Decreasing Marginal Returns Law and Legal Definition

In the short-run production of a firm, an increase in the variable input results in a decrease in the marginal product of the variable input. Decreasing marginal returns typically surface after the first few quantities of a variable input are added to a fixed input.

Suppose that one kilogram of seed applied to a plot of land of a fixed size produces one ton of crop. You might expect that an additional kilogram of seed would produce an additional ton of output. However, if there are diminishing marginal returns, that additional kilogram will produce less than one additional ton of crop . For example, the second kilogram of seed may only produce a half ton of extra output. Diminishing marginal returns also implies that a third kilogram of seed will produce an additional crop that is even less than a half ton of additional output, say, one quarter of a ton.