Leaving Cert Geography- Geoecology Essay

Describe and explain the characteristics of any one soil type you have studied

The soil type I have studied is brown earth soils. The key characteristics of soil are: colour, alkalinity, structure, humus content, texture and water content. These characteristics are affected by parent material, bedrock, topography, time and human activity.

Alkalinity
The alkalinity of soil refers to its pH value (its acidity or alkalinity). pH value affects many aspects of crop production and soil chemistry, including the availability of nutrients, the types of micro-organisms and the action of certain pesticides. Brown earths in Ireland are slightly acidic because of the high amount of rainfall and leaching of minerals in the soil. The pH of a soil is determined by climate, the bedrock, vegetation and cropping history. The addition of lime to the soil reduces pH levels. thereby reducing acidity. Fertilizers can affect soil pH, depending on what is used. C.A.N. (Calcium, Aluminium, Nitrate) has an acidifying effect. Cropping history also influences sol pH, for example if the same crop is planted it can strip alkaline nutrients from the soil leaving it acidic. The pH for most soil ranges from 5.5 to 7.5, and the most suitable pH for agriculture is 6.5. Leaching strips basic ions from soil leaving it acidic. Rotting vegetation produces CO2 which can cause a weak organic acid to form. Acidic soils lack calcium, magnesium and potassium which crops need to grow. The bedrock also influences soil pH as certain rocks produce certain soils. For example, granite in Donegal and Wicklow produce acidic soils. Neutral soils originate from limestone. 

Structure
Soil structure refers to the shape of peds in the soil. There are 3 main soil structures: crumb, platy or block. The structure of soil determines its degree of drainage and aeration. The water content of a soil is likewise influenced by structure. The moisture content of brown earth soils is influenced by the time of year and the topography. The optimum moisture content of soils is 25%. Air content is also vital and determined by the soils peds. Oxygen is needed for soil germination, plant growth, respiration and the breakdown of organic matter. The air content is influenced by climatic conditions including rainfall and human activities such as ploughing. The key geographic locations of brown earths in Ireland include the south, south-east and the midlands.

Humus Content
Humus refers to microscopic organic particles which are formed from decomposed organic matter. Soil organic material is made up of decaying remains of plants and animals. While humus is a relatively small part of soil, it is very important in determining the soils physical and chemical characteristics, including its fertility. Humus contributes to soil cation exchange capacity, water absorption and soil structure stability. It also aids the formation of soil aggregates, which controls pore size distribution, and the flow of water and air into and out of the soil. Humus also helps protect soil from erosion. The accumulation of humus in the O horizon leads to the release of nutrients into the soil. The main factors that determine the levels of organic matter in a soil are moisture, oxygen supply, pH and temperature. The humification rate varies according to climate; it is usually fast in hot humid regions and slow in cool, temperate conditions. In Ireland, for example, humification can take up to 10 years. The rich organic layer in the brown earth soils in Ireland is related to climatic conditions, which are favourable to the development of the natural deciduous forest biome. The addition of organic fertilizers (slurry and manure) and ploughing of crop residues increases organic matter and humus over time. However, the use of chemical pesticides can reduce biological activity and in turn reduces the level of humus.

Texture
Texture is the most important characteristic of a soil. The texture of soil influences drainage, nutrient content and the degree of which plant roots can penetrate it. Many of a soil's physical, chemical and biological attributes are related to texture, and textural determination is one of the essential elements in soil analysis. The texture of oil can be influenced by human activities such as ploughing, harrowing and the implementation of drainage programmes. Living organisms, especially burrowers, can also improve soil texture: moles, rabbits and earthworms can move and mix significant amounts of material over time. Parent material also has a significant role to play in influencing soil texture, for example when sandstone disintegrates it creates sandy soils, as in the Munster Valley region, while shale results in the formation of clay-dominant soils. Soil texture describes the size and distribution of individual soil particles, and the term usually refers to the amounts of sand, silt and clay in the soil. Soils are normally a mixture of all these, and a soil can be classified as loamy, sandy or clay, according to the proportions of sand, silt and clay in it. Brown earths have a loamy texture. Loamy soil has a mixture of sand, silt and clay, it is well aerated, has good drainage and retains minerals. Because of its fertility, farmers and gardeners prefer a loamy soil. In contrast, sandy soils contain more than 70% sand, they are well drained but may lose nutrients and are vulnerable to drought. Clay soils are described as heavy, and because the clay particles prevent water percolation they can become waterlogged. They can be difficult to plough and are best suited to pastoral farming.