Pasture Mass Research Articles

Assessing and Modeling Pasture Growth under Different Nitrogen Fertilizer and Defoliation Rates in Argentina and the United States

Core Ideas Model‐based approach identified sets of adaptive practices for pasture management across seasons. Suitable combinations of N rate and residual heights can improve the use of N fertilizer and water. The increment in residual pasture mass and N fertilizer may be crucial for more efficient use of water. Pasture growth responses to residual leaf area increased with N fertilization. The objectives of this research were to (i) evaluate the effects of N fertilizer, irrigation, and residual pasture heights on pasture growth, (ii) validate the ability of the SALUS model to predict dynamics of pasture growth, and (iii) evaluate during long‐term period the effects of using different N fertilizer levels and defoliation strategies on pasture growth, N fertilizer use, and water use efficiency (WUE). Eight single‐season experiments were performed at plot scale (8 m2) in Buenos Aires (Argentina, ARG) and Michigan. In ARG different N fertilizer rates (from 0–500 kg N ha−1) were imposed on both rainfed and irrigated tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] pasture during autumn, spring, and summer. In the United States, three residual pasture height treatments (30, 60, and 120 mm) were imposed on both tall fescue and ryegrass (Lolium perenne L.) pasture in the spring and summer. The SALUS was parameterized to simulate tall fescue and ryegrass growth using soil, weather, and different pasture treatments previously tested in ARG and the United States. Results showed that the SALUS accurately represented the response of herbage mass to irrigation and added N in the ARG site (RMSE < 650 kg DM ha−1) and to differences in residual pasture heights in the U.S. experiment (RMSE < 509 kg DM ha−1). Ten‐year simulations (2000–2010) demonstrated that suitable combinations of N fertilizer and residual pasture heights can significantly improve the use of N fertilizer by ∼300% and water by ∼230% through increases in herbage production.

Comparison between a laser sensor and mechanical tools to estimate pasture mass in strata of kikuyu (Pennisetum clandestinum) pastures

Pasture meters are typically calibrated to estimate total pasture mass (TPM). Recent studies have shown that animal productivity was driven by the level of utilisation of the top leafy stratum (TLS) rather than the TPM. A study of kikuyu (Pennisetum clandestinum) pasture conducted on two farms located in southeast Queensland, Australia assessed whether pasture mass of the TLS, bottom stemmy stratum (BSS) and TPM can be more accurately estimated by using not only pasture surface height but also pasture density derived from height data captured by a laser sensor. The results indicated that there was a notable improvement of the pasture mass estimates when density was included in the calibration equations. The study also compared the accuracy of the pasture mass estimates between the laser sensor and mechanical pasture meters (rising plate meter and ruler). The results indicated that all devices provided reasonable estimates of pasture mass for TLS, BSS and total (R2 ≥ 0.75). However, pasture mass was estimated with a slightly higher level of accuracy when using the laser sensor in comparison with the other pasture meters, particularly for the top leafy stratum (R2 = 0.81 vs R2 ≤ 0.77).

Summer production and survival of perennial ryegrass (Lolium perenne) and tall fescue (Festuca arundinacea) genotypes in northern Victoria under differing irrigation management

Perennial ryegrass (Lolium perenne L.) is the predominant perennial forage species used in temperate irrigated dairy-production systems in Australia. However, when temperatures are high, even with optimal irrigation strategies and nutrient inputs, dry matter (DM) production can be compromised. This research investigated the effects of perennial ryegrass and tall fescue genotypes and summer irrigation on (DM) production and survival. Ten perennial ryegrass cultivars, three hybrid ryegrasses and two cultivars of tall fescue (Festuca arundinacea (Schreb) Darbysh.) were sown in northern Victoria, Australia, in May 2014, and were managed under full irrigation or restricted irrigation (no irrigation between late December and mid-March) over a 3-year period. Measurements included net pasture accumulation (DM production), sward density (plant frequency) and water-soluble carbohydrate concentration. Apart from the expected differences in DM yield over the summer period between full irrigation and restricted irrigation, there were few differences in DM production among perennial ryegrass or tall fescue cultivars. Plant frequency declined significantly under restricted irrigation in Years 2 and 3 compared with full irrigation but there were no differences among perennial ryegrass cultivars. In Year 2, plant frequency was higher in the tall fescue cultivars than the ryegrass cultivars. The recovery pattern in DM production following recommencement of irrigation in mid-March (autumn) varied across years. In Year 1, plants recovered rapidly once irrigation recommenced in autumn. However, in Years 2 and 3, autumn and winter pasture accumulation under restricted irrigation was 30–35% less than under full irrigation. These differences were possibly related to decreases in plant frequency, as well as to differences in the amounts of residual pasture mass (or carbohydrate reserves) present when growth ceased. Analyses of the water-soluble carbohydrate concentrations in the pseudostem during summer and autumn in Year 3 showed differences in total water-soluble carbohydrate and in fructan and sucrose concentrations between irrigation treatments but no consistent differences among genotypes.

