UBC Farm Soil Workshop Series

1. UBC Farm Soil Workshop Series Class 3: Soil Sampling and Testing Chris Thoreau February 25, 2012

2. Class Outline What is Soil Testing? What are We Testing For? Soil Sampling Methodologies Soil Testing Interpreting Soil Test Results

3. Soil Testing 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

4. Soil Testing Testing for chemical properties is the most common type of soil testing and includes: • pH • Organic Matter % • Nutrients • N, P, K, Ca, Mg, Fe, Cu, S, Mn, Zn, B • C:N Ratio • Electrical Conductivity (EC) • Cation Exchange Capacity • Base Saturation • Particle size distribution (texture)

5. Soil Testing Soil testing involves three basic stages: • Sampling • Testing • Interpreting Which, ideally, lead to actions to improve our soil quality.

6. Soil Sampling 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

7. Soil Sampling Collecting Samples – 2 basic methods 1. Composite Samples: • Several samples are taken from a field and then mixed together to get a representative sample • Samples 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

8. Soil Sampling Collecting Samples • Random Sampling • Random locations • Easy way to get arepresentative sample • Must be truly random to be accurate! • Zig-zag motion can besuitable

9. Soil Sampling Collecting Samples • Topography Sampling • Variation of randomsampling method • Addresses variation in field topography or field features

10. Soil Sampling Collecting Samples 2. Variation Sampling: • Samples are taken from a field in a fixed pattern and each sample is kept separate • Good for identifying variations in a field

11. Soil Sampling Collecting Samples • Grid Sampling • Good for uniform field(s) • Does not take into consideration topography • Can be used for variationsampling

12. Sampling Methodologies Variation in Fields – e.g., OM and pH

13. Soil Sampling Collecting Samples – Tools: • Clean trowel and shovel; Oakfield probe • Clean bucket • Plastic bag Plus, if doing variation sampling: • Individual Bags • Labels • Field Map

14. Soil Sampling Collecting Samples – in the field: • After establishing sampling points… • Remove vegetation from soil surface • Using shovel, dig 20-30 cm deep hole in a small area (20 cm diameter hole) • Mix soil in hole well • Using trowel, scoop up a standard, level sample and place in bucket

15. Soil Sampling Where don’t we collect samples from? • Anomalous/non-representative locations • Around trees • Field edges • Near manure or compost piles • Around standing water

16. Soil Sampling Once all samples have been taken… • Collect about 1 litre of soil from your mixture of samples • Place it in a bag and label it • Collection date • Name of field collected from • Contact info for lab

17. Soil Sampling When is a good time to be sampling? • Close to time when soil will be “used” or Spring • Or, end of season to prepare for following year • Test for Nitrogen: mid- or late-season when soil is warmer • When soil not too wet or dry • Ideally test in the conditions in which plants will be growing

18. Soil Testing Once soil sample has been collected it needs to go to a lab… • Where do we send our samples? • Always to the same lab • Request list of methods use • Methods are all standardized • If new lab: • Confirm methods used and compare results to previous test

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24. Interpreting Soil Test Results Once you have test results you need to know what to do with them!

26. Interpreting Soil Test Results • pH - Measure of soil acidity • Or, the amount of H+ ions in soil • Must measure pH in solution and residual • Scale is from 0-14 • 0 = acidic; 14 = alkaline/basic • pH in coastal soils is usually acidic • Soil Acidity is neutralized through additions of Lime (CaCO3) • Amount of lime required depends on soil texture and OM content

27. Interpreting Soil Test Results

28. Interpreting Soil Test Results Chemistry of raising pH pH Buffering Adsorption Affinity: Al3+> Ca2+= Mg2+ > K+(H+) = NH4+>Na+

29. Interpreting Soil Test Results Basic Liming Recommendations • Contingent on measured pH, desired pH, clay content, OM %

30. Interpreting Soil Test Results

31. Interpreting Soil Test Results Organic Matter % • % is by soil weight • Ideal levels = 12-20% or more • If tests show amounts below this level – add more organic matter!

32. Interpreting Soil Test Results C:N Ratio • Should be 15:1 to 24:1 • If higher than 24:1, be careful to not add woody or high carbon materials to soil

33. Interpreting Soil Test Results Electrical Conductivity (EC) • Measure of salt content in soil • Tests should return levels below 4 mmhos/cm • Rare to have high salts in soil around here • Use gypsum to remove sodium in soil • Flushing water with soil important

34. Interpreting Soil Test Results Cation Exchange Capacity • Measure of soil’s ability to hold and release positively charged particles • Ca2+, Mg2+, K+, Na+,H+,Al+ • Higher CEC value is better • >15 meq/100g soil or 20 cmol/kg soil • OM and clay both have high CEC • CEC Animation

35. Interpreting Soil Test Results Base Saturation • Fraction of cation exchange sites occupied by base cations (Mg2+, Ca2+, Na+, K+) • Usually expressed as a percentage • Base Saturation increases with soil pH

36. Interpreting Soil Test Results Base Saturation • Ideal proportions of Base cations • 60-75% Calcium • 10-15% Magnesium • 3 – 5 % Potassium • <3% Sodium • <12% H+

37. Interpreting Soil Test Results Nutrient Levels • Nitrogen • Leaf and Stem growth; photosynthesis; proteins • Total N % = .5 -.7%; ppm = 20ppm • Phosphorus • ADP and ATP synthesis; photosynthesis; N-fixation; roots • 125 – 300 ppm • Potassium • Enzyme activator; metabolism; stomata regulation • 150 – 250 ppm

38. Interpreting Soil Test Results Nutrient Levels • Calcium • Important for cell growth and structure • 1500 – 3000 ppm • Magnesium • Essential element of chlorophyll; P carrier; enzyme activator • 14% of Calcium levels - 200 – 400 ppm • Copper • Seed formation; chlorophyll formation; enzyme activity • 5 – 10 ppm

39. Interpreting Soil Test Results Nutrient Levels • Zinc • Component of many proteins; toxic at high levels • 50 – 100 ppm • Iron • Important for e- transport: photosynthesis; toxic at high levels • 150 – 250 ppm • Manganese • Assimilation of CO2 in photosynthesis; e- transport in PS • 75 – 125 ppm

40. Interpreting Soil Test Results Nutrient Levels • Boron • Cell wall strength; cell division; too much is toxic • 2 – 4 ppm • Sulfate Sulfur • N-fixation; chlorophyll formation; seed production • 100 – 150 ppm

41. Interpreting Soil Test Results Ideals Nutrient Ratios • Calcium: Magnesium = 10:1 • 7:1 in sandy soils • Phosphorus:Potassium = 2:1 • Potassium:Sulfate-sulfur = 1:1

42. Interpreting Soil Test Results Interpreting Soil Test Results • Soil Sampling Fact Sheet • Gaia College Base Saturation • Soil Test Interpretations 1 • Soil Test Interpretations 2 • Soil Testing for Organic Gardeners