Estimation Of Herbage Mass Research Articles

Field-scale calibration of the PAR Ceptometer and FieldScout CM for real-time estimation of herbage mass and nutritive value of rotationally grazed tropical pasture

Destructive sampling method is regarded as the standard approach for evaluating pasture herbage. However, non-destructive methods for managing pastures are rapidly gaining acceptance because they provide faster results that can influence real-time decision-making. The objective of this study was to calibrate the PAR Ceptometer and FieldScout CM as non-destructive tools for real-time prediction of herbage mass and nutritive value, respectively of rotationally grazed pasture. Sixty (60) herbage samples were cut from three (3) rotationally grazed paddocks to determine herbage mass (HM) and nutritive value [crude protein (CP), apparent neutral detergent fiber (aNDF), apparent acid detergent fiber (aADF) and in vitro organic matter digestibility (IVOMD)] after leaf area index (LAI) and light interception (LI) [PAR Ceptometer], sward height (SH) and chlorophyll index (CI) [FieldScout CM] measurements were taken. There were strong positive correlations between sward physical characteristics and CI (r2 = 0.74 to 0.90) and between CI and CP (r2 = 0.81). The LAI (Y=4,287x−1762)and LI (Y=149.9x−5,925) accounted for 81 % and 75 % of variability in HM, respectively. The CI accounted for a maximum of 68 % variability of CP. However, concordance correlation coefficient (CCC) of these prediction models were poor. Models with highest prediction accuracy for HM were those with SH (cb= 0.89) and LAI (cb= 0.81). Regression bias was the main sources of error for HM prediction models, while the primary error for CI predicted aNDF (75.4 % MSPE) and IVOMD (95.5 % MSPE) occurred at random. It was concluded that the PAR Ceptometer produced unreliable estimates of HM while the FieldScout CM is capable of producing reliable predictions of aNDF and IVOMD of rotationally grazed mixed Brachiaria arrecta and Digitaria eriantha pastures.

Evaluating nondestructive forage sampling techniques in alfalfa–bermudagrass mixtures in the southeastern United States

AbstractThe increased use of legume–grass mixtures in grazing systems has resulted in the need for more accurate forage estimation techniques for these diverse mixtures. In mixed stands, variations in species composition and canopy density make the estimation of herbage mass (HM) challenging. Three nondestructive sampling techniques [a rising plate meter (RPM), a pasture ruler, and digital image analysis] were compared with traditional botanical hand separation to determine their effectiveness in predicting HM in bermudagrass [Cynodon dactylon (L.) Pers.] and alfalfa (Medicago sativa L.) pastures when harvested to a 1‐ or 4‐inch stubble height. All models calibrated to forages harvested to 1 inch failed to meet the formal assumptions of the F‐test. The height and RPM were moderately successful at predicting HM when calibrated to samples harvested to 4 inches. However, the models were unable to predict HM above 4,000 lb acre−1 in their current form. Future research in alfalfa–bermudagrass mixtures should focus on isolating how HM changes within the canopy and increase the sample area used to collect the calibration data.

Evaluation of the precision of the rising plate meter for measuring compressed sward height on heterogeneous grassland swards

Accurate estimation of herbage mass (HM) is essential for optimising grass utilisation and increasing profit for pasture-based livestock agriculture. The rising plate meter (RPM) is used for predicting HM based on average compressed sward height (CSH). Sampling resolution and distribution are primary parameters in determining spatial heterogeneity of HM. There is no definitive sampling protocol for the RPM. The objectives of this study were to: investigate spatial variation of HM within pastures, determine the number of RPM measurements required to accurately predict mean HM, and assess the precision of the RPM in terms of measurement repeatability. Intensive CSH measurements and HM reference cuts were carried out on controlled plots and grazed paddocks over two grazing seasons. Sward heterogeneity was estimated as the coefficient of variation (CV) of CSH and compared to empirically derived ‘true’ sward heterogeneity in terms of HM CV. Retrospective analysis simulations were performed to identify the effect of various reduced measurement resolutions on estimated mean CSH error. Repeated measures analysis was performed on grass samples to determine RPM measurement system precision. Results indicated that pasture heterogeneity varied by 36% across the growing season and was affected by grazing, fertilisation, sward composition and seasonality. Mean CSH could be estimated to within 5% relative prediction error by recording 24 measurements per ha in a random stratified manner. The standard deviation of RPM measurement repeatability was calculated to be 4.34 mm. The findings of this study will be used to inform the implementation of a more optimum grass measurement protocol.

