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.

14.2 Fertilizer and Agriculture Increasing fertilizer use

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.

14.3 Agricultural Chemical Use Pests are often referred to as target organisms. Many pesticides kill non-target organisms as an unwanted side effect. – Ex: Many rodenticides kill rodents as well as other living organisms in the field Persistent pesticides remain active for long periods. Nonpersistent pesticides break down quickly.

14.3 Agricultural Chemical Use In 1867, the first synthetic inorganic insecticide was formulated. In 1942, DDT became the first synthetic organic insecticide produced. Since then, over 60,000 insecticides have been produced Many newer herbicides persist in the environment and can accumulate in the food chain – Older chemicals were much shorter lived

14.3 Agricultural Chemical Use 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.

14.3 Agricultural Chemical Use Fungicides are used to: – Protect agricultural crops from spoiling – Prevent the spread of disease, and to – Protect seeds from rotting in the ground 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.