Soil fertility and mans effect on the soil
The phase soil fertility refers to how well plants will grow in a specific soil - Soil fertility and mans effect on the soil introduction. There are many aspects to soil fertility these are :-
* The type of soil
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* The structure of the soil
* The acidity
* The minerals in the soil
The type of soil refers to the texture and the type of particles that make up that soil. There are three types of particles sand, silt and clay. Each of the different particles has different characteristics which can help a soils fertility. A sandy soil is well drained and easily cultivated but they are vulnerable to drought as well as needing lots of fertilisers because the nutrients are easily leached out. A silty soil tend to lack minerals but more moisture is retained because of the smaller pore size, but heavy rain can cause cementing and the risk of sheetwater increases as well as erosion.
Clay soils are rich in nutrients but are very difficult to plough and become waterlogged easily.
The best soil is a loam soil this is because it has equal shares of the particles and uses the positive things from each one.
A soils structure is a major factor in the fertility of a soil. If the soil is layered horizontally this can cause water logging as the layers are tightly compacted the water gets trapped between each layer. The best structure for plants to grow is a crumb or granular form where there are individual particles which join together loosely.
Most of the soils in the UK are slightly acidic but this acidity increases as heavy rains leach out elements such as calcium faster the they can be replaced. Acid soils therefore need constant liming if they are to be farmed successfully.
A slightly acid soil is the optimum for farming in Britain as this helps to release secondary elements. However if the soil becomes to acidic it releases iron and magnesium which, in excess may become toxic and poisonous to the plants.
In South American in the amazon rainforest must of the forest is being taken away in a process called Slash and burn. The trees are cut down to clear space to use the fertile soil for farming and then the trees are burnt. This burning adds nutrients to the soil, but this is one of the only good things to come from Slash and Burn. Farmers grow crops on the fertile land but once the lands nutrients have been used up the farmers move on to another part of the rain forest and the process starts over again. As the trees have been removed the land is bare with no trees binding the soil together this leads to mudslides and flash floods. The tree that have been removed can’t be replaced as the have taken hundreds of years to develop.
Another form of land mismanagement is mainly in African Savannas. Overgrazing accelerates soil erosion. The tribes in Africa survive on eating their animals and the animals eat the plants on the savannas but as the number of humans expanded quickly there was a need for more herbivorous animals to support them. This surplus number of animals leads to the overgrazing of the land and the reduction of grass cover and when new shots push through after the rains they are immediately eaten by the animals which are normally either sheep, cattle, goats or camels. As the grass cover has gone when rain comes it causes erosion.
In agriculture land management is very important. Ploughing the land for crops can have adverse effects on soil. Ploughing the land too deep means that the soil structure is being destroyed as the peds are broken up and the organic material is buried too deep for the plants to use. Ploughing also loosens the topsoil which can then be blown away by the winds or carried away by water erosion. Ploughing up and down the field can cause channels which increase the rate of surface runoff.
To combat the problem of loose soil humus can be added this helps to bind the soil and reduce it vulnerability to erosion. Humus as well as clay and peat can be added to sand to give it body and improve their water holding capacity, the opposite thing can be done to heavy clay soil by adding sand this improves the drainage.