Evaluation of optical techniques for characterising soil organic matter quality in agricultural soils

Abstract

Keywords: SOM quality Hot-water extractable carbon Cold-water extractable carbon Fluorescence index EEM SUVA-254 1 H NMR Aromatic fraction A B S T R A C T Soil organic matter (SOM) is one of the main global carbon pools. It is a measure of soil quality as its presence increases carbon sequestration and improves physical and chemical soil properties. The determination and characterisation of humic substances gives essential information of the maturity and stresses of soils as well as of their health. However, the determination of the exact nature and molecular structure of these substances has been proven difficult. Several complex techniques exist to characterise SOM and mineralisation and humification processes. One of the more widely accepted for its accuracy is nuclear magnetic resonance (NMR) spectroscopy. Despite its efficacy, NMR needs significant economic resources, equipment, material and time. Proxy measures like the fluorescence index (FI), cold and hotwater extractable carbon (CWC and HWC) and SUVA-254 have the potential to characterise SOM and, in combination, provide qualitative and quantitative data of SOM and its processes. Spanish and British agricultural cambisols were used to measure SOM quality and determine whether similarities were found between optical techniques and 1 H NMR results in these two regions with contrasting climatic conditions. High correlations (p < 0.001) were found between the specific aromatic fraction measured with 1 H NMR and SUVA-254 (Rs = 0.95) and HWC (Rs = 0.90), which could be described using a linear model. A high correlation between FI and the aromatics fraction measured with 1 H NMR (Rs = À0.976) was also observed. In view of our results, optical measures have a potential, in combination, to predict the aromatic fraction of SOM without the need of expensive and time consuming techniques.

Developing a Soil Physical Quality Index (SPQi) for lowlands under different deployment times of no-tillage

“…Rainfed crops have been recently introduced into these soils, mostly cultivated under conventional tillage (CT) (Reis et al, 2016). The soybean has been an alternative for the traditional flooded rice-livestock sequence, but there is a concern with the sustainability of this production model, as no-tillage (NT) has proven more profitable and environmentally favorable in rainfed agriculture (Crittenden et al, 2015;Fernández-Romero et al, 2016;Raiesi and Kabiri, 2016) than other management systems.…”

Labile forms of carbon and soil aggregates

“…Labile fractions include various components of organic matter in soil, which are characterized by a short turnover. Cold (CWEOC) and hot (HWEOC) water extractable organic carbons are the most active pools of SOM and play an important role in the global carbon turnover (Bu et al 2011) and are a part of dissolved organic carbon (Zsolnay 2003;Fernández-Romero et al 2016). Carbon that is oxidizable with KMnO 4 (C L ) includes all organic components that are easily oxidizable with KMnO 4 , including the labile humus material and polysaccharides (Conteh et al 1999).…”

Antecedent soil moisture prior to freezing can affect quantity, composition and stability of soil dissolved organic matter during thaw

“…Hence, the amount and bioavailability of DOM released into the soil after frost under low moisture conditions was dependent on soil types, the degree of soil drying and freezing conditions.

Figure 6Comparison plots of humification index versus ( a ) fluorescence index and ( b ) biological index for water extracts of forest soils during thaw, together with different DOM data refering to results from Fernández-Romero et al . 62 , Hur et al . 63 , Tye et al .

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