D M Mihir

CONTENTS Introduction Phosphate Up-take by Plants Chemical P Fertilizers Contribution of Chemical P Fertilizers Problems of Chemical P Fertilizers Organic Farming Phosphate Rich Organic Manure Summary References

INTRODUCTION There are 14 essential plant nutrients. The primary macro nutrients are Nitrogen (N), Phosphorous (P) and Potassium (K). Secondary macro nutrients includes Calcium (Ca), Sulphur (S), Magnesium (Mg). Micro nutrients comprises of B, Cl, Mn, Fe, Zn, Cu, Mo, Ni etc.

PHOSPHATE UP-TAKE BY PLANTS Phosphorous an important nutrient is taken up by the plants in water soluble form as phosphate anions i.e [H 2 PO 4 -, HPO 4 --, PO ] Plants exude organic acids like citric and malic acids through their roots that dissolve soil phosphates, which in turn are taken up by plants through roots.

CHEMICAL P FERTILISERS The fact that P is taken up by plants in water soluble forms led to the development of chemical P fertilizers that contain P in water soluble form. Single super phosphate (SSP), Di ammonium phosphate (DAP), Nitro-phosphates, etc are some examples.

CONTRIBUTION OF CHEMICAL P FERTILISERS Introduction of Chemical P fertilizers increased agricultural production throughout the world. Around 10 million tons of high-grade rock phosphate mineral is consumed in India every year in the production of DAP and SSP.

PROBLEMS OF CHEMICAL P FERTILISERS Less than 30% of P applied to the soil in the form chemical phosphatic fertilizers is used by the plants and the rest of it is fixed by the soils (by Fe, Al, Mn ions in acidic soils or by Ca, Mg ions in alkaline Soils) into unavailable forms. Excessive use of chemical fertilizers however destroys the natural properties of soil by killing soil micro flora and fauna and reduce the soil fertility.

ORGANIC FARMING Realizing the adverse effects of chemical fertilizers the experts are now advocating the reintroduction of organic manure in agriculture. well composted manure contains humic / fulvic acids, vitamins and growth promoting chemicals, low levels of nutrient elements such as N, P, K etc.

PHOSPHATE RICH ORGANIC MANURE Enriching manure with phosphate minerals improves the levels of nutrient elements in them. PROM is produced by co-composting (or mixing) organic matter with high grade (+30% p2o5) rock phosphate mineral in fine (80% finer than 74 microns) size. Addition of phosphate solubilising microorganism enhances the effect. Research efforts since last few years show that PROM is as efficient as any other chemical phosphatic fertilizer, plus it shows residual effect. PROM is in FCO since 2012.

CITRIC ACID SOLUBLE P IN ROCK PHOSPHATE INCREASES AS SIZE OF THE PARTICLES DECREASE

SUMMARY Nitrogen applied to the soils either in organic form (organic manure for example) or inorganic form (urea, ammonium sulphate etc) boost the growth of soil bacteria that dissolve P from the rock phosphate particles and there by enhance the take up of P by plants. The primary requirement for rock phosphate mineral for application as P fertilizer in alkaline soils is the fineness of particle size. The content of P soluble in 2% citric acid (available form) increases as the mesh of grind is finer. Further conversion of P into water soluble forms is carried out in situ by organic acids released by soil micro organism (naturally present or applied to the soil) and by the plant roots. C:N ratio in manure is best at 20:1

REFERENCES Sekhar, D.M.R and Aery, N.C, Current Science, Vol.80 (9), Sekhar, D.M.R., Aery, N.C. and Gupta, D.K, Indian Chemical Engineer, Vol.44 (3), C. M. Narayanan, "Production of Phosphate-Rich Biofertiliser Using Vermicompost and Anaerobic Digestor Sludge—A Case Study," Advances in Chemical Engineering and Science, Vol. 2 No. 2, 2012, pp DMR Sekhar, Principles of Phosphate Fertilization and PROM – Progress Review tion_and_PROM__Progress_Review_2012?ev=prf_pub tion_and_PROM__Progress_Review_2012?ev=prf_pub Dharmendra Singh, Parul Jain, Abhishek Gupta and Rajeev Nema, Soil Diversity: A Key for Natural Management of Biological and Chemical Constitute to Maintain Soil Health & Fertility, International Journal of Bio-Science and Bio-Technology, Vol. 5, No. 1, February,