Can Anthrosols Inform Soil Health Practices?

Anthrosols are a soil group with properties that have been modified by human agricultural activity. Some anthrosols have been intentionally “engineered” over time to improve their function for agricultural production. Amazonian Dark Earths (ADE) are good examples of anthrosols that have been created by Indigenous peoples to boost agricultural productivity. ADE have significantly different physical, chemical, and biological characteristics when compared to nearby unmodified soils of the same type. While soils across the Amazon basin are incredibly diverse, most soils across this vast area are highly weathered, have high iron and aluminum oxides content, and have high pH levels (with some exceptions such as portions of the Brazilian state of Rondônia). In principle, such soil characteristics should limit agricultural productivity. However, the widespread use of ADE was one factor permitting significant agricultural activity across the Amazon basin prior to colonization (such activity has been maintained at smaller scales up to the present day).

ADE are created through a variety of different methods, but common ADE improvements across the Amazon basin include the addition of biochar, the incorporation of large amounts of organic matter, and the mixing of soil horizons. These amendments lead to improved soil characteristics such as lower bulk density, higher cation exchange capacity, and measurable increases in the types and overall numbers of soil microorganisms. ADE horizons can be up to 1 meter(!) in depth.

The large historical populations of Indigenous peoples across the Amazon basin resulted in between approximately 0.1% to 10% of soils across this vast region being modified into ADE. It is important to point out that it is not one magic ingredient or practice the led to the creation of ADE. They were (and still are) created as part of broader landscape management practices and it takes a significant amount of conscious effort and time to create them. Importantly, anthrosols similar to ADE have been independently developed in other parts of the world, such as West Africa.

Soil health practices have gained traction amongst commercial grain, oilseed, and pulse farmers in Canada and the United States during the past decade. As with ADE, the end goals of soil health practices are to improve the physical, chemical, and biological characteristics of soils with an explicit focus on agricultural production. Soil health principles include no-till, residue maximization, cover cropping, and livestock integration. This is a relatively new perspective in soil management since most academic, government, and farmer-developed approaches to soil management long assumed an irreversible decline in soil function after the conversion of “natural” soils to commercial production.

Anthrosol development and soil health practice implementation are highly context specific. Is there a possibility that anthrosols can provide some lessons for soil health practitioners? Biochar shows promise as a soil amendment in the commercial production of grains, oilseeds, and pulses. However, biochar is not the “silver-bullet” that it is often hyped to be. Its success as a key component of ADE hinges on the addition of other soil amendments and the use of other landscape management practices. At the same time, it remains questionable as to whether the manufacture and application of biochar at the scale needed for large grain/oilseed/pulse farms can be made commercially viable.

In conclusion, processes developed to manufacture anthrosols may not directly translate into commercially relevant soil health practices. However, the independent development of methods to improve soil characteristics for agricultural production at various times and places around the world demonstrates that soil management is an essential part of agricultural production, regardless of context.  

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