In a healthy soil a small sample the size of the tip of your little finger or about 1 gram of soil contains about 10 billion microbes. That is not a misprint 10 billion. Soil microorganisms can be used for the good of a plant like breaking down residue and returning nutrients to your crop but can also be present in quantities that can overwhelm a plant like pythium and fusarium root disease.
As farmers and agronomists, we are often preoccupied with managing the physical and chemical aspects of crops: soil texture, chemical composition of soil, compaction, seedbed preparation, residue management and chemicals that directly suppress weeds, pest insects and disease. We often emphasize practices that directly manipulate these properties and pay less attention to cultivating microorganisms that surround our crop and dramatically impact its growth.
Science and industry understandably recognize the relative ease of perfecting inputs that directly affect crops and pests, in contrast to complex microbial systems that respond to a myriad of different factors. However, we know that microorganisms above and below ground have profound effects on plant growth and vice versa.
The practice of introducing and nurturing beneficial microbes – plant-growth promoting rhizobacteria (PGPRs) – has increased, especially where regulations or availability limits fertilizer use or where diseases are resistant to conventional fungicides. Some farmers even refer to these microbes as their livestock as these organisms account for thousands of pounds of living biomass per acre. In the Corn Belt, we are seeing more microorganism-based products, including our in-house Progressive Crop Technology (PCT) products.
• dissolve nutrients, making them chemically available to plants;
• release hormones to stimulate root growth;
• produce chelates that improve micronutrient availability;
• physically deliver nutrients to plants;
• provide additional sites on roots’ nitrogen-fixing nodules;
• reduce plant stress;
• compete with and produce antibiotics that suppress plant pathogens;
• and stimulate the plant’s own immune system.
PGPRs make phosphorus and micronutrients more available for plant use by directly producing acids or stimulating plants to produce acids to dissolve phosphorus. PGPRs also produce siderophores, a kind of chelate that wraps around nutrients and protects them from both soil tie-up and use by pathogens.
Another benefit of PGPRs is the production of hormones that influence plant growth. Many produce IAA, a kind of auxin that encourages lateral root development. The result is a better-branched root system with more root hairs. In legume crops inoculated with nitrogen-fixing bacteria rhizobia, these additional root hairs provide more sites for nodule development. Even more nodules can be produced if the seed is inoculated with both rhizobia and a secondary bacteria that increases root hair development.
Plants inoculated with beneficial soil bacteria have shown reduced responses to heat stress. In this way, beneficial bacteria may reduce plant stress similar to strobulurin fungicides such as Headline and Stratego.
PGPRs also can reduce disease in at least four ways:
1. Crowding – Crowding root zones and leaf surfaces with good bacteria, they reduce sites where pathogens establish.
2. Competition – Beneficial bacteria steal nutrients from pathogens.
3. Antibiotics – Many beneficial bacteria produce their own antibiotics to fight off pathogens.
4. Immune Stimulation – Beneficial bacteria stimulate the plant’s own immune system to defend against disease.
At PCT | Sunrise, we have included beneficial microorganisms in our starter and foliar fertilizers for years. We comb through dozens of peer-reviewed university studies from around the world to identify which species are best to include in our products. Organisms are selected for biological benefits, compatibility with other ingredients and shelf-life in our products. While our exact species are trade secrets, we select spore-forming bacteria that are able to quickly enter dormancy under adverse conditions and germinate as conditions improve.
Beneficial bacteria/PGPR technology is here to stay. In the face of increasing regulations and pest resistance, they represent a win-win technology for growers who seek to improve yield and conserve the environment. Emerging technologies to identify and engineer these organisms will continue their advance in agriculture.