Crop Science 41:1857-1861 (2001)
© 2001 Crop Science Society of America
SEED PHYSIOLOGY, PRODUCTION & TECHNOLOGY
Flooding and Temperature Effects on Soybean Germination
Eileen Feilmeier Wuebker*,a,
Russell E. Mullena and
Kenneth Koehlerb
a Dep. of Agronomy, Iowa State Univ., Ames, IA 50011
b Dep. of Statistics, Iowa State Univ., Ames, IA 50011
* Corresponding author (eileen{at}iastate.edu)
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ABSTRACT
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During the germination phase of soybean [Glycine max (L.) Merr.] growth, uniform soybean emergence may be reduced when fields are periodically saturated with water from heavy rains and poor drainage. A laboratory study was conducted to determine the effects of timing and duration of flooding, germination temperature, and mechanical damage on the germination of soybean. There were little differences in germination percentage among the flooding duration treatments when flooding began 1 d after the start of imbibition. When seed were flooded 2 or 3 d after the start of imbibition, however, a significant drop in germination percentage occurred in seed flooded for 48 h. Flooding seed 3 d, compared with 1 d, after the start of imbibition was more detrimental, regardless of temperature. Seed injury was observed after only 1 h of flooding. Increasing the duration of flooding from 1 to 48 h at 15°C did not increase injury; however, at 25°C, more seed injury was observed as the duration of flooding increased up to 48 h. Overall, seed were more susceptible to flooding stress at 15°C than at 25°C. These results suggest that soybean seed are susceptible to flooding of 1 to 48 h during the early germination process and the response is influenced by germination stage.
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INTRODUCTION
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AN IMPORTANT CONSIDERATION for maximizing soybean production is establishing an optimum seedling stand following planting. In addition to seedbed conditions of soil temperature, oxygen concentration, microorganisms, and soil structure, water level is an important factor affecting the emergence and development of seedlings (Pollock, 1972). Seed may encounter cool, rainy weather following planting, which results in a cool, wet seedbed, especially when conservation or minimum tillage practices are utilized. If the cool, wet weather persists or if the field does not have adequate drainage, the field may be flooded for a number of hours or days. This flooding or saturation of the soil may result in poor germination and seedling establishment and can reduce crop yields.
The influence of flooding on soybean germination and emergence has not been widely studied. Langan et al. (1986) indicated that flooding for 3 d starting 1 d after planting delayed emergence of corn (Zea mays L.), soybean, and wheat (Triticum aestivum L.). Soybean seed exposed to preemergence flooding for 24 h only reached 50% emergence and did not emerge after flooding for 48 h (Sung, 1995). Hou and Thseng (1991) noted that most of the 50 soybean cultivars they tested for flood tolerance experienced severe losses in germination when soaking for 4 d prior to germination. They (Hou and Thseng, 1991) established a 4-d laboratory soak test at 25°C to screen soybean cultivars for flood tolerance.
Temperature plays an important role in germination and establishment of seedlings. Research has shown that the rate of hypocotyl elongation increases as temperature increases. Hatfield and Egli (1974) found that at 10°C, soybean hypocotyl elongation was extremely slow and that the rate of hypocotyl elongation reached a maximum at 30°C. Alm et al. (1993) indicated that as temperature increased from 10 to 25°C, the seedling elongation rate for corn and soybean increased. Hou and Thseng (1991) studied the interaction of temperature and flooding. Their research indicated that at 10 and 15°C temperatures, 2 to 8 d of soaking soybean seed prior to planting did not significantly affect seed germination. But, at 25 and 30°C temperatures, germination was significantly reduced as the length of soaking increased, and a complete loss in germination occurred when seed were soaked for 4 d at 30°C.
Mechanical damage of soybean seed during harvest, conditioning, handling, or planting operations can reduce seed viability and seedling stands. In addition, cracks in the seed coat are potential sites of pathogen invasion leading to disease or insect infestations (McDonald, 1985). Egli et al. (1990) noted that injury to soybean cotyledons resulted in slower emergence and seedling growth and that high-vigor seed had a higher seedling dry weight than low-vigor seed 5 or 6 d after emergence. Imposing flooding stress on mechanically damaged seed may further reduce the potential of uniform seed germination and increase seed susceptibility to disease.
