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© 2007 Plant Management Network. Evaluations of Short-Season Corn Hybrids in the Mid-South USA H. Arnold Bruns and Hamed K. Abbas, USDA-ARS, Crop Genetics and Production Research Unit, P. O. Box 345, Stoneville, MS 38776; Henry J. Mascagni, Jr., Northeast Research Center, LSU AgCenter, PO Box 438, St. Joseph, LA 71366; Richard D. Cartwright, Department of Plant Pathology, University of Arkansas, Fayetteville 72701; and Fred Allen, Department of Plant Sciences, University of Tennessee, Knoxville 37996-4561 Corresponding author: H. Arnold Bruns. arnold.bruns@ars.usda.gov Bruns, H. A., Abbas, H. K., Mascagni, H. J., Jr., Cartwright, R. D., and Allen, F. 2007. Evaluations of short-season corn hybrids in the Mid-South USA. Online. Crop Management doi:10.1094/CM-2007-1005-01-RS. Abstract Short-season corn (Zea mays L.) hybrids could allow Mid-South USA producers to spread some of their risks and begin marketing grain when supplies are low and prices high. This experiment examined the production potential of 16 short-season hybrids and compared them to two full-season hybrids commonly produced in the Mid-South in 2002 and 2003. Individual experiments were conducted at Stoneville, MS, Colt, AR, and St. Joseph, LA, both years and Knoxville, TN in 2003. All plantings utilized a randomized complete block design replicated four times, irrigated, fertilized according to yield goals of 200 bu/acre, and weeds controlled with herbicides and cultivation. Grain yield, aflatoxin, and fumonisin contamination were collected at all locations. Growing degree units (GDU 50s) at anthesis and physiological maturity, grain test weight, and kernel weight were collected at Stoneville, MS, St. Joseph, LA, and Knoxville, TN. Most of the short-season hybrids produced comparable yields to the two full-season hybrids though grain bulk densities for most of them at St. Joseph, LA were less than at other locations. Differences in mycotoxin levels were observed only at Stoneville, MS. Questions exist about short-season hybrids either requiring or just acquiring more GDU 50s when grown in the Mid-South as opposed to their adapted environments. Development of short-season hybrids for the Mid-South is warranted based upon our research. Introduction Corn production in the Mid-South USA often involves growing full-season hybrids that require ≥ 2700 GDU 50s to mature. This assumption is based on most of the area having a period between killing frosts in the spring and autumn of ≥ 200 days and that generally corn hybrids which utilize the greatest amount of an area’s growing season yield best (2,9). Planting corn hybrids of differing maturities has certain advantages for growers. Short-season corn hybrids (≤ 2450 GDU 50s) tend to reach anthesis earlier than later maturing hybrids. This spreads pollination out over several days and reduces risks of a brief period of drought and/or heat stress during peak anthesis damaging the farm’s total corn crop (2,9). Another advantage to growing corn hybrids of differing maturity classes is that a grower’s entire crop does not reach harvest maturity (15.5% of grain moisture) at the same time. This ensures more timely and efficient harvests. Ideally the last part of a grower’s corn crop should just be reaching harvest maturity as harvest of the first part is being finished. In the Mid-South, corn matures in mid-summer and can rapidly field-dry below 12.0% grain moisture if left unharvested (3). Corn grain at or below 12.0% grain moisture is susceptible to kernel breakage during harvest, handling, and transportation. This can reduce yield, test weight, and its milling value (16). Broken kernels can also reduce airflow in storage and increase the likelihood of grain spoilage. Aflatoxin, a carcinogenic secondary metabolite of the fungi Aspergillus flavus Link:Fr and Aspergillus parasiticus Speare can be a serious contaminant of corn grain, particularly in the southern USA. Pre-harvest infection and contamination of grain is often facilitated by stress during reproductive growth of the crop. Short-season hybrids are thought