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

(Multistate Research Project)

Status: Active

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

Duration: 10/01/2019 to 09/30/2024

Administrative Advisor(s):


NIFA Reps:


Statement of Issues and Justification

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.

Related, Current and Previous Work

Our previous work illustrated that forage-based hay and livestock production systems can improve farm profitability, especially when leguminous species are utilized. We also have preliminary evidence of uneven N distribution in continuously grazed pastures and have found that much of the N losses or reduced N efficiency in these systems is related to forage type, landscape position, grazing management and associated cattle behavior. Our forage- and pasture-based management strategies were developed as appropriate for each of our regional ecosystems and demonstrate the capacity to improve C capture, reduce GHG fluxes, and increase retention and utilization of N within these soil, plant, and animal production systems. These strategies do so by redistributing, recycling, or producing N within the system at minimal cost and time to the farmer. However, what we have yet to discern is the magnitude of these services and to what degree these services change with changing environments and climate. For example, which of these forage- and pasture-based management strategies will stand-up to (resist) extreme weather events, both wet and dry. Grazing and forage systems that capture and attenuate water within the grassland soil and that can help utilize or recycle nutrients may help both the environment and the farmer but it is dependent on ecosystem and management (Abdalla et al., 2017). The negative influences of GHG emissions, eutrophication of aquatic systems, and loss of farm income may be moderated at the farm scale by adaptive management such as strategic rotational grazing management, forage choice or mixtures, and incorporation of the sensitivity of landscape to changes in these grassland management systems. The amount of change will vary depending on landscape and ecosystem. Exploring potential solutions for sustainable grassland systems throughout the US will facilitate our understanding and quantification of soil C, N use efficiencies, GHG fluxes, nutrient cycling and other measures of soil health. Differences in ecosystems (positive and negative) should be considered when developing predictions on water retention (Rojas-Downing et al., 2017) and nutrient cycling when identifying the most effective management strategies for changing climates.  Pastoral systems throughout the US experience repeated droughts multiple times each decade and chronically experience patterns of very wet and very dry periods.  Of additional concern is the prediction that these extreme weather events will be exacerbated in the next 25 to 50 years (IPCC, 2012).


Surface application of N fertilizers (mineral, manures, and deposited directly by cattle) to grasslands results in losses of ammonia (NH3), nitrate (NO3), and nitrous oxide (N2O) depending on environmental variables such as temperature, relative humidity, rainfall, soil texture, litter layer, and soil water content. Our previous research on Southern Piedmont pastures in Georgia has shown NH3 losses from urea-ammonium nitrate (UAN) ranging from 6 to 33% of the applied N (Vaio et al., 2008).  These emissions of NH3 to the atmosphere decrease the efficiency of the applied N and the lost NH3 is eventually deposited back to soil or water with potential environmental problems. Ammonia deposition in riparian and forest areas contributes to soil acidification through nitrification and acts as a direct source of NO3 leaching or an indirect source of N2O, a potent greenhouse gas (Mosier et al., 1998). Ammonia deposition in surface waters may also lead to eutrophication in streams, rivers, and lakes (Lewis et al., 2011). Thus, identifying practices that reduce NH3 losses from grasslands is important to improve N and economic efficiency and to decrease potential environmental problems.


In a 12-year study of grassland systems, Franzluebbers and Stuedemann (2010) showed that grazing (whether light or heavy) resulted in a build-up of soil organic carbon (SOC) when compared to haying of grasslands. While some research results comparing rotational and continuous stocking or grazing systems and their impact on water quantity and quality are not definitive (Owens et al., 2012) and are often site-specific (Ridley et al., 2003; Hughes et al., 2006), other studies point out definitive results indicating that pastoral systems that promote soil quality and C sequestration capture more rainfall (Franzluebbers et al., 2012). These studies highlight the complexity of nutrient cycling.  Moreover they point out that more research is needed in diverse ecosystems taking into account landscape elevation and morphology. Soils with greater C sequestration in the upper surface have been shown to capture more rainfall during wetter periods and provide more grazing during drier periods (Franzluebbers et al., 2012). Of concern is the uneven distribution of forage density and quality in areas where foraging animals camp and denude the soil surface leaving it vulnerable to runoff (often at the edge-of-field).


Beef cattle-poultry grassland systems fertilized with locally-generated animal manures is a common practice in the Southern US, and can be a nutrient-efficient agronomic practice (Butler et al., 2010). In pastured systems, most N and phosphorus (P) is recycled by the grazing animals, which, if distributed throughout the pasture, can sustain and build resilience into a pastoral system. However, if animals deposit nutrients in concentrated flow areas (areas vulnerable to runoff and erosion) the amount of N and P in runoff can result in unnecessary losses of valuable nutrients (Butler et al., 2008; Franklin, et al., 2009). Integration of legumes into forage- and pasture-based farming operations may help farmers balance nutrient imports and exports in their farms (Sistani and Brink, 2008). Research has also found overseeding of grazed fields in the winter and summer can effectively lead to recycling of nutrients within the grazing system. For example, in a summer trial using overseeded pigeon pea [Cajanus cajan (L.) Millsp.], Srinivas and Northup (2012) indicated that grazing of pigeon pea increased stocker productivity and left large quantities of biomass on the surface. 