A Longitudinal Study of the Pastures Grazed and Body Condition Scores of Pony Club Horses In one Region of Australia

A cohort of Pony Club horses was observed for 13 months with data collected from owner-kept diaries and monthly property visits. All horses studied had access to pasture for all or part of the day. Whilst paddock size was seldom limiting, pasture degradation was evident and observed pasture mass and composition varied greatly. Horses’ body weight indices and body condition scores also varied greatly, closely matching seasonal variations in pasture mass. Increments in bodyweight varied in a non-linear fashion with body condition score. Most horses experienced additional year-round hand-fed supplementation and half of the study horses recorded body condition scores greater than 3.5 out of 5. This suggests that the owners of Pony Club horses did not rely on pasture as the sole source of nutrition, even though, based on estimated energy demands, well-managed pasture can meet the energy requirements of Pony Club horses. Furthermore, the fact that owners appeared not to make horse feeding decisions based on body condition score resulting in obesity, raises health and welfare concerns due to obesity related health disorders in Pony Club horses. The inappropriate feeding of supplements observed during times of high pasture growth was a concern. Whilst the ideal pasture for Pony Club horses has not been described, it is likely to differ to those considered ideal for broodmares and other livestock because of these unique health risks associated with high levels of non-structural carbohydrate content in improved pasture species. This study highlights the need to educate owners about recognising unhealthy body conditions of horses and better managing pastures and pasture access to reduce the risk of obesity related disorders, whilst at the same time reducing pasture degradation and supplemental feed costs

Methane and carbon dioxide emissions from lactating dairy cows grazing mature ryegrass/white clover or a diverse pasture comprising ryegrass, legumes and herbs

There is a growing interest in forage mixtures (Diverse pasture; e.g. containing grasses, legumes and herbs), especially those with a greater tolerance of dry conditions and a decreased nitrogen (N) content (reducing N losses), compared with ryegrass (Lolium perenne L and Lolium multiflorum L)/white clover (Trifolium repens L) pastures (RyeWC), which dominate New Zealand pastoral systems for dairy production. However, the effect of alternative forages on enteric methane (CH4) emissions is not known. The objective of the present trial was to compare CH4 emissions and milk production from dairy cows grazing either mature RyeWC or mature Diverse pasture (both approximately with pasture mass of 5600 kg DM/ha). The Diverse mixture comprised ryegrass, white clover, lucerne (Medicago sativa L), chicory (Cichorium intybus L) and plantain (Plantago lanceolata L). Milk production, measured from cows commencing at ~162 days of lactation, was less when cows grazed RyeWC than Diverse pastures (15.4 vs 16.7 kg/day; P < 0.001), whereas CH4 production (g/day) was similar for the respective treatments (411 g/day; P = 0.16). Milk composition was not affected by diet and CH4 intensity was similar for both diets (22 g/kg fat- and protein-corrected milk; P = 0.31). Methane yield [g/kg predicted dry matter intake (DMI)] averaged 22.6 and 24.9 for cows grazing RyeWC and Diverse pastures, respectively (P = 0.006). In conclusion, although the CH4 yield was greater when Diverse pasture was grazed, relative to RyeWC, there were no differences in emissions intensity or total CH4 emissions.

