It’s the end of a long, dry growing season. The earth is parched, soils have turned to dust and hungry birds have eaten the bulk of the crop, leaving next to nothing for the harvest. Perhaps expanding the field by cutting down nearby trees could help increase food supply? The soils there are full of nutrients and would offer a good chance of securing food for next year…
This is the reality that over two billion – yes, billion – smallholder farmers face around the world. Converting additional land to agriculture when existing land does not provide enough yield can often feel like the only option.
One alternative to land conversion is to add nutrients to the soil where they are depleted. In small gardens this can be done with inputs such as compost, but when we start looking at covering areas measured in hectares, chemical fertilisers are by far the most efficient and inexpensive way to replace lost soil nutrients, and thus they remain the preferred option for most farmers. Unfortunately, the addition of chemical inputs leaves the soil in a worse state once the nutrients have been taken up. But that’s not the only problem; the practice of using chemical fertilisers is also a significant contributor to global greenhouse gas emissions.
Due to both access and logistical constraints, viable alternatives to chemical inputs are not available to most smallholders in the developing world. While the fields of conservation agriculture, agroecology and regenerative agriculture present some low-cost options to allow food production that is compatible with conservation goals, these options involve large systemic changes to farming systems that risk-averse farmers can be reluctant to embrace. Farmers can slow the loss of soil nutrients via techniques such as erosion control, mulching and no-till agriculture, which reduce the need for chemical inputs, but do not eliminate it.
Alternatively, it is possible to make normally inaccessible soil nutrients available to plants. This can be achieved in a number of ways, and one interesting emerging area of study is in the association between plants and fungi. As it turns out, about 90% of flowering plants worldwide engage in a symbiotic relationship with a fungus that colonises root systems. The fungus amplifies and extends the range of the plant’s root system, allowing it to absorb previously inaccessible soil nutrients; in return, the plant supplies the fungus with the carbon it needs. These mutually beneficial fungal networks are called mycorrhizae, and it is now thought that mycorrhizal associations are what originally allowed plants to colonise Earth 450 million years ago – wow!