Q: Where does soil come from?

Dirt. Mud. Soil. In general, when we say “soil” we refer to the land surface of Earth. If you ever go visit Mars, you’ll see the eroded minerals and rocks.

Half of what makes up soil is from the simple erosion of mineral sediment. The other half is a bit more complicated. Soil is defined by the characteristic of being biologically active, as it is home to a myriad of living organisms. Soil isn’t just minerals and rocks, but also the bacteria, bugs, rotting material – all of which work together to sustain important functions. Soil is colonized by bacteria, insects, and worms, all of which slowly form an important component of the organic matter that gives soil many of its beneficial properties. This biological part takes years, sometimes centuries, to form slowly.

By this definition, the red dirt of Mars is not actually soil, as it does not host biological activity. This organic biological activity is what makes Earth’s soil incredibly different from the soil of our planet than that of the majority of the Universe.

Q: Why do we need to monitor soil health?

Soil is fundamental for life on Earth. Soil is alive, and when it is healthy, it performs many critical functions. Soil is a medium for plant growth, stores and regulates water, and is home to living organisms working non-stop to recycle nutrients, transforming dead organisms into the basis of new living things. Everything that we consume is literally grounded in soil.

This feedback loop is like a phoenix reborn from its ashes; humans rely on this feedback loop for the basis of every element of our living.

Q: Where does soil get its moisture?

We all know about the water cycle. Basically, soil gets wet when it rains.

This might seem obvious, but think of the consequences. Water stays in the soil for a significant part of its life between rainfall and evaporation. This means that soil holds this water, storing it for further use. By doing so, soil acts as a regulator of the water cycle.

Q: Why does soil moisture matter?

Think about a hot day. If you get too hot, you can walk to the store for a bottle of water or else dip in the pool. But plants cannot. They drink directly from the soil. Water retained in the soil, called soil moisture, is plants’ only access to water. Without soil moisture there would be no plants on Earth.

Q: What is soil moisture memory?

Soil moisture memory is the ability of a given soil to maintain soil moisture.

Lack of water, also known as desiccation, is one of the main abiotic stresses on plants. And of course, all soils are different. Not all soils regulate this traffic of water in the same way because there are certain properties of the soil that are better to store the water. Some soils are able to store more water or draw it from the surface more rapidly or retain water better (even in drought conditions).

What’s amazing is that many of these properties that give soil its “memory” are directly related to the living part of soils. That’s why healthy soil, which has a lot of different organic material in it, is so important. It’s this organic material that makes it physiologically possible for soil to maintain soil moisture.

This means that maintaining moisture in soils, which is so important for living things, requires life to play a role itself. This kind of relationship is what scientists call “self-organizing properties.” This is just one example of how the complexity of life on Earth underpins everything that depends on itself to exist.

Q: What does soil moisture memory have to do with monitoring soil health?

We are getting better and better at monitoring Earth from outer space. But it’s really hard to observe the microcosm of soil, except for soil moisture. We can monitor soil moisture with satellites, and by doing this we can extract a metric of how much water is in the soil, and therefore the soil health.

Q: What if soil doesn’t have good soil moisture memory? Can we do anything to improve the memory?

Yes. Actually we have been doing it for millennia: we call it agriculture. We’ve worked to help the soil, changing the memory with things like organic fertilizers, the use of worms, adding straw in the soil: we have done that for years to ameliorate the moisture capacities of the soil. But there are some agriculture practices which aren’t about “helping” soils but rather about “forcing” them. One important thing we can do is stop practices which destroy the soil, like tillage. But we can also help by supporting restoration of plants, because plants provide the soil with organic material.

Q: Soil is a functioning part of ecosystems. Does soil moisture impact or mediate climate change?

Yes, of course! Soil moisture matters for climate – it is an essential part of the climate. We don’t monitor soil moisture from space just because we are interested in the living properties of soil.

Rather, the satellites monitoring soil moisture are key for understanding how water moves, and this is essential to understand the climate.

If you listen to the weather forecast, the meteorologist is probably using soil moisture data to predict whether or not there will be storms. In fact, since we started monitoring soil moisture, the weather prognosis has become more accurate. Soil moisture does matter for climate, because it is an essential part of it.

Q: Why is soil conservation important?

If you ask us what makes Earth different from the rest of the universe, it’s that we have soil!

Soil is an essential part of our planet. It matters for everyone and everything: for climate, for water, for agriculture, for plants, for animals (including humans!), and for all the living things in the soil. Soil conservation is critical to life as we know it, and we have to work together to conserve it.