With the exception of the study by Langan et al. (1986), flooding studies on soybean seed have involved imposing the flooding stress prior to planting or immediately following planting. How flooding stress affects soybean seed that have begun to imbibe water has not been thoroughly studied. Additional information on the timing of flooding and its interaction with the duration of flooding could be useful in predicting soybean germination and establishment. Furthermore, how temperature and mechanical damage affect flooding stress may offer insights into critical times of seed susceptibility to flooding for seed of varying physical quality.
The objectives of this study were to evaluate the effects of the timing and duration of flooding on soybean germination, to study the effects of temperature variation on flooding tolerance of soybean seed, and to investigate whether mechanical damage to soybean seed magnifies the effects of flooding stress on germination.
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MATERIALS AND METHODS
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Two soybean cultivars, AG3301 and AG3002, were selected for this study. These cultivars were selected to ensure some level of genetic variability and because they are popular, high yielding cultivars grown by soybean producers. Both AG3301 and AG3002 are early Group III, indeterminate cultivars. Three lots of each cultivar, produced at different locations in Iowa during 1997, were selected to represent different production environments. To reduce seed size variation between cultivars and among lots, the seed was passed through a 0.67-cm-round screen and was held on 0.48-cm slot screen. Seed moisture varied across lots from 110 to 129 g kg-1 on a dry weight basis. The seed was kept in cold storage maintained at 10°C and 50% relative humidity until use. The germinability of the lots was established by conducting a warm germination test according to "Rules for Testing Seeds" (AOSA, 1999). Lots 1 to 3 of AG3301 had initial germination percentages of 89, 98, and 89%, respectively, and Lots 1 to 3 of AG3002 had initial germination percentages of 83, 85, and 87%, respectively.
Impact damage was applied to soybean seed by a prototype of a multiple impacter designed by Pandya (1991). The impacter was designed with a horizontally orientated cylinder divided into two identical chambers by a partition through its diameter that allows seed to drop vertically within the chamber. A sample of 250 seed was used in each chamber. As the cylinder rotated horizontally, the seed in each chamber were lifted by one end of the partition and vertically dropped onto a metal plate near the other end of the partition. With each revolution of the chamber, the seed were lifted again and dropped on the metal plate. The visible impact damage was expressed as seed coat cracks and splits. However, the level of mechanical damage necessary for this experiment was determined by amount of decrease in warm germination percentage rather than visible, physical damage. Preliminary impact studies were conducted to identify the number of impacts necessary to lower the warm germination test values to 70 to 75%. It was determined that 1000 impacts lowered the germination of cultivar AG3002 to an average of 72%, whereas 2500 impacts lowered the germination of cultivar AG3301 to an average of 68%. In the actual study, these impact treatments lowered the warm germination by 10 percentage points to 75% for AG3002 and to 82% for AG3301. Following the impact treatments, damaged whole seed from within each lot were mixed together, placed in a sealed plastic bag, and set in cold storage until planting. A bagged sample of undamaged seed from each lot was also placed in cold storage.
Seed were planted in 237-mL plastic tubs measuring 12 cm in length, 9.5 cm in width, and 2.5 cm in depth. Twenty holes were drilled in the bottom of each tub with a 1.6-mm drill bit. A layer of glass wool was placed in the bottom of each tub to prevent blocking of the holes by sand particles and the glass wool was covered with one-fourth cup (94 g) of #16 silica sand. Twenty seed were planted and pressed into the sand. Only whole soybean seed, not splits or broken seed, were planted. Three-fourths cup (275 g) of #16 silica sand was poured over the seed. The tubs were then placed on plastic racks on germination trays to allow for drainage. The trays were set in germination carts and placed overnight in temperature-controlled rooms of 15 and 25°C to allow the sand and seed to equilibrate to the appropriate temperature. Each tub, including the control treatments, was watered with 70 mL of tap water from a watering table with misting nozzles, and were returned to the appropriate temperature-controlled room. The tubs were not individually covered, but were placed in a closed germination cart. Preliminary studies determined that 70 mL of water was sufficient for the seed to double their weight within the first 12 h of imbibition. The treatment units received 12 h of fluorescent light per day on a 3 h on/off schedule at a light intensity of 1.356 µmol cm-2 s-1.
