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Penetrometer Instructions

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  • 8/13/2019 Penetrometer Instructions

    1/2

    0

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    0 2 4 6 8 10 12 14 16 18

    Depth (inches)

    Pounds

    persqua

    re

    inch

    (psi)

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    Depth (inches)

    Pounds

    persquare

    inch

    (psi)

    Zone tillage

    Conventional tillage

    Field penetration resistance

    Field penetration resistance is ameasurement of the soils strengthmeasured (in psi) with a field

    penetrometer pushed through the soil profile.Measurements should be taken when the soil

    is near field capacity. It is measured for twodepth increments in the field (0 to 6 in. and6 to 18 in.) and used to assess surface andsubsurface soil compaction.

    Basic Protocol (guidelines for use):

    Penetration resistance is measured using apenetrometer, an instrument that measuresthe soil resistance to penetration. Itconsists of a cone-tip, a metal sha, and agauge that measures resistance in poundsper square inch (psi, A).

    Most penetrometers come with two

    different sized tips which correspond totwo different gauge scales. The outer andinner scales correspond to the larger inch and the smaller inch diameter tips,respectively (A). Be sure to use the scaleappropriate for the size tip used.

    The level of soil moisture can greatlyaffect the ease with which the probepenetrates the soil. It is recommended thatpenetration reading be taken when thesoil is at field capacity (several days aerfree drainage). If the soil conditions arenot ideal, it is important to note conditionsat the time of measurment so properinterpretation of the reading can be made.

    Apply slow even pressure so penetrometeradvances into the soil at a rate of 4 secondsper 6 inches or less. Record the highest

    pressure reading measured for each ofthe two depths on the grower and fieldinformation sheet (see page 20).

    Figure 12. Soil compaction graph for a field inintensive vegetable production in 2005 (Courtesyof C.R. MacNeil).

    Figure 13. Soil compaction graph for aconventionally plow tilled field and zone-till fieldwith deep ripping on the same farm in spring of2005 (Courtesy of C.R. MacNeil).

    A

    B

    Depth (inches)

    Pounds

    persquare

    inc

    h

    (psi)

    Zone tillage

    Conventional tillage

    Root growth isreduced above 300 psi

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  • 8/13/2019 Penetrometer Instructions

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    PHYSICAL INDICATOR

    Scoring function:

    Below are the scoring function graphs for surfaceand subsurface resistance on sand, silt and claytextured soils. The red, yellow and green shading

    reflects the color coding used for the ratings on the soilhealth report (see page 40).

    How penetration resistance relates to soil function:

    Field penetration resistance is a

    measure of soil compaction. Theamount of pressure needed topush the probe through the soil can bemeasured at any desired depth but ismost useful for identifying the depth ofthe compaction layer, if present. Roots cannot penetrate the soil with penetrometerreadings above 300 psi. Field profiles ofpenetration resistance can be created byrecording the measured psi every inchthrough the soil profile and then ploingthem on a chart (Figures 12 and 13). Thesecharts can be used to identify various

    layers of compaction, if present (Figure14). For the soil health test, however, weonly target two depths.

    Figure 14.Plants growing is soil with good tilth (A) or three types ofcompaction (B). Source: Building Soils for Beer Crops, 2nd edition,

    Sustainable Agriculture Network - USDA).

    surface crust

    germinatingseed

    tightly packedcrumbs

    large blockswith few cracks

    subsoilcompaction

    (A) good soil structure (B) compacted soil

    porous(loose-fiingcrumbs and

    blocks)

    0

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    0 500400300200100

    Surface Hardness (psi)

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    Score

    Coarse, Medium & Fine

    Score

    Subsurface Hardness (psi)

    Coarse M edium Fine

    0 300 400 60500200100

    29CORNELL SOIL HEALTH MANUAL


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