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
Plant Nutrients Major Nutrients Nitrogen Phosphorus Potassium Calcium Magnesium Sulfur Micronutrients Boron Iron Manganese Zinc Copper Chloride Molybdenum
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+
Nutrient Anion Availability AnionBindingSolubility PO 4 -3 stronglow BO 3 -3 mediummedium SO 4 -2 v. weakhigh NO 3 - v. weakv. high
Organic N NH 4 + NO 3 - LeachingGases Plants, Microbes Plant residues, Manure Nitrogen Cycle
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 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.
Carbon:Nitrogen ratio Low C:N supplies N to plants High C:N ties up N by biological immobilization
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
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.
High N Content Examples Poultry manure Packaged organic fertilizers Fresh dairy or goat manure
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.
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/