Flooding treatments were imposed on individual tubs at 1, 2, or 3 d after the start of imbibition. The seed were flooded by placing the tubs in 5-cm-deep trays filled with tap water equilibrated to the appropriate temperature of 15 or 25°C. The 5-cm-deep trays were placed in a germination cart located in the same temperature-controlled room. The tubs were totally submerged in water for a period of 1, 6, 12, 24, or 48 h. Following submergence, the tubs were returned to their appropriate location within the germination carts.
Daily emergence counts were taken, with emergence defined as the number of seedlings with both cotyledons completely above the sand surface (Fehr et al., 1977). Final germination percentage was determined 3 d after 50% of the seed plants in a treatment unit had emerged in the 25°C treatments and 6 d after 50% of the seed plants in a treatment unit had emerged in the 15°C treatments. Preliminary studies determined that delaying the final germination evaluation by an additional 3 d for the treatment units in 15°C as compared with the treatment units in 25°C would reflect the delay in germination and emergence due to the lower temperature. For those treatment units where 50% of the seed plants did not emerge, a final germination percentage was determined after 10 d of germination in 25°C and 20 d of germination in 15°C. Final germination percentage was represented by normal seedlings and was determined from the "Seedling Evaluation Handbook" (AOSA, 1992). The total dry weight yield of the normal seedlings (roots and shoots) was determined by removing the cotyledons and drying the seedlings for 48 h in a 105°C oven. Average seedling dry weight yield was calculated by dividing the total dry weight yield by the number of normal seedlings.
A total of 216 treatment combinations [two cultivars, three lots, two damage levels, three times of flooding stress (1, 2, or 3 d after the start of imbibition), and six durations of flooding stress (0, 1, 6, 12, 24, and 48 h)] were examined at each of two temperature levels. The study was done in temperature-controlled rooms at 15 and 25°C. The experimental design was set up with temperatures as main plots and treatments as subplots. The treatment combinations were completely randomized with respect to the placement of the tubs in the 18 trays and in two germination carts for each temperature level. Three replications of the experiment were conducted on different dates. For the control treatment, the seeds were watered with 70 mL of tap water, but no flooding stress was imposed.
Analyses of variance were conducted by the general linear model procedure of SAS (1996) with Type III Sum of Squares. Separate analyses of variance were completed for germination percentage, total seedling dry weight yield, and average seedling dry weight yield.
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RESULTS
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Cultivar and Lot Effects
No significant differences in germination percentage between cultivars for the timing of flooding stress and germination temperature were found in this study. Small, but significant cultivar responses were noted in this study only for the timing of flooding stress and germination temperature on total seedling dry weight yield (data not shown), suggesting little cultivar influence on response to flooding. The two-way interaction of cultivars with the duration of flooding stress, germination temperature, and mechanical damage treatments was not significant in this study. The two-way interaction of seed lots with the timing and duration of flooding, germination temperature, and mechanical damage treatments was not significant in this study.
Timing and Duration of Flooding
Flooding at any time and for any duration significantly lowered germination percentage in all treatment combinations compared with nonflooded seed and the average decrease in germination percentage for 1 h of flooding was 15 percentage points (Table 1). The interaction of timing and duration of flooding stress had a significant impact on the germination of the soybean cultivars tested. For seed flooded 1 d after the start of imbibition, only small differences in germination percentage were observed among the flooding duration treatments. For seed flooded 2 or 3 d after the start of imbibition, however, a significant drop in germination percentage occurred when seed were flooded for 48 h as compared with 1, 6, 12 and 24 h.
