Seasonal dynamics of soil microbial activity after biochar addition in a dryland maize field in North-Western China

- Contrast effects of biochar on soil microbial biomass carbon (MBC) and nitrogen (MBN) in two years were observed.
- Biochar increased microbial biomass P (MBP) and alkaline phosphatise activity.
- Biochar had no effect on soil urease activities in both years.
- Soil microbial activities showed shifts due to biochar application.
- Soil factors combined with biochar rate might explain the contrast effects of biochar.

Soil microbes are of great importance in assessing key ecosystem functions due to their high sensitivity and capacity of providing ecologically relevant information. Benefits of biochar have been demonstrated, including enhancing carbon (C) sequestration and improving soil fertility. Considerable attention has been taken to effects of biochar on soil properties; however, information regarding effects of biochar on seasonal changes of soil microbial activities in field experiments in dryland soil was not well known. Based on a 2-year spring maize (Zea mays L.) field experiment, we examined changes in soil microbial biomass carbon (MBC), nitrogen (MBN), phosphorus (MBP), urease and alkaline phosphatase activities with three biochar application rates (0, 10, and 30 t ha−1) at 0-10 cm and 10-20 cm soil layers in year 2013 and 2014 in silty loam soils on the Loess Plateau in North-Western China. Our results indicated that biochar increased MBC except at silking stage (R1) in 2013, whereas it tended to decrease MBC except at 6-leaf stage (V6) in 2014. MBN in the shallower (0-10 cm) soil layer in 2013 and MBP in 2014 generally increased with biochar rates. Significant positive correlations between microbial biomass and soil water content (SWC) were observed. Results also showed that there were considerable fluctuations in enzymes activities across the growth periods and depths. Biochar significantly increased alkaline phosphatase activities in 2014, and resulted in small but detectable shifts in soil urease activities in both years. These results provided evidence that biochar addition could be an effective management practice for soil microbial activities throughout crop growing season in a dry agricultural system, although soil factors from different climates might lead to some shifts of effects of biochar.