As kids we used dirt for play – ‘mud burgers’ anyone? – and parents demanded that we wipe our feet and wash our dirty hands when we came inside the house. But soil is not dirty! In fact, soil contains an entire universe of organisms – one gram of soil contains billions of bacteria, thousands of fungi and algae. In addition to the billions of organisms, soil is also a mixture of living and non-living materials. The non-living materials include rock particles that have weathered over thousands of years from the bedrock below, plant residues and dead microbes. Soil’s living component ranges from microscopic bacteria to earthworms and rhodents. All components that are living – or once living – are categorized as organic while those that never lived, like the minerals, are referred to as inorganic. Combined, soil’s organic and inorganic components form a complex network of interactions: organic materials decompose and become soil’s highly fertile humus layer. Soil humus is a form of highly recalcitrant carbon that is stored in the soil for more than 1000 years. In fact, a handful of soil means you are holding an entire living ecosystem in your hands with some of its components more than a millennia in age.
Without soil we would not be able to grow the plants or livestock that provides our food, fibre and fuel. But soil does not only grow our food, produce fibre for clothing or fuel for transportation. Soil plays an important role in providing multiple environmental or ecological services such as helping regulate water to help prevent floods, filtering pollutants, cleaning the air, decomposing and cycles organic material that help make soil fertile, and regulating greenhouse gas emissions. More recently, soil has also been viewed as a way to store carbon to help offset the accumulation of carbon-based greenhouse gases such as carbon dioxide and methane. Humans are deeply dependent on healthy soil.
Unfortunately the soil we are so dependent on is is under immense threat of being lost or highly degraded due to the multiple demands, such as intensified agricultural production, urban expansion and industrial pollution, placed on it. But it is not easy to replace lost, or repair degraded soil. For example, it takes about 178 years to produce one 1 cm of top soil (global average). Given that timeline, we can think about soil as a non-renewable resource and therefore it is important to further prevent its loss and degradation. The soil’s environmental/ecological services are also impeded when the soil becomes degraded.
How can soil degradation and loss be avoided while still benefiting from its environmental services and the various products it helps to generate? Many different approaches have been suggested ranging from commonly used and easy to integrate agricultural management practices such as minimum tillage, cover crops, strip cropping or crop rotation. Others have gone a step further and adopted farming practices with a year-round soil cover, constructed terraces on steep slopes or embraced complex agroecosystem management practices like cereal-legume intercropping, where a cereal (e.g. corn) and a legume (e.g. soybeans) are integrated on the same land area at the same time. Another example of a complex agroecosystem are the diverse agroforestry practices that integrate trees or perennial crops with row crops and/or livestock. In fact, the United Nations’ Food and Agriculture Organization (FAO 2013) recommended the adoption of agroforestry practices for food security and as a climate smart approach to agriculture due to their resiliency to climate change. Some studies have shown that alley cropping, a type of agroforestry practice, can increase carbon by 1.1 ton per hectare per year in a tropical environment (Oelbermann et al. 2004). In Canada, establishing alley crops on marginal land could help reduce carbon emissions by 32% in less than 10 years (Oelbermann et al. 2004).
Our challenge globally is to prevent further soil loss and degradation. Everyone can help tackle this challenge by purchasing products (e.g. food, clothing) from sustainable sources, by planting trees and vegetation, adding physical structures to conserve soil. You can do this even in your own backyard by ensuring the soil is covered with plants or mulch, by constructing retaining walls especially on steeper areas, improve drainage and minimize watering.
For further reading:
Beneson, B. 2010. Dirt! the movie. Video (DVD) available on Amazon.ca.
Brown, G. 2018. Dirt to soil – one family’s journey into regenerative agriculture. Chelsea Green Publishing, Vermont, USA.
FAO. 2013. Climate smart agriculture source book. UN-FAO, Rome, Italy.
Montgomery, D.R. 2018. Growing a revolution – bringing our soil back to life. WW Norton Publishers, New York, USA.
>Nauta, P. 2012. Building soils naturally. Acres Publishing, Greely, CO, USA.
Oelbermann, M., Voroney, R.P., Gordon, A.M. 2004. Carbon sequestration in tropical and temperate agroforestry systems: A review with examples from Costa Rica and Southern Canada. Agriculture, Ecosystems and Environment 104:359-377.
Rabenberg, G. Soil works – correct the cause. Podcasts available at: https://www.acresusa.com/pages/soil-works-correct-the-cause-with-glen-abenberg-podcast
Sitka, J., Sitka, E. 2016. A soil owner’s manual – how to restore and maintain soil health. CreateSpace Independent Publishing Platform, South Carolina, USA.