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© 2007 Plant Management Network. Optimizing Plant Population and Nitrogen Rate for High-Oil Corn Eric A. Adee, Principal Research Specialist, Northwestern Illinois Agricultural Research and Demonstration Center, University of Illinois, Monmouth 61462; Emerson D. Nafziger, Professor, Department of Crop Sciences, University of Illinois, Urbana 61801; and Lyle E. Paul, Agronomist, Northern Illinois Agronomy Research Center, University of Illinois, Shabbona 60550 Corresponding author: Eric A. Adee. adee@uiuc.edu Adee, E. A., Nafziger, E. D., and Paul, L. E. 2007. Optimizing plant population and nitrogen rate for high-oil corn. Online. Crop Management doi:10.1094/CM-2007-0831-01-RS. Abstract High-oil corn (Zea mays L.) has been grown because of the increased feed value and potential for price premiums. There are only limited data on how plant population and N rates affect grain yield, grain oil content, or grain protein content, and resulting net value per acre of high-oil corn. In a study conducted over three locations and three years, grain oil content decreased slightly and grain protein content increased as N rate increased from 80 to 200 lb/acre. Increasing the plant population from 25,000 to 40,000 plants/acre did not affect grain yield, grain oil content, or grain protein. Net crop value per acre — calculated using a base price of $3.50/bu, an oil premium of $0.08/bu at 6.5% grain oil plus $0.01 for each increase of 0.1 percentage point of oil up to 8% (maximum of $0.23/bu), and a protein premium of $0.04 for each percentage point increase from 8.5 to 10.5% (maximum of $0.08/bu) — was maximized at an N rate of 159 lb/acre, at which grain yield was 163 bu/acre. Increasing the protein premium by $0.01 per percentage point of protein between 8.5 and 10.5% protein adds about $1.67/acre to net value and increases the optimum N rate by about 0.3 lb/acre. Due to increasing seed costs and lack of yield response to increasing plant population, net value decreased as plant population increased. There was no interaction between N rate and plant population for any parameter measured. Managing high-oil corn for yield rather than for grain oil or grain protein content resulted in the highest net value per acre. Optimum plant population for high-oil corn was somewhat less, while the optimum N rate for high-oil corn was similar to that recommended for normal (yellow dent) corn grown in the same environment. Introduction High-oil corn has been grown on several million acres in the US Corn Belt over the past decade because of its higher market price stemming from its increased feed value (7). Price premiums in 2001 ranged from $0.08 for 6.5% oil content to $0.23 for 8.0% oil (Monmouth Feed Service, Monmouth, IL, personal communication). In one report, the oil content of TopCross Blends of high-oil corn averaged 6.9% oil compared to 3.8% oil in conventional counterparts (7), but yielded an average of 8% less (6). Compared to normal (yellow dent) field corn, little is known about the agronomic practices needed to maximize income from high-oil corn. While there has been a considerable amount of work done to determine the optimum plant population and N rate for normal corn (2), such information is limited for high-oil or other "nutritionally enhanced" types of corn. One study reported that the effect of N rate on protein content of one type of nutritionally-enhanced (not TopCross high-oil) corn was considerably influenced by environment, indicating that getting consistent increases may prove difficult (5). Unlike normal corn, the value of high-oil corn per acre is a function of both yield and oil content. In addition, while price premiums based on higher protein content are not commonly available along with high-oil premiums, it is useful to know how N rate and plant population affect protein content as well, in order to know how protein levels might affect crop value should protein premiums become available. Research on normal corn hybrids has shown that increasing the plant population can decrease grain protein content (1). The objective of this research was to determine the optimum plant population and nitrogen rate required to maximize net return per acre from high-oil corn. Field Studies on Effect of Plant Population and N Rate on High-Oil Corn Yield This study was conducted from 1999 through 2001 at three University of Illinois Crop Sciences Education and Research Centers. One site was near DeKalb in northern Illinois, one near Monmouth in west-northwestern Illinois, and one near Urbana in east-central Illinois. Soil types were Elpaso silty clay loam and Flanagan silt loam at DeKalb, Sable silty clay loam and Muscatune silt loam at Monmouth, and Elburn silt loam and Drummer silty clay loam at Urbana. All sites are highly productive. High-oil TopCross hybrids Pioneer 34K82 (1999) and Pioneer 34B25 (2000 and 2001) were used in this study. The experimental design was a randomized complete block, split-plot design, with N rate assigned to whole plots and plant population