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PRODUCTION PAPERS

Soybean Yield Potential and Phenology in the Ultra-Short-Season Production System

^a Dep. of Crop, Soil, and Environ. Sci., Univ. of Arkansas, Fayetteville, AR 72701
^b Dep. of Hortic. and Crop Sci., The Ohio State Univ., Wooster, OH 44691
^c Dep. of Agron., Univ. of Missouri Delta Cent., Portageville, MO 63873

^* Corresponding author (sneller.5{at}osu.edu)

Received for publication May 22, 2002.

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Summer drought is a major yield limitation for soybean [Glycine max (L.) Merr.] in the Midsouth. Yield may be improved by matching crop development to periods of sufficient soil moisture, requiring a crop that matures by late July. Our objective was to evaluate early maturing lines for their ability to avoid drought and yield potential in the Midsouth. We evaluated maturity group (MG) 00 through I lines for yield and other traits in 2000 (222 lines) and 2001 (152 lines), planting irrigated plots in late April with final stands of >800000 plants ha^-1. Sixty-one lines selected from the 2000 trials were also grown in 2001. Many lines matured in <78 d from emergence and would avoid mid-July or later droughts. In different environments, the average yield of this maturity class ranged from 1310 to 2712 kg ha^-1 while the maximum yield of individual lines ranged from 2342 to 3594 kg ha^-1. Other lines matured in 78 and 91 d and would avoid August droughts. In different environments, the average yield of this maturity class ranged from 2630 to 4128 kg ha^-1 while the maximum yield of individual lines ranged from 3144 to 4676 kg ha^-1. The potential of this ultra-short-season production system to produce a viable crop in less than 78 d may have significant implications as water supplies become more limited and expensive in the Midsouth and many other regions of the world.

Abbreviations: MG, maturity group • SRVP, Soybean Research Verification Program • USSPS, ultra-short-season production system • <70d, maturity class in which lines mature in less than 70 d • 70-77d, maturity class in which lines mature in 70 to 77 d • 78-84d, maturity class in which lines mature in 78 to 84 d • 85-91d, maturity class in which lines mature in 85 to 91 d • >91d, maturity class in which lines mature in greater than 91 d

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
SOYBEAN IS GENERALLY GROWN as either a full-season crop or as a second crop in double-crop systems in the southern USA. Soybean farmers in the Midsouth typically grow MG IV, V, and VI cultivars in mid-May through early-July plantings. These full-season cultivars bloom, set pods, and initiate or complete seed fill from mid-July to early September. Drought is common from mid-July through early September in the Midsouth (Bruce et al., 1985; Scott et al., 1998). At Stuttgart, AR, a location typical of the Midsouth, the difference between rainfall and potential evaporation is -67, -75, and -69 mm in June, July, and August, respectively (Scott et al., 1998). At the same location, there is a 50% probability of rainfall being less than potential evaporation in 9 of 10 yr in July and in 8 of 10 yr in June and August (Bruce et al., 1985). While these studies indicate that a drought is likely in June in the Midsouth, the crop can likely use stored soil moisture to offset most June rainfall shortages. Soil moisture is likely to be depleted by mid-July. Thus, drought is likely by late July and during the reproductive growth stages of MG IV and later soybean lines. As a result, soybean yield is greatly reduced in most years in the Midsouth.

Midsouth soybean growers have begun to plant MG III and IV cultivars in April or early-May plantings. This system is called the early soybean production system and attempts to avoid the devastating effect of drought on yield by having the crop complete the drought-sensitive growth stages before drought occurs (Heatherly, 1999). Researchers have shown a yield advantage for early maturing soybean when combined with an early planting date in the Midsouth (Boquet, 1998; Mayhew and Caviness, 1994; May et al., 1989; Savoy et al., 1992; Sweeney et al., 1995; Kane and Grabau, 1992). In contrast, some researchers also have shown that later MGs (MG V and VI) had a higher yield than early maturing groups (Wrather et al., 1996; Heatherly, 1996; Hovermale, 1992). These inconsistent results may be due to environmental conditions because the MG III and IV cultivars in the early soybean production system often do not mature until mid-August or early September and do not avoid July droughts.

Nonirrigated soybean yield may be improved by better matching crop development to periods of sufficient soil moisture. A crop that matures by mid- to late July is required to routinely avoid drought in the Midsouth. This may be achieved by late-April or early-May plantings of MG 00 through I cultivars. We call this system the ultra-short-season production system (USSPS). In addition, the USSPS may also be a viable alternative to full-season irrigated production systems if it can produce comparable yield with reduced irrigation costs. This aspect of the USSPS may be increasingly important as concerns about water quality and quantity are increasing in the Midsouth (Scott et al., 1998); irrigation of full-season soybean may not be a viable option in the future.

