Biologicals as Fertilizers in Organics
Fact Sheet | Biologicals as Fertilizers in Organics
WHAT ARE BIOLOGICALS?
Biological amendments, or biologicals, is a broad term that includes other sub-categories. Biologicals are typically understood in three categories, depending on their effect: Biofertilizers are intended to make more nutrients available to the plant; Biostimulants are meant to stimulate plant growth or otherwise enhance crop productivity; and Biopesticides protect plants from pathogens or insects. While healthy, well-managed soils often contain these microbes and their benefits, many companies sell individual strains of microbes to perform specific functions.
The U.S. Farm Bill defines 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.” While biologicals are generating a lot of excitement in farming recently, they have been used in various forms since agriculture began. Farmers learned that when growing a crop in a new field, if they added soil from a field in which the crop was previously grown, it often did better.
Biofertilizers
Biofertilizers are not nutrients themselves, rather, they convert existing nutrients into plant-available forms. These fertilizers contain live beneficial microorganisms, the goal in application is for them to act as inoculants - reproducing in the soil so that they have a greater effect. Below are the main types of biostimulants that are available:
• Nitrogen-fixing bacteria fix atmospheric nitrogen into the soil, making it plant-available.
- Symbiotic biofertilizers work with plant roots to fix atmospheric nitrogen. The Rhizobium spp. inoculant used with soybeans and many other legumes is a classic example.
- Asymbiotic biofertilizers are free-living in the soil, and also fix atmospheric nitrogen. Many different companies produce them. These products may be an existing microbe, or they may be genetically engineered in a lab. Examples are Envita (Azotic, Guelph, Ontario, Canada), Utrisha (Corteva Agrisciences, Indianapolis, IN), ProveN (Pivot Bio, Berkeley, CA), and MicroAZ-ST (TerraMax, Bloomington, MN)
• Phosphorus-solubilizing bacteria are microbes that break down insoluble soil phosphorus into plant-available forms.
• Mycorrhizal fungi work with crop roots to increase nutrient uptake (particularly phosphorus). They can also help with salt stress and protect against plant pathogens.
Biostimulants
These biostimulants contain inert materials that improve either the soil’s functioning, by stimulating or feeding microbes, or the plant’s natural physiological processes. Below are the main types of biostimulants that are available:
• Enzymes increase the availability of nutrients in soil.
- Phosphatase enzymes increase phosphorus availability.
- Other enzymes involved in soil carbon cycling can accelerate the mineralization of nutrients for future crop uptake.
• Humic and fulvic acids can improve soil structure and are an energy source for many microbial species, which can stimulate soil nutrient cycling and availability.
• Seaweed extracts can mitigate drought stress when foliar-applied or promote root growth and soil microbial activity when applied to soil.
• Sugars (like corn syrup, molasses, etc.) provide a direct energy source for microbes when soil-applied, or help the plant mitigate stress when applied as a foliar.
HOW ARE THEY USED?
Because there are so many biological products available, there is not a single best practice for using them. Rather, the best use depends on understanding your particular product.
Biologicals are most commonly applied as foliar sprays; second most common are soil-applied, mostly in the furrow; and the third most common application method is as seed treatments. You can see that biologicals are most often applied to or near a seed or living roots.
Living biostimulants need to be handled with more care than inert products, because the goal is that they are healthy when applied and multiply quickly. Storage conditions for these products are also important. They should be kept in a cool place (the refrigerator is good) and, once mixed, used as quickly as possible. Leaving inoculants in a hot truck or outside exposed to the weather can kill some of the organisms and reduce their effectiveness. Also be wary of adding any additional products to the inoculants before applying them, because some materials can kill or weaken the product.
DO THEY WORK?
The efficacy of these products depends on many factors, including environmental conditions, crop species and cultivar, application method, concentration, species composition, timing of application, and more. Additionally, many of these products are new enough that there is not conclusive research confirming their effects on yield.
Generally, biofertilizers and biostimulants are best used together, inoculating the soil with beneficial microorganisms, biofertilizers, and providing them with their preferred food source, biostimulants. Most biologicals will enhance fertilizer use efficiency, but they will not replace the fertilizers, and they may cause other issues. For example, phosphorus-solubilizing bacteria are used to extract unavailable phosphorus out of the soil, but how many years can a farmer do that before there is no more phosphorus left?
ON-FARM TRIALS
Since the efficacy of biologicals is so environment-specific, on-farm trials are a great way to assess biologicals. Consider doing a replicated strip trial before integrating a new biological product into your entire operation. If you do, keep these points in mind:
• To see if a product makes a difference and pays for itself, consider working with an Extension Educator or a crop adviser to help set up a proper trial and interpret the results.
• If testing a biological product with different nutrient application rates, for example full rate nutrient vs. 30% less nutrient + biological product, make sure to use a strip with 30% less nutrient and no product to make sure that any effect observed is due to the biological product, not the fertilizer.
• If a company approaches a farmer with the lab-based results of their biological product and would like to get field-based results through an on-farm trial, make sure the farmer is not paying for the research. The company should provide the product for free and compensate the farmer for their time setting up and harvesting the trials.
TAKE AWAY
On-farm trials are crucial for farmers to understand their effect on their operation, because the efficacy of biologicals depends on so many farm-specific conditions.
BIOLOGICALS IN ORGANIC SYSTEMS
Most research on biologicals is conducted in conventional systems. Would biologicals be more or less efficient in organic systems without mineral fertilizers and pesticides to interact with them? Would they have even less of an effect in an already diversified system with manure and compost inputs? Consider that:
• Nitrogen-fixing bacteria are often limited by low soil carbon. Organic systems often have higher carbon inputs with green and animal manure, so nitrogen-fixing bacteria might work better in an organic system if they are soil-applied.
• Without the use of fungicides, fungi-based products may be more effective in organic systems.
• Plant protection products might be more effective in organic systems since they work best as part of an integrated system, not stand alone, and because the pathogen pressure might be lower to start with thanks to longer crop rotations.
FAST FINANCIALS
Compared to other products like pesticides and fertilizers, biologicals are fairly inexpensive.
A biological seed treatment for corn runs about $10 per acre. For corn yielding 170 bushels per acre, and selling for $9 per bushel, if the biological seed treatment increased yield by just 0.07% (just over 1 bushel per acre) it would pay for itself.
Additionally, there is typically little to no additional application cost because biologicals are often applied during existing passes over the field, such as during planting.
Research reported in this publication was supported by The Organic Center and the Foundation for Food & Agriculture Research under award number TOCFFAR-EXT-002. The content of this publication is solely the responsibility of the authors and does not necessarily represent the official views of The Organic Center and the Foundation for Food & Agriculture Research.