Grazing Wheat Research Articles

System impacts of introducing crop grazing into pasture-based systems: the McClymont Memorial Lecture

The present paper briefly discusses the impacts of introducing dual-purpose (DP) crops as a grazing resource into what were previously pasture-only grazing systems. The emphasis is on the high-value crops wheat and canola, since these have the greatest potential to increase profits by providing both winter grazing and a high-value grain or seed crop at harvest. A major potential impact of grazing on such crops is that the reduction in grain yield caused by grazing offsets the value of the grazing obtained. The paper shows that this is not the case and that if crop grazing is performed correctly, there will be minimal impact on grain or seed yield; yield may even be increased. ‘Correctly’ in this context refers mainly to the timely removal of livestock from the crop. Increases in grain yield after grazing arise principally from the conservation of soil water from the winter period through to the grain-ripening stage. The paper emphasises that although the digestibility and crude protein content of DP crops are high, the use of long-season bread wheats as a grazing resource requires that system managers pay greater attention to the sodium and magnesium status of the grazing livestock. This is because of the often high potassium and very low sodium concentrations of wheat forage, which leads to high potassium : sodium ratios in the rumen and reduced absorption of dietary magnesium. Supplementation with sodium and/or magnesium has significantly increased the liveweight gain of stock grazing wheat, but is contra-indicated when grazing canola. The paper also considers the interaction between the amount of grazing provided directly by the crop(s), relative to the possibly increased grazing available from the pasture component of the system, due to ‘pasture spelling’ while livestock are grazing the crop. Data are presented to show that, overall, the introduction of crop grazing into a previously pasture-based system greatly increases the total amount of grazing obtained. In addition, of the total extra grazing obtained in crop–pasture versus pasture-only systems, up to 40% has been found to come from spelled pasture. This has major implications for the management of the total system. The paper concludes by suggesting that, in the future, research on crop–pasture systems should continue, but should pay greater attention to the grazing of DP crops by cattle and particularly by breeding livestock. In addition, there is a need for much better data on the contribution of crop residues to the total grazing system, plus data on the effects of the introduction of DP crops on the wool production of the total grazing system.

Effects of energy supplementation on energy losses and nitrogen balance of steers fed green-chopped wheat pasture I: Calorimetry123

Cattle grazing wheat pasture in the southern Great Plains are sometimes fed an energy supplement; however, the benefits of supplementation on nutrient balance, energy metabolism, and greenhouse gas emissions have not been elucidated. Therefore, we used 10 British crossbred steers (206 ± 10.7 kg initial BW) in a respiration calorimetry study to evaluate the effects of energy supplementation on energy losses, N balance, and nutrient digestibility of steers fed green-chopped wheat forage. The study design was an incomplete replicated 4 × 4 Latin square with treatments in a 2 × 2 factorial arrangement. Steers ( = 8) were assigned to 1 of 2 BW blocks (4 steers per block) with dietary factors consisting of 1) no supplementation (CON) or supplemented with a steam-flaked corn-based energy supplement (that also contained monensin sodium) at 0.5% of BW daily (SUP) and 2) NEm intakes of 1 times (1x) or 1.5 times (1.5x) maintenance. Wheat forage was harvested daily and continuously fed as green-chop to steers during the 56-d study. There were no differences ( ≥ 0.32) between CON and SUP for OM (78.3 vs. 80.7%, respectively) or NDF (68.3 vs. 64.8%, respectively) digestibility. At the 1.5x level of intake, there was no difference ( ≥ 0.16) in energy lost in feces (4.27 vs. 3.92 Mcal/d) or urine (0.58 vs. 0.55 Mcal/d), heat production (8.69 vs. 8.44 Mcal/d), or retained energy (3.10 vs. 3.46 Mcal/d) between supplementation treatments. Oxygen consumption (1,777 vs. 1,731 L/d; = 0.67) and CO production (1,704 vs. 1,627 L/d; = 0.56) of CON and SUP steers, respectively, were not different; however, SUP steers tended to have ( = 0.06) lower CH production (115 vs 130 L/d) than CON steers. Methane, as a proportion of GE intake, was similar for CON (6.87%) and SUP (6.07%; = 0.18), as was the ME:DE ratio ( = 0.24; 86.3% for CON and 87.9% for SUP). Fractional N excretion in urine and feces, as a proportion of total N excreted ( ≥ 0.84) or N intake ( ≥ 0.63), was not different between treatments. Calculated NEm and NEg values for CON were 1.76 and 1.37 Mcal/kg DM, respectively, whereas the NEm and NEg values for the SUP treatment were 2.32 and 1.61 Mcal/kg DM, respectively. Calculated NE values for steers fed additional energy were approximately 17.5% greater than the expected difference in energy content. This was probably the result of the inconsistent response at the 1x DMI level. Under these circumstances, energy supplementation did appear to enhance NEm and NEg value of the supplemented wheat forage diet.