to sub-plots. The plots were over-planted and thinned to plant populations of 25,000, 30,000, 35,000, and 40,000 plants/acre. Planting dates were 5 May 1999, 1 May 2000, and 3 May 2001 at DeKalb; 5 May 1999, 25 April 2000, and 27 April 2001 at Monmouth; and 5 May 1999, 8 May 2000, and 19 April 2001 at Urbana. Soil insecticide cyfluthrin + tebupirimphos (Aztec 2.1G, Bayer CropScience, Research Triangle Park, NC), was applied at 7.3 lb/acre at DeKalb and Urbana in 1999, and the soil insecticide tefluthrin (Force 3G, AMVAC Chemical Corp., Los Angeles, CA) was applied at 5.4 lb/acre at Urbana in 2000 and 2001. The soil-applied rodenticide 2% zinc phosphide (Prozap, Chemtech Ltd., Northbrook, IL) bait was applied in-furrow at 6 lb/acre at Monmouth in 2000 and 2001. The four N rates were 80, 120, 160, and 200 lb/acre, applied as urea or urea ammonium nitrate (UAN) solution sidedressed after crop emergence. The subplot size was 30 ft long by 10 ft wide, with four 30-inch rows per plot and a minimum of 12 rows of border around the study. The previous crop was soybean at all locations except for DeKalb in 1999 and Urbana 2000, where the trial followed corn. Fields were chisel plowed in the fall and field cultivated in the spring prior to planting. Weeds were controlled with recommended herbicides at recommended rates, and with mechanical cultivation as needed. Yields and grain samples were taken from machine harvest of the middle two rows of each subplot. Grain oil and protein content (0% moisture basis) were determined with a Infratech 1221 near-infrared whole grain analyzer (Tecator AB, Hooganas, Sweden) with the assistance of Tolono Grand Prairie Coop, Tolono, IL in 1999, and in 2000 and 2001 with a Perten Model DA7000 (Perten Instruments Inc., Springfield, IL). Grain yields were adjusted to 15% moisture. Economic comparisons were made using typical, recent costs of seed and N fertilizer, and a typical price of corn plus premiums. We used a fertilizer N price of $0.35/lb of N, a seed cost of $1.75 per thousand ($140 per 80,000-kernel unit), and a base price of $3.50/bushel of corn. The calculation of net value ($/acre) was done by taking yield times corn price (including oil and protein premium) minus the seed cost (plant population times the cost per thousand seeds) and minus the N cost (N rate times the cost per pound of N). The grain oil premium was calculated as $0.08/bu for corn with grain oil content of 6.5%, plus an additional $0.01/bu for each additional 0.1 percentage point of oil above 6.5%, up to a maximum of $0.23/bu when oil content was 8% or greater. This was a typical premium schedule based on oil content when production of high-oil corn was widespread, in the late 1990s and early 2000s. There is no established premium for protein content in corn, but here we applied a rather conservative extra value of $0.04/bu for each percentage point of protein above 8.5%, to a maximum of $0.08/bu at 10.5% or greater protein levels. In addition, to test the sensitivity of net value and optimum input levels to protein price premium, we calculated changes in net value as the price premium increased from 0 to $0.10/bu per percentage point of protein. Data for yield, oil, protein, and net value were analyzed using the PROC MIXED procedure of SAS 8.1 (SAS Institute Inc., Cary, NC). Years, locations, reps nested within years and locations were considered random, and plant population and N rate fixed, for the analysis. Grain composition data were missing for one location (Urbana 1999), and net values for that location were assigned based on yield only, with no premium. Regression analyses were conducted using all of the data where effects of N rate and population were significant, and significance of linear and quadratic components was assessed. All regressions reported are significant at P = 0.05. Within the range of input levels used, the maximum point of the regression line describing net value was taken as the optimum input level. Economically optimum rates of inputs such as N were calculated as that point where the first derivative (slope) of the quadratic function equals the input cost:corn price ratio (4). Optimizing Net Value of High-Oil Corn While monthly rainfall amounts during the growing season varied considerably among environments, growing conditions were not particularly unusual in any of the environments (Table 1); departures from average monthly rainfall (about four inches at these locations) were generally small, and more months were wetter than normal than were drier than normal. Yields varied only moderately as well, with seven of the nine environments producing yields between 150 and 182 bu/acre, and the other two, both at DeKalb, producing 116 and 135 bu/acre. Rainfall was not atypically low for these two lower-yielding years, and there is no ready explanation for the low yields. Table 1. Monthly rainfall and yields, oil and protein content, and calculated net value per acre for high-oil corn grown in nine Illinois environments. Data are averaged over four N rates and four plant populations.
