Biologicals in agriculture are products derived from natural sources, including living microorganisms, plant extracts, and other organic materials. Farmers use them to manage crop health and productivity by promoting plant growth, enhancing nutrient availability, and protecting crops from pests and diseases. Unlike conventional synthetic chemicals, biologicals complement existing farming practices, supporting soil health and environmental sustainability. They help improve plant resilience under various growing conditions.
Defining the Core Categories
The term “biologicals” encompasses three main categories, defined by their primary function in the crop system. These distinctions are based on the product’s mode of action, whether for protection, nutrition, or growth enhancement.
Biopesticides
Biopesticides, often called biocontrols, manage pests, diseases, and weeds. This category includes microbial biopesticides, which contain living organisms like bacteria or fungi that target specific pathogens or insect pests. Biochemical biopesticides utilize naturally occurring substances such as plant extracts, pheromones, or minerals to control pests. These products are important components of integrated pest management (IPM) strategies.
Biofertilizers
Biofertilizers contain living microorganisms that enhance the availability of nutrients to the plant. These microbes, such as certain bacteria and fungi, facilitate natural processes that release or capture essential elements, rather than supplying nutrients directly. For example, Rhizobium bacteria form a symbiotic relationship with legume roots to fix atmospheric nitrogen. Other microbes, like phosphate-solubilizing bacteria, convert insoluble soil nutrients into forms that plants can readily absorb.
Biostimulants
Biostimulants are substances or microorganisms that stimulate natural processes to benefit plant growth and stress tolerance. They are not fertilizers or pesticides, as they do not primarily supply nutrients or directly control pests. Biostimulants activate internal plant mechanisms, improving nutrient use efficiency and enhancing overall crop quality. Common examples include seaweed extracts, humic acids, and amino acids, which help plants cope with abiotic stresses like drought, heat, or salinity.
Biological Functions in Soil and Plant Health
The effectiveness of agricultural biologicals stems from the specific interactions they initiate within the plant and its surrounding environment, primarily the rhizosphere. These functions go beyond simple input provision, focusing on triggering complex biological and chemical processes. Mechanisms range from nutrient transformation to the induction of internal defense pathways.
Nutrient Cycling Enhancement
Biofertilizers enhance the natural cycles that make nutrients available for plant uptake. Nitrogen-fixing microbes, such as Azotobacter or Rhizobium, convert atmospheric nitrogen gas into usable ammonium through nitrogen fixation. This pathway reduces the need for synthetic nitrogen fertilizers, which require significant energy to produce. Other beneficial microorganisms perform phosphate solubilization, releasing phosphorus that is often chemically bound and unavailable in the soil.
Mycorrhizal fungi extend the plant’s root system by forming a vast hyphal network in the soil. This symbiotic association increases the surface area for nutrient and water absorption, improving the uptake of elements like phosphorus. Microbial communities also accelerate the breakdown of organic matter, ensuring a steady supply of micronutrients. These actions improve soil fertility and the overall efficiency of nutrient use.
Stress Tolerance Induction
Biostimulants help plants build resilience against environmental challenges, a process known as abiotic stress tolerance. When facing drought or extreme temperatures, biostimulant compounds like amino acids can trigger the production of protective molecules called osmolytes. These molecules help regulate water balance inside plant cells, minimizing damage during periods of water scarcity or high heat. Some biostimulants also influence root architecture, leading to deeper root systems that are more effective at scavenging water and nutrients under stress conditions.
Disease Suppression and Antagonism
Biopesticides employ several mechanisms to suppress disease-causing organisms in the soil and on plant surfaces. One common action is antagonism, where beneficial microbes directly compete with pathogens for space and food resources. Other microbial biopesticides work through direct parasitism, where the beneficial fungus or bacterium attacks and consumes the target pathogen’s cell wall. Some microbes also produce natural antimicrobial compounds, such as antibiotics or enzymes, that inhibit the growth of disease-causing fungi and bacteria.
Application Methods and Usage
Integrating biologicals into modern farming requires specific application techniques to ensure the products reach their intended target and remain active. Since many biologicals contain living organisms, delivery methods are tailored to optimize microbial survival and colonization. Application methods are designed to place the product precisely where its beneficial action is needed, such as in the soil, on the seed, or on the foliage.
Seed Treatments
Seed treatments involve applying a concentrated formulation directly onto the seed coat before planting. This method ensures that beneficial microbes, such as Rhizobium or certain biopesticides, are immediately available to colonize the root zone upon germination. Seed treatments provide protection to the young seedling and establish a beneficial microbial community early in the plant’s development.
Foliar Sprays
Foliar sprays apply liquid biologicals, such as certain biostimulants or fungal biopesticides, directly to the leaves and canopy of established plants. This technique is often employed for products intended to enhance photosynthetic efficiency or provide protection against airborne pathogens. The timing of foliar application is often coordinated with specific plant growth stages, such as flowering, to maximize the benefit.
Soil Drench and In-Furrow Applications
Soil drench or in-furrow applications deliver the biological product directly into the soil near the planting area, often using standard spray equipment or irrigation systems. In-furrow application, done during planting, places the product directly into the seed trench to optimize contact with the developing root system. Products come in various forms, including liquids, wettable powders, and granular forms. Their shelf life and compatibility with other inputs must be managed for successful field use.