Seed World

Are Biostimulants Finally Finding Their Place?

Biostimulants were considered “snake oil” for decades, but with a new definition in the Farm Bill, are they finally finding their place amongst seed treatments in the United States?

Biostimulants, a nebulous group of biological products intended to enhance crop production, may finally be coming into focus.

These products have a long history of agricultural use, yet they lack a legal definition in the United States. The painstaking observations of Aristotle (384-322 B.C.), a Greek philosopher known as the father of biology, made the first recorded reference to the value of using supplemental products to enhance plant growth. Now, more than two millennia later, biostimulant materials are being marketed to agricultural and horticultural producers. Many products introduced during the last century had little more validation than the promoters’ promise to “trust me.” Unscrupulous claims earned biostimulants a reputation of being little more than snake oil. That cloud of doubt is being dissipated as new scientific understanding of plant physiology, biotic and abiotic seedling stresses, and the soil microbiome is leading today’s scientists to develop new, more effective biological products. Today, marketing these biostimulant products to U.S. growers is being hampered by outdated legal restrictions.

“To market a biostimulant product in the United States, it is necessary to ‘fit’ it into the existing categories as either fertilizer, soil amendment, plant amendment, or beneficial substance,” says Tom Kroll, Nufarm product and technical manager, seed treatments. “The choice of one category over the other depends on the composition of the product, the desired claims and benefits, and the supporting data that is available. Unfortunately, the category definitions and requirements are not well harmonized among the states. This leads to not only variations in label formatting and content, but also variations in the types of supporting data required, especially efficacy.

“While it may be possible for a biostimulant that is, for instance, marketed on its nutrient content, to achieve one single label across the United States, this is not the case for a product that is a soil amendment, plant amendment, or beneficial substance,” Kroll says. “On average, four to five different label versions are needed for a soil or plant amendment in order to meet varying state requirements and label formats. This is challenging for companies that want to distribute soil or plant amendment products throughout the United States.”

Companies are also limited regarding the claims they can make for these products. Terms like ‘biostimulant’ and ‘stimulate’ are not acceptable in most states. In addition, state regulators may interpret claims regarding improvement in plant growth to be pesticidal, thereby triggering the need to register the product as a pesticide.

What Are Biostimulants?

At the moment, biostimulants fall into a category of products for which there is no legal definition. These biological products fall into a category of microbial products that can best be described by what they are not.

“On one side of the spectrum of agricultural products are pesticides including biopesticides that protect plants by dealing with disease or insect pests. Biostimulants are not pesticides. They are not intended to address pests,” says Keith Jones, Biological Products Industry Alliance (BPIA) CEO. BPIA is a trade organization that promotes the responsible development of safe and effective biological products, including biopesticides and biostimulants. “On the other side of the spectrum, are fertilizer products including biofertilizers. Biostimulants are not fertilizers. They do not add nutrients to the plant, although they may increase a plant’s nutrient utilization efficiency. Biostimulants fall somewhere in between these two established categories of products.”

The BPIA along with the entire biostimulant industry and other industry trade groups including the American Seed Trade Association worked with federal legislators and agencies to include language in the Agriculture Improvement Act of 2018 (the 2018 Farm Bill) to legally define or describe biostimulants. The result of those efforts is a proposed description of biostimulants with a mandate for the USDA to submit a legal definition by 2020. The language in the Farm Bill is a general description of biostimulants, not a legal definition. The 2018 Farm Bill identifies biostimulants as:

“a substance or micro-organism that, when applied to seeds, plants, or the rhizosphere, stimulates natural processes to enhance or benefit nutrient uptake, nutrient efficiency, tolerance to abiotic stress, or crop quality and yield.”

The Farm Bill is written to acknowledge that biostimulants are a new product category. This gives the USDA and the EPA a year to come back to Congress with a plan on how to regulate these new products.

“By the end of 2019, we hope to see a recommendation to Congress on how to define biostimulants and then how to regulate and market them,” Jones says. “Ultimately, we would like to have a global legal definition.” For us, the 2018 Farm Bill description is a huge step forward for the biostimulant industry. The term ‘biostimulant’ has been around since the late 1990s but depending on who is talking; it can mean very different things. While efforts are moving forward to define biostimulants, it still means that manufacturers and marketers cannot use the term to describe or market their products. Our goal is for manufacturers to have one label for all 50 states where they can use the term biostimulant and make biostimulant claims.”

“Biological and biostimulant effects vary for many reasons. That is why it’s necessary to look at average performance over time and then ask if the good years outweigh years in which the impact was minimal or nothing at all.” Tom Kroll

Biostimulant Substances and Microorganisms

With no legal or regulatory definition of plant biostimulants, listing and categorizing the substances and microorganisms involved is somewhat indefinite. Nonetheless, there are some categories that are widely recognized by scientists, regulators, and stakeholders in both Europe and the United States. Patrick du Jardin at the Universite de Liege in Belgium, describes the main categories of biostimulant products used in agriculture and horticulture. 

Humic and fulvic acids. Humic substances are natural constituents of soil organic matter that result from the decomposition of plant, animal, and microbial residues. Humic substances also derive from the metabolic activity of soil microbes using these substrates. Most biostimulant effects of these acids refer to the amelioration of root nutrition. The variability in efficacy arises from the source material, the crop’s environmental conditions, and the dose and manner of application. Humic and fulvic acids are extracted from naturally humified organic matter (e.g., from peat or volcanic soils), composts, vermicomposts, or mineral deposits.

