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

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Presentation on theme: "Introduction to Soil Science in Sustainable Agriculture Craig Cogger WSU Puyallup Sept. 19, 2002."— Presentation transcript:

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

2 Mineral Matter Pore Space Organic Matter Soil Components

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

4 Water Movement How quickly water moves through soil Water Holding Capacity How 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 sandHalf dollar Fine clayBasketball 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 Ablation till Not compacted Permeable to water and roots Basal till Compact and cemented Barrier to water and roots Glacial till soil

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

23 How nutrients become available Mineral Matter Organic Matter K Mg Ca N S P K + NH 4 + Ca ++ SO4 -- soluble, available Not available - - -- - - - - - -- Ca ++ K+K+ clay OM - - - - - - Mg ++ K+K+

24 Nutrient Anion Availability AnionBindingSolubility PO 4 -3 stronglow BO 3 -3 mediummedium SO 4 -2 v. weakhigh NO 3 - v. weakv. high

25 Organic N NH 4 + NO 3 - LeachingGases Plants, Microbes Plant residues, Manure Nitrogen Cycle

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 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.

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

32 C:N ratio and N availability C:N <10:1 10:1 to 20:1 20:1 to 30:1 >30:1 N availability High Med - Low Very Low Negative

33 High N Content 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.

34 High N Content Examples Poultry manure Packaged organic fertilizers Fresh dairy or goat manure

35 Moderate N Content C: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 Content Examples Compost Yard debris Cover crop residues Dairy solids

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

38 Low N content Examples 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: OSU Publications: UIdaho Publications: Organic nutrient management web site:

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