Duration: 10/01/2004 to 09/30/2009

Administrative Advisor(s):

NIFA Reps:

Non-Technical Summary

Statement of Issues and Justification

The amount of nitrogen (N) applied annually to forage production systems of the Midwest exceeds plant uptake (Mosier, 2001) and relatively little of the N consumed by grazing animals is removed from the ecosystem (Jarvis and Ledgard, 2002). Significantly greater N is removed via mechanical harvesting for feed but the same problem occurs when the forage is fed. Nitrogen fixation by legumes and purchased feed supplements contribute additional N to the system. There is little potential for highly mobile N to accumulate in soils, so the fate of this surplus N is waterbodies, groundwater, the atmosphere, and adjacent terrestrial ecosystems where it can have undesirable effects.

From an agronomic perspective, much is known about fertilizer type, amount, and timing of application for maximizing crop yields (Jenkinson, 2001). Likewise, forage quality and animal nutrition research are targeting ways of improving N use efficiency by plants (Singer and Moore, 2003) and livestock (Scholefield et al., 1991). The NC-189 Committee increased our understanding of protein utilization by grazing cattle (Klopfenstein et al., 2001; Johnson et al., 1998; Coblentz et al., 1998). Although mechanisms and pathways for N transformation and loss have been determined for grasslands and pastures (Ledgard 2001; Kroeze et al. 2003), major gaps exist in our knowledge of the relationships between management and harvest strategies and N pathways on farming and ranching enterprises (Mosier, 2001).

Agronomists have long studied the effects of N-laden soil amendments on plant growth, development, and production. Economical and efficient use of these soil amendments is critical to the long-term economic stability of many farming enterprises because commercial N fertilizers are among the most costly inputs for many production systems. Animal manures and other wastes are readily available alternatives to commercial N fertilizers in some areas; however, heightened environmental concerns demand responsible use of these by-products of confinement feeding operations. In addition, recent concerns about phosphorus (P)- loading may limit the potential to meet N requirements of growing crops strictly with animal manures and other wastes.

Traditionally, the efficiency of N use by forage plants or field crops has been measured by evaluating yield, total concentrations of N in the plant or in specific plant tissues, and N uptake. For forage crops this is often repeated over several harvests throughout the year (Cherney et al., 2002; Evers, 2002). Such evaluations are useful, and they clearly need to be continued in order to maximize the uptake and capture of N from applied soil amendments. However, these studies place little or no emphasis on whether ruminants can efficiently use these forms of N. In particular, there is a great void of information describing the effects of commercial N fertilizers and animal manures on the partitioning of N within plant fractions of nutritional significance to ruminants.

New feeding models for ruminant livestock, such as the Cornell Net Carbohydrate-Protein System (Russell et al., 1992; Sniffen et al., 1992; Fox et al., 1992) and the systems for dairy and beef production proposed by the National Research Council (NRC, 1989; 1996; 2001), require in-depth knowledge of the nutritional characteristics of forage proteins. This information was unnecessary with the old feeding systems that were based only on a measurement of total N (crude protein). Proper use of these new feeding systems returns economic benefits to dairy and beef producers through improved production and more efficient use of N from forage and concentrate feedstuffs. When highly degradable forage proteins are used more efficiently by ruminants, an additional benefit is realized because less N is returned to the environment via animal waste. In order to optimize the benefits of these new feeding models, accurate knowledge of the partitioning of N within the various fiber and cell-soluble fractions of the plant, and the relative degradability of forage N within the rumen is essential. This information can only be obtained by systematic evaluation of an enormous range of climatic, agronomic, and harvest management inputs that affect plant growth and development.

An important part of N use efficiency is the animal. Forages often contain more degradable protein than animals require but insufficient undegradable protein. The excess degradable protein is excreted in the urine. Strategies to increase forage production (N fertilization, interseeding legumes, etc.) often result in forages that contain N far in excess of animal needs. Identification of optimum grazing management and(or) supplementation strategies offer opportunities to increase N utilization. There is a voluminous literature on confinement feeding of beef and dairy cattle for maximum production. However, very little work has been directed toward developing strategies for precisely meeting animal requirements for metabolizable protein and amino acids without overfeeding crude protein in grazing situations. Low protein energy supplements may be an option, including byproduct sources of highly digestible fibers, and protein supplements that resist degradation and have amino acid patterns that are complementary to ruminal microbial protein also have promise.

