Conventional vs Organic Farming: Soil Fertility

“We owe our entire existence to 10 centimetres of topsoil and the fact that it rains”

In which ways does agriculture affect our environment and our daily lives? Read the introductory post to this series here. Part 1 explored the theme of water under conventional vs. organic farming systems.

There are probably few natural resources as important as the soil. Without the soil, we couldn’t survive on Earth. We depend on the soil so much that it’s no exaggeration to claim that we are of the soil. Or, in biblical language:

“The Lord God formed the human from the topsoil of the fertile land…” *

Traces of destruction

Sadly, humankind doesn’t hold a good record regarding a sustainable, responsible management of soil. I’ve written about the devastating loss of fertile top soil through erosion & contamination on several occasions already. You might be interested in these articles:

• What is Efficient Farming?
• Challenges of Modern-Day Farming
• Healing for the Land: Solutions for the Environmental Crisis
• Making and Keeping Soils Fertile

The promises of organic

Organic farming claims to offer solutions. It values soil fertility very highly. And it restricts the use of pesticides much more than conventional farming does. I say ‘much more’ because it is a common misconception that organic farmers do not use pesticides. They do use some, but they are not synthetic (man-made). These non-synthetic pesticides are derived from natural, plant or mineral matter (like neem oil or copper). This largely reduces the potential of organic farming to contaminate the soil with hazardous chemicals.

Another thing that largely determines the fertility of the soil is the use of the plough in farming. In many parts of the world, the plough was the doom of fertile topsoil. As Wendell Berry, the famous essayist writing about agriculture, observed in his hometown in Kentucky:

“The humus stood dark and heavy over them [the hills] once; the plow was its doom.”

Very sadly, this was the fate of rich humus layers in many places.

“The estimate is that we are now losing about 1 percent of our topsoil every year to erosion, most of this caused by agriculture. The United States is losing soil at a rate 10 times faster than the soil replenishment rate while China and India are losing soil 30 to 40 times faster. With soil erosion rates so much higher than the replenishment rate, it is no wonder that the world is quickly running out of fertile topsoil.” (1)

To plough or not to plough

Ploughing, tilling, converting grassland into arable land and erosion all cause the loss of topsoil. And interestingly, organic farmers usually plough more than conventional farmers do. This is because they need to plough to get rid of weeds. Conventional farmers use herbicides to kill their weeds. Organic farmers, on the other side, mainly control the weeds on their farmland mechanically (i.e. by ploughing, tillage). Or, in the case of smaller vegetable farms, they eradicate weeds manually.

A certain advantage of organic farming certainly is its diverse crop rotation. Crop rotation (=the planting of different crops in successive years) enriches the soil, helps soil organisms thrive and improves many other properties of soil fertility.

Farming is always a weighing of alternatives whose consequences are rarely entirely foreseeable. In this sense, organic farming is no perfect system, of course! But in light of all this, I was very curious to find some reliable figures comparing the fertility of soil under conventional and organic management.

Conventional vs. organic farming

Some indicators for the fertility of soil are: the abundance of earthworms and microorganisms, the pH and structure of the soil, the content of available nutrients, the content of organic matter (=humus), the aggregate stability of the soil and soil erosion. Some results of the study (2) showed:

• the biomass of earthworms was 94% higher under organic management (even though earthworms despise ploughing!)

• acidification, which is often a problem in agriculturally used soils, was lower in organic farming (the pH was 0.4 units higher on average)

• the penetration resistance of the soil, exemplary of a good soil structure, also indicated advantages for organic farming

• regarding nutrient availability, there was no clear tendency toward one or the other system

• organic matter content was 26% higher

• the aggregate stability of the soil was 15% higher

• and soil erosion was reduced by 22% under organic farming!

I’m looking forward to exploring biodiversity in organic vs. conventional farming systems in part 3 of this series!

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Sources:

* Genesis 2,7

(1) large.stanford.edu (Stanford University)

(2) Sanders J, Hess J (eds) (2019) Leistungen des ökologischen Landbaus für Umwelt und Gesellschaft . Braunschweig: Johann Heinrich von Thünen-Institut, 364 p, Thünen Rep 65, DOI:10.3220/REP1547040572000