Release of Phosphorus from Laboratory Made Coated Phosphatic Fertilizers in Soil Under Different Temperature and Moisture Regimes

Abstract

The aim of the present study was to see the release pattern of phosphorus from laboratory made coated phosphatic fertilizers in soil under different temperature and moisture regimes. Four fertilizer materials were prepared by reacting ammonia with phosphoric acid (Product - A and Product - B) and rock phosphate with sulphuric and phosphoric acid (Product - C and Product - D). These materials were coated with polyvinyl alcohol, liquid paraffin and methyl oleate at two levels (2 and 3 %). The coated phosphatic fertilizers along with diammonium phosphate were applied @ 500 mg P kg - 1soil and incubated at two temperatures (20 and 30 _C) and two moisture regimes (10 and 20). Results indicated that release of P showed a decline trend from first to fourth hour of incubation, then increased and finally reached to a steady state in all the products, except Product - C. The release pattern followed the order: diammonium phosphate Product - B Product - A Product - D Product - C, corresponding with the mean values of 337.4, 227.9, 211.6, 147.1 and 69.0 mg P kg - 1soil, respectively. Results also showed the superiority of polyvinyl alcohol coated products over liquid paraffin and methyl oleate coated products. The rate of release of P was greater with increase in temperature from 20 to 30 _C. Thus, it may be concluded that laboratory made coated fertilizers could be used as a source of P which would release P slowly than the water soluble P like diammonium phosphate and supply P for a longer period that synchronizes the crop demand and enhances P use efficiency.