Diagnostic techniques to evaluate cultural practice effectiveness for
managing soil strengths are needed. A recording penetrometer used on a
uniform grid of penetrations produced analog records (on 3 x 5 cards)
of soil strength vs depth. These were used to develop profile contour
plots of soil strength. Digitization was done using a flatbed plotter,
programmed to aid in placement of the digitizing eyepiece. Contour
depth, shape, and frequency of strength observations were used to
compare tillage treatments. Methods of strength correction for soil
water differences and other applications are discussed

Busscher, W.J.

Sojka, R.E.

USDA - ARS - NWISRL

129PENETRATION RESISTANCE ISOPLETHS FOR ASSESSMENT OF SOIL STRENGTH UNDERVARYING MANAGEMENT REGIMESR.E. SOJKA1 and W.J. BUSSCHER2ISoil Scientist, USDA-Agricultural Research Service, Soil and WaterManagement Unit, Route 1, Box 186, Kimberly, ID 83341.2Soil Scientist, USDA-Agricultural Research Service, Coastal PlainsSoil and Water Conservation Research Center, P.O. Box 3039, Florence,SC 29502.ABSTRACTDiagnostic techniques to evaluate cultural practice effectiveness formanaging soil strengths are needed. A recording penetrometer used on auniform grid of penetrations produced analog records (on 3 x 5 cards)of soil strength vs depth. These were used to develop profile contourplots of soil strength. Digitization was done using a flatbed plotter,programmed to aid in placement of the digitizing eyepiece. Contourdepth, shape, and frequency of strength observations were used tocompare tillage treatments. Methods of strength correction for soilwater differences and other applications are discussed.INTRODUCTIONHigh soil strengths (cone index or penetration resistance) resultingfrom tillage, traffic, or genetic pans inhibit root growth (Voorhees,1987, Trouse, 1983) and limit root exploration for water and nutrients(Taylor et al., 1966; Gerard et al., 1982; Barley et al., 1965).Various management techniques prevent or eliminate high strength zonesand maintain root pathways (Busscher et al., 1988, Campbell and Phene,1977; Elkins and Hendrick, 1983; and Voorhees et al., 1978). Suitablediagnostic techniques are needed for evaluating cultural practiceeffectiveness. Cone tip penetrometers are commonly used to assess soilstrength. The earliest penetrometers involved a simple proving ringthat recorded only the maximum soil strength encountered for the depthof penetration. A new technique involves the recording penetrometer(Carter, 1967; Morrison and Bartek, 1987; Terry and Wilson, 1952).There are three types: handheld, manual, analogue; tractor-mounted,hy draulically driven, digitizing; and handheld, manual, digitizing.Cost, portability, and field ruggedness make handheld typesa ttractive. Tractor-mounted hydraulic types have the advantages ofconstant insertion rate and direct computer interface, enhancingprecision and data reduction, but are costly, have limited fieldaccessibility (e.g., in corn), and impose additional traffic. Strengthsrecorded using constant insertion rate probes and manual probes werecompared by Morrison and Bartek (1987) who concluded their agreementwas good. If care is taken to maintain reasonably uniform insertionrates, readings from manual units discriminate even subtle strengthpattern differences (Busscher and Sojka, 1987; Busscher et al., 1986a).In non-agricultural studies, handheld types may be the onlype netrometers portable to remote sites (Adams et al., 1982). Finally,the cost advantage of analogue over digitizing handheld types remains allnfactor, since analogue plots cLn be rapidly digitized with computerequipment already on hand at most research stations and have thepotential for automated image analysis. The authors have developed asystem of profile strength assessment with a commercial manual probe(Carter, 1967). This paper outlines and demonstrates the method using acomparison of fall vs spring-bedding.METHODS AND THEORYIrrigated Russet Burbank potatoes (Solanum tuberosum L.) were grownon a Greenleaf silt loam (fine-silty, mixed, mesic Zerollic Haplargids)which had been fall-bedded (FB) or