Mining soil biology the last farming frontier
Investment in agricultural technology doubled in 2017, to a massive $700M with a significant proportion of this being invested in Ag Bio tech companies. All these companies have a common goal: to harness the microbiology in soils to naturally increase plant efficiency and yield. If this is really is the Klondike of modern farming then why is the understanding of soil biology so important to the future of agriculture?
There is a very small area around the roots of every plant where a huge community of soil microbes gather to feed on root exudates and in exchange undertake some of the most fundamental functions in farming. In this rhizosphere, an area only a few millimetres in thickness surrounding the roots, this congregation of fungi and bacteria interact to fix nitrogen from the air, solubilise phosphorus and convert much of the chemistry used in modern farming into plant available nutrients. Simply put, a plant’s efficiency relates directly to the microbiology in the soil.
With an increasing awareness of the importance of the role these microbes play in plant establishment and growth, classic rotation planning is beginning to be extended to embrace the management of soil microbiology. SMART ROTATIONS is a philosophy of farm management that seeks to encourage and add to the communities of fungi and bacteria that are so important for plant efficiency. Through both ‘method’ and ‘intervention’ SMART ROTATIONS promotes a fundamental understanding of the underlying mechanism of how farming practices and microbes can work together to, within what is practical, help redress the declining condition of farming soils
It is a humbling statistic that less than 20% of nutrients applied to ground ever see a plant. Instead these additions are washed into the water course, become chemically bound in the soil or simply are left unused by the plant. It is a common misconception that the main nutrients such as nitrogen, phosphorus and potassium (NPK) are readily available to plants. The fact is that much of their accessibility relies on the inherent biology in the soil to convert them into plant available forms.
Recognised as one of the most important of all soil microbes are the remarkable mycorrhizal fungi. These thread like fungi are obligate mutualistic symbionts (they cannot survive without a suitable host plant). They feed off plant sugars (carbohydrates) that their host plants freely surrender in exchange for nutrients and water that are passed back to the plant. This is the so-called ‘the carbon cycle’. Very literally the fungus acts as a secondary root system for the plant, and in its developed form increases the root capacity by one thousand-fold. Moreover, when this union is established its relationship with the plant is so genetically intimate that the hosts ‘down-regulate’ their own phosphorus uptake pathway in preference to accepting phosphorous through the fungal network that continually spreads out into the soil exploring niches that the plants roots cannot access.
As obligate symbionts these fungi are not free living, they need a host at all times. Leaving land fallow removes this host and causes the community to fade. In addition, although these fungi are generalists and will associate with many plant groups, they do not associate with the brassica and goosefoot plant families, which contain crops such as oilseed rape and beets. A failing in classic rotation planning is that many of the crops that are strong mycorrhizal hosts like, wheat, oats or maize will suffer if they are preceded by non-associating crops such as OSR, and sugar beet.
To the first tenant of SMART ROTATIONS: if you are able do not break the plant carbon cycle, that is to say, try where possible to maintain the link between mycorrhizal fungi and an associating host plant.
Practically speaking this means endeavouring where possible not to leave land fallow but rather to employ the use of leguminous cover crops that can support mycorrhizal fungi. In the event you are planting a non-associating host, if it is practical to do so, plant an associating companion crop e.g. clover within OSR.
In the event you have no choice but to break the cycle, you have the option to inoculate the soil with mycorrhizal fungi with a suitable inoculant either drilled directly with a high value crops, such as carrots, or broadcast with a suitable cover crop.
Where a classic rhizosphere is considered to be a sheath-like area surrounding a plant’s root, with a fully developed mycorrhizal network established in the soil the ‘mycorrhizoshpere’ is a considerably larger area of functional soil, around which other microbes can work to enhance nutrient flow.