Development of a grass measurement optimisation tool to efficiently measure herbage mass on grazed pastures

Accurate and efficient estimation of herbage mass is essential for optimising grass utilisation and increasing profit for pasture farming. There is no definitive sampling protocol for grass measurement on Irish pastures. This paper presents the Grass Measurement Optimisation Tool (GMOT), designed to generate measurement protocols that optimise for time and accuracy. The GMOT was designed in the form of a decision support tool that generates interactive paddock maps that guide the farmer on how to optimally measure their pastures in a random stratified manner based on GPS co-ordinates, resulting in accurate non-biased estimations of mean herbage mass. Rising plate meter (RPM) measurements and reference herbage cuts were performed on trial plots and grazed paddocks over three years. Measurement routes were optimised using a genetic algorithm based on a traveling salesman problem. Actual survey error was estimated in terms of relative prediction error using Monte Carlo simulations that combined measurement and calibration error distributions for the RPM. Cost benefit analysis was conducted to evaluate the feasibility of using the GMOT on Irish grasslands. Actual error for the RPM decreased from 37% to 26% as measurement rates increased from 1 to 8 ha−1 and reductions in error were negligible (<1%) as measurements increased from 8 to 32 ha−1. Calibration error was the largest source of error (25.9%) compared to measurement error (8%). Optimal measurement value was achieved by performing 8 measures ha−1 and further increasing the measurement rate resulted in diminishing returns. The GMOT is compatible with a range of pasture measurement technologies.

Micro-sonic sensor technology enables enhanced grass height measurement by a Rising Plate Meter

Globally, the Rising Plate Meter (RPM) is a device used to measure compressed sward height, to enable estimation of herbage mass. Despite improved farm management practices aided by a variety of technological advances, the standard design of a RPM has remained relatively unchanged. Recently, however, a RPM utilising a micro-sonic sensor, with digital data capture capability via a Bluetooth communications link to a smart device application, has been developed. Here, we assess the comparable ability of both a standard cumulative ratchet counter RPM and the micro-sonic sensor RPM, to accurately and precisely measure fixed heights. Moreover, as correct allocation of grazing area requires accurate geolocation positioning, we assess the associated GPS technology. The micro-sonic sensor RPM was significantly more accurate for height capture than the cumulative ratchet counter RPM. Overall, across all heights, the cumulative ratchet counter RPM underestimated height by 7.68 ± 0.06 mm (mean ± SE). Alternatively, the micro-sonic sensor RPM overestimated height by 0.18 ± 0.08 mm. In relation to a practical applications, these discrepancies can result in an under- and overestimation of dry matter yield by 13.71% and 0.32% kilograms per hectare, respectively. The performance of the on-board GPS did not significantly differ from that of a tertiary device. Overall, the wireless technology, integrated mapping, and decision support tools offered by the innovative micro-sonic sensor RPM provides for a highly efficacious grassland management tool.

Regular estimates of herbage mass can improve profitability of pasture-based dairy systems

