2009 was known to many in WI as the "Year of the Yellow Bean". Growers are again experiencing yellow soybeans in 2010, but for a different reason (Image 1). We must first remember that in soybean, active N-fixtion does not begin until the V2-V3 (2 to 3 open trifoliates) growth stages. Even if you were to properly dig a soybean plant, identify and split a nodule, the red appearance does not necessarily mean that fixation has fully begun (Image 2).
Image 1. Field of yellow soybean.
Image 2. Soybean nodulation.
In 2009, dry soils were a contributing factor limiting nodulation and leading to early season low leaf N content. In 2010, our soils have been at or above field capacity for the last 10 days to 2 weeks (Figure 1). If soils are waterlogged depleted oxygen and increases carbon dioxide levels can lead to reduced root growth, shoot growth, nodulation, nitrogen fixation, photosynthesis, biomass accumulation, stomatal conductance, and plant death due to diseases and physiological stress (Oosterhuis et al., 1990; VanToai et al., 1994 and 2003). Given our growth stage and the fact that nodules are present I do not foresee any yield impact in the yellow soybeans. A few days of dry weather and warmer temperatures will quickly alleviate these symptoms.
Figure 1. Rainfall and soil water content at Arlington WI in 2010 (6/42010 to 6/16/2010)
Literature Cited:
VanToai, T.T., J.E. Beuerlien, A.F. Schmithenner, and S.K. St. Martin, 1994. Genetic variability for flooding tolerance in soybeans. Crop Sci. 34:1112-1115.
VanToai, T.T., S. K. St. Martin, K. Chase, G. Boru, V. Schnipke, A. F. Schmitthenner,and K. G. Lark. (2001) Identification of a QTL associated with tolerance of soybean to soil water-logging. Crop Sci. 41,1247-1252.
VanToai, T. Y. Yang, P. Ling, G. Boru, M. Karica, V. Roberts, D. Hua, B. Bishop. (2003) Monitoring soybean tolerance to flooding stress by image processing technique. In T.T. VanToai, et al. (ed) Digital Imaging and Spectral Techniques: Applications to Precision Agriculture and Crop Physiology. ASA Special Publication No 66. The American Society of Agronomy. Madison, WI. Pp 43-51.
