Chemistry provided the answers to many agricultural challenges faced in the 20th century. Could microbiological advances provide solutions for the 21st century? Chloe Palmer finds out more.
The interactions between plants and microorganisms have fascinated biologists for centuries and the role of beneficial microbes in the uptake and assimilation of nutrients and water by plants is now well understood. Yet, it is only recently scientists have begun to look into how these associations might be exploited for the benefit of modern agriculture.
Robert Patten, managing director of PlantWorks, a UK company leading the production of beneficial soil microbe products for agriculture and horticulture, believes harnessing microorganisms for the benefit of arable cropping has enormous potential.
He says: “Microbiology is not as predictable as chemistry but the more we understand it, the more reliable it will become. Fungi and bacteria have the most relevance to agriculture because of their role in increasing plant efficiency and enhancing soil health.”
Ensuring a soil can support a healthy population of beneficial mycorrhizal fungi and bacteria is ‘as much about process as it is about intervention,’ according to Mr Patten.
“It is vital we begin to understand the principles of ‘smart rotations’ where we seek to protect and encourage beneficial soil microorganisms to increase crop yield and soil health.
“Most cereals and vegetables support this association, but there are a few, such as the Brassicaceae family, which do not. Growing brassica crops such as oilseed rape will mean a season without food for the mycorrhizal fungi and will have a serious effect on the population.
“Equally, leaving land as fallow with no fungal partner also depletes the community so the importance of cover crops to the maintenance of mycorrhizal populations is evident.”
Jamie Stotzka, bioagronomist with PlantWorks, says cultivations can also have a deleterious effect on mycorrhizae because deep ploughing disturbs the fungi and ‘chops up’ the mycelium, the mass of branching, thread-like filaments which enable the mycorrhizal fungi to access soil nutrients.
“A combination of farming practices known to be damaging to mycorrhiza fungi would be deep ploughing, followed by OSR coupled with the application of certain chemicals. Where such practices are used, the application of a mycorrhizal fungi inoculum to the following catch or cover crop can redress this imbalance.
“Extending the rotation to include legumes and other crops, such as linseed or spring cereals, will help support the mycorrhizae in the soil,” says Ms Stotzka.
PlantWorks has been working closely with universities and research institutes to gain a better understanding of how the beneficial micro-organisms in soils function with plants to help them develop practical microbial products which can then be drilled with, or applied as, liquid sprays to crops to improve performance.
But one of the most effective ways of introducing mycorrhizal fungi to the soil is with a cover crop, Ms Stotzka says.
“We supply seed merchants with the granular mycorrhizal fungi for mixing with cover crop blends and advise on the mixture compositions to ensure optimal performance.
“A combination of mycorrhizal fungi and a cover crop provides an excellent, low cost, method to augment native soil microbiology. For high value crops such as carrots, it is also possible to drill the granular product directly with the seed.”
Ms Stotzka says the management of mycorrhiza should form part of a long-term strategy to improve soil health as positive results can be observed over several years. The mycorrhizal fungi need only by added once in an appropriate rotation after a non-associating crop.
A mycorrhiza is a symbiotic association between a fungus and the roots of a vascular host plant.
The fungus provides a secondary root system for the plant which is considerably more efficient at nutrient uptake than its own. The fungus performs this service for the plant in exchange for plant sugars, which it uses to grow. A plant with its mycorrhizal fungi partner can have more than 700 times the effective root area capacity of one without.
Mycorrhizal fungi show particular promise for future arable production because more than 90% of modern food crops are beneficiaries of mycorrhizal activity.
The organisms with potentially the most significant role to play in routine farming, due to their ease of use and benefit on a broad range of food crops, are the plant growth-promoting rhizo-bacteria (PGPR).
PGPR bio-fertilisers have been commercially available for several years but recent research has led to surprising findings, according to Ms Stotzka.
“We have carried out research trials looking at different species of beneficial bacteria which we produce here. We studied the effect of an application made from a consortium of many different bacteria compared to a bespoke mix with smaller numbers of bacteria.
