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Nutrient circularity can help supply chain participants meet sustainability targets. Across the segmented beef supply chain, opportunity exists to reinforce and introduce nutrient circularity by recycling surplus manure nutrients from cattle feedlots to lands where cattle feed is produced. We describe four datasets developed to evaluate options in U.S. and Canadian beef systems. The datasets delineate three “circular manuresheds,” each encompassing a hay‐grazing landscape where beef cattle are raised on grazingland and supplemented with hay grown nearby, and the distant feedlots where those cattle produce manure nutrients for potential import back to the hayfields. We selected the hay‐grazing landscapes of New Mexico, USA; Florida, USA; and western Canada (Manitoba, Saskatchewan, Alberta, British Columbia) because of their significant grazingland production and potential to substitute feedlot manure for commercial fertilizer on hayfields. In each circular manureshed, the manure nutrients from major feedlot destinations could supply a considerable proportion of the P used by hay for grazing cattle: 34% of the P requirements in New Mexico, 36% in Florida, and 6% in western Canada. The average distance to return the resource was 647 km for New Mexico, 1,884 km for Florida, and 1,587 km for western Canada. These magnitudes and distances suggest that the New Mexico circular manureshed may be the most economically viable in the current agri‐food system, but this reflects only part of a greater, multi‐factor assessment of tradeoffs. The circular manureshed concept provides a platform for simultaneous consideration of competing factors for sustainability via circularity. Nutrient circularity can help animal supply chain participants meet sustainability goals.The manureshed concept can help willing consortia operationalize nutrient circularity.Data delineate three circular manuresheds where feedlot manure is recycled onto hayfields in landscapes where feedlot cattle originated.Available nutrients and transport distances for the three circular manuresheds are calculated.These findings can inform a comprehensive assessment of tradeoffs of circular manureshed management.

Nitrate contamination of groundwater has been attributed to application of poultry litter to amend soil organic matter on raspberry farms in British Columbia, Canada. A field study assessed the risk of organic amendments that cause nitrate leaching and nutrient accumulation. The amendments, poultry litter, municipal compost, horse manure, and three types of dairy manure solids, were applied at 25 or 50 Mg dry matter ha–1to match farm rates before new plantings. Plots were either unseeded or seeded with a grass mix to simulate berry establishment with grass alley crop. Soil was sampled at 0‐ to 15‐, 15‐ to 30‐, and 30‐ to 60‐cm depths 15 times over 14 mo and analyzed for concentrations of NH4+and NO3–, and at 0 to 15 cm for total C, N, and P at 6 mo after application. Three grass harvests were analyzed for yield and N offtake. Poultry litter supplied more than twice the total mineral N and total P compared to the dairy solids and horse manure, while the compost was intermediate. At 25 Mg ha–1, poultry litter increased concentrations of soil (0–15 cm) NH4+and NO3–(>150 and >300 mg kg–1, respectively), compared with small short‐term increases by compost (∼70 and 100 mg kg–1, respectively). There was almost no increase from dairy and horse amendments. Grass N offtake reduced soil NO3–concentrations but did not eliminate the risk of leaching from poultry litter. We conclude that dairy solids and horse manure present less risk of nitrate leaching and P loading than poultry litter or municipal compost. Core IdeasPoultry manure and compost amendments greatly increased soil NH4+, NO3–and P.Grass ‘alley’ crop did no sufficiently mitigate soil mineral N from poultry manure.Little risk of nitrate leaching or P loading with dairy solids or horse amendments.