Related, Current and Previous Work

The NC-189 Multistate Project was very successful in coordinating development of techniques to characterize forage protein degradation in the rumen (Mathis et al., 2001; Klopfenstein et al., 2001; Mass et al., 1999; Vanzant et al., 1998). Largely because of the committee's work, ruminal degradation characteristics of forage proteins in commonly cultivated forages are becoming well documented. Alfalfa proteins have been described and this information has been summarized in recent NRC publications (NRC, 1996; 2001). Work by scientists in the Northern Great Plains also has provided a solid understanding of the protein degradation characteristics of native prairie or range grasses found throughout that region (Coblentz et al., 1999; Mass et al., 1999; Johnson et al., 1998; Hollingsworth-Jenkins et al., 1996; Vanzant et al., 1996; Redfearn et al., 1995). However, reliable information is currently unavailable or incomplete for many other forages utilized by the livestock industry. Specifically, forages such as tall fescue (Festuca arundinacea Schreb.), crabgrass [Digitaria ciliaris (Retz.) Koel], bahiagrass (Paspalum notatum Flugge), bermudagrass [Cynodon dactylon (L.) Pers.], dallisgrass (Paspalum dilatatum Poir.), johnsongrass [Sorghum halepense (L.) Pers.], annual ryegrass (Lolium multiflorum Lam.], and to a lesser extent, various clovers and small grains, have been poorly or incompletely evaluated in this respect. Work by the committee helped to characterize effects of NPN formation in forages harvested as silage (Owens et al., 2002), the influence of NPN formation on protein utilization (Albrecht and Beauchemin, 2003), and the potential of alternative forages that produce lower NPN silage (Broderick et al., 2001).

Grazing Management

Most current research that characterizes the kinetics of protein breakdown in the rumen has been obtained from hand-clipped forages or forages harvested as hay or silage. By comparison, relatively little work has evaluated protein characteristics of grazed forage diets. Dubbs et al. (2003) found that enzymatic estimates of protein degradability served as a reasonable proxy for in situ measurements with tall fescue masticate collected from ruminally cannulated steers. However, enzymatic estimates of protein degradability were as much as 20 percentage units greater with masticate as compared with clipped forage samples, and differences varied across the grazing season, indicating the importance of using animal-selected samples (masticate) for such evaluations. Johnson et al. (1998) recently described in situ disappearance kinetics of crude protein for masticate samples collected from ruminally cannulated steers grazing range sites in North Dakota between June and December. Others (Mass et al., 1999) have included masticate samples of native range in evaluations with other forages. Most recently, Coblentz et al. (2003) evaluated masticate and clipped wheat forage samples harvested at jointing, mid-elongation, and boot stages of growth for in situ disappearance kinetics of N in both grazing and confined steers. Kinetic parameters varied only minimally between the confined and grazing evaluations, suggesting that confined evaluations of masticate and other forage samples may be useful within a grazing context. Although these efforts have improved the knowledge base specific to grazing livestock, there has been little or no effort to evaluate kinetic parameters of protein degradation as affected by diet selection coupled with agronomic variables, such as N fertilization rates, manure application rates, seeding rates, or plant growth stage.

N Fertilization

Historically, most of the recommendations for fertilization of grasses with commercial sources of N have been based on expected increases in forage production relative to the cost of application. Hall et al. (2003) recently reported economically optimum N rates of 26, 32, and 29 kg N Mg-1 of forage harvested for orchardgrass (Dactylis glomerata L.), tall fescue, and timothy (Phleum pratense L.), respectively. Other factors also can influence the appropriate use of N fertilizers. Osborne et al. (1999) found that N source and timing affected recovery of fertilizer N for bermudagrass fertilized once annually at high rates (112 to 1344 kg N ha-1). Early spring applications of NH4NO3 at a rate of 112 kg N ha-1 resulted in recoveries in excess of 85%, but recoveries were much lower with late-summer applications. For cool-season grasses, Zemenchik and Albrecht (2002) reported apparent N recoveries of only 17 to 50% for Kentucky bluegrass (Poa pratensis L.), smooth bromegrass, and orchardgrass receiving spilt applications of NH4NO3 at annual rates ranging from 0 to 336 kg N ha-1. In addition to economic loss, one undesirable aspect of poor recovery of fertilizer N is the potential for leaching below the effective rooting zone (Stout and Jung, 1992), and possible contamination of ground water.

Binary Mixtures of Grasses and Legumes

Legumes contribute to the production of forage within mixed legume-grass swards by recycling biologically fixed N to grass species, and by production of legume biomass (Zemenchik et al., 2001; Farnham and George, 1994). Nitrogen replacement values can be calculated as the amount of N fertilizer required for a grass monoculture to yield as much dry matter as the same grass grown in a mixture with a legume. Zemenchik et al. (2001) reported N replacement values of 251 and 269 kg N ha-1 for kura clover (Trifolium ambiguum M. Bieb.) and birdsfoot trefoil (Lotus corniculatus L.), respectively, when grown with orchardgrass in Wisconsin. This is obviously attractive to many forage-livestock enterprises because the need to purchase N fertilizer is reduced or eliminated. Furthermore, the nutritive value of legume-grass mixtures is often improved relative to monocultures of the same grass (Sleugh et al., 2000; Zemenchik et al., 2002). However, these assessments of nutritive value have been confined primarily to estimates of crude protein, and further quantification of N fractions of nutritional significance is critical to efficient use of these forage mixtures.

