Fertilizers contain chemicals that plants need to survive and thrive. Chemists have used various compounds to produce fertilizers with nutrients needed by plants. When the plant does not have enough of these nutrients, it will not grow as fast. These fertilizers must break down in the soil so that the plant can take the nutrients up in the plant's root system. As the plant develops, other organisms, such as insects, may try to eat the plant. Pesticides poison these insects or prevent the insects from growing normally.
Soil erosion and the consumption of nutrients by surrounding plants can reduce the quantity of nutrients that remain in the soil. Different plant species have different nutritive needs, and gardeners can provide targeted amounts of nutrients based both on the plant's needs and the current quantity of nutrients. Adding nutrients to the soil also increases the quality of the vegetables we grow, which helps us when we consume these nutrient-rich foods. However, excessive quantities of certain nutrients can harm the plant, especially with iron and nitrogen.
Nitrogen is a basic part of all living cells---plants cannot survive without it. Sufficient quantities of nitrogen help plants grow rapidly. Phosphorus plays a major role in a plant's photosynthesis process and also allows plants to store their sugars and starches. Phosphorus is most helpful in a plant's flowering and in root growth. Potassium supports the process of growing proteins, plays a role in photosynthesis and helps the plant fight diseases.
Pesticides are chemicals that can suppress or kill pests. Bactericides create an environment that prevents bacteria from sustaining itself. Fungicides coat fungus and either kill the fungus or prevent it from harming the plant. Herbicides kill weeds or prevent weeds from growing. Some herbicides only harm the weeds after they have emerged from the soil, while others prevent weeds from emerging in the first place. Insecticides often dry insects out by scratching the insect's exoskeleton, while other insecticides mimic natural chemicals found in insects and cause them to grow too fast or too slow. Baits contain food that the pest normally eat that can lure the pests towards poison or a death trap. With ingested pesticides, some organisms carry the ingested pesticides to a nest, while other pests consume the pesticide from the corpse of the dead insect.
Pesticides eventually dissipate at rates that vary depending on the environment that the pesticide is sprayed in. Temperature, soil moisture, pH level and nearby microorganisms affect the deterioration. Some pesticides only harm the target species, while others can harm humans and pets; sometimes this harm occurs when the pesticide interacts with other chemicals, producing dangerous fumes, particularly for the person applying the pesticide. Gardeners should read the labels before applying pesticides.
Most organisms can develop resistance to pesticides over time. This resistance results from natural selection, in which organisms develop slight genetic variations to survive. The resistant organisms thrive, while the nonresistant organisms perish, causing the species to develop an overall resistance to the pesticide.