Certified Crop Advisor Practice Exam

As organic matter content increases, how do organic solutes behave in soils?

1. They move more quickly

2. They move more slowly

3. They are absorbed more

4. They become more volatile

The correct answer is: They move more slowly

As organic matter content increases in soils, organic solutes tend to move more slowly. This behavior can be attributed to several factors related to the properties of organic matter itself. Organic matter enhances soil structure and increases the soil's cation exchange capacity, which in turn can lead to a higher adsorption of organic solutes within the soil matrix. Moreover, organic matter provides sites for sorption, where molecules can bind to solid surfaces rather than remaining in the soil solution. As a result, increased organic matter content impedes the mobility of solutes, thus causing them to migrate more slowly through the soil. This is particularly important for managing nutrient availability and pollution control in agricultural systems. The other options suggest behaviors that don't align with the principles of soil chemistry and physics. For instance, while it might seem intuitive to think higher organic matter would increase the mobility of solutes, the reality is that the binding and retention capabilities of organic matter have the opposite effect.