Yuo should make pot-experiments with different P-fertilisers, different P applcation doses and different crops over a rotation of 2 or 3 crops. Maize  has a high P demand and is a good test plant..Parallel you should measure the P fixation capacity of your soils. The content of Fe /Al oxides is very important speclaly in highly weathert soils.

Wilhelm's answer really  is the key issue. On high aluminium soils under high rainfall soluble P is converted to Variscite which has very low solubility at normal agricultural soil pH (See Russel's Soil Conditions & Plant growth 11th ed pp 706 707) on high iron soils that go through annual wet/dry seasons soluble P is converted to Strengtite (see Russel's) With Strengtite I have observed that grasses are severely P deficient but the legumes are fine. On the above soil types a move away from high soluble phosphate fertilizers has been the course of free thinking agriculturists and the choice of alternative mineral P inputs includes:

High grade soft rock phosphate fine particle size sometimes fermented with the addition of liquid fish extract.

Di -Calcium-phosphate made from Superphosphate and lime reacted with measured added water.

There has been a great deal of scientific research done on this topic in New Zealand by Indian scientists who have settled there as well as others.

More details on your local climate and soil mineralogy would enable better targeted answers.

Yours truely

Hello to all! Allow me to add a few comments, as the question particularly referred to 'in Indian context'.

First of all we need to clarify what is meant by 'to work on slow release phosphatic fertilizers preparation'. Is it merely for scientific research, or is the purpose to make more efficient fertilisers available to farmers? In an Indian context, we need to consider that standard P fertilisers are heavily subsidized (e.g. DAP more than 50%: subsidy 12,350 INR/t, average maximum retail price 22,500), while any innovative product is not, unless included in NBS (nutrient base subsidy) scheme. For general agricultural purposes farmers are unlikely to use a non-subsidised P fertiliser.

This also casts doubt on the statement that 'phosphatic fertilizer cost depend on its P release capacity from initial reaction products, not on its nutrient content'. To be honest, this would only apply should the Indian farmer appreciate the difference in efficiency of different fertilisers and modes of application.

From personal experience (I'm engaged in extension work and product evaluation experiments in India) I can safely state that there is no chance to convince the Indian farmer (apart from the 1% progressive farmers) of more efficient fertilisers unless they are subsidised - and recommended by the regional State Departments of Agriculture.

From a scientific point of view most aspects have been addressed here already. As far as inoculation with AM and PSB is concerned, I feel that these organisms will have difficulties surviving the hot, dry season in North and Central India. In fact, that's the reason why mustard and potato can be grown every year at the same site without phytosanitary issues, which would not work in more temperate climates. Hence it would require regular inoculation with AM and PSB, which is not going to boost acceptance in India.

The high-end solution might be coated fertilisers and polyphosphates that show less retention and more mobility in soils. The low-tech option would be soft, natural rock phosphate.

Regards from India

Hi Abhijit Sarkar,

try to use the new created AUSTRIAN product WOOLETS and Xylit a usefull waste product from the brown coal industry and both are natural and cheap..

WOOLETS is a new organic fertilizer invented in AUSTRIA made of sheep wool and pelleted for fertilizer use. It contains mostly what plants need for a good growth:

79% organic matter i.DM

8.3% total nitrogen organically bound

5: 1 C / N ratio

4.9% potassium oxide K2O

0.2% phosphate P2O5

0.7% sulfur S

0.5% Fe iron

pH 9.4

Water absorption by up to 3.5 times its own weight !

 Another substrate that can be use for long term phosphorus storage and slow release is:

 XYLIT OR LIGNITE

It is treated as an aggregate for the production of potting soils and substrates for professional horticulture. Its chemical properties are close to the low available nutrient content of peat and its pH is in the acidic range. Its water-holding capacity is less than peat. The use of wetting agents in substrate production is therefore appropriate. The proportion of organic matter is in excess of 85% based on the dry matter.

Beneficial properties of XYLITE are a good structural stability and low N immobilization. There are no easily exploitable sources of carbon present and the XYLITE is subject to, as compared to other organic substances, lower degradation rate (C / N ratio> 200).

Heavy metals are included in only in traces and far below the limits of bio-waste regulation. Other relevant for Crop pollutants have not yet been demonstrated.

The analytical values vary to a small extent, depending on the grain size and origin. Since 2004, a number were conducted studies on the use in horticulture.

https://www.evernote.com/pub/jhumer/humuswirkungschafwolledngerpellets

I propose a base dressing with natural phosphate, particularly efficient for acidic middle and soil furnished with active organic matter.

Dear colleagues

I am following  very interesting discussion  on P,a critical input in agriculture in several countries.Release   from solid phase/availability to plant during growing period is crucial to get full befit of applied P.P use efficiency of 15-30% is now accepted in India. However the residual effects in subsequent crops are not taken into consideration.Syers and coworkers from Rothamsted research  reported P recovery of 70-95% by balance method.This provides support  that very considerable amount of residual P  is available to following crops. Our studies on vertisols of central India showed apparent P recovery of 44-21 % in soybean and 36-22%in wheat with application of 11-44 kg P per ha in 5 year study .Also with manure  application of 4,8,16 t/ha the recovery increased to 96,66 and 45%.This clearly indicates that the  applied P is released to subsequent crops in good amounts and this can further increase with manure application.However the residual P  availability in Andisols, Oxisols and Latosols may be a problem because of reactions with amorphous  materials,oxides and hydrous oxides of Fe, Al.Reactive rock  phosphates, organic manures,and slow  release / coated fertilisers ,band placement may work in those soils.There is a need to study the the availability of adsorbed/ reverted/ fixed to plants  in contrasting soils over medium to long term to plan strategy for application of P.In other soils  regular soli test based P application and when P status attains adequate level replacement of P removal may be sufficint.

Thank you, for your great responses. It is now clear to me, that what would be possible  techniques fort fertilizer formulation.

I think phosphatic fertilizers are very slow in nature and hardly achieve 20% PUE in Indian condition. Facts, under acidic soil availability may be higher. Their losses or adsorb on soil particles are very common. This may be applicable for highly water soluble fertilizer using in drip or sprinkler irrigation. Do work and Good Luck for this.