Young soybean plants live off the energy stored in their cotyledons to form their unifoliate and first trifoliate leaves.The immediate shot above shows how a young soybean plant remains dark green until this stage as there are sufficient plant reserves to feed these new developing tissues. The top photo above shows how the cotyledons yellow, shrivel up and start dropping off the plant during the transitional process of the plant living off the cotyledonary food reserves and the soil.It's at this point that growers often comment on how yellow their soybeans appear as plants are now living off the soil and nodules have yet to be formed and become fully functional in producing N.