Stalk Nitrate-nitrogen As Affected By Nitrogen Rate, Row Spacing And Population Density – Part 1

Dec 24, 2015

By George Silva

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 are testing two modern semi flex-ear-type hybrids, DKC49-72RIB and DKC50-84RIB, 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 is located in Mason, Michigan, and the treatments were replicated three times. The overall objective is 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 stalk nitrate levels in 2015 at two nitrogen rates in corn hybrid DKC50-84. Critical nitrate-nitrogen level is 700 ppm. The critical range is represented by the two thicker (yellow) lines.

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.

This year, the site has received excess rainfall in June and early July raising concerns about potential nitrogen 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 nitrogen treatment. Based on MSU nitrogen fertilizer recommendations, the high nitrogen 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 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 is discussed in this article.

Corn stalks

Corn nitrate interpretation guide

Stalk nitrate sample and the interpretation guide.

The overall stalk nitrate-nitrogen average for all plots receiving 120 pounds of nitrogen per acre was 211 ppm, considerably below the critical level of 700 ppm. The overall average for the plots receiving the 240 pounds of nitrogen 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 nitrogen sidedress application on June 2 may have contributed some nitrogen losses due to denitrification and leaching, creating severe nitrogen shortages at the low nitrogen 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 nitrogen application window depending on current season weather, soil type, nitrogen source and fertilizer application equipment.

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