Combined primary/secondary papermill sludge as a nitrogen source in a cabbage-sweet corn cropping sequence

Abstract

Combined primary/secondary papermill sludge (PS) is rich in N and may potentially be used as a N source for horticultural crops. A 3-yr experiment was conducted to determine the effects of PS application on crop yields, N uptake and N recovery. The PS was applied in 1996 on a Bedford silty clay (Humic Gleysol) cropped to winter cabbage (Brassica oleracea var capitata L. 'Bartolo') at 0, 8, 16, 32, and 64 Mg ha-1 (dry basis). In 1997, PS was applied at 44% of the 1996 rates to the same plots and cropped to sweet corn (Zea mays L. 'Delectable'). No PS was applied in 1998 to evaluate residual effects on corn. Treatments with ammonium nitrate (AN) at 50, 100 and 200% of N fertiliser recommendations were included each year as a reference for crop response. The PS had a C:N ratio of 42:1 in 1996 and of 28:1 in 1997. About 29% of the total N in PS was inorganic. Cabbage and corn marketable yields and N uptake increased with increasing amounts of PS applied. AN supplemented with PS further increased cabbage yields. Based on the N fertiliser replacement value, the N efficiency coefficient of PS was 44% in the first year. A N residual effect of the PS applied in 1996 was observed on the corn yield in 1997. The two PS applications also had a very significant residual effect on corn yield in the third year, although supplemental AN at 150 kg N ha-1 tended to further increase yields. The apparent total N recovery by the three crops was similar for PS and AN (i.e., 34 vs. 38%). The apparent recovery of organic N from PS decreased with increasing rates of application from 46 to 25%. These results suggest that PS is an effective source of N for crops and that significant residual N effects should be considered when estimating the N needs of subsequent crops. Key words: Cabbage, nitrogen, mineralization coefficient, paper mill residues, sweet corn