Page 26 - Nutrient Management Planning Guide

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Soil Nutrient Cycling

uptake. Exceptions to this generality include some metal elements that can be absorbed as organic complexes.

In order for ions to be absorbed by plant roots, they must come into contact with the root surface. This happens through three main mechanisms: root interception, mass flow, and diffusion.

Root Interception

Root interception is the uptake of nutrients by plant roots as they grow through the soil and incidentally come into contact with nutrients. Nutrient uptake by root interception is directly related to the volume of the root system, which in most cases is less than 1% of the total soil volume. Consequently, root interception makes a small contribution to total nutrient uptake.

Mycorrhiza and Plants— An Infectious Partnership

Plant-mycorrhizal associations increase functional root volume. Mycorrhizal fungi infect plant roots and produce their own root-like structures called hyphae, which act as extensions of the plant’s root system. Nutrient absorption is enhanced since the hyphae can increase the absorptive surface area of root systems by up to ten times compared to non-infected root systems.

Mass Flow

In mass flow, dissolved nutrients move with water towards root surfaces where they are absorbed. Mass flow is a significant mechanism for the uptake of some nutrients, such as nitrogen. Nutrient uptake by mass flow is reduced in dry conditions and at lower temperatures because the rate of transpirational water uptake is reduced (Figure 2.1.2).

Created by Len Kryzanowski

Figure 2.1.2 Transpirational Movement of Water Through a Plant

While mass flow helps the plant meet its requirements for essential nutrients, it frequently results in excess uptake of several soluble nutrients including K + , Ca 2+ , and Mg 2+ . This luxury uptake is not essential for crop growth, but can contribute to better feed or food quality of the harvested crop.

Evaporation

Translocation

Root Absorption