Soils Structure Worksheet Use Module B2 and the samples provided to answer the following questions. What is soil structure? Structure is the arrangement of soil particles (sand, silt, clay) into aggregates What forces cause flocculation? Electrical charges on the surfaces of individual soil particles cause them to come together and form flocculated clumps. What forces result in cementation? The combination of soil water and charged surfaces pulls particles together into a flocculated clump. These clumps are then cemented together by decomposing organic matter and mineral substances into stable aggregates. Identify the structures provided Massive Granular Prismatic Columnar Subangular Blocky What are the 3 characteristics of the aggregates in an ideal surface soil structure? Water stable Porous Variable in size What effects does soil structure have on soil conditions and productivity? Soil Tilth: How a soil responds to being worked Seed Germination and Seedling Development: Soil that is compact enough to hold water but loose enough that a seedling can develop Root Growth and Penetration: soil that gives the plants the ability to obtain nutrients and water Water Infiltration and Soil Aeration: Soils with blocky or prismatic subsurface structures provide good conditions for water and air to move into the subsoil Susceptibility to Erosion: Soils that have poor structure (platy, single grain, and massive) are more susceptible to soil erosion Soil Compaction: Higher compaction of the soil from vehicles, people, or other direct pressure makes a decrease in air pores in the soil Match the following soil structures with the appropriate definition and place your answer in the space provided. No recognizable natural shape Massive Rounded, loosely packed Granular Loose, structureless Single Grain Cubic shaped with rounded edges Blocky Vertical structure often round topped Columnar horizontal layer that crumble when disturbed Platy Group the soil structures above according to whether or not they limit soil productivity. Give reasons why they are good or poor. Good Structures Granular: Allows good water movement, air flow, and seedling development. It also helps to resist soil erosion. Blocky: Allows good internal drainage and plant root development. Structures that are limiting Platy: It has poor structure which is more susceptible to erosion. It also has poor tilth, low organic matter and nutrient content. Single Grain: Does not hold water very well and is susceptible to wind erosion due to its poor structure. Massive: Restricts water and air movement and restricts root penetration. Can also be susceptible to soil erosion. Columnar: Restricts water movement, air flow, and root growth when wet. Becomes extremely hard when dry and severely inhibits root penetration. Match the following soil structures with the location in which they most commonly occur. Soil Structure Common Locations Granular horizons of well-drained grassland soils Columnar Hard B horizon of Solonetzic(high sodium) soils Prismatic and blocky B horizons of well-drained grassland soils Massive horizon worked wet or C horizon Single grain Coarse sandy soils Platy horizon of a forest soil How can we destroy good soil structure? We destroy good soil structure by tilling too often and at the same depth, and driving heavy machinery over wet soil. How can we build good soil structure? We can build good soil structure by growing deep rooted perennial crops, reducing the amount of tilling, and reducing the amount of heavy machinery on wet soils. Regularly add organic matter (compost or composted manure). Encourage biological activity in the soil. Correct the pH as necessary. Avoid overworking the soil. Hoe the soil or turn it over lightly. Use mulch. We can also add organic matter to soils that are needing it (single grain or massive).