Chapter 14: Agricultural Methods and Pest Management 14.1 The Development of Agriculture 14.2 Fertilizer and Agriculture 14.3 Agricultural Chemical Use 14.4 Problems with Pesticide Use 14.5 Why Are Pesticides So Widely Used? 14.6 Alternatives to Conventional Agriculture

14.1 The Development of Agriculture Our early ancestors obtained food from nature by hunting and gathering. Development of agriculture involved manipulating the natural environment to produce food desired by humans. This allowed an increase in the size of the human population.

Shifting agriculture (slash and burn) Shifting agriculture involves cutting down and burning the trees and other vegetation in a small area of the forest. Burning releases nutrients bound up in biomass. The cleared soil is useful for 2-3 years. Once the soil is no longer suitable for raising crops, the site is abandoned. Forest eventually recolonizes the area through the process of succession. This method is particularly useful on thin nutrient-poor tropical soils. Not suitable for large, densely populated areas. Requires a long recovery time between cycles.

Polyculture Shifting agriculture often employs polyculture, or the planting of a mixture of plants. Shade-requiring plants may be helped by taller plants. Nitrogen-fixing legumes (beans, peas, peanuts, soy, etc) may provide nitrogen for plants that require it. Mixing plants may reduce insect pests problems, because some plants produce molecules natural insect repellents (garlic, tomato, mint, rosemary).

Labor-intensive agriculture Labor-intensive agriculture is practiced in much of the world. Three situations favor this type of agriculture: The growing site does not allow mechanization. The crop does not allow mechanization. The economic condition does not allow purchase of mechanized equipment. The primary reason for the use of labor-intensive agriculture is economic. Many densely populated countries have numerous small farms that can be effectively managed with human labor.

Mechanized monoculture Mechanized monoculture agriculture is typical of industrialized countries. Fossil fuel replaces human muscle power. This method requires large amounts of energy and flat land. Monocultures promote more efficient planting, cultivating, and harvesting to plant the same crop. Labor reduction in the United States: 1913: 135 hours of labor required to produce 2,500 kg of corn. 1980: 15 hours of labor required to produce 2,500 kg of corn. It takes 5 metric tons of fossil fuel to produce 1 metric ton of fertilizer. The developed world is dependent on oil to produce energy to manufacture pesticides and fertilizer and to run machines.

Mechanized monoculture Problems with mechanized monoculture agriculture include: Large tracts of bare land increases soil erosion. The planting of genetically identical seeds results in the loss of genetic diversity. Little genetic differentiation often leads to increased pesticide use. No crop rotation depletes soil nutrients, increasing fertilizer use. Fossil fuel energy use has replaced human muscle power.

The Development of Agriculture Increased production has not solved the world’s food problem because population continues to increase. Global answers are needed for difficult problems. Governments protect farmers with subsidies and trade barriers. Farming is hindered in poorer nations. High fuel costs increase food costs. High energy prices divert crops to be used as fuel crops. Higher demand for meat uses crops that could have been consumed directly by humans.

Increased yields resulting from modern technology and the total amount of land available for cultivation.

14.2 Fertilizer and Agriculture Approximately 25% of the world’s agriculture crop is directly attributed to chemical fertilizer use. Fertilizers replace soil nutrients extracted by plants. The price and availability of chemical fertilizers are strongly influenced by world’s energy prices. The three primary soil nutrients (macronutrients) are nitrogen, phosphorus, and potassium. Micronutrients (e.g., boron, zinc, and manganese) are needed in smaller amounts. When the crop is harvested, the chemical elements that are apart of the crop are removed from the field and they need to be replaced if another crop is to be grown.

Increasing fertilizer use

Fertilizer and Agriculture Chemical fertilizers do not replace soil organic matter, which is important for soil structure (decay of organic matter produces humus). Total dependency on chemical fertilizers usually reduces the amount of organic matter and can change the physical, chemical, and biological properties of the soil.

14.3 Agricultural Chemical Use A pesticide is any chemical used to kill or control populations of unwanted fungi, plants, or animals (pests). Pesticides can be subdivided into several categories based on the organisms they control. Insecticides control insect populations. Fungicides control fungal pests. Rodenticides control mice and rats. Herbicides control plant pests. Biocides kill a large variety of organisms.