Protein hydrolysates and other N-containing compounds. Amino-acid and peptide mixtures are obtained by chemical and enzymatic protein hydrolysis from agro-industrial by-products. Direct effects on plants include modulation of N uptake and assimilation and the regulation of enzymes involved in N assimilation. Nevertheless, there is a growing safety concern of using protein hydrolysates derived from animal by-products in the food chain.

Seaweed extracts and botanicals. The use of fresh seaweeds as a source of organic matter and fertilizer is as ancient as agriculture, but the biostimulant effects of these sources have been recorded only recently. This has prompted the commercial use of seaweed extracts and purified compounds, which include polysaccharides (laminarin, alginates, and carrageenans) and its breakdown products. Seaweed extracts have been reported to provide anti-stress effects are also reported. Botanical substances extracted from plants have used in plant protection products although much less is known regarding their biostimulant activities than on their pesticidal properties so far.

Chitosan and other biopolymers. Chitosan is a form of the biopolymer chitin which is produced both naturally and industrially. The physiological effects of chitosan in plants are the results of its capacity to bind a wide range of cellular components, including DNA, plasma membrane, and cell wall constituents. Chitosan also binds to specific receptors involved in defense gene activation.

Inorganic compounds. Chemical elements that promote plant growth and may be essential to particular taxa but are not required by all plants are called beneficial elements. The five main beneficial elements are aluminium, cobalt, sodium, selinium and silicon are present in soils and in plants as different inorganic salts. These beneficial functions can be constitutive, like the strengthening of cell walls by silica deposits, or expressed in defined environmental conditions. Many reported effects of beneficial elements promote plant growth, the quality of plant products, and tolerance to abiotic stress. Although the modes of action are not yet fully established, these inorganic compounds influence osmotic, pH and redox homeostasis, hormone signaling, and enzymes involved in stress response. Their function as biostimulant of plant growth, acting on nutrition efficiency and abiotic stress tolerance are distinct from their fungicidal action.

Beneficial fungi. Plants and fungi have co-evolved since the origin of terrestrial plants. An extended range of relationships has developed over evolutionary times. There is an increasing interest for the use of mycorrhiza to promote sustainable agriculture, considering the widely accepted benefits of the symbioses to nutrition efficiency, water balance, and biotic and abiotic stress protection of plants.

Fungal-based products applied to plants to promote nutrition efficiency, tolerance to stress, crop yield, and product quality are receiving increasing attention, both as plant inoculants and as model organisms for understanding nutrient transfer between fungal endosymbionts and their hosts. Some of these fungi, mainly Trichoderma spp., have been extensively studied and used for their biopesticidal and biocontrol capacities. There is convincing evidence that many plant responses are also induced, including increased tolerance to abiotic stress, nutrient use efficiency, and organ growth. These fungal endophytes may be regarded as biostimulants, although their agricultural uses are currently supported by claims as biopesticides.

Beneficial bacteria. Bacteria interact with plants in all possible ways. As with fungi, there is a continuum between mutualism and parasitism. Bacterial niches extend from the soil to the interior of cells with intermediate locations in the rhizosphere and the rhizoplane. Associations my be transient or permanent. Some bacteria can be vertically transmitted via the seed. Bacterial functions influencing plant life cover extend to the biogeochemical cycles, nutrient supply, increase in nutrient use efficiency, induction of disease resistance, enhancement of abiotic stress tolerance, and modulation of morphogenesis by plant growth regulators.

Two main types of agricultural applications should be considered within this taxonomic, functional, and ecological diversity: mutualistic endosymbionts of the type Rhizobium and mutualistic, rhizospheric plant growth-promoting rhizobacteria (PGPR). Rhizobium and related taxa are commercialized as biofertilizers such as microbial inoculants facilitating nutrients acquisition by plants. PGPRs are multifunctional and influence all aspects of plant life: nutrition and growth, morphogenesis and development, response to biotic and abiotic stress, and interactions with other organisms in the agroecosystems.

A Positive Outlook for Biological Products

When BPIA was more narrowly focused on biopesticides in the early 2000s, there were only a few companies expressing interest in biostimulants. Nearly twenty years later, hundreds of companies have biostimulant products at various stages in their research and development pipeline. A biological market forecasting firm estimates that in 1999, the global biostimulant market was $250 million. By 2017, the market had expanded to $2 billion and is projected to reach $3 billion by 2021. Much of that expansion will come from what is happening in the European Union. That market is several years ahead of the United States with its regulations for marketing biostimulant products.

Several factors are driving this increase in the EU biostimulant market. First, there is more public and consumer interest and acceptance of biological products. The EU populace is becoming more environmentally conscience, and biologicals fit right in with that perception. Second, new technology tends to build on itself. The EU industry now has decades of data to support the efficacy of biologicals and dispel earlier images of these being unreliable products with inconsistent results. Development of seed-applied applications is one of the fastest-growing areas of biostimulant market expansion. Globally, Latin America is the fastest-growing market for seed-applied biologicals. Part of that is due to the region’s climate, which puts more abiotic stress on planted seeds and seedling emergence.

“For biostimulant products with clearly identified modes of action, reliable field data sets, and rigorous quality assurance, they will continue to grow as an essential component of the ag system,” according to Luis Copeland, Bayer’s head of Global Seed Growth. “In areas where growing conditions are optimal for the plant, these types of products might seem less appealing on the surface. At the same time, weather conditions and pest and disease pressures are hard to predict. When properly priced and placed, many growers may consider these products an ‘insurance’ of sorts to address variability. In areas with environmentally stressed conditions, these products can enhance the crop’s productivity capacity.” ¬†