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Herbaceous Measurement Device Comparison
Executive Summary Introduction and Scope Inventory and monitoring are key components to land management practices. This includes the measurements of forage production to determine stocking rates and the effectiveness of certain land treatments such as burning, herbicide applications, and fertilization. Forage production values are used in conjunction with measurements of residual forage on areas that were previously grazed so forage utilization levels can be monitored on grazing allotments. Wildlife habitat managers, range management specialists, and other land monitoring employees use these plant production measurements to monitor whether livestock use levels are in compliance with maximum allowable use standards prescribed in the allotment management plans. There are various methods used to obtain plant productivity measurements. The current standard for herbaceous plant productivity is a time consuming process of clipping, weighing, and drying vegetation in an oven. This study involved a comparative analysis between various commercially available herbaceous measurement devices. Precision, accuracy, correlation, and performance characteristics of capacitance probe, oven meter, and sliding plate technologies were compared to the standard clip and weigh oven method. Findings The Sigma Delta Technologies Pty Ltd, Fuel and Soil Moisture Meter Neosystems II (Neosystems II) had the highest degree of correlation, accuracy, and consistency when compared to the standard oven. It had a 94 percent positive correlation, followed by the Tru-Test Limited GrassMaster (GrassMaster) capacitance probe with 74 percent and Jenquip Filips Folding Plate Pasture Meter (Filips Folding Plate Pasture Meter) with 58 percent. All other devices had a lower correlation. The Neosystems II unit has a better than 99 percent accuracy, unlike all the other devices tested. Development of forage constants for specific pasture plots and the issue of minimum stubble height needs to be addressed before field use for any application requiring less accuracy than currently provided by the standard oven or Neosystems II. The Neosystems II is an improvement over the standard oven. Key differences include a decreased amount of time necessary to determine forage production values, automation to reduce human error, and the capability to download data to a personal computer. It takes 21 hours for the standard oven to determine forage production values, 1 hour if using 3 Neosystems II meters or 3 hours if using 1 Neosystems II meter. In addition to the forage production measurements, there is a need to develop a field users guide for sampling, collection, and processing forage production samples, including sampling collection, handling, and processing techniques for use with the standard oven or Neosystems II meter. Introduction and ScopeThe measurement of forage production is a key component to land management practices. Measurements are made frequently when certain land treatments are applied such as burning, herbicide applications, and fertilization. By analyzing forage production on treated and untreated sites, differences can be tracked to determine what process has been the most successful in revegetation efforts. Forage production measurements are also used to estimate livestock and wildlife grazing capacity when grazing allotments are analyzed. These production values are used in conjunction with measurements of residual forage on areas that were previously grazed so forage utilization levels can be monitored on grazing allotments. Wildlife habitat managers, range management specialists, and other land monitoring employees use these plant production measurements to monitor whether livestock use levels are in compliance with maximum allowable use standards prescribed in the Allotment Management Plans. There are various methods used to obtain this measure of plant productivity. The current standard for an accurate measurement of herbaceous plant productivity is with a time consuming process of clipping, weighing, oven drying, and reweighing vegetation. There are more practical methods that include clipping and weighing plant material with ocular estimates. This project involved conducting a comparative analysis between various commercially available herbaceous measurement devices. Precision, accuracy, correlation, and performance characteristics of capacitance probe, oven meter, and sliding plate technologies were compared to the standard clip and weigh oven method. The optimum forage production measurement device promotes accuracy, consistency, and efficiency for various types of forage involved in inventory and monitoring activities. Herbaceous Measurement Device TechnologiesSix herbaceous measurement devices utilizing capacitance probe, rising plate, and portable oven meter technologies were field tested and compared to the standard cut and weigh oven method. The capacitance probe devices were the Tru-Test® Limited GrassMaster (GrassMaster), Draminski Inc. Pasture Meter (Pasture Meter), and Alstair George Manufacturing PastureGauge© (Pasture Gauge). The rising plate devices were the Kencove FarmTracker™ Rising Plate Meter (Farm Tracker) and the Jenquip Filips Folding Plate Pasture Meter (Folding Plate Pasture Meter). The field portable oven device was the Sigma Delta Technologies Fuel and Soil Moisture Meter Neosystems II (Neosystems II). Herbaceous measurement devices typically indicate the amount of forage present within a given area. Forage is the weight factor of any plant-like living organic material. Forage per land area is the weight of the combined grass, seedlings, and other small plants within a given area. Forage is usually measured in kilograms of dry matter per hectare (kg DM/ha) or pounds of dry matter per acre (lb DM/acre). Rising Plate Technology
 Figure 1—Typical rising plate meter. This movement of the sliding plate turns a manual counter or is attached to a computer where a reading is displayed electronically, depending on the device. The manufacturer recommends that 20 to 40 readings be obtained per pasture. The Folding Plate Pasture Meter has a manual counter for the number of samples taken and displays the combined estimate of forage. The amount of forage in terms of kilograms of dry matter per hectare is calculated by using these values in equations provided in the operator's manual. Corrections to the measured value are recommended for each specific cover type. The Farm Tracker has a similar design with an electronic readout for the amount of forage. Information regarding changing the reading for specific cover types is provided. Capacitance Probe Technology Figure 2—Typical capacitance probe. An electric field is set up at the bottom portion of the shaft. When the unit is first activated to measure for kg DM/ha, the unit takes an air reading. The prong is held above the forage. When the prong is placed on the ground, the bottom portion of the shaft is surrounded by forage. The change in density in the air moisture content of plant material changes the electric field characteristics. This change is recorded and used in calculations with an output reading of average kg DM/ha. Neosystems II Meter Technology Figure 3—Neosystems II meter. The Neosystems II meter is a portable oven meter with the capacity to dry plant material in 4 to 20 min, depending on the type of forage, and provide a value for forage production in terms of kg DM/ha or lb DM/acre or (figure 3). This meter contains a small oven, electronic balance, motorized conveyor, digital readout, and vacuum pump. The Neosystems II meter carrier is weighed empty. Plant material is placed on the carrier dish and into a compartment with an electronic balance scale. A conveyor moves the carrier dish between the scale and oven. The forage within the dish is compressed between two hot oven plates at a constant pressure, causing moisture to be released. The oven plates are designed with ridges and holes for the rapid removal of moisture under compression. A high flow vacuum pump pulls moisture away from the dish environment and water vapor is ejected through a plastic tube on the side of the meter. The oven temperature is uniformly 284°F (140 °C) across the plates, higher than the standard 220 °F (104 °C) oven. The manufacturer states that this increase in temperature is offset by the substantially decreased bake time (1 h versus 21 h), oven plate design, and use of a high flow vacuum pump. After a preset time period in the oven, the conveyor again places the dish back onto the electronic balance to be weighed. The Neosystems II meter computer subtracts the final weight from the initial weight and indicates the percentage of moisture content on a liquid crystal display (LCD) screen. Using a separate scale, the larger sample (total sample from a given area of the pasture) is weighed and the weight is entered into the meter to determine the forage in kg DM/ha or lb DM/acre. Other indicated values include the weight of the carrier before and after baking, and the amount of kg DM/ha or lb DM/acre. Various forage types can be evaluated with this device by varying the bake time. The standard Neosystems model allows for dual bake times. Bake times are specified at the time of purchase, or an additional add-on option allows the user to program specific bake times. The forage production value readout is in lb DM/acre unless otherwise indicated at time of purchase. The Neosystems II meter also determines moisture percent of various materials, including leaves, plant material, soil, and any material with moisture percent up to 1,000 percent. Cut and Weigh Oven Technology—Standard Production Measurement
 Figure 4—Mechanical convection oven used for cut and weigh method.
Six herbaceous measurement devices utilizing capacitance probe, rising plate, and field portable oven meter technologies were field tested and compared to the standard cut and weigh method (table 1).
Jenquip Filips Folding Plate Pasture Meter—Rising Plate Technology (figure 5). 