Removing solids from whole dairy slurry (WS) can reduce P loading on fields. This study investigated the effects of 11 yr of applications of WS, separated liquid fraction (LF), commercial fertilizer, WS plus fertilizer, and a control on total and extractable (Kelowna) soil P in perennial grass (Festuca arundinaceaSchreb.) and two subsequent silage corn (Zea maysL.) crops. Plots received 200 kg N ha−1with or without 40 kg P ha−1. Shoot biomass, P uptake, arbuscular mycorrhizal fungi root colonization, and soil microbial P were determined for corn at six leaves. Whole‐crop and grain yield, P uptake, dry matter, and grain content were determined at maturity. The LF treatment received 30% less manure P than WS, had lower extractable soil P at 0 to 15 and 15 to 30 cm, and had lower total P at 0 to 15 cm. Historical treatments had no effect on soil microbial P or arbuscular mycorrhizal fungi colonization. At six leaves, corn shoot biomass, P concentration, and P uptake were related to historical P rates in Year 2, but the relationship was not apparent in Year 1. Starter P fertilizer increased shoot yield and P uptake for all treatments in both years. At maturity, most yield parameters for WS and LF were similar in Year 1, but in Year 2, there was a significant response to starter P fertilizer and a positive relationship between historical P rate and corn performance. This study shows that long‐term LF treatments reduced the risk of P pollution with relatively little effect on the P response of subsequent corn crops. Historical N‐based LF treatments had lower P surplus and soil P than WS.Long‐term WS and LF treatments had no effect on AMF and soil microbial P.Juvenile corn responds to starter P in high‐P‐testing soils.The residual effects of long‐term LF on subsequent corn were small.Use of LF may help reduce soil P accumulation on dairy farm soils.

Orchardgrass (Dactylis glomerataL.) is a major component of many pastures in temperate North America. Early and profuse flowering in pastures is problematic, because livestock refuse to consume flowering stems, prompting many graziers to simply avoid using this species. The objective of this research was to determine the impact of reduced flowering on the quality of harvested forage under two harvest managements of orchardgrass. Six cultivars, three normal cultivars and three sparse‐flowering cultivars (mean panicle density of 141 vs. 61 panicles m⁻2, respectively), were evaluated in field experiments at 21 locations in North America under a 3‐cut harvest management. These cultivars were also evaluated at seven locations under a 5‐cut harvest management. Sparse‐flowering cultivars averaged 9% greater crude protein (CP), 3% lower neutral detergent fiber (NDF), 2% greater NDF digestibility, and 2% greater in vitro dry matter digestibility (IVDMD) than normal cultivars. For the two digestibility measures, differential panicle density between the cultivar groups explained a significant portion of variability, indicating that the increase in forage quality was proportional to the decrease in panicle density below a threshold of about 50 panicles m⁻2. Lastly, differences in regrowth forage quality between cultivar groups were smaller, less consistent, and of lesser statistical significance than for first harvest. While selection for sparse flowering in orchardgrass resulted in significant cause‐and‐effect increases in first‐harvest forage quality, these effects were too small to offset the reduced forage yield associated with the sparse‐flowering trait.

Orchardgrass (Dactylis glomerataL.) is a major component of many pastures in temperate North America. Early and profuse flowering in pastures is problematic due to livestock refusal to consume flowering stems. The objective of this research was to determine the stability and agronomic impact of recently developed sparse‐flowering orchardgrass populations across temperate North America. Six cultivars, three sparse flowering and three normal flowering, were grown at 21 locations in temperate North America and evaluated for panicle density, heading date, and forage yield. Sparse‐flowering cultivars had 57% fewer panicles than normal‐flowering cultivars, but this effect was highly dependent on mean winter temperature, with normal‐flowering cultivars showing twice as much temperature sensitivity compared to sparse‐flowering cultivars. Forage yield of sparse‐flowering cultivars was reduced by approximately 24 to 32% for first harvest and 2 to 9% for regrowth harvests compared to normal‐flowering cultivars and this reduction in forage yield was independent of mean winter temperature. The forage yield reduction associated with sparse flowering is most likely due to a combination of physiological load (loss of stems) and opportunity cost (lack of selection pressure for yield), suggesting an opportunity to improve forage yield potential of this sparse‐flowering germplasm pool.

