Effect of biochar addition on soil active nitrogen fractions
Description
We carried out a field experiment on BC addition in abandoned grasslands on the Loess Plateau to elucidate the effects of BC application on soil active N fractions (e.g., DON, MBN, NH4+-N, and NO3--N) and soil properties (e.g., physicochemical properties, microbial biomass, and related enzyme activities, etc.) in the abandoned grasslands on the Loess Plateau. We hypothesized that (1) BC addition could significantly facilitate the accumulation of soil active N fractions, but excessive addition of BC might reduce this facilitation, and (2) BC addition led to significant variations in the soil factors that influence the characteristics of accumulation and transformation of soil AON and DIN fractions. Soil water content (SWC) and temperature (ST) were determined in situ by the drying differential method and thermometer (JM624, Jinming Instrument Co., Tianjin, China), respectively (Xie et al., 2024). SOC and dissolved organic carbon (DOC) were determined through the K2Cr2O7 oxidation method, while TN and TP were determined by the Kjeldahl method and molybdenum antimony colorimetric method, respectively (Liu et al., 2022; Cao et al., 2023). In addition, NH4+-N, NO3--N, and dissolved total nitrogen (DTN) were determined by KCl solution leaching-Kjeldahl nitrogen determination and UV spectrophotometry, respectively (Zhang et al., 2022b; Chen et al., 2024a). DON was the difference between the DTN and the contents of NH4+-N and NO3--N. Microbial biomass carbon (MBC) and MBN were determined by chloroform fumigation-K2SO4 extraction, and microbial biomass phosphorus (MBP) was determined by chloroform fumigation-NaHCO3 extraction (Zhang et al., 2022b; Mao et al., 2024). Urease (Ure) was determined by the urease colorimetric method (Ren et al., 2016), and β-1,4-N-acetylglucosaminidase (NAG) was determined by the p-nitrophenol colorimetric method of Liu et al. (Liu et al., 2023).
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Soil water content (SWC) and temperature (ST) were determined in situ by the drying differential method and thermometer (JM624, Jinming Instrument Co., Tianjin, China), respectively (Xie et al., 2024). SOC and dissolved organic carbon (DOC) were determined through the K2Cr2O7 oxidation method, while TN and TP were determined by the Kjeldahl method and molybdenum antimony colorimetric method, respectively (Liu et al., 2022; Cao et al., 2023). In addition, NH4+-N, NO3--N, and dissolved total nitrogen (DTN) were determined by KCl solution leaching-Kjeldahl nitrogen determination and UV spectrophotometry, respectively (Zhang et al., 2022b; Chen et al., 2024a). DON was the difference between the DTN and the contents of NH4+-N and NO3--N. Microbial biomass carbon (MBC) and MBN were determined by chloroform fumigation-K2SO4 extraction, and microbial biomass phosphorus (MBP) was determined by chloroform fumigation-NaHCO3 extraction (Zhang et al., 2022b; Mao et al., 2024). Urease (Ure) was determined by the urease colorimetric method (Ren et al., 2016), and β-1,4-N-acetylglucosaminidase (NAG) was determined by the p-nitrophenol colorimetric method of Liu et al. (Liu et al., 2023).