We Should Worry About Climate Change’s Impact On Soil Fertility
We can breed better plants, but we can’t breed better soils
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When we think of climate change and agriculture, the first images that come to our minds tend to be yellowish plants wilting under a scorching sun or fields infested with new and exotic pests, now acclimatized to a warmer and wetter weather. What we don’t think about, is that plants are not the only organisms to be affected by the devastating impacts of climate change. While we strive to breed better plants, capable of withstanding the increasingly harsher environmental conditions, there is a delicate component of an agroecosystem that is often neglected, despite being of pivotal importance. Yes, you guessed it: the soil. The soil and its ecosystem are also dying out, and if we do not reverse this process, agriculture as it is today, will no longer exist.
Soil is more than…just soil!
To many, the soil will appear not much more than a pure physical support for the plants. Yes, soils also supply the plants with nutrients, but what else? After all, if the nutrients in the soil were to disappear, we would just need to fertilize our fields and everything would be fine, right? Well, not exactly. The soil is a very complex and delicate biochemical system, not a simple and inert support for plants’ life. It is a living being itself, and, similarly to most living beings, it is not doing very well under climate change. But why is that? And how will climate change impact soil’s life and its capacity to support plants’ growth?
How too much rain affects the soil ecosystem
Climate change is expected to have different impacts not only at the spatial level (different areas of the world will be differently affected) but also at the temporal level, meaning that the same geographical areas will experience opposite climatic events in the Summer and Winter season. Taking Southern Europe as an example (for it being a hotspot of climate change and a well studied location by climate scientists), the Summer months will experience increasingly strong heat waves and drought events, while the Winter months will be ravaged by floods and heavy rains. Now, let’s consider these effects on the soil.
What does it happen when you pour too much water to your plants in a pot? Water overflows (obviously!). However, it doesn’t end up there: there are three major soil components impacted by heavy rains and waterlogging.
- Humus. Soil organic matter (which you probably know as “humus”) is located in the first upper layers of the soil. Among its major functions, humus gives structure to the soil, increases soil water retention and keeps the macronutrients in place, preventing leaching. Under heavy rains, humus is lost via runoff, causing, as a result, a strong decrease in soil fertility.
- Nitrogen. Under waterlogging, all the pores within the soil are occupied by water, meaning that there is no more oxygen in the soil. In a oxygen-deprived soil, nitrogen, the main crop macronutrient, undergoes a denitrification process through which it is converted in nitrous oxide and it is lost into the atmosphere. Even if the soil is well drained, we still would have problems: nitrogen, the main crop macronutrient, would be lost via leaching, due to the high amount of water flowing across the soil profile.
- Soil bacteria. In an oxygen-deprived soil, aerobic microorganisms responsible for the breaking down of plant material (decomposition processes), simply die out.
Temperature and soil, a delicate relationship
Like you and me, also soil microorganisms have their preferred temperature at which they like to live and, similarly, it is not just you and me who complain when the temperature gets too hot. A study found out that in the US
soil temperature (depth of 10 cm) increased by 0.32 °C over 10 years
while in China,
the annual surface soil temperature increased by 1.90 °C (national level) during 1961–2011
Now, soil microbes aren’t exactly overjoyed by the increasing temperature across the soil layers: beyond a certain temperature threshold, soil microorganisms get inactive and eventually die off. This results in major problems at the soil fertility level.
Initially, when the soil layers get heaten up, the organic material in the ground starts to break down in a process called mineralization (the breaking down of bigger molecules of organic residues into smaller ones), and humus is created from a recombination of the organic material. If the temperature keeps increasing, the humus itself starts to break down as well into smaller components (the plants’ nutrients), which are now at risk of being easily washed out by the rain. The consequence is the loss of both humus and soil nutrients.
What can we do to minimize the impacts?
Under heavy rains, drought and tempeature increase, the soil’s future doesn’t look bright at all. As a consequence, the same goes for plants’s future and our own too. However, at field scale, something can be done to prevent (or at least limit) the heating up of the soil.
- Agroforestry practices can create a cooler microclimate in the field as well as protect the soil from havy rains.
- Mulching can help both reducing the runoff of water across the field and keeping moisture close to the crops’ roots in hot summer days.
Unfortunately, we can’t breed better soils, as we do with plants. But even if we would have plants capable of withstanding climate change scenarios, where these crops will be grown, if soil health would decrease?
Soiless agriculture can become the new agriculture, but we can’t grow forests and prairies in hydroponic systems.
