Brazilian research evaluated the direct and residual effects of sewage sludge soil application on soybean yield and composition. The treatments were 0, 1.5, 3.0, and 6.0 tons of sludge per ha. Results indicated the highest sludge treatment had the highest soybean yield for the first and second year. Soybean seed composition was not significantly different from the control and chemical fertilization treatments. These results indicate soybean composition is not greatly affected by the fertility level of the soil.
Vieira, R.F. and co-workers. 2005. Availability of soil nutrients, quality of grains and yield of soybean in soil treated with sewage sludge. Pesquisa Agropecuaria Brasileira 40(9): 919-926.