Grazing pressure impacts on two Aristida/Bothriochloa native pasture communities of central Queensland

Managing native pastures for sustainable and economic production requires a good understanding of grazing effects on pasture dynamics. The Aristida/Bothriochloa pastures of north-eastern Australia are important for cattle production but little data on grazing pressure impacts on pastures are available to guide management decisions of producers, for land management education programs, or for predictive modelling. To address this deficiency, four different continuous grazing intensities were imposed on woodland communities over 7 or 8 years at two sites: a Eucalyptus populnea (poplar box) and a E. melanophloia (silver-leaved ironbark) community. Both sites had replicated paddocks grazed at a low, medium or high grazing pressure by +/− tree killing using herbicide (12 paddocks), and 12 ungrazed (nil grazing pressure) 1-ha plots subjected to the same tree-killing contrasts. Grazed paddock areas were fixed and varied between 3.5 and 21.5 ha. Differential grazing pressures were reset each autumn, by adjusting cattle numbers to consume over the next year the equivalent of 0%, 25%, 50% or 75% of the standing pasture mass available. Pasture grasses suitable as indicators of grazing pressure were identified for both communities. Under low grazing pressure, Themeda triandra (kangaroo grass) was the only desirable grass to show a significant increase in total contribution over time at both sites, although Dichanthium sericeum (Queensland bluegrass) also increased its contribution at the poplar box site. Chloris species increased their contribution as grazing pressure increased. The proportion of less palatable Aristida spp. (wiregrasses) in the pasture was not affected by high grazing pressure, although they increased at low grazing pressure in the poplar box community. There were no consistent changes in native legumes or weedy forb species to any treatment. Increasing grazing pressure had a greater negative effect on pasture mass, ground cover and pasture crown cover area than on changing species composition. Most changes in composition due to grazing pressure were smaller than those associated with variable seasonal rainfall, and were greater in the poplar box community. In above-average rainfall years grazing up to 50% of autumn standing pasture mass had no detrimental effect on composition in treeless poplar box country in the short term. The pastures remained stable or improved in both communities when grazing pressure was set annually to utilise 25% of the standing autumn forage.

Grazing management of dairy pastures based on tall fescue in southern Australia

Tall fescue (Festuca arundinacea (Schreb) Darbysh.) has the potential to become a useful component of irrigated dairy pastures in northern Victoria owing to its high dry matter (DM) production compared with perennial ryegrass. However, tall fescue is not widely grown because its grazing management is perceived as difficult. In October 2010, a tall fescue–white clover pasture was established and irrigated. In September 2011, six grazing-management treatments were imposed over 3 years, involving grazing: at 1-leaf stage; at 2-leaf stage (1.5-leaf stage during spring); at 3-leaf stage (2.5-leaf stage during spring); at intervals based upon days between grazings ranging from 15 days in October–December to 60 days in winter; at intervals as above except for 21 days in October–December; and at intervals approximating that of a well-managed perennial-ryegrass-based pasture . Measurements included pre- and post-grazing pasture mass, nutritive characteristics, botanical composition and plant frequency. Pasture consumption from the treatment grazed at the 3-leaf stage was >3.5 t DM ha–1 year–1 (30%) greater than from the three most frequently grazed treatments. However, crude protein content was 1–3% DM units lower when grazed at the 3-leaf stage compared with the two most frequently grazed treatments. There was no effect on estimated metabolisable energy or neutral detergent fibre contents of the pasture on offer. Differences in pasture composition between the pastures grazed at the 3-leaf stage and those most frequently grazed emerged over time and were most conspicuous in the third year, with a greater plant frequency (79% v. 66%) and tall fescue content (61% v. 40% DM) and lower weed content (14% v. 28% DM). From the study, a grazing regime for tall fescue based on the 3-leaf stage appears promising because it produced the most DM over the experiment. A disadvantage of this regime was the need for an extra mowing each year. The practicality of this approach to grazing tall fescue needs to be tested at the whole-farm level.

