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© 2003 Plant Management Network. Short-Season Soybean Cultivars Have Similar Yields With Less Irrigation Than Longer-Season Cultivars Jeffrey T. Edwards and Larry C. Purcell, University of Arkansas, Department of Crop, Soil, and Environmental Sciences, 1366 W Altheimer Drive, Fayetteville 72704; Earl D. Vories, University of Arkansas, Department of Biological and Agricultural Engineering, Northeast Research and Extension Center, P.O. Box 48, Keiser AR 72351; J. Grover Shannon, University of Missouri, Delta Center, P. O. Box 160, 147 State Highway T, Portageville 63873; and Lanny O. Ashlock, Cullum Seeds, L.L.C., Fisher, AR 72479, formerly University of Arkansas Cooperative Extension Service Corresponding author: Larry C. Purcell. lpurcell@uark.edu Edwards, J. T., Purcell, L. C., Vories, E. D., Shannon, J. G., and Ashlock, L. O. 2003. Short-season soybean cultivars have similar yields with less irrigation than longer-season cultivars. Online. Crop Management doi:10.1094/CM-2003-0922-01-RS. Abstract The midsouthern USA often experiences a drought from mid-June through late-August. Short-season soybean (Glycine max. [L.] Merr.) cultivars (maturity groups [MG] 00, 0, I, II, III, and IV) were evaluated in narrow rows and at high populations for their ability to avoid drought at several locations in the mid-South. When planted in early May under nonirrigated conditions, MG 00 and 0 cultivars generally had lower yields than later-maturing cultivars. Within an irrigation treatment, cultivars from MG I, II, III, and IV generally produced similar yields under irrigated or nonirrigated conditions, but MG I and II cultivars required considerably less irrigation than cultivars from MG III and IV. April and early-May planting dates required less irrigation and generally yielded more than late-May or June planting dates for all MG and locations. This research demonstrates that yield potential in the mid-South is similar for cultivars from MG I, II, III, and IV under favorable conditions, that irrigation needs can be decreased by use of early-maturing cultivars planted in April or early May, and that risk of exposure to drought can be decreased by including MG I and II cultivars in a nonirrigated, early production system. Introduction The midsouthern USA typically experiences a drought from mid-June through late August (9), which coincides closely with the pod-fill period of MG V and VI soybean cultivars historically grown in this region (6). For this reason, many growers in the mid-South have chosen to plant MG III and IV cultivars in late March or early April, which allows them to complete seed fill prior to August drought in most years (1,2,7). This system is commonly referred to as the Early Soybean Production System, and it has been highly successful on deep soils with a large amount of plant-available water. Conditions are often not favorable for soybean planting in the upper mid-South until late April or early May. Maturity group III and IV soybean cultivars planted at this time will likely endure some period of drought stress during podfill, thus creating the need for supplemental irrigation. Further exacerbating the situation, much of the soybean production in the upper mid-South is rotated with rice on shallow soils that typically have rooting depths less than 8 inches. Soybean production on these soils requires frequent replenishment of soil water, which becomes less likely after mid-June (9). One possibility for avoiding drought under these conditions is to produce soybean cultivars from MG 00 through II, which may mature prior to the predictable drought. The objective of our research was to evaluate soybean cultivars from MG 00 through IV for yield potential and drought avoidance in irrigated and nonirrigated environments in the upper mid-South. Production of these very early-maturing cultivars may allow them to be planted in the northern portion of the Mississippi Delta in late April or early May and mature prior to mid-season droughts. Experimental Design and Procedures Field studies were conducted in 1999, 2000, and 2001 at various locations in the upper mid-South. All plots were drill-seeded in 7.5-inch rows using a cone planter at a population of approximately 400,000 seed per acre. This high seeding rate is especially important to increase canopy closure of MG 00, 0, I, and II cultivars (8). Our data indicate that MG III and IV yields, while not increased, are not decreased by the high seeding densities used in this study (Edwards and Purcell, unpublished data, 2002). Plot size was 6-ft wide by 20-ft in length. To remove any border effect, outside rows were removed and plots were end-trimmed prior to harvest. In 1999, nonirrigated trials were conducted at Fayetteville (Pembroke silt loam [fine-silty, mixed, active, mesic Mollic Paleudalfs]) and Keiser (Convent silt-loam [Coarse-silty, mixed, superactive, nonacid, thermic Fluvaquentic Endoaquepts]), AR. Experimental design was a split-plot