Specific recommendations must be tailored to the crops you want to grow, as well as other characteristics of the particular soil, climate, and cropping system. Most soil test reports use information that you supply about manure use and previous crops to adapt a general recommendation for your situation. However, once you feel comfortable with interpreting soil tests, you may also want to adjust the recommendations for a particular need. What happens if you decide to apply manure after you sent in the form along with the soil sample? Also, you usually don’t get credit for the nitrogen produced by legume cover crops because most forms don’t even ask about their use. The amount of available nutrients from legume cover crops and from manures is indicated in table 21.5. If you don’t test your soil annually, and the recommendations you receive are only for the current year, you need to figure out what to apply the next year or two, until the soil is tested again.
No single recommendation, based only on the soil test, makes sense for all situations. For example, your gut might tell you that a test is too low (and fertilizer recommendations are too high). Let’s say that although you broadcast 100 pounds N per acre before planting, a high rate of N fertilizer is recommended by the in-season nitrate test (PSNT), even though there wasn’t enough rainfall to leach out nitrate or cause much loss by denitrification. In that case, you might not want to apply the full amount recommended.
Another example: A low potassium level in a soil test (let’s say around 40 ppm) will certainly mean that you should apply potassium. But how much should you use? When and how should you apply it? The answer to these two questions might be quite different on a low organic matter, sandy soil where high amounts of rainfall normally occur during the growing season (in which case, potassium may leach out if applied the previous fall or early spring) versus a high organic matter, clay loam soil that has a higher CEC and will hold on to potassium added in the fall. This is the type of situation that dictates using labs whose recommendations are developed for soils and cropping systems in your home state or region. It also is an indication that you may need to modify a recommendation for your specific situation.
Table of Contents
- About the Authors
- Preface
- Introduction
- Healthy Soils
- Organic Matter: What It Is and Why It's So Important
- Amount of Organic Matter in Soils
- The Living Soil
- Soil Particles, Water, and Air
- Soil Degradation: Erosion, Compaction, and Contamination
- Nutrient Cycles and Flows
- Soil Health, Plant Health, and Pests
- Managing for High Quality Soils: Organic Matter, Soil Physical Condition, Nutrient Availability
- Cover Crops
- Crop Rotations
- Animal Manures for Increasing Organic Matter and Supplying Nutrients
- Making and Using Composts
- Reducing Erosion and Runoff
- Preventing and Lessening Compaction
- Reducing Tillage
- Managing Water: Irrigation and Drainage
- Nutrient Management: An Introduction
- Management of Nitrogen and Phosphorus
- Other Fertility Issues: Nutrients, CEC, Acidity, and Alkalinity
- Getting the Most From Routine Soil Tests
- Taking Soil Samples
- Accuracy of Recommendations Based on Soil Tests
- Sources of Confusion About Soil Tests
- Soil Testing for Nitrogen
- Soil Testing for P
- Testing Soils for Organic Matter
- Interpreting Soil Test Results
- Adjusting a Soil Test Recommendation
- Making Adjustments to Fertilizer Application Rates
- Managing Field Nutrient Variability
- The Basic Cation Saturation Ratio System
- Summary and Sources
- How Good Are Your Soils? Field and Laboratory Evaluation of Soil Health
- Putting It All Together
- Glossary
- Resources