Paddock selection is an important component of grazing management and is based on either an estimate of herbage mass, or the interval since last grazing for each paddock. Obtaining estimates of herbage mass to guide grazing management can be a time consuming task. A value proposition could therefore 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 herbage mass on profitability of two typical pasture-based dairy systems in New Zealand; a medium input system stocked at 3.2 Friesian-Jersey cross bred cows/ha with ~15% imported feed, and a high input system stocked at 4.5 Friesian cows/ha with ~40% imported feed. The three levels of knowledge were: (1) ‘perfect knowledge’, where herbage mass per paddock is known with perfect accuracy, (2) ‘imperfect knowledge’, where herbage mass per paddock is estimated with an average error of 15%, (3) ‘low knowledge’, where herbage mass is not known, and paddocks are selected based on longest time since last grazing. In both systems, grazing management based on imperfect knowledge increased farm operating profit by ~NZ$385/ha at a milk price of NZ$6.33/kg milksolids (fat + protein) compared with low knowledge. Perfect knowledge added a further NZ$155/ha to profit. The main driver of these results is the level of accuracy in daily feed allocation, which increases with improved knowledge of herbage 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 residual herbage mass to maximise herbage regrowth.

Evaluation of a Rising Plate Meter for Use in Multispecies Swards

Core Ideas The accuracy of rising plate meter in multispecies swards has not been tested thoroughly. Forcing X intercept to zero increases the precision of the calibration equations. Higher‐order polynomial regressions do not result in more accurate forage estimates. The rising plate meter (RPM) provides rapid estimates of herbage mass (HM). Accurate calibration of the RPM is difficult due to variability in forage management, growth, and species composition. The RPM is typically calibrated by linear regression of HM and RPM height; however, the r2 is usually low. Curvilinear regression, with the X intercept set to zero, could provide a more robust calibration equation and decrease variability in RPM estimates. Three Pennsylvania organic dairy farms grazing lactating dairy cattle on multispecies pastures were used to determine measured HM and estimated HM using a RPM. Removal of the X intercept increased the adjusted r2 of all equations between 42.8 and 89.0%. Use of quadratic and cubic regression only resulted in 0.01 to 0.02 increase in adjusted r2. Linear regression remains the simplest and preferred method of calibration; however, error can be reduced by setting calibration equations so that zero RPM height is associated with zero HM.

A method for approximate on‐farm estimation of herbage mass by using two assessments per pasture

AbstractAppropriate pasture management requires implementation of methods that reduce the time and labour required for assessing herbage mass. In this study, Monte Carlo simulations and a field study were used to evaluate a simple method for estimating herbage mass based on the corrected average of the single highest and lowest mass values in a pasture. The necessary correction factor for the method was objectively derived using a single nonlinear equation based on the scaled difference between the highest and lowest herbage mass regardless of the mean and variance of mass and pasture size. The accuracy of estimation using this method is acceptable for on‐farm use: more than 90% of the estimates had error rates below 20% of the true value when the plot size assessed was larger than 64 m2 in the simulation study; in the field experiment, approximately half of the estimates had error rates below 20% of the observed mean of random samples (R2 = 0·71). The advantages of the proposed method are that it requires only two assessments per pasture and that selection of assessment plots is straightforward. This method has potential for obtaining approximate on‐farm estimates of herbage mass that could help improve pasture management.

Incorporating a periodic function into an equation for estimating herbage mass in Zoysia-dominated pastures from rising plate readings

A rising plate meter (RPM), which enables rapid, non-destructive estimation of herbage mass of pastures, is useful in grazing management. Herbage mass is estimated from the RPM readings using a linear regression model, which has the parameters α (constant) and β (slope). In this study, we analyzed the seasonal changes in the two parameter values for total and green herbage (TH and GH, respectively) masses in Zoysia-dominated pastures, and examined the potential for incorporating a periodic function (PF) of the parameters into the equation for estimating herbage mass. The values of both α and β showed a weak seasonal periodicity for TH. No periodicity and a clear seasonal periodicity were detected in the α and β values for GH, respectively. Compared with the linear regression models developed separately for individual dates, the equation incorporating a PF for β improved the estimation accuracy for the GH mass (from 0.64 to 0.77 as R2), though it did not affect the predictability for the TH mass. Incorporation of a PF into the model relating herbage mass to the RPM reading increases the sample number and broadens the data range by allowing the use of all seasonal data, and produces a single equation useful for estimating herbage mass across seasons.

