Indicators Of Soil Organic Matter Quality Research Articles

Temperature Sensitivity of Topsoil Organic Matter Decomposition Does Not Depend on Vegetation Types in Mountains.

Rising air temperatures caused by global warming affects microbial decomposition rate of soil organic matter (SOM). The temperature sensitivity of SOM decomposition (Q10) may depend on SOM quality determined by vegetation type. In this study, we selected a long transect (3.6 km) across the five ecosystems and short transects (0.1 km) from grazed and ungrazed meadows to forests in the Northwest Caucasus to consider different patterns in Q10 changes at shift of the vegetation belts. It is hypothesized that Q10 will increase along altitudinal gradient in line with recalcitrance of SOM according to kinetics-based theory. The indicators of SOM quality (BR:C, respiration per unit of soil C; MBC:C, ratio of microbial biomass carbon to soil carbon; soil C:N ratio) were used for checking the hypothesis. It was shown that Q10 did not differ across vegetation types within long and short transects, regardless differences in projective cover (14–99%) and vegetation species richness (6–12 units per plot). However, Q10 value differed between the long and short transects by almost two times (on average 2.4 vs. 1.4). Such a difference was explained by environmental characteristics linked with terrain position (slope steepness, microclimate, and land forms). The Q10 changes across studied slopes were driven by BR:C for meadows (R2 = 0.64; negative relationship) and pH value for forests (R2 = 0.80; positive relationship). Thus, proxy of SOM quality explained Q10 variability only across mountain meadows, whereas for forests, soil acidity was the main driver of microbial activity.

Determination of glomalin in agriculture and forest soils by near-infrared spectroscopy

Determining and characterizing soil organic matter (SOM) cheaply and reliably can help to support decisions concerning sustainable land management and climate policy. Glomalin was recommended as one of possible indicators of SOM quality. Extracting glomalin from and determining it in soils using classical chemical methods is too complicated and therefore near-infrared spectroscopy (NIRS) was studied as a method of choice for the determination of glomalin. Representative sets of 84 different soil samples from arable land and grasslands and 75 forest soils were used to develop NIRS calibration models. The parameters of the NIRS calibration model (R = 0.90 for soils from arable land and grasslands and R = 0.94 for forest soils) proved that glomalin can be determined in air-dried soils by NIRS with adequate trueness and precision simultaneously with determination of nitrogen and oxidizable carbon.

Overcoming carbonate interference on labile soil organic matter peaks for midDRIFTS analysis

Mid-infrared spectroscopy has been used with various degrees of success in quantitative and qualitative analysis of soil organic matter (SOM). This study evaluated the spectral interference caused by soil carbonates on the feasibility of using the specific peak area approach obtained by diffuse reflectance infrared Fourier transform spectroscopy in mid-range (midDRIFTS) as an indicator of SOM quality and composition. A midDRIFTS peak area corresponding to more labile SOM compounds (2930 cm−1) was related to microbial biomass carbon and nitrogen (Cmic, Nmic) and hot water extractable carbon and nitrogen (CHWE, NHWE) across two contrasting agroecological regions (Kraichgau (K) and Swabian Alb (SA), Germany) with soils containing carbonates up to 41 g kg−1 soil. Although, the 2930 cm−1 peak showed its potential use as an index for representing labile soil carbon, a poor regression performance between the relative peak area at 2930 cm−1 (rPAnt 2910 cm−1) and labile SOM fractions (R2 = 0.31–0.45) was attributed to inorganic carbon (IC) potentially interfering with this particular peak. To avoid carbonate interference, a spectral-based coefficient was developed using a multiple linear regression model consisting of TOC and TIC as predictors of the difference between peak areas at 2930 cm−1 of non-acid and acid treated spectra (ΔPA 2930 cm−1) of bulk soils. Peak areas at 2930 cm−1 of non treated spectra (PAnt 2930 cm−1) were corrected using a coefficient of 0.21 for carbonates (PAcorr 2930 cm−1), which greatly improved relationships with Cmic, Nmic, CHWE and NHWE (R2 = 0.68–0.75; P < 0.0001). We further developed a regression equation to correct PAnt 2930 cm−1 for future application using the relationship between PAnt 713 cm−1 (assigned for carbonates (mainly calcite)) and PA at 2930 cm−1 (ΔPATIC 2930 cm−1) (R2 = 0.98). We concluded that PA 2930 cm−1 has a high potential to be used as an indicator of SOM composition once carbonate interference is corrected for in carbonated containing soils. The proposed approach is free of multivariate calibration and the spectral index developed (PAcorr 2930 cm−1) is suited to predict accurately labile SOM without the need of additional laboratory measurements. For general applicability of the approach, it should be tested on additional soil types of varying TOC and TIC contents.

