An economic analysis of variable rate nitrogen management on dryland spring wheat in Northern Montana
Whitmus, Jeffrey Donald.
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The objective of this study was to compare hard red spring wheat (Triticum aestivum L.) grain yield (agronomic returns) and grain value (economic returns) of variable rate and uniform nitrogen (N) management using a data set obtained from eight on-farm experiments conducted over an eleven year period (1994-2004). Field experiments were established near Simpson, Malta, Havre, and Highwood, Montana using a strip trial design where N rates were varied in replicated strips along the length of each field. A digital elevation model was created for each field site using survey quality global positioning system data. Digital elevation models were segregated into four landscape classes or management zones (Upper Slopes, Middle North Facing Slopes, Middle South Facing Slopes, and Lower Slopes) using global information system software. Geo-referenced grid soil samples were collected at each field site location to determine background soil N levels. Geo-referenced yield and protein samples were collected at all field sites using a production sized combine equipped with yield monitor. The economic analysis consisted of partial budget analysis where only the changes in costs and revenues between variable rate and uniform N management were considered as part of net returns. In addition, spatial least squares (SLS) analysis was used as the basis for establishing whether wheat yields from variable rate N management were significantly greater than those from uniform N management. The SLS analysis failed to detect a significant difference in grain yield between variable rate and uniform N management. Variable N management used more fertilizer N and was less profitable than uniform N management in seven of the eight cases. Revenues from variable N management were insufficient to offset associated costs for needed information, hardware, and software. However, if Environmental Quality Incentive Program payments of $34.57 were considered as part of net income then variable rate N management was more profitable in all cases. Little evidence existed in this study that variable rate N management improves agronomic returns and profits, or reduces N use, especially in water limited conditions found in northern Montana.