Figure 5—Jenquip Filips folding plate pasture meter. Standard model includes:
Additional options include:
Kencove FarmTracker™ Pasture Meter—Rising Plate Technology (figure 6).  Figure 6—The Kencove FarmTracker™ rising plate. Standard model includes:
Additional option includes:
Draminski Pasture Meter—Capacitance Probe Technology (figure 7).  Figure 7—Draminski Pasture Meter. Standard model includes:
Alistair George Pasture Guage—Capacitance Probe Technology (figure 8).  Figure 8—Alistair George Pasture Gauge© Standard model includes:
Additional options include:
Tru-Test Limited GrassMaster Capacitance Probe Technology (figure 9).  Figure 9—Tru-Test® Limited GrassMaster Pasture Meter. Standard model includes:
Neosystems II Fuel Moisture Meter—Portable Oven Technology (figure 10).  Figure 10—Neosystems II Fuel Moisture Meter. Standard model includes:
Additional options include:
Blue M Electric Oven—Typical Standard Mechanical Oven (figure 11).  Figure 11—Typical standard mechanical oven used for cut and weigh method. Standard model includes:
Pilot testing was conducted to determine the optimum forage sample collection, the handling and processing method, and the test procedure. No publications were found that describe detailed sampling collection, handling, and processing. In addition, sampling methodology varies according to the specific plant material. Testing with capacitance probes and rising plate devices were conducted at one test site on a grid within the pasture boundary. There were 20 and 40 points sampled for each device at the same sample point. For use in the standard oven and Neosystems II meter testing, four sample points within the test site were chosen as representative points describing the average forage over the pasture plot. Twenty grid test points, including the four original sample points, were indicated by flagging. Consequently, all devices were tested on the same grid within the same sample points for the capacitance probes, rising plate, standard oven, and Neosystems II meter decreasing the variability of measurements. The forage contained within these four sample points was collected by the use of a frame of a known area of 1 cubic foot (2.4 liters.) All plant material was collected within the plot frame to bare soil (refer to: USDA Forest Service publication Rangeland, Analysis and Management Guide, August 1996 and the National Wildfire Coordinating Group–Forest Service publication "Measuring Moisture Content in Living Chaparral). Testing was conducted in Los Angeles County in California, elevation 1,100 ft in uniform grassland, June in the year 2000. Sample collection was conducted in the afternoon, with a temperature range of 80 to 90 °F. Samples were not collected in shaded areas or within 24 h of rainfall. Plastic gloves were worn to prevent moisture and oil from the hands contaminating the samples. All samples were cooled below the condensation temperature. Cooling was achieved by using a plastic lunch pail and an ice pack. Samples were stored in a refrigerator during processing. All samples were placed in zip-lock plastic bags, and double bagged with as much air removed as practical. Samples were handled with care to prevent moisture contamination during processing. Bag contents were examined and extra debris (e.g., dirt, rocks, and pellets) were removed. Plant material was cut into 1-in (25.4 mm) pieces, the minimum sample size, to ensure uniformity and the desired accuracy of 10 g for the standard oven and 7 g for the Neosystems II meter tests. The greater the variability of plant material, the smaller the pieces need to be cut. The larger the sample size, the greater the accuracy, but a larger sample size necessitated a longer the bake time. By cutting the samples into smaller pieces, accuracy was not affected. The sample was spread uniformly across the surface of the carrier dish. Before processing the test samples, the Neosystems II nylon oven carrier was preheated in the oven meter for 20 min to remove moisture typically absorbed by nylon at room temperature. The carrier must be preheated to ensure accuracy. Large errors will result if preheating is not done. All the test samples were placed inside the pan or carrier with no plant material hanging over the edges. All equipment was calibrated daily. Bake times for this test were 16 and 20 min. This consisted of a 4 min bake with 3 repeat cycles for a total time of 16 min and a 10 min bake with 1 repeat for a total of 20 min. The method used to determine an accurate productivity measurement to represent a pasture plot was with 4 representative samples. Each sample was tested 3 times for a total of 12 tests at 20 min each. The total test time used in this project was 4 h. Further analysis indicates that at this test site, this accuracy can be achieved with 3 representative samples, each sample was tested 3 times, for a total test time of 3 h using only 1 Neosystems II meter. However, the total test time is reduced to 1 h using 3 Neosystems II meters, as compared to 21 h for the standard oven. A mechanical convection oven was used in the standard oven method at 220 °F (104°C) with a bake time of 21 h. The aluminum pans were weighed cold and hot. These weights were used appropriately in the calculation of initial and final weights. Changing the Forage ConstantThe rising plate and capacitance probe devices are indirect type measurement devices; therefore these devices require a change of the forage constant in the productivity equation to allow for different pasture types and seasonal variations. The standard oven and Neosystems II meter do not require this change in forage constant because these devices take a direct measurement of the plant material. The development of a forage constant for indirect measurement devices requires a productivity measurement by a direct device, (i.e., by the standard oven or Neosystems Oven Meter in order to determine a new forage constant). The GrassMaster Pasture Meter Company has developed a software program using statistical analysis to develop this forage constant. The input values necessary to develop a new constant are obtained by supplying a direct measurement of productivity measurement obtained by use of the standard oven or Neosystems unit. The GrassMaster provides the optimum method to determine the appropriate forage constant. The Effect of Minimal Stubble Height Grazing practices, based on established agronomic principles, indicate that stocking rates on grazed forages be managed to allow for a minimum stubble height of 2 to 3 in (50.8 to 76.2 mm) in order to maintain a productive pasture. This minimum stubble ensures that the plant has enough energy reserves after grazing to support regrowth, allowing roots to become stronger and deeper, providing for a pasture with adequate forage, resistance to insect and disease damage, and drought and weed resistance. Erosion control and water quality are also improved. Stubble also includes residue and litter mass. Sampling protocol for obtaining productivity measurements with the standard oven and Neosystems II meter is to collect the total residual biomass to bare mineral