Source: blog-crop-news.extension.umn.edu/2018/12/biostimulants-what-are-they-and-do-they.html

What are biostimulants?

A legal definition of biostimulants has yet to be decided. However, the European Biostimulants Industry Council describes them as "Substances and/or microorganisms whose function when applied to plants or the rhizosphere is to stimulate natural processes to benefit nutrient uptake, nutrient use efficiency tolerance to abiotic stress, and/or crop quality, independently of its nutrient content."

There are many categories of biostimulants. The most popular are humic acids, seaweed extracts, liquid manure composting and beneficial bacteria and fungi.

• Humic and fulvic acids - parts of soil organic matter resulting from the decomposition of plant, animal, and microbial residues.
  • e.g. peat, mineral deposits of leonardite and soft coal 
  • Dark in Color
  • Can increase the cation exchange capacity
• Seaweed  Extract 
  • Derived  through different  extraction processes.
  • Soluble  powders or liquid.
• Liquid manure composting
  • Made by mixing manure water and a blend of proprietary materials thought to feed specific bacteria in the manure. This provides adequate conditions for microbial growth. The liquid is then used as a biofertilizer.
• Beneficial bacteria and fungi - concentration of bacteria and/or fungi in the soil that help with root growth.
  • E.g. Bacillus and Rhizobium fungi
  • Majority of products marketed toward large scale commercial agriculture.

Biostimulants have been shown to increase many factors that affect plant growth including, root growth, root diameter, soil water holding capacity, increased microbial activity leading to increased nutrient availability and many more. Most of the time, however, responses are highly variable. It depends on weather, soil type, organic matter content, tillage system, and the type of crop rotation. One thing to remember is that these products cannot provide nutrients and be considered a biostimulant. They do not affect a fertilizer, but can increase/speed up the process of availability.

What does the research say?

Most data on these products is for high value horticultural crops instead of a corn/soybean system. However, research at the University of Minnesota has shown that in most cases those products are ineffective and do not live up to the expectation. For example, the products thought to increase enzyme activity rarely do compared with plots that did not receive the treatment. Products thought to provide better overall growing conditions and increase grain yield also do not show any improvements when compared to untreated.

Recommendations

When thinking about using these products we recommend doing a replicated strip trial before integrating them into your entire operation. To see these products make a difference and pay for themselves, consider contacting a local or regional Extension Educator, or your crop adviser to help you set up a trial and interpret the results.

By: Anne Nelson and Paulo Pagliari
UMN Extension Nutrient Management 
Support for this project was provided in part by the Agricultural Fertilizer Research & Education Council (AFREC).