There has been a long history of pasture-based beef cattle production in the southeastern USA and the dominant management approaches have been either continuous or minimal rotational stocking. In many parts of the region, producers feed hay for 3 to 5 months during the winter. This combination of management practices results in poor pasture condition, poor distribution of manure and nutrients, and accompanying negative impacts on soil and water quality (Osmond et al., 2007; Franzluebbers 2008). We know that through rotational management, feces and urine are more evenly deposited across the pasture landscape, leading to reduced N and P export from grasslands if water and supplemental feed stations are not in areas vulnerable to runoff. It is often difficult, however, for producers to find the time or resources to implement rotational grazing or other better management grazing practices. Implementation of these practices is often considered a risk by producers. Producer confidence and/or incentives are needed if these practices are going to be applied by producers. If conservation practices are less costly and time-consuming or are shown to enhance productivity and thus be worth the extra time, such a set of conservation practices or prescribed conservation grazing systems may be more often utilized.


Spatial variability of soil N is a major concern in most pastures because it results in less than optimum land use. Researchers (Franklin et al., 2009; Byers et al., 2005) have indicated that nutrient losses from pasture are attributed to management activities and cattle preference for certain areas of the pasture (Matthews et al., 1994; DelCurto et al., 2005). It has been documented that cattle concentration areas have significant impact on nutrient hot-spots in pastures (Sanderson et al., 2010; Matthews et al., 1994; Bailey et al., 2001), but very few efforts have been made to quantify the effects of management activities, inclusion of legumes, and landscape parameters on spatial distribution of soil N.


For many years, extension educators and conservationists have promoted the use of rotational grazing management, installation of water quality best management practices, winter grazing on stockpiled forages, and improved winter-feeding management. Implementation of technical improvements such as off-stream watering systems, exclusion fencing, and heavy use areas have been relatively successful (Byers et al., 2005; Franklin et al., 2009). However, management-based practices have been adopted much less extensively.


Another option for improving N-use efficiency is incorporation of forages with plant secondary metabolites.  Legume secondary plant metabolites such as tannins and saponnins, have been shown to reduce methane (CH4) production in the rumen. Results from a preliminary meta-analysis using data from 20 studies highlighted that incorporating clover (Trifolium sp.) at levels up to 30% of dry matter in grass-based diets reduced enteric CH4 output of dairy cows by 30g/cow/d. However, feeding clover at that rate was associated with a reduced utilization of N for milk production indicating more excretion of N in urine, which would contribute to N2O emissions from manure (Schils et al., 2013). Plant secondary metabolites such as tannins offer potential to improve this situation as tannins suppress degradation of plant protein by ruminal microorganisms (Coblentz and Grabber, 2013) and shift digestion to the small intestine (Niderkorn et al., 2011; Waghorn, 2008).  This may ultimately improve animal production (Hymes-Fecht et al., 2013) or production efficiency (Aguerre et al., 2016) while reducing total urinary N and urinary urea N (Aguerre et al., 2016) if included at an optimal amount in the diet.  However, this optimum level needs further evaluation because of considerable variability in the response to tannins across different studies (Animut et al, 2008; Martin et al., 2010) due to variability in response by different classes of animals (Aguerre et al., 2016) or variability in tannins from different plant sources (Animut et al., 2008; Kahn et al., 2009). Other forage phenolic compounds also reduced ruminal NH3 (Hymes-Fecht et al., 2013) and ruminal protein degradation (Grabber, 2008), and improved N utilization (Broderick et al., 2001) in dairy cows. However, as with tannins, it is likely that the optimum dose or dietary concentration will vary depending on the specific response measurement evaluated, making it necessary to evaluate a range of diets that include plants with greater phenolic compound concentrations.


Feeding tannins or other plant secondary metabolites may have additional benefits environmentally, as feeding tannin extracts substantially reduced direct NH3 emissions from dairy cattle manure (Powell et al., 2011b) or when manure was applied to soil in lab-scale chambers (Powell et al., 2011a). It is possible that the shift in digestion of forage protein from the rumen to the small intestine increased diversity in N-containing compounds in the urine. Environmentally, this is of importance because different N-containing compounds in the urine react differently when acted upon by soil microorganisms (Oenema et al., 1997; van Groenigen et al., 2005a,b). Less N in urine should result in less N volatilization as NH3 (Wachendorf et al., 2008), less leaching of N (Saarijärvi and Virkajärvi, 2009), and possibly less N loss as N2O (Oenema et al., 1997). Again, however, information of optimal dietary concentrations of tannins or other polyphenols needed to minimize environmentally negative N leaching or GHG emissions is limited.


