Illinois Fertilizer
Conference Proceedings
January 28-30, 1991
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F.E. Below, P.S. Brandau, and D. G. Bullock1
Excessive applications of nitrogen (N) fertilizer have been implicated in contributing to nitrate contamination of groundwater, causing fertilizer dealers and growers to be under continued pressure to justify the levels of N fertilizer they are recommending or using: The overall goal of this research is to determine if soil and/or tissue tests can be used to optimize N management practices for corn production in Illinois.
In 1990, plants of two genetically distinct corn hybrids (B73 x LH51 and LHE136 x LH82) were grown with varying rates of nitrogen at four diverse sites. The sites (located in Champaign, Tremont, and two in Geneseo) were selected to 'represent a range in inherent soil fertility and cultural practices. Although a host of parameters associated with accumulation and partitioning of dry matter and nitrogen were measured, and will ultimately be an integral part of this work, only yield data is included in this preliminary report. Yields of both hybrids were significantly increased from applications of fertilizer N at three of the four locations, with maximum yields occurring at an N rate of approximately 200 lbs per acre. At these sites, plants grown without fertilizer N produced from 66 to 72 percent of the maximum yield. The site that was non responsive to fertilizer N has regularly received large amounts of swine manure. Regardless of N rate, hybrid B73 x LH51 outyielded LHE136 x LH82 at three of the locations, while the opposite was true at one location.
These preliminary findings show that inherent soil fertility, cultural practices, and hybrid can all influence yield, response of. corn to fertilizer N. Although these data suggest an opportunity to improve fertilizer N management in Illinois, they also demonstrate the importance of annual applications of an N source to obtain maximum corn productivity.
Nitrogen fertilizer, essential for plant growth and development, is routinely
used by Illinois corn growers because soils do not have sufficient N in available
form to support desired production levels. Although countless studies have examined
corn response to N fertilization, widespread recommendations are difficult due
to the complex cycle of N in the environment. Currently, N fertilizer recommendations
in Illinois are based on expected yield goal and formulas estimating the residual
soil supply (based on soil type and organic matter, previous crop, and the amount
of manure applied). Although generally sound, problems can arise with this approach
if
the expected yield goal is unrealistic or if growers fail to accurately .assess
the residual soil N supply. Recent research indicating that yield response to
fertilizer N is also influenced by form of N, timing of application, and genotype
grown further complicates N management recommendations.
Thus, a dilemma which Illinois growers face each year is knowing how much fertilizer N is required. This problem is further complicated by limitations associated with convenience of fertilizer N application, and by uncertainty related to weather conditions, especially water availability.
For these reasons, it is understandable why some producers may misapply (either too much or too little). the N rate needed for optimum productivity. Unfortunately, N deficiency can seriously decrease corn yields, while unused fertilizer N is economically wasteful and can become an environmental hazard if it concentrates in groundwater. The tendency to over, or under, fertilizer could be reduced if corn growers had a quick and reliable method to assess availability of residual soil N, with adequate time to correct deficiencies.
Such a chemical testing approach has recently been advocated for both soils (2, 3, 6) and plant tissues (1,4,5). For example, by comparing nitrate concentrations in the top foot of soil when plants were six inches tall with yield response to fertilizer N, Blackmer and coworkers (2) discovered that most Iowa soils containing 21 parts-permillion or greater of nitrate did not respond to additional N. Recent reports from Kentucky (3) and Nebraska (6) have also related the level of residual soil nitrate to yield responsiveness from fertilizer applied N. Similarly, tissue testing is another possible diagnostic tool for evaluating N status of a corn crop. Nitrate levels in the lower stalk (1), leaf N concentrations at silking (4), and leaf chlorophyll (5) have all been associated with the level of available N. These studies provide support for the view that soil and/or tissue testing could help in assessing how much fertilizer N is needed for optimum production efficiency.
Thus, the objective of this research is to determine if soil and/or tissue
samples can be used to optimize N management practices for corn production in
Illinois. Specifically, this work is attempting to relate levels of residual
soil N, with the anticipated yield response to applications of fertilizer N.
Tissue samples from plants grown with varying rates of fertilizer N are being
used in conjunction with soil samples to determine the plant's ability to utilize
residual and fertilizer applied N. It is hoped that this research will lead
to ways of using soil and tissue analyses to ensure adequate levels of N are
available to optimize production efficiency and safeguard environmental quality.
Two genetically distinct corn hybrids (B73xLH51 and LHE136xLH82) were evaluated for response to fertilizer applied N at four diverse locations in Illinois. The individual locations and some of their soil characteristics are presented in Table l. Briefly, the locations include: 1) The Agronomy-Plant Pathology South Farm at the University of Illinois, Champaign which is devoted to agricultural research and has irrigation capabilities; 2) A grain farm in Tremont (near Peoria) which is part of a high management corn/soybean rotation; 3) A livestock/grain operation in Geneseo (Geneseo 1) that receives known amounts of hog manure and is in continuous corn; and 4) A separate site in Geneseo (Geneseo 2), that is part of a corn/soybean rotation and does not receive manure.
Treatments consisted of each hybrid grown with varying levels of soil applied N. At all locutions, the experiment was arranged in a split-plot design with three to four replications. At Champaign, N rates were main plots and hybrids the subplots, while at the other three locations hybrids were the main plots and N rates the subplots. An experimental unit consisted of eight rows of the respective hybrid that were either 20 feet (Champaign and Tremont) or 40 feet. (both Geneseo locations) in length. At Tremont, rows were spaced 36 inches apart, while the row spacing was 30 inches at the other locations. At all locations, the stand density was 26,000 plants per acre. The N levels tested were 0, 60, 120, 180, and 240 lbs N per acre at Champaign; 0, 50, 100, 150, and 200 1bs N per acre at Tremont, and 0, 25, 50, 75, 100, 125, 150, 175, and 200 lbs N per acre at both Geneseo locations. The N treatments were established when plants were at the V2 to V3 growth stage by applying varying amounts of urea or ammonium nitrate and immediately incorporating with cultivation. Six of the eight rows received the fertilizer treatment and the two outside rows serving as borders.
