Abstract
Abstract. Biochar application has received increasing attention as a means to trap recalcitrant carbon and enhance soil fertility. Hydrolytic enzymatic assays, such as β-glucosidase and phosphatase activities, are used for the assessment of soil quality and composting process, which are based on use of p-nitrophenol (PNP) derivatives as substrate. However, sorption capacity of biochar can interfere with colorimetric determination of the hydrolysed PNP, either by the sorption of the substrate or the reaction product of hydrolysis into biochar surface. The aim of the present work is to study the biochar sorption capacity for PNP in biochar-blended composting mixtures in order to assess its impact on the estimation of the colorimetric-based enzymatic assays. A retention test was conducted by adding a solution of known amounts of PNP in universal buffer solution (pH = 5, 6.5 and 11, corresponding to the β-glucosidase, acid and alkaline phosphatase activity assays, respectively), in samples taken at the initial stage and after maturation stage from four different composting piles (two manure composting piles; PM: poultry manure, CM: cow manure and two other similar piles containing 10% of additional biochar (PM + B, CM + B)). The results show that biochar-blended composts (PM + B, CM + B) generally exhibited low enzymatic activities, compared to manure compost without biochar (PM, CM). In terms of the difference between the initial and maturation stage of composting process, the PNP retention in biochar was shown higher at maturation stage, caused most probably by an enlarged proportion of biochar inside compost mixture after the selective degradation of easily decomposable organic matter. TThe retention of PNP on biochar was influenced by pH dependency of sorption capacity of biochar and/or PNP solubility, since PNP was more efficiently retained by biochar at low pH values (5 and 6.5) than at high pH values (11).
Highlights
Agricultural use of biochar has been receiving attention as an alternative strategy for mitigation of greenhouse gas (GHG) emission as well as improvement of soil properties
The measurement of enzymatic activities is utilized for the composting process and as an indicator of soil quality since they are involved in the dynamics of soil nutrient cycle (Jordan et al, 1995)
These hydrolytic enzymes are measured by colorimetric determination of pnitrophenol (PNP) which is formed as the reaction product of hydrolysis of different nitrophenyl derivatives used as a substrate: nitrophenyl-β-d-glucopyranoside (PNG) for βglucosidase activity, and p-nitrophenyl phosphatase (PNPP) for alkaline and acid phosphatase activities
Summary
Agricultural use of biochar has been receiving attention as an alternative strategy for mitigation of greenhouse gas (GHG) emission as well as improvement of soil properties. The measurement of enzymatic activities is utilized for the composting process and as an indicator of soil quality since they are involved in the dynamics of soil nutrient cycle (Jordan et al, 1995). These hydrolytic enzymes are measured by colorimetric determination of pnitrophenol (PNP) which is formed as the reaction product of hydrolysis of different nitrophenyl derivatives used as a substrate: nitrophenyl-β-d-glucopyranoside (PNG) for βglucosidase activity, and p-nitrophenyl phosphatase (PNPP) for alkaline and acid phosphatase activities. Even though several works on the relation between microbial measurements and biochar exposure have been reported (Durenkamp et al, 2010; Bailey et al, 2011; Luo et al, 2013), further research is required for understanding the biochar interaction from the chemical, physical and biochemical point of view. Thies and Rillig (2009) proposed the utilization of spiking assays with specific molecules as internal standard to overcome potential interferences in the estimation of the microbial parameters
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