Certified Crop Advisor Practice Exam

Which of the following nutrient uptake mechanisms is most important after a rainfall event?

1. Root interception

2. Diffusion

3. Mass flow

4. Cation exchange

The correct answer is: Mass flow

The uptake mechanism that is most important after a rainfall event is mass flow. After significant rainfall, nutrients are often dissolved in the soil water and are subsequently mobilized through the soil profile. Mass flow refers to the movement of nutrients with the bulk flow of water towards the roots of plants. This process is enhanced after rainfall because the influx of water increases the soil water's velocity, carrying dissolved nutrients directly to the root zone. During and after rainfall, the plant roots are submerged in nutrient-rich water, facilitating the uptake of these dissolved nutrients as water flows into the roots. This mechanism is particularly vital for macronutrients such as nitrogen, potassium, and calcium, which rely on water movement for efficient absorption. While root interception, diffusion, and cation exchange are all important nutrient uptake mechanisms, they play a lesser role immediately following a rainfall event. Root interception pertains to the ability of roots to capture nutrients as they grow through the soil. Diffusion occurs when nutrients move from high concentration areas to low concentration areas, which is relatively slower compared to the rapid movement facilitated by mass flow. Cation exchange involves the swapping of nutrient cations with hydrogen ions in the soil solution but requires a certain degree of stability in the soil solution that is not as prevalent immediately after