Oil content varied substantially among environments and showed little relationship to average yield or to seasonal rainfall patterns among environments (Table 1). This is consistent with other work showing inconsistent environmental effects on grain oil levels of nutritionally enhanced corn (5). The lower oil content at the two locations where it was measured in 1999 could have been related to the use of a different hybrid that year, though oil content of the hybrid used in 2000 and 2001 was lower at Urbana in 2001 than at either location in 1999. Oil content in most environments, and on average, was sufficient (> 8%) to have earned maximum price premiums at four of eight environments. Protein content varied more widely among environments than did oil, with a range from less than 7 to more than 10% (Table 1). Among environments, the correlation between protein and yield was weak, as was that between oil and protein. Nitrogen rate significantly affected yield, grain oil and protein content, and net value (Table 2). Averaged over all environments, grain oil content decreased as N rate increased. This decrease was less than 0.3 percentage point (3.2%) from the lowest N rate (80 lb/acre) to the highest N rate (200 lb/acre.) The relationship between grain oil content and N rate was described by the linear equation % oil = 8.3 - 0.0026N (adj. R² = 0.02, N = 496). Oil percentage did not vary by more than 0.5 percentage points due to N rates within any single environment. Table 2. Effect of N rate on yield, oil, protein, and net value of high-oil corn, averaged over nine Illinois environments. Data are averages over four plant populations.
* Significant at P = 0.1 ** Significant at P = 0.05. Protein content increased as N rate increased, from 8.9% at 80 lb/acre to 9.6% at 200 lb/acre (Table 2). The response to N was described by the linear function, % protein = 8.4 + 0.0063N (adj. R² = 0.06, N = 496). Using the price premium that we assigned to increased protein, the premium would have been $0.02/bu at an N rate of 80 lb/acre and $0.05/bu at 200 lb/acre. Increasing the protein premium from zero to $0.10/bu per percentage point of protein between 8.5 and 10.5% increased the net value by $16.74/acre, and the N rate needed to produce the maximum net value increased by about 3 lb/acre. The yield response of high-oil corn to N rate is described as the quadratic equation, Yield = 98.5 + 0.73N – 0.002N² (adj. R² = 0.09, N = 559). Using a corn price of $3.76/bu (base of $3.50/bu plus premiums of $0.21 for oil and $0.05 for protein) and an N cost of $0.35/lb, optimum N rate was found to be 158 lb/acre, corresponding to a grain yield of 163 bu/acre. The response of net value (NV) to N rate was described by the quadratic relationship, NV = $302.48 + 2.48N – 0.0078N² (adj. R² = 0.03, N = 559). The maximum NV occurred at an N rate of 159 lb/acre, at which N rate the yield was 163 and the NV was $500/acre. The slight difference in optimum N rate using these two methods comes from the fact that actual grain oil and protein values (and premiums) are used in the net value calculation, while premiums are averaged into a single corn price in the yield-based response. With no price premium (corn at the base price of $3.50/bu), the optimum N rate based on the yield response decreases by only 2 lb/acre. While the oil content was decreased and protein increased as N rate increased, the overall profitability was much more influenced by grain yield than by premium. Fertilizing high-oil corn for optimum yield (maximum return to N) is therefore much more important than managing to maximize the oil or protein content of the grain. These findings indicate that N rates for high-oil corn are similar to those recently found to be optimal for normal corn grown in similar environments (4). Corn plant population had no significant effect on grain oil content, grain protein content, or grain yield (Table 3.) Response of the high-oil hybrids to plant population was somewhat less than plant population responses we have observed for normal corn hybrids in recent studies at the same locations (unpublished results from the authors). Given that these hybrids (other than the 10% or so pollinator plants) are agronomically similar to normal hybrids on which they are based, this lack of response to populations above 25,000/acre is somewhat surprising. Yields responded significantly to population in four of the nine environments, with yields increasing with population in three cases and decreasing in the fourth. There was not a clear relationship between response to population and yield level; two of the positively responding sites were Monmouth in 1999 and 2001, both of which had high yields, and another was at DeKalb in 2000, where yields were low. The one site with decreasing yield at higher populations occurred at Urbana in 2000, where yields were average. We did not find support for the idea that high-oil hybrids may need to be planted at higher populations than normal corn (6). We also did not find, as others have reported for normal corn hybrids (1), that grain protein content decreased as plant population increased. Table 3. Effect of plant population on yield, oil, protein, and net value of high-oil corn, averaged over nine Illinois environments. Data are averages over four N rates.
