Development of improved flow analysis prototype method for measuring and understanding agricultural non-point source (NPS) nitrogen (N) and phosphorus (P) pollution.

•A novel Perturbation-dispersion FA method using a Chemical Reaction Chamber.•FA method with a steady-state process, and adapting various standards, specifications.•Powerful, automatic technique for fast measurement and controlling the NPS pollution.•A combined LED light source with the optical path lengths of 10–30 mm, optionally.•Improved FA measures the concentrations of NPS pollution with lowest detection limits.