Soils, soil organisms, soil amendments, and their relation to plant health Thanks to Craig Cogger Extension Soil Scientist WSU-Puyallup http://www.puyallup.wsu.edu/soilmgmt

Outline Introduction to soils Local soil types Soil organisms Choosing organic amendments Compost quality How much organic amendment to use

Soil Components Mineral Matter Pore Space Organic Matter

The soil ecosystem Residue decomposition Nutrient cycling Aggregation and porosity Enhance plant growth Break down contaminants

Water Movement How quickly water moves through soil Water Holding Capacity How much water a soil can hold available for plant growth

Soil pores and water movement Macropores: Infiltration and drainage Capillary pores: Available water Micropores: Unavailable water

Soil properties that affect porosity Soil texture Soil structure Compaction and disturbance Organic matter

Soil Particle Sizes Sand .05-2 mm Silt .002-.05 mm Clay <.002 mm Coarse Fragments >2 mm

Hand texture technique

Soil Structure Aggregation of sand, silt, and clay particles Structure affects: Macroporosity Infiltration Aeration

Formation of 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

Urban and suburban soils Compaction: Loss of structure and macropores Cuts: Loss of topsoil, less structure, shallow depth Fills: Unstructured “dirt”

Disturbed soil: Cut and compacted.

Effects of development on soils Increased bulk density Resistance to root penetration Loss of structure Reduced porosity Reduced infiltration Reduced rooting depth Reduced nutrient and water availability

Consequences Increased stress on plants Increased risk of runoff and erosion

Prescription Incorporate organic matter

Expected benefits of organic matter Physical: Improved bulk density, structure, porosity, permeability, Biological: More activity Available water: Increase depends on soil and irrigation regime Runoff: Better structure and porosity reduces runoff and erosion Nutrients: Significant for some materials

Soil Organisms Bacteria, fungi, actinomycetes, protozoa, nematodes, arthropods, earthworms Pictures courtesy M. Fauci and D. Bezdicek

Roles of soil organisms Residue decomposition Nutrient cycling Aggregation and porosity Contaminant breakdown Nitrogen fixation Enhance root function Pathogens Predators Mary Fauci

Soil food web and nutrient cycling Phytophagous nematodes Predacious mites Roots Collembolans Nematode Feeding mites Cryptostigmatid mites Mycorrhizae Noncrypto- Stigmatid mites Predacious nematodes Fungivorous nematodes Fungi Omnivorous nematodes Detritus Flagellates Amoebae Bacteria Bacterivorous nematodes

Organic matter stimulates soil organisms Formation of soil structure Nutrient cycling Plant disease suppression/stimulation

Choosing organic amendments

Organic materials: Fertilizers vs. Soil amendments vs. mulches Fertilizer 1. High nutrient content and availability. 2. Main benefit is nutrients. 3. Relatively small amounts applied. Soil amendment 1. Low nutrient content and availability. 2. Main benefit is organic matter. 3. Large amounts applied. Mulch 1. Negative available nutrients 2. Applied to surface to control weeds and conserve moisture

Carbon:Nitrogen ratio Ranges from <5:1 to >500:1 in organic materials Low C:N supplies N to plants High C:N 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 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.

Examples: Poultry manure Packaged organic fertilizers Fresh grass clippings Fresh, undiluted rabbit manure Heat-dried biosolids

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 Expect some N immobilization (tie-up) shortly after application.

Examples: Compost (yard debris, most manures, biosolids) Mixed fresh yard debris Cover crop residues Dairy manure solids

Woody stuff, C:N > 30:1 N immobilization Need to add N along with organic amendment Use as mulch or bulking agent for compost

Examples: Straw Sawdust Paper waste Horse manure rich in bedding

Compost Quality

Why use compost as a source of organic matter? Locally produced, recycled material Home, farm, or commercial Can usually be applied at high rates to increase organic matter benefits Hot composting kills pathogens

What is composting? Biological transformation of raw organic materials into biologically stable, humus-rich substances suitable for growing plants

What can compost be made of? Feedstocks include yard debris wood waste biosolids dairy solids feedlot manure poultry manure fair waste and more

Compost Quality Quality depends on specific use (landscape incorporation vs. mulch vs. potting mix component)

Compost Quality: Important things to know Moisture Particle size Organic matter Nutrient availability Salts Biological stability Contaminants

Compost moisture affects handling Dry compost (< 35% moisture) is dusty Wet compost (> 60% moisture) is clumpy

Compost particle size Particle size < 1 inch is good for incorporation in landscape beds

Compost organic matter Typically 40 to 60% If a compost contains large amounts of soil, the organic matter content will be lower (this may be true of backyard and feedlot composts)

Keys to compost nutrient availability Carbon to Nitrogen (C:N) ratio Biological stability

Soluble salts Less of a problem in humid climates than in arid climates General recommendation is soil:compost blend < 2.5 to 6 mmho/cm, depending on sensitivity of plants

Biological Stability Unstable compost can harm plants (phytotoxic compounds include organic acids and high levels of ammonia). Indicators include color, odor, very low or high C:N, stability test kits.

Compost contaminants Inerts (plastic etc.) affect aesthetic appeal. Metals (lead, cadmium etc.) tend to be low in Northwest composts. Pesticides: Clopyralid was a concern in some composts, but no problems have been reported since 2001.

Other organic amendments Cover crops Yard debris (leaves, grass clippings) Uncomposted manures (horse, dairy solids, rabbit, goat, etc.) Class A biosolids (such as Tagro) Food waste (coffee grounds, vegetable trimmings)

Amending soil with organic materials

How much to add? Physical benefits are most apparent with high rates of amendments. Materials must have low nutrient availability to avoid potential N leaching when high rates are used. Most research has been done on agricultural soils. Maximum rates studied are about 1/3 by volume.

Landscape plantings Most research has focused on amended planting holes. Little or no benefit of amending holes. Not much data available for planting beds. Recommend 1/3 by volume based on results from ag research and field experience.

Annual Beds Establishing raised beds. You can use up to 30 to 50% by volume of suitable material. Expect settling. Annual amendments. One half to one inch per year to maintain OM.

Organic Mulches Cover ground, reduce erosion Reduce growth of weeds Reduce evaporation Buffer surface soil temperature Decompose to become part of soil organic matter

Organic Mulches for Landscapes Coarse, woody material (bark, wood chips) are good for weed control in landscapes Apply 3” deep, keep away from trunks Compost mulches may not control weeds well after the first few months Woody mulches may slightly reduce N availability to plants in first year after application

Which mulch where? Landscapes: Woody mulches Annual gardens: Mulch in winter with compost or straw, or grow cover crops (living mulch) Turf: Do not mulch