soil. This total residual biomass is weighed and used in the forage productivity calculation. In contrast, rising plate and capacitance probes are not able to measure total residual biomass by design. The shaft of the rising plate has a 1.25?in- (31.75-mm-) diameter metal washer on the end, preventing the tip from penetrating the residual biomass. Capacitance probe shafts are 1 in- (25.4 mm-) diameter with a 0.25-in (6.4?mm) metal prong tip at the end. The tip is designed to prevent the shaft from direct contact with the ground. However, the residual biomass mat is thicker, typically 2 to 3 in (50.8 to 76.2 mm) in some pasture plots. The 1?in- (25.4-mm-) diameter shaft prevents the probe from penetrating the biomass mat beyond the 0.25-in (6.4-mm) tip for a complete measurement of the residual biomass. Consequently, the rising plate and capacitance probe device measured values were expected to vary from the measured values for the standard oven method and the Neosystems II meter. Results Seven herbaceous measurement devices were used to collect data from the same pasture plot. The standard error and correlation between all devices and the standard oven were determined. The findings are indicated in tables 2 and 3. There is significant variability between the direct and indirect type measurement devices. This is anticipated due to a need to change the forage constant for all indirect devices and the effect of collecting on bare soil rather than minimum stubble height, as is the current practice in the direct measurement devices.
Standard error—Standard error is a measure of variability or dispersion of data compared to the standard oven method. The least variability is indicted in the Neosystems II meter at less than 1 percent, with all other devices indicating a high standard error. Correlation coefficient—The correlation coefficient (r) is a measure of the degree that the measured data from two devices move together or in opposition. When r = 0, there is no correlation. When r = 1.0, there is perfect correlation. The higher the r, the greater the correlation. General practice indicates that r values be generally evaluated as follows:
r = 0.00 to 0.25 = doubtful correlation The Neosystems II unit had a 0.94 correlation with the standard oven. This degree of positive correlation is considered superior. The GrassMaster had a 0.74 correlation and the Filip Folding Plate Pasture Meter had a 0.58 correlation, all considered good. However, forage constants for the GrassMaster and Filip Folding Plate Pasture Meter devices need to be developed for specific pasture plots and the issue of minimum stubble height needs to be addressed before these devices are used in the field for any application requiring less accuracy than currently provided by the standard oven or Neosystems II meter. Precision denotes degree of repeatability in taking of the measurement. The range of percent differences is an indicator of precision. The data reduction results are presented in table 3.
Percent inaccuracy—Percent inaccuracy is the specification that could be met at the 95 percent confidence level. Assumptions are made that the data here was not a 1-in-20 or rarer anomaly and that the test measurements follow a normal distribution with the mean equal to the standard measurement. Accuracy denotes the absolute nearness to the true value. The smallest inaccuracy determined was with the Neosystems II meter at 2.6 percent; with the Pasture Gauge at 61 percent less than the oven measured value. All other devices had less accuracy. Accuracy can be improved, up to a point, with some devices by the collection of more samples. Testing was conducted using sample sizes of 10, 20, 30, and 40, with each of two operators. These values were compared to the standard oven method. The greatest increase in accuracy with increased sampling was realized with rising plate technology by increasing the sample size to 40. Percent bias—Percent bias indicates if the device is consistently over or under measures values. Bias can be used as a correction factor for measured values to obtain the true value. This correction factor is specific for each device and may vary across the range of measured values. The smallest bias standard is met by the Neosystems II meter at 0.4 percent, followed by the Pasture Guage, the Farm Tracker, the Filip Folding Plate Pasture Meter, and the GrassMaster. Percent difference—Percent differences were calculated between measured values for the standard oven and the test device. The smaller the range of percent differences the better. The smallest range of percent differences is met by Neosystems II meter, followed by GrassMaster, Farm Tracker, and Filip Folding Plate Pasture Meter. Variability—There is significant variability between all sliding plate and capacitance probe devices as compared to the standard oven method. However there was minor variability between measured values for the Neosystems II unit and the standard oven. Sources of variation contributing to these variable results include differences among operators, ambient atmospheric conditions, test procedures, test instruments, and differences over time. Pilot testing, conducted prior to testing, determines the best test method with decreased variability and increased repeatability. A detailed test plan was developed from pilot testing with concise specific instructions for each device, including standard test conditions, test procedures, and test conditions. Testing of all devices was conducted over a minimum time period to reduce the variability over time. Variability was expected between the direct and indirect measurement devices. The Neosystems II and standard oven methods take a direct measurement. A direct measurement can be expected to have improved accuracy over an indirect method, such as capacitance probe and rising plate technology (see previous section). Findings of this study support this with the best accuracy and lowest standard error from Neosystems II, followed by capacitance probe and rising plate technologies. Comparison Between Neosystems II Meter and Standard Oven The Neosystems II portable oven has the highest degree of correlation, accuracy, and consistency of all devices when compared to the standard oven. The time to obtain a productivity measurement representing a pasture plot with best accuracy is with 3 representative samples for the lot, each sample was tested 3 times at 20 min each. It takes 1 h to determine productivity measurements if 3 Neosystems II meters are used or 3 h if 1 Neosystems II meter is used. This is an improvement over 20 to 24 h for the standard oven. The Neosystems II does not require the determination of the forage constant. In addition, this device is designed for use in various types of forage involved in inventory and monitoring activities. Consequently, it is recommended that consideration be given to designating the Neosystems II meter as the standard for obtaining production and utilization measurements. Operator Comments Comments were solicited from the operators participating in pilot and field testing. Their comments are recorded in table 4.
