Introduction to Soil Science in Sustainable Agriculture

1. Introduction to Soil Science in Sustainable Agriculture Craig Cogger WSU Puyallup Sept. 19, 2002

2. Soil Components MineralMatter Pore Space Organic Matter

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

4. Water MovementHow quickly water moves through soilWater Holding CapacityHow much water a soil can hold available for plant growth

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

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

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

8. Approximate surface areas of 1 gram samples Coarse sand Half dollar Fine clay Basketball court

10. Hand texture technique

11. Soil Structure Aggregation of sand, silt, and clay particles

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. Soil Structure • Improves macroporosity • Promotes aeration • Promotes infiltration

14. Major soil types of the Puget Sound area

15. Most local soils formed from glacial materials • Glacial Till (Ice laid) • Glacial Outwash (Meltwater) • Lacustrine (Lakebed)

17. Glacial till soil • Ablation till • Not compacted • Permeable to water and roots • Basal till • Compact and cemented • Barrier to water and roots

18. 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

19. Glacial lacustrine (lakebed) soil Fine texture, high water holding capacity, hard to work when wet or very dry.

20. Soil fertility and nutrient management

21. Nutrient Management • Meet crop nutrient needs • Maintain soil quality • Conserve resources • Protect water quality -- reduce leaching and runoff risk

22. Major Nutrients Nitrogen Phosphorus Potassium Calcium Magnesium Sulfur Micronutrients Boron Iron Manganese Zinc Copper Chloride Molybdenum Plant Nutrients

23. 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

24. Nutrient Anion Availability Anion Binding Solubility PO4-3 strong low BO3-3 medium medium SO4-2 v. weak high NO3- v. weak v. high

25. Nitrogen Cycle Plant residues, Manure OrganicN NH4+ Plants, Microbes NO3- Leaching Gases

26. Organic Materials • Little or no processing • Low nutrient content • Slow release of nutrients • Plant, animal, or mineral sources

27. 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.

28. 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.

29. Nutrient uptake • The forms of nutrients taken up by plants are the same for all types of fertilizer -- manufactured or organic.

30. 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.

31. Carbon:Nitrogen ratio • Low C:N supplies N to plants • High C:N ties up N by biological immobilization

32. 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

33. 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.

34. High N ContentExamples • Poultry manure • Packaged organic fertilizers • Fresh dairy or goat manure

35. 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.

36. Moderate N ContentExamples • Compost • Yard debris • Cover crop residues • Dairy solids

37. Low N contentC:N > 30:1 • N immobilization • Need to add N along with organic amendment • Use as mulch or bulking agent for compost

38. Low N contentExamples • Straw • Sawdust • Paper waste

39. Soil Testing Nutrients Contaminants Biological Soil Quality

40. What is a soil nutrient test? • A chemical extraction of “plant-available” nutrients. • Used to predict nutrient availability and fertilizer need.

41. Soil Nutrient Tests • Standard agricultural tests (P, K, Ca, Mg, B, pH, lime requirement) • Nitrate tests • Sampling Reference: UIdaho Bulletin 704. Soil Sampling

42. 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.

43. How often to sample? • Sample each unit every 1 to 3 years, or at least once every crop rotation.

44. 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.

45. 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.

46. 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?

47. 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

48. 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/