14 Soil Resources

Soil

Uppermost layer of earth’s crust that supports plants, animals and microbes

Soil Forming Factors Parent Material (Start with)

underlying geological material (generally bedrock) which is slowly broken down

Weathering process Time Climate Organisms Topography

A continuous process that takes thousands of years

P-COTT

Soil Composition - “typical soil” Mineral Particles (45%)

Weathered rock Organic Material (5%)

Litter, animal dung, dead remains of plants & animals

Water (25%) Air (25%) 50% of soil is pore space

Air & water fill this space (good for plants)

Humus is a mix of many organic compounds Helps to bind nutrients, minerals ions and hold water in the soil

Soil HorizonsOrganized into distinctive layers

- Rich in organic material

- Topsoil, dark and rich in humus

- Beneath the extent of most roots

Often saturated with water

Only Animals Expect Body CountS

Soil Organisms

Soil Organisms

There are millions of microorganisms in 1 tsp of fertile agricultural soil Scientist have identified ~170,000 species

Ecosystem services - (bacteria & worms provide this)

Humankind benefits from a multitude of resources and processes that are supplied by ecosystems. Decaying & cycling organic material Breaking down toxic materials Cleansing water Soil aeration

Soil Properties

Soil Texture Relative proportion of sand, silt and clay Gravel 2mm and up (Largest) Sand: 2mm–0.05mm Silt: 0.05mm–0.002mm Clay: >0.002mm (smallest)

Know the smallest to largest or visa versa

Soil Properties

Soil texture & pH affects soil properties Coarse textured soil (sandy)

Excellent drainage

Fine textured soil (high in clay) Poor drainage Low oxygen levels in soil Due to negatively charged surface, able to hold onto

important plant nutrients (K+, Ca2+, NO2-)

Soil Acidity Affects solubility of certain plant nutrients pH of most soils range from 4–8 Optimum soil pH is 6–7 (nutrients are most available)

Soil Problems

Soil Erosion (Caused primarily by water and wind) Loss in soil fertility

organic material & nutrients are eroded Fertilizers must be used to replace nutrients lost

Desertification relatively dry land region becomes increasingly arid

Salinization Gradual accumulation of salt in the soil

Accelerated by poor soil management practices

Soil Problems - Soil Erosion

The wearing away or removal of soil top soil from the land

Causes Most often caused by wind & water Poor agricultural processes, removal of plant

communities, unsound logging processes

Effects Reduces plant growth Causes loss of soil fertility Requires additional fertilizer applications, Leads to sediment and fertilizer deposition in waterways

Case in Point: American Dust Bowl

Great Plains low precipitation and subject to drought

1930–1937 severe drought extensive removal of native prairie grasses to plant crops

Overgrazing unusually severe wind and storm conditions. Winds blew soil as far east

as NYC and DC. Farmers went bankrupt

Soil Problems - Desertification

The process of fertile land transforming into desert inappropriate agriculture

Variety of factors Deforestation** Drought Climate change  And other human activities

Desertification has played a significant role in human history, contributing to the collapse of several large empires, such as Carthage, Greece, and the Roman Empire, as well

as causing displacement of local populations

The world's most noted deserts have been formed by natural processes interacting over long intervals of time

Soil Problems - Salinization

Gradual accumulation of salt in the soil due to improper irrigation techniques

Often in arid and semi-arid areas Salt concentrations get to levels toxic to plants

Soil Erosion, Desertification & Salinization

Soil Conservation

Conservation Tillage Residues from previous year’s

crops are left in place to prevent soil erosion

Crop Rotation Planting a series of different

crops in the same field over a period of years

Contour Plowing Plowing around hill instead of

up-down

Soil Conservation

Strip Cropping Alternating strips of different

crops along natural contours

Terracing Creating terraces on steep

slopes to prevent erosion

Strip CroppingStrip Cropping

TerracingTerracing

Soil Reclamation

Two steps Stabilize land to prevent further erosion Restoring soil to former fertility

Best way to do this is shelterbelts Row of trees planted to

reduce wind erosion of soil

Preserving Soil Fertility

Organic fertilizers Animal manure, crop residue, bone meal and compost Nutrient available to plants only when material

decomposes Composting is a natural fertilizer (small or large scale)

Inorganic fertilizers Manufactured from chemical compounds Soluble

Fast acting, short lasting Mobile- easily leach and pollute groundwater

Soil Conservation Policies in US

Soil Conservation Act 1935 Authorized formation of Soil Conservation Service, now

called Natural Resource Conservation Service (NRCS) Assess soil damage & develop policies to improve soil

Food Security Act (Farm Bill) 1985 Farmers with highly erodible soil had to change their

farming practices Instituted Conservation Reserve Program

Pays farmers to stop farming highly erodible land