Herbage mass thresholds rather than plant phenology are a more useful cue for grazing management decisions in the mid-north region of South Australia

Research was conducted in the mid-north of South Australia over the period 2000–05 to evaluate the effects of different grazing management cues on composition and production of a grassland. The management cues were based on calendar, plant phenology or herbage mass thresholds using grazing exclusion as a control. There were five grazing treatments: (i) regional practice (RP), where sheep grazed continuously for the period April–December; (ii) autumn rest, where sheep grazing was restricted to June–December; (iii) spring rest, where sheep grazing was restricted to April–August; (iv) high density and short duration (HDSD), where herbage mass thresholds determined when grazing occurred and for what duration; and (v) nil (NIL) grazing by domestic herbivores. Mean annual estimates of herbage mass were highest for NIL and HDSD and inclusion of the estimate of herbage consumption by sheep resulted in greatest primary plant production in HDSD. The contribution of perennial grasses to herbage mass declined with RP and seasonal grazing treatments. Frequency of perennial grasses was unaffected by grazing treatment but the number of perennial grass plants increased over time in RP and seasonal treatments. HDSD allowed maintenance of basal cover whereas bare ground increased with RP and seasonal treatments. Litter accumulated in NIL but this was associated with a decline in perennial basal cover. Seasonal grazing treatments did not provide an advantage over RP and there appeared to be no benefit from including phenology in management decisions. In contrast, HDSD resulted in a stable and productive grassland ecosystem, with stocking rate estimated at 78% greater than other treatments. These features offer a desirable mix for future industry adoption in the mid-north of South Australia.

53. Copper toxicity in dairy cows — a case history

Accurate and efficient estimation of herbage mass is essential for optimising grass utilisation and increasing profit for pasture farming. There is no definitive sampling protocol for grass measurement on Irish pastures. This paper presents the Grass Measurement Optimisation Tool (GMOT), designed to generate measurement protocols that optimise for time and accuracy. The GMOT was designed in the form of a decision support tool that generates interactive paddock maps that guide the farmer on how to optimally measure their pastures in a random stratified manner based on GPS co-ordinates, resulting in accurate non-biased estimations of mean herbage mass. Rising plate meter (RPM) measurements and reference herbage cuts were performed on trial plots and grazed paddocks over three years. Measurement routes were optimised using a genetic algorithm based on a traveling salesman problem. Actual survey error was estimated in terms of relative prediction error using Monte Carlo simulations that combined measurement and calibration error distributions for the RPM. Cost benefit analysis was conducted to evaluate the feasibility of using the GMOT on Irish grasslands. Actual error for the RPM decreased from 37% to 26% as measurement rates increased from 1 to 8 ha−1 and reductions in error were negligible (<1%) as measurements increased from 8 to 32 ha−1. Calibration error was the largest source of error (25.9%) compared to measurement error (8%). Optimal measurement value was achieved by performing 8 measures ha−1 and further increasing the measurement rate resulted in diminishing returns. The GMOT is compatible with a range of pasture measurement technologies.

Practical use of the rising plate meter (RPM) on New Zealand dairy farms

Herbage mass and rising plate meter (RPM) height was estimated using the RPM as part of a farmlet trial, at No. 2 Dairy, Dexcel Hamilton. Herbage mass estimations were collected over a 3-year period, from pre- and post-grazing and weekly farm walk estimates. The aim of the study was to determine how appropriate the RPM was for use on New Zealand dairy farms. The RPM gives reliable information using 50 readings per paddock for paddock selection, grazing residual, and average herbage mass between 1000 and 4000 kg DM/ha. There was a tendency however, for the RPM to underestimate herbage mass when compared with visual estimates. The RPM is limited in its estimation of herbage mass above 4000 kg DM/ha and cannot be relied upon to give useful results for dry matter intake and net herbage accumulation (particularly with weekly farm walk data). As long as RPM limits are observed, overall results show that the RPM is an inexpensive tool to aid in farm monitoring and decision making. Keywords: dairy farming, grazing residual, herbage mass, rising plate meter, RPM height

A comparison of three methods for measuring the vertical distribution of herbage mass in grassland

