Soil Sampling and Nutrient Soil Sampling and Nutrient Recommendations Recommendations Kent Martin Kent Martin SW Agronomy Agent Update SW Agronomy Agent Update 12/1/2009 12/1/2009
Outline Outline How to take a soil sample How to take a soil sample What is the appropriate depth for soil tests What is the appropriate depth for soil tests How many should you take How many should you take How often should we sample How often should we sample Preparing samples for lab analysis Preparing samples for lab analysis Good or not- -so so- -good soil tests good soil tests Good or not Nutrient Recommendations Nutrient Recommendations N recommendation Model N recommendation Model P and K (Sufficiency and Build- -Maintain) Maintain) P and K (Sufficiency and Build
Why Should We Soil Test? Why Should We Soil Test? Determine plant available nutrients in soil Determine plant available nutrients in soil Estimate crop responses to nutrient additions Estimate crop responses to nutrient additions Record long- -term soil fertility trends term soil fertility trends Record long Problem solving Problem solving Generate nutrient recommendations Generate nutrient recommendations Make financial decisions Make financial decisions
Appropriate Soil Sample Depth Appropriate Soil Sample Depth Consistently take samples from the same depth Consistently take samples from the same depth 6 inch sample – – P, K, pH, Organic Matter P, K, pH, Organic Matter 6 inch sample Approximate depth of historical tillage Approximate depth of historical tillage 24 inches – – Nitrate, Chloride, Sulfate Nitrate, Chloride, Sulfate 24 inches Mobile nutrients can be taken up from deeper in the Mobile nutrients can be taken up from deeper in the soil soil
Number of Soil Samples Number of Soil Samples Number of soil samples for specific accuracy Number of soil samples for specific accuracy pH P K OM pH P K OM +/- - # +/- - # +/- - # +/- - # +/ # +/ # +/ # +/ # 0.1 337 1 337 10 164 0.1 89 0.1 337 1 337 10 164 0.1 89 0.2 85 5 14 25 27 0.2 23 0.2 85 5 14 25 27 0.2 23 0.3 38 10 4 50 7 0.3 10 0.3 38 10 4 50 7 0.3 10 0.4 21 15 2 100 2 0.4 21 15 2 100 2 Kansas State University
Number of Soil Samples Number of Soil Samples Number of composite samples submitted to the Number of composite samples submitted to the lab depends on management areas lab depends on management areas 15- -20 subsamples for each composite sample 20 subsamples for each composite sample 15
Number of Soil Samples Number of Soil Samples Number of composite samples may depend on Number of composite samples may depend on field variability field variability Identify management zones Identify management zones
Number of Soil Samples Number of Soil Samples Number of composite samples may depend on Number of composite samples may depend on field variability field variability Identify management zones Identify management zones Creek Slope Low land
Number of Soil Samples Number of Soil Samples Number of composite samples may depend on Number of composite samples may depend on field variability field variability Identify management zones Identify management zones Creek Sandy Silt Loam Slope Loam Low land Sandy Loam
Number of Soil Samples Number of Soil Samples Grid soil sampling Grid soil sampling Requires more samples and ultimately more cost Requires more samples and ultimately more cost 60 ac field divided into ~2 ac grids 60 ac field divided into ~2 ac grids
Grid Soil Sampling Grid Soil Sampling May be beneficial in highly variable fields May be beneficial in highly variable fields GPS and precision application equipment make this GPS and precision application equipment make this possible possible
How Often Should We Sample How Often Should We Sample Every year until a history is established Every year until a history is established Historical trends is a strong point of soil testing Historical trends is a strong point of soil testing Generally recommended every 3- -4 years 4 years Generally recommended every 3 Soil Test → Crop Removal < Fertilizer Crop Removal > Fertilizer Time →
Preparing Samples for Lab Preparing Samples for Lab Know your objectives Know your objectives Laboratory data is only as good as the sample Laboratory data is only as good as the sample submitted – – regardless of the lab regardless of the lab submitted Combine subsamples into composite samples Combine subsamples into composite samples Keep uniform depth and mix thoroughly Keep uniform depth and mix thoroughly Avoid contamination – – buckets used for mixing buckets used for mixing Avoid contamination Know how much sample to submit – – a sandwich a sandwich Know how much sample to submit bag is usually enough bag is usually enough
Lubricants for Soil Sampling? Lubricants for Soil Sampling?