MG 00 to I cultivars are commonly grown north of 42° N lat where they are full-season cultivars adapted to the long days of summer. The relatively short daylength in May and June in the Midsouth (about 33° N lat) does not suppress the flowering of these cultivars. The phenology and yield response of MG 00 to I lines to the USSPS is not known. The objectives of this study were to (i) evaluate phenology of MG 00 through I cultivars and breeding lines for the potential to avoid drought in the Midsouth, (ii) evaluate the yield potential of USSPS, and (iii) determine traits associated with seed yield in the USSPS.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Field experiments were conducted at Fayetteville, AR, in 2000 (Leaf silt loam, clayey, mixed, thermic Typic Albaquult) and 2001 (Johnsburg silt loam, fine-silty, mixed, active, mesic Aguic Fragiudult) and at Portageville, MO, in 2001 (Tiptonville silt loam, fine-silty, mixed, thermic, Typic Argiudoll). Research on the yield potential of a production system generally would use a few adapted varieties that are known to yield well in the region and related production systems. This was not possible for our study as MG 00 to I genotypes are bred for performance in the northern USA and we did not have any prior knowledge of how they might adapt to the USSPS. We chose to assess many MG 00 to I lines so that we would be likely to include at least some lines that were adapted to the USSPS and thus get a good assessment of its real potential. A total of 222 MG 00 to I lines were evaluated in 2000, and 152 MG 00 to I lines were evaluated in 2001. The lines consisted of all entries and checks in the 2000 and 2001 USDA Uniform MG 00 to I tests, plus MG 00 through I lines selected for excessive height in plant row nurseries in Minnesota and Ontario by Dr. Jim Orf and Dr. Elroy Cober. From the 2000 trials, 61 lines were selected for maturity adapted to the USSPS, high yield, and above-average plant height for testing in 2001. The following checks were grown in all tests, locations, and years: ‘Jim’ (MG 00), ‘Traill’ (MG 0), ‘Lambert’ (MG 0), and ‘Parker’ (MG I). Planting dates were 25 April in Arkansas in 2000 and 2001 and 19 April in Missouri in 2001. Seeds were treated with captan [N-(trichloromethylthio)-4-cyclohexene-1,2-dicarboximide] in 2000 and apron {mefenoxam [(R)-2-[(2,6-dimethylphenyl)-methoxyacetyl-amino]-propionic acid methyl ester]} in 2001 and drill-planted at a rate of 94 seeds m^-2 in all experiments in an attempt to establish 80 plants m^-2. The seven-row plots were 5 m long with 0.2 m between rows. The entire experimental area was surrounded by a solid-seeded border to minimize border effects on plots on the edge of the area. A sprinkler irrigation system was used to irrigate the plots once in 2000 and twice in 2001 at Fayetteville with 50 mm of water each time and four times at Portageville with 25 mm of water each time. Fertilizer and herbicides were applied as needed.

Plots were irrigated as needed to create nondrought environments as our objective was to assess yield potential of the lines in the USSPS, assuming no drought occurred before maturity. The ability of a line to avoid drought is a function of stored soil moisture and occurrence of rainfall before maturity, factors that could vary dramatically from year to year. The probability that MG 00 to I lines in the USSPS would avoid drought in a particular environment would be best assessed by analyzing maturity dates from nondrought environments along with long-term weather data and soil properties to model the probability of a drought before a particular date for a particular environment and not by an empirical evaluation in a limited number of years.

Seed yields, adjusted to 130 g kg^-1 moisture, were obtained by machine-harvesting seven rows of a plot. Percentage stand was visually estimated on all plots 2 wk after emergence. (We counted plants per square meter on some full-stand plots to establish a visual reference of 100% stand.) Some plots in the 2000 trial had poor stands. Data from plots with uniformly thin stands of less than 75% of the target population of 80 plants m^-2 were eliminated from the analysis. For plots where more than one-half of the plot area had a stand greater than 75% of the target, just the portion of the plot with an acceptable stand was harvested, leaving an unharvested portion to allow for border effects. Yields for such plots were adjusted for the harvested area. Adjusted plot yield was not correlated to stand ratings. Day of emergence (Ve) and days to R1, R5 (2001 tests only), R7, and R8 were noted when 50% of the plants in a plot reached the growth stage, as described by Fehr and Caviness (1977). We calculated days to flowering (Ve to R1), reproductive period (R1 to R8), and days to maturity (Ve to R8). Plant height was measured from the soil surface to the tip of the main stem at R8. The number of nodes on the main stem was counted at R8. Weight of 100 seeds was obtained on 100 randomly selected seeds.