In a native pasture, landscape properties influence soil moisture more than grazing management

It has been proposed that changes to grazing systems, from continuous to rotational grazing, alter the pasture mass and composition, which are reflected in changes to stored soil water. Additionally, in highly variable landscapes, determining whether the variation in soil water is due to the inherent landscape properties rather than the imposed grazing management has long been a contentious argument. To address this question, soil moisture was measured across a highly variable landscape under three differing grazing treatments (1-, 4- and 20-paddock systems). From the soil-water measurements, plant-available water and plant-available water capacity were determined. Different production zones (high, medium and low) were identified in the landscape by visually estimating green herbage mass in late spring. There were no observed differences in the measured plant-available water capacity across the grazing treatments; however, significant differences occurred in plant-available water capacity across the three production zones (high-production zone, 114 mm; medium-production zone, 102 mm; low-production zone, 88 mm) within the study period. There appears to be a trend between the plant-available water capacity and near-surface gravel content as measured in production zones. The high production zones held more plant-available water than did the low production zones, enabling more biomass and longer pasture growth during spring and autumn. The plant-available water in the low production zones significantly decreased with time. In all, 22 of the 50 soil-moisture monitoring locations displayed high temporal stability and were identified as being catchment-average soil water-content monitoring locations. A majority of these locations occurred in the medium production zone, demonstrating that representative soil moisture can be measured in these landscapes.

The multi-year cumulative effects of alternative stocking rate and grazing management practices on pasture productivity and utilization efficiency

The production and utilization of increased quantities of high quality pasture is of paramount importance in pasture-based milk production systems. The objective of this study was to evaluate the cumulative effects of alternative integrated grazing strategies, incorporating alternative stocking rate (SR) and grazing severities, on pasture productivity and grazing efficiency over multiple years within farm systems using perennial ryegrass dominant pastures. Three whole-farm SR treatments were compared over 4 complete grazing seasons (2009 to 2012 inclusive): low (2.51 cows/ha; LSR), medium (2.92 cows/ha; MSR), and high (3.28 cows/ha; HSR). Each system had its own farmlet containing 18 paddocks and remained on the same treatment for the duration of the study. Stocking rate had a significant effect on all grazing variables with the exception of soil fertility status and sward density. Increased SR resulted in increased total annual net pasture accumulation, improved sward nutritive value, and increased grazed pasture utilization. Total annual net pasture accumulation was greatest in HSR [15,410kg of dry matter (DM)/ha], intermediate for MSR (14,992kg of DM/ha), and least for LSR (14,479kg of DM/ha) during the 4-yr study period. A linear effect of SR on net pasture accumulation was detected with an increase in net pasture accumulation of 1,164.4 (SE=432.7) kg of DM/ha for each 1 cow/ha increase in SR. Pregrazing pasture mass and height and postgrazing residual pasture mass and height were greatest for LSR, intermediate for the MSR, and lowest for the HSR. In comparison with the LSR, the imposition of a consistently increased grazing severity coupled with increased whole farm SR in MSR and HSR treatments arrested the decline in sward nutritive value, typically observed during mid-season. Incorporating the individual beneficial effects of SR on pasture accumulation, nutritive value, and utilization efficiency, total proportional energy (unité fourragère lait) utilization per hectare increased significantly with increasing SR (+0.026 and +0.081 for MSR and HSR, respectively). These results quantify the significant effect of grazing management practices on the feed production capability of modern perennial ryegrass pastures for intensive grazing dairy production systems. Furthermore, these results highlight the importance of consistently imposing grazing treatments over multiple years, and within integrated whole farm systems, to accurately assess the longer term effects of alternate grazing management practices on pasture productivity.

