Long-Term Effect of Sludge Compost Amendment on the Temporal Pattern of Nitrogen Supply in Its Amended Soil

Abstract

As by-product of sewage treatment, the sludge contains abundant plant nutrients such as nitrogen; therefore, the sludge compost is usually regarded as an amendment source of nitrogen for soil. However, the nitrogen supply pattern characterized by sludge-amended soil remains unclear. In this work, changes in nitrogen supply patterns with time in amended soil, including total nitrogen content, alkali-hydrolyzable nitrogen, and urease activity, as well as levels in the associated humus and total extractable carbon (TEC), were investigated in the case of long-term amendment of sludge compost to soil. Periodical monitoring results showed that concentration-significant and time-retardant peaks in alkali-hydrolyzable nitrogen, urease activity and humus and total as well as TEC emerged at the fourth year, with highest values of 7.28 mg/g/day, 133.8 mg/kg, 3.24 g/kg and 37.4 g/kg, respectively, except for total nitrogen, indicating that there is a slow-release of nitrogen supply in response to the amendment of sludge compost to soil. Moreover, maximal alkali-hydrolyzable nitrogen content (152.2 mg/kg) and urease activity (8.87 mg/g/day) happened respectively in response to the incorporation frequencies of triple and double times, indicating that enough mixing of sludge compost with soil also improved nitrogen supply potential. Taken together, the results indicated that the amendment of sludge compost to soil promoted the conversion from organically combined nitrogen to mineralized one.