Global adoption of transgenic crops reached 67.7 million hectares in 2003 from 2.8 million in 1996. Delivery has occurred almost entirely through the private sector and adoption has been rapid in areas where the crops addressed serious production constraints and where farmers had access to the new technologies. Three countries (USA, Argentina and Canada), three crops (soybean, cotton and maize) and two traits (insect resistance and herbicide tolerance) account for the vast majority of global transgenic area.

In the past 50 years, the application of synthetic nitrogen (N) fertilizer to farmland resulted in a dramatic increase in crop yields but with considerable negative impacts on the environment. New solutions are therefore needed to simultaneously increase yields while maintaining, or preferably decreasing, applied N to maximize the nitrogen use efficiency (NUE) of crops. In this review, we outline the definition of NUE, the selection and development of NUE crops, and the factors that interact with NUE.