Grazing winter and spring wheat crops improves the profitability of prime lamb production in mixed farming systems of Western Australia

Grazing immature cereal crops, particularly different varieties of wheat, has become widely adopted in the high rainfall areas of southern Australia. Recently, there has been growing interest in applying this technology in drier parts of the mixed farming zones of Western Australia. A modelling study was conducted to examine farm business returns with or without the grazing of immature wheat (winter and spring varieties) in different locations of Western Australia (Merredin, Wickepin and Kojonup), representing the low to high rainfall (319–528 mm) cropping regions, respectively. A combination of APSIM (crop simulation model) and GrassGro (pasture and livestock simulation model), were used to evaluate the changes in farm gross margins with the grazing of cereal crops at three locations of Western Australia. The results of the study showed that grazing the two wheat varieties (dual-purpose winter and spring) at the high rainfall location increased the profitability of the livestock enterprise by 2.5 times more than grazing crops at both low rainfall locations (P < 0.05). Across all years and sites, the average supplementary feeding costs were reduced by the inclusion of grazed winter (12%) and spring (2%) wheat crops in the lamb production system. The comparative reduction in the cost of supplementary feeding varied between locations and by crop variety within locations, due to both the frequency and average duration of the grazing of wheat crops in these regions, and the farm-stocking rate that was chosen. Both wheat varieties were grazed frequently at the lowest rainfall site (68% and 30% of years for winter and spring wheat varieties respectively), whereas grazing spring wheat was less frequent at the higher rainfall location and averaged 16% of years due to a greater difference in the relative availability of wheat crops versus pasture for grazing among regions. The grazing model assumed that there were abundant productive mixed ryegrass and subterranean clover pasture in the farming system. Overall, this study suggests that both winter and spring wheat crops are likely to supply green feed during the winter feed shortage (April–July) and reduce supplementary feed requirements for a short period of time in some seasons. The value of grazing crops is likely to be higher on farms with poorer soils and less productive pastures.

Erratum to: New perspectives on the mineral nutrition of livestock grazing cereal and canola crops

The grazing of cereal and canola crops during winter is an increasing component of grazing systems in southern Australia. The capacity of such crops to meet the requirements of young livestock and reproducing animals for sodium (Na), magnesium (Mg), calcium (Ca) and potassium (K) is reviewed. The growth responses of young stock to Na and/or Mg supplements when grazing wheat are discussed. These responses differ from ‘literature expectation' in that they are rapid in onset and involve no clinical signs. We demonstrate that more insight about the variability in supplement response, both between and between crops species, is obtained when mineral contents are viewed from the perspective of their frequency distributions, rather than their mean values. The pivotal importance of high K concentration, low Na and the resultant K:Na ratio of forage is stressed, as is the interaction of these minerals in relation to Mg absorption. We also present frequency distributions for a range of mineral indices that ‘capture' mineral interactions, including the ‘tetany index', forage K: (Na+Mg) ratio and dietary cation–anion difference. It is concluded that the last two indices warrant a much closer investigation. Possible effects of forage aluminium and organic acid contents are briefly discussed; these also deserve closer examination. As research in this area continues, it would be prudent to provide Na and/or Mg supplements for livestock grazing wheat and possibly oats and barley, and calcium supplements for livestock grazing oats or for reproducing animals grazing all three cereals.

