Sweet Corn Response to Application of Three Sewage Sludges

Anaerobically digested sewage sludges from Portland, Salem, and Rock Creek, Oreg., and (NH4)2SO4 were applied to Willamette silt loam soil for 3 consecutive years to determine their effects on yield and elemental composition of sweet corn (Zea mays L.) leaves and kernels. In the first and second year, sweet corn ear yields increased nearly proportionally to the sludge NH4‐N content at the low rate of sludge application, but were not further increased at the high rate of sludge application. In the first 2 years ear yields of plants grown on sludge‐amended soils were less than yields obtained with the optimal rate of (NH4)2SO4. However, in the third year yields on sludge‐amended soils equaled or exceeded those with optimal (NH4)2SO4. Banding concentrated superphosphate at planting tended to increase yields, particularly of fully mature ears. Response to banded P was more pronounced with (NH4)2SO4 than with sewage sludge as the N source. Leaf‐tissue Zn and Cd content increased with sludge or commerical N application, with the highest Zn and Cd content occurring in plants grown on soils amended with the sludge that contained the highest concentration of trace metals. Kernel metal content varied less with N rate or source than did leaf metal content. Liming had little effect on yield or the metal content of kernels. Metal content of kernels did not increase with second and third sludge applications.