Agroecosystem N efficiency

Nitrogen (N) that is applied to agroecosystems but not removed in livestock or crop biomass is surplus N (Jarvis and Ledgard, 2002) because it performs no beneficial agronomic function. Estimates of surplus N in grazed temperate grasslands range from 30 to 50% of N inputs (Carran et al., 1995; Ledgard, 2001), which include fertilizer, exogenous manure, biological fixation, and atmospheric deposition. Surplus N from agroecosystems throughout the Midwest has been identified as the primary cause of periodic hypoxia in the Gulf of Mexico (Rabalais et al., 2002; Turner and Rabalais, 2003). Gaseous N emissions from soils contribute to the greenhouse effect (Robertson et al., 2000; Mosier, 2001) and eutrophication of terrestrial ecosystems (Vitousek et al., 1997; Carpenter et al., 1998; Ferm et al., 1998).

Perennial crops receive less N as fertilizer and the soils on which they grow retain greater amounts of N than annual row crops (Randall et al., 1997; Huggins et al., 2001). Many forage crops are grown in the North Central Region but the dominants are cool- and warm-season grasses, alfalfa, clover, and mixtures of these groups. Perennial crops such as these maintain vegetative cover that is important for conserving topsoil while providing feed for livestock production that is removed by mechanical harvesting or grazing. In general, forage production in the Midwest is improved with addition of N fertilizer (Jenkinson, 2001). Recommendations of 50 to 200 kg N ha-1 by university extension services are common and this is usually applied as ammonium nitrate or urea.

Plant species composition is known to affect N dynamics directly, primarily via N2-fixation by legumes (Ledgard, 2001). Furthermore, legumes and non-legumes alike differ in their capacity to absorb soil N (Ridley et al., 1990). Differences in the form and amount of fertilizer can significantly alter the amount and fate of N loss from the terrestrial environment (Ledgard, et al., 1999; Dobbie and Smith, 2003). The presence or absence of grazing is known to affect ecosystem-wide N losses in Europe and Oceania (Ruzjerez et al., 1994; Williams et al., 1998), but large information gaps exist with respect to the question: What grazing systems, forage mixtures, and dietary manipulations promote N retention in forage-based agroecosystems of the midwestern U.S.?

Surface water, groundwater, and the atmosphere are undesirable N sinks because the forms in which N is found in these environments can contribute to O3 production (Holland and Lamarque, 1992), acidic deposition (Ferm 1998), the greenhouse effect (Schlesinger, 1997; Robertson et al., 2000), eutrophication of aquatic systems (Carpenter et al., 1998), and human health concerns (Fan and Steinberg, 1996). The exception to this is the emission of dinitrogen gas to the atmosphere, which itself is 78% N2. In soils, the potential exists for excreta N to be taken up by plants or microbes for recycling, thereby conserving N within the terrestrial environment.

NH3 volatilization. About 40 to 80% of cattle excreta N is in urine, which is 10 to 95% urea (Rodhe et al., 1997; Biermann et al., 1999; Huntington, 1999). Contact with water and the enzyme urease, which is found universally in feces and soils (Hoult and McGarity, 1986), causes rapid conversion to gaseous ammonia (NH3). Ammonia is a strong base whose atmospheric concentrations are highly correlated with a strong odor (Pain and Misselbrook, 1991). Once NH3 is airborne, it either quickly dissolves in water forming NH4+ that is redeposited on the landscape (Asman et al., 1998; Aneja et al., 2001) and available for biotic uptake; otherwise NH3 is taken up directly by plants from the atmosphere (Ferm, 1998). Higher moisture and temperature increase NH3 emissions from excreta and pasture soils. Alternative grazing and forage systems will affect these emissions directly by altering vegetation structure and physiology, but effects have not been quantified. Plant species differ in their ability to absorb or emit NH3 (McGinn and Janzen, 1998), so forage species composition could affect atmospheric NH3 concentrations. Urea production, urea recycling to the digestive tract, and urinary excretion of urea by grazing ruminants respond to a variety of dietary (e.g., forage N content and degradability) and metabolic (e.g., growth promotants, lactation) factors. Balanced solutions to multifaceted problems must be identified by conducting studies that incorporate measures of urea N metabolism of grazing animals into measures of forage production, N flow through ecosystems, animal performance, and overall economic considerations.

NO3- leaching loss. Nitrogen returns in animal urine have been shown to have an impact on NO3- leaching (Stout et al., 1997). A recent review ranked grazed pastures similar to arable cropping systems with respect to this phenomenon (Di and Cameron, 2002). Work in the northeastern U.S. has shown that NO3- levels can be relatively high in leachate below intensively grazed pastures (Stout et al., 2000a; Stout et al., 2000b) with concentrations exceeding the U.S. EPA maximum surface water standard of 10 ppm NO3-N. Nitrate concentrations beneath restored native prairie in southern Wisconsin were quite low (<1 ppm NO3-N) compared to adjacent corn fields (>30 ppm NO3-N) (Brye et al., 2001). Again, rankings among grazing systems have not been made, hindering the ability to make informed management decisions. Stout et al. (2000b) have compared N leaching under various cool-season forage mixtures subjected to intensive rotational grazing. They found lowest soil NO3- concentrations under orchardgrass (Dactylis glomerata) compared to ryegrass (Lolium perenne), while white clover (Trifolium repens)-grass mixures tended to have lower leachate N than alfalfa (Medicago sativa)-grass mixtures.

