Sweet Corn Yield and Tissue Metal Concentration after Seven Years of Sewage Sludge Applications

Abstract

The amount of sewage sludge applied to land is limited by Environmental Protection Agency (EPA) recommendations regarding soil pH and cation exchange capacity and the amount of Cd applied. Sewage sludges from Salem, Portland, and Rock Creek, OR, were added to a moderately acid Willamette silt loam (fine-silty, mixed, mesic Pachic Ultic Argixeroll) soil in a field experiment to investigate the effects of multiple applications of sludges with differing, low metal concentrations on sweet corn (Zea mays L.) yield and elemental concentration in leaf and kernel tissue and how these responses compare with those from commercial N fertilizer. Ammonium sulfate (0, 100, 200, and 300 lb N/acre) and sewage sludge (a low rate—approximately 200, and a high rate—approximately 400 lb N/acre, and 400 lb N/acre plus lime) were added to the soil annually for 7 yr. Fresh ear weight was taken and elemental analyses were conducted in Year 1, 2, 3, and 7. Higher yields were obtained on limed plots than on unlimed plots at the high sludge rate in Year 7. Six out of nine sludge treatments had higher total yields than 200 lb N/acre as (NH4)2SO4 in Year 7. Concentrations of leaf Cd, Zn, and Mn were significantly greater in Year 7 than in Year 3 due to application of sludge. In Year 7, leaf Cd and Zn concentrations were higher in corn fertilized with sludge than with (NH4)2SO4. The Zn, Cd, and Mn concentrations in leaf tissue were lower with than without lime addition. Sludge and (NH4)2SO4 treatments had no effect on kernel Cd concentration. Only Portland sludge applications exceeded EPA recommendations (3 out of 7 yr). All sludges were satisfactory N sources for sweet corn growth.