New perspectives on the mineral nutrition of livestock grazing cereal and canola crops

The grazing of cereal and canola crops during winter is an increasing component of grazing systems in southern Australia. The capacity of such crops to meet the requirements of young livestock and reproducing animals for sodium (Na), magnesium (Mg), calcium (Ca) and potassium (K) is reviewed. The growth responses of young stock to Na and/or Mg supplements when grazing wheat are discussed. These responses differ from ‘literature expectation’ in that they are rapid in onset and involve no clinical signs. We demonstrate that more insight about the variability in supplement response, both between and between crops species, is obtained when mineral contents are viewed from the perspective of their frequency distributions, rather than their mean values. The pivotal importance of high K concentration, low Na and the resultant K : Na ratio of forage is stressed, as is the interaction of these minerals in relation to Mg absorption. We also present frequency distributions for a range of mineral indices that ‘capture’ mineral interactions, including the ‘tetany index’, forage K : (Na+Mg) ratio and dietary cation–anion difference. It is concluded that the last two indices warrant a much closer investigation. Possible effects of forage aluminium and organic acid contents are briefly discussed; these also deserve closer examination. As research in this area continues, it would be prudent to provide Na and/or Mg supplements for livestock grazing wheat and possibly oats and barley, and calcium supplements for livestock grazing oats or for reproducing animals grazing all three cereals.

Phenolic Compounds Affect Bloat Potential of Wheat Forage

Winter wheat (Triticum aestivum L.) is the major source of high‐quality winter forage for grazing cattle (Bos taurus L.) in the southern Great Plains of the United States. High concentrations of crude protein and soluble nitrogen fractions in wheat forage are often associated with frothy bloat conditions in cattle. The death loss of stocker cattle grazing wheat due to bloat ranges 2 to 3% in the southern Great Plains each year. The occurrence of frothy bloat in cattle grazing on wheat forage is affected by a number of factors, including complex relationships among wheat plant metabolism, cattle genetics, environmental conditions, and ruminal microbial activity. Traditional approaches to control frothy bloat rely on feed supplements such as surfactants and ionophores, grass hay, and condensed tannins. In a series of experiments conducted at Vernon and Chillicothe, TX, during 2004 to 2006, we determined correlations between total phenolic concentrations in wheat forage and foam strength (an estimate of the bloat potential) in a range of wheat breeding lines and commercial cultivars evaluated by the Wheat Breeding Program of Texas A&M AgriLife Research. Total phenolic concentration was inversely correlated with foam strength in each growing season. Wheat cultivars and experimental breeding lines differed in total phenolic concentration in forage, suggesting a potential for development of cultivars with higher phenolic content in forage as a measure to decrease bloat occurrences in grazing cattle.

Distribution and influence of grazing on wheat curl mites (Aceria tosichella Keifer) within a wheat field

AbstractWheat streak mosaic virus (WSMV) is a serious disease of wheat and is primarily transmitted from infected to healthy plants by the wheat curl mite, Aceria tosichella Keifer. Although wheat is the primary plant host of A. tosichella, wheat curl mites have been recorded on more than 60 different plant hosts; this broad host range allows mites to survive outside the wheat‐growing season by providing a ‘green bridge’. Despite the fact that A. tosichella can only crawl short distances, the mites can disperse via wind and thus have the capacity to readily infest wheat crops from neighbouring refuges. In this study, we undertook field trials to investigate the temporal movement of A. tosichella, as well as the importance of wind and livestock grazing on mite dispersal late in the cropping season. We demonstrate there is a window in spring when A. tosichella undergo significant movement in south‐eastern Australia, and this is likely related to the development stage of wheat plants, and may also be influenced by wind direction. We found that grazing wheat crops reduced mite numbers, suggesting that any increase in WSMV issues in ‘grain and graze’ crops is likely due to the longer season wheat varieties used in these systems rather than the direct effects of grazing. These results emphasize the importance of crop management strategies in the control of A. tosichella.