A protocol for sampling pastures in hill country

To develop a protocol to guide pasture sampling for estimation of paddock pasture mass in hill country, a range of pasture sampling strategies, including random sampling, transects and stratification based on slope and aspect, were evaluated using simulations in a Geographical Information Systems computer environment. The accuracy and efficiency of each strategy was tested by sampling data obtained from intensive field measurements across several farms, regions and seasons. The number of measurements required to obtain an accurate estimate was related to the overall pasture mass and the topographic complexity of a paddock, with more variable paddocks requiring more samples. Random sampling from average slopes provided the best balance between simplicity and reliability. A draft protocol was developed from the simulations, in the form of a decision support tool, where visual determination of the topographic complexity of the paddock, along with the required accuracy, were used to guide the number of measurements recommended. The protocol was field tested and evaluated by groups of users for efficacy and ease of use. This sampling protocol will offer farmers, consultants and researchers an efficient, reliable and simple way to determine pasture mass in New Zealand hill country settings. Keywords: hill country, feed budgeting, protocol pasture mass, slope

Calibration of GrassMaster II to estimate green and dry matter yield in Mediterranean pastures: effect of pasture moisture content

Accurate assessment of standing pasture biomass in livestock production systems is a major factor for improving feed planning. Several tools are available to achieve this, including the GrassMaster II capacitance meter. This tool relies on an electrical signal, which is modified by the surrounding pasture. There is limited knowledge on how this capacitance meter performs in Mediterranean pastures. Therefore, we evaluated the GrassMaster II under Mediterranean conditions to determine (i) the effect of pasture moisture content (PMC) on the meter’s ability to estimate pasture green matter (GM) and dry matter (DM) yields, and (ii) the spatial variability and temporal stability of corrected meter readings (CMR) and DM in a bio-diverse pasture. Field tests were carried out with typical pastures of the southern region of Portugal (grasses, legumes, mixture and volunteer annual species) and at different phenological stages (and different PMC). There were significant positive linear relations between CMR and GM (r2 = 0.60, P < 0.01) and CMR and DM (r2 = 0.35, P < 0.05) for all locations (n = 347). Weak relationships were found for PMC (%) v. slope and coefficient of determination for both GM and DM. A significant linear relation existed for CMR v. GM and DM for PMC >80% (r2 = 0.57, P < 0.01, RMSE = 2856.7 kg ha–1, CVRMSE = 17.1% to GM; and r2 = 0.51, P < 0.01, RMSE = 353.7 kg ha–1, CVRMSE = 14.3% to DM). Therefore, under the conditions of this current study there exists an optimum PMC (%) for estimating both GM and DM with the GrassMaster II. Repeated-measurements taken at the same location on different dates and conditions in a bio-diverse pasture showed similar and stable patterns between CMR and DM (r2 = 0.67, P < 0.01, RMSE = 136.1 kg ha–1, CVRMSE = 6.5%). The results indicate that the GrassMaster II in-situ technique could play a crucial role in assessing pasture mass to improve feed planning under Mediterranean conditions.

A comparison of conventional and automatic milking system pasture utilization and pre‐ and post‐grazing pasture mass

AbstractAutomatic milking systems (AMS) present an opportunity for dairy farmers to not only improve their lifestyle and conditions of work, but also save on labour costs and/or increase the time available to focus on overall farm management. However, the viability of AMS will rely on achieving high levels of pasture utilization. Well‐established pasture management principles are implemented on many conventional milking system (CMS) farms and high levels of pasture utilization are achieved; however, the ability to follow these same principles on AMS is unknown. This study compared levels of pasture utilization and pre‐ and post‐grazing pasture mass between AMS and CMS farms at the same site when managed by the same pasture management principles. From 1 March 2007 to 29 February 2008, pre‐ and post‐grazing compressed height, milk yield and milk composition data were collected for two CMS farms and one AMS farm at the Elizabeth Macarthur Agricultural Institute, Camden, Australia. Despite differences in pre‐ and post‐ grazing pasture mass between milking systems, pre‐grazing mass was predominantly maintained within the bounds of 2200 and 2500 kg DM ha−1 and post‐grazing mass between 1400 and 1500 kg DM ha−1 (5–6 cm height). Similar levels of pasture utilization (mean 13 500 kg DM ha−1 year−1) were recorded between AMS and CMS farms. These findings highlight the ability to follow established grazing management principles and achieve high levels of pasture utilization on pasture‐based AMS farms.