Physical, chemical, or biological treatment of animal liquid manure generally produces a dry‐matter rich fraction (DMF) that contains most of the initial phosphorus (P). Our objective was to assess the solubility and plant availability of P from various DMFs as a function of soil P status. Eight different DMFs were obtained from liquid swine (LSM) and dairy cattle (LDC) manures treated by natural decantation, anaerobic digestion, chemical flocculation, composting, or mechanical separation. The DMFs were compared with mineral P fertilizer in a pot experiment with oat (Avena sativaL.) grown in four soils with varied P‐fixing capacities and P saturation levels. The DMFs were added at a rate of 50 mg P kg−1soil and incubated 14 d before seeding. Soil water–extractable P (PWT) at all water:soil extraction ratios (2:1, 20:1, and 200:1) was slightly higher when DMFs were derived from LDC rather than LSM. Soil PWTat the 2:1 ratio was lower with anaerobically digested LSM. At the 2:1 extraction ratio, DMF P was less soluble than mineral P as P saturation in soils increased. In soils with a lower P‐fixing capacity, DMF P appeared less water soluble than mineral P under 20:1 and 200:1 extraction ratios. After 72 d of plant growth, DMFs produced yields comparable to mineral P fertilizer. Although the plant availability of P from DMFs was comparable to mineral P fertilizer, P from DMFs could be less vulnerable to leaching or runoff losses in soils with a high P saturation level or low P‐fixing capacity.

Efficient use of manure nutrients by crops is necessary to minimize losses to the environment. This field study examined the possibility of replacing side‐banded mineral P with precision‐placed high‐P sludge (6.2–11.0% dry matter) obtained after settling dairy manure slurry. The sludge was injected at about 30 kg P ha−1(36.0–51.2 m3ha−1) into the soil at corn row spacing, and the corn was planted 5, 10, and 15 cm beside the injection furrow. Controls included no added P and side‐banded commercial P fertilizer. The treatments were tested on corn with low and high root colonization by arbuscular mycorrhizae (AM). The study showed that sludge did not impede AM root colonization, corn germination, or seedling growth. Corn plants with both high and low levels of AM colonization responded to the sludge from the three‐leaf stage and showed the greatest benefit at the six‐leaf stage. Corn responded more to sludge placed at 5 than at 15 cm from the corn rows, whereas the response at the 10‐cm spacing was intermediate. There was little difference in seedling growth or final harvest parameters between the side‐banded fertilizer P and the 5‐cm sludge treatment. The results show a new way to use manure nutrients, namely precision‐placement sludge for corn. This may obviate the need for chemical fertilizers for improving farm nutrient balances. Other anticipated benefits are less energy use for hauling and injection of the sludge fraction and reduced risk of nutrient loss by runoff and volatilization (ammonia) and nuisance odors due to injection.

Removing solids from slurry manure helps balance nutrients to plant needs and may increase soil infiltration rate to reduce loss of ammonia. The long‐term effects of applying the separated liquid fraction (SLF) of dairy slurry with surface banding applicators are not well known. This 6‐yr study compared the yield, N recovery, and stand persistence of tall fescue (Festuca arundinaceaSchreb.) receiving SLF at 300 (SLF300) and 400 (SLF400) kg ha−1yr−1of total ammoniacal N (TAN); whole dairy slurry (WS) at 200 (WS200), 300 (WS300), and 400 (WS400) kg TAN ha−1yr−1; and mineral fertilizer at 300 kg N ha−1yr−1The slurries were applied four times per year by surface banding, a technique that reduces ammonia emission and canopy contamination. Grass yield and N uptake were significantly higher for SLF300 than WS300 at equivalent rates of TAN. At similar total N, yield and N uptake were much greater for SLF than WS (2 Mg DM ha−1and 75 kg N ha−1, respectively). Apparent total N recovery was 63% greater for SLF300 than WS300 due to less ammonia loss and less immobile N. The apparent recovery of total N was 31% higher for Fert300 than for SLF300. Yield and N uptake for SLF300 and WS300 were similar in Harvests 1 and 4, but SLF had higher values under hot and dry conditions in Harvests 2 and 3. Using SLF rather than WS will increase crop yield and allow higher application volumes near barns, which will reduce hauling costs.