Small effects of deferment of annual pastures through grazing spring wheat crops in Western Australia can benefit livestock productivity

Grazing sheep on cereal crops in winter has become widely adopted in medium–high-rainfall zones of Australia. Interest in this practice has spread to the lower rainfall parts of the cereal–livestock zone where it is being applied to shorter season crop varieties. A farm-system modelling study was conducted to investigate the value of deferment of annual pastures by grazing spring wheat in their place. The biophysical simulation model, based on a representative wheat and sheep farming system in the wheatbelt of Western Australia, involved two grazing-management scenarios and used climate data for the period 1962–2011 for three locations in Western Australia representing low-, medium- and high-rainfall cropping regions: Merredin, Wickepin and Kojonup. The grazing-management policy of the main scenario, ‘crop grazing’, placed livestock on the crops only until the crop reached Zadoks growth stage 30, provided the green biomass of the farm’s annual pastures was <800 kg/ha. A second ‘shadow-grazing’ scenario was run in which a group of ewes identical to the main ewe flock was used to graze annual pastures simultaneously with the main ewe flock whenever the main flock grazed wheat crops. The difference between the two scenarios represented the pasture deferment value associated with grazing wheat crops. Pasture deferment had little effect on total pasture production during the period when crops were grazed. However, there was a small benefit to feed supply through the accumulation of pasture during the period of crop grazing. This feed was available at a time of year when feed is scarce. This was reflected in improved animal production, with the weight of lambs at weaning being higher in the crop-grazing scenario than the shadow-grazing scenario. These results suggest that although increases in pasture productivity and feed supply associated with spring crop grazing are only marginal, grazing of spring wheat crops can still lead to changes in lamb production because this enterprise is sensitive to the feed supply in winter.

Does cattle grazing of dual-purpose wheat accelerate the rate of stubble decomposition and nutrients released?

Decomposition and nutrient release of winter annual forages in integrated crop-livestock systems could be affected by the resultant alterations in structure and quality of residues caused by grazing, but little information is available to test this hypothesis. Information on residue dynamics is needed to synchronize nutrient release from cover-crop litter to cash-crop nutrient demand and to overcome potential deficiencies with appropriate fertilization strategies. We evaluated the influence of different grazing period lengths (0, 21, 42, 63, 85, and 105 days) of dual-purpose wheat (Triticum aestivum L.) pasture on the release rate of N, P, K, Ca, and Mg from decomposing wheat straw in a field experiment at the Agronomic Institute of Paraná, Brazil. Wheat litter decomposition and nutrient release were assessed with litter bags placed at the soil surface in a completely randomized design with seven collection periods (0, 15, 35, 63, 98, 139, and 196 days) during the subsequent growth of soybean [Glycine max (L.) Merr.]. Wheat residue decomposition and nutrient release followed an exponential function with time. Enhanced decomposition of wheat residue with previous grazing did occur, but the influence was relatively small (range of 6–11% greater release, except for 4% inhibition of K). In integrated crop-livestock systems, the effect of residual forage mass at the cessation of the grazing season (structure) would have much greater impact on nutrient cycling than composition of plant litter (quality). Nutrient cycling via animal excrement was not investigated, but was considered another significant mechanism for enhanced nutrient cycling with integrated crop-livestock systems. Grazing of wheat tended to have negative consequences on soybean grain yield, declining 9kgha−1 for every day of grazing (i.e. 19% lower yield at 105 days of grazing compared with no grazing). Minor changes in nutrient release dynamics can be expected with grazing of winter cover crops, but these changes are important for managing nutrients in integrated crop-livestock systems.

Extent of utilisation of dual-purpose wheat for grazing by late-pregnant and lambing ewes and producer-reported incidence of health issues in southern New South Wales.

To investigate the extent of using dual-purpose wheat for grazing by late-pregnant and lambing ewes in southern New South Wales (NSW) and the effect on ewe health. A questionnaire was mailed to sheep producers in the mixed-farming districts of the Hume Livestock Health and Pest Authority area in NSW, seeking information on whether there had been grazing by late-pregnant or lambing ewes of dual-purpose wheat during the period 2005-10. Information collected included general farm operation details, as well as the producers' experiences specific to grazing reproducing ewes on wheat, including causes and extent of disease and the producers' supplementation practices. Of the 202 respondents to the survey, 43% identified that they had grazed late-pregnant and/or lambing ewes on dual-purpose wheat during the period 2005-10. Of the producers, 71 had grazed reproducing ewes on wheat in 2010 and reported a mean disease incidence of 2.6% (range, 0.0-21.3%). Dystocia, pregnancy toxaemia, foot abscess and grass tetany were the most commonly reported diseases in ewes grazing wheat in 2010. The majority of producers (92%) supplied supplement to ewes grazing wheat in 2010, including mineral supplements (85%), roughage (58%) and grain (18%). Thirty percent of producers who grazed ewes on wheat between 2005 and 2009 experienced higher than normal rates of ewe health problems, reporting a mean of 7.9% ewes in these flocks with health problems. Metabolic diseases such as pregnancy toxaemia, hypocalcaemia and grass tetany appear to be important diseases of reproducing ewes grazing wheat pasture.