with four replications. The main plot was MG (00, 0, I, II, III, IV) and sub-plot was soybean cultivar (MG 00: Glacier and McCall; MG 0: Dawson and MN 0301; MG I: Asgrow 1553 and Parker; MG II: Burlison and Dwight; MG III: Williams 82; MG IV: Asgrow 4922). Plots were drill seeded on May 19 at Keiser and on May 20 at Fayetteville, and emergence was May 25 and 27, respectively. In 2000, a split-split-plot design with four replications was conducted at Fayetteville, AR. Plots were drill seeded April 24 and emergence was April 29. The main plots were plus or minus irrigation; the sub-plots were MG (00, 0, I, II, III, IV), and the sub-sub-plots were cultivars (MG 00: Glacier, Maple Arrow, McCall, and Trail; MG 0: AC Comoran, Dawson, Lambert, and MN 0301; MG I: Asgrow 1553, MN 1401, MN 1801, and Parker; MG II: Burlison, Dwight, IA 2008, and IA 2021; MG III: Macon, Maverick, Pana, and Williams 82; MG IV: MPV 437, Pioneer 94B01, RT 3975, and TV 4479). Soil-water deficit was estimated by using the University of Arkansas’ Irrigation Scheduling Program, which is widely used by mid-South farmers and is available for download (11). This program subtracts daily estimates of crop evapotranspiration from daily inputs of either irrigation or rainfall (3). Irrigation is recommended once the cumulative soil-water deficit reaches a critical value that is determined by soil characteristics and rooting depth (3). At Fayetteville, irrigated treatments were applied by overhead sprinklers when the estimated soil-water deficit reached 1.5 inches. The amount of irrigation varied from 0.5 to 1 inch per application depending upon wind conditions. At Keiser, irrigated treatments were flood irrigated once the estimated soil-water deficit reached 1.5 inches. We assumed that the soil was fully recharged by irrigation and that the net quantity of water applied at each irrigation was 1.5 inches. At Portageville, irrigated treatments were flood irrigated once the estimated soil-water deficit reached 2 inches. The quantity of water applied was approximately 1 inch per application. In 2001, studies were conducted at Fayetteville and Keiser, AR, and Portageville (Dundee silt loam [fine-silty, mixed, thermic Aeric Ochraqualfs]), MO. The experimental design consisted of an early and late planting of a split-split-plot design in which the main plots were plus or minus irrigation, the sub-plots were MG (00, 0, I, II, III, IV), and the sub-sub-plots were cultivars (MG 00: Agassiz, Jim, Lena, and Trail; MG 0: AC Comoran, Lambert, LO 292, Surge; MG I: IA 1006, MN 1401, MN 1801, and Parker; MG II: Asgrow 2247, Dwight, IA 2008, and PB 230; MG III: Macon, Maverick, Pana, and Williams 82; MG IV: MPV 437, Pioneer 94B01, RT 3975, and TV 4479). Planting dates were April 16, May 6, and April 19 for the early-planted tests and June 7, June 10, and May 17 for the late-planted tests at Fayetteville, Keiser, and Portageville, respectively. A fourth location was planted April 30 at Marianna, AR (Loring silt loam [Fine-silty, mixed, active, thermic Oxyaquic Fragiudalfs]). This location was not irrigated and consisted of a split-plot design with eight replications. Main plots were MG (00, 0, I, II) and sub-plots were cultivars consisting of the same MG 00, 0, I, and II cultivars used at the other 2001 locations. All data were analyzed using the MIXED procedure of SAS V8 (SAS Institute, Cary, NC) and means were separated by Fisher’s protected LSD at the 0.05 level of significance. Maple Arrow had an unusually low yield compared with other MG 00 cultivars in 2000 and was removed from statistical analysis. Similarly, the cultivar Agassiz (19 bu/acre) was deleted from the analysis of data from the Marianna location in 2001. Cultivar nested within MG was nonsignificant at all locations in 1999 and 2001; therefore, data are presented as MG means. In 2000 the cultivar effect was significant, and data are presented for individual cultivars. Yield Potential Under Nonirrigated Conditions Late planting and early onset of drought led to low yields for the nonirrigated trials in 1999 (Fig. 1). At both locations, all cultivars flowered within 5 days of June 22, which closely coincided with the beginning of a drought. In contrast, there was approximately 5-week difference in growth stage R6 (4) between MG 00 and IV cultivars (data not shown). The delayed pod-fill of later-maturing cultivars exposed them to late-season drought. Low harvest indices (seed weight/weight of above-ground plant biomass at harvest) also indicated that yield limitations were the direct result of stress during seed fill and not during vegetative growth (data not shown). This was particularly evident for MG III and IV cultivars, which had harvest indices of 0.11 and 0.17 at Fayetteville, as compared to harvest indices of 0.29 and 0.33 for MG 0 and I. The Kesier location benefited from a much deeper soil with greater water holding capacity. This was reflected in the higher yields of MG I, II, and III cultivars at Keiser as compared to Fayetteville.