The influence of 12 years of tillage and crop rotation on total and labile organic carbon in a sandy loam soil

Information on which management practices can enhance soil organic matter (SOM) content and quality can be useful for developing sustainable crop production systems. We tested the influence of 12 years of no-till (NT) versus conventional tillage (CT), and four crop sequences on the organic C pools of a Grey Luvisolic sandy loam soil in northwestern Alberta, Canada. The crop sequences were: continuous wheat ( Triticum aestivum L.), field pea ( Pisum sativum L.)–wheat–canola ( Brassica rapa L.)–wheat, red clover ( Trifolium pratense L.) green manure–wheat–canola–wheat/red clover and fallow–wheat–canola–wheat. Soil samples from 1992, when the study was initiated, and 1996, 2000 and 2004 were analyzed for total organic C (TOC), the light fraction (LF) and its C content, and water-soluble and mineralizable C. Total organic C in the top 15 cm of soil was higher in the red clover rotation than either the pea or fallow rotation by 1996. The tillage effect became significant only in 2004 with NT having a higher TOC than CT. The LF dry matter (DM) increased from 6.9 g kg −1 soil in 1992 to a range of 10–13 g kg −1 in 2000 and 2004. It was higher under NT than CT in 2 of 3 years and in the red clover rotation than the pea or fallow rotation in 1 of 3 years. The LF C content exhibited a similar trend as LF DM. The water-soluble and mineralizable C pools were not affected by tillage but decreased with time. Among crop rotations, the red clover rotation tended to result in higher levels of hot water-soluble and mineralizable C. It is concluded that tillage had a greater influence than crop rotation on the LF DM and LF C (as indicators of C storage), whereas the converse effect applied to mineralizable C and, to a lesser degree, hot water-soluble C (as indicators of SOM quality).

Amino sugars in arctic soils

Amino sugars in soils are assumed to be of microbial origin. Their levels in soil, can provide insights into the microbial contribution to soil organic matter (SOM) and might serve as an indicator of SOM quality. Four amino sugars, glucosamine, galactosamine, mannosamine, and muramic acid were determined by gas chromatography in five soils from the tundra Alaska before and after incubation for 4 months at 4 and 25°C. Glucosamine and muramic acid analyses were utilized to represent fungal biomass and bacterial biomass, respectively. Total amino sugar N represented 0.8 to 3.3% of the total soil N in these five tundra soils, and the proportion of soil N as amino sugars increased with depth. Total amino sugar and fungal glucosamine N increased or remained constant during incubation at 4 and 25°C (except site 3 Cf horizon which decreased after incubation at 4°C), suggesting that total microbial biomass and fungal biomass increased. Bacterial biomass had an increase after incubation at 4°C, and a relative decrease at 25°C (except for Cf horizon). Fungal glucosamine to muramic acid ratios demonstrated that fungal biomass increased faster than bacterial biomass at 25°C, and slower at 4°C, indicating that at higher temperature, fungi dominated the microbial biomass in the soils studied. The mechanisms involved in the accumulation and decomposition of amino sugars in soil during incubation were not clear. No correlations were observed between the amino sugar contents and CO2 evolution during incubation, indicating that amino sugar abundance may not be an indicator of the bioavailability of SOM in soils. However, they can provide insights into the microbial contribution to SOM.