Supplemental Energy

Grazing beef steers respond to undegraded protein (Klopfenstein et al., 2001). The degradable protein requirement of grazing cattle is usually met with 6 to 9% degradable protein or 7 to 11% total dietary protein in the forage DM (NRC, 1996). Most green, growing forages have excess protein (NRC, 1996). Klopfenstein and Erickson (2002) have shown that N excretion is minimized when both degradable and undegradable proteins are fed to meet but not exceed the requirements. This is much more difficult to manage with pasture cattle. Lake et al. (1974) supplemented yearling cattle grazing pastures of smooth bromegrass, orchardgrass, and alfalfa with corn and increased efficiency of N utilization. Fieser and Vanzant (2003) increased N retention by supplementing energy (corn or soybean hulls) to beef steers consuming tall fescue hay when hay contained from 8 to 16% CP, but not with vegetative hay that contained 17.4% CP, suggesting that ability to alter N use efficiency through supplementation depends on forage composition. Little additional research has been conducted recently because of lack of concern about N use efficiency.

High quality forages are typified by having high concentrations of proteins that are rapidly and extensively degraded to NH3 in the rumen resulting in poor protein utilization by the animal and concomitant increases in excretion of N to the environment. A strategy is to provide dietary supplements of rapidly degraded carbohydrates, which promotes incorporation of NH3 into microbial cells and lowers pH, thus decreasing absorption of NH3 from the gut. Bach et al. (1999) found that supplementing corn, beet pulp, or soybean hulls with high quality forage concomitantly decreased NH3 concentrations and increased N captured by bacteria. Shifting carbohydrate digestion from the rumen to the intestine increases N excretion in the feces (Bierman et al., 1999; Elizalde et al., 1999), probably because greater hindgut fermentation increases fecal microbial N. Though total N excretion remains unchanged as a result of site of carbohydrate digestion, N losses to the environment via volatilization are reduced as the proportion of N excreted in the feces increases (Erickson et al., 2002).

Peripheral tissues metabolize amino acids extensively. Catabolic pathways for amino acids involve removal of N moieties, generating hydrocarbon skeletons for re-synthesis of amino acids or oxidation for cellular energy (Riis, 1983). Although this process allows for salvaging carbon and N in the case of amino acids, it is inherently energy and N inefficient, resulting in urinary urea excretion (Blaxter, 1989). Whole animal energetic and N utilization is reduced when energy is insufficient and(or) amino acid supply is in excess of tissue demands. This is the case in ruminants consuming temperate forages where energy typically limits tissue protein synthesis (Dubbs et al., 2003; Fieser and Vanzant, 2003). Thus, supplemental energy fed to ruminants consuming high quality forages can improve not only energy and N efficiency in the animal, but also minimize N loss to the environment.

Feeding too much concentrate with too little effective fiber results in ruminal acidosis and other metabolic problems such as laminitis (Nocek, 1997); therefore, this limits the amount of readily fermented concentrate that can be fed to support microbial capture of degraded N from forages (Valadares et al., 2000). Ruminal pH in dairy cows fed large amounts of fermentable carbohydrate (Ekinci and Broderick, 1997; Weimer et al., 1999) and grazing high quality pastures (G. R. Oetzel, unpublished) often average well below 6.2, the pH below which microbial growth may be inhibited (Russell et al., 1992). De Veth and Kolver (2001) reported that, when pH in ruminal continuous culture fermenters was reduced from 6.3 to 5.4 for periods of 0, 4, 8, and 12 hours/day, there was a negative linear relationship between microbial protein yield and the length of time pH was at 5.4.

In a review of the CRIS database, no projects were found that focus specifically on N cycling and efficiency in forage-based livestock production systems. There are a few projects that deal with N utilization and loss in livestock enterprises; most of these are studies conducted in NCT196 states by project participants or collaborators of project participants. Research is being conducted in Wisconsin (WIS04666) to investigate alternative dietary strategies that maintain or enhance N utilization by dairy cattle while reducing potential losses of ammonia-N to the environment. Another project (ARK01748) in Arkansas has an objective of evaluating the N use efficiency in grazing and confinement feeding situations, using cattle and several different forage legumes and grasses. A variety of grass/legume rations for finishing goats are being evaluated for effect on overall performance, carcass characteristics, and nitrogen use efficiency; grazing is not a part of this Virginia project (58-1932-9-040). Three other projects (NEB-42-024, 6218-12000-003-00D, WNP00373) focus on N cycling and management in cropping systems that include forage crops and soil amendments (e.g., commercial fertilizer, animal wastes, and plant co-products).

