Linking organic matter chemistry with soil aggregate stability: Insight from 13C NMR spectroscopy

Soil aggregation is considered as a crucial process in agro-system sustainability due to the role in soil physical, chemical and biological dynamics. Here we tested the hypothesis that the initial chemical traits of organic matter (OM) may help to explain the variability of soil aggregation dynamics after organic amendment. We characterized ten OM types (alfalfa litter, biochar, cellulose, glucose, green compost, maize litter, manure compost, meat powder, sawdust, and solid digestate) by 13C-CPMAS NMR and elemental chemical features to investigate the effects of amendment quality on soil aggregation. In a manipulative factorial experiment, dry samples (200 g) of three soil types (S1, S2 and S3) with different texture, high pH (7\u20139), and similar OM content, were incorporated with 4 g (2% w/w) of dry, 2 mm-grounded OM, incubated in mesocosms for 300 days under controlled temperature (18 \ub1 2 \ub0C night and 24 \ub1 2 \ub0C day), and sampled at 4 dates for measuring aggregation index (AI), based on water stability of soil aggregates (WSA). We found that meat powder and alfalfa litter induced a rapid initial increase of AI, exceeding that of the controls by one to two orders of magnitude, likely acting as a C source for microbes. Biochar incorporation in soil barely affected AI, with intermediate effects with other OM types. Considering C bond types corresponding to OM 13C-CPMAS NMR spectral regions, carbonyl C was only correlated to early AI, possibly due to overlapping signals of amide structures; O-alkyl C and di-O-alkyl C (carbohydrate fraction) were positively associated to AI, indicating a promoting effect on soil structure, while aromatic C fractions showed an opposite pattern, possibly related to aggregate protection by coatings associated to water repellency, or to direct aggregate internal binding. This study demonstrates that OM chemical quality plays an important role in soil aggregation process, with the molecular composition defined by 13C-CPMAS NMR spectroscopy being more predictive of aggregation dynamics compared to classical elemental features. As such, this study provides a significant novel contribution to clarify the relationships between OM chemistry and soil aggregation

Linking organic matter chemistry with soil aggregate stability: Insight from 13C NMR spectroscopy

Soil aggregation is considered as a crucial process in agro-system sustainability due to the role in soil physical, chemical and biological dynamics. Here we tested the hypothesis that the initial chemical traits of organic matter (OM) may help to explain the variability of soil aggregation dynamics after organic amendment. We characterized ten OM types (alfalfa litter, biochar, cellulose, glucose, green compost, maize litter, manure compost, meat powder, sawdust, and solid digestate) by 13C-CPMAS NMR and elemental chemical features to investigate the effects of amendment quality on soil aggregation. In a manipulative factorial experiment, dry samples (200 g) of three soil types (S1, S2 and S3) with different texture, high pH (7\u20139), and similar OM content, were incorporated with 4 g (2% w/w) of dry, 2 mm-grounded OM, incubated in mesocosms for 300 days under controlled temperature (18 \ub1 2 \ub0C night and 24 \ub1 2 \ub0C day), and sampled at 4 dates for measuring aggregation index (AI), based on water stability of soil aggregates (WSA). We found that meat powder and alfalfa litter induced a rapid initial increase of AI, exceeding that of the controls by one to two orders of magnitude, likely acting as a C source for microbes. Biochar incorporation in soil barely affected AI, with intermediate effects with other OM types. Considering C bond types corresponding to OM 13C-CPMAS NMR spectral regions, carbonyl C was only correlated to early AI, possibly due to overlapping signals of amide structures; O-alkyl C and di-O-alkyl C (carbohydrate fraction) were positively associated to AI, indicating a promoting effect on soil structure, while aromatic C fractions showed an opposite pattern, possibly related to aggregate protection by coatings associated to water repellency, or to direct aggregate internal binding. This study demonstrates that OM chemical quality plays an important role in soil aggregation process, with the molecular composition defined by 13C-CPMAS NMR spectroscopy being more predictive of aggregation dynamics compared to classical elemental features. As such, this study provides a significant novel contribution to clarify the relationships between OM chemistry and soil aggregation

Faster N release, but not C loss, from leaf litter of invasives compared to native species in mediterranean ecosystems

Plant invasions can have relevant impacts on biogeochemical cycles, whose extent, in Mediterranean ecosystems, have not yet been systematically assessed comparing litter carbon (C) and nitrogen (N) dynamics between invasive plants and native communities. We carried out a 1-year litterbag experiment in 4 different plant communities (grassland, sand dune, riparian and mixed forests) on 8 invasives and 24 autochthonous plant species, used as control. Plant litter was characterized for mass loss, N release, proximate lignin and litter chemistry by 13C CPMAS NMR. Native and invasive species showed significant differences in litter chemical traits, with invaders generally showing higher N concentration and lower lignin/N ratio. Mass loss data revealed no consistent differences between native and invasive species, although some woody and vine invaders showed exceptionally high decomposition rate. In contrast, N release rate from litter was faster for invasive plants compared to native species. N concentration, lignin content and relative abundance of methoxyl and N-alkyl C region from 13C CPMAS NMR spectra were the parameters that better explained mass loss and N mineralization rates. Our findings demonstrate that during litter decomposition invasive species litter has no different decomposition rates but greater N release rate compared to natives. Accordingly, invasives are expected to affect N cycle in Mediterranean plant communities, possibly promoting a shift of plant assemblages

