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An optimized spectroscopic method combining quantitative evolved gas analysis via Fourier transform infrared spectroscopy (FTIR-EGA) in combination with a qualitative in situ thermal reaction monitoring via diffuse reflectance Fourier transform infrared spectroscopy (in situ_T DRIFTS) is being proposed to rapidly characterize soil organic matter (SOM) to study its dynamics and stability. A thermal reaction chamber coupled with an infrared gas cell was used to study the pattern of thermal evolution of carbon dioxide (CO₂) in order to relate evolved gas (i.e., CO₂) to different qualities of SOM. Soil samples were taken from three different arable sites in Germany: (i) the Static Fertilization Experiment, Bad Lauchstädt (Chernozem), from treatments of farmyard manure (FYM), mineral fertilizer (NPK), their combination (FYM + NPK) and control without fertilizer inputs; (ii) Kraichgau; and (iii) Swabian Alb (Cambisols) areas, Southwest Germany. The two latter soils were further fractionated into particulate organic matter (POM), sand and stable aggregates (Sa + A), silt and clay (Si + C), and NaOCl oxidized Si + C (rSOC) to gain OM of different inferred stabilities; respiration was measured from fresh soil samples incubated at 20 °C and 50% water holding capacity for 490 days. A variable long path length gas cell was used to record the mid-infrared absorbance intensity of CO₂ (2400 to 2200 cm⁻¹) being evolved during soil heating from 25 to 700 °C with a heating rate of 68 °C min⁻¹ and holding time of 10 min at 700 °C. Separately, the heating chamber was placed in a diffuse reflectance chamber (DRIFTS) for measuring the mid-infrared absorbance of the soil sample during heating. Thermal stability of the bulk soils and fractions was measured via the temperature of maximum CO₂ evolution (CO_2max).

Results indicated that the FYM + NPK and FYM treatments of the Chernozem soils had a lower CO_2max as compared to both NPK and CON treatments. On average, CO_2max of the Chernozem was much higher (447 °C) as compared to the Cambisol sites (Kraichgau 392 °C; Swabian Alb 384 °C). The POM fraction had the highest CO_2max (477 °C), while rSOC had a first peak at 265 °C at both sites and a second peak at 392 °C for the Swabian Alb and 482 °C for the Kraichgau. The CO_2max increased after 490 day incubation, while the C lost during incubation was derived from the whole temperature range but a relatively higher proportion from 200 to 350 °C. In situ_T DRIFTS measurements indicated decreases in vibrational intensities in the order of C-OH = unknown C vibration < C-H < −COO/C =C < C = C with increasing temperature, but interpretation of vibrational changes was complicated by changes in the spectra (i.e., overall vibrational intensity increased with temperature increase) of the sample during heating. The relative quality c...

In temperate forest soils, N net mineralization has been extensively investigated during the growing season, whereas N cycling during winter was barely addressed. Here, we quantified net ammonification and nitrification during the dormant season by in situ and laboratory incubations in soils of a temperate European beech and a Norway spruce forest. Further, we compared temperature dependency of N net mineralization in in situ field incubations with those from laboratory incubations at controlled temperatures. From November to April, in situ N net mineralization of the organic and upper mineral horizons amounted to 10.9 kg N (ha · 6 months) -1 in the spruce soil and to 44.3 kg N (ha · 6 months) -1 in the beech soil, representing 65% (beech) and 26% (spruce) of the annual above ground litterfall. N net mineralization was largest in the Oi/Oe horizon and lowest in the A and EA horizons. Net nitrification in the beech soil [1.5 kg N (ha · 6 months) -1 ] was less than in the spruce soil [5.9 kg N (ha · 6 months) -1 ]. In the range of soil temperatures observed in the field (0-8°C), the temperature dependency of N net mineralization was generally high for both soils and more pronounced in the laboratory incubations than in the in situ incubations. We suggest that homogenization of laboratory samples increased substrate availability and, thus, enhanced the temperature response of N net mineralization. In temperate forest soils, N net mineralization during the dormant season contributes substantially to the annual N cycling, especially in deciduous sites with large amounts of litterfall immediately before the dormant season. High Q 10 values of N net mineralization at low temperatures suggest a huge effect of future increasing winter temperature on the N cycle in temperate forests.

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An optimized spectroscopic method combining quantitative evolved gas analysis via Fourier transform infrared spectroscopy (FTIR-EGA) and qualitative in situ thermal reaction monitoring via diffuse reflectance Fourier transform infrared spectroscopy (in situ_<i>T</i> DRIFTS) is being proposed to rapidly characterize soil organic matter (SOM) to study its dynamics and stability. A thermal reaction chamber coupled with an infrared gas cell was used to study the pattern of thermal evolution of carbon dioxide (CO₂) in order to relate evolved gas to different qualities of soil organic matter (SOM). Soil samples were from three different sites, i.e. (i) the Static Fertilization Experiment, Bad Lauchstädt (Chernozem) from treatments of farmyard manure (FYM), mineral fertilizer (NPK), combination (FYM + NPK) and control without fertilizer inputs, and cropped soils from the (ii) Kraichgau and (iii) Swabian Alb (Cambisols) areas, Southwest Germany. Soils from Kraichgau and Swabian Alb were further fractionated into particulate organic matter (POM), sand and stable aggregates (Sa + A), silt and clay (Si + C), and NaOCl oxidized Si + C (rSOC) to gain OM of different inferred stabilities. Fresh soil samples from the Kraichgau and Swabian Alb were incubated at 20 °C and 50% water holding capacity for 490 days in order to measure soil respiration under controlled conditions. A variable long path length gas cell was used to record the mid-infrared absorbance intensity of carbon dioxide (2400 to 2200 cm^&minus;1) being evolved during soil heating from 25 to 700 °C with a heating rate of 68 °C min⁻¹ during an initial ramping time of 10 min and holding time of 10 min. Separately the heating chamber was placed in a diffuse reflectance chamber (DRIFTS) for measuring the mid-infrared absorption of the soil sample during heating. Thermal stability of the bulk soils and fractions was measured via the temperature of maximum CO₂ (2400 to 2200 cm^&minus;1 evolution (CO₂). Results indicated that the FYM + NPK and FYM treatments of the Chernozem soils of Bad Lauchstädt had a lower CO₂max as compared to both NPK and CON treatments. On average CO₂max in Bad Lauchstädt was much higher (447 °C) as compared to the Kraichgau (392 °C) and Swabian Alb (384 °C) sites. The POM fraction had the highest CO₂ (477 °C), while rSOC had a first peak at 265 °C at both sites and a second peak at 392 °C for the Swabian Alb and 482 °C for the Kraichgau. The CO₂ was found to increase after 490 day incubation, while the C lost during incubation was derived from the whole temperature range but a relatively higher proportion from 200 to 350 °C. In situ_<i>T</i> DRIFTS measurements indicated decreases in vibrational intensities in the order of C-OH = unknown C vibration...