Page 46 - Nutrient Management Planning Guide

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Basic Soil-Plant Interactions

Table 2.2.2 Changes in Organic Matter Content (%) of Alberta Soils Due to Cultivation

Condition

% Organic Matter in Alberta Soil Zones

Black

Dark Brown

Brown

Dark Gray

Gray

Native state

6-10 4-6 4-5 4-5 1-2

Under cultivation

4-6 3-4 2-3 2-3 1-2

Source: Lickacz and Penney 2001

Management practices that help build soil organic matter include applying solid or composted livestock manure, more root and above ground crop residue production, reduced tillage, continuous cropping, direct seeding, avoiding straw removal, green manuring and perennial forage production. Optimizing soil fertility can also help build soil organic matter. Healthy, vigorous crops provide denser ground cover, which reduces the risk of erosion. High yield crops also leave greater volumes of organic residues in the form of roots, stems and other unharvested materials.

Soil Fertility Implications of Organic Matter

Organic matter has a large influence on soil fertility for crop production. It exerts this influence in several ways:

It is an important source of nutrients required by •

crops and is a critical component of nutrient cycling in soils. Organic matter can be described as a “revolving nutrient bank account”. It increases cation exchange capacity of soils by •

providing a large number of additional exchange sites (Figure 2.2.3). This additional exchange capacity is pH dependent.

It improves soil structure, aggregate stability •

(measure of ability for soil particles to withstand disintegration) and tilth. These properties increase water infiltration and reduce water erosion, which is a significant mode of nutrient and organic matter loss.

Adapted from Brady and Weil 2000

Figure 2.2.3 Chemical Groups in Organic Matter Responsible for the High CEC of Organic Matter

pH

The pH of a soil is a measure of the concentration of hydrogen ions (H + ) in soil solution. It is expressed on a logarithmic (power of 10) scale, which ranges from 1 to 14. A one-point change on the pH scale represents a 10-fold change in the acidity of a solution (e.g., a solution with pH 4 has 10 times the concentration of hydrogen ions than a solution with a pH of 5 and 100 times more than a solution with a pH of 6).

A neutral soil has a pH near 7. Acidic soils have a pH of less than 6, while basic or alkaline soils have a pH greater than 7. Crops differ in their tolerance to pH conditions, but most crops grown in Alberta prefer a pH in the range of pH 6.5 to 7.

An advantage of manure application (primarily solid manure) to soil is that it directly and indirectly contributes to soil organic matter. In contrast, commercial fertilizers indirectly contribute to soil organic matter by increasing crop yield and residue.

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