to be more susceptible to aflatoxin contamination because the grain is more exposed to insect and bird injury due to their husk cover characteristics. Such hybrids have a low number of loose, short husks that increases the rate of grain drying in the field (13). Drought and heat stress are the more common culprits in facilitating contamination (3). Maximum aflatoxin contamination levels of 20 ppb have been set by the United States Food and Drug Administration for corn grain entering interstate commerce (14). Fumonisin, another potential carcinogen produced by the fungus Fusarium verticillioides (= F. moniliforme) can also contaminate corn pre-harvest. It too appears to be more prevalent on corn that experiences stress. Maximum levels for fumonisin contamination have been established at 4.0 ppm for grain entering the food chain and 20 ppm for livestock feed (15). Recent research has demonstrated some shorter season hybrids yield as well as several full-season hybrids (4,5). The GDU 50s required for some short-season hybrids to attain both anthesis and physiological maturity, when grown at Stoneville, MS were greater than was stated by their suppliers when grown in their adapted environments (4). Later it was observed that mid-season corn hybrids (2610 GDU 50s to 2657 GDU 50s required for maturity), not only had similar yields to full-season hybrids but that aflatoxin contamination levels did not differ between the two maturity groups (5). Growing short-season hybrids as part of their overall corn acreage, would benefit corn producers in the Mid-South by allowing them to sell cash grain on the market when supplies are usually low and prices are at their highest. It would also spread their harvest time and reduce the risks of losses due to grain remaining in the field past harvest maturity. The objective of this research was to evaluate the production potential of several short-season corn hybrids at multiple locations throughout the Mid-South. Examining the Potential of 16 Short-Season Hybrids The experiment was conducted at several locations in the Mid-South during 2002 and 2003. The locations were Stoneville, MS, Colt, AR, and St. Joseph, LA. A fourth location at Knoxville, TN was added in 2003. The experimental design used at all locations was a randomized complete block replicated four times. Soil types at the four locations were a Dundee silty clay (fine-silty, mixed, thermic Aeric Orchaqualf) at Stoneville, MS; a Calloway silt loam (fine-silty, mixed, thermic Glassaquic Fragiudalf) at Colt, AR; a Commerce silt loam (fine-silty, mixed, nonacid, thermic Aeric Fluvaquent) at St. Joseph, LA; and a Sequatchie silt loam (fine-loamy, siliceous, thermic, Humic Hapludults) at Knoxville, TN. Corn were planted in early to mid-April at all experiments to an expected final plant population of about 32,500 plants/acre. Individual experimental units were four rows spaced 30 inches apart and 30 feet long. Nitrogen, P, and K fertilizers were applied at all locations to a yield goal of 200 bu/acre. All locations were irrigated to schedules developed for the individual locations. The hybrids selected for this experiment are listed in Table 1. All hybrids in the experiment, except 32R25 and N79-L3Bt, are classed as short-season and not normally planted in the Mid-South. Both 32R25 and N79-L3Bt are classed as full-season hybrids and were popular with corn growers in the Mid-South at the initiation of this experiment. Table 1. Maturity rates of corn hybrids used in Mid-South short-season