The USDA uniform tests of MG 00, 0, and I lines were grown as three separate tests in Arkansas (2000 and 2001) and Missouri (2001). The lines selected from the Minnesota and Ontario nurseries were only grown in Arkansas. Due to the large number of lines from Minnesota and Ontario, these lines were evaluated in four separate tests in 2000 and in two tests in 2001. The lines selected from the 2000 Arkansas tests were assigned to three maturity classes based on the 2000 maturity data. We tested these lines by maturity class in Arkansas and Missouri in 2001. Each test at each location and year was conducted as a randomized complete block design with three replications. Data from all lines were analyzed within each year–location combination. Data from the 61 lines selected in 2000 and tested in 2001 were analyzed across environments considering each location–year combination as an environment. Lines were considered a fixed effect while replication and environment were considered random factors.

The maturity date of lines varied within each test, year, and location, despite our attempts to use prior maturity data collected in the northern USA to create a set of entries that would have a uniform maturity date within a test. In addition, the lines selected from the Minnesota and Ontario plant rows were not identified by MG before planting in Arkansas. To meet our objective of estimating the yield potential of lines that mature by a certain date in the Midsouth, we assigned all lines from all tests grown in an environment to one of five maturity classes: those maturing in <70 d (termed <70d), 70 to 77 d (70-77d), 78 to 84 d (78-84d), 85 to 91 d (85-91d), or >91 d ( >91d) from Ve. We chose the <70-d criteria as this was a maturity class that would likely avoid a drought that starts in mid-July, assuming emergence in early May. Lines that mature in >91 d would likely be affected by an August drought, assuming emergence in early May.

The performance of lines within an environment was analyzed separately for each maturity class by pooling all data from all lines from a maturity class over all tests grown in that environment. This analytical approach confounds line and test effects when comparing the means of two lines grown in different tests within an environment or the mean of two maturity classes. But our objective was not to compare lines or maturity classes to one another; rather, it was to demonstrate the yield potential of the USSPS, and this does not require a statistical comparison of means. The confounding of test and genotype effects does not compromise the estimates, just comparisons. Test effects within an environment were evident even though all of the tests in an environment were grown adjacent to one another in the same field, planted at the same time, and irrigated at the same time. Common checks were grown in all tests in each environment. The mean of the checks within an environment had a range of about 800 kg ha^-1. Test effects on maturity class means are likely to be minimal as each maturity class mean was derived from data sampled from each test within an environment, though each test was not equally sampled, diluting any test effect on maturity class means. We did not make a statistical comparison of the means from this study due to the possible confounding of maturity class and line effect with test effects.

Simple correlations were used to assess the relationship between yield and other traits using appropriate means. Correlations were obtained from the CORR procedure of SAS version 8e (SAS Inst., Cary, NC) while the standard errors of yield means were obtained from the MEANS procedure of SAS.

	RESULTS AND DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Environments
Temperatures and rainfall during the May to August growing season varied over the three different environments (Table 1). Temperatures were cool in May and June, and there was considerable rain during this period in Arkansas in 2000. That environment received 350 mm of rain in June when most lines bloomed, set pods, and initiated seed fill. The ample moisture undoubtedly contributed to the high yields obtained from the 2000 tests (Table 2). In contrast, 2001 at Arkansas was characterized by warm temperatures in May and June and was relatively dry (Table 1). The Missouri 2001 environment received less rain than the other environments, perhaps contributing to the low yields obtained from this environment.

View larger version (27K): [in this window] [in a new window]   Fig. 1. Box plot for (A) days in vegetative period (days from Ve to R1), (B) days in reproductive period (days from R1 to R8), and (C) days to maturity (days from Ve to R8) for soybean lines in different maturity classes grown in three environments. The horizontal line within a box indicates the median value, the lower and upper boundaries of the box represent the 25th and 75th percentiles, the lower and upper whiskers represent the 10th and 90th percentile, and the black circles represent the 5th and 95th percentile. Not all box components are presented for each box due to insufficient data. <70d, maturity class in which lines mature in less than 70 d; 70-77d, maturity class in which lines mature in 70 to 77 d; 78-84d, maturity class in which lines mature in 78 to 84 d; 85-91d, maturity class in which lines mature in 85 to 91 d; >91d, maturity class in which lines mature in greater than 91 d.