Objectives

1. Quantify N efficiency of forage-based ecosystems and determine the fate of excreta N.
   
2. Quantify the effect of dietary and animal factors on utilization and excretion of forage N by beef and dairy cattle.
   
3. Determine the influence of plant/soil manipulations on efficiency oon by forages.
   
4. 
   

Methods

Objective 1. Experiment 1: N efficiency of various forage and grazing systems (WI, NE, NC, ND, KY, OK): The N dynamics and N use efficiency of various forage-based livestock production systems will be determined (Van der Hoek, 1998). Ecosystem N efficiency will be calculated in various field trials in each of the cooperating states: N efficiency = (N product/N input) 100 where, N product is the amount of N leaving the ecosystem in the animal, sometimes called "take-off" (Janzen et al., 2003). For cattle, this factor equals 10 to 15% of total annual weight gain (Bouwman and Booij, 1998). Weight gain will not be a standard measurement across sites because cattle will not be on the experimental plots/paddocks for the entire year. Land resource limitations and logistic challenges at most sites restrict our ability to keep cattle on the experimental units year-round. Instead, total annual weight gain will be calculated in short-term studies by estimating forage intake studies from hand-clipped plots inside and outside grazing exclusion cages. The N content of forage species will be measured from the clipped forage samples. Nitrogen "take-off" will be estimated from body composition and weight gains estimated using NRC (1996) equations. N input is the sum of N in applied fertilizer, manure, symbiotic fixation, and atmospheric deposition. Each research site will record all fertilizer types and amounts as well as manure applied to a given area for each year. The contribution of N from symbiotic fixation will be derived by standardized estimation of species composition and biomass scaled to literature-based estimates of total N fixation for a given species mixture and abundance under particular environmental conditions. Regional estimates of atmospheric wet and dry deposition will be taken from the literature. Specifically, N efficiency will be calculated for each treatment in a replicated experiment comparing grazing systems in southern WI as well as an experiment examining N-utilization efficiency of different mixtures of cool- and warm-season grasses and legumes in NE. Other standard measurements across sites will include soil texture, total soil C and N, temperature, and precipitation. These ancillary data will help interpret differences in N dynamics. Experiment 2: NH3 loss from excreta and grazed pasture (NE): To estimate the amount of N volatilized from excreta, a wind tunnel (Duysen et al., 2003; Schmidt and Bicredo, 2002) will be placed over fresh urine and feces to measure the amount of NH3 flux to the atmosphere. Fluxes over time with different temperature and moisture conditions will be determined. Experiment 3: N2O, N2, and NO3- from grazed pasture (WI): At the Franbrook Farm, a University of Wisconsin research property located about 25 km south of Madison, WI, grazing treatments were established in summer 2003 to mimic management intensive rotational grazing (MIRG), continuous grazing (CONT), periodic harvesting of pasture forages for hay (HARV), and removal from production as in a Conservation Reserve Program site (CRP). Treatments are arranged in a randomized block design with three blocks. All treatment paddocks are currently grazed continuously (CONT) by 60 cow-calf pairs of beef cattle. Separate herds of about 30 cow-calf pairs [30 animal units (AU)]) will graze each block beginning spring 2004. MIRG paddocks will be grazed at high stocking densities for 1 to 2 days and then allowed to rest for 28 days. During the MIRG-rest period, each herd will graze the CONT paddocks (6 to 8 ha in size). The CONT paddocks will have lower stocking rates and paddocks will be rested only during the 1 to 2 days the herd is confined to MIRG paddocks within each block. Grassland biomass will be mechanically harvested 2 to 3 times annually for the HARV treatment to mimic the making of hay typical to confinement operations. Grassland will also have no harvest (CRP). Each block will be split and granular ammonium nitrate fertilizer will be applied to one-half of each block at the recommended rate. Soil gas fluxes and soil water leachate will be sampled in situ April, June, August, and October 2005. Soil gas fluxes will be estimated by repeated sampling of the headspace of closed, vented chambers placed over the soil surface (Livingston and Hutchinson, 1994). Leachate will be collected from soil cores taken at 50-cm increments to a 2-m depth. Objective 2: Experiment 1: Nitrogen dynamics in cattle as affected by grazing management and supplementation strategies (NE, NC ,ND, KY, OK). Grazing experiments will be conducted with calves or yearlings grazing forages typical of the state. In some cases, the forages will include legumes. Treatments will be either grazing management strategies or supplementation strategies. The goal is to increase N capture by the animals (primarily microorganisms) and reduce N excretion, especially in the urine. Supplements may include grains, corn bran, wheat midds, and soyhulls. These supplements, in general, are very high in energy and not as high as the forage in protein. Corn grain, for example, is quite deficient in degradable protein but is a good source of undegradable protein. The energy in the starch, which is digested in the rumen, increases the requirement for degradable protein. This matches very well with the forage which is high in degradable protein and low in undegradable protein. Starch, however, can be inhibitory to fiber digestion so highly digestible fiber sources such as soyhulls and corn bran may be good alternatives. Daily gains of the cattle will be measured and N removal from the pasture estimated with NRC (1996) equations. Diet samples will be collected with esophageally or ruminally fistulated cattle. Intakes will be estimated with the use of NRC (1996) energy equations. Intakes of forage and