Which fertilizer recommendation concept best increases soil fertility levels most slowly?

The concept of Crop Sufficiency focuses on providing just enough nutrients to meet the needs of the crop, rather than exceeding those needs. This approach is grounded in the understanding that crops can perform adequately with a certain level of nutrients but may not reach their maximum potential. As a result, the aim is to maintain soil fertility levels to a point that meets the crop's demands without necessarily increasing nutrient levels significantly in the soil over time.

This method contrasts with systems like Crop Removal, which tends to focus on how much nutrient is taken away by harvested crops, and Soil Testing, which can reveal the soil's nutrient status and initiate strategies to amend deficiencies. Lastly, the Economic Threshold approach revolves around ensuring that input costs remain below the potential economic return, which may lead to more aggressive fertilizer application to optimize yield.

In summary, Crop Sufficiency leads to a more gradual increase in soil fertility levels since it targets minimal necessary input, focusing on sufficiency rather than excess. This method tends to maintain a stable, sustainable nutrient balance over time, hence its slower addition to soil fertility levels compared to the other approaches.