x Information acquired from companies’ sales literature. y Acquired from companies’ sales literature and/or Gregoire (7). z Classified as full-season hybrids commonly produced in the Mid-South. Weed control at each location was achieved with a combination of commonly used pre-emergence herbicides and cultivation prior to plants reaching growth stage V6 (six fully extended leaves) as defined by Ritchie et al. (11). At Stoneville, MS, St. Joseph, LA, and Knoxville, TN dates to growth stage R1 (anthesis) and growth stage R6 (physiological maturity) were recorded for all hybrids. Using these data and maximum and minimum temperatures throughout the growing seasons at each location, the Growing Degree Units (86°F/50°F) (GDU 50s) were calculated by procedures outlined by Shaw (12). Grain was harvested from the two center rows of each experimental unit at all locations when it reached approximately 15.5% moisture content. A 4 lb grain sample was collected from each plot at harvest to determine aflatoxin and fumonisin contamination levels at Stoneville, MS and Colt, AR both years of the experiment, at St. Joseph, LA in 2002, and at Knoxville, TN in 2003 using methods described by Abbas et al. (1). Grain yields were adjusted and reported on a 15.5% moisture content basis. Test weight was recorded and statistically analyzed for Stoneville, MS, St. Joseph, LA, and Knoxville, TN in 2003. Kernel weights were determined on plots harvested at St. Joseph, LA for both years of the study, at Stoneville, MS in 2002, and at Knoxville, TN in 2003 by weighing a 100-kernel sample. Grain yield, kernel weights, and mycotoxin data were analyzed for individual locations using procedures outlined by Gomez and Gomez (6) and the PROC MIXED procedure of the Statistical Analysis System (SAS Institute Inc., Cary, NC). Correlations were conducted between GDU 50s at R1 and R6, among years, locations, and yields. Growing Degree Units Accumulated GDU 50s at both growth stages R1 (anthesis) and R6 (physiological maturity) for Stoneville, MS and St. Joseph, LA varied among hybrids within and between years (Tables 2 and 3). The GDU 50s calculated from data acquired at Knoxville, TN also showed differences among hybrids, though generally they were greater at both growth stages than those observed at the other locations. Table 2. Growing degree units (GDU 50s) to physiological maturity of 16 short-season and 2 full-season corn hybrids grown at Stoneville, MS; St. Joseph, LA; and Knoxville, TN.
x From companies’ sales literature or calculated using methods outlined by Gregoire (7). y Means of 4 replications. Table 3. Growing degree units (GDU 50s) to anthesis of 16 short-season and 2 full-season corn hybrids grown at Stoneville, MS, St. Joseph, LA, and Knoxville, TN.
x Means of 4 replications. Data on GDU 50s at Stoneville, MS for some hybrids were similar to data acquired for the same hybrids in previous experiments (4,5). In those experiments it was determined that short-season hybrids, when grown in the Mid-South, generally acquired more GDU 50s when reaching growth stages R1 and R6 than they do when produced in their adapted environment. With few exceptions, this appears to be the case in this series of experiments as well. Correlations of GDU 50s at R1 and R6, between or within years, hybrids, and locations failed to identify any significant relationships with these two growth stages. No trends could be established for data between years and hybrids within a location or between hybrids at two locations for the same year. Yields at Knoxville, TN in 2003 and both years at Stoneville, MS and St. Joseph, LA were not correlated with any of the calculated GDU 50s at either growth stage. In a previous study grain yield was positively correlated to GDU 50s at growth stage R1 (5). However, no such relationship was identified in any of the data of these experiments. The failure of GDU 50 data to show any discernable trends in this series of experiments indicates that such data may have limited value for determining hybrid maturity in the Mid-South. The formula presented by Shaw (12) may also have limitations when used with temperatures experienced during the growing season in the Mid-South. Differences in solar radiation between the Mid-South and the Central or Northern Cornbelt, where many of these hybrids are normally grown, may also influence the GDU 50s accumulated in their adapted environments verses what we observed in these experiments. Grain Yields Grain yields from this series of experiments varied considerably from location to location and the hybrid × year interaction was statistically significant (P ≤ 0.05) at Stoneville, MS, Colt, AR, and St. Joseph, LA (Table 4). In general highest yields were recorded at Knoxville, TN. In that experiment the two full-season hybrids (32R25 and N79-L3Bt) produced greater (P ≤ 0.05) yields than several short-season hybrids. Hybrids A6333Bt and RX634 had yields comparable to both 32R25 and N79-L3Bt while RX452, RX393YG, DKC42-22, and DKC46-26, produced grain yields similar to N79-L3Bt. Table 4. Grain yields of corn hybrids (bu/acre) grown Stoneville, MS, Colt, AR, St. Joseph, LA in 2002 and 2003 and Knoxville, TN in 2003.x