Factors involved in high ewe losses in winter lambing flocks grazing dual-purpose wheat in southern New South Wales: a producer survey

A comparative survey was undertaken with 43 sheep producers in southern New South Wales using a semi-structured interview to investigate factors associated with high ewe mortality rates in winter lambing flocks grazing dual-purpose wheat. Participants were classified as either control (n = 23), who had not observed abnormally high ewe deaths, or case (n = 20), who had observed abnormally high ewe mortality rates when sheep grazed dual-purpose wheat. Ewe losses associated with grazing wheat were higher in the case group compared with the control group (8.6 vs 1.8%; P < 0.001) and there was also more deaths attributed to metabolic disease (3.4 vs 0.6%; P < 0.05). A higher proportion of control respondents had provided magnesium or sodium supplementation to ewes grazing wheat (P < 0.05). The body condition score of ewes entering the grazing period was significantly higher in the control group (3.2 vs 2.8; P < 0.05). The proportion of respondents who fed roughage to ewes grazing wheat did not differ significantly between control and case groups (48 vs 35%). A higher proportion of respondents in the case group had supplied grain to ewes (25 vs 0%; P < 0.05), which may have been associated with the lower body condition of sheep in these flocks compared with the control group. It was concluded that supplying ad libitum access to mineral supplements that include magnesium, sodium and possibly calcium, and maintaining adequate body condition score can reduce the risk of high ewe mortality rates when reproducing ewes graze dual-purpose wheat.

Variable Environment and Market Affect Optimal Nitrogen Management in Wheat and Cattle Production Systems

Fertilizer nitrogen use efficiency (NUE) is about 33% worldwide. The application of crop models has the potential to improve NUE by allowing managers to optimize and synchronize N supply with crop demand. We used a wheat (Triticum aestivum L.) grazing model to predict optimal N rates that maximize either grain yield for a grain‐only system or net economic return for a dual‐purpose system for selected climate, soil water reserve, and market conditions. Simulated probabilistic distributions of optimal fertilizer N rates for grain‐only wheat revealed a 55% chance that optimal N was <40 kg ha−1 when precipitation from August to February was <30 cm, and a 90% chance that optimal N was between 90 and 120 kg ha−1 when precipitation during the same period was >40 cm. This result supports a split N application with <45 kg ha−1 applied pre‐plant and additional N top‐dressed in February according to precipitation and yield potential. Dual‐purpose winter wheat with an initially wet soil profile required about 20, 60, 80, and 90 kg ha−1 of pre‐plant N to maximize cattle (Bos taurus) live weight gain for stocking densities of 1, 2, 2.5, and 3 head ha−1, and about 120 kg N ha−1 to maximize total net economic returns. In contrast, total optimal N for dual‐purpose wheat with an initially dry soil ranged from 0 to 90 kg ha−1, depending on climate. Precipitation between August and February was a good predictor of N requirement. Wheat grazing model was a useful tool for optimizing N management in north‐central Oklahoma.

Use of dried distillers grains throughout a beef production system: Effects on stocker and finishing performance, carcass characteristics, and fatty acid composition of beef1