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Table 1. Comparison of the effects of the timing and duration of flooding stress on mean germination percentage of soybean.
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Germination Temperature and Timing of Flooding
The interaction between germination temperature and the timing of flooding was significant for the germination percentage of soybean (Table 2). At 15°C, there was a significant difference in germination percentage when seed that had imbibed water for 2 or 3 d were subjected to flooding compared with seed that had imbibed water for 1 d. At 25°C, flooding of seed 3 d after the start of imbibition significantly lowered germination percentage compared with flooding seed 1 or 2 d after the start of imbibition. Overall, the greatest flooding injury occurred at the 15°C germination temperature. Flooding of seed 1 d after the start of imbibition at 15°C reduced germination percentage by 18 percentage points compared with an 11 percentage point decline in germination at 25°C. Loss in germination from flooding was similar between the two temperature treatments at 25 to 26 percentage points when flooding stress was imposed on seed 3 d after the start of imbibition. This suggests that seed were better able to withstand flooding imposed during the first 2 d after the start of imbibition at higher germination temperatures. However, seed that had imbibed water for 3 d were more susceptible to flooding injury regardless of germination temperature.
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Table 2. Comparison of the effects of the timing of flooding stress and germination temperature on mean germination percentage of soybean.
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Results for total seedling dry weight yield showed a significant interaction between the germination temperature and timing of flooding stress (Table 3). At 15°C, flooding seed 2 or 3 d after the start of imbibition resulted in a significantly lower total seedling dry weight yield than flooding seed 1 d after the start of imbibition. At 25°C, however, total seedling dry weight yield decreased significantly with increasing imbibition time prior to flooding. In this study, flooding seed 3 d after the start of imbibition compared with 1 d after the start of imbibition at 25°C resulted in a 0.14 g decrease in total seedling dry weight yield compared with a 0.05 g decrease at 15°C. No significant differences in average seedling dry weight yield for the interaction of germination temperature and timing of flooding stress were found in this study.
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Table 3. Comparison of the effects of the timing of flooding stress and germination temperature on total seedling dry weight yield of soybean.
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Germination Temperature and Duration of Flooding
The duration of flooding stress had a significant interaction with germination temperature for germination percentage, total seedling dry weight yield, and average seedling dry weight yield (Tables 4 and 5). Flooding for as little as 1 h at 15°C lowered germination percentage by over 20 percentage points compared with the nonflooded control. It took approximately 36 more hours of flooding for seed at 25°C to experience the same loss in germination as 1 h of flooding at 15°C. Results for total seedling dry weight yield and average seedling dry weight yield had a similar trend, although the loss in seedling dry weight yield at 25°C was not equal to the 1 h loss at 15°C until approximately 48 h of flooding had occurred. Additional flooding stress beyond 1 h to 48 h at 15°C did not result in further loss of germination percentage, total seedling dry weight yield, or average seedling dry weight yield. At 25°C, however, germination percentage, total seedling dry weight yield, and average seedling dry weight yield generally declined with duration of flooding stress. Germination percentage dropped over 20 percentage points and total seedling dry weight yield declined by more than 50% from 24 to 48 h of flooding stress at 25°C.
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Table 4. Comparison of the effects of the duration of flooding stress and germination temperature on mean germination percentage of soybean.
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Table 5. Comparison of the effects of the duration of flooding stress and germination temperature on total and average seedling dry weight yield of soybean.
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Germination Temperature and Impact Damage
The interaction of germination temperature and impact damage was significant for germination percentage and total seedling dry weight yield (Table 6). The interaction was not significant for average seedling dry weight yield. At 25°C, the germination of damaged seed was 16 percentage points lower than undamaged seed. The germination of damaged seed was only 8 percentage points lower than damaged seed at 15°C germination temperature. Total seedling dry weight yield responses were similar to germination percentage. These data suggest that the injurious effects of impact damage were more pronounced at the higher germination temperatures than at the lower temperatures.
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Table 6. Comparison of the effects of impact damage and germination temperature on germination percentage and total seedling dry weight yield of soybean.
