Soils

1. Soils Plant Material Maintenance

2. Soil • Soil is the top layer of the Earth’s crust. • Millions of years to make • Being lost at a rate of 5.2 tons/acre/year (Iowa state-wide average)

3. SOLIDS + PORE SPACE = SOIL

4. Pore Space air water • Two kinds: • Macro pore space • Micro pore space

6. The Ideal Soil

7. In undisturbed soils organic matter helps bind soil particles into larger aggregates.

8. Soil Horizons and the Soil Profile: O – Thin layer of decomposing organic matter. A – Primarily composed of inorganic materials (sands, silts, and clays) it is also normally rich in organic matter. This horizon has a characteristic dark color. E – Not present in all soils and not pictured in the illustration to the left. B – Zone of accumulation where materials that have leached from the surface mix with soil particles from the lower parent material. C – Composed of partially weathered parent material.

9. Inorganic (Mineral) Soil Particles Sand Silt Clay

10. Properties of sand, silt, and clay:

12. Water-holding Capacity Soils with a large percentage of micropores have a high water-holding capacity - clay Soils with a larger percentage of macropores over micropores have a lower water-holding capacity - sand

13. Gravitational Water • Water that drains from the macropores under the force of gravity after a rain/irrigation event.

14. Field Capacity • A soil is said to be at field capacity immediately after the gravitational water has drained away. • Water that remains held in the micropores is called capillary water. • available • unavailable

15. Permanent Wilting Point • When available water is depleted, and no additional water is added, plants may reach the permanent wilting point.

16. Soil Texture Determined by the percentages of sand, silt, and clay a soil contains. Textural triangle.

18. Loam Soils • Ideal balance of 3 particles • Results in high fertility and good water retention • Drains well • Desired for gardening

19. Organic Matter (OM) • Generally only present in very small quantities; 5% or less. • Most OM in the form of humus: stable, decomposed plant and animal life. • In sandy soils - increases water and nutrient holding capacity. • In clay soils - improves drainage, air movement, and helps form aggregates.

20. Cation-Exchange Capacity • Capacity of a soil to attract and hold nutrients on the surface of soil particles. • Soil and organic matter have negative charges. • Nutrients have positive charge, so are attracted to the negative charges . • Clay soils and soils high in organic matter have higher CEC rates.

21. pH Scale • Measures the acidity/alkalinity. • pH affects the nutrient availability in the soil. • Ranges from 0 to 14. pH of 7 is neutral. • Less than 7 is acidic. • More than 7 is alkaline. • pH of 6 is 10 times more acidic than 7 pH. • pH of 5 is 100 times more acidic than 7 pH.

22. Nutrient availability and pH • At certain pH levels, some micronutrients become unavailable to the plant. They become chemically bound to the soil particles. • pH level of 6.5-7.0 is the optimal range for most micronutrients. • Iron is commonly deficient due to high pH soil.

24. Adjusting pH levels • Low pH soils (acidic) • Add lime • High pH soils (alkaline) • Very difficult to lower pH on large scale • Add sulfur • Add organic amendments • Oak leaves, sphagnum moss, pine needles

25. Mychorrhizal Fungi A symbiotic relationship between plant roots and fungi. The fungi help roots absorb water and nutrients. The roots provide the fungi with food (sugar). Most plants growing in “undisturbed” soils have mychorrhizal fungi growing in association with their roots.

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