Preparing Samples for Lab Preparing Samples for Lab Drying samples Drying samples Not necessary except nitrate samples that are not Not necessary except nitrate samples that are not submitted immediately submitted immediately Nitrate – – lay out on paper, turn on fan lay out on paper, turn on fan Nitrate Don’ ’t t – – put it in the oven or microwave it put it in the oven or microwave it Don Freezing is an option for nitrate samples Freezing is an option for nitrate samples Fill out paperwork including relevant historical Fill out paperwork including relevant historical information information
Sample Information Sheet Sample Information Sheet
Where To Send Your Samples Where To Send Your Samples Your objectives! What is important? Your objectives! What is important? Tests appropriate for your area Tests appropriate for your area Accurate results Accurate results Turn around time Turn around time Cost Cost Service Service Part of a government program? Part of a government program? Ask your local extension agent what tests are Ask your local extension agent what tests are required – – Don Don’ ’t assume all labs provide the same t assume all labs provide the same required required tests! required tests!
Choosing Soil Tests Choosing Soil Tests pH (1:1 soil:water soil:water) ) pH (1:1 Very accurate and reliable Very accurate and reliable Substantial research conducted on pH Substantial research conducted on pH Determines if lime is needed Determines if lime is needed pH > 7.3 – – calcium carbonate present (free lime) calcium carbonate present (free lime) pH > 7.3 pH < 5.8 – – crop response to lime crop response to lime pH < 5.8 Buffer pH (Buffer Index) Buffer pH (Buffer Index) Very accurate and reliable Very accurate and reliable Tells how much lime to add Tells how much lime to add SMP is most common SMP is most common
Choosing Soil Tests Choosing Soil Tests Phosphorus Phosphorus Variety of tests Variety of tests Bray P- -1 1 Bray P Most correlation/calibration data Most correlation/calibration data Inaccurate on calcareous soil (reads low) Inaccurate on calcareous soil (reads low) Olsen P Olsen P Specific to high pH soil (abundant data on high pH) Specific to high pH soil (abundant data on high pH) Mehlich 3 3 Mehlich Works on a wide range of soil pH (acid → → calcareous) calcareous) Works on a wide range of soil pH (acid Limited correlation/calibration data Limited correlation/calibration data Most common Most common
Choosing Soil Tests Choosing Soil Tests Potassium Potassium Exchangeable ammonium acetate Exchangeable ammonium acetate Fairly good test Fairly good test Most useful for watching trends over time Most useful for watching trends over time Nitrate Nitrate KCl extractable extractable KCl Abundant data Abundant data Based on expected yield Based on expected yield Adjusted based on organic matter, previous crop, Adjusted based on organic matter, previous crop, fallow fallow
Choosing Soil Tests Choosing Soil Tests Organic Matter (%) Organic Matter (%) Modified Walkley Walkley- -Black or loss on ignition Black or loss on ignition Modified Reliable, consistent data Reliable, consistent data May be inflated if crop residue is in sample May be inflated if crop residue is in sample Warm season crop N adjustment = %OM× ×20 20 Warm season crop N adjustment = %OM Cool season crop N adjustment = %OM× ×10 10 Cool season crop N adjustment = %OM Zinc Zinc DTPA extract – – diethylenetriaminepentacetic diethylenetriaminepentacetic acid acid DTPA extract Good predictor of crop response Good predictor of crop response Reliable on high pH soil, less on acid soils Reliable on high pH soil, less on acid soils
Choosing Soil Tests Choosing Soil Tests Sulfate Sulfate Calcium phosphate extract Calcium phosphate extract Little calibration data Little calibration data Variable crop response Variable crop response Credit from organic matter (2.5 × × % OM) % OM) Credit from organic matter (2.5 CEC (Cation Cation Exchange Capacity) Exchange Capacity) CEC ( Measured by summation (K + + , Ca , Ca ++ ++ , Na , Na + + , H , H + + ) ) Measured by summation (K Soil’ ’s potential to s potential to ‘ ‘hold hold’ ’ nutrients nutrients Soil Overestimates on calcareous soils Overestimates on calcareous soils
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