Effects of Agriculture on the Environment Chapter 12 Effects of Agriculture on the Environment

Many environmental problems result from agriculture: Soil erosion Sediment transport and deposition downstream On-site pollution from fertilizers and pesticides Deforestation Desertification Degradation of water aquifers Salinization Accumulation of toxic metals and organic compounds Loss of biodiversity

Loss of Nutrients Soil is KEY to sustainable farming, but… Organic matter is not cycled back into the soil. Soil is exposed to sunlight (This speeds up decomposition of organic matter)

Loss of soil fertility The rate of loss of fertility is : measured as the time required for the soil to lose ½ of its original store of chemical elements necessary for crop growth. Depends mostly on climate : warmer and wetter climates accelerate this process

How do we combat this? Organic fertilizers – Cow manure Don’t provide enough of the chemical elements lost Industrial Produced Fertilizers – Major increase in crop production in 20th century Nitrogen – nitrogen gas is converted to nitrate Phosphorus – bird guano, mined

Where Eroded Soil Goes: Sediments Also Cause Environmental Problems -Downstream -Into lakes and ponds – brings fertilizer with it – **Eutrophication**

Ways to slow erosion Making Soil Sustainable Contour Plowing Fall plowing, multiculture, terracing, crop rotation Contour Plowing No-Till Agriculture Combination of farming practices that include not plowing the land and using herbicides to keep down weeds.

Controlling Pests Pests = undesirable competitors, parasites or predators Insects Nematods (worms) Bacterial & viral diseases Weeds rodents

Crop Loss Pests account for an estimates loss of: 1/3 potential harvest (weeds) 1/10 harvested crops (herbivores) Weeds – Early successional plant Fast growing Seeds spread easily Successful in harsh environments

History of Pesticides Pre-Industrial Revolution Little could be done Slash and Burn agriculture – decreased density of pests Aromatic herbs – repel insects – citronella Search for “narrow spectrum pesticide” – single target Earliest pesticides – inorganic compounds - arsenic

History Cont’d 1930’s Petroleum based sprays and natural plant chemicals. Many plants naturally produce chemicals to protect against disease and pests Ex/ Nicotine – primary agent in pesticides today Not as effective as desired

History Cont’d Artificial Organic Compounds DDT Aldrin all have side effects that affect Dieldrin living organisms These pesticides were prone to Bioaccumulation!!!

History Biological Control Use biological predators and parasites to control pests Bacterium – Bacillus Thuringiensis Disease that affects caterpillars Spores of BT sold commercially Important in controlling Gypsy Moths Harmless to mammals Wasps – parasites to caterpillars Ladybugs Sex pheromones – bait in insect traps

End of History Integrated Pest Management Goals: Control of agricultural pests using several methods together, including biological and chemical agents Goals: To minimize the use of artificial chemicals To prevent or slow the buildup of resistance by pests to chemical pesticides

Genetically Modified Crops Development of hybrids for small grains has increased productivity in 20th century Worry !!! ------ production of “super hybrid” – would be overly productive and grow everywhere ----- OR ---- Could interbreed with weeds – creating a “superweed”. Resistant to pesticides --- OR— “super hybrid” may require more fertilizer, pesticide and/or water.

The Terminator Gene A genetically modified crop which has a gene to cause the plant to become sterile after the first year Prevents GMC from spreading Farmers MUST purchase seed each year WORRY --- crop growth could be controlled by whoever has the seeds.

Grazing on Rangelands Overgrazing occurs when the carrying capacity is exceeded. It can cause severe damage to lands It is important to properly manage livestock, including using appropriate lands for gazing and keeping livestock at a sustainable density

Desertification Desertification is the deterioration of land in arid, semi- arid and dry sub humid areas due to changes in climate and human activities Can be caused by Poor farming practices Conversion of marginal grazing lands to croplands