Source: Robert Mullen, Greg LaBarge, Ohio State University

Robert Mullen, Greg LaBarge wrote an article discussing the issue of nitrogen rate and higher corn populations last May, but we thought we would provide an update based upon information from the previous cropping season. As producers consider (or continue) pushing higher seeding rates for corn, the question often asked is, "Do I need to push higher N rates to exploit the higher seeding rates for more yield?" Intuitively, it may seem logical that a higher population would require more N, but the scientific data being collected does not necessarily support the concept.

Ohio State University has been conducting field research the last five years at the Northwest Research Station near Custar, Ohio, to determine if higher seeding rates require a higher N rate to achieve maximum yield. Two different cropping rotations were evaluated — corn after corn and corn after soybeans. The two seeding rates used were 30,000 and 40,000 seeds/acre (in 2006 the highest seeding rate was 36,000).

In six out of 10 site-years, we have found no difference in the optimum N rate for the different seeding rates. In two site-years the higher seeding rate required more N, and in two other site-years the lower seeding rate required more N.

In 4 out of 10 site-years, the higher seeding rate did result in higher yields. Those yield responses tended to be when corn followed corn. Interestingly, 3 of the 4 site-years that revealed higher seeding rates could result in more yield also showed differences in the optimum N rate required to achieve the higher yield. However, only 1 out of those 3 site-years revealed the higher N rate (and higher yield) was required at the higher seeding rate.

We have included the N response curves from this past experimental year. When corn followed soybean there was no yield increase observed at the higher seeding rate nor was the optimum N rate different (Figure 1). When corn followed corn, the higher seeding rate resulted in a higher yield, and it required a higher N rate to achieve that yield (Figure 2). As stated in the previous paragraph, this is the only site-year that shows higher seeding rate results in higher yield and a higher N rate requirement.

In summary, our current data does not support the idea that higher seeding rates necessarily translate into higher rates of N. 

Click here to see Figures 1 and 2