Soil Sampling
UBC Farm Soil Workshop SeriesClass 3:Soil Sampling and Testing
Chris Thoreau February 25, 2012
Class OutlineWhat is Soil Testing?What are We Testing For?Soil Sampling MethodologiesSoil TestingInterpreting Soil Test Results
What is Soil Testing?What are We Testing For?Soil Sampling MethodologiesSoil TestingInterpreting Soil Test Results
2Soil TestingWhat is Soil Testing?
Soil testing is the use of various laboratory methods to discover chemical and/or biological qualities of a soil sample as part of an overall soil management plan
Soil testing can also be used to discover the presence of contaminants such as heavy metals or pollutants
What is Soil Testing?
Soil testing is the use of various laboratory methods to discover chemical and/or biological qualities of a soil sample as part of an overall soil management plan
Soil testing can also be used to discover the presence of contaminants such as heavy metals or pollutants
3Soil TestingTesting for chemical properties is the most common type of soil testing and includes:pHOrganic Matter %NutrientsN, P, K, Ca, Mg, Fe, Cu, S, Mn, Zn, BC:N RatioElectrical Conductivity (EC)Cation Exchange CapacityBase SaturationParticle size distribution (texture)
Testing for chemical properties is the most common type of soil testing and includes:NutrientsN, P, K, Ca, Mg, Fe, Cu, S, Mn, Zn, BpHOrganic Matter %Electrical Conductivity (EC)Cation Exchange CapacityBase SaturationParticle size distribution (texture)
4Soil TestingSoil testing involves three basic stages:
SamplingTestingInterpreting
Which, ideally, lead to actions to improve our soil quality.
Soil testing involves three basic stages:
SamplingTestingInterpreting
Which, ideally, lead to actions to improve our soil quality.
5Soil SamplingSoil Sampling:
The process of collecting soil to be submitted for testing. The collected soil is called a sample
Soil must be collected carefully to ensure a representative sample is submitted for testing
Soil Sampling:The process of collecting soil to be submitted for testing. The collected soil is called a sample
Soil must be collected carefully to ensure a representative sample is submitted for testing
6Soil SamplingCollecting Samples 2 basic methods
1. Composite Samples:Several samples are taken from a field and then mixed together to get a representative sampleSamples must be taken randomly or in a set pattern to ensure a statistically representative sample is collected as we are collecting a small amount of soil to represent a large areaCollecting SamplesComposite Samples:Several samples are taken from a field and then mixed together to get a representative sampleSamples must be taken randomly or in a set pattern to ensure a statistically representative sample is collected as we are collecting a small amount of soil to represent a large area
7Soil SamplingCollecting Samples
Random SamplingRandom locations Easy way to get arepresentative sampleMust be truly random to be accurate!Zig-zag motion can besuitable
Collection Methods
Random SamplingRandom locations Easy way to get arepresentative sampleMust be truly random to be accurate!Zig-zag motion can besuitable
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Soil SamplingCollecting Samples
Topography SamplingVariation of randomsampling methodAddresses variation in field topography or field features
Collection Methods
Topography SamplingAddresses variation in field topography or field features
9Soil SamplingCollecting Samples
2. Variation Sampling:Samples are taken from a field in a fixed pattern and each sample is kept separateGood for identifying variations in a field Collecting SamplesVariation Samples:Samples are taken from a field in a fixed pattern and each sample is kept separateGood for identifying variations in a field
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Soil SamplingCollecting Samples
Grid SamplingGood for uniform field(s)Does not take into consideration topographyCan be used for variationsampling
Collection Methods
Grid SamplingGood for uniform field(s)Does not take into consideration topographyCan be used for variationsampling
11Sampling MethodologiesVariation in Fields e.g., OM and pH
Soil SamplingCollecting Samples Tools:Clean trowel and shovel; Oakfield probeClean bucketPlastic bag
Plus, if doing variation sampling:Individual BagsLabelsField Map
Collecting Samples Tools:Clean trowel or shovelClean bucketPlastic bag
Plus, if doing variation sampling:Individual BagsLabelsField Map
13Soil SamplingCollecting Samples in the field:After establishing sampling pointsRemove vegetation from soil surfaceUsing shovel, dig 20-30 cm deep hole in a small area (20 cm diameter hole)Mix soil in hole wellUsing trowel, scoop up a standard, level sample and place in bucket
Collecting Samples in the field:After establishing sampling pointsRemove vegetation from soil surfaceUsing digging tool, dig 20-30 cm deep hole in a small area (20 cm diameter hole)Mix soil in hole wellScoop up a standard, level sample and place in bucket
14Soil SamplingWhere dont we collect samples from?Anomalous/non-representative locationsAround treesField edgesNear manure or compost pilesAround standing water
Where dont we collect samples from?Anomalous/non-representative locationsAround treesField edgesNear manure or compost pilesAround standing water
15Soil SamplingOnce all samples have been taken
Collect about 1 litre of soil from your mixture of samplesPlace it in a bag and label itCollection dateName of field collected fromContact info for lab
Once all samples have been taken
Collect about 1 litre of soil from your mixture of samplesPlace it in a bag and label itCollection dateName of field collected fromContact info for lab
16Soil SamplingWhen is a good time to be sampling?Close to time when soil will be used or SpringOr, end of season to prepare for following yearTest for Nitrogen: mid- or late-season when soil is warmerWhen soil not too wet or dryIdeally test in the conditions in which plants will be growing
When is a good time to be sampling?Close to time when soil will be used or SpringOr, end of season to prepare for following yearTest for Nitrogen: mid- or late-season when soil is warmerWhen soil not too wet or dryIdeally test in the conditions in which plants will be growing
17Soil TestingOnce soil sample has been collected it needs to go to a lab
Where do we send our samples?Always to the same labRequest list of methods useMethods are all standardizedIf new lab:Confirm methods used and compare results to previous test
Once soil sample has been collected it needs to go to a lab
Where do we send our samples?Always to the same labRequest list of methods useMethods are all standardizedIf new lab:Confirm methods used and compare results to previous test
18Soil Testing
Soil Testing
Soil Testing
Soil Testing
Soil Testing
Interpreting Soil Test ResultsOnce you have test results you need to know what to do with them!Once you have test results you need to know what to do with them!
