Stalk Nitrate-Nitrogen as Affected by Nitrogen Rate, Row Spacing and Population Density
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.