Page 27 - Nutrient Management Planning Guide

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Chapter 2.1

Diffusion

Diffusion is the process by which nutrients spread from areas of high concentration to areas of low concentration. When roots absorb nutrients from soil solution the concentration of nutrients surrounding the root drops. As a result, nutrients in areas of higher concentration in soil solution migrate toward the root. Diffusion is an important process in crop uptake of P and K.

Table 2.1.2 Relative Contributions of Root Interception, Mass Flow, and Diffusion in Nutrient Transport to Corn Roots

Relative percentage of nutrients absorbed from the soil by a 12 t/ha (200 bu/ac) corn crop through root interception, mass flow, and diffusion

Nutrient

Root Interception

Mass Flow Diffusion

N 1 99 0 P 2 4 94 K 2 20 78 Ca 120 440 0 Mg 27 280 0 S 4 94 2

Adapted from Havlin et al. 2005

Nitrogen

Nitrogen is a key component of soil organic matter and is required by plants in large quantities. It is often the first limiting nutrient in prairie cropping systems.

Nitrogen forms a part of every living cell. It is an essential component of amino acids — the building blocks for proteins. The amount of N supplied to plants influences the production of plant proteins such as enzymes, mitochondria and carrier, storage and structural proteins.

Chlorophyll is the N-based plant component responsible for photosynthesis. The amount of chlorophyll in a plant is reflected by the shade of green in plant leaves. Therefore, plant leaves can provide a visual clue to the N status of a crop (e.g., lighter shades of green in plant leaves could suggest an inadequate N supply).

N Cycling in Soils

Nitrogen forms present in soil are constantly undergoing change. Nitrogen cycling is a relationship involving gains, losses and transformations of N among pools in the soil (Figure 2.1.3).