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Interpreting Soil Test ResultspH - Measure of soil acidity Or, the amount of H+ ions in soilMust measure pH in solution and residualScale is from 0-14 0 = acidic; 14 = alkaline/basicpH in coastal soils is usually acidicSoil Acidity is neutralized through additions of Lime (CaCO3)Amount of lime required depends on soil texture and OM contentpH - Measure of soil acidity Or, the amount of H+ ions in soilMust measure pH in solution and residualScale is from 0-14 0 = acidic; 14 = alkaline/basicpH in coastal soils is usually acidicSoil Acidity is neutralized through additions of Lime (CaCO3)Amount of lime required can depend on soil texture
26Interpreting Soil Test Results
Interpreting Soil Test ResultsChemistry of raising pH
pH Buffering
Adsorption Affinity:
Al3+>Ca2+=Mg2+>K+(H+) =NH4+>Na+
Chemistry of raising pH
pH Buffering
Adsorption Affinity:
Al3+>Ca2+=Mg2+>K+=NH4+>Na+
28Interpreting Soil Test ResultsBasic Liming RecommendationsContingent on measured pH, desired pH, clay content, OM %
Basic Liming RecommendationsContingent on measured pH, desired pH, clay content , OM %
29Interpreting Soil Test ResultsTable 3. Lime Application Rates to Raise Soil pH to Approximately 7.0Existing Soil pHLime Application Rate(pounds per 1,000 square feet)SandyLoamyClayey5.5 to 6.05.0 to 5.53.4 to 5.03.5 to 4.5203040502540557035508080 Lime application rates shown in this table are for dolomite, ground, and pelletized limestone and assume a soil organic matter level of approximately 2% or less. On soils with 4 to 5% organic matter, increase limestone application rates by 20%. Individual applications to turf should not exceed 50 pounds of limestone per 1,000 square feet. Avoid the use of hydrated or burned lime because it is hazardous to both humans and turf (can seriously burn skin and leaves). If hydrated lime is used, crease application rates in the above table by 50% and apply no more than 10 pounds of hydrated or burned line per 1000 square feet of turf.
30Interpreting Soil Test ResultsOrganic Matter %% is by soil weightIdeal levels = 12-20% or moreIf tests show amounts below this level add more organic matter!
Organic Matter %Ideal levels = 12-20% or moreIf tests show amounts below this level add more organic matter!
31Interpreting Soil Test ResultsC:N RatioShould be 15:1 to 24:1If higher than 24:1, be careful to not add woody or high carbon materials to soil
C:N RatioShould be 15:1 to 24:1If higher than 24:1, be careful to not add woody or high carbon materials to soil
32Interpreting Soil Test ResultsElectrical Conductivity (EC)Measure of salt content in soilTests should return levels below 4 mmhos/cmRare to have high salts in soil around hereUse gypsum to remove sodium in soilFlushing water with soil important
Electrical Conductivity (EC)Measure of salt content in soilTests should return levels below 4 mmhos/cmRare to have high salts in soil around hereUse gypsum to remove sodium in soilFlushing water with soil important
33Interpreting Soil Test ResultsCation Exchange CapacityMeasure of soils ability to hold and release positively charged particlesCa2+, Mg2+, K+, Na+, H+, Al+Higher CEC value is better>15 meq/100g soil or 20 cmol/kg soilOM and clay both have high CECCEC Animation
Cation Exchange CapacityMeasure of soils ability to hold and release positively charged particlesCa2+, Mg2+, K+, Na+, H+, Al+Higher CEC value is better>15 meq/100g soil or 20 cmol/kg soilOM and clay both have high CECCEC Animation
34Interpreting Soil Test ResultsBase SaturationFraction of cation exchange sites occupied by base cations (Mg2+, Ca2+, Na+, K+)Usually expressed as a percentage
Base Saturation increases with soil pH
Base SaturationFraction of cation exchange sites occupied by base cations (Mg2+, Ca2+, Na+, K+)Usually expressed as a percentage
Base Saturation increases with soil pH
35Interpreting Soil Test ResultsBase SaturationIdeal proportions of Base cations60-75% Calcium10-15% Magnesium 3 5 % Potassium
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