INADEQUACY OF THE LIEBIG LIMITING-FACTOR PARADIGM FOR EXPLAINING VARYING CROP YIELDS

Historically, the limiting-factor paradigm has been used to describe how crop yields may be constrained by the individual input resources required by plants. The limiting-factor paradigm proposes that plant growth is constrained only by a single resource whose availability is so low that it solely inhibits greater growth or growth rates. However, this paradigm ignores the great flexibility of plants to acclimate morphologically and physiologically to changing environmental conditions. In view or the inadequacy of the limiting-factor paradigm, an analysis analogous to that used in economic studies to describe well-managed businesses was developed. Investment of capital reserves (i.e., photosynthate) is allocated to obtain various input resources (i.e., water, minerals, etc.) in order to maximize output (i.e., crop growth). The important criterion in the allocation of reserves is that the capital reserves should be allocated to the resources with the greatest marginal returns. Since the marginal return for each resource is likely to change as the crop develops and the environment changes, resource allocation (i.e., plant development and physiology) is predicted to be dynamic and continually adjusting through the plant life cycle. An interesting outcome predicted for this acclimatable plant development is that under many conditions a number of resources will be simultaneously limiting crop growth. It is suggested that the types or data and analyses required to assess resource limitation on crop yield need to be reevaluated.