Regular estimates of paddock pasture mass can improve profitability on New Zealand dairy farms

Paddock selection is an important component of grazing management and is based on either some estimate of pasture mass (cover) or the interval since last grazing for each paddock. Obtaining estimates of cover to guide grazing management can be a time consuming task. A value proposition could assist farmers in deciding whether to invest resources in obtaining such information. A farm-scale simulation exercise was designed to estimate the effect of three levels of knowledge of individual paddock cover on profitability: 1) "perfect knowledge", where cover per paddock is known with perfect accuracy, 2) "imperfect knowledge", where cover per paddock is estimated with an average error of 15%, 3) "low knowledge", where cover is not known, and paddocks are selected based on longest time since last grazing. Grazing management based on imperfect knowledge increased farm operating profit by approximately $385/ha compared with low knowledge, while perfect knowledge added a further $140/ha. The main driver of these results is the level of accuracy in daily feed allocation, which increases with improving knowledge of pasture availability. This allows feed supply and demand to be better matched, resulting in less incidence of under- and over-feeding, higher milk production, and more optimal post-grazing residuals to maximise pasture regrowth. Keywords: modelling, paddock selection, pasture cover

Mass to height relationships in annual pastures and prediction of sheep growth rates

The relationship between pasture height and mass influences the availability of pasture for grazing, and is important for predicting intake of pasture and liveweight change by sheep. The relationship between pasture mass and structure and sheep production is poorly defined for low-mass, clumpy pastures in low-rainfall regions. Between 2001 and 2004, 480 quadrats of pastures were measured in 23 paddocks throughout the Victorian Mallee. Pasture height was related to live mass for medic (linear; r2 = 0.70; P < 0.001) and grassy medic (asymptotic; r2 = 0.64; P < 0.001) pastures, and prediction of grassy medic pasture height was improved by inclusion of proportion live groundcover. During 2004, pasture dry matter accumulation and liveweight changes in sheep grazing annual pastures were measured and compared with predicted outputs from GrazFeed, a software model used to estimate feed intake and liveweight change in sheep. Improved predictions of liveweight gain in grazing sheep were obtained using measured height rather than the GrazFeed default height. The results show that the height to mass relationship of annual pastures in the Victorian Mallee differs between pasture types, between years, and may differ from other published relationships. This study provides information that may assist in the development of models of grazing systems.

Effect of grazing management on herbage protein concentration, milk production and nitrogen excretion of dairy cows in mid‐lactation

AbstractThe objective of this experiment was to use diurnal and temporal changes in herbage composition to create two pasture diets with contrasting ratios of water‐soluble carbohydrate (WSC) and crude protein (CP) and compare milk production and nitrogen‐use efficiency (NUE) of dairy cows. A grazing experiment using thirty‐six mid‐lactation Friesian x Jersey cows was conducted in late spring in Canterbury, New Zealand. Cows were offered mixed perennial ryegrass and white clover pastures either in the morning after a short 19‐day regrowth interval (SR AM) or in the afternoon after a long 35‐day regrowth interval (LR PM). Pasture treatments resulted in lower pasture mass and greater herbage CP concentration (187 vs. 171 g kg−1 DM) in the SR AM compared with the LR PM but did not affect WSC (169 g kg−1 DM) or the ratio of WSC/CP (1·0 g g−1). Cows had similar apparent DM (17·5 kg DM cow−1 d−1) and N (501 g N cow−1 d−1) intake for both treatments. Compared with SR AM cows, LR PM cows had lower milk (18·5 vs. 21·2 kg cow−1 d−1), milk protein (0·69 vs. 0·81 kg cow−1 d−1) and milk solids (1·72 and 1·89 kg cow−1 d−1) yield. Urinary N concentration was increased in SR AM, but estimated N excretion and NUE for milk were similar for both treatments. Further studies are required to determine the effect of feeding times on diurnal variation in urine volume and N concentration under grazing to predict urination events with highest leaching risk.

