1 Soils, soil organisms, soil amendments, and their relation to plant health Thanks to Craig Cogger Extension Soil Scientist WSU-Puyallup
2 Outline Introduction to soils Local soil types Soil organisms Choosing organic amendments Compost quality How much organic amendment to use
3 Soil Components Pore Space Mineral Matter Organic Matter
4 The soil ecosystem Residue decomposition Nutrient cycling Aggregation and porosity Enhance plant growth Break down contaminants
5 Water Movement How quickly water moves through soil Water Holding Capacity How much water a soil can hold available for plant growth
6 Soil pores and water movement Macropores: Infiltration and drainage Capillary pores: Available water Micropores: Unavailable water
7 Soil properties that affect porosity Soil texture Soil structure Compaction and disturbance Organic matter
8 Soil Particle Sizes Sand Silt Clay.05-2 mm mm <.002 mm Coarse Fragments >2 mm
10 Hand texture technique
11 Soil Structure Aggregation of sand, silt, and clay particles Structure affects: Macroporosity Infiltration Aeration
12 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
13 Urban and suburban soils Compaction: Loss of structure and macropores Cuts: Loss of topsoil, less structure, shallow depth Fills: Unstructured dirt
14 Disturbed soil: Cut and compacted.
15 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
16 Consequences Increased stress on plants Increased risk of runoff and erosion
17 Prescription Incorporate organic matter
18 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
19 Soil Organisms Bacteria, fungi, actinomycetes, protozoa, nematodes, arthropods, earthworms Pictures courtesy M. Fauci and D. Bezdicek
20 Roles of soil organisms Mary Fauci Residue decomposition Nutrient cycling Aggregation and porosity Contaminant breakdown Nitrogen fixation Enhance root function Pathogens Predators
21 Soil food web and nutrient cycling Roots Phytophagous nematodes Collembolans Predacious mites Mycorrhizae Cryptostigmatid mites Nematode Feeding mites Noncrypto- Stigmatid mites Predacious nematodes Fungi Fungivorous nematodes Omnivorous nematodes Detritus Flagellates Amoebae Bacteria Bacterivorous nematodes
22 Organic matter stimulates soil organisms Formation of soil structure Nutrient cycling Plant disease suppression/stimulation
23 Choosing organic amendments
24 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
25 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
26 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
27 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.
28 Examples: Poultry manure Packaged organic fertilizers Fresh grass clippings Fresh, undiluted rabbit manure Heat-dried biosolids
29 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.
30 Examples: Compost (yard debris, most manures, biosolids) Mixed fresh yard debris Cover crop residues Dairy manure solids
31 Woody stuff, C:N > 30:1 N immobilization Need to add N along with organic amendment Use as mulch or bulking agent for compost
32 Examples: Straw Sawdust Paper waste Horse manure rich in bedding
33 Compost Quality
34 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
35 What is composting? Biological transformation of raw organic materials into biologically stable, humus-rich substances suitable for growing plants
36 What can compost be made of? Feedstocks include yard debris wood waste biosolids dairy solids feedlot manure poultry manure fair waste and more
37 Compost Quality Quality depends on specific use (landscape incorporation vs. mulch vs. potting mix component)
38 Moisture Particle size Organic matter Nutrient availability Salts Biological stability Contaminants Compost Quality: Important things to know
39 Compost moisture affects handling Dry compost (< 35% moisture) is dusty Wet compost (> 60% moisture) is clumpy
40 Compost particle size Particle size < 1 inch is good for incorporation in landscape beds
41 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)
42 Keys to compost nutrient availability Carbon to Nitrogen (C:N) ratio Biological stability
43 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
44 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.
45 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.
46 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)
47 Amending soil with organic materials
48 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.
49 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.
50 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.
51 Organic Mulches Cover ground, reduce erosion Reduce growth of weeds Reduce evaporation Buffer surface soil temperature Decompose to become part of soil organic matter
52 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
53 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