SOIL BASICS & CONSERVATION
What Is Soil? Soil is a mix of eroded rock, minerals, water, air, living things, and decaying matter. Ecosystem Services of Soil Provides nutrients for plants Provides support for plants Purifies water Stores water Stores carbon in the soil Provides habitat for organisms
How Is Soil Organized? Soil is organized into horizons (layers) O Horizon (organic layer) mainly humus (small bits of organic matter) and large organic matter pieces A Horizon (topsoil) contains mix of humus and inorganic materials (minerals) E Horizon (zone of eluviation) -- minerals are leached from this horizon; usually white B Horizon (subsoil/zone of illuviation)- mostly inorganic material in the form of small broken up rock bits from the layer below C Horizon (parent material) bedrock; large chunks of hard earth
What Horizon Relates to Farming? A Horizon has the most biological activity Most organisms live in this horizon. Plants root and grow in this horizon. A horizon is a key factor in judging the quality of the soil for farming The A horizon is a crossroads of other horizons: B horizon and lower has eroded inorganic materials (minerals), which moves up to A horizon Humus from O horizon moves down to A horizon
What Influences the Formation of Soil? There are 5 soil-forming factors: Climate Organisms Parent Material Topography Time COPTT!
Soil Qualities/Characteristics Physical Qualities Soil Texture Water-holding Capacity -- how much water can soil hold due to pore space Density Color Compaction Structure does soil clump? If so, how? Chemical Qualities ph Salinity (salt content) Humus content (organic material) Nitrogen content Phosphorus content Potash content Trace heavy metal content
Soil Texture Three Mineral Components of Soil Sand largest particle size Silt medium particle size Clay smallest particle size Loam fairly even mixture of all three textures (usually ideal for many uses)
Why Is Soil Texture Important? It gives insight on the ability of the soil to: Drain or hold water Sand drains water most easily Clay holds water in pores once inside Support buildings/construction Farm Likelihood of soil compaction Work with any sort of land use
How Do You Determine Soil Texture? Method 1: Measure the amount of each textural component in soil! Then use your friend, the soil textural triangle!
How Do You Determine Soil Texture? Sample Problem: What is the soil texture class of a soil that has 10% clay, 30% sand, and 60% silt?
How Do You Determine Soil Texture? Now calculate the formal soil textural class for these 3 soil samples: Sample 1 -- 30% clay, 20% silt, 50% sand Sample 2 -- 40% sand, 45% silt, 15% clay Sample 3 -- 50% silt, 45% clay, 5% sand Check with your friends! See what they got!
Sample 1 -- 30% clay, 20% silt, 50% sand
Sample 2 -- 40% sand, 45% silt, 15% clay
Sample 3 -- 50% silt, 45% clay, 5% sand
How Do You Determine Soil Texture? Method 2: Ribbon Test Add water to the soil and squeeze it into a ball. Then form a ribbon and squeeze ribbon over the thumb. Measure how long the ribbon lasts before falling Clay particles are so small that they can cling together well longer ribbon Sand particles leave too much air space which prevents particles from clinging little to no ribbon
Degradation of Soil Soil is often overlooked as a key factor to monitor in a healthy environment. Worldwide soil resources have been degraded heavily in the last 150 years. Ways soil is degraded: Desertification Salinization Erosion
Desertification The conversion of once productive lands into non-productive, desertlike land Occurs on 1/3 of all worldwide cropland affects over 250 million people Caused by poor farming practices, overgrazing, soil erosion, deforestation, and/or climate change This lowers the economic potential of the land with food production
Salinization Soil Salinization -- salt buildup in soil from repeated irrigation Freshwater still has small amounts of salt. Irrigation water is used by plants or evaporates and salts are left in soil Over time, salts build up and prevent plant growth Only solution is to flush soil out with LOTS of water This causes waterlogging so much water flushed below kills the root systems of the plants with salty water from above
Soil Erosion Soil is renewable! It takes decades to make a new inch of soil Soil erodes 17 times faster than it is made. What causes soil to erode? Wind and Water! Runoff takes soil with it into waterways Wind picks up loose soil particles
Types of Soil Erosion Three types: Sheet thin sheet of soil runs off with draining water Rill small channels of soil Gully canyon of soil removed/washed out Problems with erosion Reduces soil fertility topsoil disappears Pollutes water makes water silty, which kills some organisms and clogs pipes
Examples of Soil Erosion Historic Soil Erosion Issues Dust Bowl of 1930s Poor farming practices and drought caused most soil to be wind eroded. Iraq (ancient Mesopotamia) the fertile crescent Overirrigation caused salinization and poor farming practices eroded most topsoil Once location where most food was grown, it is still not useful 10,000 years later China has over 1/3 rd of soil affected by erosion. India has areas larger than US and Canada stricken with erosion
How Do We Prevent Soil Degradation? Use Soil Best Management Practices (BMPs) These are land use practices that attempt to have least impact on land and soil resources Examples: Alley cropping Contour farming Conservation Tillage/No-till Farming Cover Crops Mulching Shelterbelts/Windbelts Strip cropping Terracing