A 2-yr study was conducted using a 3 × 2 factorial arrangement of treatments to evaluate the effects of feeding dried distillers grains throughout a beef production system on performance, carcass characteristics, and fatty acid profile of beef. Factors were wheat pasture supplement [no supplement (CON), dry-rolled corn (DRC), and dried distillers grains (DDG)] fed at 0.5% BW daily and finishing diet [steam-flaked corn based diet containing 0 (SFC) or 35% (35DDG) DDG]. Each year, 60 preconditioned Hereford steers (initial BW = 198 kg ± 3) grazed winter wheat pasture with or without supplement. Body weight gain was 8% greater for steers consuming DDG supplement compared with CON and DRC steers (P < 0.01). After the grazing period, pastures within supplement treatment were randomly assigned to SFC or 35DDG. There was no supplement by finishing diet interaction for any performance or carcass variable of interest (P ≥ 0.41). Previous supplementation on winter wheat affected BW at feedlot entry and adjusted G:F (P ≤ 0.05) but had no effect on finishing ADG or carcass traits (P ≥ 0.12). On a carcass-adjusted basis, steers consuming 35DDG had reduced final BW, ADG, G:F, and total BW gain throughout the system (P ≤ 0.04) compared with SFC. Additionally, steers consuming 35DDG had reduced HCW, dressing percent, and fat thickness (P ≤ 0.03) compared with SFC. There was a supplement by finishing diet interaction (P = 0.02) for 18:0, in which cattle supplemented with DRC and fed the SFC finishing diet had the lowest concentration of 18:0 but DRC supplemented steers fed the 35DDG diet had the greatest concentration. The interaction was not significant (P ≥ 0.18) for other fatty acids. Main effects of supplement and finishing diet affected (P ≤ 0.05) several other fatty acids of interest, particularly 18:2, which is associated with reduced flavor-stability of beef. The use of DDG as a supplement to wheat pasture resulted in greater ADG during wheat grazing and heavier BW at feedlot entry, but final BW was not different from CON or DRC groups. Feeding DDG at 35% DM in steam-flaked corn-based finishing diets reduced ADG, G:F, and HCW, and affected the fatty acid composition of beef.

Evaluation of tropically adapted straightbred and crossbred cattle: Postweaning BW gain and feed efficiency when finished in a temperate climate1,2

Beef cows in the subtropical USA must be adapted to the stressors of the environment, typically supplied by using Brahman (Br) breeding. Calves produced in the region, however, are usually grown and finished in more temperate regions, and have a perceived reputation for poor ADG and feed efficiency during finishing. Compromised fertility and carcass quality often associated with the Br have increased interest in tropically adapted Bos taurus breed types. The objective of this study was to evaluate 3 breeds [An = Angus (Bos taurus, temperate); Br (B. indicus, tropical); and Ro = Romosinuano (B. taurus, tropical)] and all possible crosses during various segments of post-weaning growth, and for feed efficiency during the finishing phase. Steer calves (n = 473) born over 3 yr were weaned in late September, backgrounded for at least 21 d (BKG), shipped 2,025 km to El Reno, OK, in October, fed a preconditioning diet for 28 d (RCV), grazed wheat (Triticum aestivum L.) pasture from November to May (WHT), finished on a conventional feedlot diet (FIN), and serially harvested after approximately 95, 125, and 150 d on feed. Body weight and ADG during each segment were tested using a mixed model that included calf age at weaning, year (Y), breed of sire (SB), breed of dam (DB), and interactions. In addition, winter treatment (continuous wheat or reduced grazing of wheat with supplement) was included for the wheat and feedlot phases. Sire within SB × SB [and pen (barn × year) for feedlot phase] were considered random. The SB × DB interaction was significant for all traits (P < 0.01) except exit velocity taken at weaning and ADG during FIN, but both traits were affected by 3-way interactions with Y or harvest group. Tropically-adapted purebred steers had greater (P < 0.01) ADG than AnAn through weaning and BKG in FL but the reverse was true during the RCV and WHT segments. Similar, but less pronounced results were noted for F(1) steers with 100% tropical influence compared with those with only 50%. Heterosis was numerically greater for most traits for An × Br (11 to 64%) compared with An × Ro and Br × Ro (3 to 42%), which were similar. In a subset of the steers (n = 261), G:F was not influenced by level of tropical breeding, but tropically adapted steers were more efficient (P < 0.05) by residual feed intake. No heterosis was evident. These data show that in temperate zones, winter is the period when productivity of tropically adapted cattle is compromised.

