Feeding the World

Feeding the World

Magnesium • Also absorbed in +2 ion form • Essential in the formation of chlorophyll

Cells deficient in magnesium will have yellow spots where chlorophyll is not produced • Chlorosis – the collective term for a plant deficient in either nitrogen, magnesium, or iron

Sulfur • From the negatively charged sulfate ion • SO42- • Used in methionine and cysteine (two very important amino acids) • Also used in Coenzyme A, an enzyme used in respiration and the synthesis and breakdown of fatty acids and vitamins

Comes from volcanoes and the burning of wood (sulfate is a pollutant that plants remove from the environment)

Fertilizers • As plants consume the nutrients in the soil we have to replace them • Fertilizers replace the missing nutrients

Straight fertilizer – contains only one nutrient • Mixed fertilizer – contains N, P, K and rated by their percent abundance in the fertilizer • 6-12-12 • 30-15-6

Compost generally has a much lower NPK rating but helps to aerate the soil and retain the nutrients • The usual NPK for compost ranges from • 0.5-0.5-0.5 to 4-4-4 • So if the NPK rating of compost is so low why do some people consider it the better fertilizer?

Damage control • Each year thousands of pounds of food crops fall victim to natural predators • Over the years many advances in crop protection have been made

The three most damaging predators of crops are insects, other plants, and fungi

Insects • There are thousands of species of insects and many are very beneficial • Without honey bees it would take billions of dollars to pollinate all of our crops

However some insects feed on crops and thus must be controlled • Aphids • Mites • Worms

Pesticides • 3 main types exist • Chlorinated hydrocarbons • Organophosphates • Carbamates

Chlorinated Hydrocarbons • Excellent longevity – they remain active for months to years • Nonpolar – not water soluble so they will not wash off from rain • Usually not biodegradable – no existing biochemical pathway exists to break down these molecules

DDT • DDT - dichlorodiphenyltrichloroethane

Benefits • Used in the 1940s and 50s • Showed excellent control of insect populations • Added to water supplies to control mosquitoes, lice, tsetse flies • Very high crop yields for about 10 years

The down side • Bioaccumulation – the buildup of chemicals through the food chain • DTT is fat soluble

DDT resistant insects appeared • DDT was banned in the early 70s • However many third world countries still use it today

Alternatives • Methoxychlor

Organophosphorus and Carbamates • Both are readily decomposed by water • Short lived effect on crops • Very toxic to insects as well as animals • Detrimental to honey bees as well

Herbicides • 600 million pounds used per year in the US • Selective herbicides developed to kill weeds but not harm plants

Agent Orange • 2,4-dichlorophenoxyacetic acid (2,4-D) • 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) • TCDD is a byproduct of making the previous compounds

Mimic plant growth hormones and are selective to broad leaf plants • this leaves grasslike crops such as corn and wheat alone • 2,4,5-T discontinued in 1985 because of TCDD contamination

Alternatives • Atrazine – toxic to common weeds but grasslike crops can metabolize it (detoxify) • Paraquat – kills weeds during the sprouting phase • Glyphosate – nonselective herbicide, targets the biosynthesis of tyrosine and phenylalanine • Low toxicity in animals • Round-up

Fungicides • Fungi are very necessary to decompose dead matter but often spoil harvested crops (particularly fruits) • Annually 100 million pounds are used in the US

Root rot – besides damaging harvested crops fungi can also damage root systems of plants • Generally happens when excess water is present

Improvements • Crop production has greatly increased over the past 100 or so years • These improvements also have some disadvantages

Pesticides and herbicides are toxic and thousands of workers yearly are treated for exposure • A portion of every fertilizer is washed away to streams, river, lakes, and ponds and upsets the ecosystem there

Fertilizer runoff can also contaminate our drinking water supply • Excess nitrate ions in drinking water compete with oxygen in our blood

Loss of topsoil • Plowing under weeds • Use of synthetic fertilizers not compost • 1930s

Irrigation problems • Flooding • Sprinklers • Evaporation

Excessive use of underground water • Land subsidence

Salination of the Soil • Flooding and irrigation lead to increased salts in the soil • Too much salt is detrimental to plants • The further from fresh water the more salt in the soil

Better Methods • Excessive fertilizer and pesticide use is bad for topsoil, crops, and our health • We need to protect the topsoil and fresh water sources

Better Irrigation • Microirrigation – supplies water directly to plant roots • Benefits • Reduces evaporation • Reduces soil salinization • Prevents topsoil erosion

Organic Farming • - use of only naturally occurring chemicals • Crop rotation • Corn>Legume>Corn • Natural fertilizer • Compost/manure • Natural insect control • Predators (birds, spiders, snakes)

Organic farming uses less than half the energy of traditional farming • Much of the energy saved is in the production of fertilizers/pesticides/herbicides • The US uses 300 million barrels of oil to produce nitrogen fertilizers

Is organic food better for human consumption?

Integrated Crop Management • Managing crops profitably in an area while conserving resources • Use of crop rotation or multicrop fields • Intermix a legume with a non nitrogen producing plant • Reduces pests and increase soil fertility

Planting only crops that suit a particular climate

Integrated Pest Management • Also uses crop rotation • Plant trees and bushes around or in fields to provide a natural habitat for insect predators • Use plants that are naturally resistant to certain pests • Use hearty crops that can out compete weeds

GPS helps target pesticides and fertilizers • Pests can also be hand picked off of plants • Weeds can be plowed under the soil

Pheromones • - insect signaling chemicals • How insects communicate • These can be used to attract harmful insects to a certain area to minimize the application of pesticides

Plant Defenses • Plants also release volatile chemicals much like bugs do • However these chemicals have several functions • Send signals to other plants • Send signals to beneficial insects

Genetic Engineered Crops • For centuries plants and animals have been bred to exhibit specific traits • This took years or decades to make changes in a population

By inserting specific genes into plants or animals we can get a specific trait in a very short amount of time • These are transgenic organisms because they contain genes from another organism

Feeding the World