NC1182: Management and Environmental Factors Affecting Nitrogen Cycling and Use Efficiency in Forage-Based Livestock Production Systems

(Multistate Research Project)

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Nitrogen use efficiency and improvement thereof is a recurring subject of investigation regarding grazing systems. The amount of N applied annually to these systems exceeds plant uptake, and only little of this N is removed by animals and subsequently the ecosystem. Significant quantities of N fertilizers are applied to forage crop and grazing systems because N is usually the most limiting nutrient for plant growth.

Although nutrient cycles in grazing systems are less open than in systems that rely on concentrated feed such as poultry production, loss of N from pastures is an unsolved problem to which fertilizer N and supplemental feed contribute (Li et al. 2012). In the Midwest, loss of N from any agricultural systems 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 (Mosier et al., 1998). The magnitude of N loss and resulting negative impacts on ecosystems are influenced by the timing, frequency, and intensity of management practices within the ecosystems.

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. Our experiments will examine alternative strategies to enhance legume establishment and persistence, improve N harvest efficiency, and reduce greenhouse gas (GHG) footprints in pastures; assess secondary plant metabolites in forage legumes for increased N retention and altered N cycling in dung and urine excretions from grazing ruminant animals; and quantify the effects of intensive pasture management strategies on N harvest efficiency and spatiotemporal patterns of N cycling in grassland agro-ecosystems.

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 environmental quality. In addition, this work will facilitate the identification 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 and 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 pasture to low-input pastures). 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 to conduct complementary experiments to help stakeholders make informed decisions about rural landscapes. Multifunctional farming systems provide multiple ecosystem services. These services can include provisioning (i.e., meat, milk, and fiber production) as well as supporting, regulating, and cultural services. Supporting services include soil building and nutrient retention whereas carbon sequestration and water storage are regulating services, and cultural services include spiritual, aesthetic, and educational factors. 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 amongst these services, which should allow more informed decision-making and long-range improvements in U.S. agriculture as a result.

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