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Flooding and Impact Damage
The interactions between impact damage and the timing or duration of flooding were not significant so averages for the two damage treatments were computed for flooded seed and compared with the nonflooded control seed (Table 7). Impact damage lowered germination of flooded seed 11 percentage points compared with 17 percentage points for nonflooded control seed. There was no significant impact damage by flooding interaction, suggesting that the effects of damage and flooding are additive.
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DISCUSSION
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In this study, cultivar effects were small or nonsignificant. In previous research, cultivar differences in flooding response of soybean have been noted with a wider selection of cultivars under a different flooding methodology (Hou and Thseng, 1991). In this study, cultivars were analyzed, however, so that large differences between cultivars were necessary to detect differences among treatments. The lack of significant cultivar effect in this study does not preclude that cultivar response and flooding stress is not important.
The results of this study were consistent with previous studies in that flooding of soybean seed reduces seed viability as evidenced by reduced germination and seedling growth. The data suggest that if seed are further into the germination process when flooding occurs, the seed are more susceptible to flooding stress.
The data generated by this study indicate that the duration of flooding is an important consideration in anticipating losses due to flooding. The results suggest that flooding for as briefly as 1 h has the potential to cause significant losses in germinability; however, when the duration of flooding increased to 48 h, the potential loss in seedling germinability was much greater. The loss in germinability at 1 h may be associated with physical damage to the seed (Woodstock and Taylorson, 1981). The excess water could cause imbibitional damage to the seed membrane, which the seed is unable to repair (Tully et al, 1981; Ladror et al., 1986). The loss of germinability at 48 h may be associated with physiological damage to the seed. Previous studies have suggested many potential physiological mechanisms, including ethanol toxicity, oxygen deprivation, and carbon dioxide accumulation. Perhaps one or more of these factors along with other unidentified factor(s) contribute to the overall breakdown of the seed metabolism and the inability of the seed to produce a normal seedling. It may also be suggested that pathogen infestations could reduce seed germinability. Small, inconsistent increases in fungal pathogens were noted in this study for some treatment units, but there was not enough pathogen infestation to account for the differences in germinability between the treatments (data not shown).
The interaction between temperature and flooding treatments was not consistent with results offered by other studies. Previous studies have indicated that warmer soil temperatures relate to greater losses in seedling emergence because of flooding compared with lower temperatures. Research by Hou and Thseng (1991) indicated that soaking soybean seed for up to 8 d at 10 and 15°C prior to germinating the seed caused no loss in germination, but that germination decreased as the length of soaking time increased at 25 and 30°C. Field research with corn reported greater losses in emergence when hybrids and inbreds were flooded for 48, 96, and 144 h at 25°C compared with 10°C (Fausey and McDonald, 1985). The data presented in this study, however, suggest that flooding seed 1 to 3 d after the start of imbibition or for 1 to 24 h was more detrimental to germination at 15°C than at 25°C. Perhaps 1 h of flooding causes a physical, imbibitional damage to the seed that is further aggravated by the chilled conditions (Tully et al., 1981; Ladror et al., 1986). Also, earlier studies imposed the flooding stress prior to planting or immediately following planting. Possibly allowing the seed to begin the germination process and imbibe water for 1 to 3 d prior to flooding caused the difference in temperature response in this study compared with other studies. Although not observed, factors other than flooding stress may contribute to the loss of germination at 15°C. Possible factors include chilling injury and imbibitional damage.
The response of seed to mechanical damage indicates that seed with seed coat cracks or with internal damage to the seed structure have a greater loss in viability than undamaged seed. Imposing impact damage to the seed lowered germination and seedling growth in this study. Damage to the seed coat integrity may cause injury to the seed under flooding conditions because the seed is unable to regulate the amount of water imbibed (Tully et al., 1981; McDonald, 1985). Internal damage to the seed structure may prevent development of a normal seedling because of a broken radicle, detached cotyledon, or lesion in the hypocotyl.