Optimal ruminal fermentation is dependent upon microbial growth which is affected by the concurrent availability of fermentable carbohydrates and N from the breakdown of dietary protein to NH3 and numerous C-containing structures (Theodorou et al., 2006; Calsamiglia et al., 2010). This synchrony is difficult to achieve in forage-based diets however because of differential rates of microbial breakdown of the compounds that contain N and those primarily composed of cellulose. The most logical approach to optimize rumen function is to feed balanced diets to ruminants (Garg et al., 2013). Forage-based diets are not balanced generally because of fluctuations in forage quality throughout the growing season leading to great fluctuations in the C:N ratio. Means to improve fermentation efficiency by ruminant animals consuming forage-based diets are available (Gerber et al., 2013), but practical application of many of these principles is not commonly achieved (Hoekstra et al., 2007). Supplementation with concentrates or other fermentation-enhancing compounds may be used to improve the C:N ratio and improve overall animal efficiency by capturing more C and N into animal tissue and concurrently reducing N excretion, especially in urine (Dijkstra et al., 2013; Lee et al., 2014). Furthermore, fermentation may be enhanced by supplementation with different enzymes which may reduce the need for further protein supplementation. However, in many instances, supplementation practices are based on economics and feedstuff availability rather than having a primary focus of optimizing capture of C and N in the animal and reducing nitrogenous excretions by the animal.


In summary, considerable progress has been made in the understanding of the complexities of factors that affect N-use efficiency in the ruminant animal and in the environment.  However, much work is needed to develop linkages between the various factors influencing N-use and associated environmental factors and to develop practical, producer-friendly management practices and decision-support tools that improve N-use efficiency in forage-based livestock production systems. In our proposed work, we look to discover more efficient means to redistribute N from animal wastes with management while concordantly reducing export of N from pastures to the atmosphere and/or ground and surface wasters. We will also further explore means to quantify the influence of a variety of forage species (both grasses and legumes) and feeding strategies to improve feed efficiency, reduce GHG emissions, and improve N-use efficiency. Much work is needed to integrate practices that improve N-use efficiency at the soil-plant-animal-environment interface. This multi-state committee is comprised of scientists with expertise in soil, forage, and animal N-use efficiency as well as environmental and economic modeling. The projects proposed herein by those scientists with the described diversity in expertise and locations will produce information for the development of guidelines that will improve N-use efficiency at all levels of the soil-plant-animal-environment interface for several ecosystems.


Networking with other Regional Projects:


A number of other regional projects are currently working on forages and may include livestock components.  Overall, each of these projects currently has members on that specific committee that are also members of the current NC1182 committee or are located in the same department as a current NC1182 member.  Furthermore, the focus of those committees does not align with the specific focus of NC1182 which is to ultimately improve nitrogen-use efficiency at the landscape level in forage-based livestock systems across a vast geographical region.  The NC1010 project is a forage breeding project that proposes to evaluate a number of forage characteristics which include forage quality, but other than possibly using one of the cultivars released by this committee, interests are different.  The NC1181 committee has somewhat similar objectives, and the NC1181 and NC1182 committees have met together on multiple occasions in recent years.  However, it was determined that the focus of that committee and that of NC1182 are sufficiently different to warrant separate meetings.  The NC1181 is focused more specifically on issues in the mid-western US and include a crop residue emphasis and annual forages to extend grazing using cropland.  Furthermore, NC1181 and NC1182 have multiple common participants which allows sharing of information among the group without a concurrent meeting. The NCCC31 objectives are to evaluate current forage-related issues and develop collaborative efforts to address these.  This objective is much broader than that of the NC1182.  There are multiple members on both the NCCC31 and NC1182 committees and other NC1182 members work closely with members of the NCCC31 committee that are at their respective institutions.  Because of the specific focus of the NC1182 and the general focus of the NCCC31, a common meeting would not be advantageous at the present time.  The WERA1040 is another committee with the focus of reviewing western regional issues and developing collaborative research proposals and extension publications to address these issues.  The WERA1040 and NC1182 committees have one common member and other members at the same institution.  Based on this, and considering the tight schedules that occur at the current annual meetings, it is better use of time and resources to interact with the other committees through common members and co-workers rather than reduce the collaborative interactions of the current NC1182 meetings. 