Most lines flowered within 5 d of one another, regardless of maturity class (Fig. 1A), with the maximum difference being 9 d. In contrast, the difference between reproductive periods of the latest- and earliest-maturing lines was 21 d in Arkansas 2000, 23 d in Arkansas 2001, and 36 d in Missouri 2001 (Fig. 1B). The observed range in reproductive period is reflected in the range of days to maturity (Fig. 1C). Thus, variation for maturity among lines in the USSPS is primarily due to variation in the duration of the reproductive period.

Yield and Agronomic Traits
On average, yield potential increased as days to maturity increased (Table 2). The shortest growing season occurred in 2001 in Missouri where the average yield of lines in the <70d class was only 1310 kg ha^-1 though the yield of the best line in the <70d class was 2342 kg ha^-1 (Table 2). The average yield of lines in the 70-77d and 78-84d maturity classes ranged from 1886 to 2977 kg ha^-1 over the three environments (Table 2). The highest yield of an individual line in the 70-77d and 78-84d maturity classes ranged from 2390 to 4325 kg ha^-1 over the three environments (Table 2). These superior-yielding lines tended to be later and taller than average for each maturity class (Table 2). The greatest yield was obtained from the 85-91d and >91d maturity classes whose average yield ranged from 3011 to 4128 kg ha^-1 over the three environments (Table 2). The highest yield of an individual line in the 85-91d and >91d maturity classes ranged from 3526 to 4676 kg ha^-1 over the three environments (Table 2).

The best estimate of yield potential of the USSPS is from the 61 lines selected from the 2000 Arkansas trials and tested in 2001 as these estimates are based on data from three environments. No line matured in less than 70 d when averaged over environments. As with the estimates from individual environments, yield increased with increasing maturity class (Table 2). Values for average yield and yield of the highest-yielding line tended to be lower than those reported for individual environments. The genotype x environment interaction was significant (P < 0.05) for yield and days to maturity, but not for final height, for each of the three maturity classes (70-77d, 78-84, and 85-91d) with enough lines to perform a meaningful analysis. The genotype x environment interaction accounted for 15.2, 12.4, and 10.0% of the total sum of squares for yield of the 70-77d, 78-84d, and 85-91d maturity classes, respectively. These percentages are similar to those reported for full-season cultivar tests conducted in the Midsouth (Sneller et al., 1997), indicating that the yield stability of lines in the USSPS is similar to that of full-season production systems and lines. The Spearman rank correlation (within a maturity class) of genotype yield between environments ranged from 0.19 to 0.58 among the three test environments, indicating that yield ranking of lines varied between some environments. More extensive testing will be required to accurately assess yield stability within the USSPS.

We did not generate data on conventional production systems using MG IV to VI lines for comparisons with the yields of the USSPS. The MG IV to VI lines planted at the same locations used for the USSPS in this study would have matured from late August to mid-October, meaning the MG IV and VI lines would have been exposed to a different environment (temperatures, soil moisture, precipitation, humidity, and pests) at different growth stages than lines in the USSPS. Thus, a comparison of USSPS and conventional systems would be confounded by environmental effects, even if data from both systems are collected in the same location. We therefore chose to use historical data to estimate the yield of conventional systems as these estimates are derived from data collected over many environments. We used data from the University of Arkansas Cooperative Extension Service (2001) Soybean Research Verification Program (SRVP). This program involves soybean growers and extension service personnel. Growers enter select fields into the program. Growers and extension personnel determine the inputs and management of the field. Extension personnel generally visit the field once a week and make management recommendations to maximize yield. Yields from SRVP fields usually greatly exceed the state average due to the intensive management.

The SRVP has managed 36 nonirrigated fields planted with MG V to VI cultivars from 1985 to 1998. The average yield of these nonirrigated fields was 1881 kg ha^-1 (Univ. of Arkansas Coop. Ext. Serv., 2001). With the exception of the <70d maturity class at Missouri in 2001, the average yield of all maturity classes in all environments, as well as those averaged over environments (Table 2), exceeded this value. The highest yield of an individual line in each maturity class and environment also exceeded the 1881 kg ha^-1 yield level. As discussed earlier, lines in the USSPS that mature in less than 78 d are capable of avoiding mid-July or later droughts, and their relative yield potential may make the USSPS system a viable alternative to a full-season nonirrigated production system.