supplements will allow calculation of N use efficiency. In addition, the economics of supplementation practices will be determined to estimate cost benefit ratios of reducing N losses to the environment. Experiment 2: Dietary effects on production and N dynamics in dairy cattle (WI). Effects of dietary factors on production, supply of metabolizable protein and metabolizable amino acids (AA), and N excretion patterns will be quantified in lactating dairy cows. Responses will be measured in studies comparing legume silages (i.e., red clover, birdsfoot trefoil, low non protein N alfalfa silage) versus conventional alfalfa silage, and alternative supplementation regimes (carbohydrate sources including corn processed in different ways, barley, soluble sugars, pectin sources; high undegradable protein sources) versus corn grain and solvent soybean meal. Latin square feeding studies will be used to assess dietary effects on yield of milk and milk components. Excretion of N in urine and feces will be quantified using total collections in one or two squares per trial, and in all animals using spot sampling and creatinine and indigestible ADF as markers (Broderick, 2003). Omasal sampling, which allows measurement of digesta leaving the rumen in cows having only ruminal cannulae (Huhtanen et al., 1997; Ahvenjdrvi et al., 2000), will be used to quantify microbial protein, RUP and AA flows from the rumen, and MP supply to the animal. Microbial markers will be 15N and total purines (Reynal et al., 2003; Makkar and Becker, 1999). Flows of protein and individual AA contributed by feed undegradable protein will be estimated by difference. Although source and level of CP will vary in most trials, diets generally will be formulated for early lactation cows (i.e., with about 28% NDF and 43-45% NFC). The Latin squares will have 4 week periods and trials generally will not exceed 16 weeks in length. The first 2 weeks of each period will be allowed for adaptation to treatment; production of milk and milk components will be determined over the last 2 weeks, with omasal sampling over the last 1 week. Results showing significant quadratic effects will be solved for maxima (or minima) to identify optimal (or least effective) levels of those experimental variables. Experiment 3: Effect of carbohydrate and forage sources on protein utilization (KY, USDFRC). Replicated Latin square studies will evaluate effects of supplemental carbohydrate and site of digestion. Steers fitted with ruminal and abomasal infusion cannulae and duodenal sampling cannulae will be fed basal diets of high-quality forages. Partially-hydrolyzed starch will be infused into into the rumen and abomasum (Richards et al., 2003) and intestinal nutrient flow will be measured at the duodenum (Streeter et al., 1991). Forages will be fed at restricted levels to avoid affects of feed refusals. Fecal and urinary N will be quantified by total collection. Intravenous infusion of 15N:N15-urea (Archibeque et al., 2001) with subsequent urine and blood sampling will be used to determine serum urea N concentrations, total body urea production, gastrointestinal urea entry rate, and return of urea to the ornithine cycle using the model of Lobley et al. (2000). This approach will enable determination of how carbohydrate affects movement of N within the gastrointestinal tract and the efficiency of N use from endogenous urea. The influence of diet on net portal absorption of amino acids and splanchnic and peripheral tissue utilization of essential and non-essential amino acids will be evaluated using steers also fitted with ruminal and abomasal infusion cannulae and prepared with permanent indwelling catheters in the hepatic, hepatic-portal and mesenteric veins, and mesenteric artery (Huntington et al., 1996). 13C-labeled leucine and 13C-labeled glutamate will be infused intravenously to study metabolism of essential and nonessential amino acids. Proportions of splanchnic and non-splanchnic tissue oxidation will be determined by estimating whole body CO2 production, calculated from sodium [13C] bicarbonate infusion (Lapierre et al., 2002) and analysis of 13C enrichment of respired and blood CO2. Objective 3: Experiment 1: Nitrogen cycling in cool- and warm-season grasses (IA, NE, OK). Participating stations will evaluate the relationship between N partitioning in cool- and warm-season grasses and developmental morphology. While uptake of N as a function of plant growth stage will be a key component of this study, scientists will place considerable emphasis on relating N fractions of nutritional significance to growth stage. Forages to be evaluated may include, but are not limited to, reed canarygrass (Phalaris arundinacea L.), smooth bromegrass, tall fescue, orchardgrass, switchgrass, big bluestem (Andropogon gerardii Vitman), and indiangrass [Sorghastrum nutans (L.) Nash]. In addition to quantifying total N within each forage and/or plant part, forage N may be partitioned as described by the Cornell Net Carbohydrate-Protein System (Sniffen et al., 1992), and/or estimates of rumen protein degradability may be obtained by various in situ (Vanzant et al., 1998), in situ-NDIN (Mass et al., 1999) or enzymatic (Coblentz et al., 1999) methods. Other institutions may contribute analytical expertise to this project, particularly the determination of kinetic parameters associated with ruminal protein degradation. A goal of the study is to relate kinetic parameters associated with ruminal protein breakdown to plant growth stage by regression or modeling techniques. Experiment 2: Evaluating binary mixtures of cool-season grasses and legumes (IA, NE, OK). Participating institutions will evaluate binary mixtures of birdsfoot trefoil, red clover, white clover (Trifolium repens L.), kura clover, and alfalfa with smooth bromegrass to assess the potential N replacement value of each legume to the sward. A titration approach will be used to evaluate N replacement values (Zemenchik et al., 2001); smooth bromegrass will be fertilized with N from commercial sources at graded rates and the DM yield will be determined at each rate. Nitrogen replacement value will