In 2000 under nonirrigated conditions, there were few differences in yield among or within MG, and yields were generally higher than in 1999 (Table 1). Earlier planting resulted in flowering on or around June 5, and all cultivars within MG 00 through II had completed pod-fill by July 12, which was about the same time that significant rainfall for the summer had ceased. Nonirrigated yields of MG IV cultivars were generally less than those for cultivars from earlier MG, indicating that soil moisture was inadequate for seed-fill. Harvest indices generally decreased as MG increased and were approximately 0.43 for MG 00 and 0 cultivars, 0.22 for MG III cultivars, and 0.18 for MG IV cultivars (data not shown). For the nonirrigated treatment, some cultivars (e.g., Glacier and MN 0301) failed to develop greater than 90% canopy closure (data not shown), which likely contributed to low yields as compared to other cultivars within their respective MG. Table 1. Soybean yield for maturity groups (MG) 00 to IV in irrigated (IR) and nonirrigated (NI) production systems at Fayetteville in 2000.
*Inches of irrigation applied to the irrigated treatment between emergence Planting dates were earlier in 2001 than in 2000 due to favorable weather conditions, which gave a better indication of the full yield potential of these cultivars under nonirrigated conditions in the mid-South (Fig. 2). All cultivars had > 90% canopy coverage (data not shown) at growth stage R6. Harvest indices were also higher than previous years with values ranging from 0.37 to 0.48 for the early-planted study and 0.29 to 0.40 for the late-planted study (data not shown). Data from the early-planted study indicate that cultivars from MG 00 and 0 had lower yield potential than cultivars from later MGs evaluated in the study. Keiser and Marianna data indicate that under the right conditions, MG I and II cultivars have yield potential equal to that of MG III and IV cultivars. However, at Fayetteville and Portageville yield potential of MG I and II cultivars was less consistent than yield of MG III and IV cultivars when planted early.
Even though canopy coverage exceeded 90% by R6, early maturity also lessens the total amount of light that can be intercepted during a short growing season compared to later-maturing cultivars. Cool and overcast conditions that are common in late April and May would also decrease the total amount of light available for interception by these early-maturing cultivars. Nevertheless, nonirrigated yield of MG I through IV cultivars in this study was greater than the average yield in 2001 for Arkansas of 23 bu/acre (1). Fayetteville data indicated that early planting was critical to success on shallow soils with low water-holding capacity. This was demonstrated most clearly in the late-planted study. Deeper soils at Keiser and Portageville provided more moisture for late-season soybean growth, even though late-season rainfall was less frequent at these locations than at Fayetteville. The data from all locations indicate, however, that soybean producers using a nonirrigated short-season production system would benefit from early planting. Heatherly (5) found similar advantages to April soybean planting in Mississippi under both nonirrigated and irrigated conditions. Yield Potential Under Irrigated Conditions Yield potential was greater for irrigated than nonirrigated treatments in 2000, and yield potential of MG 00 and 0 cultivars was lowest of the MGs evaluated (Table 1). Higher yield of later-maturing cultivars was realized at the expense of increased irrigation demands. From emergence to R6, MG 00 and 0 cultivars received only 1 inch of irrigation, whereas MG I and II cultivars received 5 inches, and MG III and IV cultivars received 10 inches. Since all MG flowered around June 7, the differential need for irrigation among MGs was a direct result of a 32-day difference in seed-fill duration between MG 00 and IV soybean. In 2001, yields of MG 00 and 0 cultivars were less than those of MG I through IV cultivars (Fig. 3). While there were no significant differences among cultivars within a MG, there were numerical differences. Yields were generally higher for early-planted soybean than for late-planted soybean. For the early planting date, mean yields for MG I through IV were close to, or greater than 50 bu/acre, except at Portageville where MG I cultivars averaged 40 bu/acre. The early planting date at all locations had specific cultivars within MG I through IV that had yields greater than 45 bu/acre (data not shown). In the early-planted Fayetteville study, for example, the cultivar IA 1006 (MG I) yielded 47 bu/acre and Parker (MG I) yielded 62 bu/acre, indicating that cultivar selection within MG is of key importance. Furthermore, yield potential of MG I through IV cultivars was greater than the Arkansas state-wide yield of 38 bu/acre for full-season, irrigated soybean in 2001 (1).
