TY - JOUR

T1 - Analysis of peat soil organic carbon, total nitrogen, soil water content and basal respiration

T2 - Is there a ‘best’ drying temperature?

AU - Dettmann, Ullrich

AU - Kraft, Nicky Nancy

AU - Rech, Raimund

AU - Heidkamp, Arne

AU - Tiemeyer, Bärbel

N1 - Funding Information: We are grateful to Annika Feld for laboratory advice. We also thank Dominik Düvel, Adina Schlegel, Jessica Hügen and Lena Lüttjohann for their laboratory support. We would like to express our thanks to Kerstin Gilke and Andrea Oehns-Rittgerodt for their gas chromatograph analyses and to Prof. Dr. Rolf Nieder for his support. The samples originated from projects in the FACCE-JPI ERA-NET Plus project on Climate Smart Agriculture on Organic Soils (CAOS), which was funded by the German Federal Ministry of Education and Research (BMBF) under grant No. 031A543A (Arndt Piayda), the German Agricultural Soil Inventory funded by the German Federal Ministry of Food and Agriculture (Annelie Säurich), and SWAMPS funded by the European Regional Development Fund, the Lower Saxony Ministry of Food, Agriculture and Consumer Protection and the Lower Saxony Ministry of the Environment, Energy and Climate Protection. We appreciate Alexandra Elbakyan’s efforts in disseminating knowledge. We are grateful to Prof. Daniel Said-Pullicino as Editor and the anonymous reviewers for their helpful comments.

PY - 2021/12/1

Y1 - 2021/12/1

N2 - Soil needs to be dried in order to determine water content, soil organic carbon content (SOC) and total nitrogen content (N). Water content is commonly measured using standard methods that involve drying temperatures of 105–110 °C. Recommended drying temperatures differ for the determination of SOC and N. However, at moderate drying temperatures, microbial activity might lead to organic matter mineralisation and nitrification, and thus to an underestimation of SOC and N. Furthermore, low drying temperatures might not dewater soils sufficiently to correctly determine water content or bulk density. Chemical processes such as thermal decomposition and volatilisation might occur at higher temperatures. This raises the question of whether the same sample can be used to determine water content, SOC and N. Further, the effect of drying, especially at different temperatures, on basal respiration of peat soils determined by incubation experiments is so far unknown. Effects of drying temperature might be especially severe for peat soils, which have high SOC and water contents. This study systematically evaluated the effect of different drying temperatures (20, 40, 60, 80 and 105 °C) on the determination of mass loss (proxy for water content), SOC and N over a wide range of 15 different peat soils comprising amorphous, Sphagnum and sedge peat substrate. The investigated peat soils had SOC contents ranging from approximately 16.8–52.5% with different degrees of decomposition. They were thus separated into two ‘peat groups’ (amorphous and weakly decomposed). In a subsequent investigation, an incubation experiment was carried out on a subset of five peat soils to investigate the pre-treatment effect of different drying temperatures on basal respiration. The results showed that amorphous samples should be dried at 105 °C to determine water content. The weakly decomposed peat soils in the study had reliable water contents for drying temperatures above 60 °C. For temperatures below 80 °C, the determined SOC and N were biased by residual water. This could be corrected for weakly decomposed samples, but for amorphous samples only for drying temperatures ≥60 °C. Thus, mineralisation of soil organic matter is likely to take place at lower drying temperatures which are not recommendable especially for amorphous peat prone to high mineralisation rates. This is supported by the results of the incubation experiment: The effect of peat type (amorphous topsoil vs. weakly decomposed subsoil) was greater than the effect of different drying temperatures, which nonetheless affected respiration rates. The differences between all five soils were consistent, irrespective of the drying temperature. Thus, incubation experiments might be possible using peat dried at moderate temperatures.

AB - Soil needs to be dried in order to determine water content, soil organic carbon content (SOC) and total nitrogen content (N). Water content is commonly measured using standard methods that involve drying temperatures of 105–110 °C. Recommended drying temperatures differ for the determination of SOC and N. However, at moderate drying temperatures, microbial activity might lead to organic matter mineralisation and nitrification, and thus to an underestimation of SOC and N. Furthermore, low drying temperatures might not dewater soils sufficiently to correctly determine water content or bulk density. Chemical processes such as thermal decomposition and volatilisation might occur at higher temperatures. This raises the question of whether the same sample can be used to determine water content, SOC and N. Further, the effect of drying, especially at different temperatures, on basal respiration of peat soils determined by incubation experiments is so far unknown. Effects of drying temperature might be especially severe for peat soils, which have high SOC and water contents. This study systematically evaluated the effect of different drying temperatures (20, 40, 60, 80 and 105 °C) on the determination of mass loss (proxy for water content), SOC and N over a wide range of 15 different peat soils comprising amorphous, Sphagnum and sedge peat substrate. The investigated peat soils had SOC contents ranging from approximately 16.8–52.5% with different degrees of decomposition. They were thus separated into two ‘peat groups’ (amorphous and weakly decomposed). In a subsequent investigation, an incubation experiment was carried out on a subset of five peat soils to investigate the pre-treatment effect of different drying temperatures on basal respiration. The results showed that amorphous samples should be dried at 105 °C to determine water content. The weakly decomposed peat soils in the study had reliable water contents for drying temperatures above 60 °C. For temperatures below 80 °C, the determined SOC and N were biased by residual water. This could be corrected for weakly decomposed samples, but for amorphous samples only for drying temperatures ≥60 °C. Thus, mineralisation of soil organic matter is likely to take place at lower drying temperatures which are not recommendable especially for amorphous peat prone to high mineralisation rates. This is supported by the results of the incubation experiment: The effect of peat type (amorphous topsoil vs. weakly decomposed subsoil) was greater than the effect of different drying temperatures, which nonetheless affected respiration rates. The differences between all five soils were consistent, irrespective of the drying temperature. Thus, incubation experiments might be possible using peat dried at moderate temperatures.

KW - Carbon dioxide flux

KW - Mineralisation

KW - Soil incubation experiment

KW - Soil moisture

KW - Soil organic matter

UR - http://www.scopus.com/inward/record.url?scp=85107766128&partnerID=8YFLogxK

U2 - 10.1016/j.geoderma.2021.115231

DO - 10.1016/j.geoderma.2021.115231

M3 - Article

AN - SCOPUS:85107766128

VL - 403

JO - GEODERMA

JF - GEODERMA

SN - 0016-7061

M1 - 115231

ER -