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Introduction to Soil Science in Sustainable Agriculture. Craig Cogger WSU Puyallup Sept. 19, 2002. Soil Components. Mineral Matter. Pore Space. Organic Matter. The soil ecosystem. Residue decomposition Nutrient cycling Aggregation and porosity Enhance plant growth
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Introduction to Soil Science in Sustainable Agriculture Craig Cogger WSU Puyallup Sept. 19, 2002
Soil Components MineralMatter Pore Space Organic Matter
The soil ecosystem Residue decomposition Nutrient cycling Aggregation and porosity Enhance plant growth Break down contaminants
Water MovementHow quickly water moves through soilWater Holding CapacityHow 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
Approximate surface areas of 1 gram samples Coarse sand Half dollar Fine clay Basketball court
Soil Structure Aggregation of sand, silt, and clay particles
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
Soil Structure • Improves macroporosity • Promotes aeration • Promotes infiltration
Most local soils formed from glacial materials • Glacial Till (Ice laid) • Glacial Outwash (Meltwater) • Lacustrine (Lakebed)
Glacial till soil • Ablation till • Not compacted • Permeable to water and roots • Basal till • Compact and cemented • Barrier to water and roots
0 to 4”gravelly sandy loam 4 to 10”, very gravelly loamy sand 10” +sand and gravel Glacial outwash soil Very low water and nutrient holding capacity
Glacial lacustrine (lakebed) soil Fine texture, high water holding capacity, hard to work when wet or very dry.
Nutrient Management • Meet crop nutrient needs • Maintain soil quality • Conserve resources • Protect water quality -- reduce leaching and runoff risk
Major Nutrients Nitrogen Phosphorus Potassium Calcium Magnesium Sulfur Micronutrients Boron Iron Manganese Zinc Copper Chloride Molybdenum Plant Nutrients
How nutrients become available Mineral Matter Organic Matter N K P Not available Mg Ca S - - K+ NH4+ Ca++ SO4-- soluble, available Mg++ Ca++ K+ - - - - - - - - K+ - - - - - - - clay OM
Nutrient Anion Availability Anion Binding Solubility PO4-3 strong low BO3-3 medium medium SO4-2 v. weak high NO3- v. weak v. high
Nitrogen Cycle Plant residues, Manure OrganicN NH4+ Plants, Microbes NO3- Leaching Gases
Organic Materials • Little or no processing • Low nutrient content • Slow release of nutrients • Plant, animal, or mineral sources
Organic Materials:Slow release nutrients • Plants can only take up nutrients that are in available form (simple, soluble ions). • Most nutrients in organic materials are in complex organic molecules or minerals, and are not immediately available to plants.
Slow release nutrients • Biological processes slowly release the nutrients in organic amendment into available forms. • Rate of nutrient release depends on the nature of the amendment and environmental conditions.
Nutrient uptake • The forms of nutrients taken up by plants are the same for all types of fertilizer -- manufactured or organic.
Organic materials:Fertilizers vs. Soil amendments • Fertilizer1.High nutrient content and availability. 2. Main benefit is nutrients. 3. Relatively small amounts applied. • Soil amendment1.Low nutrient content and availability. 2. Main benefit is organic matter. 3. Large amounts applied.
Carbon:Nitrogen ratio • Low C:N supplies N to plants • High C:N ties up N by biological immobilization
C:N <10:1 10:1 to 20:1 20:1 to 30:1 >30:1 N availability High Med - Low Very Low Negative C:N ratio and N availability
High N ContentC: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.
High N ContentExamples • Poultry manure • Packaged organic fertilizers • Fresh dairy or goat manure
Moderate N ContentC:N 12:1 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.
Moderate N ContentExamples • Compost • Yard debris • Cover crop residues • Dairy solids
Low N contentC:N > 30:1 • N immobilization • Need to add N along with organic amendment • Use as mulch or bulking agent for compost
Low N contentExamples • Straw • Sawdust • Paper waste
Soil Testing Nutrients Contaminants Biological Soil Quality
What is a soil nutrient test? • A chemical extraction of “plant-available” nutrients. • Used to predict nutrient availability and fertilizer need.
Soil Nutrient Tests • Standard agricultural tests (P, K, Ca, Mg, B, pH, lime requirement) • Nitrate tests • Sampling Reference: UIdaho Bulletin 704. Soil Sampling
When to sample? • Standard tests can be taken at any time before fertilization. • It is best to be consistent from year to year. • Nitrate tests are taken at specific times.
How often to sample? • Sample each unit every 1 to 3 years, or at least once every crop rotation.
How to sample • Divide farm into units (based on soil type, crop, management). • Small, diverse farms will need to group crops for sampling. • Take 10 to 20 cores per unit (0 to 12 inch depth). • Avoid unusual areas.
Sample handling • Keep moist samples cool during and after sampling. • Refrigerate, freeze, or bring directly to lab. • OR, spread in thin layer and air dry • Send about 1 pint to lab, carefully labeled.
Choosing a lab • Does the lab routinely do ag tests? • Do they use OSU or WSU test methods? • Do they give fertilizer recommendations? • What information do they need? • How to send sample? • Cost? Turn-around time? • What does report look like?
Interpreting soil tests • Nutrient status Low, medium, high • Fertilizer recommendation • You will need to interpret for organic fertilizers. • You will need to interpret if one test represents multiple crops. • Reference: EC 1478. Soil Test Interpretation Guide
Web Addresses • WSU Publications:http://pubs.wsu.edu/ • OSU Publications:http://eesc.orst.edu/ • UIdaho Publications:http://info.ag.uidaho.edu/ • Organic nutrient management web site:http://www.puyallup.wsu.edu/soilmgmt/