Do soil microbial inoculants hold the solution for future food security?


Safe, reliable access to nutritious food is a challenge for many nations, and Earth’s changing climate adds yet another level of complexity to an already difficult situation. Ensuring food security needs environmentally sustainable production, and that’s where soil microbial inoculants may be able to form one part of the solution.


Dr Maureen O’Callaghan and her team from AgResearch Ltd have reviewed the current literature to understand how introducing microbes into the soil may improve soil health.


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Hello and welcome to ResearchPod.  Thank you for listening and joining us today. In this podcast we are exploring how soil microbial inoculants can be used for sustainable agriculture. Soil microbial inoculants are a growing global market and Dr Maureen O’Callaghan from AgResearch Ltd, along with her team, have reviewed published research to discover their limitations and opportunities for use.


Our global population is constantly increasing, and the United Nations recently estimated that we had reached the milestone of eight billion people. Food security, that is to say having reliable access to nutritious food, is a challenge for many nations. Food production needs to be sustainable, with as few negative environmental impacts that can result from intensive agriculture practices as possible. The Earth’s changing climate adds an additional, and complex challenge for ensuring good crop productivity.


So far, improvements in crop growth and control of diseases and pests have been achieved, in part, using agricultural chemicals, also known as agrichemicals, such as synthetic fertilisers and pesticides. However, the overuse of these has resulted in environmental issues. For example, nitrogen and phosphorous are commonly used as plant fertilisers in agriculture. Unfortunately, increased use of these fertilisers has led to water quality deterioration as they drive faster growth of algae than the ecosystem can handle, leading to a reduction in oxygen and a breakdown of the natural habitat.


Residues from pesticides have been detected in the food chain and in some cases have also spread far beyond the site of their original use to otherwise pristine environments. Overuse of agrichemicals has also been linked to population decline in pollinators, which is another key global issue for food security. The loss of pollinators leads not only to lower crop yields,  but also impacts other  wild habitats.


Soil is widely acknowledged to be extremely important for crop productivity and society’s wellbeing, but there has been a significant reduction in soil quality as well as global soil loss as agriculture. We need more sustainable approaches for maintaining agricultural production while still ensuring protection of the natural environment for future generations. Soil microbial inoculants may be part of the solution. Dr Maureen O’Callaghan from AgResearch Ltd and her team have assessed published research literature to understand the opportunities and limitations of soil microbial inoculants.


It is widely recognised across the scientific community that soil microbes have the potential to protect seedlings from pests and diseases, and improve the uptake of soil nutrients in plants. There has been extensive laboratory research which shows that soil microbes can target a variety of problem areas and help to maximise crop productivity. Bacteria and fungi are being used as microbial inoculants in the growing global industries of biofertilisers and biopesticides in agriculture. By using bacteria and fungi, they avoid some of the environmental issues that come with the use of inorganic fertilisers and synthetic pesticides.


Different soil microorganisms can be introduced into the soil environment to perform different roles in biocontrol and plant growth promotion. Dr O’Callaghan and her team have reviewed the current scientific literature, which includes extensive laboratory testing and real-world examples of microbial inoculant use, to better understand their impacts and limitations.


Currently, biofertilisation is the most common use of soil microbial inoculants. Some microorganisms can ‘fix’ nitrogen in the soil, taking it from the atmosphere and combining it with other elements to create nutrient-rich compounds. These are taken up by plants, supporting healthy growth and development. Nitrogen-fixing microbial inoculants are most commonly found in the root systems of plants. Using nitrogen-fixing bacteria that form a symbiotic relationship for the growth of legume plants, such as those that produce soybeans, lentils, and chickpeas, has been standard practice for many years and can eliminate, or at least reduce, the need for nitrogen fertiliser to be added to the soil. Microbial inoculants have also demonstrated an ability to convert phosphorous into a form that can be more readily taken up by plants.


Scientists have also assessed a range of bacteria and fungi from different environments that support the promotion of plant growth using a wide range of mechanisms on a cellular level, often providing multiple benefits to the plant. For example, Trichoderma is a fungus that is used worldwide to enhance plant growth through the control of soil pathogens, improving resistance to disease and insects, and increasing the development of root systems. There has been less research into the use of bio-inoculants for the control of soil-dwelling invertebrate pests, but as many of them target seedlings and the root systems of adult plants, introducing microorganisms that can control damaging insect populations is likely to be one of their future uses.


Soil microbial inoculants have key roles in mitigating the effect of climate change. There is evidence that their use can improve plant tolerance to stressful conditions, including drought, temperature extremes, and increased salinity, all of which may occur as a result of Earth’s changing climate. Microbial inoculants can alter a plant’s root morphology to improve water uptakes from the soil, as well as stimulate a plant’s defence mechanisms to help overcome challenging environmental conditions.


Healthy soils are an important carbon sink, helping mitigate climate change, but they can also help control the amount of nitrous oxide in the atmosphere. Nitrous oxide is a greenhouse gas that is up to 300 times more powerful than carbon dioxide. The use of fertilisers can increase the release of nitrous oxide from the soil into the atmosphere, so it will be important for soil bio-inoculants to be able to provide plants with efficient fertilisation, minimising the release of nitrous oxide.


While it seems that soil microbial inoculants may hold the answers for improving crop productivity while also limiting negative environmental impacts, there are important considerations that must be taken into account before applying them to the soil. Firstly, it must be determined whether it is appropriate to apply the microbial inoculant product by asking whether it is truly needed. Each microbial inoculant addresses a specific limitation in the soil, therefore it is only beneficial to apply it to soil that needs it. For example, there is little point introducing a microorganism that helps provide missing nutrients into a soil that needs to combat a disease, and vice versa.


Further considerations include whether there are hostile soil conditions for the microbial inoculant, as the soil structure and physicochemical properties must suit the bacteria or fungi. Each microorganism requires specific environmental conditions for optimal survival. The application strategy of the microorganism to the soil environment must also suit both the organism and the soil. Dr O’Callaghan and her team have noted that whilst many of the microbial inoculant products currently on the market are a single species of microorganism, researchers have agreed that the best strategy is likely to be a mixture of microorganism species with the ability to target the challenges to crop productivity.


Finally, Dr O’Callaghan explains there is a growing awareness of the need to protect the indigenous microbial diversity in soils, as introducing a foreign bacteria or fungi could have a devastating effect. There are also biosecurity concerns if microbes are moved across borders. If inoculants are used too freely across widespread areas, it may cause invasions of microbial species, or improve conditions for invasive plants to the detriment of crops and the local ecology.


As the need for new tools to support sustainable farming practices grows, so too does the microbial inoculant industry. Many of the products currently on the market have not been scientifically validated and we need to better understand how they work. It’s also important to put controls in place to ensure their use is appropriate. Further research is required, as well as validation in the field –  not just in controlled laboratory settings. There are broad considerations required before the application of bio-inoculants, and we need to understand how they will impact existing ecologies. Microbial inoculants are contributing to sustainable crop production with reduced environmental impacts, but further research is needed to ensure that they are produced and used according to guidelines based on sound scientific evidence. High quality, well researched microbial inoculant products used correctly will be part of the toolbox needed to contribute to our future food security.


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