Discussion The Neosystems II meter temperature is set at 284 °F (140°C) across the plates. The temperature for the standard oven was set at 220 °F (104°C), 64 °F (18 °C) lower than the Neosystems II meter. This increase in oven temperature alone would typically increase the release of volatile oils from the plant material and adversely affect the accuracy of the measurement. The manufacturer of the Neosystems II meter states that this was taken into consideration in the design. A fine balance was developed between an increase in oven temperature, offset by a substantial decrease in time to bake (1 h versus 21 h), oven plate designed with ridges and holes for the rapid removal of moisture, vacuum pump, and oven plates compression. All focused on significantly decreasing bake time, without increasing the release of volatile oils from the plant material. Differences in readings between operators are due to technique, such as using a greater force in positioning the rising plate meter or capacitance probe onto the ground. Also, all readings must start in open air and the device must be brought straight down (vertically). The capacitance probe shaft picks up debris and must be cleaned frequently. This must be recognized and performed by the operator. Capacitance probe meters were having difficulty picking up readings in the plant material with low fuel moisture content, such as dry, cured grasses. Occasionally, the capacitance probe would indicate a reading and display a value of "500 kg DM/ha," in dry, not cured grass. This was determined to be a minimum reading for the given unit and did not reflect an accurate measurement. Capacitance probe measured values are directly proportional to plant moisture content. It is important that the operation of the device be understood and followed to obtain accurate measurements. Conclusions The findings are as follows:
Recommendations Based on the findings of this study, the following is recommended:
Herbaceous Measurement Devices Manufacturer Information
Draminski Inc. Tru-Test Limited
Jenquip
KencoveFarm Fence Inc. Alistair George Manufacturing
Sigma Delta Technologies Pty Ltd. Neosystems II Meter—Model Fmm-1 Please see the operator's manual for specific detailed instructions. Warnings
Operation
See the full manual for specific detailed features and other functions. Sampling and Obtaining Consistent Results At each point of the sampling (collection, measuring, and putting into the carrier) there is a potential source of errors. These errors may even be cumulative so care should be taken at each step.
Data output Data may be downloaded from the oven meter to the PC. This is achieved with Hyperterminal. In Windows 95, Hyperterminal is located in the accessories folder and in Millennium Edition it is located in accessories/communications. The Hyperterminal program can be used to capture the data coming from the Neosystems II meter in ASCII, comma delimited data. From there the file can be imported into a spreadsheet program or data acquisition program, such as Labview. Incorrect results—Results of 0.0 percent can arise if no sample is put in the sample holder and "START" is pressed. Readings too low—This will occur if you have not prepared the sample. It could also occur if the sample moisture is very high. This may mean that a repeat reading is necessary. It could also result from some species where bound water is such that a longer time is necessary in the oven. Repeat samples will get over most of these problems. Another solution where the sample is uniform is to reduce sample size. Reducing sample size when the sample is not uniform will lead to variable results. Readings too high—This could be due to incorrect balance readings or oils being driven off. High readings can be due to the inner carrier or sample protruding above the level of the outer carrier. The high readings may also show on the display as D12.5% for instance where the alphabetical character may be A, B, C, D, E, or F. This says that the readings are above 1,000 percent, which should never occur. This indicates that the initial wet weight is higher than it should be and is caused by an incorrect balance reading. If you encounter this continuously, leave the lid open so you can observe any interference to the weighing operation. Error on results—This will be due to the dry weight being more than the wet weight, something that should never occur. The cause of this could be incorrect balance readings due to the sample holder not being free of the balance ring. |
 
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