The use of fertilisers in farming.

The use of fertilisers in farming

Plants or in this case crops make their own food through photosynthesis, but in order to do so require nutrients. These come in two main forms: Macronutrients and Micronutrients.

The primary nutrients that plants use include nitrogen, phosphorus and potassium, of which are usually depleted first in the soil because plants use large amounts of them for their growth. Secondary nutrients are calcium, magnesium and sulphur, but there are usually enough of these nutrients in the soil.

Micronutrients include boron, copper, iron, chloride, manganese, molybdenum and zinc of which are all elements essential for plant growth but are only required in small amounts.

In order to produce a good harvest plants need ideal conditions to grow. This includes having the right amounts of light, water, an appropriate temperature and a supply of inorganic ions such as nitrate, phosphate and potassium.

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In farming the crop plants are harvested. Thus, nutrients are removed from the soil instead of allowing the inorganic ions present in the plants to decompose back into the soil. Unlike natural ecosystems fertilisers are needed to restore nutrient levels in the soil to provide optimum plant growth conditions to maximise yields. Under natural conditions the soil nutrients are recycled. Once the plant dies, it is decomposed by bacteria/putrefying bacteria, which breaks down organic molecules and releases the nutrients back into the soil. In natural ecosystems, plants obtain their nitrogen from nitrogen fixing bacteria in the soil. Dinitrogen gas (N2) in the atmosphere can be used by soil microorganisms and converted into forms that can be used by plants, either symbiotically or non-symbiotically. Leguminous plants that contain Rhizoium bacteria may fix enough N2 to meet almost 80% of the plants nitrogen needs.

The represents one of the most important nutrient cycles found in terrestrial ecosystems. Nitrogen is used by living organisms to produce a number of complex molecules like , , and . The largest store of nitrogen is found in the atmosphere where it exists as a gas (mainly N2). Other major stores of nitrogen include organic matter in soil and the oceans. Despite its abundance in the atmosphere, nitrogen is often the most limiting nutrient for plant growth. This problem occurs because most plants can only take up nitrogen in two solid forms: ion (NH4+) and the ion (NO3- ). Most plants obtain the nitrogen they need as nitrate from the . Ammonium is used less by plants for uptake because in large concentrations it is extremely toxic.

Ammonia can be taken up directly by plants, usually through their roots. However, most of the ammonia produced by decay is converted into nitrates. This is accomplished in two steps:

-Bacteria of the genus Nitrosomonas oxidize NH3 to nitrites (NO2-).

-Bacteria of the genus Nitrobacter oxidize the nitrites to nitrates (NO3-).

These two types of bacteria are nitrifying bacteria. Through their activities nitrogen is made available to the roots of plants.

In most ecosystems nitrogen is primarily stored in living and dead . This organic nitrogen is converted into inorganic forms when it re-enters the via decomposition. , found in the upper soil layer, chemically modify the nitrogen found in organic matter from (NH3) to salts (NH4+). This process is known as and it is carried out by a variety of bacteria, , and .