Grazing wheat did not reduce beef cow pregnancy rates

Beef producers can lower feed costs by extending the grazing period and reducing the need for harvested forages. Complementary forage systems extend the native range grazing season; wheat pasture is common in the southern portion of the High Plains. Anecdotal reports have been made concerning lowered fertility in beef cows bred on lush forage such as wheat pasture; however, ruling out other possible causes of low fertility is difficult. In lactating dairy cows, fertility is lower during consumption of high-protein diets that result in high blood urea nitrogen content. Lower uterine pH that in turn affects embryo survival is thought to be the general mechanism responsible for lower fertility. Little information is available on the fertility of beef cows consuming high-protein diets. Therefore, the objective of this study was to compare pregnancy rates of springcalving cows consuming either wheat pasture or native range before and during the early breeding season.

Influences of Agricultural Practice and Summer Grazing on Soil Compaction in Wheat Paddocks

Agriculture in the Southern Great Plains (SGP) relies on production systems that combine yearling cattle and grazing of winter wheat. Incorporating summer legumes into the fallow period of wheat would allow longer grazing seasons and potential improvements in livestock gain, but may adversely affect soil conditions. This study examined the impacts of additional grazing during summer on soil compaction within paddocks of grazed wheat. Four 1.6 ha paddocks were used to study two systems of producing forage by conservation tillage during 1999 and 2000. Both systems combined winter and spring grazing of wheat with either grazing of an annual legume during summer (SL) or chemical fallow during summer (SCF). Enclosures (n = 2) were established in each paddock to serve as ungrazed controls. Soil compaction was measured by resistance to a cone penetrometer to 300 mm soil depth on three dates (May and December 1999, June 2000), and measures of bulk density and soil moisture were collected. Regression analyses showed a significant relationship between resistance and bulk density across agricultural practices, and separate relationships for grazing treatments. The SL agricultural practice produced greater compaction of soil than SCF below 75 mm depth, with gradual increases over the last two sampling dates. In contrast, grazing generated increases in compaction at all depths on all dates, with the largest increases noted between 50 and 100 mm. Results suggest that combining grazing of wheat with grazing legumes during the summer, under conservation tillage, may not represent sustainable management in the short term.

Grazing Initiation Timing Affects Net Return of Dual-Purpose Wheat Systems

Limited experimental data are available to allow direct evaluation of the effects of grazing initiation timing on net returns to dual-purpose wheat systems. The objectives were to simulate the effect of grazing initiation dates on net returns to a wheat (Triticum aestivum L.) cattle (Bos taurus) enterprise, and to determine economically optimal dates of grazing initiation for selected grazing scenarios. A wheat grazing model was used to simulate the dual systems in north-central Oklahoma for six to eight grazing initiation dates (ranging from 10 October to 30 January), six stocking rates (SR 0.5 to 3 head ha-1), four planting dates (1 September to 1 October), three climate scenarios (dry, average, and wet), and an initial wet soil with 75% plant available water. Net returns were further estimated using an enterprise budget approach for the 1999 (favorable to beef production) and 2005 (neutral) markets. For the wheat-cattle production scheme studied in this work, grazing should be initiated as soon as wheat plants are anchored or top dry biomass reaches approximately 1120 kg ha-1, irrespective of planting dates and climate. As a rule of thumb, for initial wet soils, regardless of climate, the most profitable practices in the region are early September planting, early grazing initiation (before mid-November), and heavy stocking (1.5 to 3 head ha-1), while lower SR such as 0.5 are preferable for later grazing initiation. Uncertainty in net return pertaining grazing initiation timing decreases as SR decreases, indicating that high SR appeal to risk lovers and low SR to risk averters.

Optimizing Stocking Rate for Maximum Return to a Wheat–Cattle Enterprise Using Model Simulation and Economics

Managing dual‐purpose wheat is complex because of the tradeoff relationship between cattle (Bos taurus) and wheat (Triticum aestivum L.) production. Stocking rate (SR) and planting date are key decision variables of the dual systems. The objective was to develop decision support information that help farmers boost profits by adapting SR and planting date to particular production and market conditions. A wheat grazing model was used to simulate the systems for seven SR (0–3 head ha−1), five planting dates, three climate scenarios, and two initial soil moisture profiles. Net returns were estimated for three representative markets. Net returns under optimized management doubled those under the business‐as‐usual for the comparable planting dates, indicating great potentials to boost net returns with better management. Optimal SR depends on markets and forage availability. For market that overwhelmingly favors grain production, grain‐only wheat should be used; whereas dual‐purpose wheat is preferred under other market conditions. For wet soil at planting, maximum returns are attained in early September planting at high SR of &gt; 2 head ha−1 despite climates; however, the high optimal SR should be adjusted down with delayed planting in wet and average but maintained in dry climate for water conservation. For dry profile at planting, optimal management is dual‐purpose wheat with SR of 3 in wet, grain‐only wheat in average, and fallow in dry climate. Had wheat been established in severely dry years, moderate grazing at 0.5 to 1.5 SR could reduce net losses. Under most circumstances, grazing should not be allowed to pass first hollow stem to maximize returns.

