By George Silva, Senior Educator

There is considerable interest in maximizing corn yields by combining new hybrids with improved production practices. In 2015, Michigan State University Extension and DEKALB/Asgrow brands of Monsanto Co. tested two modern semi flex-ear-type hybrids, DKC49-72RIB and DKC50-84RIB.

The two hybrids were tested in 20- and 30-inch row spacings, three populations of 30,000, 36,000 and 42,000 per acre, and two nitrogen (N) application rates of 120 and 240 pounds N per acre. The experiment is located in Mason, Mich., and the treatments were replicated three times. 

The overall objective was to find how these hybrids will interact with non-limiting plant populations and N rates to produce the highest grain yield per acre.

The 20-inch row spacing was included to provide a more desirable geometric spacing for plants at high populations. This means higher within-row distances between plants for a given population rate compared to 30-inch rows. The trial was planted under ideal weather conditions on April 27, 2015. All plots received 25 pounds of N per acre at planting. The balance of N was sidedressed as 28% liquid N, injected on June 2.

In 2015, the site received excess rainfall in June and early July raising concerns about potential N losses and shortages. Some of the heaviest rainfall was received a few days after the sidedress application. At times, this field was temporarily flooded. 

Corn at the V7-V8 stage looked healthy, but we started to notice early firing starting in September, mostly in the low N treatment. Based on MSU N fertilizer recommendations, the high N rate (240 pounds per acre) is considered an adequately fertilized treatment.

The end-of-season corn stalk nitrate test is a diagnostic tool that can assess N fertilizer practices and adequacy to corn throughout the season. We analyzed stalk samples from all plots at the MSU Soil and Plant Nutrient Laboratory.

The overall stalk nitrate-N average for all plots receiving 120 pounds of N per acre was 211 ppm, considerably below the critical level of 700 ppm. The overall average for the plots receiving the 240 pounds of N per acre was 2,630 ppm, above the optimum upper level of 2000 ppm. 

Based on this data, we speculate that heavy rainfall received after the N sidedress application on June 2 may have contributed some N losses due to denitrification and leaching, creating severe N shortages at the low N application rate. 

Based on climate and rainfall patterns we have observed in the past few years, farmers will benefit by having options to stretch the sidedress N application window depending on current season weather, soil type, N source and fertilizer application equipment.