Soil Composition: Mineral Matter

• Mineral matter, organic matter, water, and air form different percentages of any soil and play a major role in soil development.

Aspect 1: Mineral Matter

• Mineral matter comprises 45% of soil and originates from the parent material, which is the most important soil component.
• Mineral matter impacts soil development in terms of texture, soil color, soil pH, and the minerals available for uptake by plants.
• Soil texture refers to the proportion of sand, silt, and clay in the soil.
• Sandy soils have a coarse texture and are well-drained; the weathering of sandstone results in quartz grains in soils on the Comeragh Mountains in Co. Waterford.
• These grains result in large pore spaces and well-drained soils.
• Clay soils have a fine texture and small pore spaces, which leads to waterlogged conditions.
• These conditions have led to gley soils forming on lowlands and uplands around Ireland, e.g., Co. Mayo.
• Loamy soils have an equal mix of sand, silt, and clay and are well-drained soils, e.g., brown earth soils, which occur in the east of Ireland.
• Mineral matter impacts soil pH; calcium released from limestone by carbonation results in the development of an alkaline soil.
• Chemical weathering of granite by hydrolysis results in the mineral feldspar, which binds quartz and mica together, being broken down into a type of clay called kaolin.
• Clay particles result in poorly drained soil, and quartz will give the soil an acidic pH.
• The weathering of sandstone also leads to the release of quartz, which leads to the development of acidic soils.
• Fertilizers may need to be added if a soil is too acidic or alkaline to make it more neutral and suitable for agriculture.
• The color of the soil can be impacted by the type of mineral matter.
• Oxidation of iron particles in mineral matter change them into iron oxide, giving the soil a red color.
• If a soil undergoes podzolization, a form of extreme leaching where quartz is the only mineral left behind, the soil will turn ash grey.

Aspect 2: Organic Matter

• Organic matter consists of plant roots, microorganisms, and decaying plant litter, making up only 5% of soil components.
• Microorganisms break down plant litter into humus, which is the end product of organic matter.
• Humus is a gel-like substance, full of nutrients and essential for plant growth, and is quite sticky, which binds soil together, allowing soil to hold and store water.
• Water mixes with humus, making it possible for plant roots to take in this nutritional humus.
• Humus prevents the loss of nutrients by leaching due to the binding of the soil and storage of water.
• Brown earth soils, found in the south and east of Ireland, are formed under deciduous woodland and are rich in humus, which was formed by the microorganisms decomposing leaves that fall in autumn.
• Peat soils are found in the midlands.