bedded before spring planting (SB).Following planting, traffic was limited to a mid-season herbicideapplication. Soil strength was compared by determining profilestrength contours shortly before harvest at two field locations(replications) for each treatment.Strength assessment involved analogue recording of a grid of soilstrengths by making penetrations at 11.4 cm intervals perpendicular toknown sources of strength variation (e.g.. planted rows, wheel ruts,etc.). Probing depths were to 60 cm (20 cm below the tillage) toreduce spurious reading effects three replicate probings spaced 10-12cm apart, parallel to the strength variation for each position ofmeasurement, were recorded on an index card as strength vs depth. Noattempt to order the replicated probings was made. Each card wasplaced on a flatbed plotter, used as both a digitizer and an eyepiececontroller, and digitized at 5 cm depth increments via a semi-automatedprocess (Busscher at al., 1986b). The method is similar to those usedwith freely moving digitizers, but here the computer positions theeyepiece on the baseline, greatly accelerating digitization. A singleoperator can process up to 300 cards (12,000 digitized entries) perday, including automatically averaging the three separate tracings ateach depth and recording the data electronically. After the last depthof each card was digitized, the baseline was redigitized. If the slopeof the baseline was not zero when all points were entered, they werecorrected for the change in strength due to the slope (tilting of thecard). Cone indices were thus known for each intersection of a gridwith intervals 5 cm deep by 11.4 cm wide. Isopleths were drawn fromthe matrix giving a penetration resistance contour map.Log transformed cone indices (Cassel and Nelson, 1979) werestatistically tested using both the general linear models procedure(GLM) and the regression procedure (REG) of SAS (SAS Institute, 1985).The GLM design used was Tillage, Rep., Tillage x Rep., Depth, Position,Depth x Tillage, and Position x Tillage, with depth and positionconsidered covariants with the tillage variable. Since strength doesnot vary linearly with position, position squared was used in the GLMprocedure.A regression equation modeled strength vs soil depth and lateralposition using the first four orders of the depth and position and thefirst and second order interaction terms. Regressions were performedfor each treatment and for selected combinations of treatments thatwere compared. Significance among treatments was determined bycalculating an F statistic from the respective error mean squares ofthe selected combinations and the appropriate individual treatments,using a 10% level of significance with the Bonferroni adjustment for131multiple comparison procedures (Draper and Smith, 1966). The Bonferroniadjustment divides the significance by the number of comparisons. TheP < 0.10 level of significance for 100 samples uses a 0.001 F table.Individual comparisons were not made if the treatments were notstatistically different in the GLM table. The regression proceduresimulates strength as a function of position and depth and comparesthe simulation of fit. If the simulations significantly describe thedata, a simple F-statistic can be calculated from the error meansquares and degrees of freedom. The GLM and REG procedures used inthis manner rejected the null hypothesis if either strengths weredissimilar or were distributed differently.Gravimetric soil water contents (W) from regular depth intervals forall treatments and probing dates were statistically tested by analysisof variance at the 5% level using GLM. Correcting strengths forsignificant differences in W between probings permits examination ofsoil strength aspects other than those caused by W (Busscher, 1987).Perumpral (1987) examined various soil-water correction methods, andBennie (1986) showed that cone index could be predicted as a functionof moisture content and bulk density by:Log (C) - a* LOG (B) + b* LOG (W) + Log (c)	[11where C is cone index, B is bulk density, W is gravimetric watercontent and a, b, and c are soil dependent