Objectives

  1. Quantify environmental and economic effects of forage- and pasture-based management strategies and climate change on N-use efficiency by ruminant animals, N cycling in herbage and soils, aquatic N losses, and GHG and other pollutant emissions from grassland agro-ecosystems. (AR, GA, KY, MI, NE, TN, UT, WA, TN). Specific objectives: (i) Investigate effects of management strategies that alter spatiotemporal distribution of soil N pools, grazing and nutritive value of forage on ruminant performance, protein metabolism, and N harvest efficiency; (ii) Evaluate environmental and economic effects of management strategies and climate change on herbage mass and accumulation, nutritive value, botanical composition, and N use efficiency across growing seasons and pasture landscapes; (iii) Determine N pool and cycling (soil, plant, atmosphere, and water), N-use efficiency and biological activity, and economic responses to management strategies in forage-based ruminant production systems with or without forage legumes across variable soil environments and climatic conditions; (iv) Determine the impact of legumes on the GHG footprint and economic returns of livestock production systems.
  2. Assess the efficacy of secondary plant metabolites in legume species for increasing N retention and improving N-cycling in forage-livestock systems. (AR, KY, MO, UT). Specific objectives: (i) evaluate effects of legumes containing tannins or other secondary plant metabolites on N partitioning in fecal and urine excretions; (ii) Determine soluble phenolic effects on forage legume protein fractionations and N availability; (iii) Evaluate effects of tannin or other secondary plant metabolites and their concentrations on soil N availability in mixed legume/grass swards.
  3. Assess the efficacy of supplementation practices including alternative feedstuffs or feed additives on N-use efficiency in ruminant animals in forage-based livestock production systems (AR, KY, NE) and how these practices affect composition of feces and urine and rumen microbial efficiency.
  4. Disseminate research results through coordinated extension/education activities, including extension publications, university course material, and national, regional and state conferences on legume establishment, interseeding and management of grass-legume mixtures, and N cycling and use efficiency. (AR, GA, KY, MI, MO, NE, OH, UT, WA).

Methods

Objective 1:

(i)

Uneven spatial distribution of soil N in conventionally managed pastures is a function of various biotic and abiotic factors and results in poor land use efficiency.  In these studies, we will measure soil inorganic N (0-5, 5-10, and 10-20 cm depth) in a 50-m grid and specific areas of interests (AOIs) from 8 conventionally managed beef-pastures (~ 17 ha each), within the Piedmont of the South Atlantic region to assess the effect of management, landscape, and cattle locus on spatial distribution of soil inorganic N. This baseline collection has been completed and post treatment analysis is currently underway. Treatments include 4 pastures remaining as conventionally managed and 4 converted to strategic rotational grazing practices which include:  exclusion of cattle from critical source areas; overseeding of these areas (winter and summer grass/legume forage mixes), mob grazing of exclusions, weekly rotations with strategic placement of hay, portable shades, and waterers. Soil health measures (respiration, potential N mineralization, runoff losses of inorganic N, NH3 volatilization, and permanganate C), nutritional value and productivity of forage (NDVI estimation from sentinel satellite images), cattle performance, and time-stamped GPS annual cattle data (cattle density maps from 2 cows/pasture) will be analyzed “Initial” and “Post” (after treatment application) soil nutrient contour maps, runoff water quality, forage quality, and cattle positions will be assessed and compared to evaluate impact of grazing technologies.

How legumes and N fertilization affect beef cattle N intake, retention, excretion, and use efficiency will also be determined in the North Central region both pre- and post-grazing in rotationally stocked pastures across the growing season. Nitrogen intake will be measured by clipping forages pre- and post-grazing and N analysis and N balance will be determined to evaluate N use efficiency on an animal and system basis (expressed per ha). The animal N balance will include inputs from forage and outputs calculated using N retention, with the difference equaling surplus or excreted N. Retention of N will be calculated from total body weight gains using NRC (1996) equations. The amount of N in trampled forage and litter returning to the pasture surface will also be measured in the post-grazed forage samples to determine how pasture management affects N cycling.

In several ecosystems across Tennessee, we will investigate N efficiency in integrated crop and livestock systems with and without legumes. We will incorporate living mulch systems with dairy production using a comprehensive approach with forage and livestock producers across the state measuring long-term soil health benefits. Treatments will include grain corn with white clover, silage corn with white clover, grain corn with crimson clover, and silage corn with crimson clover. Dairy heifers will be balanced by body weight and body condition score and assigned to forage treatments to determine the effect of pasture treatment on animal productivity, energy, and N retention. Heifers will rotationally graze forage treatments according to current management practices of grazing cool season grasses of the East South Central and West South Central US. Forage samples will be collected to characterize the nutritive value of the sward canopy during the entire grazing period. Soil health benefits from the integrated crop-livestock-living mulch system will be evaluated by collecting samples twice/year, for 3 years. This project will demonstrate long-term products that will give Tennessee stakeholder’s options on cost-effective clover living mulch production management and dairy production.

 (ii)

Work in Arkansas will continue collaboration with the US Dairy Forage Research Center (USDFRC) in Wisconsin to evaluate the impact of different forage and fertility management strategies on N-balance in sheep. Storing forages as haylage is of growing interest in many parts of the country because untimely rain events delay harvest resulting in excessive maturity. Tall fescue, meadow fescue, and orchardgrass will be fertilized with commercial N fertilizer or with dairy slurry (Marshfield, WI). Subsequent cuttings will be harvested from replicated field plots and stored as haylage in large round bales. These bales will then be transported to Arkansas and offered to growing lambs housed in individual pens with expanded metal floors fitted with trays to facilitate collection of separated feces and urine. Feces and urine will be analyzed for total N and urine will be analyzed for different urine N constituents to evaluate their potential for NH3 and N2O emissions. Nitrogen balance in growing lambs will be calculated.

