Sewage Sludge Provided Nitrogen To Maize (Zea Mays L.) Very Rapidly, Demonstrating a High Short-Term Net Mineralization Rate

This study aims to evaluate the potential of sewage sludge as a sustainable alternative to traditional farmyard manures, considering the limited availability of such resources in many regions specializing in crop production. This study compared the application of sewage sludge (SS) and cow manure (CM) at equivalent nitrogen (N) rates in silage maize (Zea mays L.) cultivation over two growing seasons. Organic amendments were applied at rates of 50 (SS50, CM50), 100 (SS100, CM100), and 200 (SS200, CM200) kg ha⁻¹ of N, alongside an unfertilized control (N0), with three replicates per treatment in a completely randomized design. Dry matter yield (DMY) increased significantly with the applied dose but showed no significant differences between amendments. N availability indices, including the pre-side-dress soil nitrate test, leaf N concentration, and stalk nitrate test, revealed higher N availability from sewage sludge compared to cow manure at equivalent application rates. Apparent N recovery (ANR) by the end of the second growing season was 99.8%, 90.8%, and 74.5% for SS50, SS100, and SS200, respectively, and 76.7%, 75.4%, and 50.5% for CM50, CM100, and CM200, respectively. The rapid mineralization of sewage sludge likely results from its low carbon (C)/N ratio and the absence of lignin and other low-energy organic compounds, which are less metabolically accessible to soil microorganisms. These properties position sewage sludge as an intermediate between conventional organic compost and mineral fertilizers, making it particularly suitable for cropping systems requiring high short-term N availability.