In this blog SylgenBio Director, Romney Jackson, explores why the performance of biofertilisers can be variable, and how we can manage their in-field environment to optimise productivity.
Historically, biological inputs have had variable performance in the field and have earned a reputation for being ‘muck and magic’.
But is it fair?
There is little doubt that the regulatory and approvals processes governing the authorisation of biological inputs have not kept pace with the development of products. And no doubt, there are a few disingenuous individuals and organisations that have taken advantage.
However, there are many more who have been diligent in their research and spent considerable time and money formulating products that are highly effective.
The fact that many of the multinational crop protection manufacturers are now investing in biological solutions adds credibility to their potential, as does the development of organisations like the International Biocontrol Manufacturers Association (IBMA).
Performance in the field, however, continues to be variable. And in this blog, we’re going to explore why that’s the case, using biofertilisers and other biological solutions that are affecting soil and/or use soil-born microbes as an example.
Soil microbes need good soil structure
In dairy farming we optimise the environments our cattle live in. Indoors, we consider temperature, ventilation and bedding, for example and know that a sub-optimal environment will compromise cow performance.
The same is true for soil-born microbes. Beneficial bacteria and fungi thrive in soils that are well structured, Compaction restricts air flow, access to food sources and hinders movement and growth.
However, one of the benefits of plant growth promoting bacteria and fungi is improved soil structure. In producing the enzymes and metabolites that break down their food sources, they inadvertently excrete substances that hold small particles together. Fungi also produce a fine network of mycelia which acts as a net, holding these small aggregates together into macro-aggregates.
Together these two mechanisms help to maintain soil structure. But it is most effective, where soil structure is already good.
It’s a vicious cycle in both directions; where soil structure is bad, microbial activity suffers and their ability to enhance soil structure is impeded, but where soil structure is good, these microbes thrive and they will maintain or even enhance aggregation, enabling soils to be more resilient to extreme conditions like, floods, droughts and traffic.
Soil microbes need food
Microbes’ abilities to cycle nutrients by breaking down dead organic matter are widely known but it is only part of the story and the devil, as ever, is in the detail.
The organisms that break down dead and decaying organic matter are feeding on ‘labile carbon’ – that’s the readily decomposable fraction of soil organic carbon. In doing so, the microbes release many other nutrients that the plants use for their life processes such as phosphorous, nitrogen and potassium.
Where soils are devoid of trash, crop residue, organic fertiliser or other dead or decaying organic matter, most beneficial soil microbes will not thrive. Labile carbon is their primary food source and while they might not die where it is absent, they won’t thrive and multiply and provide the continual benefits that are claimed and which we have come to expect.
Soil microbes need incentives
We often marvel at the plant root and microbial interactions. And it is incredible that some bacteria and fungi have developed symbiotic relationships with plants. But these relationships rely on plants attracting microbes with carbon-rich exudates. If there’s no reward for the microbes, they won’t reciprocate with the plants. And, when there are no healthy roots, there are far fewer carbon-rich exudates and fewer opportunities for colonisation.
Yet these microbes are able to do many things humans and plants can’t (or can’t effectively) including:
– access water that roots can not reach (particularly in drought conditions when water is scarce);
– release nutrients from dead organic matter, rocks and other sources inaccessible to plants roots;
– and, trigger plant defences to pests and pathogens.
Plant requirements vary throughout the year depending on conditions and growth stage, for example. In conventional farming systems we’ve tried to back-fill some of the roles microbes play with irrigation and fertilisers but we can’t quickly and easily tell what plants need and when. By the time we’re seeing the symptoms of water or nutrient deficiencies (or had tissue sample results returned from the lab), plants have already lost yield potential.
However, plants have evolved a mechanism that effectively ‘tells’ the microbial what they need. By changing the chemical composition of their exudates they attract microbes with specific capabilities and in doing so, can affect which nutrients they receive. In comparison with fertiliser applications which tend to be based on averages or tissue samples, the plant-microbe relationship is far more responsive to the conditions and plant needs.
Soil microbes need a pH of 5.5 – 7.5
The microbes commonly found in biological fertilisers are sensitive to pH, as are the enzymes they excrete to break down organic matter. A soil pH of 4.5, for example, will negatively affect the microbes’ ability to metabolise i.e. feed and use the energy and nutrients for life processes.
Optimising the performance of biological inputs in the field
As with any living being we cannot expect microbes to thrive in an unsuitable environment.
Ensuring soils are well aggregated will ensure that any beneficial bacteria and fungi added are able to breathe. Leaving crop residue or applying another source of organic matter will ensure that they are well fed. And having living roots in the soil at application will facilitate the forming of symbiotic relationships. Correcting soil pH is also important.
SlurryForSoil is designed for the relatively hostile environment of a slurry store. Its 18 different bacteria and fungi are more resilient to unfavourable conditions in comparison with many other beneficial microbes,.
However, it is no coincidence that those on-farm trials where SlurryForSoil has dramatically increased grass growth have taken place in fields where soil is well structured and the host farmer regularly checks soil pH.
Optimising the use of biological inputs isn’t that different from getting the best from conventional products and when they are used alongside good farming practices, products like SlurryForSoil can make a significant contribution.