Rapid infiltration of liquid manure into the soil reduces emissions of ammonia (NH3) into the atmosphere. This study was undertaken to assess the effects of two low‐cost methods of assisting infiltration of applied dairy slurry on emissions of NH3, nitrous oxide (N2O), and on crop N uptake. The two methods were removing of solids by settling‐decantation to make the manure less viscous and mechanically aerating the soil. Ammonia emissions were measured with wind tunnels as percentage of applied total ammoniacal nitrogen (TAN) while emissions of N2O were measured with vented chambers. Mechanically aerating the soil before manure application significantly reduced emissions of NH3relative to the nonaerated soil in spring (38.6 to 20.3% of applied TAN), summer (41.1 to 26.4% of applied TAN) and fall (27.7 to 13.6% of applied TAN) trials. Decantation of manure had no effect on NH3emissions in spring, tended to increase emissions in summer and significantly decreased emissions in fall (30.3 to 11.1% of applied TAN). Combining the two abatement techniques reduced NH3emission by 82% in fall, under cool weather conditions typical of manure spreading. The two abatement techniques generally did not significantly affect N2O emissions. Uptake of applied N by Italian ryegrass (Lolium multiflorumLam.) was generally significantly greater with decanted than from whole manure but the effect of aeration was generally small and not significant. The study shows that low cost methods that assist manure infiltration into the soil may be used to greatly reduce ammonia loss without increasing N2O emissions, but efficacy of abatement methods is affected by weather conditions.

The effect of mechanically aerating grassland before liquid manure application in the fall on surface runoff and transport of nutrients and solids was studied in a high rainfall area. The two treatments were control and aeration, the latter receiving one pass with an aerator perpendicular to the slope before fall application of liquid manure (dairy in Years 1–3 and swine in Year 4). Treatments were randomly assigned on 3 to 5% sloping land with a silt loam surface soil (Aquic Dystroxerept) planted in orchardgrass (Dactylis glomerataL.). Runoff from natural rainfall events was sampled for nutrient and solids analysis. Aeration significantly reduced runoff and loads of suspended solids, total Kjeldahl N (TKN), and dissolved reactive P in all years. Annual runoff amounts were reduced by 47 to 81%, suspended and volatile solid loads by 48 to 69% and 42 to 83%, respectively, TKN loads by 56 to 81%, and total P (TP) loads by 25 to 75%. Loads of the soluble nutrient NH4–N, dissolved reactive P, and K were reduced by 41 to 83%. The first three runoff events after manure application accounted for approximately one‐third of the annual total runoff and solid and nutrient loads when averaged across treatments, with loads of TKN, K, and NH4–N totaling 4.4, 3.3, and 1.9 kg ha−1, respectively. Aeration slightly increased downward movement of NO3–N, but not other nutrients in the soil. Thus mechanical aeration can be an effective tool for reducing runoff and loads of solids and nutrients after surface application of liquid manure on sloping grassland.

Annual forage yield in the northern Great Plains depends primarily on quantity and temporal distribution of precipitation. This study was conducted to examine the effect of water deficit on yield, leaf area, and net assimilation rate (NAR) of three forage grasses under field conditions. The grasses, smooth bromegrass (Bromus inermisLeyss.) (Br), Altai wildrye [Leymus angustus(Trin.) Pilger] (AWr), and crested wheatgrass [Agropyron cristatum(L.) Beauv. spp. pectinatum(Bieb.) Tzvel.] (CWg), were chosen because of their contrasting morphologies. The grasses were grown on deep black soil (Melfort silty clay, Typic Cryoboroll) under two moisture regimes: DRY plots were covered by rain‐out shelters starting at the end of May, and IRR plots were watered when soil water potential averaged −0.07 MPa. Crested wheatgrass expanded leaf area more rapidly in spring than Br and AWr, and responded to increasing soil water deficits by sharply reducing its leaf area through senescence of older leaves. Altai wildrye developed its leaf area slowly, probably because more dry matter was required to produce a unit of leaf area. It responded to soil water deficit by reducing rate of leaf expansion. Smooth bromegrass developed its leaf area rapidly although somewhat later than CWg. The effect of soil water deficit on leaf expansion was less in Br than AWr, and its effect on reduction of leaf area through leaf senescence was less in Br than CWg. In late May, AWr yielded less than CWg but more than Br. At the end of June, yield of CWg was greater than both Br and AWr in 1983, and greater than AWr but similar to Br in 1984. Altai wildrye recovered most rapidly after clipping among the species in both years but yielded more regrowth only in 1984. No interaction was found between moisture regime and species for either leaf area or yield on any of the sampling dates, probably because soil water deficits developed gradually under the conditions of this experiment, thus minimizing the effects of the different growth patterns. Soil water deficit affected leaf area proportionately more than NAR in AWr and CWg but not in Br. The findings suggest that the relative effect of drought on these two yield components depends on species and environment.