Work in Kentucky is evaluating the response of 3 tall fescue cultivars, each either infected with a fungal endophyte symbiont or not, to climate change conditions of elevated temperatures and altered precipitation regimes. The project consists of 20 hexagonal plots (each ~3m diameter) divided into 5 blocks, where each block contains 2 plots surrounded by Salamander infrared heaters or by heater housing units but no heating capability. These plots are on a relatively level area of deep (>1m) limestone-derived soils. Sheet aluminum was installed (50cm depth) around each plot to prevent runoff and water movement within the root zone. Plots with infrared heaters are kept at 3oC above ambient temperature conditions, day and night, throughout the growing season. Non-heated plots are kept at ambient temperature. One heated and one ambient plot per block are subjected to an altered precipitation regime. The other heated and ambient temperature plots per block are kept at ambient rainfall, receiving whatever rain falls at the site during the year. To achieve the altered precipitation regime, plots are covered by movable rain-out shelters which are used to exclude all rainfall. Rain is then reapplied, by hand, under less frequent but more intense storms, and is based on the rainfall manipulation conducted at Konza Prairie LTER (Knapp et al. 2002). These treatments take into consideration that future rainfall events are likely to become more intense and less frequent (Karl et al. 2009). Therefore, the climate manipulations reflect the current state of knowledge on future temperature and precipitation regimes for the east-central US (Burkett et al. 2001; IPCC 2012). In all treatments, we will measure air and soil temperature (continuously using thermocouples) and surface soil moisture (Time Domain Reflectometry).

 Also in the East South Central region, experimental climate treatment plots are sub-divided into 6 smaller plots, in which 3 cultivars of tall fescue that are readily available to forage producers via the seed industry (KY-31, Jesup MaxQ, and Texoma MaxQII) were planted. KY-31 is the oldest and most common cultivar of tall fescue in the eastern US but associates with the common toxic strain of E. coenophiala (CTE), which is known to produce animal toxicity issues. Jesup MaxQ was one of the first (2002) so- called ‘novel, non-toxic’ endophyte (AR542) containing cultivars on the market (Bouton 2009), and Texoma MaxQII is a newer release (2010), and contains a different novel, non-toxic endophyte (AR584). All 3 endophyte strains differ in their alkaloid production capability. We also planted heat-treated sub-samples of the acquired endophyte- infected seed which successfully removed the endophyte. Paired subplots (0.5m × 0.5m) of endophyte-infected and endophyte-free seed were sown in each climate treatment plot in Oct 2015 and allowed to establish through the winter and early spring. Endophyte status of fescue growing in the plots in April 2016 was checked (via immunoblot) and confirmed that endophyte treatments were as planned. Climate manipulations began in April 2016 and are continuing until present. We are measuring fescue yield, forage quality (including protein and N content), and alkaloid concentrations every spring and fall. This experiment will allow us to determine which fescue cultivar is most resilient to predicted future climatic conditions and how N use efficiency of the forage responds, as well as the role of fungal endophyte symbiosis in these responses.

Work in Ohio will quantify management practices affecting forage production for extensive and intensively managed pastures. Two studies will measure legume production, persistence and nutritive value (including fiber and crude protein) under optimum (alfalfa at the Western Agric. Res. Center, South Charleston OH), and suboptimum (Trifolium stoloniferum at 9 undeveloped sites in southern Ohio) management. Alfalfa is an N-fixing species with high N-inputs, while T. stoloniferum is a non-nodulating species with no N-fixation. Results for the alfalfa study will be combined with data from prior years to develop fertilization models for P, K and S (and their effects on N-uptake). Tristate (MI, IN, OH) fertilizer recommendations for alfalfa have not been revised for 25 yr, and changes in S supply, losses of these nutrients in surface waters, and production economics suggest that alternative fertilization strategies are possible.

 (iii)

In the Central Mountain region, four grass species will be evaluated as grass-legume mixtures (no N fertilizer) and grass monocultures (N fertilizer added) within Utah’s dairy systems. The impact on nutrient cycling will be examined by determination of the nutrients in each phase (plant, soil, and soil water). A rotational grazing management system will be used. Plant samples will be collected prior to, and after grazing events and analyzed for total N. Herbage dry matter analyses and yield measurements will be utilized to calculate the nutrients being removed in the plant phase. Soil samples will be collected at three depths (0-30 cm, 30-60 cm, and 60-90 cm) at the beginning and end of each grazing season and analyzed for available N (NO3-N, ammonium NH4-N), total N, and total C. Leachate samples will be collected bi-weekly through the growing season via zero-tension lysimeters and analyzed for NO3-N. The N balance technique will be used to estimate N losses due to volatilization. This will be done by comparing total N outputs (recovery in the plant, soil, and soil water phases) against the total amount of N inputs.

