Paul Snyder, Secrest Arboretum, OARDC What’s the Dirt on Soil? Paul Snyder, Secrest Arboretum, OARDC

Why is soil important?

It supports life. Living things need the proper temperature, oxygen, water, carbon and other nutrients.

What is soil?

How is soil made? Parent Material Weathering/Erosion Organic material Soil Microorganisms Bacteria, fungi, lichens, nematodes Organic material

Parent Material Bedrock Igneous Sedimentary Metamorphic Formed by the cooling and solidification of molten materials deep in the earth. (I.e. granite) Sedimentary Forms when loose material such as sand or mud are deposited by water or wind, are slowly cemented by chemicals and/or pressure into rock. (i.e. shale) Metamorphic Formed when igneous or sedimentary rock are subjected to heat. (i.e. marble)

Glacial deposits Wind deposits Water deposits Sand, gravel, clay Loess soils Wind deposited silt particles Water deposits Alluvial soils Parent material was carried and deposited by moving fresh water. Marine deposits

Volcanic ash Organic deposits Contain more than 20% organic matter. Form under water as aquatic plants die.

Soil horizon Horizons are layers found within the soil Soils change over time in response to their environment. As soils age, minerals and smaller particles leach down to create a new horizon.

A: Topsoil. Surface mineral layer where organic matter accumulates O: Organic matter. Made up completely of decayed plant and animal matter. A: Topsoil. Surface mineral layer where organic matter accumulates Best environment for microorganisms and roots. E: zone of maximum leaching (iron, clay, and other minerals). Usually found in forest soils. B: subsoil. The zone where minerals and particles from the A and E horizons accumulate.

C: The parent material. Lacks the properties of A and B horizons C: The parent material. Lacks the properties of A and B horizons. Little touched by soil forming processes. May include bedrock or other parent material R: the bedrock.

Soil texture Soil texture is the proportion of three soil particles. Sand: large Silt: medium Clay: small Soil texture influences all other soil traits.

Macropores: largest pores. Largely determine the movement of air and water through the soil. Micropores: small pores Retain water as it drains through the soil.

Silt

Nutrients and pH Macronutrients Micronutrients Chlorine Nitrogen Iron Phosphorus Manganese Molybdenum Potassium Micronutrients Nickle Zinc Calcium Sodium Magnesium Silicon Sulfur Cobalt Boron Copper

Cation Exchange Capacity Cation Exchange Capacity (CEC) Refers to the soils ability to gain and hold nutrients (ions). Clay and hummus hold cations. High CEC: 11-50 units (cmol/Kg) Low CEC: less than 11 CEC influences fertilizer application What type of soil has a high CEC?

Soil Compaction Occurs when pressure is applied to the soil surface. Reduces the pore space Can also crush soil aggregates. Changes soil porosity and permeability. Loss of macropore space Loss of pathways for gas and water movement. Wet soils are more prone to compaction than dry soils. Soil particles slide past each other more easily.

Soil Compaction: Effects Reduced porosity and permeability Reduced air exchange. Reduced soil available water. Decreased water infiltration Increased erosion due to greater run off Restricted root growth

Soil Compaction: Plants Plants try to compensate for compacted soil by changing their growth habits. Roots are less branched and thicker. While this protects roots from soil pressure, it decrease root function Decreased ability to absorb water and nutrients

Tilling can alleviate soil compaction Where tillage is not possible compaction presents a problem to many plant species. Plow pans form as the result of repeated tillage operations.

Soil Amendments Amendments can help improve Soil structure Soil fertility Drainage or water-holding capacity Amendments should be incorporated into the top 4-6” of soil. Layering effect of different textures Can be tilled or incorporated by hand. Soil may not need amended.

Use similar or native soil to backfill the hole. Any organic amendments should not exceed the soil backfill by any more than 10% by volume. Amend site soil as needed. (Usually not recommended). This allows the tree to establish into the native soil much faster. Why is it not sustainable to amend the entire site? To have lasting impact you would need to amend a much larger site than just the planting hole.

Fungi Mycorrhizae Fungi that form a symbiotic relationship with plant roots that allows the plant to better absorb certain nutrients and water. Mycorrhizae improve soil aggregation. Ectomycorrhizae: Common on Woody Plants Grow on the outer layers of cells Endomycorrhizae: Common deciduous woody and herbaceous plants. Grows inside plant cell walls.

Both types act as ‘extensions’ of the roots Both types act as ‘extensions’ of the roots. Because fungal hyphae are thinner than roots they can penetrate small soil pores than root hairs. Soil tillage disrupts fungal hyphae. High phosphorus levels suppress mycorrhizae. Most plants (65-95%) have mycorrhizal associations.

Soil Test Why should you soil test? Determine fertility needs Levels may be too low, too high, or just right. To make plant selections To diagnose plant problems

When should you soil test? Before planting Before making plant selections Before applying fertilizer Samples can be taken any time of the year.

How to Collect Soil Samples Use a soil probe or garden trowel Take samples from the top 6-8” of soil Remove organic matter (such as much/ grass) from soil sample. Sample beds or law in a random, z or x pattern. If sampling multiple garden beds, keep the samples separate. Take 15-20 samples from a given area.

Combine samples from similar area into a bucket Mix samples together. Allow soil to dry at room temperature Spread out on newspaper Break into pieces the size of a grain of wheat. Send sample to lab.

Sample A Sample C Sample B

Interpreting a Soil Test Soil pH. 7 is neutral 6.5 is ideal for most plants. 5 is acidic Above 7 is alkaline Buffer pH (basically how easily can the pH be changed). 6.8-7.0 or Lime Test Index 68-70

Phosphorus (P) Potassium (K) Calcium (Ca) Magnesium (Mg) 30-60 Lbs/acre or 15-30 ppm Potassium (K) Varies based on the CEC Calcium (Ca) 800-16,000 lbs/acre or 400-8,000 ppm Magnesium (Mg) 150-2,000 lbs/acre or 75-1,000 ppm.

CEC:11-50 Base Saturation The extent to which a soil is saturated with exchangeable ions other than hydrogen or Aluminum % Ca: 40-80 % Mg: 10-40 % K: 1-5

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