Soils Chapter 5 SOIL • Is the soft material that covers the surface of the earth and provides a place for the growth of plant roots. • It also contains minerals, organic matter, air, and water. Parent Material Igneous rocks – heat created from deep in the earth. Granite, quartz Sedimentary rocks – formed by moving particles (wind water and glacial) and then recombining. Limestone, sandstone Metamorphic – rocks that have changed due to high pressure and or high heat. Marble and slate Formation of Soil (weathering) • Water – Movement – Freezing • • • • • Wind Glacial Chemical Temperature Mechanical – Roots, earthquakes, landslides Five factors control soil formation • • • • • Parent material Time Climate Vegetation Topography Composition of soil. 5% 20-30% Water Air 45% Mineral 20-30% O.M. Soil Textures is the amount of sand, silt and clay in the soil. Clay – fine and plat like, holds a tremendous amount of water and nutrients poor drainage. Smallest Silt – in between particle between clay and sand. Medium. Sand – excellent drainage, warms up quickly in the Spring, poor water retention and fertility. Largest. Texture Triangle Soil Profile • Refers to the arrangement and properties of the various soil layers. • Top soil • Sub soil • Parent Material Soil Horizons • • • • O Horizon A Horizon B Horizon C Horizon • Depth & Colors Soil Water Relationship • Why is water needed in the soil? – Movement of minerals into the plant – Movement of glucose – Photosynthesis – Cooling • Water types – Gravitational water – Capillary water – Hygroscopic water – Crystal lattice water Soil Water Relationship cont. 1) Hygroscopic Water is held so strongly by the soil particles (adhesion), that it is not available to the plants 2) Capillary Water is held by cohesive forces greater than gravity and is available to plants 3) Gravitational Water is that water which cannot be held against gravity – as water is pulled down through the soil, nutrients are "leached" out of the soil (nitrogen) Saturation Percentage • Immediately following an irrigation, the film of water is thick, and smaller pores are full of water. The soil particles can not hold the water. It is easily lost to the plant. • 1/10 Atmosphere (Near Saturation) What is Field Capacity? • when the soil contains the maximum amount of available water, the greatest amount of water it can hold against gravity. • 1/3 Atmosphere • ½ saturation % What is Permanent Wilting Point? • the soil has so little water, that plants can no longer recover from wilting. • roots can no longer take in water. • 15 Atmospheres. • ¼ Saturation % What is Available Water? • the amount of water between field capacity and wilting point Chemical Properties • Soil pH – The amount of hydrogen ions in the soil. • Soil pH range is 0 to 14. • Acid soil is soil with a pH below a 7 -Probably high rainfall and possibly high in organic matter. -Use lime to raise pH -Many fertilizers have an acid affect on the soil. pH cont. • Alkaline soil is that which is above a pH of 7 -Low rainfall areas -Use sulfur to lower pH • Neutral at a pH of 7 -Gypsum acts a buffering agent Cation Exchange Capacity Used to determine fertilization schedules • Sodic and Saline Soils – High amounts of sodium with a pH of 8.5 or above. • Saline-sodic Soils = same as Sodic but with a pH of 8.4 or below. Organic Matter • Improves physical condition & structure. • Increase water infiltration. • Decrease erosion losses. • Supply plant nutrients. • Micro-Organisms enrich the soil. Soil Classification • Why classify soil? • How can it help you? Soil Management • Erosion – Sheet & Rill – Gully • Conservation – – – – – Contour Cropping Strip cropping Terraces Grass Waterways Conservation Tillage • No-Till • Minimal Till • Ridge Planting System Soil Compaction • What is soil compaction? Soil Compaction • How do we prevent soil compaction? • How do we repair soil that is compacted?