The optimal N/P ratio for phytoplankton growth, known as the Redfield Ratio, is 16:1 (based on molecular concentrations). Large differences from 16 at low N/P ratios can be an indication for potential nitrogen limitation and at high N/P ratios, potential phosphorus limitation of the primary production of phytoplankton. The results is the potential altered biological state of the ecosystem, especially in the phytoplankton biomass, species composition and food web dynamics. ^[1]

This is the common definition for Redfield ratio, other definitions can be discussed in the article