Types of fertilizer

Certain weather and soil conditions can lead to nitrogen immobilisation, denitrification, volatilization or leaching, all reducing fertilizer efficiency. In response, the industry has developed special types of fertilizers designed to reduce these effects. They include foliar, slow and controlled release fertilizers, as well as fertilizer additives such as urease and nitrification inhibitors.

The most common phosphate fertilizers are single superphosphate (SSP), triple superphosphate (TSP), monoammonium phosphate (MAP), di-ammonium phosphate (DSP) and ammonium polyphosphate liquid.

Different fertilizer products have different release profiles and need different spreader settings for efficient application.

Potassium is also available in a range of fertilizers which contain potassium only or two or more nutrients and include Potassium chloride (KCl), Potassium sulphate (K2SO4) or sulphate of potash (SOP), Potassium nitrate (KNO3), known as KN.

Calcium (Ca), magnesium (Mg) and sulphur (S) are essential  secondary plant nutrients. They are not usually applied as straight fertilizers but in combination with the primary nutrients N, P, and K.

Sulphur is often added to straight N fertilizers such as ammonium nitrate or urea. Other sulphur sources are single superphosphate (SSP), potassium sulphate (SOP) and potassium magnesium sulphate (Kainite), the latter also containing magnesium.

Kieserite is a magnesium sulphate mineral that is mined and also used as fertilizer in agriculture, mainly to correct magnesium deficiencies. Calcium is mainly applied as calcium nitrate, gypsum (calcium sulphate) or lime/dolomite (calcium carbonate), of which calcium nitrate is the only readily plant available source of calcium.

Today, a large number of special fertilizers are available to supply plants with important micronutrients such as iron, manganese, boron, zinc and copper. These can be either inorganic or organic compounds, with the inorganic varieties further divided into water-soluble and non-soluble products.

There are two major types of inhibitors today available for farmers in the EU.

Nitrification inhibitors are chemical compounds that delay the nitrification of ammonium by suppressing the activity of nitrosomonas bacteria in the soil. The objective is to preserve the ammonium in its soil-stable form and slow its conversion to nitrate. This temporarily reduces the proportion of nitrate in the soil, and thus the potential for leaching losses into water or the formation of N₂O gas in the atmosphere.

• Urease inhibitors are chemical compounds that delay the first step of degradation of urea in the soil, the hydrolysis that can create NH3 emissions and which may occur before its transformation to ammonium. They contribute to reducing significantly ammonia emissions to the air, one of the major air pollutants.