Introduction to integrated methods in the vegetable garden
Chapter : Crop soil
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⇒ The motor hoe, the spade fork and the grelinette
For several decades, the rotovator has become the preferred soil cultivation tool for the amateur gardener, replacing the flat spade of our grandparents. The rotovator is very effective in loosening and aerating cultivated soil to a depth of 15 to 25 cm. There are also small tillers with one or two removable bases for individuals with areas of more than 500 m2 to install another tool such as a cutter or a crumbler.
Confusion between the work of a rotovator (often mistakenly called a tiller) and that produced by the ploughshare of a plough is quite common. The rotovator, because it mixes the soil, is similar to one of the tillage techniques known as "no-till farming" (Techniques Culturales Sans Labour in French = TCSL). The ploughshare performs a ploughing operation (turning over the soil). TCSL has in common that it does not turn the soil. Depending on the depth of tillage performed by the cutter, the rotovator produces a "pseudo-tillage" (about 25 cm), or a shallow tillage (about 15 cm).
For the amateur gardener, the rotovator makes soil cultivation much easier, but it also has its drawbacks:
The rotation of the cutter does not do the earthworms any favours and they are cut into several pieces. Only the end of the worm that contains the head and vital organs has a chance of surviving. The other pieces are doomed to die. However, the cutter do not cut up the soil micro-organisms that are essential to the balance of the ecosystems.
The roots of weeds are cut into small pieces without being destroyed. In the end, there is a risk of ending up with more weeds. This can be partly avoided by using a rake with long enough tines to try to pick up the root pieces. You can also remove as many weeds as possible with a fork wiper before using a rotovator.
It is certain that the rotovator modifies the biodiversity of the soil. But this is not necessarily negative. If certain macroscopic populations are disadvantaged, the most useful microorganisms are boosted. The life of the soil depends mainly on these microorganisms and not on macro-organisms. It is the aerobic microorganisms that completely recycle the organic matter into mineral salts that can be assimilated by plants. It is also aerobic microorganisms that fix atmospheric nitrogen in the soil. By increasing soil aeration, the rotovator allows aerobic microorganisms to colonise the soil more easily at depth, which has the advantage of increasing soil fertility. Of course, as the soil is more aerated, the humus in the soil is more quickly mineralised, which means that more compost has to be added every year to compensate for this loss. For small areas, such as those found in most homes nowadays, the addition of organic compost is not a problem. Balanced organic fertilisers are readily available in specialised shops for the maintenance of cultivated soil without breaking the bank.
For a small area, an ideal tillage consists of a pseudo-tillage with the introduction of inputs (composts, corrective sand or calcium amendments, complete bottom fertilizers, etc.). At the same time, the weed roots, wireworms and other predators living in the soil are removed.
The use of a fork spade with a handle can easily remove the roots of some tough weeds such as quackgrass, and eliminate wireworm larvae that are known to be very resistant to pesticides. This is probably the most effective way to get rid of this dreaded pest without the use of toxic chemicals. The arrangement of the blades of the spade avoids injuring a large number of earthworms. This tool is suitable for mixing soil with soil improvers and composts without using a rotovator. The principle is to turn over a clod 2 to 3 times while trying to crumble the soil with the tines of the fork. Then you can use a wolf-type « wolf ». A wolf crumbler, however, has the disadvantage of cutting the worms if they have not been removed at the time of ploughing. Of course, the use of this tool requires strength and many passes. The work will be all the more difficult if the soil is compact. In terms of ease of use and results, a manual crumbler will never be able to match the work of a rotovator.
For small areas of about 100 m², the spade fork is still the best tool for pseudo-tillage when you want to preserve the original biodiversity of the soil. But its use requires more elbow grease. It is very often necessary to spread the tillage over several days. Many people do not have the physical capacity to undertake pseudo-tillage with a fork spade. The loss of biodiversity is not as catastrophic as some detractors claim, and the rotovator is still a very practical and effective tool for aerating the soil.
Because of the reduced engine power, most of these tools are actually motorised hoes reserved for shallow tilling of the soil to about 10 cm after ploughing. These electric tillage are very suitable for preparing a semi on a previously ploughed plot. For a more in-depth work of the soil, you should not hesitate to acquire a heavier and more powerful tool equipped with a 2000 W electric motor such as the Texas ELTEX2000 hoeing machine equipped with an adjustable handle to control the depth of the soil cultivation (available here). Be careful, as with all tillers, the performance of this machine is acceptable on soil without pebble. The latter can block the cutter, or even damage it and the drive system. The finer the soil, the better the machine will perform.
There are still improvements to be made on these new electric machines to gain in robustness and performance. For example, the use of a reverse gear for the heaviest machines or a control of the speed of the spindles as found on the most efficient combustion engine machines.
For amateur gardeners, there are tillers with combustion engines whose performance is far superior to that of electric tillers. For example, the Pubert Meso tiller is very suitable for a 100 m2 vegetable garden. It is equipped with a reverse gear, its 4 tines allow a working of the soil up to 29 cm and its handlebar is adjustable in all directions. So you can steer your machine without trampling the soil.
In recent years, another method of manual digging has appeared: organic digging with the grelinette (also known as biofork or organic fork). This method consists of digging without turning over the soil for about 25 cm to avoid burying the top layer rich in organic matter. In this way, this technique respects the location of the different horizons. I do not prefer its permanent use for the following reasons:
Pest larvae such as wireworms cannot be picked up by hand. As the soil is not turned over, pests that have taken refuge deep in the soil in early autumn will not be destroyed by birds or winter frosts.
The roots of deep-seated weeds cannot be recovered. The roots cut by the tool will produce as many new seedlings. In the end, you end up with more weeds.
Weeds cannot be buried to produce humus.
It is not possible to mix the organic amendments with the original soil to quickly increase the volume of humus-rich garden soil. You have to wait for the mixing to be done by earthworms, which takes years.