Amount of irrigation to reach growth stage R6 in 2001 varied by MG, location, and planting date (Fig. 3). Overall, irrigation demands were higher at Fayetteville due to shallow soil with low water-holding capacity. Similar differences in total irrigation demands for each MG, however, were observed for all locations, and irrigation demands typically increased for later-maturing cultivars. The irrigation savings associated with shorter-season cultivars in the early-planted test were, however, reduced when short-season cultivars were planted late. Implications and Limitations The primary concept illustrated by this research is one of coordinating crop maturity and rainfall. Soybean growers in the mid-South are currently taking advantage of this concept by planting MG III and IV cultivars early in the year and thereby reducing the potential for drought stress and need for supplemental irrigation. These research findings indicate that MG I and II soybean cultivars have yield potential similar to MG III and IV cultivars. Therefore, growers can use a mix of short-season cultivars of different MG to further reduce the risk of drought exposure in nonirrigated production systems and to reduce irrigation needs in irrigated systems. While this research does indicate that many short-season soybean cultivars are adapted to growing conditions in the mid-South, care must be exercised when selecting a cultivar. Extensive screening of MG I and II cultivars currently available would be of great benefit to soybean producers considering this system. Breeding efforts to develop short-season cultivars adapted to the mid-South would be particularly important for disease and nematode resistance. One risk of short-season cultivars is that their short seed-fill duration has the potential to increase their susceptibility to drought, herbicide injury, and other stresses early in the growing season. Early-season stresses may prevent full canopy development and decrease the total amount of light intercepted by these cultivars. Due to the longer periods of reproductive growth, MG IV and later cultivars typically have time to compensate for short periods of unfavorable conditions by intercepting light for a longer duration. Therefore, it is imperative for short season soybean cultivars to quickly establish leaf area and thereby take full advantage of available solar radiation. High seeding rates required to achieve rapid canopy closure with short-season cultivars may lead to increased seeding costs and thereby affect marginal returns. While not without risks, short-season soybean production still has numerous potential agronomic advantages as well as potential marketing benefits. Acknowledgments The authors thank the Arkansas Soybean Promotion Board for funding for this project. We would also like to acknowledge the extensive work of Andy King, Bob Glover, Shawn Lancaster, Monty Malone, and Heather Nichols in carrying out the day to day operations of this research. Literature Cited 2. Boquet, D. J. 1998. Yield risk utilizing short-season soybean production in the mid-southern USA. Crop Sci. 38:1004-1011. 3. Bowers, G. R. 1995. An early soybean production system for drought avoidance. J. Prod. Agric. 8:112-119. 4. Cahoon, J., Ferguson, J., Edwards, D., and Tacker, P. 1990. A micro-computer-based irrigation scheduler for the humid mid-south region. Appl. Eng. Agric. 6:289-295 5. Fehr, W. R., and Caviness, C. E. 1977. Stages of soybean development. Special Report 80. Coop. Ext. Service, Agric. Exp. Stn., Iowa State Univ., Ames, IA. 6. Heatherly, L. G. 1996. Yield and germinability of seed from irrigated and nonirrigated early and late-planted MG IV and V soybean. Crop Sci. 36:1000-1006. 7. Heatherly, L. G. 1999. Soybean irrigation. Pages 119-142 in: Soybean production in the midsouth. L. G. Heatherly and H. F. Hodges, ed. CRC Press, Boca Raton, FL. 8. Heatherly, L. G. 1999. Early Soybean Production System. Pages 103-118 in: Soybean production in the midsouth. L. G. Heatherly and H. F. Hodges, ed. CRC Press, Boca Raton, FL. 9. Purcell, L. C., Ball, R. A., Reaper, J. D., III, and Vories, E. D. 2002. Radiation use efficiency and biomass production in soybean at different plant population densities. Crop Sci. 42:172-177. 10. Purcell, L. C., Sinclair, T. R., and McNew, R. W. 2003. Drought avoidance assessment for summer annual crops. Agron. J. 95:1566-1576. |
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