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Phosphate/Phosphorus

Main Nutrient
Phosphorus is a vital nutrient. It encourages the growth of plants (as does nitrogen with the construction of proteins) and the development of the root-system.

Phosphate appears in the soil in different forms. We analyse standard three forms of phosphate. Total phosphate, root extractable phosphate and the amount of phosphate in the soil that is easily absorbed by plants (phosphate soluble in a low concentration of neutral calcium chloride). Then with help of other analysis in the standard package we calculate the organic phosphor and the fixated inorganic phosphor.

A high phosphorus in soil, but the plant still doesn’t get its phosphate.
We measure this phenomenon too often. The total phosphate / phosphor is high, but the amount that can be absorbed or reached by plants is low. Only a huge amount of P-fertilizer OR a change in the microbiology in the soil can improve the availability of the phosphor. Different types of mycorrhiza are one of the solutions to this problem. Furthermore there are specific bacterial and enzymes in the soil that can improve the solubility of the phosphor.

A high inorganic phosphor.
When the amount on inorganically phosphorous is high, much phosphate has been fixated throughout the years. Fertilization with inorganic phosphate is of no use here. Also, rock phosphate amendments are not wise in this case. This because there is enough of this phosphate in the soil already, but it won’t move.

Phosphate Fixation.
Phosphate fixation takes place if there is too much mobile aluminium, iron and/or zinc present in the soil. The phosphate that is soluble in the water in the soil reacts with free Zinc, Iron, aluminium and manganese. Phosphate is then fixed in the form of manganese- zinc-, iron- and aluminium phosphate minerals which are insoluble and in most cases useless for plants. A high content of calcium in combination of a high soil pH can also be responsible for a phosphate fixation. This almost insoluble calcium phosphate can possibly become available for plants at a later stage when it is broken down by soil life into a phosphate which is soluble in water. Because high soluble zinc, manganese and aluminium are due to problems with soil structure. Also, problems in the subsoil can manage to elevate these free metal ions in the soil. Taking care of a good structure in the whole soil profile and prevention of water logging can therefore improve the phosphate condition of a soil. Different types of mycorrhiza can free this fixed phosphate and bring it into the roots of the plants.

A high organic phosphor
Organic phosphate is for the most part built in protein. Protein is a part of the humus, organic matter of the soil. A high amount will tell that every year from mineralisation a good amount of phosphorus can be expected.

Silicon:
Silicates have some of the same chemical properties. I high soluble silicate concentration will prevent fixation of phosphate.

Environmental Aspects of Phosphate Fertilization
Phosphate, even when applied in the form of artificial fertilizer, will not or hardly wash out to the ground water. This occurs only in soils without organic matter and with an extreme low clay content. With repeated continuously over fertilizing with phosphate will lead to cumulation of phosphorus in the soil. With a high fertilization with organic manure or compost more phosphorus is given to the soil than the plants can take up. In the long run the soil can become polluted by phosphate. Then the fixation process will be reversed. The high presence of phosphate wipes out the free zinc, iron and manganese. The result is a shortage of these elements and poor growth of plants, or a lower nutritional value of those plants for man and animals.