parameters. To correct coneindices of one treatment for differences in W between it and anothertreatment, the model takes the form:C1/C2 = (W1/W2) 13	[2]RESULTS AND DISCUSSIONResearchers disagree about the precise limits of penetrationresistance to root growth, which varies with species and soilproperties (Taylor et al., 1966; Camp and Lund, 1968; Campbell et al.,1974, and Gerard et al., 1982). Most literature indicates that 2.0 MPaas measured by a 5-mm flat-tipped penetrometer is a limit. Thiscorresponded to 2.5 to 3.0 MPa for a 13-mm diameter 30 degree cone-tipped recording penetrometer (Busscher et al. 1986a). Once thecritical penetration resistance is established, relative profile soilstrengths can be evaluated. Figure 1 shows the soil strength contoursof SB and FB treatments at field water contents (a and b, respectively)and FB corrected to the SB field water content (CB) in Figure lc. Itapparent that the uncorrected strengths of the FB treatment (Fig.lb) result in part from a drier profile, because upon correction,contours change depth and shape (Fig. lc). Mean strengths for SB, FB,and CS were 3.82, 2.18 and 2.34 MPa, respectively. Spring Bedding (SB)was significantly different from FE and CB. Depth to the 1 MPa strengthcontour in Figure la is well above 0.2m but in lo is well below 0.2m.,-ImiLarly the 3.0 and 4.0 MPa isopleths are deeper in Figure lc. Since, --,e is no intervening shallower high strength zone this indicates acr g= favorable rooting volume for FB as profile W varies. A zone oftrar fic-related compaction is identifiable in St as the lobes of 2.0MPa and 3.0MFa strength centered under the trafficked inter-row in--- 1lre Ia. The frequency distribution of strength (Figure 2) verifiesFB should favor rooting since Low strengths occur more frequentlythe ED and CE treatments observed.132There are various approaches to correction for W. Asady, Hook, andThreadgill (1987) considered the water effects separately as acovariate. Busscher (1987) compared equations that corrected C inflat-tipped penetrometers for differences in W among treatments. Oneof the better equations solved a boundary value problem to obtain asigmoid relationship between C and W. Here C was a function ofSecant(x/2*(W/SAT-1)-1) where SAT is the porosity of the soil.Recently Busscher and Sojka (1988) scaled profile cone indices from 0to 1 to provide patterns of relative strength. This permittedcomparison of cone indices with W differences without correction.Other strength evaluation approaches (not shown) include determiningmean depth to critical penetration resistance, taking the simple meanof profile strength readings, or finding the mean profile cross-sectional areas between given strength limits. Since water andnutrient availability depend on the volume of rootable soil it isuseful to compare the cross-sectional areas of soil below a givenpenetration resistance, provided shallow high-strength layers do notoverlie non-limiting layers which, though inaccessible by roots, wouldincrease calculated rootable volume. Each approach has validity andcan be used with crop data to determine strength-dependentrelationships via regression analysis. An example of this approachwould be the regression of yield on the area of profile below thecritical soil strength.CONCLUSIONDetermination of soil penetration resistance isopleths provides aneffective means of evaluating effectiveness of cultural practices formanaging soil strength.REFERENCESAdams, J. A., Endo, A. S., Sto/zy, L. H., Rowlands, P. G., and Johnson,H. B. 1982. Controlled experiments on soil compaction produced byoff-road vehicles in the Mojave desert, California. J. AppliedEcology 19:167-175.Asady, G. H., Hook, J. E., and Threadgill, E. D. 1987. Tillage inducedmodification of cone index and bulk density in a coastal plain sandysoil. Agronomy Abstracts p. 235, ASA, Madison, Wisconsin.Barley, K. P., Farrell, D. A., and Greacen, E. L. 1965. The influenceof soil strength on the penetration of a loam by plant roots. Aust.J. Soil Res. 3:69-79.Bennie, A.T.P. 1986. Personal communication.Busscher, W. J. 1987. Effect of water content changes on