There is a growing interest in the use of biostimulants and biofertilizers in crop production including agronomic, vegetable, fruit and ornamental horticulture crops.  Matt Kleinhenz, OSU Extension Vegetable Production specialist, and some of his graduate students have been evaluating some of these products the past couple of years.  The following article comes from the July 5 issue of the OSU Extension VegNet newsletter available on-line at: http://vegnet.osu.edu/newsletter.

          Naturally-occurring microbes dwelling in the root zone are invisible, abundant, and influential.  Some affect crops in either clearly negative or positive ways, while the effects of others are unclear.  Over many years, people have identified microbes that can help crops grow faster, produce more, and/or withstand stress (e.g., moisture, fertility) more successfully.  As a result, beneficial microbes, usually certain bacteria and/or fungi, are included in products sold as biostimulants and biofertilizers.  Various types of evidence indicate that manufacturing and selling these products is a huge industry in the U.S. and Europe and that more and more growers experiment with or use them in field, high tunnel, and greenhouse settings.

          However, growers say that there is a lot to learn about getting the most from microbe-containing biostimulants and biofertilizers.  People agree that the process involves selecting the correct product for the crop (i.e., a productive crop-microbe combination), storing and handling the product correctly, and applying it at the right time, at the right rate, to the right place, and in the right way.  Research and on-farm tests have not provided all the ‘rights’ for most crop-product combinations.  Still, one trend currently stands out: microbe-containing biostimulants and biofertilizers tend to have the greatest effect where background soil fertility is low to moderate, not extremely low or high.

          Different explanations are given for this trend. One says that microbes in the products are unlikely to colonize crop roots when fertility levels, perhaps especially nitrogen (N), phosphorus (P), and potassium (K), are high.  According to another explanation, microbes in products cannot survive when fertility levels (including carbon) are extremely low.  These soils lack enough nutrients to support microbial life (at least enough to form productive associations with crop roots).

          There are three take-aways from research and on-farm tests regarding the influence of soil fertility on the efficacy of microbial biostimulants and biofertilizers.  One is that responses to inoculation tend to be greatest where soil fertility levels are low to moderate: enough to support microbial life but low enough to promote colonization of crop roots.  A second is that using certain products may allow growers to reduce the use of synthetic and other sources of fertility (e.g., N, P, and K) by ten to thirty percent without reducing yield.  A third is that application rarely harms the crop.  So, some growers apply microbial biostimulants and biofertilizers as an “insurance policy.” Unfortunately, whether these insurance applications actually enhance profit is another question.   Growers who try these products are encouraged to leave some control strips in the field or planting that are not treated with the product to determine if there is some positive effect or benefit.

          Developing guidelines for using microbe-containing biostimulants and biofertilizers most effectively will take teamwork, with contributions from researchers, educators, growers, and manufacturers.