x Means of 4 replications. At Stoneville, MS in 2002 N79-L3Bt yielded more (P ≤ 0.05) grain than 9185Bt, DKC46-56, DKC42-70, RX634, and A6257. Hybrid 32R25 yielded less than three short-season hybrids, A6333Bt, DKC42-22, and 2590. In 2003 RX634, DKC42-70, DKC46-26, 2953, and 598CL produced more (P ≤ 0.05) grain than the previous year. Hybrid 32R25 surpassed only 8830, 9185Bt, and 8946 in grain yield in 2003 while N79-L3Bt had a greater (P ≤ 0.05) grain yields than seven of the short-season hybrids (Table 4). Hybrid 32R25 yielded more (P ≤ 0.05) grain than all the short-season hybrids in 2002 except A6333Bt in the experiment at Colt, AR (Table 4). Hybrid N79-L3Bt yielded comparable to all other hybrids that year except 38P06, 2953, 8830, and 8946 which produced less (P ≤ 0.05) grain. Between years, 32R25, 38T27, A6333Bt, and A6257 yielded less (P ≤ 0.05) in 2003 than in 2002 while DKC42-22 yield more grain in 2003 than 2002. In 2003 N79-L3Bt produced a greater (P ≤ 0.05) grain yield than 32R25, 8946, 38T27, A6257, 38P06, and 9185Bt. All other hybrids in the experiment that year in Colt, AR yielded comparable to N79-L3Bt. Yield data from St. Joseph, LA in 2002 showed there to be few differences among hybrids in grain yield. The hybrids RX634 and RX393YG had higher (P ≤ 0.05) grain yields than 38P06 and 38T27. The yield of 38P06 was comparable to 11 of the other hybrids in the experiment (Table 4). In 2003 at St. Joseph, LA grain yields of seven of the hybrids were comparable to A6333Bt which yielded 179 bu/acre. Nine hybrids in the experiment that year had grain yields comparable to 9185Bt which produced 115 bu/acre. The hybrids DKC42-70, 8946, 9185Bt, and 8830 produced less grain in 2003 than 2002 (Table 4). Kernel Weights Sufficient data were acquired on kernel weights from Stoneville, MS and St. Joseph, LA in 2002 and Knoxville, TN in 2003 to make comparisons among hybrids and environments (Table 5). Few differences were noted in the data. The hybrid × year interaction was not statistically significant for data from Stoneville, MS or St. Joseph, LA. Mean kernel weight of 8830 at Stoneville, MS was less (P ≤ 0.01) than ten other hybrids in the experiment. Hybrid 8946 also had less (P ≤ 0.01) kernel weight than RX634. No other differences were noted for this location. Data acquired from St. Joseph, LA showed RX393YG, 38P06, 32R25, and N79-L3Bt had less (P ≤ 0.01) kernel weight than 8946. No other differences were observed for this location. Grain harvested at Knoxville, TN had kernel weights that differed among several hybrids. Hybrid 8946 had a mean kernel weight that was less (P ≤ 0.01) than ten other hybrids in the experiment. Mean kernel weight of 32R25 was greater (P ≤ 0.01) than nine other hybrids. Comparing across locations 8830, 8946, 2590, and 32R25 were the only hybrids to have differences in mean kernel weights (Table 5). Except for 32R25, mean kernel weights of these hybrids was greater (P ≤ 0.01) for grain produced in St. Joseph, LA than that grown at Stoneville, MS. Grain of 32R25 grown at Knoxville, TN had greater kernel weight than grain produced in Stoneville, MS or St. Joseph, LA. Table 5. Weights (oz) of 100 kernel samples of sixteen short-season
LSD @ P ≤ 0.01 for means within a column and row = 0.18. x Means of 4 replications. Grain Test Weights Sufficient data were available from three locations (Stoneville, MS, St. Joseph, LA, and Knoxville, TN) in 2003 to make comparisons on test weights (Table 6). Hybrid N79-L3Bt had a greater (P ≤ 0.01) test weight than most hybrids at all three locations. It surpassed most short-season hybrids grown at Stoneville, MS. At St. Joseph, LA, N79-L3Bt exceeded all other hybrids in test weight, including the other full-season hybrid 32R25. Data from Knoxville, TN showed that only 8946 had less test weight than N79-L3Bt. No other differences were observed at this location. Table 6. Grain test weights (lb/bu) of sixteen short-season and
