From Bedrock to Soil

What is soil? Soil is a loose mixture of small mineral fragments, organic material, water, and air that can support the growth of vegetation.

All soil is different Soil (weathered rock fragments) can be made of many different types of rock. The type of rock that the soil was made from is called parent rock.

Bedrock Bedrock is the layer of rock beneath the soil. Some soil is made from bedrock, so it remains above the parent rock.

Soil Horizons Soil is usually layered with humus-rich soil on top, sediment below that, and bedrock on bottom.

Humus Humus is the dark, organic material in soil that is formed from decayed remains of plants and animals.

Air & Water Air must be present in soil to allow water to flow and roots to grow. Water is essential in dissolving the minerals present in the rock material and distributing it to plant roots.

leaching Leaching is the removal of nutrients that can be dissolved from rock or layers of soil due to the passing of water.

Properties of Soil Soil texture Soil structure Soil moisture Aeration Soil fertility

Soil texture Soil texture is defined as the quality that is based on the proportions, or size, of the particles. What is its consistency? Soil texture can influence infiltration of water

Soil structure Soil structure is defined as the arrangement of soil particles. (not always spread out evenly) Can determine infiltration Sand, less than 2mm in size Silt, less than .05mm, but more than .002mm Clay, less than .002mm in size

Soil fertility Soil fertility is the ability for soil to hold nutrients and to supply nutrients to a plant. Which looks like it had the fertile soil?

Fertility can be determined by Soil color Soil temperature Soil moisture Humus content

Soil color Dark brown or back: contain high levels of humus, very fertile Reddish or Yellowish: contain oxidized iron, also fertile Whitish: usually contain salt, unsuitable for farming

Soil Temperature & moisture Plant growth is slowed if soil temperature is too high or too low. The water that is held in the spaces between soil particles is soil moisture Amount of moisture in soil determines if water to infiltration or cause run-off

Soil Types and Climate

Desert Climates Less than 25cm precipitation per year, so leaching not a problem Low rate of chemical weathering means slow soil formation & no mineral distribution Less ability to support plants or animals High concentration of salt from evaporation

Tropical Rainforest Climate Air is very humid and land received large amounts of water Temperatures are warm year round allowing rapid decomposition, forming rich humus Topsoil is thin, and nutrient poor due to leaching and high demand for nutrients from lush plant life

Temperate Forest & Grassland climates Right balance of moisture and temperature Changes in temperature results in frost action Thick, very fertile soil develops Very productive for farming

Arctic Climates Like cold deserts Extreme low temperature, low precipitation Little plant or animal life Low decomposition rate, limits humus Little chemical weathering, so slow soil formation

So…. What is the source of soil, and how do they differ? How do climates affect soil formation?

Soil Destruction

Erosion Erosion is the process by which wind, water, gravity, or ice transport soil and sediment from one location to another. Soil unprotected by plant growth can be lost.

salinization The accumulation of salts in soil is know as salinization. Common to parts of the world where rainfall is low.

Deforestation Clearing of trees from and area without replacing them is deforestation. Leaves soil exposed to erosion.

Land Degradation When soil is overused it loses its nutrients it is called land degradation. This can happen from poor farming techniques, over mining, cutting trees or overgrazing.

Desertification Desertification is a process where land becomes more desert-like as a result of change in climate, prolonged drought, or human activity.

Soil Conservation Soil Conservation is a method to maintain the fertility of soil by preventing erosion and the loss of nutrients.

Soil Conservation There are many ways that farmers help prevent erosion. We will focus on the physical measures. Contour plowing Terracing No-till farming Cover crops Crop rotation

Contour Plowing Plowing across the slope of hills to prevent erosion.

Terracing Changing one steep field into a series of small, flat fields.

No-till farming No-till farming is a method of farming where the farmer harvests his crops without turning over the soil.

Cover crops Cover crops are crops that are planted between harvests to replace certain nutrients in the soil and prevent erosion.

Crop rotation Rotating crops from one year to the next in order to slow down nutrient depletion. And reduce insect damage to crops.

So… How does soil quality affect us? How can we show good stewardship?