Meta-analysis of the effect of pasture allowance on pasture intake, milk production, and grazing behavior of dairy cows grazing temperate grasslands

Daily pasture allowance (PA) is defined as the product of pregrazing pasture mass and offered area, and is the major grazing management factor determining pasture utilization per unit area and daily performance of grazing dairy cows. The objective of the present study was to perform a meta-analysis reviewing the effect of PA on pasture intake, milk production, milk composition, and grazing behavior of dairy cows. Experiments studying the effect of PA on pasture intake or milk production, which eventually included milk composition or grazing behavior data, or both, were selected to create a database. Papers were selected only if at least 2 PA were compared under the same experimental conditions, particularly the same pasture mass (i.e., where PA levels were only obtained through changes in daily offered area). The final database included 97 PA comparisons reported in 56 papers. For analytical purposes, the database was subdivided into 3 subsets that varied according to the estimation height (EH) at which PA was determined; that is, PA above ground level (PA0 subset), PA above 2.5 to 3.5cm (PA3 subset), and PA above 4 to 5cm (PA5 subset). Statistical analyses were conducted independently on the PA0, PA3, and PA5 subsets and on the whole database (global analysis) by using linear and nonlinear mixed-model procedures. The curves, either exponential, quadratic, or linear, describing the effects of PA on pasture intake, milk production, or grazing behavior of dairy cows are conceptually similar, whatever the EH. The equations describing these curves are, however, specific for each EH. Accordingly, from typical low to high PA, the increase in pasture intake (0.13 vs. 0.21 vs. 0.28kg/kg of PA), milk production (0.11 vs. 0.17 vs. 0.24kg/kg of PA), and milk solids production (0.008 vs. 0.010 vs. 0.013kg/kg of PA) per kilogram of increase in PA was lower for PA0 than for PA3, and for PA3 than for PA5. Grazing time increased from low to medium PA and did not vary from medium to high PA. Pasture intake rate seemed to increase from low to medium PA because of greater bite mass, whereas it increased from medium to high PA because of greater biting rate. The present meta-analysis demonstrated that the general relationship between PA and any dependent variable is quite strong and independent of EH. This suggests no specific relationship for some parts of the world or methodology approach, with a high portability of the global equations calculated here. These results are useful for improving grazing management and modeling on pasture-based dairy systems.

Calibration and use of plate meter regressions for pasture mass estimation in an Appalachian silvopasture

A plate meter for measuring pasture mass was calibrated at Agroforestry Research Site in Blacksburg, Virginia, USA, using six ungrazed plots of established tall fescue overseeded with orchardgrass. Each plot was interplanted with bare root honey locust and black walnut seedlings spaced along a gradient ranging from 1.8 to 11.0 m. Plate height (PH) of forage between trees was measured by placing a 46 mm × 46 mm × 5.6-mm-thick acrylic plastic plate meter on pasture canopy at six locations four times a season. PH was measured between ground and plate as it rested on pasture canopy. To calibrate the plate meter against a known dry matter yield, 50 × 50-cm clip plots followed each PH measurement. The resulting regression slope was 421 kg ha−1 cm−1, with an r 2 value of 0.86. Unique research investigating the response of forage mass to site elevation is presented using the developed equation. The field-calibrated regression slope of ruler height (RH) to PH was 1.71 cm cm−1, with an r 2 value of 0.87, showing good correlation between RH and PH. A comparable regional regression equation was found to adequately predict independent calibration clip plot data reported at this site. The results support the application of regression equations for estimating pasture mass in areas having similar climates and pasture composition.

Process-based modelling to understand the impact of ryegrass diversity on production and leaching from grazed grass-clover dairy pastures

Ecological studies often suggest that natural grasslands with high species diversity will grow more biomass and leach less nitrogen (N). If this diversity effect also applies to fertilised and irrigated pastures with controlled removal of herbage, it might be exploited to design pastures that can assist the dairy industry to maintain production while reducing N leaching losses. The purpose of this study was to test whether pasture mixtures with a high functional diversity in ryegrass traits will confer on the system higher water- and N-use efficiency. The hypothesis was tested using a process-based model in which pasture mixtures were created with varying levels of diversity in ryegrass traits likely to affect pasture growth. Those traits were: the winter- or summer-dominance of growth, the ability of the plant to intercept radiation at low pasture mass, and rooting depth. Pasture production, leaching and water- and N-use efficiency were simulated for management typical of a dairy pasture. We found that the performance of the diverse ryegrass–clover mixtures was more strongly associated with the performance of the individual components than with the diversity across the components. Diverse pasture mixtures may confer other benefits, e.g. pest or disease resistance and pasture persistence. The testing here was within a selection of ryegrasses, and the greater possible diversity across species may produce different effects. However, these results suggest that highly performing pastures under fertilised and irrigated grazed conditions are best constructed by selecting components that perform well individually than by deliberately introducing diversity between components.