Three stratified clip methods for the estimation of herbage mass and its vertical distribution in grass swards were compared. The first method used a herbage‐gripping device, which held a sample from a 2 × 9 cm area while it was harvested and cut into layers in the field. For the other two methods, turfs of herbage were dug and brought into the laboratory where areas defined by 10 × 10 cm or 2 × 9 cm quadrats were cut into layers. For the comparisons, two operators collected independent samples from a sward shortly before it was cut for silage, a sward grazed by cattle and a sward grazed by sheep.The total mass of herbage dry matter collected depended on the method used, with the herbage‐gripping device producing greater estimates than the turf quadrats in two of the swards. The different methods produced similar estimates of the vertical distribution of mass. The larger quadrat usually produced the least variable results, while the herbage‐gripping device collected samples most quickly. There were also small differences between the estimates produced by different operators. It was concluded that because the herbage‐gripping device was the most cost‐effective it would often be the most appropriate method to use. However, when a higher level of precision per quadrat is required the large quadrat, following turf collection, would be more appropriate.

Quantifying Spatial Heterogeneity in Herbage Mass and Consumption in Pastures

A sward-based technique for quantifying the spatial heterogeneity in herbage mass and consumption was developed and tested in a bahia grass (Paspalum notatum Flugge) pasture grazed by cattle. For five, 2-day grazing periods from May to October, preand post-grazing herbage masses were nondestructively estimated with an electronic capacitance probe at 182, 50 x 50 cm locations along 2 permanent line transects. At the same time, undisturbed herbage accumulation during grazing was measured inside exclosures and the results used to estimate accumulation under grazing at each location. Estimation of herbage mass was relatively good; R2= 0.88 to 0.98. Spatial heterogeneity in herbage mass and the stability of the spatial pattern were well quantified. The pattern of spatial heterogeneity observed early in the grazing season remained quite stable for 5 months until the late grazing season. Spatial heterogeneity in the rate of defoliation was also well quantified in spite of some negative values. The technique is of potential value for quantifying the spatial heterogeneity in herbage mass and consumption by animals in grazed pastures, though further studies are necessary for testing the applicability of the technique to pastures of other plant species or of multiple species.

Quantifying spatial heterogeneity in herbage mass and consumption in pastures

A sward-based technique for quantifying the spatial heterogeneity in herbage mass and consumption was developed and tested in a bahia grass (Paspalum notatum Flügge) pasture grazed by cattle. For five, 2-day grazing periods from May to October, pre- and post-grazing herbage masses were nondestructively estimated with an electronic capacitance probe at 182, 50x50 cm locations along 2 permanent line transects. At the same time, undisturbed herbage accumulation during grazing was measured inside exclosures and the results used to estimate accumulation under grazing at each location. Estimation of herbage mass was relatively good; R2= 0.88 to 0.98. Spatial heterogeneity in herbage mass and the stability of the spatial pattern were well quantified. The pattern of spatial heterogeneity observed early in the grazing season remained quite stable for 5 months until the late grazing season. Spatial heterogeneity in the rate of defoliation was also well quantified in spite of some negative values. The technique is of potential value for quantifying the spatial hetero-geneity in herbage mass and consumption by animals in grazed pastures, though further studies are necessary for testing the applicability of the technique to pastures of other plant species or of multiple species.

Comparison of Three Indirect Methods for Prediction of Herbage Mass on Timothy-Meadow Fescue Pastures

A comparison of a disk meter, sward stick and capacitance meter was conducted to determine the prediction ability of different methods for estimation of herbage mass (HM) on timothy (Phleum pratense L.)-meadow fescue (Festuca pratensis Huds.) pastures. A total of 714 paired observations was made on each instrument and corresponding cut HM (<1 cm). The variation in HM was adequately explained by linear models. Comparison was made separately for each occasion (DAY) since DAY had a significant influence on the parameter estimates for the sward stick and capacitance meter. The r 2 values varied between 0 and 0.91 and the residual standard deviations (RSD) between 132 and 1151 kg ha-1. The disk meter and the sward stick predicted most accurately HM kg ha-1, while the capacitance meter was the least accurate. The advantage of the disk meter was the stability of model parameters from day to day. The advantage of the sward stick is that the readings can be applied directly into practice. None of the methods is reliable enough when precise HM estimates are needed from small-scale experiments, but they are useful in large areas or when HM estimates tolerate larger errors.

