By James Hoorman, Hoorman Soil Health Services
Biologicals are simply live microbes that perform many important soil and plant functions. Some microbes are biofertilizers (microbes that improve plant nutrition); biopesticides (microbes that control or kill pathogens, insects, other pests); others produce plant growth hormones or help plants survive environmental stresses (drought, temperature, soil pH, wet soils) etc. Biologicals are starting to become more common as farmers learn how to take advantage of the benefits they supply, especially in healthy soils and plants.
Farmers have inoculated legumes and clovers with bacteria to fix nitrogen (N) in nodules. Now farmers can inoculate plants for bacteria that are free living and also supply N to all plants. There are at least 200 strains of bacteria that are known to live inside plants and around plant roots. With the new discovery of rhizophagy (plant roots eating bacteria for nutrients and growth), applying biologicals may soon be a common practice.
Corn (C), Soybeans (S) and Wheat (W) share several beneficial bacteria. A broad group of bacteria in the genera Bacillus and Pseudomonas are widespread in nature, soil, and all around and within plants. Bacillus are gram positive (G+) bacteria found in C-S-W that help with plant nutrient acquisition (especially zinc), provide plant hormones for increased growth, decrease plant pathogens, and decrease plant stress. Pseudomonas (P) bacteria are gram positive (G+) and help control fungus while promoting above and below ground growth. There are at least 191 P. species, including P. syringae which increases the freezing point of water. Many solubilize phosphorus and help plants avoid many stresses (drought, climate change, pathogens).
Corn and soybeans also share beneficial Endobacterium (E.) and Agrobacterium(A.) bacteria. E. species improve soil porosity, some fix N and solubilize phosphorus, protect from pathogens, live in plant seeds, and increase plant growth. Farmers need to be careful when they use seed treatments because some bacteria can die. Bacteria in seeds increase germination and seedling survival. Some bacteria seed species date back thousands of years, but some have been lost over time due to either changing farm practices or changing soil environment. A. species are G-, are free living N fixers, promote plant growth, but also transfer DNA to plant cells. This A. species, like many bacteria species, can also cause plant damage as a pathogen called Crown Gall. So bacteria may be helpful in healthy soils under most conditions, but when conditions get tough and they want to survive (especially in unhealthy soils), they can become pathogens.
Corn (C ) has at least 7 additional beneficial bacteria genera: Achomobacter, Curtobacterium, Herbaspirillum, Microbacterium, Micrococcus, Paenibacillus, Serratia. While the names are hard to spell and even harder to pronounce, I list them because if you want to start using biologicals, you have to have the right ones. Many are already in our soils, especially the common ones. Some do well in the greenhouse, but not as well in the field, probably due to soil conditions. However, yield increases of 16-32% have been shown in good soils with improved plant growth. That makes them highly valuable if they work. Some soil bacteria, although fairly rare or in small numbers, can create huge benefits while needing only a small plant meal.
Soybeans (S) benefits from an addition 4 bacteria genera: Rhizobium, Klebsiella, Agrobacterium, and Pantoea. Wheat (W) benefits also from Azospirillum, Herbaspirillum, Klebsiella, and Micrococcus. For tomato growers: Pseudomonas and Escherichia, strawberries: Bacillus and Sphingopyxis, potatoes (all the corn bacteria species plus Acinetobacter, Comamonas, and Methylobacterium). Many stores and the internet can help you find these beneficial bacteria that stimulate plant growth and increase plant yield. While I have given you general bacteria groups called genera, in many cases you will be buying individual bacteria species. How do you apply biologicals? That varies by product, so follow their directions. In general, avoid direct sunlight, apply on a cloudy day. Keep them cool and store in a refrigerator, generally around 500F. Hot temperatures and sunlight (UV rays) eliminate many bacteria. Bacteria need adequate moisture to survive so a little water or rain after applicationis a good thing. Compost, humus and a little manure are good food sources and are also, good sources of beneficial bacteria (as are red worms). Some biologicals are applied to seeds with a nutrient coating to get them off to a good start. Others can be applied at the base of the plants to the roots and some are foliar applied to leaves. Finally, watch the soil pH, most beneficial bacteria can survive a 6.5-7.0 pH, but that varies by species. To increase biological survival, follow the 4 soil health principles: minimize or eliminate tillage, keep surface residue, use cover crops (live roots), increase soil biodiversity (rotate crops).