Effect of Biochar and Manure on Soil Carbon Fractions and Microbial Activity of Eroded and Depositional Landscape Position.

Biochar has been proposed as a management strategy to improve soil physical and chemical properties and climate change mitigation. However, the effect of biochar on soil microbial activity is highly uncertain and few data from field experiments are available. Therefore, the objective of our study was to investigate the influence of biochar and manure on soil carbon fractions, enzyme activity, and microbial community structure in field conditions. Three plant based biochar materials, produced from carbon-optimized gasification of corn stover (Zea mays L.) (CS), ponderosa pine (Pinus ponderosa Lawson and C. Lawson) wood residue (PW), and switchgrass (Panicum virgatum L.) (SG); dairy manure (DM); and a mixture of manure and pinewood biochar (DMP) were applied at 10 Mg ha^-1 rate at depositional and eroded landscape positions. Soil samples were collected before planting, one month after planting and after harvesting soybean in 2015 (three years after the application biochar and manure). The results showed that application of biochar and manure significantly affected the carbon and nitrogen fractions, soil enzyme activity and bacteria to fungi ratio. However, biochar had minor effects on hot water and acid extractable carbon and fractions but manure significantly increased these carbon fractions. The addition of DM and DMP promoted fungi at eroded landscape position, where it was 114 and 87% higher as compared to control (CNT). Moreover, biochar and manure increased the beta-glucosidase and urease activity, and more profound effects were observed with manure application. The cold and hot water-extractable carbon and nitrogen positively correlated with beta-glucosidase and urease activity. However, long-term studies are recommended to determine the effects of biochar and manure on soil microbial activity using different rates under different environmental conditions.