LECTURE 25 – Environmental Impact of Agriculture and World Food IssuesCurrent agricultural practices are aimed at increasing and maximizing yields:New Crop Varieties– bred for high yield, easier harvestingFertilizers– use of chemical fertilizers to nourish the cropsPesticides– use of chemical pesticides to control pests and increase yieldsHerbicides– chemical herbicides to kill off weedsThe 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 RevolutionSix environmental problems created by current agricultural practicesDeclining BiodiversitySoil ErosionSoil SalinizationDesertificationChemical fertilizer pollutionPesticide/herbicide pollutionDeclining biodiversitySeed companies focus on a few varieties for farmers (high yielding, easier to harvest, resistant to disease)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 worldWild populations have greater genetic diversityThis contributes to a populations long-term survival (variation = adapting to changing conditions)Domesticated crops have much less genetic diversitySelective breeding à results in crop uniformity (traits may be lost)Lower genetic diversity => likely for crop to succumb to unexpected stresses (new diseases, pests, drought, flooding, high UV, etc)Pests evolve much more rapidly : insects, fungi, bacteria, virusesUniform domesticated populations are more vulnerableNew diseases don’t hurt wild populations as much, b/c of genetic diversitySolution: Polyculture, diverse crop varietiesSoil erosionLoss of soil comes from tilling (plowing) the land and the effects of wind and waterSoil is made of organic and inorganic matterOrganic matter – gives texture (for root growth) and feeds microorganisms that plants needTopsoil is richest in organic matterHumusProblems: Soil erodes at about 18 to 100 metric tons per hectare per yearSoil forms about 1 metric ton per hectare per yearTopsoil is lost (it contains nutrients etc.)Subsoil is left after erosion: contains less nutrients, minerals, holds less waterSolutions: less plowingLess annual plants, more perennialsNo-till agricultureCrop rotationGreen manure cropsShelterbelts (windbreaks)Contour croppingStrip intercroppingSalinizationBecause of irrigation– salt builds-up in the soilWhy? 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.Solutions: New trickle irrigation systems that deliver water directly to roots.Laser leveling of fields, to prevent soggy areasRestoration of salt-damaged land, by adding excess water, (it’s a very expensive process)DesertificationDesertification: 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 activityRate of desertification: 15 million acres/yr.Causes of desertificationOvergrazing– livestock consuming more plants than can recover à exposed soil à soil gets eroded à plant life not reestablishedCultivating crops on nearly arid land, droughts cause crop lossà exposes soil, etc.Improper irrigationà excessive salinization, plants don’t grow in the soil à exposed soil, etc.Deforestation– removal of trees without adequate replanting à exposed soil à soil gets eroded, etc.SolutionsReplanting with drought-tolerant plants (like grasses) to cover the soilRetiring the land – 10-20 years without grazing or crop cultivationNot feasible in some overly populated areas‘Catch-22’ in sub-Saharan Africa: if they rest land, not growing food will lead to starvation;if they keep grazing and farming, they degrade the land further and will lead to starvationChemical fertilizersExcessive use of commercial fertilizersFertilizers 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 à less water-holding capacityRun-off excessive fertilization to riversFertilizer pollution in water à overgrowth of algae à damages aquatic ecosystems (like Chesapeake Bay)Nitrate poisoning of groundwaterSolutionsUsing organic fertilizers (slow-release)Can improve soil texture – composting, humusCrop rotation with leguminous crops (provides nitrogen fixation)Water treatment to remove nitrate runoffPesticidesWidespread use of pesticides, chemicals used to control insects, fungi, bacteria, nematodes which injure cropsPests reduce productivity (15 – 20%), sometimes can wipe out whole cropProblems: Consumer demand unblemished fruit and vegetablesInsects are developing resistance to pesticidesProblems with pesticidesInsect resistance to pesticides à leads to use of more toxic pesticidesPesticides untested for health effects – some may cause cancer or birth defectsExcessive use of pesticidesPesticides often used as a preventative measure by farmers (some applied 20 times in apples)Leads to pollution of soil and waterBroad use of insecticides kill many beneficial insects, as well as harmful ones: disrupts the food chainsPesticide contaminationSome foods have been found to contain residues of pesticides: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.Least contaminated: Avocado, asparagus, banana, broccoli, cauliflower, corn, kiwi, mango, onion, papaya, pineapple, peas.Reducing pesticide exposureIn some cases, yes, the pesticide can be washed off or reduced from the fruit/vegetable.But in other cases, the pesticide is taken internally into the plant, or it doesn’t wash off easilyRecommendations:Eat a varied dietWash all fruit and vegetablesChose organic whenever possibleSolutions to avoid the use of chemical pesticides:Biological control – using living organisms to eat the pest insect (e.g., ladybugs eat aphids)Parasitoid insects, predators, pathogens and