strength forsoutheastern coastal plain soils. Agronomy Abstracts p. 237, ASA,Madison, Wisconsin.Busscher, W. J., Karlen, D. L., Sojka, R. E., and Burnham, K. P. 1988.Soil and plant response to three subsoiling implements. Soil Sci.Soc. Am. J. (in press).Busscher, W. J., and Sojka, R. E. 1987. Enhancement of subsoilingeffect on soil strength by conservation tillage. Trans. ASAE 30:888-892.Busscher, V. J., and Sojka, R. E. 1988. Scaling of soil strengthdifferent tillage management treatments. Soil Till. Res. (inreview).133Busscher, W. J., Sojka, R. E. and Doty, C. W. 1986a. Residua/effects of tillage on coastal plain soil strength. Soil Sci.141:144-148.Busscher, V. J., Sojka, R. E., Sadler, E. J. and Doty, C. V. 1986b.Simplified data analysis for an inexpensive manual analoguepenetrometer. Comput. Elec. in Agric. 1:197-204.Camp, C. R., and Lund, Z. F. 1968. Effect of mechanical impedence oncotton root growth. Trans. ASAE 11:188-190.Campbell, R. B., and Phene, C. J. 1977. Tillage, metric potential andmillet yield relations in a layered soil. Trans. ASAE 20:271-275.Campbell, R. B., Reicosky, D. C. and Doty, C. W. 1974. Physicalproperties and tillage of Paleudults in the southeastern coastalplains. J. Soil Water Conserv. 29:220-224.Carter, L. M. 1967. Portable penetrometer measures soil strengthprofiles. Ag. Engr. 48:348-349.Cassel, D. K., and Nelson, L. A. 1979. Variability of mechanicalimpedance in a tilled one-hectare, field of Norfolk sandy loam. SoilSci. Soc. Am. J. 43:450-455.Draper, N. R., and Smith, H. 1966. Applied Regression Analysis. JohnWiley and Sons, New York.Elkins, C. B., and Hendrick, J. G. 1983, A slit-plane tillage system.Trans. ASAE 26:710-712.Gerard, C. J., Sexton, P. and Shaw, G. 1982. Physical factorsinfluencing soil strength and root growth. Agron. J. 74:875-879.Morrison, J. E., and Bartek, L. A. 1987. Design and field evaluationof a hand-pushed digital soil penetrometer with two cone materials.Trans. ASAE 30:646-651.Perumpral, J. V. 1987. Cone penetrometer applications - a review.Trans. ASAE 30:939-944.SAS Institute, Inc. 1985. SAS User's Guide: Statistics, Version 5Edition. SAS Institute, Inc., Cary, NC. 956 pp.Taylor, H. M., Robertson, G. M. and Parker, J. J. 1966. Soilstrength-root penetration relations for medium and coarse texturedsoil materials. Soil Sci. 102:18-22.Terry, C. W., and Wilson, H. M. 1952. The Cornell soil penetrometer.Ag. Engr. 33:425.Trouse, A. C., Jr. 1983. Observations on under the row subsoilingafter conventional tillage. Soil Till. Res. 3:67-81.Voorhees, W. B. 1987. Assessment of soil susceptibility to compactionusing soil and climatic data bases. Soil Till. Res. 10:29-38.Voorhees, V. B., Senst, G. C., and W. W. Nelson. 1978. Compaction andson structure modification by wheel traffic in the northern cornbelt. Soil Sci. Soc. Am. J. 42:344-349.• -Cc) \%,RANI< OF STRENGTHS1	 2	 3	 4Strength (MPa)— CB ---FE	 ----SB660C3 40a2010080Figure 1.--Soil isostrength con-tours of (a) spring bedded, SB,at field water content (b) fallbedded, FB, at field water con-tent and (c) fall beddedcorrected to the water contentdistribution of the springbedded treatment, CB. Contourlines are in MPa. Asterisksare row locations. 1340.20.4E0.2_ca) 0.400.20.40.60	 0.45	 0.9	 1.35	 1.8Position (m)_ 1.0	 	 2.0--__ 3.0 ---4.0	 MPaFigure 2.--Distribution ofstrength values for fallbedded, and spring beddeddata at field watercontents and for fallbedded data corrected to thewater content distributionof the spring beddedtreatment.International Soil Tillage Research Organization11th international ConferenceEdinburgh, Scotland11 -15th July, 1988TILLAGE and TRAFFICinCROP PRODUCTIONPROCEEDINGSVOLUME 1

Penetration resistance isopleths for assessment of soil strength under varying management regimes

Northwest Irrigation & Soils Research Laboratory Publications

https://eprints.nwisrl.ars.usda.gov/id/eprint/1048/1/659.pdf

Penetration resistance isopleths for assessment of soil strength under varying management regimes

Abstract

Similar works

Full text

Available Versions

USDA - ARS - NWISRL

Northwest Irrigation & Soils Research Laboratory Publications