All of these criteria are quantifiable but also have a time dimension. Obviously, closed or static systems, though ecologically stable, are not productive enough to meet present demands and future needs. It is not only the energy efficiency but also the total energy flux that is very important in sustainability.
Indirect costs are indeed important goals to be considered.
For example, reducing the use of off-farm input may necessitate bringing additional land into production. The latter may be marginal, subject to severe problems of accelerated erosion and other degradative processes. Substitution of inorganic fertilizers with organic amendments of, green manure may equally endanger the quality of surface and ground water and emit radiatively active gases into the atmosphere, thereby aggravating the greenhouse effect. Therefore, the choice of a criterion to assess sustainability would depend on the hierarchy to be evaluated. Agronomic yields and productivity are useful criteria at the level of crop or cropping system.