two
LSD @ P ≤ 0.01 for means within a column = 3.4 and row = 2.6. x Means of 4 replications. At Stoneville, MS only five hybrids (A 6333Bt, RX 634, 9185Bt, 2593, and 38P06) had similar test weights to what was observed at St. Joseph, LA. All other hybrids at Stoneville, MS had greater test weights than grain produced at St. Joseph, LA. Only four hybrids (A 6333Bt, DKC46-26, 8830, and 38P06) grown at Stoneville, MS had test weights that were less than what was produced at Knoxville, TN. Test weights from plots grown at St. Joseph, LA were all significantly less than those from grain produced at Knoxville, TN except for N79-L3Bt, which was not different. Maximum daily temperatures at St. Joseph, LA frequently exceed 90°F during kernel filling compared to Knoxville, TN which only experienced a total of 16 days above 90°F in 2003 and above average rainfall during 1-15 July that year. These climatic differences would help explain the observed differences in test weights of the two locations (8,10). No statistically significantly hybrid × year interaction was observed for these data from Stoneville, MS or St. Joseph, LA. Corn grain prices are most commonly based on US Grade No. 2 yellow which has a minimum test weight of 54 lb/bu. Based on this, five of the hybrids produced at Stoneville, MS and all but one hybrid grown at St. Joseph, LA did not meet this standard. Grain from these hybrids would likely have been docked in price when sold. On the other hand all of the grain grown at Knoxville would have met this standard and would not have been docked due to low test weight. Aflatoxin and Fumonisin Levels No significant hybrid × year interactions were found at any location for aflatoxin contamination. Aflatoxin contamination differed (P ≤ 0.01) among hybrids only at Stoneville, MS. Hybrids DKC42-22 and 8946 had aflatoxin levels greater than A6333Bt, 32R25, and N79-L3Bt (Table 7). Aflatoxin contamination of the grain produced at Colt, AR and St. Joseph, LA did not differ among hybrids. No differences in aflatoxin contamination were also noted for plots in Knoxville, TN. In fact at Knoxville, TN none of the mean levels of contamination were above the 20.0 ppb action level set by the US Food and Drug Administration for interstate commerce and food consumption (14). For on-farm livestock feed none of the observed aflatoxin levels at any location exceeded the 300 ppb maximum allowable level set by the US Food and Drug Administration (14). Table 7. Mean aflatoxin contamination levels (ppb) of short-season corn hybrids produced at Stoneville, MS, Colt, AR, St. Joseph, LA, and Knoxville, TN.
x Means of 4 replications and 2 years (2002 and 2003). y Means of 4 replications in St. Joseph, LA (2002) and Knoxville, TN (2003). The hybrid × year interaction was significant (P ≤ 0.05) for fumonisin contamination levels at Stoneville, MS (Table 8). Fumonisin contamination was less for A6333Bt and N79-L3Bt than RX634, DKC42-22, and 2590 in 2002. Contamination level of N79-L3Bt was also less (P ≤ 0.05) than 8946 that year. In 2003 A6333Bt and N79-L3Bt again had less (P ≤ 0.05) fumonisin contamination than several other hybrids while fumonisin levels for 2590 and 2953 were higher (P ≤ 0.05) in 2003 than 2002. No other hybrid differences between years were noted. Fumonisin contamination at Colt, AR, St. Joseph, LA, and Knoxville, TN were not significantly different. For human food consumption most all hybrids at all locations exceeded the 4 ppm maximum allowable contamination level set by the US Food and Drug Administration, but none of the observed fumonisin levels at any location exceeded the maximum 20 ppm contamination level set for livestock feed (15). Table 8. Mean fumonisin contamination (ppm) of short-season corn hybrids produced at Stoneville, MS, Colt, AR, St. Joseph, LA and Knoxville, TN.
