M.L. Ruffo, A.S. Henninger, and F.E. Below 1
Large projected increases in ethanol production from corn grain and the potential premiums farmers can earn from producing high-quality grain for the food industry should result in much more end-use corn being produced in Illinois in the future as a means to improve farming profitability.
Currently, the two major end-use grain groups include high extractable starch (or high fermentable starch) for wet milling or dry grinding into ethanol, and hard endosperm for dry milling into food products. Food-grade and high-extractable starch are two end uses of corn that provide a premium for grain quality. Interestingly, the optimum grain quality traits for each of these end-use types appear to be opposite, with low protein and high starch being best for high starch extractability, whereas high protein and hard endosperm are the most desirable for food-grade corn. Other increasingly important end-uses are high protein corn for export markets and high oil/high protein corn grain for feed.
Although management factors such as hybrid selection, nitrogen (N) fertilization, plant population, and the previous crop can all exert big effects on the different grain quality traits (as well as on crop productivity), there is very limited up-to-date information to help guide crop management for these specific end-use types. Some studies (Ahmadi et al., 1993; Aidson et al., 2005) showed that grain protein concentration, and other desired characteristics of hard endosperm corn, increase with N fertilization. In contrast to grain protein, grain starch concentration typically decreases with N fertilization in a manner that is almost exactly opposite to grain protein. Opposite to the effects of N fertilization, increasing the plant population decreases grain protein and increases grain starch (Ahmadi et al., 1993). Because plant population and N rate are also both crucial factors to obtaining maximum grain yield, their differential effect on grain quality suggests vastly different production strategies depending the grain’s end-use. Other management factors can also affect grain quality, especially if they impact yield levels or N availability. For example, previous crop (i.e. corn or soybean) could affect starch or protein levels, and some hybrids may respond differently to both previous crop and to the fertilizer N rate.
The objective of this research is to analyze the effects of the major corn management practices on productivity and grain quality for specific end-uses.
The experiment was conducted at four locations in Illinois to better understand how N fertilizer, plant population, and previous crop affect a hybrid’s productivity and grain quality.
An expanded version of the experiment was conducted at the Crop Sciences Research & Education Center in Champaign IL to examine the effect of corn or soybean as the previous crop. An individual experimental unit consisted of one 17.5 foot long row, spaced 30 inches apart. Treatments were arranged in a split-split-split plot experimental design with previous crop as main plots (corn or soybean), plant population as the subplots, N as the sub-subplots, and hybrids as the sub-sub-subplots. There were four replications of all treatments.
Similar experiments were conducted at the Northern Illinois Agronomy Research Center in Shabonna (DeKalb County), at the Northwestern Illinois Agricultural Research and Demonstration Center in Monmouth (Warren County), and at the J.F. Richards Land Laboratory, Demonstration and Research Farm in Joliet (Will County), except that previous crop was not included (soybean was the previous crop at these three locations). Treatments were arranged in a split-split plot experimental design with hybrids as main plots, plant population as the subplots, N as the sub-subplots. An individual experimental unit consisted of four 17.5 foot long rows, spaced 30 inches apart.
The same hybrids representing different and contrasting corn end-uses were planted in all locations. The corn hybrids planted were: DeKalb DKC57-79 RR/YGPL (107 RM) a yellow corn hybrid (YC); DeKalb DKC60-18 RR2/YGPL (110 RM) a high extractable starch hybrid (HES); DeKalb DKC63-74 YGPL (113 RM) a hard endosperm hybrid (HEC); and Asgrow RX756 (112 RM), a Nutridense hybrid (ND). The same nitrogen rates and plant populations were also used at all locations. Nitrogen rates were 0, 50, 100, 150, 200, and 250 lbs N per acre and plant populations were 28, 32, 36, and 40 thousand plants per acre.
Planting date ranged from April 24th (Champaign) to April 27th (Monmouth). A soil insecticide was applied at planting at all sites. The crop was over-seeded and thinned at the V5/V6 stage to the desired plant populations. The fertilizer N source was granular ammonium sulfate applied in a diffuse band down the center each row at approximately the V3 growth stage, and incorporated with a field cultivator. Other established management practices conducive for high productivity were used according to local recommendations.
Soil samples (0-12”) were collected at planting and analyzed for pH, organic matter, P, K, and nitrate-N. Grain yield estimates were obtained by hand in Champaign and by using a plot combine in the other locations. Grain samples were collected at harvest in each location and analyzed for protein, starch, oil and extractable starch using a Foss 1241 NIT grain analyzer.
Soil Fertility
Soil fertility attributes at each site are presented in Table
1. Soil nitrate-N concentration was 9 ppm for continuous corn and 14 ppm
for corn after soybean in Champaign. Nitrate-N was 13, 14, and 12 ppm in DeKalb,
Joliet, and Monmouth, respectively.
Grain Yield
There was a large difference among the sites in grain yield. The highest grain
yield was obtained in DeKalb, which averaged 232 bu/ac, whereas the other locations
yielded similarly between 203 and 209 bu/ac (Table 2).