be calculated as the amount of N fertilizer required for the grass monoculture to yield as much DM as the binary grass-legume mixture. Although the primary measurement for this study will be DM yield, samples of these grass-legume mixtures may be retained and N fractions of nutritional significance may be determined as described in Study 1. Grazing opportunities for complementary cool-season perennial grasses in the southern Great Plans in the spring have averaged only 60 to 70 days (Reuter and Horn, 2002). Furthermore, the growth cycle of these cool-season perennials has not coincided with grazing termination for dual-purpose wheat. Thus, the addition of other cool-season forages to improve the length of the grazing would be beneficial. Also, there is minimal information regarding the contribution of legumes planted into established cool-season perennial forages grown in low pH soils in the southern Great Plains. A pasture grazing study will be initiated (OK) to evaluate the effects of legume growth and production in established cool-season perennial grass pastures. Alfalfa (Medicago sativa L.), button meid [Medicago orbicularis (L.) Bartal.], and rose clover (Trifolium hirtum All.) will be planted from mid- to late-September into existing smooth bromegrass and pubescent wheatgrass pastures. Total available forage biomass, nutritive value, and species composistion will be measured as well as measures of nitrogen cycling. Experiment 3: Fertilization of bermudagrass on sites with histories of animal waste application (AR, OK). Participating institutions will assess the apparent N recovery and N use efficiency for bermudagrass fertilized with graded levels of NH4NO3 using methods similar to those described by Zemenchik and Albrecht (2002). These methods include adjustment for forage production in unfertilized check plots. In addition, forage samples will be retained and evaluated for fractions of nutritional significance and/or estimates of ruminal protein degradation as described in Experiment 1. An objective of the study is to relate nutritionally relevant N fractions and/or rumen degradability estimates to N fertilization rates by regression techniques. This study will be closely integrated with P management. This experiment will be conducted on two types of sites, one having no history of animal waste (particularly broiler litter) application and the other having a long history of waste application. Sites with long histories of waste application frequently have high levels of soil-test P, which is undesirable environmentally because surface runoff from these pastures can contribute to eutrophication of lakes, rivers, and reservoirs. When soil-test P is already high, P can be mined from the soil via continuous hay or silage production, but DM production must be driven by N fertilizers purchased commercially. It remains unclear how bermudagrass should be most efficiently fertilized when the primary goal is P uptake and removal. Nitrogen use efficiency of commercial N fertilizers for bermudagrass grown on sites with high organic N loads likely will be poorer than observed for sites with low organic N loads. For sites with no history of waste application, assessment of the effects of commercial applications of NH4NO3 will provide useful information, particularly if nutritional indices of significance can be related to fertilization rate. An alternative approach on these sites would be to apply graded levels of broiler litter to assess the maximum annual application rate before soil-test P accumulates to unacceptable levels. In this case, nutritional indices of significance will be monitored as described previously, and may be related to application rate by regression or other techniques. Experiment 4: Comparisons of ruminal protein degradation kinetics for harvested and grazed forages (OK, NE, ND). Generally, there is a need for more information assessing the impact of diet selection on the kinetic parameters associated with ruminal protein degradation. Much of our current information is based on harvested or hand-clipped forages, rather than masticate samples selected by grazing livestock. This effort likely will be incorporated into ongoing grazing studies at participating institutions and will be conducted to compare the effects of diet selection at different plant ages or maturities, or potentially across fertilization rates. Experiment 5: Nitrogen uptake potential of various annual grasses (AR, IA). Across the states represented by participating institutions, there is often a need for summer annual forage production. Potential forage options include forage sorghums [Sorghum bicolor (L.) Moench], sorghum-sudangrass [Sorghum bicolor (L.) Moench], pearlmillet [Pennisetum americanum (L.) Leeke], and crabgrass. However, the two diverse situations described for Experiment 3 are common across participating states. In some areas, the organic N load is relatively low, primarily because animal wastes have not been used extensively as soil amendments. In these cases, efficient use of fertilizer N is desirable, and forages that maximize uptake of N may be preferred choices under these conditions. In contrast, it is likely that summer annual forages grown on sites with high organic N loads would need to be evaluated differently. Many summer annual grasses (particularly sorghum-sudangrass) are notorious accumulators of nitrates; concentrations of nitrates can easily reach toxic or even lethal levels on these sites with minimal N fertilization. Under these conditions, summer annual grasses that maximize N uptake may be undesirable because of these excessive nitrate levels, and forages that actually minimize N uptake may be the most desirable to producers. An alternative approach under these conditions may be to use legumes, such as alfalfa. While high organic N loads may have a negative impact on nodulation and subsequent N fixation, the N removed from the soil may be incorporated into more useable (protein) forms. As described in Experiment 3, this study will be closely linked to P management, and P removal will be determined in addition to assessing N uptake and use.

