Microbe Mastery – Inoculums for Disease Management & Nitrogen Fixing
The use of biological inoculums in farming amounts to re-charging the life force in the soil to reap the benefits of a new, task-specific workforce. There are specific inhibitory bacteria or predatory fungi that are the mainstay of resilient soils and plants. The six organisms with most promise in this context include mycorrhizal fungi, Trichoderma, Pseudomonads, Bacillus strains, Azotobacter and Nitrogen-fixing Endophytes.
Mycorrhizal fungi are a critical component of this protective team. There is comprehensive research linking plant resilience to mycorrhizal colonisation. Part of this increased defence capacity comes from the biological delivery of phosphate (arguably the most important mineral for plant immunity, as it fires glucose production and is the building block for ATP which fuels the multiple enzymic reactions involved in resilience). There is also evidence that mycorrhizal fungi produce biochemicals that support an immune response in the plant. We have witnessed many cases of improved plant health and resilience following mycorrhizal colonisation.
Trichoderma is a cellulose digesting, free living fungi, which is often compromised by farm chemicals, including copper. Trichoderma does more than build humus, however, it is also a beneficial fungi that feeds upon a wide range of other organisms and it produces metabolites that further compromise the organisms. It releases acids that solubilise locked-up phosphate in your soils and most importantly, in this context, Trichoderma supports plant defence mechanisms via the production of protein-based immune supporters.
Pseudomonas fluorescens is a ubiquitous, protective bacteria that is seriously compromised by glyphosate and as this herbicide is widely used in all forms of agriculture, there is a question mark about the disease-suppressive capacity of these soils. A recent two year USDA study on soybeans showed dramatic reductions of beneficial pseudomonads and other beneficial organisms where glyphosate was used. These organisms produce a variety of anti-social compounds including hydrogen cyanide. However, Pseudomonas fluorescens also offer protection-based benefits involving frost events. Frost crystals are caused by ice nucleating bacteria and organisms that predate on these bacteria can effectively halt frost damage. Pseudomonas fluorescens is a competitive antagonist that lacks the ice nucleating protein and it has proven highly effective as a tool to reduce frost damage in many crops.
Nitrogen Fixing Bacteria Explained
Nitrogen fixing bacteria are single celled organisms that are essentially miniature urea factories, turning N2 gas from the atmosphere into plant available amines and ammonium via a specific and unique enzyme they possess called nitrogenase. Although there are many bacteria in the soil that ‘cycle’ nitrogen from organic material, it is only this small group of specialized nitrogen fixing bacteria that can ‘fix’ atmospheric nitrogen in the soil.
Most growers are familiar with legume nitrogen fixing bacteria called Rhizobium and the colonies they form inside nodules, visible white lumps on the roots of legumes. It is well established that specifically selected, high performance strains of these symbiotic legume bacteria can fix between 50 to 200 units of nitrogen per season, depending on soil moisture. To do this job, these specific strains need to be inoculated into the legume seed to ensure their numbers are high enough to colonize each plant and to bring about a significant influence on the total nitrogen production. There are also selected endophyte strains which colonise a plants vascular system, utilising plant produced carbohydrates as an energy source in return producing plant available ammonium nitrogen.
The Plant – Bacteria Communication / Feedback System
N fixing bacteria use plant carbon as a high calorie energy source to fuel the biological reaction that converts N2 gas into plant available N compounds. Whether it be the soil dwelling species or the endophyte N fixing species, the plant is controlling the amount of energy (plant carbon) the N fixing bacteria receive to perform their N fixation function. As such the quantity of nitrogen being fixed for plant use is controlled by the plant itself. For example, when there is limited soil moisture nitrogen fixation slows down, dictated by the plants diminishing nitrogen requirements and subsequent frugal supply of carbon to the bacteria. When soil conditions are optimum, nitrogen fixation is maximized by the plant’s increasing supply of carbon to the bacterial colony, in turn increasing N fixation to meet the increasing nitrogen requirements. It works like a feedback system and assures the plant receives just the right amount of nitrogen it requires based on the growing conditions at the time.
Using beneficial microbes can reduce the reliance on expensive NPK products and chemicals, designed to control pathogens. If the right types of beneficial species are introduced to both the soil and plant, then natural Biological processes, including competition and microbial balance can occur.
A recent study conducted at Newcastle university looked at the benefits of applying pyroligneous acid (Pyro AG) and its effect on beneficial plant growth promoting bacteria. The study showed tremendous enhancement of colony-forming units of many strains of beneficial bacteria, including nitrogen fixers, bacillus and pseudomonas, when Pyro Ag was applied at weak concentrations on the soil.