Welsh Poultry Centre

Howglowin the dark urineled to the discovery of Phosphate, The Bringer of Light

Phosphate, (P) is one of the threemacronutrients required for plant growth, (the other two being Nitrogen, (N)and Potassium, (K)). A German, Hennig Brandt, first discovered phosphate in1669. In an alchemistic career, which was to drain the wealth of two wives,Hennig discovered not gold, but, upon boiling his own urine, white phosphate. 

White phosphate, which is an inorganiccomponent of dissolved urine, glows in the dark. This is because when exposedto oxygen the white phosphate slowly burns, giving off the glow. However, asneither heat nor flames were apparent this was not realised at the time. Thename phosphorus comes from the Greek word, phosphoros meaning light bearing orbringer of light.

Wheredoes it come from?

The Phosphate we now use in fertiliser isalmost entirely from Rock Phosphate. An inorganic element that is mined. How itgot there is not so certain. It appears to be a sedimentary deposit created underspecial conditions in which no other sediment is present. Some suggest that ithas been absorbed by ocean plants that then die. As they decompose so thephosphate accumulates.

Despite many theories there is, at thispoint, no certainty about its origin. There are also some igneous rock that arerich in phosphate, (often called hard rock phosphate), although sedimentarysources are far more plentiful.

Guano- now a depleted source of phosphate

Today, America, China and Morocco are themajor producers of rock phosphate, each making up about a quarter of the worldsupply. In the past another source of phosphate was Guano. Guano is theexcrement and urine of bats, seabirds and seals. In some places, notably Peruand some pacific islands, the reserves of Guano were huge.

It was mined for its phosphates andammonia. Nauru, a small island in the Pacific, was for a time one of therichest countries in the world per capita, due to exporting Guano. After 80% ofits surface had been strip-mined this source of phosphate has now beenexhausted, as it has in other parts of the world.

Howdoes it work?

Phosphate is important to plant growthbecause it allows the transfer of energy within  plants cells, thus adequate levels of P are required tostimulate growth and create the changes that bring about maturity.

There is often a lot of P in a soil,varying from 500kg/ha to 2500kg/ha, (depending on the soil type, soil textureand depth). However only a fraction of this P is available to the plant. The Pneeds to be in the soil solution as soluble orthophosphate to be available tothe plant*. Often the available P is as low as 10g/ha. Cereal crops needbetween 12-16kg of P per ha while root crops require between 17-25kg per ha.

The reserves of P in a soil are in basicallyin two forms; Mineral P and Organic P. Mineral P, as the name suggests is theinsoluble and strongly absorbed P that exists in most soils. It is notavailable to plants although, through chemical transformation within the soilsmall amounts do become soluble and available. It's a bit like a reservoir ofwater with a dripping tap. The amount of the drip is dependant on soil type,ph, soil texture and soil organic matter.

Howdo phosphates become available to plants?

The Organic P is the return of organic cropresidues, compost and farm yard manures. It is dependant on the microbialactivity in the soil. This living activity converts (mineralise) the phosphatesfrom the residues and makes them available to the plant.

Both the chemical and the microbialactivity replenish the P in the soil solution as it is used by the plant. It isthe interaction of soil organisms and soil organic matter that creates 80-90%of all soil processes. Organic matter is the main food source for soilorganisms, breaking down the complex organic materials to obtain energy. Manymicro-organisms (bacteria and fungi) are therefore able to mineralise organicP. Some of these organisms also excrete organic acids which are able to realiseP from the Mineral reserve.

This process happens in a range of soiltypes although it is heavily dependant on soil organic matter levels andactivity. It appears to be most efficient when soil Ph is between 6-7; nearneutral.

It is important to note that soil testingdoes not indicate the level of organic P or the likely production of Pavailable to the plants from this source. The routine soil test for P measurethe labile P in mineral form together with the soil solution P. Therefore the organic half of thesoil P cycle is invisible when routine soil test are considered alone.

Phosphatemovement in the soil

Phosphate moves very slowly through soils.Unlike Nitrogen, phosphates are attached to other elements. Nitrogen will leachout of a soil after heavy rain, whereas phosphate will leave with the soil, egwhen soil erosion occurs. Because of this the root length and distribution inthe soil is important. The more roots spread through the soil the more P itwill be able to come into contact with. Hence maintaining good soil structureand reducing possible compaction of the soil is of critical importance. Againthe higher levels of organic matter present the more likely the soil will havea good structure.

