American Society of Agricultural and Biological Engineers

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1 ASAE EP542 FEB1999 (R2013) Procedures for Using and Reporting Data Obtained with the Soil Cone Penetrometer American Society of Agricultural and Biological Engineers ASABE is a professional and technical organization, of members worldwide, who are dedicated to advancement of engineering applicable to agricultural, food, and biological systems. ASABE Standards are consensus documents developed and adopted by the American Society of Agricultural and Biological Engineers to meet standardization needs within the scope of the Society; principally agricultural field equipment, farmstead equipment, structures, soil and water resource management, turf and landscape equipment, forest engineering, food and process engineering, electric power applications, plant and animal environment, and waste management. NOTE: ASABE Standards, Engineering Practices, and Data are informational and advisory only. Their use by anyone engaged in industry or trade is entirely voluntary. The ASABE assumes no responsibility for results attributable to the application of ASABE Standards, Engineering Practices, and Data. Conformity does not ensure compliance with applicable ordinances, laws and regulations. Prospective users are responsible for protecting themselves against liability for infringement of patents. ASABE Standards, Engineering Practices, and Data initially approved prior to the society name change in July of 2005 are designated as "ASAE", regardless of the revision approval date. Newly developed Standards, Engineering Practices and Data approved after July of 2005 are designated as "ASABE". Standards designated as "ANSI" are American National Standards as are all ISO adoptions published by ASABE. Adoption as an American National Standard requires verification by ANSI that the requirements for due process, consensus, and other criteria for approval have been met by ASABE. Consensus is established when, in the judgment of the ANSI Board of Standards Review, substantial agreement has been reached by directly and materially affected interests. Substantial agreement means much more than a simple majority, but not necessarily unanimity. Consensus requires that all views and objections be considered, and that a concerted effort be made toward their resolution. CAUTION NOTICE: ASABE and ANSI standards may be revised or withdrawn at any time. Additionally, procedures of ASABE require that action be taken periodically to reaffirm, revise, or withdraw each standard. Copyright American Society of Agricultural and Biological Engineers. All rights reserved. ASABE, 2950 Niles Road, St. Joseph, Ml , USA, phone , fax , hq@asabe.org

2 ASAE EP542 FEB1999 (R2013) Procedures for Using and Reporting Data Obtained with the Soil Cone Penetrometer Developed by the ASAE Soil Dynamics Committee; approved by the Power and Machinery Division Standards Committee; adopted by ASAE February 1999; reaffirmation extended for one year February 2004; reaffirmed June 2004, February 2009; reaffirmed December Keywords: Compaction, Penetrometer, Soil 1 Purpose and Scope 1.1 This Engineering Practice establishes standard methods for planning, using, and reporting data obtained with a soil cone penetrometer, which is defined by ASAE S313. Although data are relatively simple to obtain with the soil cone penetrometer, the described procedures should be followed in obtaining and reporting the data to minimize measurement variability. 2 Normative References The following standards contain provisions which, through reference in the text, constitute provisions of this Engineering Practice. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this Engineering Practice are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Standards organizations maintain registers of currently valid standards. ASAE EP236.1 DEC98, Guide for Planning and Reporting Tillage Experiments ASAE S313.2 FEB99, Soil Cone Penetrometer ASTM D , Standard Test Method for Deep, Quasi-Static, Cone and Friction-Cone Penetration Tests of Soil 3 Definitions 3.1 cone penetrometer: A 30 circular stainless steel cone with driving shaft as defined by ASAE S base area: The cross-sectional area at the base of the cone expressed in mm 2 (in. 2 ). 3.3 cone index (CI): The force per unit base area required to push the penetrometer through a specified small increment of soil. Cone index was originally defined to mean the average penetration resistance for the top 150 mm of soil, but the term has since been broadened to include penetration resistance values at any depth. Values may be reported as: (X MPa) cone index at (Y m) depth (abbreviated CI Y ) or (X MPa) average cone index in the (Y to Z m) depth (abbreviated CI Y-Z ). Cone base size should be stated. ASAE EP542 FEB1999 (R2013) Copyright American Society of Agricultural and Biological Engineers 1

