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Topic 5 Part 1 soil What is soil and why do we care about it? complex mixture: weathered mineral materials from rocks partially decomposed organic molecules Ecosystem services Soil formation Many factors contribute to this LONG process ClORPT Help determine soil type Temperature and Moisture influence the speed of chemical reactions, which in turn, control how fast rocks weather and dead organisms decompose. Soils develop fastest in warm, moist climates, and slowest in cold and arid ones. The shape of the land and the direction in faces makes a difference in how much sunlight the soil gets, and how much water it keeps. Deeper soils form at the bottom of a hill than at the top because gravity and water move soil particles down the slope. Just like you inherited some characteristics from your parents, every soil inherits traits from the material from which it formed. Soils that form in limestone bedrock are rich in calcium, Soils that formed from materials at the bottom of lakes are high in clay. Time Older soils differ from younger soils because they have had longer to develop EXAMPLE: In the Northern U.S., soils tend to be younger, because glaciers covered the surface during the last ice age, which kept soils from forming. In the southern U.S., there were no glaciers. There, the soils have been exposed for a longer time, so they are more weathered. Soil Texture Ratio of soil particle size determines some soil properties Determining soil type Soil Properties: Porosity Affects water infiltration, water holding capacity, aeration, workability Soil Properties: Chemical Cation exchange capacity (aka nutrient holding capacity) SOIL Profile Soil Profiles in Different Biomes mollisols aridisols Mosaic of closely packed pebbles, boulders Alkaline, dark, and rich in humus Weak humusmineral mixture Dry, brown to reddish-brown, with variable accumulations of clay, calcium carbonate, and soluble salts Desert Soil (hot, dry climate) Clay, calcium compounds Grassland Soil (semiarid climate) Soil Profiles in Different Biomes alfisols oxisols Forest litter leaf mold Acidic lightcolored humus Humus-mineral mixture Light, grayishbrown, silt loam Iron and aluminum compounds mixed with clay Tropical Rain Forest Soil (humid, tropical climate) Dark brown firm clay Deciduous Forest Soil (humid, mild climate) Soil Properties: Biotic surface = algae top few cm of soil = bacteria & fungi roundworms, segmented worms, mites, insects farther down: burrowing animals--gophers, moles, insect larvae, worms even farther: some plant roots Soil Community Soil Community -- Mycorrhizae mycorrhizal symbiosis mutualism between plant roots & fungi Redwood seedlings with (right) and without (left) mycorrhizae. Pine seedling showing how mycorrhizal roots from one tree spread to inoculate other tree roots.