In Arkansas, urine and feces from lambs offered forages from different management scenarios will be applied individually or as a slurry (urine + feces) to individual plots of tall fescue or bermudagrass that are separated by metal strips embedded to 30 cm to provide a containment border for each plot. Commercial N fertilization controls and negative controls (no fertilization) will be included. Within each plot, static chambers (30 cm diameter × 45 cm length PVC pipe) will be inserted into the soil (30 cm deep with 15 cm headspace for grass growth). Nitrous oxide, NH3, carbon dioxide (CO2), and CH4 emissions will be measured for each enclosure using static chambers consulting GRACEnet project protocol recommendations (Parkin and Venterea, 2010). Measurements will be made immediately after application, daily during the first 5 days, and at specified time intervals afterward. Grass will be clipped (5-cm) inside each enclosure 1 wk prior to the beginning of gas measurements to maintain a consistent forage height during initial gas emissions measurements. Forage will be harvested (5 cm above the soil surface) from each enclosure immediately prior to fertility addition and on days 21 and 42 to determine forage mass. Soil will be collected at the surface (0-5 cm) for each treatment immediately prior to fertilization (day 0) and at day 14, and analyzed for electrical conductivity, pH, NO3, ammonium, dissolved organic carbon (DOC) and N (DON), particulate organic matter (POM), and the soil microbiome to determine treatment effects on soil properties. At the end of each static chamber experiment, soil will be sampled at the 0-5, 5-15, and 15-30 cm depths for bulk density, particle size analysis, electrical conductivity, pH, NO3, ammonium, Mehlich-III extractable nutrients, microbial biomass C and N, DOC, DON, POM, total soil C and N, and the soil microbiome to determine treatment effects on soil properties. The soil microbiome will be analyzed at the soil surface for each treatment immediately and at day 14, and at each depth for each treatment at day 42.

(iv)

In an exploratory pasture trial investigating GHG emissions in grass-fed Michigan beef systems we will: a) determine the forage and beef productivity of grass-finishing systems based on simple (alfalfa, orchardgrass) or complex (alfalfa, orchardgrass, timothy, red clover, white clover, birdsfoot trefoil, meadow fescue, and chicory) forage mixtures containing legumes; b) determine impact of forage type on enteric CH4 and N2O emissions; c) compare soil C and N stocks and dynamics; d) create a flux assessment to balance the in and out flows of enteric CH4 and N2O. The project has 4, 3.2-ha pastures grazed by 6 to 8 finishing cattle from May to October in 2018 and 2019. Production measurements include animal weights and forage biomass and nutritive composition. Soil GHG flux will be measured for 1 wk early and late in the grazing season using static chambers. Enteric CH4 will be measured on each pasture twice each year using a GreenFeed system (C-Lock Inc., Rapid City, SD). Soil health measures, total soil C and N, particulate organic C, permanganate oxidizable C, mineral N, soil dissolved N, and potential denitrification will be measured at the beginning and end of the trial.

Data from the above studies (i-iv) will be used to modify and validate a spreadsheet decision support tool and farm enterprise budgets that can be used by producers to calculate economic returns and GHG emissions from pasture-based livestock production systems.

Objective 2i, ii, and iii:                                                                         

Research in the Central Mountain region (Utah) will compare 4 grass species as monocultures versus grass-legume mixtures using birdsfoot trefoil that contains tannins in a rotational grazing system. Heifer body weight, blood urea N (BUN), urine urea and total N and fecal ammonium-N, and total N will be measured prior to grazing, and after the completion of each grazing rotation.. Soil samples will be collected at 3 depths (0-30 cm, 30-60 cm, and 60-90 cm) at the beginning and end of each grazing season and analyzed for available N (NO3-N, ammonium NH4-N), and total N to determine the impact of tannins on soil N availability.

From the North Central region using metadata from Iowa as well as from all of the US, we will quantitatively summarize the effects of legumes containing secondary plant metabolites on N partitioning in fecal and urine excretions of dairy and beef cattle using-meta-analytical approaches. Secondary plant metabolites such as tannins and saponins in legumes have been shown to reduce CH4 production in the rumen. To extend a preliminary meta-analysis, data from this renewal and a comprehensive literature search will be extended to obtain more data on CH4 emissions, feed intake, and production of not only dairy cows but also beef cattle. Additional data on fecal and urinary N excretions and manure N2O emissions of cattle fed legume-based diets will be collected. The latter data will be used to develop models to describe the relationship between fecal and urinary N excretions and N2O emissions from manure. Such models will help evaluate correctly the impact of feeding legumes on GHG emissions, N partitioning and utilization efficiencies in forage-based cattle production systems.

