Soil enzyme activities following paper sludge addition in a winter cabbage-sweet corn rotation

Combined primary and secondary papermill sludge (PS) is a good source of C and other nutrients for soils devoted to intensive horticultural production . A field study was conducted to evaluate the effect of PS, spring-applied alone or in combination with ammonium nitrate (AN), on the enzymatic activi ty of a Bedford clay (Humic Gleysol) in the province of Quebec, Canada. The experiment was started in 1996 with winter cabbage (Brassica oleracea var. capitata L.) and continued in 1997 and 1998 on the same plots with sweet c orn (Zea mays L.). The PS was applied at 0 (control), 8, 16, 32 and 65 Mg h a(-1) in 1996 and at 44% of these rates in 1997. No sludge was applied in 1 998. Additional treatments consisted of AN applied yearly at 100% of the pl ant N requirements and a PS and AN combination. Soil arylsulfatase and acid and alkaline phosphatase activities were measured at three different times in each growing season. The PS rate linearly increased the soil acid phosp hatase activity in all 3 yr. In contrast, the alkaline phosphatase and aryl sulfatase activities were enhanced in 1997 by the 8-16 Mg PS ha(-1) treatme nts, whereas larger amounts of PS showed activity comparable to the control . The second PS application promoted phosphatase activities mostly in fall, but did not sustain arylsulfatase activity. The AN gave lower phosphatase activities than PS, and depressed arylsulfatase. Addition of AN to PS incre ased only acid phosphatase activity as compared with PS alone or the contro l. This study indicated that addition of PS improved enzyme activity of thi s horticultural soil but rates in excess to 32 Mg ha(-1) may be detrimental .