Effect of addition of biopolymer coated DAP on phosphorus release kinetics over an incubation time

Phosphorus (P) use efficiency is very low (5 to 25%) due to fixation with Ca⁺²/Mg⁺² in alkaline/calcareous soils and Fe²⁺/Al³⁺ in acid soils, reduces the availability of phosphorus in soil. Among the various approaches used to enhance PUE, polymer coated fertilizers are relatively a new concept. Therefore, to alleviate the effects of low use efficiency of inorganic fertilizers and its losses in soil, the incubation study was conducted during 2020 at Tamil Nadu Agricultural University to check the slow-release behaviour of coated DAP fertilizer using biopolymers like chitosan and sodium alginate. The incubation experiment was made with six different coatings of biopolymers and uncoated DAP for studying the release behaviour of P from coated fertilizers. Randomized block design was followed with seven treatments in triplicate and sampling was taken at the intervals of 2^nd hour, 4^th hour, 120^th hour, 7, 14, 28, 35, 42 and 49 days of incubation. A study on slow-release property of coated fertilizers indicated that the treatment combination of both chitosan and sodium alginate (C₅A₅ - CSACDAP) coated DAP performed well by releasing the P from coated fertilizer was achieved till 35^th day of incubation followed by the combination of both chitosan and sodium alginate (C₄A₄ -CSACDAP). This study indicated that the combination of both the polymers forms a strong polyion complex and tends to give the P release for a longer period than the individual coatings of both polymers on the DAP granule.