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Title: MODELING SOYBEAN VEGETATIVE DEVELOPMENT USING DATA FROM THE MISSISSIPPI VALLEY

Author
item Pachepsky, Yakov
item ACOCK, B - DUKE UNIVERSITY
item Reddy, Vangimalla
item WHISLER, F - MISSISSIPPI STATE UNIV

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2003
Publication Date: 12/31/2002
Citation: N/A

Interpretive Summary: Yields of soybean crops depend primarily on the ability of the crop to intercept sunlight and to use the energy to turn carbon dioxide into plant dry matter. The amount of sunlight intercepted in turn depends on the rate of leaf appearance (RLA). Temperature is recognized as the principle determinant of RLA. However, the reported relationships between RLA and temperature are very changeable. We, therefore, tested several equations t see which would best describe the RLAs observed for eight soybean cultivars grown in the field. The plant and weather data were collected between 1991 and 1997 in seven southern states in the Mississippi Valley. In most data sets, just after emergence there was a pause in vegetative development, the length of which depended on both the cultivar and the temperature. Treating this pause as a loss of vegetative stages (Vlost) accounted for its dependence on temperature. This lost stages equation proved to be much superior to linear and quadratic equations as a predictor of RLA. The parameters of the equation differed between cultivars and values of Vlost up to 2.55 were observed. RLA's measured in the field were slower than those measured in controlled-environments. The reason for this is not known and needs further study. These results indicate, whereas, controlled-environments are needed to study plant responses to environmental variables and to determine the general form of the equations relating them, the values of the parameters in these equations must be determined from field data for each cultivar separately.

Technical Abstract: Yields of soybean crops depend primarily on the crop's ability to intercept solar radiation, which in turn depends on the rate of canopy development. Rate of leaf appearance (RLA) is an important indicator of canopy development, and temperature is recognized as its principle determinant. Reported dependencies of RLA on temperature are very changeable. We, therefore, tested several models to see which would best describe the RLA' observed for eight soybean cultivars grown in the field. The plant and weather data were collected between 1991 and 1997 in seven southern states in the Mississippi Valley. In most data sets, just after emergence there was a pause in vegetative development, the length of which was cultivar-specific and temperature-dependent. Treating this pause as a loss of vegetative stages (Vlost) accounted for its temperature dependence. This lost stages model, proved to be superior to linear and quadratic models as a regression-type predictor of progress in vegetative stages. The parameters of the model were cultivar-specific and values of Vlost up to 2.55 were observed. Developmental rates in the field were slower than those measured in controlled environments. The reason for this is not known and seems to warrant further study. These results indicate, whereas, controlled-environments are needed to study plant responses to environmental variables and to determine the general form of the equations relating them, crop models must be written with cultivar-specific parameters, and the values of these must be determined from field data.