 In Kentucky, collaborative work with the USDA-ARS Forage Animal Production Research Unit is exploring the role of a red clover-produced isoflavone, Biochanin A, on rumen microbial dynamics and N retention within the animal and excreted via urine and feces. Biochanin A has been shown to selectively inhibit rumen bacteria that convert feed amino acids to NH3 (Flythe & Kagan 2017). When biochanin A or red clover was fed to grazing steers, NH3 production was inhibited and daily gain increased (Harlow et al. 2017). In a lamb trial, animals will be fed no biochanin A or biochanin A applied at 2 levels and feces and urine will be collected from the animals and measured for N content.

In Arkansas, lambs will be offered diets of alfalfa haylage alone or with different levels of sericea lespedeza to achieve different levels of condensed tannins on N concentrations in feces and urine, composition of urine nitrogenous compounds, and N balance using procedures outlined in subobjective 1.ii. Resulting feces and urine will be applied to plots of tall fescue as outlined in subobjective 1.iii and emissions and soil measurements will be conducted as outlined in that subobjective.

 Objective 3:

Lablab is an annual legume that has high production potential, but is not used extensively in the US. Lablab does not contain tannins, but contains high levels of other total polyphenols, thus providing interest as a supplemental forage to alter urine and fecal N composition and constituents. Lambs will be offered diets of alfalfa haylage alone or with different levels of lablab to achieve different levels of total polyphenols in the diet (Arkansas).  Additional N balance studies will be conducted with lambs offered forage-based diets with different supplementation strategies to provide additional macronutrients, enzymes, plant extracts, or other microbial products.  Resulting feces and urine will be applied to plots of bermudagrass as outlined in subobjective 1.iii and emissions and soil measurements will be conducted as funding permits.

In Kentucky, in collaboration with the USDA Forage Animal Production Research Unit, a steer trial will be conducted evaluating the effect of bitter acids produced by hops plants on animal N use efficiency and daily gain. Bitter acids in hops have been shown to have similar effects to red clover-produced Biochanin A (Flythe et al. 2017). Animals will be fed craft brewer yeast with and without hops, and feces and urine will be collected and measured for N content. Animal daily gain and N content of the various feeds will also be quantified. We will also assess whether bitter acid-derived changes in N content within urine and feces alters soil-to-atmosphere GHG fluxes, soil inorganic N concentrations, and soil microbial community dynamics in the lab using a modified static incubation procedure (Fierer et al. 2003; Iqbal et al. 2012). CO2, CH4, N2O, and NH3 concentrations will be measured over time using either a photoacoustic gas analyzer or a gas chromatograph (Iqbal et al. 2013; Clough et al. 2010). Measurements will occur on days 1, 2, 3, 5, and 7, and weekly thereafter for 60 days. Rates of trace gas emissions and total quantities emitted will be calculated per chamber. Inorganic N concentrations and microbial community characteristics will be assessed at the beginning and end of the incubation.

Objective 4:

Historically NC1182’s annual gathering to review participating states findings has been hosted by one of the participating states. The purpose of this annual meeting is to review, discuss, and discern similarities and dissimilarities and research findings. In this renewal, the dissemination of research results will be done through annual meetings and coordinated extension/education activities, including extension publications, scientific journal publications, development of related university course material, and presentations at national, regional and state conferences on legume establishment, interseeding and management of grass-legume mixtures, and N cycling and use efficiency.

Measurement of Progress and Results

Outputs

  • At our annual meetings we will discuss our results and methods, identifying similarities and differences, as well as opportunities for new collaborations and research. After these meetings, we will publish our findings at the state, regional and national levels, as annual reports and extension and research publications when appropriate. Our results will include findings on N efficiency relative to forage quality and productivity and animal gain, losses in runoff, leachate, and the atmosphere and will indicate where within the N-cycle, and how, efficiencies were gained. For instance, was N loss reduced in leachate or runoff when comparing different management practices and were the differences comparable in the Northern US and the Southern US or for Utah with more alkaline soils than Arkansas with more acidic soils. In publications, we will highlight consistent results between regions and differences as results indicate. When results indicate, we will identify why differences between locations/ecosystems/landscape positions occurred. Comments: Two economist will be working with us on this project. They are list below: Dr. Michael Popp (AR) and Dr. Cesar Escalante (GA) have been added to the participant list. Both are agricultural economists who have worked with environmental issues facing cattle in grazing scenarios and grazing enterprise budgets. Mr Popp has developed an elaborate excel model that predicts GHG under different grazing scenarios and associated costs and values and Dr. Escalante has expertise in developing and measuring budgets which incorporate “opportunity losses” calculated for productivity losses and the quantification of “opportunity benefits” of grazing gains practices which include ecosystem services.

