Purdue University in their study emphasized that over the past 70 years, yield and nitrogen efficiency of hybrid corn varieties have increased significantly. The study's purpose is to identify how corn plant utilized nitrogen throughout the years to guide breeders in their decision making involving future hybrids. According to Tony Vyn, a professor at Purdue's Department of Agronomy, they observed a "progressive improvement" in the nitrogen use efficiency in corn hybrids, which then results in higher yields as modern hybrids are able to absorb more of the nitrogen fertilizer applied. 

Results highlight that genetic improvements in corn hybrids have led to an 89 percent increase in grain yields and a 73 percent increase in nitrogen use efficiency from early hybrids up to the present. Having less nitrogen fertilizer not absorbed and wasted, the grain created from the absorbed nitrogen increased from 42 pounds of grain per pound of nitrogen taken up in the plant to 65 pounds of grain. Moreover, suggestions for breeders about how to continue improvements in yield and nitrogen use efficiency were also included in the study. 

Read more at Purdue University Agriculture News.

Figure: An early corn hybrid from 1958 (right) versus a more modern hybrid from 2015 (left). The modern crops retain leaf nitrogen longer, keeping leaves green for continued photosynthesis that allows plants to increase kernel number and size.