If We Have HMAs Do We Need Synthetic Fertilizers?
By Drs. David Boyle and Elizabeth Spence
In Part One we saw that HMAs carry out a huge number of processes that allow plants to grow successfully.
But what happens when we try to “help” plants over and above the natural systems?
Gardening and agriculture in general changed profoundly after about 1918 when the Haber-Bosch process for nitrogen fixation was invented.
This process allows atmospheric nitrogen gas (N2) to be converted to ammonia
(2NH3). Nitrogen is abundant in the atmosphere, but it is essentially inert and not
available to plants. It has to be ‘fixed’ by combining it with hydrogen (H2) to give
ammonia.
A ‘Green Revolution’ resulted because nitrogen fertilizer (ammonia, nitrate or urea) was now readily available. Plants were selected and agricultural systems developed that were highly responsive to fertilization. Other chemical fertilizers were developed to provide phosphorous, potassium, etc.
The green revolution was incredibly effective. It is estimated that about half the
population of earth is dependent on food grown on nitrogen that is ‘fixed’ by
industry.
The plants could now be grown in ‘dead’ soil or essentially sterile mixes like peat moss, vermiculite and perlite which have very few HMAs in them, providing they were fertilized and chemical pest control agents were used.
They could even be grown in liquids – hydroponics is one example.
Even compost, if it is used and produced under the Canadian Compost Guidelines is almost sterile, with low microbial diversity since it is heated during production to kill potential pathogens.
It will therefore not contain living mycorrhizae or rhizobium, although it may contain heat tolerant bacteria like the “microbe of the year for 2023,” Bacillus subtilis
As an aside, some years ago, I did research into whether potting soils claiming to contain mycorrhizae actually did contain any live ones. They did not.
If these potting soils are stored outside in the blazing sun, it is highly likely that the heat killed the mycorrhizae.
If you are buying these from a place that stores them outside, you can’t possibly know if the fungi are alive or dead without testing, but they’re probably dead. (Note by Elizabeth: well, well, well.)
Something interesting happens to HMAs if their job is being done by chemicals:
they retreat. In fact, if a lot of fertilizer is used, mycorrhizae and nitrogen fixing
bacteria will disappear completely. This makes sense from the plant’s point of view since the HMAs no longer serve a purpose.
In the absence of HMAs, other fungi and bacteria that are adapted to a chemical-laced environment will occupy the root zone. Some of these cause problems that require more and more chemical control.
The stated advantage of vegetables that are grown exclusively with the help of fertilizers rather than HMAs is that they have very high yields, are sometimes as big as they can be, and come as the blemish-free produce we have all come to expect in our supermarkets. As noted, they do feed about half the world’s population as well.
How can you harness your HMA Elephant?
When it comes to our own gardens, we could, of course, increase the size and yield of our vegetables and recreate our own ‘green revolution’ by using lots and lots of chemical fertilizers. But do we want to do that? It comes down to personal choice in the end. If we do want to use organic methods, then HMAs are the answer.
Fortunately, it is worth emphasizing again, the HMAs are present in the billions in most native garden soil providing it has not been too badly mistreated. They will also still be available to help the plants after the garden soil is supplemented with small amounts of fertilizers or moderate amounts of aged compost, peat or artificial soil mixes.
Indeed, it deserves stressing that so many of the problems in agriculture, in the garden and indeed in the general environment are caused by the overuse of chemical fertilizers.
By way of illustration, if there is a lot of nitrate present in the soil and if oxygen is limited -for example in a water-saturated soil – some bacteria use the nitrate to make nitrous oxide, which can diffuse into the atmosphere. This is a significant greenhouse gas. It is about 400x as potent as CO2.
General advice here: you can use fertilizer, but don’t overdo it.
There are other amendments which will not harm the HMAs.
- If a soil needs more nitrogen it is better to use complex sources such as fish meal or protein.
- Nitrogen-fixing legumes such as peas and beans can be grown either as a crop, or as a green manure. If you incorporate them into the soil before they go to seed, more nitrogen-containing organic matter will be added to the soil and will stimulate HMAs.
- Other amendments to the soil should be fully composted. Well-aged manure or compost that have a higher nitrogen content are best.
- Un-composted, partially or non-composted materials should be used as mulch (See this website’s article on mulching here). They should not be incorporated into the soil, since unfortunate reactions might occur. For instance, sawdust, with its low nitrogen content (C/N often over 100) will feed the fungi that can degrade the woody material, but these may then outcompete the plants for what is sometimes a growth limiting amount of ammonia or nitrate.
Avoiding herbicides and pesticides, or being careful which you use is important. Roundup (glyphosate) can kill or interfere with the functioning of some mycorrhizae. Use of non-chemical methods is preferable – hand-weeding and picking off the bugs, for example. Insecticidal soaps are also good and relatively harmless to HMAs. They may also have some activity against some fungal plant pathogens.
Some fungicides applied to kill disease fungi, can also kill or interfere with the functioning of mycorrhizae or other fungal HMAs. Fungal disease itself can often be controlled by increasing air circulation around the plants and making sure residues from diseased plants are removed.
Overall, one of the fundamentals of successful organic gardening lies in
maintaining a heathy, productive soil based on the activity of our elephant, the
HMAs.
Being versed in how they function, recognizing the broad-ranging work they do to support our plants and applying the appropriate methods of cultivation can only improve our results, and perhaps our peace of mind as well.
Organic gardeners need not compare what they grow with what is found in the
supermarket. We are not necessarily going to achieve that sort of perfection nor
do we particularly need to. It’s not the point.
On the contrary our produce is likely to have blemishes, smaller yields and some
insect damage, but boy, does it taste great! And we did it ourselves!
Thank you HMAs, our own personal elephant in the garden! We are closer to understanding you now!
For Part One, click here