Modern agriculture relies on chemical inputs to achieve the high yields and consistent quality needed to feed a growing global population. These substances are applied throughout the crop’s lifecycle, serving distinct functions from fueling growth to protecting against biological threats. The use of these compounds allows farmers to manage large-scale production efficiently. Farming inputs fall into several distinct categories, each designed to address a specific challenge in plant development or environmental competition.
Chemicals for Pest, Disease, and Weed Control
The largest category of chemical inputs used in crop production are those designed to eliminate biological competitors, collectively known as pesticides. These compounds are formulated to deter, incapacitate, or kill organisms that threaten crop health and productivity. Pesticides are broadly separated into three groups targeting weeds, insects, and fungi.
Herbicides
Herbicides are chemicals used to control or destroy unwanted vegetation that competes with crops for light, water, and nutrients. These compounds are classified as either selective or non-selective based on their action. Selective herbicides target specific plant types, eliminating weeds without damaging the cultivated crop. Non-selective types destroy most plant tissue they contact. Glyphosate, one of the most widely used herbicides globally, is a non-selective type often applied before planting or on genetically modified crops resistant to its effects.
Insecticides
Insecticides control insect populations that feed on or damage crops by interfering with their biological systems. These substances work through different mechanisms. Contact action kills the insect upon physical exposure to the compound. Systemic insecticides are absorbed by the plant and move throughout its tissues, making the entire plant toxic to feeding insects. Neonicotinoids are a widely used class of systemic insecticides. Pyrethroids are synthetic compounds that mimic natural compounds found in chrysanthemums and often act via contact.
Fungicides
Fungicides manage fungal diseases that can devastate crop yields and storage quality. These chemicals protect plants by preventing fungal spores from germinating on the surface or by inhibiting the growth of an established infection within the tissue. Copper compounds, for instance, have historically provided control against a range of fungal and bacterial issues. Proper application of fungicides is timed precisely to protect the plant during periods of high disease risk, such as cool, wet weather or stages of rapid growth.
Chemicals for Plant Nutrition and Soil Health
Beyond protecting crops, farmers ensure plants receive adequate chemical elements for healthy growth through the application of fertilizers. These inputs supply necessary nutrients that may be depleted in the soil or naturally insufficient for optimal crop development. The required elements are divided into two main groups based on the quantity a plant needs.
Macronutrients
Macronutrients are elements required by plants in large amounts, identified by the abbreviation N-P-K (Nitrogen, Phosphorus, and Potassium). Nitrogen (N) is fundamental for chlorophyll production and vigorous leafy growth. Phosphorus (P) plays a significant role in root development, energy transfer, and seed formation. Potassium (K) helps regulate water movement, fruit formation, and overall plant health. Secondary macronutrients, such as Calcium, Magnesium, and Sulfur, are also supplied to support processes like cell wall formation and enzyme activation.
Micronutrients
Micronutrients, or trace elements, are essential for plant health but are only needed in small quantities. These elements participate in biochemical processes, ranging from enzyme function to photosynthesis. A deficiency in any one micronutrient can severely limit crop yield and quality, illustrating the principle of Liebig’s Law of the Minimum. Fertilizers are applied using various methods, including broadcasting dry, granular compounds over the field or delivering liquid formulations directly to the soil or foliage.
Trace Elements
- Zinc
- Iron
- Manganese
- Boron
Compounds Used to Modify Plant Development and Application
A distinct set of chemical inputs is used to control the physical development of the plant or improve the efficiency of other applications. These compounds allow farmers to manipulate the timing and characteristics of the crop to meet market demands and improve harvestability. This specialized chemical management focuses on process modification rather than pest elimination or feeding.
Plant Growth Regulators (PGRs)
Plant Growth Regulators (PGRs) are chemicals, often synthetic versions of natural plant hormones, that influence processes like flowering, fruit ripening, and stem elongation. For example, PGRs containing auxins can thin excess fruit from a tree, ensuring the remaining fruit grows larger and of better quality. Other regulators, like those containing gibberellins, can delay ripening or improve fruit firmness to extend the harvest window. These compounds allow for precise control over the crop’s life cycle, such as applying growth retardants to prevent excessive height in grain crops like corn, which reduces the risk of lodging in high winds.
Adjuvants
Adjuvants are added to the spray tank to enhance the performance of a pesticide or PGR, though they are not active ingredients themselves. Surfactants, for instance, reduce the surface tension of spray droplets, allowing them to spread and stick better to the plant leaf. Drift retardants increase the viscosity of the spray mixture, resulting in larger, heavier droplets less likely to be carried off-target by the wind. By improving the physical characteristics of the application, adjuvants ensure active chemicals are delivered effectively to the intended target.
Ensuring Safe Use and Compliance Standards
The application of agricultural chemicals is subject to rigorous oversight to protect human health and the environment. The Environmental Protection Agency (EPA) evaluates the safety of all chemical products, including pesticides, and registers them only if they can be used without unreasonable adverse effects. This regulatory process involves setting legally permissible limits for chemical residues, known as tolerances, that may remain on or in food commodities.
Restricted Use Pesticides (RUPs)
For certain higher-risk chemicals, designated as Restricted Use Pesticides (RUPs), federal law imposes strict controls on who can purchase and apply them. Any individual who applies or supervises the use of an RUP must first be certified as either a private or commercial applicator. This certification requires training and demonstration of practical knowledge regarding proper handling, application techniques, and legal responsibilities.
Pre-Harvest Interval (PHI)
A core requirement for chemical application is the Pre-Harvest Interval (PHI), a mandatory waiting period between the final application of a product and the day the crop can be harvested. The PHI is specific to each chemical and crop combination and is printed directly on the product label. This waiting time is established through extensive testing, allowing natural processes like sunlight and rain to break down the chemical. This ensures that any remaining residue on the harvested product is below the tolerance level set by the EPA.