On average across sites, the HEC and YC hybrids showed the highest yields averaging
224 bu/ac, followed by the HES hybrid, which yielded 212 bu/ac, and the ND
hybrid which yielded 192 bu/ac. The hybrid with the longest relative maturity,
the HEC one (RM 113), was the highest yielding hybrid in the southernmost environment
(Champaign), whereas the HES hybrid (RM 110) was the highest yielding one in
the Northern environments (DeKalb, Joliet and Monmouth). The ND hybrid produced
the lowest yields in all four environments.
Corn yield response to N fertilizer at each location is presented in Fig. 1. Nitrogen fertilizer increased grain yield at all the sites, although they differed in the magnitude of response and the maximum yield achieved. The highest yielding site was DeKalb at 240 bu/ac, followed by Champaign (230 bu/ac), and Joliet and Monmouth (220 bu/ac). The smallest response to N fertilizer was observed in Monmouth and DeKalb. In contrast, the largest yield response (107 bu/ac) was obtained for continuous corn in Champaign, although rotated corn was also the largest (79 bu/ac) among the sites with soybean as previous crop.
The average yield for continuous corn was 194 bu/ac, whereas corn after soybean yielded 208 bu/ac. Grain yield increased with N fertilizer from 123 bu/ac for unfertilized continuous corn to 230 bu/ac with 250 lb N/ac, whereas rotated corn responded from 152 bu/ac to 231 bu/ac (Fig. 1). Interestingly, the same maximum yield was achieved by both rotations, but continuous corn required 222 lb N/ac to reach it compared to only 146 lb N/ac for rotated corn.
Corn yield response to plant population differed among sites, increasing with population in the Northern sites, but not in Champaign (Fig. 2). Even in the responsive environments, the effect of plant population was of much smaller magnitude than that of N fertilizer. The largest increase in grain yield with plant population was observed in DeKalb and Joliet (13 bu/ac). There was no population effect on grain yield for continuous or rotated corn.
Grain Composition
Hybrids showed large differences in grain composition (Table
3). On average across
environments, the highest protein concentration was obtained with the HEC hybrid
(8.4%), whereas the HES hybrid had the lowest protein concentration (7.3%).
Conversely, the HES hybrid had the highest starch and extractable starch concentrations
(73.8% and 68.3%) and the ND hybrid the lowest (72% and 63.1%). However, the
ND hybrid produced grain with the highest oil concentration (5.5%) and the
HES hybrid the lowest (3.9%).
Grain protein concentration increased with N fertilizer in every environment (Fig. 3). On average grain protein increased 1.3% units with N fertilizer. The highest protein concentration was obtained in DeKalb where it reached slightly more than 9%. However, the largest increment in grain protein occurred in Champaign, the environment with the lowest protein concentration, where it increased from 6.5 (with soybean as previous crop) to 8.2%. Grain protein concentration of unfertilized continuous corn (6.2%) was lower than rotated corn, but both reached the same maximum protein concentration (8.2%) with high rates of N fertilizer.
Plant population had a negative effect on grain protein concentration at all sites. This negative effect was more pronounced in Champaign, irrespective of the crop rotation (Fig. 4). The steepest decrease in protein concentration occurred between 28,000 and 36,000 pl/ac, and was minor between 36,000 and 40,000 pl/ac.
In contrast to grain protein, extractable starch decreased with N fertilization at all four sites (Fig. 5). The magnitude of decrease ranged from 1.7% units in Champaign to 0.8% units in Monmouth. This decrease occurred between the unfertilized treatment and the highest N rate, but even between 100 lb N/ac and 200 lb N/ac there was a 1% unit decrease in Champaign, and a 0.9% unit decrease in Joliet.
Opposite to the effect of N rate, increasing the plant population increased grain extractable starch concentration at all sites (Fig. 6). Interestingly, extractable starch showed a more pronounced response in the environments that had higher extractable starch concentration, such as DeKalb and Champaign, where it increased 0.9% units between 28 and 40 thousand plants/ac. This is in contrast to Joliet, which produced the lowest grain extractable starch concentration, where the response was 0.5% units between the same plant populations. Previous crop did not affect how extractable starch responded to plant population.
Plant population and N rate decreased grain oil concentration, particularly for the ND hybrid, although the magnitude of these effects was smaller than for protein or extractable starch (data not shown).
Hybrid selection plays a large role to optimize grain composition for specific end-uses, although crop management practices also have an important impact on grain composition. Grain protein concentration is maximized with management practices that increase N availability. Soybean as a previous crop should be preferred over corn, the plant population should be maintained as low as possible without affecting grain yield, and N fertilizer should be applied at a slightly higher rate than the optimal N rate for grain yield. Conversely, extractable starch can be maximized by management practices that limit N availability. The results of this research indicate that, in order to maximize grain extractable starch concentration, continuous corn is preferable over rotated corn, plant population should be increased and over fertilization of N should be avoided.
Figure 1. The effect of N rate on grain yield of corn grown at four locations in Illinois in 2006.
1M. L. Ruffo is a Research Associate, A.S. Henninger is a Research Assistant, and F.E. Below is a Professor, Dept. of Crop Sciences, University of Illinois, Urbana, IL.
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