3 4 Types of Penetrometers 4.1 The soil cone penetrometer evolved from the need to measure soil strength for predicting off-road trafficability of vehicles. Its use for agricultural trafficability was developed and later investigated by the U.S. Army Corps of Engineers, Waterways Experiment Station (1948, 1969) and subsequently introduced to the scientific community as a viable instrument for soil strength measurement (Freitag, 1965; Melzer, 1971). The evolution of the cone penetrometer has resulted in modification of the instrument from a simple hand-held device to a modern sophisticated instrument. 4.2 Manual push cone penetrometers. Manually operated soil cone penetrometers are forced into the soil by one person pushing on handles attached to the rod. There are essentially two classes of these instruments. The first class is a proving ring or pressure gauge instrument requiring a notekeeper to log force and depth as the operator pushes the cone tip into the soil. These penetrometers require substantial time for data collection. The second class of manual push cone penetrometers consists of hand-pushed units with force and depth recorded by a data logger. Manual push cone penetrometers are subject to substantial data variability because of an inconsistent penetration rate caused by varying soil hardness, but they have the advantage of not being restricted in use by crop height. 4.3 Mechanical cone penetrometers. Mechanical cone penetrometers are usually mounted on a tractor, truck, or trailer. They employ mechanical, hydraulic, or electric power to force the cone into soil, while CI and depth are recorded using a microprocessor-based data acquisition system. Because hydraulic systems may not necessarily have constant penetration rates, results from these machines have been found to be similar to manual push cone penetrometers (Morrison and Bartek, 1987). Mechanically activated cone penetrometers permit rapid data collection at a constant penetration rate, and thus provide more reliable data about the soil profile. However, use of mechanical penetrometers is restricted by field conditions and crop height unless mounted on a high-clearance vehicle (Tollner and Verma, 1984). Further, they are relatively expensive and more complex, and require an additional power source as compared to manual push cone penetrometers. One type of mechanical cone penetrometer that is highly portable utilizes a manual crank and gear mechanism to maintain a constant penetration rate. 5 Obtaining Soil Cone Penetrometer Data 5.1 The cone should be pushed into the soil at a uniform rate of approximately 30 mm/s (72 in./min). The surface reading is measured at the instant the base of the cone is flush with the soil surface. Subsequent readings should be made continuously, or as frequently as possible while maintaining a 30-mm/s (72-in./min) penetration rate. If automatic recording of CI is not possible, manual readings should be made by a second person at depth increments of 50 mm (2 in.) or less. These depths should be indicated by markings on the shaft of the cone penetrometer. Should it be necessary to stop the penetrometer at some depth (as would be the case where only one person was performing the test), penetration and measurements may be resumed without introducing excessive errors. In very hard soils, it may not be possible to achieve a rate as high as 30 mm/s (72 in./min), but somewhat slower rates will not result in significant errors. For adhesive soils, the cone and shaft should be thoroughly washed and wiped between each penetration. 6 Determining Sample Location and Size 6.1 Cl data taken at random locations for agricultural applications will not provide statistically reliable estimates of CI (Cassel, 1982). The variation in CI may depend more on tillage and traffic patterns than soil heterogeneity; therefore, penetrometer sampling shall be done with respect to tillage and traffic. Transects that are perpendicular to rows, with penetrometer samples taken at least 150 mm apart along the transects, are recommended (Cassel, 1982; Manor et al, 1991). Also, breaking the field into smaller sections and taking random samples within each section may increase the precision of sampling the entire field. For a complete description of this topic see Petersen and Calvin (1986). 6.2 The two greatest factors affecting CI are soil density and water content. Researchers normally use CI as an indication of soil strength. To minimize the effect of water content on the CI measurement, it is desirable to ASAE EP542 FEB1999 (R2013) Copyright American Society of Agricultural and Biological Engineers 2

4 sample when the soil water content is near field capacity. To obtain a better understanding of forces that roots are subject to, and if soil strength comparisons are desired, CI measurements are sometimes taken at water contents other than at field capacity. Every effort shall therefore be made to ensure that significant water content changes do not take place while multiple CI readings are being obtained. Consideration should therefore be given to minimize the length of time over which CI data are taken. 6.3 The minimum sample size needed to provide a reliable estimate of mean CI was given by Cassel (1982) as: where: α is probability level n = t t is Student s t distribution with (n 1) degrees of freedom at a probability level of α s is mean sample standard deviation d is acceptable error that is a percentage of the estimated mean (x). 2 α s This equation assumes independent samples and that the individual observations have a Gaussian distribution. To use this equation, x and s should first be obtained from preliminary sampling. For n 30, Student s t distribution can be replaced by the standard normal distribution, z. Alternatively, Warrick and Nielsen (1980) recommended the sample size, n, be 20 at least. 2 / d 2 7 Reporting Soil Cone Penetrometer Data 7.1 If the CI data are part of a tillage study, then the procedure for planning and reporting the study is outlined in ASAE EP236. This procedure should be followed even for non-tillage experiments involving CI measurements. For a given site, the average CI value obtained at each depth increment should be calculated, as well as the standard deviation and coefficient of variation. The CI (in units of MPa) is then plotted against depth (in meters) for each test location. 7.2 The operator s name, the location of the tests, and the date should be recorded. The report should also include the size of penetrometer tip used, the type of thrust machine, thrust and tip calibration information (see ASAE S313), any zero-drift noted, the method used to provide the reaction force, the method of tip advancement (continuous or stop-and-go), the method of recording, the condition of rods and tip at conclusion, and any difficulties or other observations concerning the performance of the equipment (ASTM D3441). 7.3 The report should include a description of the test location in relation to tillage surface condition, wheel tracks, plant rows, and other soil surface nonuniformities. Morphological descriptions should be given for each site and soil structure classifications for each horizon according to the USDA NRCS system as described in Agricultural Handbook 436 (Bradford, 1986). 7.4 Associated soil properties The following associated soil properties shall be reported: soil type/texture (report percent clay); organic matter content; water content by horizon or layer; bulk density by horizon or layer; cropping/tillage history (2 previous years), ASAE EP236, clause 6.2. ASAE EP542 FEB1999 (R2013) Copyright American Society of Agricultural and Biological Engineers 3