ESTIMATION OF HERBAGE MASS IN RYEGRASS/WHITE CLOVER DAIRY PASTURES

The pasture probe, rising plate meter (RPM), ward height and visual assessment methods were compared for the estimation of the herbage mass of dairy pastures. The pasture probe and calibrated visual assessment were slightly more accurate than others. Visual assessment without calibration was less accurate than all other methods. There was little difference between operators of the pasture probe and RPM, but operator variation was large with visual assessment. Variation between calibrations from different days, seasons, and sites was large. Only dead material content was identified to influence this variation. Pooling of calibrations, double sampling procedures, and derivation of different calibration slopes for each day from an equation fitted to calibration data are procedures discussed for the estimation of herbage mass by farmers, advisors and researchers. Wide adoption of methods such as the pasture probe or RPM with "universal" calibrations could reduce inconsistent advice offered to farmers, and can be used with confidence. Keywords: capacitance probe, rising plate meter, visual assessment, ward height, grassland management, pasture composition, pasture assessment.

An investigation into the use of ranked set sampling on grass and grass‐clover swards

AbstractFour experiments were conducted to assess the performance of ranked set sampling relative to random sampling for the estimation of herbage mass and clover content in grazed swards. The expected theoretical efficiencies were not observed due to the method of selection of quadrats and the nature of the distribution of herbage mass. Nevertheless there should be worthwhile improvement in precision over random sampling, provided that the quadrats within a set are as well spaced as possible, allowing, if necessary, for visual comparison.

The relative efficiency of three methods of estimating herbage mass in veld

Abstract Three methods of estimating herbage mass were compared in terms of their relative efficiencies when precision obtained per unit effort required was taken as criterion. The methods involved were randomly placed circular quadrats; randomly placed narrow strips; and disc meter sampling. Disc meter and quadrat sampling appear to be more efficient than strip sampling. In a subsequent small plot grazing trial the estimates of herbage mass, using the disc meter, had a consistent precision with 95% confidence limits being approximately 10,5% of the mean estimate.

The estimation of herbage mass of perennial ryegrass swards: a comparative evaluation of a rising‐plate meter and a single‐probe capacitance meter calibrated at and above ground level

AbstractA rising‐plate meter and a single‐probe capacitance meter were calibrated on perennial ryegrass swards (cultivars S23, Endura, Melle) over the spring and summer (13 March to 14 September 1981). The swards were rotationally grazed by cattle and from mid‐June onwards they were irrigated and cut at 5 cm after grazing to remove rejected herbage. Linear regressions were calculated relating meter readings to herbage dry matter mass as measured by cutting 0–2 m2 quadrats to either 18 mm above ground or to ground level.The regression for the rising‐plate meter was constant over the spring (slope 275 kg DM ha−1 cm−1) and again over the summer (slope 385 kg DM ha−1 cm−1). The regression for the capacitance meter changed slightly over the spring (slope 11.2 to 14.0 kg DM ha−1 unit reading−1) and was also constant over the summer (slope 20.3 kg DM ha−1 unit reading −1). Correlation coefficients were always above 09 and residual standard deviations ranged from 258–525 in Spring up to 636–918 kg DM ha−1 in summer. Residual standard deviations were lower with the plate meter than with the capacitance meter and were lower with the above‐ground cutting height. Neither meter was able to give accurate results with tall rejected herbage containing a build‐up of senescent material.Herbage mass below 18 mm was greater on summer than spring swards. When compared with a ground level cut. cutting above ground underestimated herbage mass on summer relative to spring swards; there was also a tendency to underestimate herbage mass on tall pastures relative to short pastures.There was no evidence of a curved relationship between herbage mass and meter reading with either meter and both meters gave readings related to herbage dry matter mass rather than mass of green herbage or water.