Control of water loss is essential for plants growing in the northern Great Plains. The objectives of this study were to examine seasonal changes in leaf conductance (g1) of three forage grasses, smooth bromegrass (Bromus inermisLeyss.) Altai wildrye [Leymus angustus(Trin.) Pilger], and crested wheatgrass [Agropyron cristatus(L.) Beauv. ssp. pectinatum(Bieb.) Tzvel.] growing under contrasting water regimes to relate changes in gLto leaf water status, and to examine the relationship between leaf rolling response and leaf water status in crested wheatgras (CWg). The study was conducted on deep black soil (Melfort silty clay, Typic Cryoboroll) at Melfort, Saskatchewan. Rainout shelters and irrigation were used to impose two contrasting water regimes. Altai wildrye (AWr) generally had higher gLthan the other species, while smooth bromegrass (Br) had low gLearly in the season when its leaf water potential (ψL) was high. Under favorable moisture, CW8had lowest proportion of conductance from abaxial surface among the species, although abaxial conductance in Br and AWr declined more rapidly than adaxial conductance under drought. Much of the variation in gLwas not accounted for by ψLin all three species. Leaf conductance also changed gradually with leaf pressure potential (ψp) over a wide range of ψpvalues, particularly in the mornings. In contrast, leaf rolling in CWg was strongly related to both, ψLand ψp. The data suggest that other factors such as the rate of leaf water loss affect stomatal response to tissue water loss.

Water is the predominant environmental factor controlling yield of forages in the northern Great Plains. This study was conducted to compare the effects of contrasting soil water regimes on the water relations of smooth bromegrass (Bromus inermisLeyss.), crested wheatgrass [Agropyron cristatum(L.) Beauv. ssp. pectinatum(Bieb.) Travel.], and Altai wildrye [Leymus angustus(Trin.) Pilger]. The grasses were grown on deep black soil (Melfort silt)' clay, Typic Cryoboroll) under two soil water regimes: DRY plots were covered by rain‐out shelters beginning at the end of May and IRR plots were watered when soil water potential averaged −0.07 MPa. Measurements of soil water potential (ψs), leaf water potential (ψ/L), osmotic potential (ψ,), and relative water content (RWC) were taken periodically during first and second growths in 1983 and 1984. Crested wheatgrass (CWg) generally had lower ψLand RWC than smooth bromegrass or Altai wildrye. At a specific ψs, ψLof CWg was 0.3 to 0.7 MPa lower than that of Br, possibly resulting from small xylem vessels in CWg. Osmotic adjustment in CWg and smooth bromegrass was similar, but CWg lost more water for a change in pressure potential(ψp), which helped it maintain ψp. Differences in water relations reflected growth patterns and drought resistance strategies previously reported for these species.

