Development of new Phosphorus fertilizers
Authors: Rajendra Kumar Yadav, Chiranjeev Kumawat and Deep Mohan Mahala
PhD. Scholar, Division of Soil Science & Agricultural chemistry, ICAR-IARI, New Delhi-110012


Phosphorus (P) is an important nutrient but the concentration of plant available P is generally low in soils. Further, nearly 70% of the applied phosphate fertilizer is converted to unavailable forms and its availability is restricted. Thus, application of phosphate fertilizers is a must for good crop. Phosphate fertilizers are mainly synthesized from rock phosphate. Total rock phosphate reserves in India are estimated about 132 m tons which at current rate of exploitation have life period of 83 years. Rock phosphate reserves in the whole world are about 20,000 Tg, containing of about 13% phosphorus. Thus, pure phosphorus can be estimated to 2,600 Tg which at the present annual consumption rate of 20 Tg P would give phosphorus resources a life-time of about 130 years. Therefore, it is important to utilize native P both to reduce the cost of production and sustain the mineral reserves for longer period.

The nano fertilizer technology is an innovative strategy. Fertilizer particles can be coated with nano membranes that facilitate in slow and steady release of nutrients thereby reducing loss of nutrients and enhancing its use efficiency of crops. Nano clay composites have been developed in order to supply with range of nutrients in desirable proportions.

1. Preparation of slow release nano-clay polymer composites (NCPCs) fertilizer loaded with phosphorus

Sarkar in 2011 prepared NCPC phosphorus fertilizer by adding Acrylic acid (AA) and Acryl amide (Am) in 15 ml distilled water and then neutralized with ammonia in a four necked flask equipped with a stirrer, a condenser, a thermometer and a nitrogen line.Then placed on a magnetic stirrer with heating control. Clay was then added and dispersed in the partially neutralized monomer solution, under nitrogen atmosphere, the crosslinker N,N'-methylenebisacrylamide was added to the AA/Am/clay mixture solution and the mixed solution stirred on the magnetic stirrer at room temperature for 30 min. then the temperature will be increased slowly to 70°C with vigorous stirring after the radical initiator ammonium perslfate (APS) was introduced to the mixed solution. After completion of the polymerization reaction the resultant product will be washed several times with distilled water and then will be dried at 100°C to a constant weight. Finally, the dried products will be milled and screened.

The loading of DAP was carried out by immersing pre-weighed dry gels into the aqueous solution of these compounds for 20 h to reach swelling equilibrium. Thereafter, the swollen gel was dried at 60°C for 6 days. Finally the dried products milled and screened.

2. Double coated slow release fertilizer

A double-coated slow-release NPK compound fertilizer with superabsorbent and water-retention was prepared by Wu et al. (2008) by the crosslinking of poly (acrylic acid)/diatomite - containing urea (the outer coating), chitosan (the inner coating), and water-soluble granular fertilizer NPK (the core). The effects of the amount of crosslinker, initiator, degree of neutralization of acrylic acid, initial monomer and diatomite concentration on water absorbency were investigated and optimized. The water absorbency of the product was 75 times its own weight if it was allowed to swell in tap water at room temperature for 2 h. Atomic absorption spectrophotometer and element analysis results showed that the product contained 8.47% potassium (shown by K2O), 8.51% phosphorus (shown by P2O5), and 15.77% nitrogen. It was also investigated that the water-retention property of the product and the slow release behavior of N, P and K in the product. This product with excellent slow release and water-retention capacity, being nontoxic in soil and environment-friendly, could be especially useful in agricultural and horticultural applications.

3. Synthesis of surfactant-modified nano-zeolite(SMZ) as a slow release fertilizer for phosphorus

The commercial zeolite-A used by Bansiwal et al. (2006) for the slow release phosphorus fertilizer preparation. Surfactant modification of the zeolite was carried out using the surfactant, hexadecyltrimethylammonium bromide (HDTMABr) (E. Merck, Germany). A preweighed quantity of washed zeolite sample was mixed with HDTMABr solution in a 1:100 (solid:liquid) ratio. The concentrations of HDTMABr solutions used for preparation of SMZ-1, SMZ-2, and SMZ-3 were 50, 100, and 200 mg/L, respectively. The solution was agitated for 7-8 h at 150 rpm on an orbital shaker. The solution was then filtered, and the solid residue was washed with double-distilled water and air-dried for 4-6 h. The synthesized SMZ was then mechanically ground with a mortar and pestle to a fine particle size. The SMZs with different loadings of HDTMABr were subjected to treatment with KH2PO4 to prepare the nutrient-loaded slow release fertilizers.

About Author / Additional Info:
Ph.D Scholar, Division of Soil Science and Agricultural Chemistry, IARI New Delhi ,India