Measurement of Progress and Results

Outputs

• Refereed publications on N dynamics and N use efficiency of various forage-based livestock production systems, N uptake and cycling in cool- and warm-season grasses under different environmental and management conditions, N dynamics in cattle as affected by grazing management and supplementation strategies, animal performance and forage crop production in different grass-legume systems, and dietary effects on production and N dynamics in dairy cattle.
• Outreach publications and popular-press articles for an audience of forage/livestock producers, crop and nutrition consultants, advisors with federal and state agencies, managers of public and private agricultural lands, and policy makers in the state and federal governments. The publications will present strategies/methods of efficiently using N in forage-based livestock production systems, identify factors affecting N uptake and cycling in a forage-livestock system, and describe the pertinent N dynamics in common forage plants.
• A database of the total N content and N partitions (as described by the Cornell Net Carbohydrate-Protein System) of the common warm-season and cool-season forage plants in the NCR.
• A model relating kinetic parameters associated with ruminal protein breakdown to plant growth stage.
• A website to provide information on the project structure and organization, access to project publications, and links to relevant resources.

Outcomes or Projected Impacts

• Ranking of management strategies in terms of N use efficiency, particularly as it relates to the capture and excretion of N in the environment. Adopting strategies/practices that ensure efficient use of N will have a positive influence on environmental quality in the NCR.
• Identification of management strategies and forage systems that minimize N inputs and production costs. Minimizing N inputs (e.g., fertilizers) in forage-based livestock production systems will enhance their profitability.
• Identification of management strategies and forage plants that increase N use efficiency and performance in the ruminant animal.
• Identification of forage plants that have potential use in the uptake and removal of excessive soil nutrients (P).

Milestones

(2005): Establishment of field trials to determine the N dynamics and N use efficiency in different forage-based livestock production systems.

(2005): Establishment of field trials to determine N cycling in cool- and warm-season grasses commonly used as forage plants.

(2005): Establishment of field trials of grass-legume mixtures to determine the potential N replacement value of the legumes to the mixture.

(2005): Establishment of field trials of bermudagrass, annual grasses, and legumes to determine soil nutrient uptake potential of these forage plants.

(2005): Establishment of a grazing study to determine the effect of grazing management strategies and supplementation strategies on N capture and N excretion.

(2005): Establishment of field trials to determine the dietary effect on production and N dynamics in dairy cattle. (2008): Data analyses completed so that manuscripts can be written and submitted for publication and the database developed.

Projected Participation

View Appendix E: Participation

Outreach Plan

The timing and purpose of the proposed project is extremely relevant because nitrogen use efficiency and the dynamics of associated soil nutrients are foci of production agriculture systems in the NCR. Furthermore, there is a large audience needing research-based information for making decisions. Results of the project will be made available to intended users, listed in the Outputs section, through a number of avenues. Several of the participants in NCT196 have extension appointments and most of the research scientists in NCT196 work closely with extension specialists in the region. Results of this project will be incorporated in extension programming of each participating state. Methods used will include extension publications available to producers and extension educators, publication of results in such journals as the Forage and Grazing Land Journal and Crop Management Journal used by crop and livestock consultants, county/area training sessions, grazing workshops, field days, and individual consultations. The database on forage N content and partitions will be posted on the projects website. The database may be used by producers and advisers with computer models in developing livestock rations. The website also will provide access to project updates and publications and other relevant resources. Finally, project results will be available through refereed publications. These publications should be particularly important to scientists and policy makers seeking the most current information on N dynamics and N use efficiency in livestock production systems.

Organization/Governance

The technical committee will organize and function in accordance with the procedures described in "Manual for Cooperative Regional Research." The voting members will elect three officers (Chair, Secretary, and Secretary-elect). These officers plus the immediate past Chair (after the first year) will constitute the executive committee. Specific task subcommittees and coordinators will be appointed as necessary to help coordinate activities among states. The executive committee will conduct any necessary business between annual meetings of the technical committee. The Chair will be responsible for presiding over the annual meeting of the technical committee, preparing the meeting agenda, appointing any necessary subcommittees, and for preparing the annual project report for the year ending with the meeting at which he presides. The Secretary will record and distribute the minutes of the annual meeting. At the end of the annual meeting, the Secretary will become Chair and the Secretary-elect will become Secretary.

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