Thus, for instance, in the example above, it may be the case that increased use of potash will increase the marginal value products of nitrogen and phosphate, thereby requiring an increase in their use as well.

• 比如，在上述例子中，增施钾肥可能会增加氮肥和磷肥的边际产值，因而氮肥和磷肥的用量也需要提高。