Dr.Ghosh,please provide some background information on phospho silicate fertilizer.
Those fertilizers were famous during the times when P rich ores were used for steel making, especially in industrial Germany. Well known names were Thomasphosphate, which derived from the slag obtained during the oxygen blowing in the Thomas bulb or, from processing rock P with carbonates and silica in tubular rotating concrete furnaces as so called Rhenania Phosphate. With processing of mainly low P ores preferably imported from South America the P concentrations in those slags dropped below the legal minimum concentration described for those fertilizer types in the European fertilizer ordinances. The technical remains of this sort of waste valorisation are the basic slags found on some niche markets. It has been a very valuable form of P solubilization the entire P of those fertilizers was soluble in neutral ammonium citrate solution. The reason why its gone from the market: the energy costs of the process are too expensiv if run only for the P processing.
I understand that the basic slags of yesterday are now phospho silicate fertilizers .Dr.Schnug , I agree with you that the present day basic slags have low P content.Now they are being promoted for use as liming material for acid soils.Some trails are in progress in India.In steel industry basic slags the main problem will be the associated metals/heavy metals which may pose problem in soil if applied in large quantity or over long time. Dr.Schnug, can you give some idea of the nature and extent of problem with the associated metals in basic slags if applied in large quantity.
Great answer from Dr. Schnug.
Any marketable is time and cost driven. We need to have a policy regarding what form of materials required with its use efficiency into consideration.
Phospho silicate has never been tried our country in any farm conditions, except for some academic interest.
I once again request Dr.Ghosh or Dr .Mahapatra,what they mean by Phospho silicate fertilizer.In the market there are commercial formulations with the same name containing water soluble silicon,organophosphorus and L aminoacid. There are at least three types of slags-blast furnace slag,basic slag (Thomas slag belongs to this group) and electric-furnace slag.First one is from pig iron industry,second one is from steel making industry and third one is from the process of elemental P manufacture.A lot of Indian work including field experiments is available on basic slag staring from sixties- seventies(my Ph.D guide Dr.A.B.Ghosh is one of early workers) to current date.Basic slag is a recommended amendment for acid soils in Odissa and West Bengal states(I am not sure of the interest of Dr.Ghosh so I am not providing any references).
Cr is of major concern in such slags and here espcially Cr VI,
The most of Cr in slags id Cr III, but its still unclear how much of this may convert to Cr VI in soils. Other hazardous elements especially As. Cd and U are low compared to P fertilizers made from sedimentary rock phosphates.
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