Agroforestry Word of the Week - August 12, 2020 - Leaching

Leaching -/lēCH'ng/ - process

August 12, 2020


Definition: The downward movement of dissolved nutrients across the soil.

A Closer Look: Leaching occurs when the soil's water-carrying capacity is surpassed, resulting in the excess water percolating down through the topsoil and under the subsoil and the rooting zone. In consequence, any nutrients carried by the water will be lost.


What type of soil is prone to leaching?

All soil is prone to leaching. However, different types of soil are more prone to nutrient leaching than others.

Sandy soil: Sandy soil is the largest in particle size. As a result water drains through it rapidly, carrying nutrients with it. It is the most prone to nutrient leaching as few plants are able to grow in sandy soils since their roots do not have the chance to absorb the water and nutrients that flow quickly through them.

Silty soil: Silty soil is made of particles much smaller than sand, and is able to retain water for longer. While silty soil is less prone to leaching than sandy soil, it may still not be the most effective way of mitigating nutrient loss from leaching.

Clayey soil: Clayey soils have the smallest particles of the three types. Water is much slower to drain in clay, and it holds nutrients much better. While this may be critical in preventing leaching, clayey soil can become very hard and dense, especially when dry, making it difficult for plants to get the air they need to grow.

How do you mitigate nutrient leaching in soils?

To mitigate nutrient leaching in soils, it’s critical to find a balance between silty and clayey soils. The proper balance ensures that the particles are not all too small to inhibit flow of water and nutrients through the soil but also not so large that they allow the water to flow through the soil too quickly, preventing plants and roots from taking in the nutrients dissolved in the water. Want to easily identify what kind of soil you are working with? Learn how to carry out a simple soil test in Chapter 5 of the Technical Manual.
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