Soil Composition Soils come in many varieties and ensuring that you have the best possible blend will improve the quality of your lawn. Soil is typically categorized by a combination of its physical properties (texture, structure, density, etc), its composition and its chemistry (nutrient exchange capacity and pH). This article will focus on the main elements that effect lawn growth.
Soil is composed of a mixture of organic matter (the non-mineral component of soil), minerals (mainly sand, silt, and clay), gases (mainly air), liquids (mainly water), and organisms that together support life. For a typical healthy soil 50% is composed of air and water, 45% minerals, and just 5% organic matter.
Soil Texture Soil texture describes the percentages of sand, silt, and clay in the soil. Size, shape and amount of each in the soil influences drainage, moisture and nutrient holding ability. A soils texture can be used to determine grass type suitability and to predict the response of the soil too environmental and management conditions such as drought or nutrient requirements. A soils texture determines many of the properties of the soil, in particular how it retains or disperses water. Of these minerals clay is the smallest particle and sand is the largest – and this largely dictates how they react with water.
Different Types of Soil – Sand, Silt, Clay and Loam Soil can be defined in many ways. In civil engineering, soil is a naturally occurring, loose/un-cemented/weakly cemented/relatively unconsolidated mineral particles, organic or inorganic in character, lying over the bed rock which is formed by weathering of rocks. Soil is formed by different particles such as gravel, rock, sand, silt, clay, loam and humus.
1. Sand It is most extensively used construction material. It consists of particles of rock and hard minerals, such as silicon dioxide. They are the largest type of soil particles, where each particle is visible to naked eye. The large, relatively stable sand-particle size increases soil aeration, improves drainage in tight soils and creates plant-growth supporting qualities, or tilt.
2. Silt Silt is a sediment material with an intermediate size between sand and clay. Carried by water during flood it forms a fertile deposit on valleys floor. The particle size of silt ranges from 0.002 and 0.06 mm.
Silt is a non-plastic or low plasticity material due to its fineness. Due to its fineness, when wet it becomes a smooth mud that you can form easily into balls or other shapes in your hand and when silt soil is very wet, it blends seamlessly with water to form fine, runny puddles of mud.
3. Clay Clay particles are the finest of all the soil particles, measuring fewer than 0.002 mm in size. It consists of microscopic and sub-microscopic particles derived from the chemical decomposition of rocks. Clay is a fine grained cohesive soil. They stick together readily and form a sticky or gluey texture when they are wet or dry.
Clay is made of over 25 percent clay, and because of the spaces found between clay particles, clay soils hold a high amount of water. Clay expand when in contact with water and shrink when getting dry. Compared to sand particles, which are generally round, clay particles are thin, flat and covered with tiny plates.
4. Loam Loam is a mixture of clay, sand and silt and benefits from the qualities of these 3 different textures, favoring water retention, air circulation, drainage and fertility. These soils are fertile, easy to work with and provide good drainage. Depending on their composition they can be either sandy or clay loam.
The way the other particles combine in the soil makes the loam. For instance, a soil that is 30 per cent clay, 50 per cent sand and 20 per cent silt is a sandy clay loam, with the soil types before !loam” listed in the order their particles are most dominant in the loam. The labels !clay loam,” “silt loam” and !sand loam” are used to refer to soils that are composed predominantly of those ingredients.
Lets address high clay soils specifically A high clay soil holds on to nutrients, stays wet longer, and is slow to warm up and dry off in spring. These soils are slimy and can be formed in your hand when wet. Avoid working high clay soils when wet – this leads to compaction. Clay soils are made of extremely small particles that are packed close together. When lawns growing on clay soils receive even moderate foot traffic, the particles mash together in what is known as compaction. There is little room for water and air, because the voids are reduced. The limited space tends to fill up with water after a rainfall, leaving little or no oxygen for the root system. Water does not pass quickly through clay soils, and often will move downward only after the soil voids are completely saturated. The roots remain wet, and are vulnerable to rot.
Clay soils do have their advantages. They hold water well, reducing the loss of nutrients through runoff. Lawns growing in soils predominant in clay can be fertilized and watered less often, due to their holding capacity.
What is the Best Soil for Grass? Ideal soils for lawns have a loose structure to allow water, air, and nutrients to penetrate through them. Soil that contains too much clay will pack down, making it difficult for the plants to spread their roots and access much-needed moisture. Soil that contains too much sand becomes very loose and allows too much water to flow through, without allowing the plants time to absorb the moisture. Ideal soil contains organic matter known as humus. Humus is made up of the remains of decaying organisms and is packed with natural nutrients that not only help give soil a good crumbly or friable structure, but also act as a natural fertilizer for plants. Unlike manufactured fertilizers, organic matter releases nutrients slowly into the soil, keep it nourished for long periods of time. A good lawn soil also includes an element that aids with moisture retention and keeps the plants well hydrated.
The ideal soil mineral composition for most turf grass consists of about 70% sand, 15% clay and 15% silt.