Video http://www.youtube.com/watch?v=UB4ezMiopAM

Pesticides Pests are often referred to as target organisms. Many pesticides kill non-target organisms as an unwanted side effect. Persistent pesticides remain active for long periods. Nonpersistent pesticides break down quickly.

Insecticides The discovery of chemicals that could kill insects was celebrated as a major advance in the control of disease and the protection of crops. Mosquitoes are known to carry over 30 diseases harmful to humans. In 1867, the first synthetic inorganic insecticide was formulated. In 1942, DDT became the first synthetic organic insecticide produced. Several new categories of these compounds have since been developed.

Pesticides Chlorinated hydrocarbons are a group of complex, stable-structure, long-lasting, persistent pesticides. They remain effective for long periods after application. They tend to accumulate in soil and animal bodies. They affect many non-target organisms. They are no longer used in many parts of the world. They are still used in many developing countries to protect crops and public health. Because of their persistence and continued use in many parts of the world, they remain present in the food chain.

Pesticides Organophosphates and carbamates are short-lived pesticides that do not persist in the environment. Both work by interfering with the ability of the nervous system to conduct impulses normally. These pesticides affect the nerve cells of humans and other vertebrates as well. Persons who apply such pesticides must use special equipment and should receive special training in safe application practices.

Herbicides Herbicides are used to control unwanted plants and are heavily used in genetically modified crops. About 60% of pesticides used in U.S. are herbicides. Weeds compete with crops for soil nutrients. Traditional weed control methods are expensive in terms of time and energy. Several major types of herbicides are in current use. Synthetic plant growth regulators mimic natural growth regulators (auxins: plant hormons): 2,4-D; 2,4,5-T Photosynthetic disruptors Enzyme inhibitors stop cell division

Herbicides Some herbicides are toxic to all plants (nonselective), and some are selective as to the plant species they affect. Atrazine is often used to control broad-leaf and grassy weeds. Glyphosate (Roundup) is a broad-spectrum, nonselective, systemic herbicide used to control annual and perennial plants.

Fungicides and Rodenticides Fungicides are used to protect agricultural crops from spoilage, to prevent the spread of disease, and to protect seeds from rotting in the ground before they can germinate. Methylmercury is extremely toxic to humans. In some parts of the world, governments pay a bounty to people who kill rats because they can destroy agricultural crops. Rodents also carry diseases harmful to humans. Rodenticides must be used with great care to prevent poisoning non-target organisms.

14.4 Problems with Pesticide Use A perfect pesticide would have the following characteristics: Inexpensive Only affect target organisms Short half-life Break down into harmless materials Newer pesticides have fewer drawbacks than early pesticides, but none are devoid of problems.

Problems with Pesticide Use Persistent pesticides become attached to small soil particles and are easily moved by wind or water. They may be distributed throughout the world from local applications. Persistent pesticides have been discovered in polar ice and are present in detectable amounts in the bodies of animals, including humans, throughout the world.

Problems with Pesticide Use Bioaccumulation is the process of accumulating higher and higher amounts of material within an organism’s body. Many persistent pesticides are fat soluble and build up in fat tissues. Biomagnification is the process of acquiring increasing levels of a substance in bodies of higher trophic-level organisms. DDT and mercury are all known to accumulate in ecosystems. DDT was banned in the U.S. in the early 1970s.

The biomagnification of DDT

Problems with Pesticide Use Pesticide resistance is a problem associated with the widespread use of pesticides. Insecticides only kill susceptible individuals. Most surviving individuals have characteristics that allowed them to tolerate the pesticide. Survivors pass on genetic characteristics for tolerance. Subsequent pesticide applications become less effective.

Problems with Pesticide Use Most pesticides are not species-specific, and kill beneficial species as well as pest species. Many kill predator and parasitic insects that normally control pest insects. Insecticides may change the population structure of the species present so that a species not previously a problem may become a serious pest.

Health issues Short-term and long-term health effects to persons applying pesticides and the public that consumes pesticide residues in food are also concerns. Acute poisoning during application sometimes occurs when farmers cannot read caution labels on packaging or do not have access to protective gear. The WHO estimates between 1 million and 5 million acute pesticide poisonings occur annually, resulting in 20,000 deaths.