Biochar and Compost Application either Alone or in Combination Affects Vegetable Yield in a Volcanic Mediterranean Soil

The aim of this work was to compare the application of biochar, compost, and their mixtures on soil fertility and crop yields using a volcanic Mediterranean soil. For this reason, three types of organic amendments (OAs) were selected: compost1, made from olive mill waste and orchard pruning residues; compost2, made from olive mill waste, animal manure and wool residues; and biochar made from beech wood pyrolyzed at 550 °C. When selected, the OAs were characterized chemically for organic carbon (OC), total N, pH, electric conductivity (EC) and the bulk fraction of organic matter using 13C CPMAS NMR spectroscopy. In addition, soil chemistry was analysed at the end of each year for the following parameters: pH, OC, total N, CaCO3, P2O5, NH4, FDA and EC. Results showed that biochar had the highest OC and the lowest N and EC compared to both composts. Moreover, 13C CPMAS NMR showed that biochar had the lowest content of O-alkyl, methoxyl- and alkyl-C and the highest content of aromatic-C. On the other hand, compost2 and compost2+biochar mixture reduced Aubergine yield by −60% and −40%, respectively, and tomato yield by −50% and −100%, respectively. Nevertheless, a significant increase in onion and rape yields were observed when compost1, compost1+biochar and compost2 were applied, while biochar and compost2+biochar significantly decreased the yield of these crops. Overall, our results highlight that the effect of OAs on crops yield is largely variable and influenced by the interaction with soil chemistry

Biochar and Compost Application either Alone or in Combination Affects Vegetable Yield in a Volcanic Mediterranean Soil

The aim of this work was to compare the application of biochar, compost, and their mixtures on soil fertility and crop yields using a volcanic Mediterranean soil. For this reason, three types of organic amendments (OAs) were selected: compost1, made from olive mill waste and orchard pruning residues; compost2, made from olive mill waste, animal manure and wool residues; and biochar made from beech wood pyrolyzed at 550 °C. When selected, the OAs were characterized chemically for organic carbon (OC), total N, pH, electric conductivity (EC) and the bulk fraction of organic matter using 13C CPMAS NMR spectroscopy. In addition, soil chemistry was analysed at the end of each year for the following parameters: pH, OC, total N, CaCO3, P2O5, NH4, FDA and EC. Results showed that biochar had the highest OC and the lowest N and EC compared to both composts. Moreover, 13C CPMAS NMR showed that biochar had the lowest content of O-alkyl, methoxyl- and alkyl-C and the highest content of aromatic-C. On the other hand, compost2 and compost2+biochar mixture reduced Aubergine yield by −60% and −40%, respectively, and tomato yield by −50% and −100%, respectively. Nevertheless, a significant increase in onion and rape yields were observed when compost1, compost1+biochar and compost2 were applied, while biochar and compost2+biochar significantly decreased the yield of these crops. Overall, our results highlight that the effect of OAs on crops yield is largely variable and influenced by the interaction with soil chemistry

Frequent Applications of Organic Matter to Agricultural Soil Increase Fungistasis

Soil–borne plant pathogens are among the most important limiting factors for the productivity of agro–ecosystems. Fungistasis is the natural capability of soils to inhibit the germination and growth of soil–borne fungi in the presence of optimal abiotic conditions. The objective of this study was to assess the effects of different soil managements, in terms of soil amendment types and frequency of application, on fungistasis. For this purpose, a microcosm experiment was performed by conditioning a soil with frequent applications of organic matter with contrasting biochemical quality (i. e., glucose, alfalfa straw and wheat straw). Thereafter, the fungistasis response was assessed on four fungi (Aspergillus niger, Botrytis cinerea, Pyrenochaeta lycopersici and Trichoderma harzianum). Conditioned soils were characterized by measuring microbial activity (soil respiration) and functional diversity using the BIOLOG EcoPlatesTM method. Results showed that irrespective of the fungal species and amendment types, frequent applications of organic matter reduced fungistasis relief and shortened the time required for fungistasis restoration. The frequent addition of easily decomposable organic compounds enhanced soil respiration and its specific catabolic capabilities. This study demonstrated that frequent applications of organic matter affected soil fungistasis likely as a result of higher microbial activity and functional diversity

