Law of Diminishing Return

A German scientist Mitscherlich calculated the effect of different quantities of various growth factors on the yield of plants by means of a mathematical equation. This equation assumes that a plant, under optimum conditions should give maximum yield.  A "theoretical highest possible yield" is assumed for each set of growth conditions when an optimum supply of a given growth factor e.g. a plant nutrient is present. This yield, designated as A, will vary with the supply of other nutrients, climatic conditions, system of cultivation, etc. When the said factor is not at its optimum concentration, then a corresponding decrease in yield takes place and the obtained yield (actual yield) is given as 'y'.