Outcomes or Projected Impacts

  • By improving beef and dairy systems with combinations of grass and legume forages, hay, and integrated crop-grazing strategies and subsequently improving soil health, we expect to quantify improvements in N efficiencies and nutrient storage in soil and forages throughout the pastures. Stockpiled forages in cattle exclusion areas and rotationally grazed paddocks will increase rooting systems, sequestering and moving C deeper in the soil profile and allowing forages to uptake nutrients that would have either been lost in runoff, leaching, or to the atmosphere as a GHG. By allowing animals to periodically harvest those nutrients through short-term grazing and thereby dispersing those nutrients across the field, we may more efficiently utilize those nutrients and prevent contamination of aquatic systems and reduce atmospheric losses of N. Doing so in a diverse set of ecosystems will further improve our understanding of the capacity of forage- and pasture-based management strategies to improve C capture, reduce GHG fluxes, and increase retention and utilization of N within these soil, plant, and animal production systems. The optimization will be based on improving N efficiency by accounting for N from a variety of legumes, and associated N in feces and urine. On per animal and system bases, pastures containing legumes should increase the ratio of N returned through excreta relative to trampled forage and litter compared to N-fertilized pastures due to increased soil C in the latter, thereby promoting soil-plant N cycling. Secondary plant metabolites such as tannins have the potential to shift N from the urine to the feces and reduce N volatilization, which in turn would increase C and N retention in the soil profile which should help reduce N leaching, reduce GHG emissions, and thereby retain more N for greater forage production and crude protein content and improve prosperity by reducing the need for off-farm N inputs. Projected impacts of this research will be increased support and adoption by producers of legumes in pastures relative to N fertilization and improve N-use efficiency at all levels of the soil-plant-animal-environment interface. In eastern, central, and western dairy systems using recommended grazing/feeding systems in each region, we will gain substantial progress in understanding changes in soil health and nutrient cycling differences with and without legumes in both wet and dry systems. Exploring these differences across regions gives us the ability to make a substantial impact on long-term soil health benefits, production gains or costs in terms of forage, animal, and milk yield and productivity and environmental exchanges of N thereby adding both direct and indirect economical value of this research.

Milestones

(0):Research evaluating beef and dairy management, including addition of legumes and strategic placement of legumes, and N fertilization effects on animal N intake, retention, excretion, and use efficiency in ruminant animals, soil health measures, and litter N cycling in varied landscapes will be conducted during the first 4 years of this project. Grazing studies will be conducted beginning in 2019 to determine how different management practices including legumes and N fertilization impact N cycling and N-use efficiency at the animal and pastoral level. Digestion and N-balance studies will be conducted in 2019 through 2022 to determine the influence of different plant secondary metabolites and forage supplementation programs on N excretion in feces and urine and N-use efficiency in the animal. Manure and urine will be applied to forage plots to determine the impacts of management and dietary manipulations on N cycling and measurements of NH3 and GHG. Modeling of N cycling and computations of N balance in pastures will begin in 2023. Updated forage management recommendations will be discussed annually at our annual meeting and multistate recommendation will be developed by 2024 to help producers manage forage for optimal N-use efficiency in the pasture and animal.

Projected Participation

View Appendix E: Participation

Outreach Plan

We will disseminate research results through coordinated extension/education activities, including extension publications, university course material, and national, regional and state conferences on legume establishment, interseeding and management of grass-legume mixtures, and N cycling and use efficiency. Several educational products and decision-support tools will be developed as part of this project. The foundation of these products will be a collaborative Extension bulletin (“Managing N and Understanding the N-Cycle in Pastures”) that is jointly published by the participating institutions, and then cross-linked on www.eXtension.org and other supporting regional and state websites. This publication will provide specific management recommendations and BMPs based on the available literature on N BMPs and the complexities of the N cycle, as well as the findings from the proposed experiments. Further, this article will provide a venue to properly explain these BMPs and give producers and associated Extension educators/consultants a written resource. A producer-oriented spreadsheet will be modified using research information developed at the different stations that can be used to model economic returns and net greenhouse gas emissions and N-use efficiency based on inputs at the individual farm level. 


We will educate Extension Agents/Educators through an online webinar training on www.eXtension.org (or similar) for Extension Agents in the partner states and develop presentation slide sets that will be posted online and made available for download by Extension Agents/Educators that  cover the information and recommendations from this and prior research. The slide set will focus on training producers on the opportunities for utilizing N in pasture-based production systems more efficiently, provide them with specific BMPs and show them the rationale for these BMPs.  We will also provide intuitive management and economic decision aids, and work with Extension specialists to provide on-site and in-depth consultations to ensure BMPs are successfully employed and to obtain feedback from these producers to determine strategies for future Extension efforts.

Organization/Governance

The NC1182 committee elects a secretary at the annual meeting.  The secretary is responsible for gathering individual state reports and combining them into the committee report that is submitted to NIFA.  The secretary becomes the committee chair at the end of the following annual meeting.  The committee chair oversees the organization and implementation of the annual meeting and is responsible for ensuring that appropriate deadlines are adhered to. Meeting locations are determined by vote of the entire membership at the annual meeting.

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