Assessing and Amending Your Garden Soil Craig Cogger, Soil Scientist Emeritus Washington State University Puyallup The soil is the great connector of our lives, the source and destination of all. - Wendell Berry
Healthy Soil: Water movement and water holding capacity Biology/ecosystem Nutrient supply
Soil Physical Components Pore Space Mineral Matter Organic Matter
The Soil Ecosystem Residue decomposition Nutrient cycling Aggregation and porosity Enhance plant growth Break down contaminants The nation that destroys its soil destroys itself. Franklin Delano Roosevelt
Soil Air and Water Water Movement How quickly water moves through soil Water Holding Capacity How much water a soil can hold available for plant growth
Pore Space and Air-Water Relations Soil acts like a sponge Macropores control infiltration and drainage Capillary pores control water holding capacity Micropores hold unavailable water
Backyard soil tests tell us about water movement and water holding capacity Texture Structure Depth To forget how to dig the earth and to tend the soil is to forget ourselves. - Gandhi
Texture: Proportions of Sand, Silt, and Clay Sand Silt Clay.05-2 mm.002-.05 mm <.002 mm Coarse Fragments >2 mm Soil Texture Video http://puyallup.wsu.edu/soils/soils/
Soil Structure Aggregation of Sand, Silt, and Clay Particles Structure affects: Macroporosity Infiltration Aeration
A healthy soil ecosystem builds soil structure. Growth of roots and movement of organisms create pores and aggregates Soil organisms break down organic residues, producing glues that stabilize aggregates Fungi provide structural support to aggregates Physical, chemical processes also involved
Plant Nutrients Major Nutrients Nitrogen Phosphorus Potassium Calcium Magnesium Sulfur Micronutrients Boron Iron Manganese Zinc Copper Chloride Molybdenum
Soil is full of nutrients, but most are not available to plants Mineral Organic K Ca Insoluble, unavailable N S Ca ++, K + Soluble, available NH 4+, SO -- 4
What affects nutrient supply? Soil parent material and climate Organic matter Fertilization history Soil ecosystem ph
Soil ecosystem and N supply: Nitrogen Cycle Organic N Ammonium NH 4 + Nitrate NO 3 - Soil organic matter, Plant residues, Manure Plants, Microbes N fixation Leaching Gases (N 2, N 2 O) Atmosphere
Soil ph Indicates relative acidity or alkalinity ph 7 = neutral; less than 7 = acid; more than 7 = alkaline or basic Logarithmic scale
Why is ph Important? Nutrient availability Availability of toxic metals Microbiological activity
Desirable ph Ranges Most Vegetables 6 to 7.5 Blueberries 4.5 to 5.5
Modifying soil ph Lime (CaCO3) neutralizes acidity and increases ph Elemental sulfur generates acidity and decreases ph http://images-of-elements.com/sulfur-4.jpg
Soil nutrient testing tells us about nutrient supply and fertilizer needs. A chemical evaluation of nutrient availability. Soil test results are calibrated with crop response research to develop fertilizer recommendations.
Soil Nutrient Test Basic test: P, K, Ca, Mg, B, ph, lime requirement Options: Micronutrients (Zn, Mn, Cu, Fe), N, S, CEC, base saturation, organic matter, salts
Interpreting soil tests Nutrient status Low: fertilizer response likely Medium: sometimes a fertilizer response High: fertilizer response unlikely Fertilizer recommendation Reference: Reference: EC 1478. Soil Test Interpretation Guide Oregon State University. Revised 2011
Soil sampling video http://puyallup.wsu.edu/soils/soils/ Take 8-15 small samples! Mix them in a plastic bucket 0-12 inches deep
Guidelines for garden fertilization
Fertilizer Labels 5 10 10 % Nitrogen % Phosphate % Potash Phosphate = units of P 1 lb P = 2.3 lb phosphate (P 2 O 5 ) Potash = units of K 1 lb K = 1.2 lb potash (K 2 O)
How much fertilizer do I need to apply? Estimate the amount of fertilizer needed based on soil test results, crop needs and area to receive fertilizer Organic fertilizer application rates are usually based on amount of available N supplied by the fertilizer.
Choosing Organic Amendments
Carbon:Nitrogen ratio Low C:N or N-rich, supplies N to plants High C:N or N-poor, ties up N by biological immobilization
Types of Organic Amendments Hot stuff C:N <10:1 Cool stuff C:N 15:1 to 25:1 Woody stuff C:N > 30:1
Hot Stuff Poultry manure Fish and feather meals Fresh grass clippings Fresh rabbit manure
Hot Stuff C:N < 10:1 Rapid N availability Use as a fertilizer Over application leads to excess nutrient levels in soil -- potentially harming crop and water quality.
Cool Stuff Compost (yard debris, most manures, biosolids) Fresh materials: o Yard debris o Cover crop residues o Dairy manure solids o Coffee grounds
Cool Stuff, C:N 15:1 to 25:1 Slow N availability Can add large amounts without risk of over-fertilization Use as a soil amendment
Tagro products combine Class A biosolids with sawdust and sand or bark to make soil amendments that are easy to use
Woody Stuff Straw Sawdust Paper waste Horse manure rich in bedding
Woody Stuff, C:N > 30:1 N immobilization Need to add N along with organic amendment Use as mulch or bulking agent for compost
Organic Application Guidelines (Middle-of-the Road Estimates) Poultry manure: 3-5 gal/100 sq. ft. Rabbit manure: 20-40 gal/100 sq. ft. Animal by-products: Use like inorganic fertilizers Horse manure, dairy solids: 1 inch Compost: Up to1 inch per year in annual bed Compost: Up to 30 to 50% when making raised beds.
More information on organic amendments http://puyallup.wsu.edu/soils/gardening/
Questions? http://puyallup.wsu.edu/soils/gardening/
Raised beds: To build or not to build? Preferred when soil is too shallow, compact, or contaminated for normal gardening
Useful when high water table limits crop choice (such as raspberries)
Enable gardening for people with limited mobility.
Raised bed soils Usually a mixture of sandy fill and compost. Mix raised bed material with the underlying soil to prevent layers. (Do not mix if your soil is contaminated). Buyer Beware! Sometimes material sold as garden fill soil is unsuitable.
Raised beds can be framed or unframed
Raised bed framing materials
Raised Beds Disadvantages Manufactured soil is seldom as good as native soil. More frequent irrigation Higher level of management Use raised beds when you have a good reason to, but not otherwise.
Protecting water quality by reducing runoff from urban gardens
Framed raised beds and mulched buffers reduce runoff risk. Hilltop Urban Gardens
Cover crops also reduce runoff risk. Hilltop Urban Gardens
Simple parking strip garden with grass buffers