Illinois
Fertilizer Conference Proceedings
January 27-29, 1997
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Assesing Post-Maturity Stalk Nitrate in Different Corn Hybrids
E.D. Nafziger1
Introduction
The use of a lower-stalk nitrate test, run on samples taken after corn harvest,
to detect when excess N has been used on a field has been described by Binford
et al. (1990). Though they reported this test to be quite useful for this purpose,
they did not acknowledge the possibility that hybrids may differ inherently
in the amount of N remaining in the stalk at maturity. They suggested that the
optimal range of stalk nitrate was 0.25 to 1.80 g N03-N per kg (parts per thousand),
but later modified that range to 0.7 to 2.0 parts per thousand (Binford et al.,
1992). The latter study included a number of different hybrids, but they were
in different fields and so could not be directly compared.
While corn hybrids are known to differ in their ability to use N efficiently
(Tsai et al, 1984; Eichelberger et al., 1989), little is known about possible
genetic effects on lower stalk N03 content. Stay-green - the ability of hybrids
to retain green leaf color late in grainfill - is considered a useful trait
agronomically, probably due to the ability of such hybrids to produce carbohydrate
late in the grainfilling period, thus helping to keep stalks healthy as grainfill
ends. At the same time, it could be that green leaves, which retain substantial
amounts of N, might also be associated with differences in the lower stalk nitrate
content at maturity.
This study was designed to provide an estimate of the variation in post-maturity
lower stalk nitrate among commercial corn hybrids. In addition, green leaf area
was estimated late in grainfill to see if there might be a correlation between
green leaf area and lower stalk N03 that could improve the usefulness of this
diagnostic test.
Materials and Methods
Fifty of the corn hybrids that were entered by commercial companies in the corn
hybrid performance trials at both Brownstown and Urbana were chosen (from about
70 hybrids common to both locations) for inclusion. These trials were planted,
managed, and harvested by the crop variety testing personnel of the Crop Sciences
Department, University of Illinois.
The Brownstown trial was located on Cisne silt loam soil, and was planted on May
24 and harvested on September 30, 1996. Urea was applied during land preparation
at the rate of 160 lb N/acre. Summer rainfall was low, with 2.25 inches in July
and 0. 89 inches in August, and yields were quite low. The Urbana trial was planted
on April 18 in a Flanagan silt loam. Pre-plant N was applied at the rate of 2001b
N/acre. Growing conditions were almost ideal, and very high yields were harvested
on October 7-9.
Plots at both locations consisted of four rows about 20 ft. long, with rows 30
inches apart. Plant populations of 24,000 and 28,000 per acre were established
by thinning at Brownstown and Urbana, respectively. The percentage of the leaf
area that remained green was estimated visually at Brownstown on September 24,
and at Urbana on September 22. Within a week or so after harvest, stalk samples
were taken for nitrate analysis. The portions of stalks from 6 to 12 inches above
the soil surface were cut, with six stalks from the two outside (border) rows
sampled per plot. Stalks were ground and analyzed for nitrate by A & L Labs,
Ft. Wayne, IN.
Results and Discussion
Green leaf area remaining was probably assessed a week or so later than would
have been ideal; about a third of the hybrids had no green leaf area left at Brownstown,
and the percentages were quite low at both locations (Table
1). Lower stalk nitrate averaged above 2,500 ppm at Brownstown, but there
were no significant differences among hybrids. Relatively high levels may have
resulted at this location due to poor growing conditions and a lack of kernels
to serve as a sink for N; with an average yield of only 89 bu/acre, crop removal
would have accounted for only about half the applied N.
There were differences among hybrids at Urbana, with about 20 of the hybrids having
levels above 2,000 ppm and a similar number having levels of less than 1,000 ppm.
Yields were very high at this location, and stalk nitrate contents averaged less
than 1,800 ppm (Table 1).
Tests showed few correlations among yield, green leaf area, stalk nitrate, and
grain moisture at either of the locations. A small, negative correlation between
grain moisture and yield at Brownstown probably reflected the fact that the longer-season
hybrids were damaged more than the shorter-season ones under poor growing conditions.
There were no correlations among any of these parameters at Urbana. This study
will continue in 1997.
Tables and Figures
Table 1: Grain yields, grain moisture, late-grainfill
green leaf area and lower stalk nitrate content of fifty hybrids grown in the
commercial corn hybrid trials at Brownstown and Urbana, Illinois, 1996
Footnotes and References
1 Emerson D. Nafziger is Professor of Crop Production, Dep. of Crop
Sciences, Univ. of Illinois, Urbana, IL
Binford, G.D., A.M. Blackmer, and N.M. El-Hout. 1990. Tissue test for excess
nitrogen during corn production. Agron. J. 82:124-129.
Binford, G.D., A.M. Blackmer, and B.G. Meese. 1992. Optimal concentrations of
nitrate in cornstalks at maturity. Agron. J. 84:881-887.
Eichelberger, K.D., R.J. Lambert, F.E. Below, and R.H. Hageman. 1989. Divergent
phenotypic recurrent selection for nitrate reductase activity in maize. II.
Efficient use of fertilizer nitrogen. Crop. Sci. 29:1398-1402.
Tsai, C.Y., D.M. Huber, D.V. Glover, and H.L. Warren. 1984. Relationship of
N deposition to grain yield and N response of three maize hybrids. Crop Sci.
24:277281.
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