Process-based modelling to understand which ryegrass characteristics can increase production and decrease leaching in grazed grass–legume pastures

A significant challenge for the pastoral farming systems is to maintain or increase production while reducing leaching of nitrogen, and for pastoral systems, this means reducing leaching from urine patches. Here we explore the potential impact of four ryegrass characteristics to increase pasture production and reduce leaching from ryegrass–white clover pastures. We focus on understanding which characteristics are desirable, the stage before investigating the achievability of those characteristics in a breeding program. Those characteristics were: the winter- or summer-dominance of growth (GP); the ability of the plant to intercept radiation at low pasture mass (LI); rooting depth (RD); and resistance to moderate water stress (WF). The impact of these ryegrass characteristics, both singly and combined within a ryegrass–clover pasture, was explored across a range of soils, climates, irrigation management, and urine patch concentrations using the process-based model APSIM. Of the four characteristics tested, LI was the most effective in increasing production and reducing leaching in all environments. The characteristics RD and WF were moderately effective, with RD having a greater impact on reducing leaching whereas WF had a greater effect on increasing production. The characteristic with the least impact was GP and it seems that ryegrass is currently well adapted for typical temperatures in New Zealand. The production and environmental effects of the characteristics were additive. The characteristics should be investigated further in the typically more diverse mixtures normally found in pastures but show promise for achieving improved production while reducing leaching provided they can be achieved in a breeding program.

Meta-analysis of the effect of pregrazing pasture mass on pasture intake, milk production, and grazing behavior of dairy cows strip-grazing temperate grasslands

Grazing management is a key factor in pasture-based dairy systems, which can be improved given advanced knowledge of the effects of pregrazing pasture mass (PM) on the performance of dairy cows. The aim of this study was to quantify the effects of PM on the pasture intake, milk production, milk composition, and grazing behavior of strip- or rotational-grazing dairy cows, based on a meta-analysis of published research papers. A database was created that included experiments in which the effects of PM on pasture intake and milk production of dairy cows were studied. Papers were selected only if at least 2 PM were compared under similar experimental conditions, particularly the same pasture allowance (SPA). The final database included 15 papers with 27 PM comparisons. For analytical purposes, the database was subdivided into 3 subsets that varied according to the estimation height at which pasture allowance was determined; that is, where PM were compared at the SPA above ground level (SPA0 subset), above 2 to 3cm (SPA3 subset), and above 4 to 5cm (SPA5 subset). Statistical analyses were conducted on the entire database (global analysis) and within each subset using linear model procedures. An interaction between PM and estimation height was found for pasture intake and milk production in the global analysis. On the basis of the predictive equations, pasture intake increased by 1.58kg of dry matter/d per tonne increase in PM when PM were compared at SPA0, was not affected by PM when PM were compared at SPA3, and decreased by 0.65kg of dry matter/d per tonne increase in PM when PM were compared at SPA5. This is consistent with the effect of PM on milk production, which was positive and negative (1.04 and −0.79kg/t of PM, respectively) when PM were compared at SPA0 and SPA5, respectively. Grazing time was only slightly affected by PM, irrespective of estimation height, because the effect of PM on pasture intake was mainly dependent on the variation in pasture intake rate. Pasture intake rate increased with increasing PM at SPA0 but decreased with increasing PM at SPA5. This meta-analysis clearly demonstrates that the effects of PM on pasture intake, milk production, and behavior of strip-grazing dairy cows depend largely on the height at which the PM and pasture allowance are measured. These results have methodological implications for future grazing research because it can be recommended that PM be compared at similar levels of pasture availability (i.e., at the same pasture allowance above 2 to 3 cm) to avoid possible misinterpretations of results. They also reveal the benefits of improving grazing management and intake prediction through modeling in pasture-based dairy systems.