Impacts of 1.5-Year Field Aging on Biochar, Humic Acid, and Water Treatment Residual Amended Soil

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While biochar research has progressed, there is relatively little field-scale data over time, which constrains our understandings of biochar’s “true” effects on soil quality and our ability to make appropriate recommendations to users, especially in comparison to other amendments. Thus, this study compares 2 successive years’ field-scale soil data with biochar and other amendments added to a scalped silty clay loam soil at an application rate of 0.5%. None of the amendments significantly affected any of the measured soil physicochemical properties and greenhouse gas emissions even after 1.5 years of field aging. However, some of the measured soil properties were significantly changed after the second year compared with those of the first year. On temporal scale, soil electrical conductivity and penetration resistance significantly increased under most treated soils, and soil available water capacity significantly increased only under biochar. Although no differences in soil properties were detected, there was a trend toward higher corn dry grain and biomass yields under biochar compared with those of the control. Biochar was able to reduce N2O emissions from soil, only in the first year, whereas gaseous emissions were not different from control in the rest of the experiment. Thus, the findings of this study suggest that the improvements in soil fertility due to biochar amendment were not because of changes in most of the observed physical properties of the soil, but some other effects (changes in microbial community or nutrient additions) may have controlled the crop yield. In addition, these data demonstrate that selected amendment application rate of 0.5% (wt/wt) was not sufficient to cause significant changes in most observed physical properties beyond 1.5 years of field aging, suggesting additional research using higher rate of application.

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