exture (it’s not practical to add more clay), a farmer’s primary solution to increase soil fertility is to increase SOM. (See this post for how to increase SOM).
Many coffee farms have soils that are naturally acidic (lots of H+, low pH). In soils with a high CEC, hydrogen molecules crowd out nutrients on cation exchange sites. To raise the pH to more “plant friendly” levels (giving more space to nutrients), liming (applying gypsum) can help neutralize the acid in the soil by saturating the exchange sites with cations (nutrients) like calcium and magnesium. (In CRS’ field research, they are finding that many coffee farms are very acidic, so farmers are often wasting money on fertilizer when they could get a lot more benefit from applying gypsum, which is far cheaper!).
Note: High CEC soils require more liming than soils with low CEC. In contrast, low CEC soils need to be limed more frequently than high CEC soils. Acidity is a logic puzzle!
All aspects of soil heath and fertility are connected. When we see that nutrient holding capacity increases with SOM, and that, for example, SOM increases with more sustainable farming practices, it should motivate us to identify the best practices for increasing SOM.