I often find that I learn a lot, or gain significant insights, when things don’t work as I expected
them to, especially when something fails.
While digging out this crop of potatoes in the Black Plot I became quite disillusioned.
I wasn’t expecting a great yield for a variety of different reasons but as I dug them out,
I realised that things were worse than I expected them to be .
Although I was digging up a lot of big potatoes, many of them were riddled with slug holes.
I have had a lot of slug damage with my potato crops in the past, and it remains one of the
persistent pest issues that I am trying to deal with.
As I continued to dig out the long rows of buried tubers, I began to notice that there
were a lot of earthworms - more than usual.
The presence of earth worms is a good sign, as they are highly beneficial to soil development.
The general idea is that the more there are, the better and healthier the soil is, or will become.
I would expect there to be a fair number of earth worms in this soil, as it had been turned
over in the spring, burying a lot of organic matter which would have provided a lot of
worm food.
But there seemed to be more worms in this section of the soil, than in other parts of
the plot that had received the same treatment.
Then I noticed an interesting correlation.
In parts of the bed where more of the potatoes were eaten by slugs, there were more earthworms.
And in areas where there was less damage there were fewer worms.
It was only then that I realised what was probably happening here.
The potato plants were storing huge amounts of carbon in the form of starchy carbohydrates
in the underground potatoes.
Slugs were consuming some of these potatoes, and the worms were feeding off of the wastes
from the slugs, either directly or by consuming the bacteria and fungi that fed off of the
slug wastes.
This is a simple but effective food chain, funnelling huge amounts of food to the soil
biology, with the potato plants acting as primary producers, and the slugs acting as
primary consumers.
Of course, I would much rather harvest a full crop of slug free potatoes, but the loss of
a crop is not a total loss - it never really is in a garden.
The potatoes that won’t be feeding me will be feeding the soil, and this increased soil
biology and fertility will only benefit the next crops that I plant in this part of the plot.
Potato plants are extraordinary for the amount of carbon they can pull out of the air and
sequester as carbohydrates in the tubers.
This is why we grow them.
But what is food for us, can also be food for the soil biology - and in this case there
is lots of it.
I started to wonder if potato plants can be used as a green manure.
Green manures are plants that are specifically grown to build soil fertility, to fix nitrogen,
to improve soil texture, and to increase soil organic matter.
A important role of green manures is to feed the soil biology by putting carbon into the
ground, and that is exactly what is happening with part of this potato crop.
So, I began to think about the idea of planting a crop of potatoes with the purpose of leaving
them in the ground to feed the soil.
If enough slugs were around as primary consumers, it seems that a lot of food could be supplied
to the soil ecosystem, including the worms.
This would really benefit the soil structure and the crops that grew in that soil in the
following seasons.
But, the slugs that ate the potatoes would only go on to make many more slugs, which
is not a good thing in a vegetable garden.
Unless you had something that ate the slugs, like ducks.
Now that could be an interesting integrated approach that would be worth exploring at
some point in the future.
Another issue is that potatoes that were not eaten by slugs could sprout again in the following
spring, which would be problematic.
Beyond becoming a persistent weed within the next crop, these second generation potato
plants could become a source of potato blight to infect next years' crops, which is definitely
something I want to avoid.
Overall, it is probably not a great strategy for my gardens, unless I could find a way
of killing off the slugs, having them eaten by something, and to make sure that all remaining
potatoes were removed.
But I am intrigued by the possibilities of using potatoes, and even other crops, to actively
feed the soil instead of providing a harvestable yield.
From this simple observation about the number of worms corresponding to the amount of slug
damage, I realised the positive impact that this could have on the soil.
In hindsight this now seems rather obvious.
I have read about these type of soil processes in books, and understand the basics of what
is involved.
But, as with many things, it took direct experience to make that knowledge my own, rather than
simply relying on the experiences and teachings of others.
So, I decided to find out how many earth worms there actually were among these slug eaten potatoes.
I dug out about a quarter of a square meter of soil - about two and a half square feet
- from around one potato plant that had had moderate slug damage.
I counted 85 worms in total, and there would be significantly more worms around the plants
that had had more slug damage.
As most of them appeared to be immature common worms, it would seems that their population
has substantially increased quite recently - which makes sense with all of the extra food.
This number of worms translates to more than 300 worms per square meter - more than 30
per square foot - which is apparently at the high end, or the upper end of what I should
expect to find in healthy organic soils.
So, inadvertently, the soil in this part of the Black Plot is off to a good start!