Beyond mycorrhizal fungi there are a series of beneficial soil dwelling bacteria that function in the rhizosphere to release nutrients, fix nitrogen and create natural plant hormones that stimulate the development of top and root growth. These Plant Growth Promoting Rhizobacteria (PGPR), although offering many of the benefits of mycorrhizal fungi differ in one very significant way to the fungi: they are free living, that is to say, they do not need a host plant to associate with to survive in the soil. In addition these bacteria can be blended for use on non-mycorrhizal crops and so within SMART ROTATIONS every part of the cycle can be supported through the use of active biology. The fact that these beneficial bacteria are free living, and are also somewhat easier to culture than their mycorrhizal fungal partners, offers far greater opportunities to deploy them as a practical product for farming.
Recent developments in delivery systems now allow for stable liquid formulations of bacteria with extremely high cell counts (more formally known as Colony Forming Units CFU) to be simply sprayed directly onto the land or crops. Typical treatments are applied pre-emergence or as a dual application three weeks after drilling and again three weeks after this. Research is increasingly informing us on the mix of bacteria that should be applied to increase plant efficiencies. There is a significant move away from products with large consortia of bacteria as research results confirm that these blends need to be targeted at different crop types and in consequence a consortium designed for wheat, for example, may not function at all with barley.
The second tenant of SMART ROTATIONS reads that plants generally perform better with optimum levels of both AMF and PGPR. Mycorrhizal plants can be treated with a combination of these organisms. Brassicas and the goose foot family can still be treated with PGPR alone for increased plant health and productivity.
Accepting that with an understanding of SMART ROTATIONS modest changes in farming practise can have a significant effect on soil microbiology, what are the options for augmenting these with inocula? Good mycorrhizal inocula are difficult to manufacture and are subsequently relatively expensive. Based on your planned rotation their application can be limited to a few times over a rotation plan, particularly after a break in the carbon cycle. Potentially after a non-mycorrhizal crop has been harvested, broadcast inoculum blended with a suitable cover or break crop, to act as host, at a cost of £40 / hectare.
Whilst mycorrhizal fungi are used at time of planting, beneficial bacteria can be deployed at various stages in the growing cycle. Dispersed in standard sprayer at a recommended dilution rate of 200 litres of water per hectare, the cost of each inoculation ‘on farm’ is £20 per hectare. Again care should be taken in ensuring the inoculum is correctly tuned for the target crop and is of a sufficiently high CFU level to have an effect.
Once we stand back and comprehend the value that beneficial biology in the soil offers our plants, in terms of plant efficiency, it seems logical that we should seek to manage these populations and where possible augment them. A more efficient plant is not only more efficient at collecting nutrients, it is healthier and more robust in terms of its ability to resist stresses. SMART ROTATIONS is a philosophy rapidly being adopted both to increase farming yields and to manage and improve the most value of all resources: arable soils.
It is a fact that harnessing soil microbiology is considered the next, and indeed the last, frontier of modern farming. It is no surprise then that investments in its use have doubled in the last twelve months, as the reality of the effect of pending restriction of chemical inputs resonates through the farming supply chain
For further information
Ms Jamie Stotzka
Office: +44(0)1795 411527
PlantWorks is a leading agricultural and horticultural research firm that specialises in sustainable, natural plant growth solutions. Based at the Kent Science Park and NIAB EMR, PlantWorks has a core science team embracing the disciplines of soil biology, bacteriology and plant science.
PlantWorks is one of the largest producers of mycorrhizal fungi in Europe growing five well characterised strains within its controlled growing facilities split between East Malling Research and Kent Science Park. PlantWorks maintains a large collection of Plant Growth Promoting Rhizobacteria (PGPR) that it routinely cultures and formulates in support of farming trials and new product offerings.
In 2014 PlantWorks commenced its farming programme that has seen it collaborate in joint research and trials programmes with the country’s leading agriculture research stations as well as many of the UK’s leading agronomy companies and directly with farming groups. This work has yielded the development of the SMART ROTATIONS programme, and associated products, that support the general concept of maintaining high levels of microbial activity in soil to increase natural plant efficiency, consequently reducing fertigation requirements and enhancing natural plant health and defences