Should we feed Plants to avoid Pests and Diseases?
In recent posts I have been discussing specific topics in plant nutrition. Let me step back and take a look at one of the aspects that might lead people to address plant nutrition with fertilisers and amendments. If anyone is interested, in future posts I might describe Living Soil Garden's specific approach to plant fertilisation.
There has been lots of talk within regenerative agriculture about the potential of healthy plants to be completely immune to pests and diseases. This is a fascinating idea, advocated among others by John Kempf and lots of anecdotal evidence is available to corroborate this view.
The story goes like this: insects and diseases are attracted to plants (or any other organism for that matter) which are weak and unbalanced. A plant with poor nutrition will have poor defence mechanisms, and this obviously makes it inherently more prone to attacks. But advocates of this theory argue that insects and pathogens are not even trying to attack healthy plants, because they are not attractive to them. Weak plants send out signals and are effectively asking to be taken down, for the benefit of their remaining companions. According to the proponents of this viewpoint, this would be an evolutionary strategy.
In large-scale regenerative vegetable production, these arguments have lead to an approach that emphasizes the important of plant nutrition and supplementation. Healthy soil is made by healthy plants and microbes, so if we make our plants healthy by tweaking their nutrition, we can literally create great soil, by virtue of the plants’ interactions with microbes in the rhizosphere. This, in turn makes plants more able to get fine-tuned nutrition from the soil, and thus become more resistant to pests and diseases.
Thus, a grower may spray targeted mineral nutrients foliarly, and combine this input with microbial solutions which facilitate nutrient uptake and plant vigour.
On a large scale this often involves using mined, imported or even synthetic inputs, and this is justified with the aim of reducing or removing pesticide and herbicide application completely, as well as improving the nutritional content of crops.
On a smaller scale, Korean Natural Farming has a similar approach, but uses only natural and mostly local, low-cost solutions, although some of these (such as cane sugar) can create sustainability concerns.
Now, this approach is obviously a huge step forward when compared with conventional agriculture, because, if complemented by no-till techniques, it leads to lower use of chemicals, increase in soil and insect biodiversity, as well as higher nutritional value of agricultural crops.
However, I would argue that it is a timid step forward. We should not be deluded into thinking that addressing plant nutrition is a systemic or holistic approach. And here is why.
An agricultural ecosystem is made up of many components and lots of interactions among these. The ecological role of insects and diseases is not too different from our own, and has two levels: a subjective and an systemic one.
From a subjective point of view, the subject (the insect, in this case) has a genetic program which pushes it to survive and reproduce. From a systemic point of view, coevolution has integrated this program with that of other ecological niches, including the one in which we find ourselves. This integration is synergistic, dynamic, fluid, layered, complex.
Arguing that insects fulfil their role by taking down weak plants presents two issues. First, it shows a philosophical bias towards anthropocentrism. Second, it is scientifically inaccurate, because there isn’t enough scientifically sound evidence to corroborate the statement that insects only attack weak plants (or specifically, as argued by John Kempf, plants with low Brix index).
True, it may be a matter of time until we find out which conditions lead insects either to prefer weak plants or to compete with us for the ones we find nutritious. This ecological flexibility is not surprising; we do see it in our own behaviour: factors such as climate, material resources, psychology and social pressure, culture, etc. all modify our species’ nutritional behaviour and preferences. This behavioural multiplicity is yet another expression of the ecosystem’s complexity. Similar expressions are quorum sensing phenomena in bacteria and the huge versatility of soil fungi.
I tend to favour an approach that is more explicitly ecosystemic and holistic. Focussing on and targeting mainly plant nutrition is, in my view, a limited approach because it emphasizes the subjective aspects of the plant role within the ecosystem.
It is tempting to think that we can address plant nutrition and thus solve once and for all the issue of imbalanced pest and disease pressure. It is possible, as I see it, but this perspective does not differ much from tilling the soil in order to oxygenate it.
The ecosystem is complex, and acting on the plant’s subjective strategy by interfering with its nutrition is very simplistic. When we condone the use of synthetic inputs it can even be invasive and backfire. It also amplifies the competition aspect of this interaction, rather than its synergistic ones.
On the contrary, if we want to take a truly regenerative approach, which is integral, holistic and systemic, we have to sharpen our observation skills. We have to study natural and agricultural ecosystems closely. In healthy and stable ecosystems, pathogen and insect attacks are regulated by a wealth of different effects: plant nutrition; natural predation; biodiversity; availability of food, habitat for both preys and predators; the interaction between vegetables, insects and microbial populations (which are evolutionarily more “established” within the same environmental conditions).
Intervening on the ecosystem as such, and gently directing its balance often involves lots of observation, a little design and very little action - in my experience.
The introduction of multi-layered, agroforestry systems is a starting point. Vegetables are a highly selected version of weeds, and therefore thrive in an early stage of ecological succession, with oxygen-rich soils, high bacterial populations, etc. These stages are usually characterised by little balance and lots of dynamism; different populations move in from neighbouring, more mature ecosystems and start to interact, compete and collaborate to find a new equilibrium which culminates in the continuation of ecological succession on a progressively slower time scale.
By introducing several layers in our systems, such as in a forest garden or in mixed alley cropping, we can tweak this dynamics of interaction by creating the perfect conditions for predators and buffering species, as well as a heterogeneous and diverse landscape that produces more food than just a vegetable garden.
Optimal plant nutrition and the availability of food for all ecological niches (including insects and humans) are two examples of properties that emerge naturally and dynamically within the ecosystem, without the need for a targeted intervention on our part. Just by careful design, informed by sharp and close observation.
An even more important emergent property is the dynamic resilience of the ecosystem, which becomes more able to deal with new introduction or invasions, which become more common in a changing climate.
If anyone is interested, in a future post I may describe our particular approach to plant nutrition and how we supplement it with a mixture of KNF, no-dig and green manures. Let us know in the comments!