x Means of 4 replications. St. Joseph, LA (2002) and Knoxville, TN (2003). y Means of 4 replications and 2 years (2002 and 2003). Conclusions These data demonstrate that several short-season hybrids produce comparable grain yields to two popular full-season hybrids being produced in the Mid-South at the initiation of this series of experiments. Low kernel weights, low test weights, or high mycotoxin contamination levels did not appear to be a consistent handicap for short-season hybrids in this study. This may not be true for all short-season hybrids. However, the development of short-season germplasm for production in the Mid-South may be feasible based on our findings. Questions concerning the use of GDU 50s for maturity classifications of corn grown in the Mid-South are raised by this research. Whether short-season hybrids require or just acquire more GDU 50s to reach growth stages R1 and R6 has yet to be fully determined. The impact of very early planting on this class of hybrids when grown in the Mid-South must also be determined. In the area of the USA that most of these hybrids were developed for production, risks of being exposed to cold weather and possibly frost for several weeks after planting does exist. This is not a risk in the Mid-South on the dates they were planted in this series of experiments. Disclaimer Trade names are used in this publication solely for the purpose of providing specific information. Mention of a trade name, propriety product, or specific equipment does not constitute a guarantee or warranty by the USDA-ARS and does not imply approval of the named product to exclusion of other similar products. Literature Cited 1. Abbas, H. K., Zablotowicz, R. M, Weaver, M. A., Horn, B. W., Xie, W., and Shier, W. T. 2004. Comparison of cultural and analytical methods of determination of aflatoxin production by Mississippi Delta Aspergillus isolates. Can. J. Microbio. 50:193-199. 2. Aldrich, S. R., Scott, W. O., and Hoeft, R. G. 1986. Modern Corn Production, 3rd Ed. A&L Publ., Champaign, IL. 3. Bruns, H. A., and Abbas, H. K. 2004. Effects of harvest date on maize in the humid sub-tropical mid-south USA. Maydica 49:1-7. 4. Bruns, H. A., and Abbas, H. K. 2005. Response of short-season corn hybrids to a humid sub-tropical environment. Agron. J. 97:446-451 5. Bruns, H. A., and Abbas, H. K. 2006. Planting date effects on Bt and non-Bt corn in the Mid South USA. Agron. J. 98:100-106 6. Gomez, K. A., and Gomez, A. A. 1984. Statistical procedures for agricultural research, 2nd Ed. John Wiley & Sons, New York, NY. 11. Ritchie, S. W., Hanway, J. J., and Benson, G. O. 1997. How a corn plant develops. Spec. Rep. 48. Iowa State Univ. of Sci. and Technol. Coop. Ext. Serv., Ames, IA. 12. Shaw, R. H. 1988. Climate requirement. Page 617 in: Corn and Corn Improvement 3rd Ed. G.F. Sprague and J.W. Dudley, eds. Amer. Soc. Agron., Madison, WI. 13. Troyer, A. F., and Ambrose, W. B. 1971. Plant characteristics affecting field drying rate of ear corn. Crop Sci. 11:529-530. 16. Watson, S. A. 1988. Corn marketing, processing, and utilization. Page 894 in: Corn and Corn Improvement 3rd Ed. G. F. Sprague and J. W. Dudley, eds. Amer. Soc. Agron., Madison, WI. |
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