Download Understanding Soils: Their Functions, Formation, and Importance for Plant Growth - Prof. D and more Study notes Agricultural engineering in PDF only on Docsity! Soils and Cultivation Soils are defined as the loose surface of the earth, or that material which nourishes and supports growing plant, or the material which supports foundations, roads, etc. But common sense tells us that soils are the solid medium in which plants grow. Functions of Soils Plant support Supplies H2O, Oxygen Supplies Nutrients Protection from stresses Magic -symbiotic relationships -unknown chemicals/substances Where Do Soils Come From? Parent Rock breaks down into smaller rocks, then gravel, then further into sand sized particles. Sand is further broken down into silt sized particles. To this point, it is mainly a matter of subdividing the original parent rock. This means that the chemical composition of sand and silt is very similar to the parent rock. Clay, on the other hand, is very different. In addition to being much smaller than the other particles, it has unique structures, and is unlike the parent rock material. Clay has a very large surface area; surfaces are where things happen in a soil. Clay is chemically very reactive, and dominates the soil in terms of its effect on soil processes. Weathering is the process that converts parent rock material into a soil. It is a very long term process. Several different components contribute to weathering, including the type of parent material, climate (temperature, rainfall, freeze/thaw cycles), plants, and microorganisms. Soil Components Solids - sand, silt and clay, organic matter Pore spaces - water-filled air-filled Balance of Aeration and Moisture Characteristics of Soils Physical Properties Chemical Properties (Nutrition) Reactivity (pH) Organic Matter Biological Activity Soil Class Soils are usually composed of several or many “separates”. The proportions of the component separates determines the soil class. For example, a soil might contain 20% clay, 40% silt and 40% sand. This mixture is classified as a loam, based on the soil textural triangle. Soil texture is very important, but so is soil structure. Soil Structure How the soil particles are arranged and associated with each other is called soil structure. Individual particles aggregate together, glued by attractive forces and by microbial activity plus organic matter. Soil structure can improve a poor soil texture. Soil Porosity Pores exist between individual soil particles. These may be either large (macropores) or small (micropores), which is largely determined by the size of the individual particles and aggregates. Pore size is important because it determines permeability and percolation rate. Soil Percolation, Infiltration Percolation is how quickly water moves through a soil Infiltration is how quickly water moves into a soil from the surface
