Productivity is the rate of production of biomass, expressed in terms of

I. $\left({\mathrm{Kcal}}^{-1}{\mathrm{m}}^{-3}\right){\mathrm{yr}}^{-1}$

II. ${\mathrm{gm}}^{-2}{\mathrm{yr}}^{-1}$

III. ${\mathrm{g}}^{-1}{\mathrm{yr}}^{-1}$

IV. $(\mathrm{Kcal} {\mathrm{m}}^{-2}){\mathrm{yr}}^{-1}$

Primary production is defined as the amount of biomass or organic matter, which is produced per unit area, over a time period by plants during the process of photosynthesis. It is expressed in terms of weight (g–2) or energy (kcal m^–2). The rate of biomass production is expressed in terms of g m^–2yr^–1 or (kcal m^–2) yr^–1.