Growth of cool season grasses in the northern Great Plains occurs mainly in the spring, and summer pasture consists of mature, quiescent, and drought‐affected vegetation. This study was conducted to determine drought effects on leaf'stem ratio, leaf senescence, and nutritional quality of three grasses, ‘Parkway’ crested wheatgrass [Agropyron cristatum(L.) Beauv. spp. pectinatum(Bieb.) Tzvel.], ‘Magna’ smooth bromegrass (Bromus inermisLeyss.), and ‘Prairieland’ Altai wildrye [Leymus ungustus(Trin.) Pilger] commonly grown on the northern Great Plains. The grasses were grown in the field on deep black soil (Meifort silty clay, Typic Cryoboroll) at Melfort, Saskatchewan under two moisture regimes: plots subjected to drought (DRY) were covered by rain out shelters starting at the end of May; and irrigated (IRR) plots were watered when soil water potential averaged −0.07 MPa. Altai wildrye maintained its quality through the season (as indicated by N, P, in vitro digestibility, and lignin) better than the other species because it had the lowest proportion of stems and least leaf senescence. Crested wheatgrass had the lowest quality from June to August because it had the greatest leaf senescence and highest proportion of stems. Water deficit (DRY plots) increased the rate of seasonal decline in N and P concentration probably by increasing leaf senescence. However, drought reduced the seasonal decline in digestibility by reducing the rate of increase in acid detergent fiber and lignin. Drought increased leaf senescence more in floral than in nonfloral tillers, suggesting that leaf senescence was controlled hormonally. Because leaf senescence was lower in nonfloral than in floral tillers, the quality of midsummer pasture may be improved by introducing cultivars having a high proportion of nonflowering tillers.

Thiol-containing antioxidants such as 4-(mercaptoacetamido)-diphenylamine (MADA) undergo ready addition of-SH groups to the double bonds in diene rubbers in the presence of initiators. The reaction is a radical chain process leading to rubbers with improved thermooxidative resistance. The modification reaction has been carried out on high cis-polyisoprene and polybutadiene, and conditions under which the physicochemical properties (e.g., inherent viscosity, gel content, and microstructure) are less affected have been found. An oxygen absorption test and DSC were used as rapid methods for evaluation of thermooxidative stability of modified rubbers. The superiority of rubbers with MADA chemically attached (ranging from 1 to 4 phr) was shown by a circulating air oven test and by an extraction process which simulates the aggressive environments experienced by many rubbers under practical conditions. The results obtained show that a small degree of modification (1 phr MADA) is large enough to provide good thermooxidative stability without alteration of the molecular characteristics of the parent rubbers. At higher degrees, cistrans isomerization can occur.

The use of nitroso derivatives in rubber compounds leads to a reinforcing effect with important practical implications. The mechanism of action of these promoters is explained on the basis of the theory according to which the reinforcing effect is due to the strain-crystallization process. This process is dependent on various factors, one of them being the presence of a network based on weak "rubber…carbon black" bonds. The properties of crude and cured blends on natural rubber, polyisoprene, and modified polyisoprene are compared. When nitroso derivatives are used, the active sites on the polymer chain are probably the nitroxyl radicals formed during the modification process. According to the mechanism proposed by the authors in previous papers, the formation of nitroxyl radicals is accompanied by changes of macromolecular characteristics which permit us to explain the reinforcement as well as the modification of viscoelastic and physical-mechanical properties of crude and cured compounds. On the basis of assumptions made on the whole set of reactions regaxding both polymer modification with nitroso derivatives and that of rubber compounds, one can explain not only some of the properties but also the conditions in which modification should be made in order to obtain an optimal reinforcing effect.

Rainout shelters are used in drought studies because they provide a means of controlling the input of water. Our objective was to design a hand‐operated rainout shelter that would be inexpensive, sturdy, easy to operate, and large enough to cover a 2.1‐ by 6‐m field plot. The shelter was comprised of a stationary wood frame, a retractable cover of clear polyethylene (0.15 mm), and a tank to collect excluded water. Twelve shelters were built in 1983 and 1984. Each could be covered or uncovered by two people in 1 to 2 min. The shelters withstood winds of 6.9 m s−1, a rainfall rate of 8.8 mm in 15 min, and were effective in creating uniform water deficits for sampling areas of 4.5 m2as indicated by growth, leaf senescence, leaf rolling, and leaf water potential. The shelters provided an artificial microclimate useful for experiments emphasizing comparisons within, rather than between, moisture regimes. Our shelters are more portable and less costly than automated units but require more labor for operation and maintenance.