Does soil management affect soil health?

There is a huge amount of research work done and a significant portion is so specific that you can’t make application to anything in the real world. On the other side there is research that is so broad and almost meaningless that there is no way to apply it in the real world.

I like this study because it took a look at the relationship between a soil management index (SMI) they developed for the research and soil health indicators that were developed at Cornell called the CASH (Comprehensive Assessment of Soil Health) protocol. This CASH system looks at the physical, biological and chemical properties of a soil to develop an overall quality score. The Haney soil test does the same sort of thing.

The soil management index (SMI) for the over 20 farms in the study was developed by (1) quantifying the crop diversity, (2) the frequency of soil disturbance and the (3) number of applications of external organic amendments (manure). These 3 items would make up the SMI score and then they compared that to the soil health indicators for those particular farms. Clear as mud? Don’t worry because what matters are the results!

What are the results?

• Soil management significantly affected all measured soil health indicators.
• Fields with a higher soil management index (SMI) showed better soil health.
• Soil health of farm fields was generally poorer in comparison with unmanaged soil. Unmanaged soil was a forest area or good pasture area.
• The ratio of soil health of farmed to unmanaged soil increased with increasing SMI. (This is important!)

So, what they found was that all the soil health measures got better the higher the SMI number was. Generally, this would make sense and be what we would expect. What I was surprised by was that there were two soil health indices that were strongly influenced by the soil management – wet aggregate stability and extractable soil protein (organically bound nitrogen available to microbes). Soil texture seemed to have more effect on these other three soil health indicators – active carbon, soil respiration and soil organic matter. Soil management did have an effect on these three, but texture had a stronger effect.

Wet aggregate stability is a measure of how well the soil stays together in a rainfall simulation. Aggregate stability means the soil is stable, held together but all kinds of things, one of which is the glue our microbes supply if they are active. Good soil aggregation means less compaction, room for water movement and root growth. Second, the extractable soil protein is a measure of the food available to those microbes. I think it makes sense that a high SMI would mean a high Soil Health Score! Wouldn’t you expect that to happen if you reduce tillage, add in cover crops or change up your crop diversity and add soil organic amendments?

Lastly, there is some thought that a tool like SMI, properly developed, could be a way to know if we are increasing soil health. This research analysis is showing they are highly correlated and that is a good thing. Also, it might be a way to measure and pay for potential carbon sequestration because a healthy soil does sequester carbon.