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

Case Study – Clean-Water Farms Concern: erosion and water quality How concern was addressed: convert some areas to grass and rotate animals through newly created paddocks Results: evenly distributed wastes, prevented overgrazing, able to increase size of herd Intensive Rotational Grazing/Management Intensive Grazing – addresses which theme?

12.1 – How Agriculture Changes the Environment Soil erosion Sediment transport/deposition down stream On-site pollution Off-site pollution Deforestation Desertification Degradation of aquifers Salinization Accumulation of toxic metals Accumulation of toxic organic compounds Loss of biodiversity

12.2 – The Plow Puzzle Fig. 12.2 – Only ants eat bread crumbs ….“man is everywhere a disturbing agent. Wherever he plants his foot the harmonies of nature are turned to discords.” “The equation of animal and vegetable life is too complicated a problem for human intelligence to solve, and we can never know how wide a circle of disturbance we produce in the harmonies of nature when we throw the smallest pebble into the ocean of organic life.” Fig. 12.2 – Only ants eat bread crumbs George Perkins Marsh

12.3 – Our Eroding Soils American Dust Bowl of the 1930’s -soil erosion rates in the U.S. have decreased but regeneration is slow https://www.youtube.com/watch?v=CKt-iaZ1P9g&list=PL5V9GXQlS0_v-GNP3Ck8h-VBHeIyo3dPv&index=5 Decline in organic matter due to: a)vegetation is cleared/crops planted and harvested b) less input of dead organic matter c) soil is exposed to sun speeding rate of decomposition

12.3 continued What factors increase the rate at which soil fertility is lost? Organic vs synthetic? Paper or plastic? Conversion of nitrogen gas to nitrates and phosphorus from guano and marine fossils

12.4 – Where Eroded Soil Goes Physical effects: sediments fill in productive waters and can destroy coral reefs Chemical effects: http://archive.riversymposium.com/index.php?element=T_s2_A2_Yellow+River_China.pdf http://earthobservatory.nasa.gov/Features/WorldOfChange/yellow_river.php

12.4 continued Making soils sustainable – amount lost = amount produced - 1mm can take from 10 to 40 years to form - options include: a) fall plowing, b) multiculture, c) terracing, d) crop rotation, e) contour plowing, and f) no-till agriculture

12.4 continued Contour plowing – land is plowed ┴ to the slopes and as horizontally as possible Single most effective in decreasing erosion http://www.teachertube.com/video/contour-plowing-18299

12.4 continued No-till – uses herbicides and IPM to control weeds - decreases release of CO2 - leave unused portions of plants to decay - 17.5% of farms in U.S.

12.5 – Controlling Pests Define pest Insects Nematodes Bacterial/viral diseases Weeds Vertebrates Account for a loss of 1/3 potential and 1/10 of harvested crops(in U.S.)

12.6 History of Pesticides Remove weeds by hand/planted aromatic herbs Search for “magic bullet”/early pesticides were highly toxic Ex) arsenic 1930’s – petroleum-based sprays/natural plant chemical Ex) nicotine - safe, but not as effective

12.6 continued Artificial organic compounds Ex) DDT(broad-spectrum) Biological control – a) Bt, b) wasps, c) ladybugs, d) pheromones

12.7 – Integrated Pest Management Biological Control, use of some chemical pesticides, some methods of planting crops Key: control vs elimination of pests Monitoring of pesticides: a)breakdown may be slow, b) intermediate may be toxic, c) many unanswered questions

12.8 Genetically Modified Crops Positive Negative Natural “superhybrid” “superweed” Growth on marginal lands 3 methods ----- 1. faster/more efficient development of new hybrids Ex) symbiotic relationship w/bacteria

2. Introduction of the terminator gene http://www.wavsource.com/snds_2012-05-06_8109235143609609/movies/terminator/t2_terminator.wav Positive Negative Prevents gm crop from spreading Not for economically disadvantaged

3. Transfer of genes Positive Negative Improved nutritional value Novel effect Ex) rice w/beta-carotene Non-target organisms affected

12.9 Grazing on Rangelands ~ ½ of Earth’s land area is used as rangeland I – Traditional and Industrialized Use – overgrazing vs feedlots are source of local pollution II – Biogeography of Agricultural Animals- 2 major environmental affects – 1. native vegetation may be greatly reduced and threatened with extinction

12.9 continued Introduced animals may compete with native herbivores Ex) Brazilian Amazon Basin – burn forest - plant crops(~4yrs) - convert to rangeland(~4yrs) - move on

12.9 continued III – Carrying capacity- varies with rainfall, topography, soil type, soil fertility - exceed carrying capacity overgrazing decrease plant diversity/increase soil erosion/leads to dominance by plant species undesirable to cattle

12.10 – Desertification – Regional Effects and Global Impact Expanding due to: changes in climate human activities  destroy a soil’s ability to store water The geographic location of deserts is controlled by descending air masses. They occur on the leeward side (rain shadow) of a mountain range. They also occur at latitudes 30 degrees N and 30 degrees S as a result of global air circulation Rising air masses expand, cool, and precipitate moisture. Descending air masses compress, warm, dry, and evaporate moisture I – What causes deserts? a) poor forestry and farming practices b) overgrazing c) conversion of rangelands to croplands d) irrigation

12.10 continued II – Preventing desertification Step 1 – detect symptoms such as: lowering of water table, increase in salt concentration in soil, decrease in surface water, loss of native vegetation, and increase in soil erosion Step 2 – attempt to control activities listed above

12.11 – Does Farming Change the Biosphere? Affects species diversity Increases CO2 in atmosphere Changes in biogeochemical cycles Change in land cover a) change in reflection of light by surface b) changes in rate of evaporation of water c) change in rate of exchange of chemical compounds produced/removed by living things