ABSTRACT
The knowledge that fragile physical and chemical resources may pose significant constraints to the future productivity of US cropland enhances the need to understand which crop technologies might lead to tomorrow's yield improvements. This chapter utilizes the chronological development of scientific advances in a specific crop technology, biological nitrogen fixation, to exemplify the principle, although the methodological analysis could be applicable to any crop technology. It argues that the time has come for a shift from predictions of productivity advances based on retrospection to predictions based on scientifically realistic expectation or anticipation. The delivery system tor crop technologies developed in public institutions generally conforms to a five-tier pyramidal model. The science of plant breeding involves the recombination of desirable genes and application of new knowledge to the development of improved crop cultivars or germplasm. The time from basic scientific advance in a crop technology to successful practical applications of the technology is often lengthy.
