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.

Diversification of cropping systems with legumes is a common practice used to overcome soil fertility and weed control challenges in organic farming systems. The current study assessed different legume-intensive cropping systems with the potential to minimize management risks for dryland, organic wheat growers in the Inland Pacific Northwest region of the United States. Several cropping systems ranged from cereal-intensive cash crops to legume-intensive green manure and forage, and were grown for the three-year transition period prior to organic certification. The goal was to identify systems that would produce high quality, certified organic wheat. All cropping systems that included a legume for at least one year during the transition phase improved soil inorganic nitrogen (N) levels, but systems that included legumes for the duration of the transition also reduced weeds as a result of repeated mowing. Weed control is as great of a concern as soil N for producing organic wheat and in this study, reduced weed pressure improved wheat yield and protein levels throughout the transition and into organic production. Intercropping a legume cover crop with wheat was used as an additional method to improve soil inorganic N. Competition for soil moisture stress was not a concern, and although N from the legumes was not immediately available to the growing wheat crop, intercropped legume and wheat systems could be grown in rotation with other crops for soil management and weed control. Mechanical removal of the intercrop with a precision inter-row cultivator was a useful crop control method and offered opportunities for further research on cover crop and weed management. Using competitive cultivars and crop-types was also necessary. Intensive management of legumes as intercrops, cover crops, and forage demonstrated the potential to greatly improve organic winter wheat production. However, supplemental soil nutrient sources would need to be added in addition to legumes in order to sustain organic wheat production over time. Organic production of dryland wheat is possible but complex management strategies must be consistent and focus on weed control as much as soil fertility.

Nitrogen in the Environment: Sources, Problems, and Management is the first volume to provide a holistic perspective and comprehensive treatment of nitrogen from field, to ecosystem, to treatment of urban and rural drinking water supplies, while also including a historical overview, human health impacts and policy considerations. It provides a worldwide perspective on nitrogen and agriculture. Nitrogen is one of the most critical elements required in agricultural systems for the production of crops for feed, food and fiber. The ever-increasing world population requires increasing use of nitrogen in agriculture to supply human needs for dietary protein. Worldwide demand for nitrogen will increase as a direct response to increasing population. Strategies and perspectives are considered to improve nitrogen-use efficiency. Issues of nitrogen in crop and human nutrition, and transport and transformations along the continuum from farm field to ground water, watersheds, streams, rivers, and coastal marine environments are discussed. Described are aerial transport of nitrogen from livestock and agricultural systems and the potential for deposition and impacts. The current status of nitrogen in the environment in selected terrestrial and coastal environments and crop and forest ecosystems and development of emerging technologies to minimize nitrogen impacts on the environment are addressed. The nitrogen cycle provides a framework for assessing broad scale or even global strategies to improve nitrogen use efficiency. Growing human populations are the driving force that requires increased nitrogen inputs. These increasing inputs into the food-production system directly result in increased livestock and human-excretory nitrogen contribution into the environment. The scope of this book is diverse, covering a range of topics and issues from furthering our understanding of nitrogen in the environment to policy considerations at both farm and national scales.