Catalyst-Free Microwave Digestion and Estimation of Nitrogen and Phosphorus Contents in Chicken Manure Adopting Competitive Analytical Methods

Abstract

ABSTRACT For enhanced soil fertility, the application of animal manure has been recognized as an alternative mean to synthetic fertilizers. A major issue in current manure application practices is the rapid, reliable estimation of nutrients, such as nitrogen (N) and phosphorus (P). Estimation of N and P in manure involves the use of harsh chemicals and conditions, and considerable analytical time. In this work, microwave-assisted digestion condition is being reported for N and P estimation into chicken fermentation slurry. At comparative lower temperature 200°C and duration 1 h, digestion involves the use of half of the amount of acid and that too without the aid of a catalyst. Furthermore, N and P contents were determined from automatic Kjeldahl (AKj), manual Kjeldahl (MKj) and flow injection methods (FIA). The advantage of FIA is that it provides simultaneous detection of P and N. Additionally; P contents were analyzed and compared by colorimeter (Clr). To obtain a clear view of the performance of competing analytical procedures, a single sample analysis (SSA) time was measured. Thus, for N estimation; the SSA by AKj was superior, i.e.,, AKj ˃ MKj ˃ FIA which was 6:10:70 mins, respectively, and for P; Clr˃FIA which was 30:70 mins, respectively. However, when the adoptive methods were judged on the basis of effectiveness or by overall performance/ease in handling, the order of competing methods for N became AKj ˃ FIA ˃ MKj and for P it was FIA ˃ Clr. Statistical evaluations from the analytical data were also in accordance.