Submitted to: Acta Horticulture Proceedings
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/15/2001
Publication Date: 1/1/2002
Citation: Reddy, V., Pachepsky, L.B., Whisler, F.D. 2002. Effects of temperature and photoperiod on development rates of nine soybean varieties in mississippi valley. Acta Horticulture Proceedings. 593:201-207. Interpretive Summary: Growth and development of soybean crops depend on temperature and day length. When planted late in the season, most of the soybean varieties reach the flowering stage much faster as compared with those planted earlier. Increases in temperature and changes in the day lengths cause this accelerated development. Planting dates vary widely for soybean crops in the United States, as well as the temperature regimes within the growth seasons. Therefore, estimating development rates of soybean crops delivers important information for tactical management decisions, as well as, risk assessment for soybean growers under varying weather patterns. The objectives for this paper were to observe and to simulate differences in field soybean crops encountering significantly different day length's patterns. Data were collected at two farms in Mississippi. Nine soybean cultivars were planted at sandy loam and clay soils on May 1, May 26, and June 11, 1999. Some of those cultivars were monitored in previous years. Together, 36 growth and development data sets were available encompassing wide range of soil properties, weather conditions, planting dates, and irrigation schedules. For each crop, reproductive and vegetative stages were determined weekly for 20 plants at each of the five replicated sites. We found that the daily increment in reproductive stages before flowering could be described as a simple linear function of day length only. This function appeared to be different before and after the solstice for all soybean cultivars and growing conditions. Results of this work can be used in decision support for soybean production in the Southern United States. One of the applications is to use the reproductive development tailored to the cultivar being grown at a particular farm.
Technical Abstract: Time to flowering in soybeans Glycine max (L.) Merr. is affected by environmental conditions, temperature and photo period being the leading environmental variables. Most of the available experimental data in the Mississippi valley and models using them reflect to mid and late spring planting. Planting dates in soybean crops vary significantly, and late planting is common, especially in years with extreme spring weather events, The objective of this study was to quantify differences in development rates in field soybean crops encountering significantly different day length patterns. Nine soybean varieties were planted on three different days in two soil types. Each crop had five replications. We confirmed the earlier proposed hypothesis that the daily increment in a reproductive stage could be simulated as a linear function of photo period with slopes of these linear, different functions before and after the solstice.