Reducing Chlorophyll Content in Soybeans Alters the Surface Energy Balance

In the United States approximately 80 million acres of soybean are planted each year, which makes soybeans a major form of land cover and a key component of the surface energy balance. The chlorophyll content of a plant leaf determines its color and ability to absorb sunlight for growth, as well as the radiation balance with the atmosphere. In dense monoculture crops, such as soybean, chlorophyll content may actually be too great since leaves at the top of the canopy absorb most of the incoming radiation and little reaches the lower layers of the canopy. If this is true, we hypothesize that reducing chlorophyll will increase light penetration deeper into the canopy, which may increase soybean yield and also alter the canopy energy balance. For this presentation, we will focus on the role of reducing chlorophyll by ~30 to 50% on the radiation balance of soybean canopies and its impact on the canopy and soil temperature, as well as sensible, and latent heat flux. We predict that the soybean with less chlorophyll is likely to have a higher albedo than the fully green control plants and thus able to reflect more of the incoming solar radiation. This could in turn reduce the canopy temperature and/or the available energy to drive the exchange of heat and moisture via sensible and latent heat fluxes. During the 2013 growing season we used micro-meteorological techniques to measure the balance of 3 replicated 21 m2 plots of reduced chlorophyll and control soybean at the University of Illinois South Farms. Preliminary results support our prediction of increased albedo, and further analysis is underway to examine the impacts on the overall energy balance. The outcome of this investigation is far reaching, as increased global demand for soybean will stress US food security. If viable, reduced chlorophyll varieties of soybean may increase US yield potential and impact the radiation budget.