5 7.4.2 Also, the following should be reported: soil moisture retention curve by horizon; drainage condition, ASAE EP236, clause 6.4.5; plastic limit; size of soil structural units (clods). 7.5 Specific applications of penetration data Mobility/trafficability. Traction models typically use the average CI for the top 150 mm (6 in.) of soil depth Depth of root-impeding layers. CI values are used to determine the depth of soil layers that inhibit root growth. These compacted soil layers may be due to natural causes or produced by external sources such as vehicle traffic Root growth. Plant roots are flexible and grow through zones of least resistance. Therefore, minimum CI values may have more meaning than maximum or average horizon resistance values in terms of root growth (Bradford, 1986). 8 Handling Data Errors 8.1 Irregularities in CI can be due both to soil variability and instrumentation errors. These irregularities can manifest themselves to the point of causing a data point to be missed, or an unusual value to be recorded. Locating these erroneous data points and deciding upon the appropriate procedure for handling them is one of the most challenging aspects of CI data analysis. 8.2 Regression analysis and residual examination. Regression analysis can be used with penetrometer data with CI as the independent variable (x) and another soil parameter as the dependent variable (y). Conversely, for other situations, CI is used as the dependent variable, and another soil parameter (such as depth in the following example) is used as the independent variable. where: CI is cone index (MPa), β 0 is y-intercept, β 1 is slope, D is depth (m), ε is residuals. CI = β 0 + β 1 D + ε Analyzing the residuals from the regression analysis should allow the outliers to be determined; they can be dealt with appropriately. 8.3 Missing data. If at all possible, multiple data points should be obtained for each depth for which CI is desired. If more than three measurements are taken within a 50-mm (2-in.) depth range (the maximum depth range normally used), then the absence of one data point would still allow an average value per depth to be reported. If it is not possible to acquire this quantity of data within the depth range, then it is best to simply eliminate a missing value from the model without trying to recreate it from other replications. Caution should be ASAE EP542 FEB1999 (R2013) Copyright American Society of Agricultural and Biological Engineers 4

6 exercised, however, to avoid excessive errors associated with serial correlation when data are pooled to obtain an average for a particular depth (Christenson et al, 1989). 8.4 Outliers. Outliers are created when the cone penetrometer hits a rock or other hard object or a soft object, such as a void; when other unexplainable conditions cause data points to be outside the norm; or when erroneous electronic signals are recorded. Determining whether a data point is real or an outlier requires field and equipment experience. One method of determining outliers is by visual examination of the data when plotted on an x-y graph. Another method is to determine the average over a depth range, and then calculate the variation over this same range. If extreme variation is found at a particular depth, an outlier may be present. Further investigation through appropriate statistical methods as described in Snedecor and Cochran (1967) may eliminate an erroneous measurement or outlier. Annex A (informative) Bibliography The following documents are cited as reference sources used in the development of this Engineering Practice: Bradford, J. M Penetrability. In Methods of Soil Analysis: Part 1 Physical and Mineralogical Methods, 2d ed., A. Klute (ed.), ch. 19. Madison, WI: American Society of Agronomy. Cassel, D. K Predicting Tillage Effects on Soil Physical Properties and Processes, ch. 4, Madison, WI: ASA, SSSA. Christensen, N. B., J. B. Sisson, and P. L. Barnes A method for analyzing penetration resistance data. Soil & Tilage Res 13: Freitag, D. R., and B. Y. Richardson Application of trafficability analysis to forestry. Misc. report Vicksburg, MS: U.S. Army Corps of Engineers Waterways Experiment Station. Manor, R. L., et al Soil cone index variability under fixed traffic tillage systems. Transactions of the ASAE 34(5): Melzer, K. J Relative density and cone penetration resistance. Technical report Vicksburg, MS: U.S. Army Corps of Engineers Waterways Experiment Station. Morrison, J. E., Jr., and L. A. Bartek Design and field evaluation of a hand-pushed digital soil penetrometer with two cone materials. Transactions of the ASAE 30(3): Petersen, R. G., and L. D. Calvin Methods of Soil Analysis, ch. 5, Madison, WI: ASA. Snedecor, G. W., and W. G. Cochran Statistical Methods, 6th ed., Ames, IA: The Iowa State University Press. Tollner, E. W., and B. P. Verma Modified cone penetrometer for measuring soil mechanical impedance. Transactions of the ASAE 27(2): U.S. Army Corps of Engineers Trafficability of soils Development of testing instruments. Technical memo 3-240, 3d suppl. Vicksburg, MS: U.S. Army Corps of Engineers Waterways Experiment Station. U.S. Army Corps of Engineers Effects of cone velocity and size on soil penetration resistance. Technical report AD-A Vicksburg, MS: U.S. Army Corps of Engineers Waterways Experiment Station. Warrick, A. W., and D. R. Nielson Applications of Soil Physics, ch. 13, New York: Academic Press. ASAE EP542 FEB1999 (R2013) Copyright American Society of Agricultural and Biological Engineers 5

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