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CONCLUSIONS
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The data for germination percentage and total seedling dry weight yield generally indicated that seed exposed to 15°C germination temperature was more susceptible to flooding stress than seed exposed at 25°C germination temperature. When flooding seed 3 d after the start of imbibition or flooding for 48 h, differences due to germination temperatures were less evident. Flooding seed 3 d after the start of imbibition for 48 h in the laboratory caused the largest reductions in germination. Mechanical damage to seed reduced the production of normal seedlings.
Field research to investigate the relevance of these laboratory results further is warranted. In a field study, uncontrollable environmental factors of temperature, light, and moisture may play a critical role in the seed's response to flooding. In addition, the variability of soil drainage, microbial populations, and disease pressure across a field may have considerable influence on how seeds respond to flooding stress. The data of this laboratory study suggest that with additional field research it may be possible to predict the level of seedling stand losses due to the timing and duration of flooding.
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NOTES
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Journal Paper No. J-18452 of the Iowa Agric. and Home Econ.Exp. Stn., Ames, IA, Project No. 3244, and supported by Hatch Act and State of Iowa funds.
Received for publication March 27, 2001.
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REFERENCES
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- Alm, D.M., E.W. Stoller, and L.M. Wax. 1993. An index model for predicting seed germination and emergence rates. Weed Technol. 7:560–569.
- Association of Official Seed Analysts (AOSA). 1999. Rules for Testing Seeds. Association of Official Seed Analysts (AOSA). 1992. Seedling Evaluation Handbook. AOSA, Lincoln, NE.
- Egli, D.B., D.M. TeKrony, and R.A. Wiralaga. 1990. Effect of soybean seed vigor and size on seedling growth. J. Seed Technol. 14:1–12.
- Fausey, N.R., and M.B. McDonald, Jr. 1985. Emergence of inbred and hybrid corn following flooding. Agron. J. 77:51–56.[Abstract/Free Full Text]
- Fehr, W.R., and C.E. Caviness. 1977. Stages of soybean development. Spec. Rep. 80. Iowa Agric. Home Econ. Exp. Stn., Iowa State Univ., Ames, IA.
- Hatfield, J.L., and D.B. Egli. 1974. Effect of temperature on the rate of soybean hypocotyl elongation and field emergence. Crop Sci. 14:423–426.[Abstract/Free Full Text]
- Hou, F.F., and F.S. Thseng. 1991. Studies on the flooding tolerance of soybean seed: Varietal differences. Euphytica. 57:169–173.
- Ladror, U., R.L. Dyck, and M.J. Silbernagel. 1986. Effects of oxygen and temperature during imbibition of seeds of two bean lines at two moisture levels. J. Am. Soc. Hortic. Sci. 111(4):572–577.
- Langan, T.D., J.W. Pendleton, and E.S. Oplinger. 1986. Peroxide coated seed emergence in water-saturated soil. Agron. J. 78:769–772.[Abstract/Free Full Text]
- McDonald, M.B., Jr. 1985. Physical seed quality of soybean. Seed Sci. Technol. 13:601–628.
- Pandya, L.S. 1991. A multiple impact damage simulator for seed soybeans. M.S. Thesis. Iowa State Univ., Ames, IA.
- Pollock, B.M. 1972. Effects of environment after sowing on viability. p. 150–171. In E.H. Roberts (ed.) Viability of seeds. Syracuse University Press, Syracuse, NY.
- SAS Institute. 1996. The SAS System for Windows 6.12. SAS Inst., Cary, NC.
- Sung, J.M. 1995. The effect of sub-optimal O2 on seedling emergence of soybean seeds of different seed size. Seed Sci. Technol. 23:807–814.
- Tully, R.E., M.E. Musgrave, and A.C. Leopold. 1981. The seed coat as a control of imbibitional chilling injury. Crop Sci. 21:312–317.[Abstract/Free Full Text]
- Woodstock, L.W., and R. B. Taylorson. 1981. Soaking injury and its reversal with polyethylene glycol in relation to respiratory metabolism in high and low vigor soybean seeds. Physiol. Plant. 53:263–268.
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ABSTRACT
INTRODUCTION
