scientifically how does different soils affect plants?

Answer 1

Soil is made up of various mineral components and bio-organic substances. Minerals are divided by size. Clay particles are the smallest of the three, silt are intermediate in size, and sand, the largest. Together the organic and mineral parts in differing proportions make up the soils texture. If clay is more than 40% of the texture it is called a clay soil. Loam has the three in equal amounts.
The relationship of the minerals and organics make up the soils structure. How porous, how compacted, how the soil particles are assembled as aggregates. This all affects the movement of air, water, nutrients and the living creatures that inhabit the soil, the edaphon. Plants are happiest in a looser, more crumbly or granular structure refered to as the soils tilth.

Acidity or alkalinity of the soil is determined by the mineral content. It is described, scientifically, as the pH value, this is a measure of hydrogen (H+) ions available, an acid soil has a low pH, neutral is pH 7 and alkaline is greater than pH 7. The pH affects the availability of nutrients the plants need to grow. Most plants grow best at a pH of 6.5 as most plant nutrients are available for uptake by the roots at this pH level, the pH range of most soils is between 5.5 and 7.5. While slightly acidic soils range form pH 5.8 to 6.5 and extremely acid soils range from pH 4.0-5.0. But plants, such as azaleas, rhododendrons, blueberries, white potatoes and conifer trees, tolerate strong acid soils and grow well at pH5.0 - 5.5. A pH level of around 6.3-6.8 is also the optimum range preferred by most soil bacteria, although fungi, molds, and anaerobic bacteria have a broader tolerance and tend to multiply at lower pH values.

The presence of calcium ions (Ca++) is usually what determines the pH of soil, as they displace hydrogen ions in solution. A soil particle with a full amount of H+ ions is weakly acid, but the presence of calcium ions makes it neutral or alkaline. Calcium is leached away so soils have a tendency to become acid and this occurs faster in sandy soils. The humus coating on soil particles and the adherent properties of clay particles both hang on to calcium and reduce the leaching.
The Edaphon consists of; 40% fungi/algae , 40% bacteria/actinomycetes, 12% earthworms, 5% macrofauna, & 3% micro/mesofauna