Global Trend: Where Did All the Farms Go? Poor farming practices = loss of soils and farmland –Erosion –Salinization Development in United States = loss of 1.4 million acres of farmland per year

Why a Study of Soil Is Important 90% of the world’s food comes from land- based agriculture. Maintenance of soil – key to sustainable civilizations. Foundation of terrestrial life.

Topsoil Formation

Soil Profile

Soil Texture Soil texture refers to the percentage of each type of mineral particle found in the soil. Loam soil – good for agriculture –40% sand, 40% silt, and 20% clay.

Soil Texture Particle size –Large  Sand > Silt > Clay  Small –Size of particles determines… Water and nutrient holding capacity Infiltration Aeration

Soil Texture and Properties TextureWater Infiltration Water- holding Capacity Nutrient- holding Capacity Aeration SandGoodPoor Good SiltMedium ClayPoorGood Poor LoamMedium

Plant–Soil–Water Relationships

Water Transport by Transpiration

Soil pH and Salinity Plants require near neutral pH and low salt Causes of pH and salinity changes –Erosion –Salt water intrusion –Fertilizer runoff –Salination

Productive Soil Good supply of nutrients and nutrient- holding capacity Infiltration, good water-holding capacity, resists evaporative water loss Porous structure for aeration Near-neutral pH Low salt content

Humus Partly decomposed organic matter High capacity for holding water and nutrients Typically found in O horizon

Formation of Humus

The Soil Community

The Results of Removal of Topsoil: Sand and Gravel

The Importance of Humus to Topsoil

Erosion Wind and Water –Deforestation –Use of inorganic fertilizers –Over irrigation –Over tilling –Over grazing

Contour Farming and Shelterbelts

Dry lands and Desertification: Formation of Desert Pavement

Causes of Soil Degradation

Overcultivation Tilling soil exposes top soil to erosion –Alternative No-till/Low-till farming –Top soil remains intact –Dead weeds or previous crop allowed to form humus

Fertilizer –Inorganic Large yields but… –Humus forming organic matter removed during harvesting –Mineralization and soil degradation occurs –Organic Lower yields but… –Helps support biotic community of detritus –Decreases water loss and improves aeration –Improves LONG TERM use of agricultural land

Salinization: Results

Salinization Occurs in drylands –Area is irrigated –Water is allowed to evaporate –Salts remain Runoff can be devastating to nearby fertile lands A form of desertification, since land is rendered useless

Conserving the Soil Cover the soil Minimal or zero tillage Mulch for nutrients Maximize biomass production Maximize biodiversity

Genetically Modified Foods What is meant by GM Foods? What are the risks? What are the benefits? Can an organism be patented?