Page 42 - Nutrient Management Planning Guide

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Basic Soil-Plant Interactions

This chapter will discuss soil characteristics and processes that influence plant nutrient availability including: ion exchange in soils, organic matter, pH (acidity and alkalinity), and salinity.

Important Terms

Table 2.2.1 Key Terms and Definitions

Term Definition

Aerobic The presence of oxygen.

Aggregate

A soil structure unit formed from primary soil mineral particles (sand, silt, clay) and organic matter that are grouped together. Anaerobic The absence of oxygen.

Anion An atom or group of atoms (e.g., a molecule) with a net negative charge.

Base Saturation

Is the percentage of total cation exchange capacity occupied by base cations such as calcium, magnesium, sodium and potassium. Buffering Capacity The resistance of a soil to change in pH.

Calcium Carbonate Equivalent

The carbonate content of a liming material that is calculated as if all the carbonate is in the form of calcium carbonate.

Cation An atom or group of atoms (e.g., a molecule) with a net positive charge.

Cation Exchange Capacity

The capacity of a soil for exchange of positively charged ions between the soil and the soil solution.

Ions

Are atoms or groups of atoms (e.g., a molecule) that carry an electrical charge due to the loss or addition of one or more electrons.

Osmotic Stress The adverse response of a plant to a high salt concentration in the soil relative to the plant. Saline Seep Intermittent or continuous saline discharge at or near the soil surface under dryland conditions.

Salt Index

Expresses a fertilizer’s potential to cause salt injury in germinating seedlings. It is based on a relative rating to sodium nitrate that is assigned an index value of 100.

Soil Solution

The liquid phase of the soil and its solutes, consisting of ions dissociated from the surfaces of the soil particles, and other soluble materials.

Tilth

The physical condition of the soil, especially in relation to its suitability for tilling, planting or growing a crop.

Ion Exchange in Soils

Ion exchange is the movement of ions (charged nutrients) between soil particle surfaces and the soil solution. It is the most critical soil process that affects crop nutrient availability.

Soil particle surfaces carry static electric charge. While soil particle surfaces can have both positive and negative charges, most Alberta soils carry a net negative charge. The location where ions interact with a charged soil particle is called an exchange site. Negatively charged exchange sites attract positively charged ions (cations) such as potassium