14soil resources. soil uppermost layer of earth’s crust that supports plants, animals and...
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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