claims 7
Claim · model-written summary
Dead forage and accumulated degree days explained 75.9% of standing-crop nitrogen variation.
Verbatim
e0“This equation accounted for 75.9% of variation in percent N, and prediction error variance was 0.026”
t0“Northern Mixed-Grass Prairie”
e2“N content of forage using dead:green ratios”
Claim · model-written summary
The fitted equation had prediction error variance of 0.026.
Verbatim
e0“prediction error variance was 0.026”
t0“Northern Mixed-Grass Prairie”
e2“N content of forage using dead:green ratios”
Claim · model-written summary
Predicted and observed nitrogen content correlated at 0.79 in validation data.
Verbatim
e0“The resulting correlation between predicted and actual values was 0.79”
t0“Northern Mixed-Grass Prairie”
e2“N content of forage using dead:green ratios”
Claim · model-written summary
The regression coefficient of observed on predicted nitrogen was 0.995 +/- 0.125.
Verbatim
e0“The regression coefficient for actual values on predicted values was 0.995 +/- 0.125”
t0“Northern Mixed-Grass Prairie”
e2“N content of forage using dead:green ratios”
Claim · model-written summary
The validation intercept did not differ from zero.
Verbatim
e0“The intercept did not differ from 0.0 (P = 0.22)”
t0“Northern Mixed-Grass Prairie”
e2“N content of forage using dead:green ratios”
Claim · model-written summary
Validation prediction error variance was 0.042.
Verbatim
e0“prediction error variance was 0.042”
t0“Northern Mixed-Grass Prairie”
e2“N content of forage using dead:green ratios”
Claim · model-written summary
The authors say the equation can predict forage nitrogen in Northern Great Plains rangelands.
Verbatim
e0“This equation has utility for predicting N level of forage from Northern Great Plains rangelands”