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Background and aims: Agroecology practices can induce profound positive changes in soil physical and chemical properties, and inevitably influence soil biological properties and soil functioning. However, we still lack understanding of how soil biodiversity responds to agroecology practices and to what extent such practices, alone or combined, can be beneficial for soil functioning and ecosystem services. Understanding soil biological activities under different agroecology practices is important for predicting carbon cycling in agroecosystems. Methods: By taking advantage of a long-term agricultural experimental research station in northern France, we monitored soil microbes, nematodes and soil respiration over three to five years in response to agroecology practices that varied in the rate of nitrogen (N) fertilization (low vs high), the tillage type (deep vs reduced), and the crop residue management (retain vs removal). Results: Shifting from conventional to agroecology practices had a strong effect on microbial biomass, nematode community and soil respiration. Specifically, reduced N and reduced tillage significantly increased microbial biomass carbon, bacterivore and fungivore density. Perennial biomass crop significantly decreased total nematode density and herbivore density, but increased microbial biomass carbon. Perennial biomass crop also significantly increased the structure and maturity index, but decreased the plant parasite index. Structural equation modelling showed that microbial biomass carbon had a positive correlation with soil respiration in reduced nitrogen, reduced tillage, and residue removal treatments. Bacterivores had a positive correlation with omnivores/predators and soil respiration, while herbivores had a negative correlation with soil respiration in all the treatments. Conclusions: The different agroecological practices tested in this 5-year trial revealed the resilience of nematode communities and associated functions like CO2 respiration according to practices. [ABSTRACT FROM AUTHOR]

Background and aims: The use of summer cover crops (SCCs) as residue inputs in agricultural systems can lead to a potential environmental trade-off between the amount C and N retained and the emission of N as the potent greenhouse gas, nitrous oxide (N2O). Our objectives were to relate N2O fluxes to the quality of SCCs residues and to select SCCs species with high C and N addition and low N2O emissions.Methods: We measured SCC biomass production and N2O fluxes after SCCs termination - velvet bean, pearl millet, dwarf pigeonpea, sunn hemp, showy rattlebox and jack bean - under subtropical no-till conditions.Results: The N2O fluxes in the first 30 days after SCCs termination corresponded to 65% of cumulative N2O emissions measured during 165 days in 2010 and 150 days in 2011. The cumulative N2O emissions varied from 0.46 to 1.38 kg N ha-1 and were not proportional to aboveground biomass N addition. Cumulative N2O emissions were positively correlated to water-soluble C and N and the N content of crop residues and negatively correlated to cellulose and hemicellulose content. The N2O emission factor values varied from 0.24 to 0.64% and did not differ among SCCs.Conclusions: Sunn hemp and dwarf pigeonpea are the most suitable species for inclusion in crop systems because they combined high C and N input and low N2O emissions. [ABSTRACT FROM AUTHOR]

Background and aims: Crop residues and soil types play an important role in soil C and N storage. The objectives of this study were to quantify the effects of crop residue quality and interactions with soil type on soil C and N, in the short- and medium-term, and to determine the responses related to the priming effect (PE). Methods: Residues of vetch ( Vicia sativa L.), pea ( Pisum sativum L.) and wheat ( Triticum aestivum L.) crops with different chemical compositions and labelled with C and N were left to decompose on the surface of either a sandy-loam soil or a clay soil incubated under laboratory conditions at 25 °C for 360 days. We measured the total CO-C and CO-C emitted during decomposition, the soil mineral N content and the amounts of C and N remaining in both the surface residue particles and the bulk soil. Results: Over the short-term, the vetch residues decomposed faster than those of wheat and pea on the soil surface due to their more favourable chemical composition for biodegradation; after one year, however, this difference disappeared. We observed extra soil C mineralization in all cases, i.e., the PE was positive for all treatments and was directly related to the water-soluble (vetch > pea > wheat) and soil C contents (clay soil > sandy-loam soil). Conversely, the fate of the added N and net N mineralization differed considerably between the three residues and was strongly related to the initial N content of the residue. Conclusions: Crop residue quality and soil type affected the soil PE and soil C balance but not the fate of crop residue-C after one year. Net soil N mineralization was observed in all crop residues, with large early differences (vetch > pea > wheat), which were maintained on a medium-term basis. Our results emphasize the need to jointly consider C and N dynamics as well as short- and medium-term effects to manage agricultural and environmental services provided by the recycling of crop residues to agricultural soils. [ABSTRACT FROM AUTHOR]

Aims: The role of precipitation on the decomposition of residue mulches is of primary importance for the adequate management of nutrients in no-tilled agrosystems. The objective of this work was to understand the interactions between water dynamics and crop residue quality and their effect on carbon (C) and nitrogen (N) mineralization. Methods: The decomposition of two residue mixtures (wheat + alfalfa and maize + lablab) left at the surface of repacked soil columns, was studied under controlled conditions, at 20 °C over 84 days. Simulated rain pulses were either light and frequent or heavy and infrequent. A loamy soil (Luvisol) and a sandy soil (Ferralsol) were used. Results: The maize/lablab mulch remained wetter between rain pulses which induced greater decomposition than the wheat/alfalfa mulch. Frequent/light rain pulses maintained the mulches wetter between pulses than infrequent/heavy rain pulses, and therefore these mulches decomposed faster. The loamy soil favored the moistening of the mulch layer in contact with the soil which enhanced its decomposition, compared to the sandy soil. Conclusions: The water dynamics (water content of the mulches and soil, evaporation, and drainage) was highly modified by residue quality, rain regime and soil type, which in turn significantly affected the mineralization of C and N. [ABSTRACT FROM AUTHOR]

