Soil is a word which has a different meaning a natural body comprised of solids (organic and minerals matters), gasses, and liquid that occurs on the land surface, occupies space, and is characterized by layers, or horizons, that are distinguishable from the initial material as a result of additions, losses, transfers, and transformations of energy and matter or the ability to support rooted plants in a natural environment.
The farmer and gardener think of the soil as the top few centimeters – the depth of plough or cultivation for the former and a spade or garden fork depth of the latter (the ‘topsoil’). They tend to ignore what’s underneath. Yet this deeper material (or ‘subsoil’) is very important for plant growth, storing and supplying nutrients and water. Also, a number of chemical substances (whether naturally produced within the soil or added by human activity) pass from the topsoil through to the subsoil. These may eventually reach underground water stores and rivers, burns or lochs. The soil consists of horizons near the Earth’s surface that, in contrast to the underlying parent material, have been altered by the interactions of climate, relief, and living organisms over time.
Soil is a o home to number of different organisms, bacterias which help to provide nutrients to the plant. In fact, scientists believe that there are probably more individual species living below ground than above the surface e.g. Worms, beetles, caterpillars, ants and larger soil creatures. However, just one teaspoon of soil will also contain up to several million protozoa (probably the simplest form of animal life), bacteria, algae and nematodes (microscopic worm-like animals). Many of these species are vital to the proper functioning of soils. Unfortunately we know nowhere near enough about them to describe the roles of more than just a few.
So a a grower we need to be more cautious about the soil health and should take proper steps to maintain the health of soil.
Descriptive terms commonly associated with certain ranges in soil pH are:
Extremely acid : < than 4.5; lemon=2.5; vinegar=3.0; stomach acid=2.0; soda=2–4
Very strongly acid : 4.5–5.0; beer=4.5–5.0; tomatoes=4.5
Strongly acid : 5.1–5.5; carrots=5.0; asparagus=5.5; boric acid=5.2; cabbage=5.3
Moderately acid : 5.6–6.0; potatoes=5.6
Slightly acid : 6.1–6.5; salmon=6.2; cow’s milk=6.5
Neutral : 6.6–7.3; saliva=6.6–7.3; blood=7.3; shrimp=7.0
Slightly alkaline : 7.4–7.8; eggs=7.6–7.8
Moderately alkaline : 7.9–8.4; sea water=8.2; sodium bicarbonate=8.4
Strongly alkaline : 8.5–9.0; borax=9.0
Very strongly alkaline : > than 9.1; milk of magnesia=10.5, ammonia=11.1; lime=12
What it Means- Soil pH
Soil reaction or soil pH is an indication of the acidity or alkalinity of soil and is measured in pH units. Soil pH is defined as the negative logarithm of the hydrogen ion concentration. The pH scale goes from 0 to 14 with pH 7 as the neutral point. As the amount of hydrogen ions in the soil increases the soil pH decreases thus becoming more acidic. From pH 7 to 0 the soil is increasingly more acidic and from pH 7 to 14 the soil is increasingly more alkaline or basic.
pH Affects Nutrients, Minerals and Growth
The effect of soil pH is greater on the solubility of minerals or nutrients. Before a nutrient can be used by plants it must be dissolved in the soil solution. Most minerals and nutrients are more soluble or available in acid soils than in neutral or slightly alkaline soils. Phosphorus is never readily soluble in the soil but is most available in soil with a pH range centered around 6.5. Extremely and strongly acid soils (pH 4.0-5.0) can have high concentrations of soluble aluminum, iron and manganese which may be toxic to the growth of some plants. A pH range of approximately 6 to 7 promotes the most ready availability of plant nutrients. But some plants, such as azaleas, rhododendrons, blueberries, white potatoes and conifer trees, tolerate strong acid soils and grow well. Also, some plants do well only in slightly acid to moderately alkaline soils. However, a slightly alkaline (pH 7.4-7.8) or higher pH soil can cause a problem with the availability of iron to pin oak and a few other trees in Central New York causing chlorosis of the leaves which will put the tree under stress leading to tree decline and eventual mortality.
The soil pH can also influence plant growth by its effect on activity of beneficial microorganisms Bacteria that decompose soil organic matter are hindered in strong acid soils. This prevents organic matter from breaking down, resulting in an accumulation of organic matter and the tie up of nutrients, particularly nitrogen, that are held in the organic matter.
Changes in Soil pH
Soils tend to become acidic as a result of:
Rainwater leaching away basic ions (calcium, magnesium, potassium and sodium);
Carbon dioxide from decomposing organic matter and root respiration dissolving in soil water to form a weak organic acid;
Formation of strong organic and inorganic acids, such as nitric and sulfuric acid, from decaying organic matter and oxidation of ammonium and sulfur fertilizers. Strongly acid soils are usually the result of the action of these strong organic and inorganic acids.
Some common liming materials are:
Calcic limestone which is ground limestone;
Dolomitic limestone from ground limestone high in magnesium; and
Miscellaneous sources such as wood ashes. The amount of lime to apply to correct a soil acidity problem is affected by a number of factors, including soil pH, texture (amount of sand, silt and clay), structure, and amount of organic matter. In addition to soil variables the crops or plants to be grown influence the amount of lime needed.
In addition to monitoring soil pH the nutrient status of the soil test should be conducted regularly for proper status of soil pH.