The SRVP has managed 166 full-season irrigated fields from 1982 to 2001. The average yield for these fields is 3245 kg ha^-1 (Univ. of Arkansas Coop. Ext. Serv., 2001). The average yield of the lines in the 85-91d and >91d maturity classes in all environments was similar to or exceed this value. In most instances, the highest yield of an individual line in 70-77d or later maturity classes exceeded 3245 kg ha^-1. Lines that mature in 78 to 91 d would be capable of avoiding August droughts while producing yields that may be competitive to those produced by full-season irrigated systems. It is important to note that these USSPS yields were obtained with limited irrigation (due to short USSPS growing season and limited drought in June) and were similar to yields attained from full-season irrigated system that often requires considerable irrigation in August and September. Using these lines in an irrigated USSPS would allow soybean growers to conserve water resources for use on other crops or to reduce irrigation costs of soybean production.

Correlations of Yield with Other Traits
All lines in all tests were short and had a limited number of main-stem nodes (Table 2), indicating that the yield potential of individual plants is limited in the USSPS. Thus, a key factor to attaining high yields from the USSPS is establishing a large number of plants per square meter. There was a trend for increased yield with increased maturity, height, number of nodes at R8, and seed weight (Table 2). Yield was correlated (P < 0.05) with height, days to maturity, and seed size when analyzed over all lines and maturity classes (Table 3). Height and number of nodes at R8 were correlated with maturity (data not shown), with correlation coefficient values exceeding 0.60 in all cases. As noted earlier, the longer growth cycle of some lines in the USSPS arises from a longer reproductive period (Fig. 1), which results in more height and nodes than in lines with shorter growth cycles. These are important to yield given the very short growth cycle and limited vegetative growth in the USSPS.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Our results show that a combination of early planting dates and lines that mature in less than 77 d provides an opportunity to avoid drought that starts in mid-July and produce acceptable yield. In addition to using these short-season lines, cultural practices that maximize soil moisture storage and conservation to minimize the yield-reducing effect of limited rainfall in June and early July can be incorporated in the USSPS.

Similarly, a USSPS using lines that mature in less than 91 d produced acceptable yields and would avoid drought that starts in August. While some early lines in the USSPS may avoid drought in the Midsouth, it also appears that the short growing season of the USSPS can be used to reduce water usage for growers who irrigate their soybean crop while still producing acceptable yields. The potential of the USSPS to produce a viable crop in less than two and a half months may have dramatic implications as water supplies become more limited in the Midsouth and many other regions of the world.

	ACKNOWLEDGMENTS

 
The authors greatly appreciate the help of Dr. Jim Orf (University of Minnesota) and Dr. Elroy Cober (Ag Canada), who selected, harvested, and shipped the seed of many lines used in this study and the help of Gary L. Nowling (USDA-ARS, Purdue University), who coordinated our timely access to seed of the lines in the USDA Uniform Trials. Salaries and research support provided by state and federal funds appropriated to the Ohio Agricultural Research and Development Center, The Ohio State University, and The University of Arkansas. Manuscript number HCS01-42.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 

• Boquet, D.J. 1998. Yield and risk utilizing short-season soybean production in the mid-southern USA. Crop Sci. 38:1004–1011.[Abstract/Free Full Text]
• Bruce, R.R., A.W. Thomas, V.L. Quisenberry, H.D. Scott, and W.M. Snyder. 1985. Irrigation practice for crop culture in the southeastern United States. Adv. Irrig. 3:51–106.
• Fehr, W.R., and C.E. Caviness. 1977. Stages of soybean development. Iowa Agric. Home Econ. Exp. Stn. Spec. Rep. 80. Iowa State Univ., Ames.
• 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.[Abstract/Free Full Text]
• Heatherly, L.G. 1999. Early soybean production system. p. 103–118. In L.G. Heatherley and H.F. Hodges (ed.) Soybean production in the Midsouth. CRC Press, Boca Raton, FL.
• Hovermale, C.H. 1992. Effects of planting date and tillage method on soybean varieties from four maturity groups. Tech. Bull. 180. Mississippi Agric. and Forestry Exp. Stn., Mississippi State.
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• Scott, H.D., J.A. Ferguson, L. Hanson, T. Fugitt, and E. Smith. 1998. Agricultural water management in the Mississippi delta region of Arkansas. Res. Bull. 959. Arkansas Agric. Exp. Stn., Fayetteville, AR.
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This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (3) Citing Articles via Google Scholar Google Scholar Articles by Ishibashi, T. Articles by Shannon, G. Search for Related Content PubMed Articles by Ishibashi, T. Articles by Shannon, G. Agricola Articles by Ishibashi, T. Articles by Shannon, G. Related Collections Water Management Soybean Dryland Cropping Systems Other Cropping Systems