2nd May 2023
Gardeners and farmers alike are suffering from the effects of climate change.
As heat waves sweep across the world, water levels are dropping – and tomato yields are particularly affected.
However, a new study may have the answer – at least for tomatoes.
Morrocan researchers compared the use of conventional chemical fertilizers to biostimulants in drought conditions. .
These biostimulants combined compost and fungus – specifically arbuscular mycorrhizal fungi (AMF).
To measure the impact of the biostimulants, the researchers measured a number of factors associated with the yield, such as polyphenols and flavonoids.
What is Arbuscular mycorrhizal fungi?
Arbuscular mycorrhizal fungi (AMF) is a beneficial fungus that forms a symbiotic relationship with the roots of plants.
These fungi help plants absorb nutrients like phosphorus and nitrogen from the soil, which the plant can use for growth and development.
In return, the plant provides the fungi with carbohydrates that the fungi need to grow.
The relationship between AMF and plants is mutually beneficial and can help improve plant growth, yield, and overall health.
What did the study find?
The study found that biostimulants yielded impressive results.
For example, polyphenols in tomatoes increased by 310% and flavonoids by 158%.
The use of compost alone increased the amount of sugars in the tomatoes by 60% and the amount of protein by 20%.
The researchers also found that using compost and mycorrhizal fungi leads to improved resistance to oxidative stress and more efficient photosynthesis.
While the study focussed on tomatoes, the researchers told Compost Magazine that the results could be transferred to other vegetables, cereals, legume crops, and even other fruit trees.
Compost & fungus v. artificial fertilizers
The authors highlighted that both compost and fungus have different roles to play in the soil, but that using the two together can improve tomato yields.
However, while conventional fertilizers have some use, their effectiveness was limited in this study.
For example, compost improved flavanoid count by 160%, while the fertilizers increased flavanoids by just 7% when compared to untreated soil.
That’s good news, as not only are traditional fertilizers made from scarce resources, their production, transport around the world and use is hugely damaging to the environment.
If we can replace even some of it with locally made compost, that should be a win for the environment.
What can we do in our gardens?
It won’t surprise you that at CompostMagazine we’re pretty keen on using compost.
After all, this study is only one of many to highlight the benefits of using it.
We’re also pretty keen on using a NoDig approach to gardening, as it avoids disturbing existing mycorrhizal fungi in the soil.
In my own tomato beds, for example, I follow the Charles Dowding NoDig approach, and simply apply a layer of compost every year.
My homemade compost is quite woody, as I use a lot of sawdust as a source of carbon.
Whether it’s because of No Dig or because of the wood, fungus already seems to thrive in my polytunnel.
As you can see from the Q&A with the researchers below, they also believe that a No-Dig approach is the most beneficial, although they added a caveat that more research was needed.
But should gardeners also add mycorrhizal fungi?
We asked the researchers this, and they explained that while it could be beneficial:
- Certain soil conditions need to be met
- You need to be sure of the quality of the mycorrhizal fungi
- The mycorrhizal fungi used should match the specific needs of the plants you are growing
See the Q&A below for more details!
Q&A with the researchers
Q: Do you think the results will apply to other plants in addition to tomatoes? From the results of your study, do you have any advice to offer for gardeners and composters who want to grow tomatoes?
A: Yes. The compost-AMF formulation used in our study can be transferred to other vegetables, cereals, legume crops, and even other fruit trees.
We tested the formulation in these plants and confirmed the success of this biostimulant as a strategy for better growth and quality/functionality.
As advice for gardeners and composters who want to grow tomatoes, they should take into consideration the optimal NPK (in the compost) requirements for tomatoes, specifically 134 Kg N (ammonium nitrate)/Ha; 127 Kg P2O5 (superphosphate), and 332 Kg K2O (potassium sulphate)/Ha.
Q: Is it enough to just use compost, and perhaps use a No Dig approach, or should we also consider adding mycorrhizal fungi to our compost?
A: The answer depends on the objectives.
Compost alone can be sufficient to increase yields, especially in the case of our green waste-based compost, at rates ranging from 5 to 20 tons/ha.
The strategy developed by our team (with our expert Prof Meddich Abdelillah) is to combine low doses of compost + arbuscular mycorrhizal fungi (AMF) to not inhibit these microorganisms and to ensure better synergy between the two entities, and then try to use economically profitable doses of compost < 10 Tons/ha.
It is worth noting that the application of mycorrhiza is prior to the addition of compost to ensure better root mycorrhization.
Therefore, it is a no-dig method where the soil is undisturbed, so its organisms can work and multiply, and the AMF (see other organisms) can have (the slow) access to compost organic matter/nutrients on the surface as roots ‘ask’ AMF for nutrient and/or water.
AMF work best when undisturbed, which is why perhaps we can see stronger growth in no-dig soil (this has to be scientifically tested). The compost mulches serve as a rapid source of nutrients for soil microorganisms (e.g. AMF) and enhance their activity, thus improving soil structure.
Q: If you are getting mushrooms growing naturally among your compost, is that a sign there is likely sufficient Mycorrhizal Fungi in the soil?
A: Not necessarily.
While mushrooms and AMF (our main focus, and not the ectomycorrhiza) are closely related, the presence of mushrooms growing in the compost does not necessarily indicate the presence of AMF in the soil.
Mushrooms can grow from various types of fungi, some of which may not be beneficial to the soil. Additionally, even if the mushrooms are growing from mycorrhizal fungi, it doesn’t necessarily mean that there is enough of it in the soil to have a significant impact on plant growth.
The best way to determine the presence of (sufficient) AMF in the soil is through laboratory testing. To ensure that the soil has sufficient levels of AMF, one can consider adding a native or ‘exotic’ AMF inoculant to the soil.
Q: Should gardeners use AMF?
Yes, mycorrhizal fungi (AMF) are useful and can benefit both crops and plants.
Just make sure that the soils where the crops are grown are low in organic and mineral matter and do not have high levels of available phosphorus so that the establishment of mycorrhization is stimulated, because the plant shows a need for AMF when conditions are difficult such as poor soil and lack of water. Also, make sure of the quality of the AMF used!
The commercial solutions available can offer advantages, and as it was pointed out by my colleague Prof. Baslam, to be beneficial, they should meet the needs of the targeted crops and which are variable from one crop to another.
This also depends on their age, their stage of development and other factors of course including environmental conditions (soil texture, fertility, frequency of watering and others …).
For the example of tomato as it is specified by Prof Baslam, the needs in potash are high, but if the contents in phosphorus, and especially in nitrogen are high they can have a negative impact on this culture (decrease of the yield, the possibility of rotting part aerial and root, in addition to pathogen attacks.)
Mycorrhizal root tips photo via Wiki Commons