Health issues For most people, the most critical health problem is inadvertent exposure to small quantities. Farmers who were occupationally exposed to pesticides over many years show that they have higher levels of certain kinds of cancers than the general public. Chronic minute exposures to pesticide residues in food or through contaminated environments are also of concern.

Health issues A variety of factors is likely to make people in developing countries, especially farmers and agricultural workers, more vulnerable to the toxicological effects of pesticides: Low literacy and education levels Weak or absent legislative and regulatory frameworks Climate factors that make the use of protective clothing during pesticide application uncomfortable Inappropriate or faulty spraying technology Lower nutritional status (weaker physiological defenses against toxic substances)

14.5 Why Are Pesticides So Widely Used? Food Production Worldwide, pests destroy 35% of crops. Economic Concerns Pesticides increase yields and profits. Health Reasons Insecticides curtail many diseases.

14.6 Alternatives to Conventional Agriculture Prior to the invention of synthetic fertilizers and other agrochemicals, Animal manure and crop rotation provided soil nutrients. A mixture of crops prevented regular pest problems. Manual labor killed insects and weeds.

Alternatives to Conventional Agriculture With the development of mechanization, many farmers changed from mixed agriculture to monocultures. This presented greater opportunities for pest problems to develop. Chemical pesticides were used to “solve” the problem.

Alternatives to Conventional Agriculture Alternative agriculture includes all nontraditional agricultural methods. Sustainable agriculture seeks to produce adequate, safe food supplies in an economically viable manner while protecting or enhancing ecosystem health. There are many different types of sustainable pest and weed control practices.

Alternatives to Conventional Agriculture They are guided by some general principles that include: Keeping insecticide, herbicide, fungicide, and fertilizer use to a minimum. Conserving soil and water resources. Staying economically viable. Encouraging biological diversity. Healthy, biologically active soils lead to healthier, more insect- and disease-resistant plants and animals. Natural or supplemented populations of beneficial insects (“good bugs”) will keep pests (“bad bugs”) below economically damaging levels.

Organic Agriculture Organically grown is a legally defined term in the U.S. that tells you how a food or fiber crop was grown. The U.S. Federal Organic Foods Production Act of 1990 defines national organic standards, which generally: Require organic farms and handlers to be “certified,” or inspected by a disinterested third party. Require that an organic farm be increasing its soil fertility through sustainable soil-building techniques. Prohibit synthetic pesticides and fertilizers.

Organic Agriculture While the cost of organic products can be more expensive, they may be thought of as less expensive in the long run. The organic market, while growing, is still limited by low supply, so prices are higher than they might otherwise be. Most organic food is produced by smaller farms that do not have the economics of large-scale industrial agribusiness.

Changes in agricultural production methods Changes in agricultural production methods can help to reduce the problems of soil compaction and loss of organic matter: Reducing the number of trips farm equipment must make over the land reduces soil compaction. Incorporating crop residue into the soil builds organic matter. Reducing fertilizer runoff helps aquatic ecosystems. Careful selection, timing, and use of pesticides decreases the extent to which these materials become environmental contaminants.

Precision agriculture Precision agriculture is a new technique that addresses many of these concerns. With modern computer technology and geographic information systems, it is possible, based on soil and topography, to automatically vary the chemicals applied to the crop at different places within a field. Crop rotation is an effective way to enhance soil fertility, reduce erosion, and control pests.

Integrated pest management Integrated pest management (IPM) uses a variety of methods to control pests rather than relying solely on pesticides. It requires information about: Crop plant metabolism Biological interactions between pests and their predators and/or parasites Climatic conditions favoring pests Techniques to encourage beneficial insects. Several methods are employed in IPM: Disrupting reproduction Female pheromones Male sterilization Natural predators Aphids can be controlled with ladybugs Bacterial strains

Genetic engineering Developing resistant crops Genetic engineering or biotechnology involves inserting specific pieces of DNA into the genetic makeup of organisms. Genetically modified organisms can be developed for pest and herbicide resistance, although some groups are opposed to the use of genetically modified organisms. The European Union will not import genetically modified grains from the U.S.

Alternatives to Conventional Agriculture Modifying farming practices Crop rotation tends to prevent the buildup of specific pests that typically occurs when the same crop is raised in a field year after year. Selective use of pesticides Identification of the precise time when pesticide application will have the greatest effect at the lowest possible dose is a useful practice.