Physical Properties of Soils Introduction to Agriculture

Soil Texture Minerals in the soil come in many sizes and are generally classified as: Coarse particles - anything in the soil larger than 2 mm Fine particles - less than 2 mm SAND mm SILT mm CLAYLess than mm

Textural Classes Soil texture is the percentage of sand, silt and clay in the soil Sandy Soils – 70% sand or more Silty Soils – 80% silt or more Clay Soils – 40% clay or more Loam Soils – perfect mix of sand, silt and clay, most desirable for growing crops

Soil Triangle A soil triangle is a chart that shows the soil texture class based on the percentage of sand, silt and clay How to read a soil triangle: Must know % of at least two particle sizes Read along lines to where two % meet CLAY (across) → SILT (down) ↓ SAND (up) ↑

Soil Type ClaySiltSand AerationPoorGoodExcellent Bulk DensityLowModerateHigh Internal DrainagePoorGoodExcellent TemperatureWarms SlowlyWarms ModeratelyWarms Quickly TillageDifficultModerateEasy Water Holding CapacityHighModerateLow Compaction PotentialHighModerateLow

Soil Color Black-BrownYellow-RedWhite-Light Grey Bluish-Grey

Soil Structure Soil structure is the arrangement of particles in the soil Structure affects aeration, water movement, heat transfer, and root growth Granular is ideal for agriculture, allows for maximum pore space

granular blocky prismatic columnar platymassivesingle grained

Soil Tilth Soil tilth is the workability of the soil based on texture, structure and some other factors Soil moisture and compaction play a role Often due to over-working the soil and preventing root penetration

Review Questions 1.Name the 3 soil texture particles. Which is the largest? Which is the smallest? 2.What is soil texture? 3.What affects does soil structure have? 4.Define soil tilth. Why is good soil tilth important?

Review Questions 5.Which soil type (particle) has the best drainage and density? Why? 6.A soil that is 20% sand, 30% silt, and 50% clay has what texture? 7.A soil that is 10% sand, 55% silt, and 35% clay has what texture? 8.A soil that is 60% sand, 10% silt, and 30% clay has what texture?