* Significant at P = 0.1 ** Significant at P = 0.05. Increasing the plant population did not increase yield but increased seed cost, thus net value decreased as plant population increased, at least above 30,000 plants/acre (Table 3). Based on the net values calculated, the optimum plant population for the high-oil corn hybrids we used is between 25,000 and 30,000/acre. This is somewhat less than the plant population currently recommended for normal corn hybrids on these soil types in Illinois (3). Across the nine environments, there was no interaction between N rate and plant population for any of the variables measured. The N rate by population interaction was significant for yield at three of the four individual environments in which population had a significant effect on yield, including the two years at Monmouth where yield increased with plant population and the one year at Urbana where yield decreased as population increased. This lack of interaction at most individual environments may have partly resulted from having used relatively high starting population (25,000) and N rate (80 lb), which appeared to have limited consistent responses to increasing levels of these inputs. Price premiums for grain oil and protein content increase the price of corn, thereby decreasing the N:corn price ratio and increasing the optimum N rate (Table 4). The size of this effect depends mostly on the yield response to N along with the price of corn (base price plus premium) and the price of N; effects of N rate on grain composition (and premium) are small. Adding the premium when the corn base price is $2.00/bu increases the optimum N rate by 5 lb (from 138 to 143 lb/acre), while adding the price premium to a base corn price of $4.00/bu increases the optimum N rate by only 2 lb/acre (Table 4). Such small N rate increases have very little effect on grain yield. This suggests optimizing N based on the yield response and prices, with little regard to N effects on grain composition. Table 4. Sensitivity of optimum N rate to base corn price and to corn price including a premium for grain oil and protein content. Optimum N rate is calculated based on the response of yield to N, and uses an N price of $0.35/lb and a price premium of $0.26/bu.
We conclude that high-oil corn should generally be managed much like normal corn with regard to N rate, and that optimum N rate is affected little by the influence of N rate on grain oil and protein levels. Plant population responses, however, were less than we had anticipated, and increasing the plant population above the lowest level used (25,000/acre) produced little added yield, but did decrease net value due to increasing seed cost. While the ability to earn price premiums will greatly influence the willingness of producers to choose to grow high-oil (and other nutritionally-modified) corn hybrids, we find little evidence that choosing plant population or N rate based on their effects on grain composition will pay off. Instead, profitability of production of these hybrids will depend mostly on managing for optimum yield. Acknowledgement We thank Martin Johnson, Dave Lindgren, and Darin Joos for their work on this project. Pioneer Hi-Bred International funded this work. Literature Cited 1. Ahmadi, M., W. J. Wiebold, J. E. Beuerlein, D. J. Eckert, and J. Schoper. 1993. Agronomic practices that affect corn kernel characteristics. Agron. J. 85:615-619. 2. Hoeft, R. G., Nafziger, E. D., Johnson, R. R., and Aldrich, S. R. 2000. Modern corn and soybean production. MSCP Publ., Champaign, IL. 3. Nafziger, E. D. 2002. Corn. Illinois Agronomy Handbook 23rd Edition. Ext. Pub. 1372. Univ. of Illinois Ext. Service., Univ. of Illinois at Urbana-Champaign. 4. Sawyer, J. E., and Nafziger, E. D. 2005. Regional approach to making nitrogen fertilizer rate decisions for corn. Proc. of the North Central Ext.-Industry Soil Fertility Conf., November 16-17, 2005, Des Moines, IA. 6. Thomison, P. R., Geyer, A. B., Lotz, L. D., Seigrist, H. J., and Dobbels, T. L. 2002. TopCross high oil corn production: agronomic performance. Agron. J. 94:290-299. 7. Thomison, P. R., Geyer, A. B., Lotz, L. D., Seigrist, H. J., and Dobbels, T. L. 2003. TopCross high oil corn production: select grain quality attributes. Agron. J. 95:147-154. |
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