Soil Aggregation in Relation to Organic Amendment: a Synthesis

Soil aggregation, a key aspect of soil physical health, is a crucial component of agroecosystem sustainability as it affects numerous soil processes and agroecosystem productivity. Application of organic amendment (OA) plays a vital role in improving soil aggregation. In this review, we provide a comprehensive synthesis and a critical assessment of the current state of knowledge in soil aggregation in relation to OA. We first highlight factors (such as soil texture and clay mineralogy, source and type of OA, OA application rate and frequency, and OA application mode) determining the effect of OA on soil aggregation. Secondly, we review how OA regulates soil aggregation and point out that OA improves soil aggregation mainly via: (i) increasing soil organic carbon (SOC) content where OA acts as an external source of SOC, (ii) promoting soil biotic activity where OA acts as a substrate for microbes, and (iii) increasing soil hydrophobicity, thus reducing aggregate turnover. Finally, we draw reader’s attention to the complex linkages between OA quality and soil aggregation. The OA quality defined by 13C-NMR spectroscopy in terms of organic C type can explain variable effects of OA on soil aggregation better than C/N and lignin/N ratio indices. Considering organic C types, OA rich in carbohydrate C fractions tends to induce rapid but short- and medium-term effects on soil aggregation, while OA riched in aromatic C fractions barely affects soil aggregation. We conclude that soil structure can be significantly modified through better agronomic practices of OA application which will enhance soil aggregation, reduce soil erosion, and subsequently increase overall productivity

Sugarcane bagasse: a potential low-cost biosorbent for the removal of hazardous materials

The contamination of surface water sources by organic and inorganic pollutants is a major concern in rapidly industrializing countries, and the removal of these potentially hazardous contaminants from the aquatic environment using environmentally friendly technologies is therefore crucial. Biosorption, the passive binding of pollutants using dead biomass, can be achieved using various low-cost agro-industrial residues, which are a convenient substitute to the existing technologies for removing pollutants from aqueous solutions. This review deals with the implementation of sugarcane bagasse as a cost-effective natural biosorbent. We have extensively reviewed the status of research into sugarcane bagasse-based biosorbents in raw and modified forms and explore their efficacy in the removal of pollutants. For this purpose, we considered the bagasse modification processes, modifying agents, and the effects of different experimental variables (for example, biosorbent dosage, initial pollutant ion concentration, solution pH and temperature, contact time, and adsorbent particle size) on the adsorption process and potential. Moreover, we propose the following important goals for future research: (1) determine the adsorption potential of sugarcane bagasse at pilot and industrial scales, (2) demonstrate the efficacies of biosorption techniques for real effluents, and (3) conduct a molecular modeling study to elucidate sugarcane bagasse-associated adsorption mechanism(s)

Linking plant phytochemistry to soil processes and functions: the usefulness of 13C NMR spectroscopy

The organic matter cycle is one of the most fundamental processes in ecosystems affecting the soil and controlling its functions. The soil complex microbiome is made up of thousands of bacterial and hundreds of fungal strains that coexist on the many different available organic carbon sources. In natural plant communities, freshly fallen leaf-litter and dead roots are subject to decomposition by a complex food-web composed of both microbial saprotrophs and invertebrate detritivores. The litter chemical composition varies dramatically among species in relation to plant life forms (conifer, broadleaf, nitrogen-fixing, graminoid) and, within species, with plant organs (leaf, root, woody tissues). This paper reviews the usefulness of advanced chemical technologies to study the composition of both plant litter and organic amendments, supporting the description of their mechanism of action and attention to their potential applications. First, a critical review is presented on the limitations of C/N and lignin/N ratios, still widely used as basic indicators of litter chemistry. Second, the potential of the solid state 13C-CPMAS NMR is reported as a powerful tool to assess the chemical composition of both litter and organic amendments. Finally, six different study cases are reported to provide evidence of the usefulness of such metabolomic approach for the description of organic matter chemistry aimed to an effective prediction of its impact on soil ecosystem functions

Species\u2010specific root proliferation of tree seedlings in tropical litter: do nutrients matter?

Litter decomposition mobilizes nutrients that sustain ecosystem productivity, but decomposition by\u2010products may also hamper root proliferation by phytotoxicity. The aim of this study was to assess the litter substrate preferences of tropical tree seedlings in relation to litter chemical traits. We characterized 44 litter types (11 species at four decomposition ages; 0, 30, 90 and 180 days) for nutrients (N, P, K, Mg, Mn, Na, Fe and Zn) and proximate chemical parameters (cellulose, extractive, lignin and C) and tested the effect of such litter materials on seedling root growth of Albizia procera, Dalbergia sissoo and Terminalia arjuna. Albizia procera root growth was inhibited by all litter types and ages, including conspecific materials, while different heterospecific litters had inhibitory or stimulatory effect on D. sissoo and T. arjuna root growth, compared to the control. Interestingly, inhibitory and stimulatory effects of heterospecific litters significantly changed with litter age, although with no clear\u2010cut pattern among target species and litter species and age, while conspecific litters consistently inhibited root growth when aged, but not when fresh. Litter nutrient, extractive, C, cellulose and lignin showed no consistent association with root growth of tested plants. Albizia procera root growth was positively associated with Na content and N:P ratio. Dalbergia sissoo root growth was positively associated to C:N and lignin:N ratios, and negatively to K, Na and Zn content. Finally, T. arjuna root was positively associated to cellulose and N:P ratio, but negatively to extractive. We conclude that studied nutrient, cellulose and lignin do not consistently explain the species\u2010specific response of root of tree seedlings to decomposing litter