“We found the bespoke mixture was significantly more effective and we believe this is because the microbiological ecosystem in the soil becomes tuned to the crop it is supporting. Hence general bacteria blends become less productive when treating mono crops.
“This was illustrated by the results with barley where one consortium of bacteria encouraged the plant to invest in an extensive root system but we did not see a corresponding increase in biomass above the ground. We think this bacteria mix would be better applied to root crops.
Plant growth-promoting rhizo-bacteria have the ability to fix atmospheric nitrogen and unlock soil-bound phosphorus. They work in synergy with the mycorrhizal fungi, allowing for efficient transport of released nutrients to the plant.
PGPR also support a robust plant immune system for healthier crops and produce phytohormones, such as auxins and cytokinins, aiding growth and development of plants.
“We have used a different bacteria consortium for a wheat crop and the results have been encouraging.”
These PGPR products are supplied by some manufacturers in a freeze-dried powder but this can lead to losses in efficacy, adds Ms Stotzka. When supplied as a liquid formulation, they can be applied at a recommended dilution rate of 200 litres of water per hectare using standard sprayer equipment.
“Combining an application of a mycorrhizal fungi and PGPR delivers a compound effect because of the positive synergies between the two different microorganisms,” says Ms Stotzka.
She believes the future for the use of beneficial soil microbes for agriculture is bright, but it will require a slight change of mindset.
“By fostering the mycorrhizae in a rotation and using the right bacteria consortium for a specific crop, our results show it is possible to make the most of nature’s grand design to increase yields and save on artificial inputs.”
Simon Chiles is a farmer and contractor in Kent. Alongside his contracting business he contract farms 150 hectares of arable land and makes 120ha of hay for the equestrian market. On some of the land he claims no Basic Payment Scheme support, instead relying entirely on the income from crops.
Mr Chiles first became aware of the potential of microbiological additives when he was managing land for a client.
He says: “My client wanted to limit the amount of fertiliser he applied to grassland so I looked at other opportunities for increasing grass production. I applied a product containing nitrogen fixing bacteria and it definitely made a difference in what was a poor grass growing season.”
Mr Chiles has used a mycorrhizal inoculant for several years and although he is starting with a good baseline with relatively healthy soils and good soil biology, he believes he sometimes sees a noticeable increase in yield.
“The mycorrhizal inoculant has made a discernible difference, especially in conditions which limit nutrient or water availability because of the increased rooting area provided by the mycorrhizal fungi.
Past experience has persuaded Mr Chiles to look into similar microbial products for his grass and arable land. He is carrying out a number of his trials to test the effectiveness of the different products he is using and he has bought a handheld device to measure the nitrogen content and pH of sap in the foliage.
“It occurred to me there is no point in doing these trials if I do not know what is happening in the plant. So by measuring the nitrogen content and pH of the plant, I will be able to understand how levels vary over time.
“Dramatic variations in nitrogen and pH in the plant sap can make them more susceptible to disease so I hope by using PGPR and mycorrhiza and reducing the amount of fertiliser applied to the crop, I will be getting a more uniform uptake of nitrogen and will therefore have healthier crops.”
Mr Chiles applies the PGPR products through fertiliser nozzles as a stream jet, using a dilution rate of 300 litres/ha.
“I am using a higher quantity of water than recommended because I think this may allow better uptake. I will also be applying molasses and fulvic acid to the crop to help feed the bacteria and encourage them to breed,” Mr Chiles explains.
Mr Chiles admits his varied rotation – which includes wheat, barley, oats, beans, triticale, soya beans, millet and other legumes – ‘is key to all this’. His focus is on a healthy soil biology and he is hoping the addition of manufactured microbial products will help reduce his cost of production.
“Where farmers are working with depleted soil biology due to deep cultivations and the growing of brassicas and root crops, I think adding PGPR and mycorrhiza could be even more effective. However I do not think these products are a magic wand as I suspect we need to learn how to manage them for our best advantage,” he adds.