
Healthy plant roots are essential for good crop yields. Roots are clearly influenced by the soil in which they live and are good indicators of soil quality. If the soil is compact, is low in nutrients or water, includes high populations of root pathogens, or has other problems, plants will not grow well. On the other hand, plants also influence the soil in which they grow. The physical pressure of roots growing through soil helps form aggregates by bringing particles closer together. Small roots also help bind particles together. In addition, many organic compounds are given off, or exuded, by plant roots and provide nourishment for soil organisms living on or near the roots. The zone surrounding roots is one of especially great numbers and activity of organisms that live off root exudates and sloughed-off cells. This increased activity by microorganisms, plus the slight disruption caused as roots grow through the soil, enhances the use of active (“dead”) organic matter by organisms—also enhancing nutrient availability to the plant. A sticky layer surrounding roots, called the mucigel, provides close contact between microorganisms, soil minerals, and the plant (figure 4.3). Plant roots also contribute greatly to organic matter accumulation. They are usually well distributed in the soil and may be slower to decompose than surface residues, even if incorporated by plowing or harrowing. For plants with extensive root systems, such as grasses, the amount of living tissue below ground may actually weigh more than the amount of leaves and stems we see above ground.
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