Effects of Level of Dried Distillers Grain Supplementation on Native Pasture and Subsequent Effects on Wheat Pasture Gains

Crossbred steers (225 ± 16.8 kg) were stratified by BW, blocked by grazing group, and randomly assigned to treatment to determine the effects of level of dried distillers grain (DDG) supplementation on native pasture ADG, subsequent wheat pasture ADG, supplement efficiency, and economic return to supplement. One hundred twenty steers grazed dormant rangeland for 56 d and were supplemented 3 times/wk with the equivalent of 7 d of corn DDG at 0, 0.25, 0.50, or 0.75% of BW per day (DM basis). Average daily gain increased linearly (P < 0.001) with level of DDG. After grazing rangeland, supplementation ceased and 60 steers (1 grazing block) were moved to wheat pasture for 76 d. During wheat grazing, nonsupplemented steers compensated and final BW was not different between the nonsupplemented and 0.25% of BW groups. However, final BW tended (P = 0.08) to increase with level of DDG after wheat grazing. Supplement efficiency while grazing range was 0.427, 0.369, and 0.338 kg added ADG/kg supplement DM, respectively, for the 0.25, 0.50, and 0.75% of BW treatments. However, total system efficiency was reduced to 0.017, 0.218, and 0.171 kg added ADG/kg supplement DM, respectively, after grazing wheat pasture. Economic return was greatest for 0.75% of BW when steers were marketed after dormant range grazing. If marketing occurred after wheat grazing, returns were maximized by 0.50% of BW unless the delivered cost of DDG was low. If the delivered cost of DDG was $100/US ton, economic returns were maximized by 0.75% of BW supplementation after wheat grazing.

Opportunities and trade-offs in dual-purpose cereals across the southern Australian mixed-farming zone: a modelling study

Dual-purpose cereals are employed in the high-rainfall zone of southern Australia to provide additional winter forage. Recently there has been interest in applying this technology in the drier environments of South and Western Australia. It would therefore be useful to gain an understanding of the trade-offs and risks associated with grazing wheat crops in different locations. In this study the APSIM (Agricultural Production Systems Simulator) crop and soil simulation models were linked to the GRAZPLAN pasture and livestock models and used to examine the benefits and costs of grazing cereal crops at 21 locations spanning seven of the regions participating in the Grain &amp; Graze research, development and extension program. A self-contained part of a mixed farm (an annual pasture–wheat rotation plus permanent pastures) supporting a breeding ewe enterprise was simulated. At each location the consequences were examined of: (i) replacing a spring wheat cultivar with a dual-purpose cultivar (cv. Wedgetail or Tennant) in 1 year of the rotation; and (ii) either grazing that crop in winter, or leaving it ungrazed. The frequency of early sowing opportunities enabling the use of a dual-purpose cultivar was high. When left ungrazed the dual-purpose cultivars yielded less grain on average (by 0.1–0.9 t/ha) than spring cultivars in Western Australia and the Eyre Peninsula but more (by 0.25–0.8 t/ha) in south-eastern Australia. Stocking rate and hence animal production per ha could be increased proportionately more when a dual-purpose cultivar was used for grazing; because of the adjustments to stocking rates, grazing of the wheat had little effect on lamb sale weights. Across locations, the relative reduction in wheat yield caused by grazing the wheats was proportional to the grazing pressure upon them. Any economic advantage of moving to a dual-purpose system is likely to arise mainly from the benefit to livestock production in Western Australia, but primarily from grain production in south-eastern Australia (including the Mallee region). Between years, the relationship between increased livestock production and decreased grain yield from grazing crops shifts widely; it may therefore be possible to identify flexible grazing rules that optimise this trade-off.