Prior to planting, the soil at each site was sampled (to a depth of 12 inches) for analysis of available N03 and NH y. In order to track the residual soil N status, other soil samples were periodically collected during the growing season from plots that did not receive fertilizer N but that contained plants. At flowering and physiological maturity, the above ground portions of, four representative plants were harvested from each plot, separated into leaves, stalk (including leaf sheaths), grain, and a reproductive support fraction consisting of husk, shank, tassel and cob. After drying (80 C) to constant weight, all fractions were weighed, ground, and stored for chemical analysis. Although not yet completed, these data will be used to determine the effect of hybrid, location, and fertilizer N rate on: 1) accumulation and partitioning of total N and dry matter by the plant; 2) the amount of these constituents accumulated after flowering, and; 3) the proportion of grain N derived from remobilization.
Once the grain had field-dried to an acceptable moisture content, the center
two rows of each plot were combine harvested for the two Geneseo locations and
hand harvested for the other two locations in order to estimate grain yield.
Yield is expressed as bushels per acre at 15.5 percent moisture. Data for each
location was analyzed separately by analysis of variance procedures and an LSD
(0.05) calculated to compare N rates for a given hybrid.
Grain yields of both hybrids were significantly increased from. applications of fertilizer N at three of the four locations (Fig 1). These included Champaign, Tremont and one of the Geneseo (Geneseo 2) locations. For each of these N responsive locations, maximum yields were obtained with an N rate of approximately 200 lbs per acre, while plants relying solely on soil residual N produced from 66 to 72 percent of the maximum yield. The N response curves for each of these locations exhibited a pattern of decreasing increments of yield increase with successive N rates, but yields had not yet plateaued at the Tremont or Geneseo 2 sites. Thus it is unclear if additional N would have resulted in even higher yields at these sites in 1990.
In contrast, yields did reach a plateau at the Champaign and Geneseo 1 sites.
These sites also produced higher yields without fertilizer N averaging 142 and
161 bushels per acre for Champaign and Geneseo 1, compared to 127 and 126 bushels
per acre for Tremont and Geneseo 2. The Geneseo 1 site, which was nonresponsive
to fertilizer N, has regularly received large amounts of swine manure and has
a high level of residual
soil N (data not shown). Regardless of .N rate, hybrid B73 x LH51 outyielded
LHE136 x LH82 at Champaign and both Geneseo locations,. while the opposite was
true at Tremont.
Collectively, these data demonstrate the variable effect of existing soil N
levels, management practices, and hybrid selection on yield responsiveness of
corn to fertilizer applied N.
Despite the proven importance of N fertilizer in obtaining maximum productivity of corn, excessive applications of N have been implicated as contributing to nitrate contamination of groundwater. As a result, fertilizer dealers and growers are under continued,., pressure to justify the levels of N fertilizer they are recommending or using. The research being conducted in this project is prompted by these concerns. Reliable and-up-to-date information on how corn plants use N will add to information required to- improve N management of Illinois soils, and will help to minimize the adverse environmental, impacts of N fertilizer use.
In addition to helping address the question of how much fertilizer N is needed to optimize production efficiency, this research is also examining N use and fertilizer needs from a plant perspective. Information regarding the physiological basis for requirement and use of N with current hybrids and management strategies is surprisingly lacking. The preliminary findings obtained so far indicate that inherent soil fertility, cultural practices; and hybrid can all influence yield response to fertilizer N. These data are supportive of the view that N management could be improved by the ability to better predict the plant's need for fertilizer applied N. However, these data also clearly indicate the importance of annual applications of an N source to obtain maximum productivity of corn.
Figure 1. Nitrogen Applied vs Yield graph.
The authors wish to express their gratitude to Gary Johnson, Edward Kiefer, and Carl Sinn for their efforts at the extramural locations.
Binford, G.D., A.M. Blackmer, and N.M. El-Rout. 1990. Tissue tests for excess nitrogen during corn production. Agron. J. 82:124-129.
Blackmer, A.M., D. Pottker, M.E. Cerato, and J. Webb. 1989. Correlations between soil nitrate concentrations in late spring and corn yields in Iowa. J. Prod. Agric. 2:103109.
McCracken, D.V., S.J. Corak, M.S. Smith, W.W. Frye, and R.L. Blevins. 1989. Residual effects of nitrogen fertilization and winter cover cropping on nitrogen availability. Soil Sci. Soc. Am. J. 53:1459-1464.
Schepers, J.S., and F.E. Below. 1987. Influence of corn hybrids on nitrogen uptake and utilization efficiency. p. 172-186. In_ D. Wilkinson (ed.) Proc. Annu. Corn and Sorghum. Industry Res. Conf., 42nd, Chicago, IL. 10-11 Dec. Amer. Seed Trade Assoc. Washington, DC.
Schepers, J.S., D.D. Francis, and C. Clausen. 1990. Techniques to evaluate N status of corn. p. 280. In Agronomy Abstracts. ASA, Madison, WI
Schepers, J.S., K.D. Frank, and C. Bourg. 1986. Effect of yield goal and residual soil nitrogen considerations on nitrogen fertilizer recommendations for irrigated maize in Nebraska. J. Fert. Issues. 3:133-139.
