By George Silva, Michigan State University Extension
Stalk nitrate-nitrogen levels of corn hybrid DKC49-72 receiving both high and low nitrogen rates had nitrate-nitrogen levels considerably below the critical level of 700 ppm.
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 Company tested two modern semi flex-ear-type hybrids, DKC50-84RIB and DKC49-72RIB, at two-row spacings of 20 inches and 30 inches, three populations of 30,000, 36,000 and 42,000 per acre, and two nitrogen application rates of 120 and 240 pounds nitrogen per acre. The experiment was located in Mason, Michigan, and treatments were replicated three times. The overall objective was to find how these hybrids will interact with non-limiting plant populations and nitrogen rates to produce the highest grain yield per acre.
End of season cornstalk nitrate levels in 2015 at two nitrogen rates in corn hybrid DKC49-72. Critical nitrate-nitrogen level is 700 ppm and is represented by the thick yellow line.
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 nitrogen per acre at planting. The balance of nitrogen was sidedressed as liquid nitrogen (28 percent) injected on June 2. Based on MSU nitrogen fertilizer recommendations, the high nitrogen rate (240 pounds per acre) is considered an adequately fertilized treatment.
In 2015, the site received excess rainfall in June (7 inches) and early July, raising concerns about potential nitrogen losses and shortages. Some of the heaviest rainfall was received few days after the nitrogen sidedress application. This field was temporarily flooded several times. Corn at the V7-V8 stage looked normal, but we started to notice early firing starting in September.
The end of season cornstalk nitrate test is a diagnostic tool that can assess nitrogen 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 stalk nitrate-nitrogen as affected by the nitrogen rate in the second hybrid, DKC49-72, is discussed in this article.
Stalk nitrate sample and the interpretation guide.
The overall stalk nitrate-nitrogen average for all plots receiving 120 pounds of nitrogen per acre was 47 ppm. The overall average for the plots receiving the 240 pounds of nitrogen per acre was 187 ppm. Both low and high nitrogen rates produced stalk nitrate-nitrogen levels considerably below the optimum lower level of 700 ppm. This data is in sharp contrast to the first hybrid DKC50-84 (see Part 1). The data supports our speculation that heavy rainfall received in June/July after the nitrogen sidedress application may have contributed to substantial nitrogen losses due to denitrification and leaching, creating severe nitrogen shortages in the field.
Based on climate and rainfall patterns we have observed in the past few years, corn farmers will benefit by having rescue nitrogen application options when necessary, and be able to stretch the sidedress nitrogen application window based on current season weather, soil type, nitrogen source and fertilizer application equipment availability. Sticking to a predetermined nitrogen fertilizer rate has proved to be too risky in the past two years.