Pastoral and forage-based ruminant production systems dominate production of meat, milk, and fiber across the globe. However, forage-based production systems are among the most inefficient in terms of feed conversion and nitrogen (N)-use efficiency when compared with other meat-producing production systems such as poultry. Forage-based ruminant production is often on land not suited for crop production and is important to food security (Mottet et al., 2017). Nitrogen use efficiency and improvement thereof is a recurring subject of investigation in these systems (Gerber et al., 2015). The amount of N applied annually to these systems through fertilization and/or supplemental feedstuffs can exceed plant uptake, and animal utilization of N, whether from forage or other feedstuffs, is relatively low (avg. of approximately 25%) and highly variable (10 to 40%; Calsamiglia et al., 2010). This can result in overabundance or toxic levels of N in forages and/or the ecosystem. Significant quantities of N fertilizers (mineral and animal) are applied to forage crop and grazing systems because N is often the most limiting nutrient for plant growth. Providing supplemental N to forage-based livestock production systems is expensive whether supplied as fertilizer N to the forage or as supplemental crude protein to the animal. Therefore, continued investigations into measures to improve N-use efficiency at the soil, plant, and animal interface is necessary to improve long-term, sustainable livestock production while concurrently reducing potential pollutants and greenhouse gas (GHG) emissions.

Although nutrient cycles in grazing-forage systems are less open than in systems that rely on concentrated feed such as poultry production, grazing systems cover more than a quarter of the earth’s land surface (Asner et al., 2004) and loss of N from pastures is an unsolved problem to which fertilizer N, climate and edaphic conditions, grazing density and supplemental forage and feed contribute (Zhou et al., 2017; Li et al., 2012). The magnitude of N loss and resulting positive and negative impacts on ecosystems and forage productivity are influenced by the timing, frequency, and intensity of management practices within the ecosystems. In the Midwest, loss of N from any agricultural system may contribute in a large fashion to periodic hypoxia in the Gulf of Mexico. In addition, gaseous N emissions from pastures contribute to the greenhouse effect (Gerber et al., 2016). More in-depth analysis is needed regionally (Franzluebbers, 2005) especially related to grazing management systems (Gerber et al., 2017) as grazing can improve carbon (C) and N storage depending on management (Wang et al., 2016) and environment.

Increased demand for meat products by consumers during past decades has encouraged producers to respond with an increased intensification of forage-based livestock production. Hence, there is an urgent need for scientific information to help producers make decisions about how to best manage rural landscapes and to produce agricultural commodities while maintaining soil, water, and air quality (Gerssen-Gondelach et al., 2017). The foci of our experiments will examine alternative strategies to concurrently improve N harvest efficiency while reducing N losses from forage-based livestock production systems. This overall objective will be achieved through pastoral and other forage management strategies to enhance N retention and utilization at the soil, plant, and animal level. Such strategies include improving legume establishment and persistence, alteration of spatiotemporal distribution of soil N pools, use of varied fertility practices in legume and non-legume systems, use of legumes with various secondary plant metabolites, and use of various supplementation practices while concurrently evaluating the impacts of management, climate change, and forage nutritive value on N-use efficiency. Our results will then be disseminated through coordinated extension/education activities and at national, regional and state conferences.

Expected outcomes and predictions will include advice on management strategies in terms of N use efficiency, particularly as it relates to the capture and excretion of N in the environment. The ultimate goal is to help producers adopt strategies/practices that ensure efficient use of N in order to positively influence forage and animal productivity and environmental quality. In addition, this work will facilitate the identification of forage systems that minimize N inputs and production costs. Minimizing expensive N inputs (e.g., fertilizers) in forage-based livestock production systems has tremendous potential to enhance their profitability. These impacts are most likely achieved through the development and implementation of a multiple-state project. The members of our proposed project represent a geographically diverse set of states from the Southeast through the Midwest and Great Plains to the Intermountain West. Our objectives of analyzing N use efficiency of grassland production systems will be based on a wide range of environments (humid to semi-arid) and levels of management intensity (irrigated to low-input grassland systems). The expertise, facilities and other resources required to design and conduct the proposed research are not found at a single institution. The synergy coming from a multiple-state effort in this area greatly enhances the likelihood of success in characterizing N use and developing appropriate management strategies for grassland agro-ecosystems. Furthermore, the technical feasibility of this type of research is questionable for a single university but becomes realistic when several institutions combine resources and expertise.

We propose to continue conducting complementary experiments pertaining to N-use efficiency in forage-based livestock production systems to help stakeholders make informed decisions about rural landscapes. Forage-based livestock production systems provide multiple ecosystem services including meat, milk, and fiber production as well as supporting, regulating, and cultural services. Supporting services include soil building and nutrient retention, banking, and filtering rain and melting snow waters through the soil profile. Carbon sequestration and water storage are also regulating services, and cultural services include spiritual, aesthetic, and educational factors. Forage and perennial grasslands vary greatly in their ability to provide these types of ecosystem services because of differing environmental and management characteristics. We will assess tradeoffs among these services, which should allow more informed decision-making and long-range improvements in U.S. agriculture as a result.