Background and aims: Our objective was to relate chemical composition of roots of a wide range of annual crops to root decomposition, so as to assess roots potential contribution to soil carbon (C). Methods: Roots from 20 different crops and 4 botanical families, collected under field conditions were incubated in soil for 120 days at 25 °C. The initial chemical composition of roots was determined. The C mineralization was assessed by the continuous measurement of CO release and using single exponential model. PCA analysis was used to explore qualitative pattern in root quality and decomposition. Results: PCA analysis showed that chemical characteristics (traits) differentiated plant families. The mineralization of root C varied greatly in terms of kinetics and in the total amount of C mineralized (36 % to 59 % of added C). Mineralization constant ( k value) was negatively correlated with hemicelluloses and positively with N content. Poaceae roots that combined high hemicelluloses, low cellulose and low total N, showed low degradation rate and cumulative C mineralization. Conclusions: The chemical composition of roots, as for the above-ground parts of plants, can correctly predict their rate of decomposition in soils. The taxonomic affiliation enhances the understanding of the chemical determinants of quality of roots. [ABSTRACT FROM AUTHOR]

Background and aims: The water storage properties of plant residues play an important role in the regulation of water retention and water transport in no-till agricultural soils. The objective of this work was to understand how the characteristics of crop residues determine their water absorption and retention properties. Methods: A range of eleven undecomposed crop residues and maize stem residue of different particle sizes at three stages of decomposition were characterized regarding their physical and chemical features. Water immersion for varying periods of time was used to determine the kinetics of water absorption and the maximal water storage for each type of residue. Results: The immersion time required to reach an equilibrium moisture content varied greatly according to the residue type, ranging from 6 to 30 h at 20 °C. The maximal water content ranged from 1.28 to 3.81 g HO g dry residue for undecomposed residues and increased with increasing decomposition. The proportions of cellulose, hemicellulose and lignin in the plant cell walls did not explain the water storage capacities. Differences in porosity, resulting from different tissue densities and the creation of pores during decomposition, were highly correlated with differences in water storage properties. Conclusions: The tissue density of plant residues, which can be inferred from simple characteristics of residue mass and volume, is a relevant criterion for explaining the maximal water storage capacity of plant residues. [ABSTRACT FROM AUTHOR]

To predict the environmental benefits of energy crop production and use, the nature and fate of biomass residues in the soil need to be quantified. Our objective was to quantify Miscanthus x giganteus biomass recycling to soil and to assess how harvesting time and N fertilization affect their characteristics and subsequent biodegradability. The quantification of aerial and belowground biomass and their sampling were performed on 2- and 3-year-old Miscanthus stands, either fertilized with 120 kg N ha year or not fertilized, in autumn (maximal biomass production) and winter (maturity). Plant biomass was chemically characterized (total sugars, Klason lignin, C/N) and incubated in optimum decomposition conditions (15°C, −80 kPa) for 263 days, for C and N mineralization. Accumulation of carbon in rhizomes and roots was 7.5 to 10 t C ha and represented about 50% of total plant biomass C. Senescent leaves represented about 1.5 t C ha year. All residues, especially the roots, had high lignin contents, while the rhizomes also had a high soluble content due to their nutrient storage function. The C mineralization rates were closely related to the chemical characteristics of the residue, higher sugar and lower lignin contents leading to faster decomposition, as observed for rhizomes. [ABSTRACT FROM AUTHOR]

The biochemical characteristics or quality of crop residues is an important factor governing soil residue decomposition. To improve C and N biotransformation models the process underlying this decomposition needs to be better understood and new quality criteria found to describe it. The aims of this explorative study were to (i) improve our understanding of residue decomposition from detailed studies of cell wall biochemical compositions and tissue architecture (ii) find new ways of exploring generic indicators of organic matter quality. To do this, the cell wall composition and tissue architecture of wheat leaves, internodes and roots, before and after their incorporation into soil were determined. Results showed that leaves which were poorly lignified decomposed faster in soil than internodes and roots. Cellulose was the most degraded polysaccharide irrespective of wheat residue. However, cellulose was much more degraded in the case of leaves as compared to internodes and roots. Leaves also presented a highly condensed lignin structure and the extent to which uncondensed leaf lignin was affected by soil decomposition suggests that the contribution of leaf lignin to C mineralization during incubation was very low. Roots which contained similar amounts of lignin than the internodes decomposed more slowly. Roots were enriched in phenolic acids, and more particularly p-coumaric acid (pCA) and presented a more condensed lignin structure than internodes. Phenolic acids are involved in the formation of lignin–polysaccharide complexes known to be recalcitrant to enzymatic attack. Microscopic investigations confirmed that the vessels were the most resistant tissues to decomposition in soil and this could be related either to their lignin content or to the quality of this lignin (condensed-like type lignin). Therefore, cell wall biochemical analyses have revealed that phenolic acids, which in their esterified form represent only 0.1–1% of plant dry matter, have cross link functions within the cell walls that could be of major interest in estimating soil residue degradability. Lignin quality (monomers, level of condensation) was another crucial criterion that could explain why residues with similar amounts of lignin decomposed at different rates in soil (roots vs. aerial parts). Visualization of residue cell walls before and after decomposition in soil underlined the interest of a microscopic approach coupled with image analysis. This study, corroborated by the extensive literature on forage digestibility, confirmed that the proportions of vascular tissue and sclerenchyma cells in plant material are determinant factors affecting plant degradability. In the future, classification of plant material based on these criteria could lead to the definition of new quality parameters for models of C and N biotransformation in soil. [ABSTRACT FROM AUTHOR]