05 05 2011 LECTURE 25 Environmental Impact of Agriculture and World Food Issues Current agricultural practices are aimed at increasing and maximizing yields New Crop Varieties bred for high yield easier harvesting Fertilizers use of chemical fertilizers to nourish the crops Pesticides use of chemical pesticides to control pests and increase yields Herbicides chemical herbicides to kill off weeds The Green Revolution the introduction of scientifically developed food crops that can produce high yields under conditions of high inputs of water fertilizers and pesticides The Green Revolution saved millions of people from starvation in developing countries But with serious environmental consequences These practices deplete and destroy future capacity to produce food Dr Norman Borlaug Father of Green Revolution Six environmental problems created by current agricultural practices Declining Biodiversity Soil Erosion Soil Salinization Desertification Chemical fertilizer pollution Pesticide herbicide pollution Declining biodiversity resistant to disease Seed companies focus on a few varieties for farmers high yielding easier to harvest Monoculture growing single crop Putting all your eggs in one basket Out of 30 000 edible plants only 22 are major sources of food in the world Wild populations have greater genetic diversity This contributes to a populations long term survival variation adapting to changing conditions Domesticated crops have much less genetic diversity o Selective breeding results in crop uniformity traits may be lost o Lower genetic diversity likely for crop to succumb to unexpected stresses new diseases pests drought flooding high UV etc o Pests evolve much more rapidly insects fungi bacteria viruses o Uniform domesticated populations are more vulnerable o New diseases don t hurt wild populations as much b c of genetic diversity Solution Polyculture diverse crop varieties Soil erosion Loss of soil comes from tilling plowing the land and the effects of wind and water Soil is made of organic and inorganic matter Organic matter gives texture for root growth and feeds microorganisms that plants need Topsoil is richest in organic matter Humus Problems Soil erodes at about 18 to 100 metric tons per hectare per year o Soil forms about 1 metric ton per hectare per year o Topsoil is lost it contains nutrients etc o Subsoil is left after erosion contains less nutrients minerals holds less water Solutions less plowing o Less annual plants more perennials o No till agriculture o Crop rotation o Green manure crops o Shelterbelts windbreaks o Contour cropping o Strip intercropping Because of irrigation salt builds up in the soil Why Freshwater for irrigating crops contains some salts as water evaporates salts accumulate In salty soils plants cannot absorb water high salt can even kill the plant New trickle irrigation systems that deliver water directly to roots Solutions Laser leveling of fields to prevent soggy areas Restoration of salt damaged land by adding excess water it s a very expensive Salinization process Desertification Desertification expansion of desert at the expense of cropland or rangeland Problem 40 of world s surface is arid or semiarid desert Deserts increasing due to natural processes and human activity Rate of desertification 15 million acres yr Causes of desertification o Overgrazing livestock consuming more plants than can recover exposed soil soil gets eroded plant life not reestablished o Cultivating crops on nearly arid land droughts cause crop loss exposes soil o Improper irrigation excessive salinization plants don t grow in the soil o Deforestation removal of trees without adequate replanting exposed soil etc exposed soil etc soil gets eroded etc Solutions o Replanting with drought tolerant plants like grasses to cover the soil o Retiring the land 10 20 years without grazing or crop cultivation o Not feasible in some overly populated areas o Catch 22 in sub Saharan Africa if they rest land not growing food will lead o if they keep grazing and farming they degrade the land further and will lead to starvation to starvation Chemical fertilizers Excessive use of commercial fertilizers Fertilizers used because growing and harvesting depletes soil of essential minerals that are taken by the plant fertilizers contain N P K Problem chemical fertilizers decrease organic matter in the soil less water holding capacity Run off excessive fertilization to rivers Fertilizer pollution in water overgrowth of algae damages aquatic ecosystems like Chesapeake Bay Nitrate poisoning of groundwater Solutions o Using organic fertilizers slow release o Can improve soil texture composting humus o Crop rotation with leguminous crops provides nitrogen fixation o Water treatment to remove nitrate runoff Pesticides Widespread use of pesticides chemicals used to control insects fungi bacteria nematodes which injure crops Pests reduce productivity 15 20 sometimes can wipe out whole crop Problems Consumer demand unblemished fruit and vegetables Problems with pesticides Insects are developing resistance to pesticides o Insect resistance to pesticides leads to use of more toxic pesticides o Pesticides untested for health effects some may cause cancer or birth defects o Pesticides often used as a preventative measure by farmers some applied 20 o Leads to pollution of soil and water o Broad use of insecticides kill many beneficial insects as well as harmful ones Excessive use of pesticides times in apples disrupts the food chains Pesticide contamination o Some foods have been found to contain residues of pesticides o Top 12 most contaminated fruits and vegetables a k a The Dirty Dozen Apples peaches strawberries spinach nectarines celery bell peppers cherries imported grapes pears potatoes raspberries o Least contaminated Avocado asparagus banana broccoli cauliflower corn kiwi mango onion papaya pineapple peas Reducing pesticide exposure o In some cases yes the pesticide can be washed off or reduced from the o But in other cases the pesticide is taken internally into the plant or it doesn t fruit vegetable wash off easily o Recommendations Eat a varied diet Wash all fruit and vegetables Chose organic whenever possible Solutions to avoid the use of chemical pesticides o Biological control using living organisms to eat the pest insect e g ladybugs eat aphids Parasitoid insects predators pathogens and antagonists IPM Integrated Pest Management combine natural biological controls with chemical