Earthwormsand phosphate

As well as the microorganism, the fungi andbacteria, the common earthworm also plays its part in the cycling of organic P.T J Barrett in his book, HarnessingThe Earthworm, carried out an experiment. He found thata box of soil containing earthworms, increased available phosphate by 10%compared with a box of soil with no earthworms. An analysis of worm casesdemonstrated that it contained five times the amount of Nitrogen, seven timesthe amount of P and eleven times the amount of Potassium compared with theparent soil. Indirectly this is also dependant on soil organic matter. Justlike the micro-organisms the earth worm depend on organic matter for food.Numbers of worms in a soil will depend on the level of organic matter availablefor them.

Plantsand phosphate

A plants roots are much more than just adrinking straw for the plant. The area immediately around a root (about 1mmaround the root), is called the rhizosphere. Within the rhizosphere the plantcan have a direct influence through root secretion. Sloughed off plant cells,proteins and sugars realised by the root increase bacterial activity. Protozoaand nematodes graze on such bacteria and are in abundance within therhizosphere.

Differences in plant species, rootingpatterns and the way that some plants manipulate the rhizosphere mean that someplants are better able to access P than others. Experiments carried out by the Institute of OrganicTraining and Advice (IOTA), showed that buckwheatliberated P much more effectively than other crops, moving it from the mineralto the organic reserve.

It would therefore be much more availableto following crops. Work carried out in Israel suggests that chicory may alsohave this property. Green manures are largely selected for their nitrogenfixing abilities or their organic matter. It may also be worth considering themfor their ability to liberate mineral P.

Phosphateand the future

It is likely that there are huge depositsof rock phosphate still under the oceans of the world, particularly around thecontinental shelf. At present these are too expensive to extract. However, asthe deposits on land are not estimated to exceed the next 35-50 years, it ispossible that these reserves will have to be mined at some stage.

Phosphate is one of the limitingmacronutrients upon which our present agricultural systems are reliant. It is amined resource with ever increasing demands placed upon it. Just like Nitrogenit will only increase in cost over the coming years. As with Nitrogen Phosphatepollutes watercourses, causing euthophication. 26% of phosphate in rivers hasbeen estimated to be of agricultural origin, entering the watercourses as soilerosion.

Thedecline in soil organic matter

Few soils are deficient in actualphosphate. Most contain sufficient reserves to support plant growth, if theywere made available. However, to make them available we have to reverse thedecline in organic matter. We have to start looking at the health of the soilrather than looking at the health of the crop.

It is estimated that each year in the UK172000 tons of phosphate and 123000tons of potassium are flushed into our riverand sea. We then import 700000tons of North African rock phosphate and potash.With proper rotations and proper management of the soil this could be reduceddramatically.

In looking for short-term rewards we havemanaged to become dependant on the ever-increasing cost of the inputs necessaryto sustain ourselves. At the same time we have reduced the capacity of oursoils by regarding them as a medium rather than as a living organism upon whichwe depend.

©Stephen Merritt. All rightsreserved.

About the author

Stephen Merritt is a partner in The Welsh PoultryCentre and an accredited advisor and board member of The Institute of OrganicTraining and Advice and has spent over 30 years working in sustainable agriculturein developing countries, England and Wales.  In the last 8 years Steve has specialised in free range andorganic poultry production and their integration into sustainable farm systemsand now offers on farm advice and training to this sector.

-------------------------------------------------------------------------------------------------------

If you like this article, feelfree to share it with your own list, post it on your site, on your blog, or addit to your autoresponder. Twitter it, Facebook it, translate it.

As long as you leave it intactand do not alter it in anyway. All links must remain in the article. No textualamendments permitted. Only exception is Twitter.

If you've enjoyed thisarticle, why not sign up for the monthly Welsh Poultry Times e-newsletter soyou can keep up to date with all the lastest news, information and events forcommercial poultry producers.  Signup at www.welshpoultrycentre.co.uk

TO FOLLOW ME:

Twitter: http://twitter.com/welshpoultryctr

Blog: http://keepingchickenswales.wordpress.com

The Welsh Poultry Centre,Llwyncrychyddod, Llanpumsaint, Carmarthen SA33 6JS, Wales, UK