Hamed Fathi Dokht - PhD Student of Soil Science, Department of Soil Sciences, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran
Seyed Alireza Movahedi Naeini - Associate Professor of Soil Science, Department of Soil Sciences, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran
Esmaeil Dordipour - Associate Professor of Soil Science, Department of Soil Sciences, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran
Liz Wollsene De Jong - Professor of Soil Science, Department Agroecology, Aarhus University, Aarhus, Denmark

Background: The application of biochar as a soil amendment has achieved popularity and has been found to improve considerably soil nutrient status and plant productivity in low fertile soils. Methods: This study used two different methods to apply sewage sludge and sewage sludge biocharwith three replicates in a completely randomized block design. The experiment included (1) control, (2) mulch biochar (20 t/ha), (3) incorporated biochar (20 t/ha), (4) mulch sewage sludge (45 t/ha),and (5) incorporated sewage sludge (45 t/ha). This study aimed to investigate the potential benefits of sewage sludge and its biochar as mulch and incorporated into the top-soil for soil fertility, growth,yield, and shoot nutrient concentration of soybean and the effects of treatments on dry bulk density, water content, and mechanical resistance.Results: The results showed higher values of height, biological yield, grain yield, and number of pods in the biochar mulch treatments (116.5, 10627.01, 4180, and 71.2, respectively). Moreover, itwas determined that the addition of biochar and sewage sludge to soil resulted in increased shootnitrogen (N), phosphorous (P), and potassium (K) concentrations, soil P, soil K, and total soil N (TN) compared with the control plots. Results from this study also showed that biochar and sewage sludgehad positive impacts on the physical properties of soil. Bulk density and soil mechanical resistance were decreased, and volumetric water content was increased. Conclusion: Heating sludge removed all pathogens. It is recommended that short- and long-term studies be conducted in the region to investigate further increases in the combined biochar and sewage sludge application rates.

Nitrogen (N), Phosphorous (P), Potassium (K), Pathogens