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Soil moisture strongly affects the balance between nitrification, denitrification and N2O reduction and therefore the nitrogen (N) efficiency and N losses in agricultural systems. In rice systems, there is a need to improve alternative water management practices, which are designed to save water and reduce methane emissions, but may increase N2O and decrease nitrogen use efficiency. In a field experiment with three water management treatments, we measured N2O isotopocule signatures (δ15N, δ18O and site preference, SP) of emitted and pore air N2O over the course of six weeks in the early rice growing season. Isotopocule measurements were coupled with simultaneous measurements of pore water NO3-, NH4+, dissolved organic carbon (DOC), water filled pore space (WFPS) and soil redox potential (Eh) at three soil depths. We then used the relationship between SP x δ18O-N2O and SP x δ15N-N2O in simple two endmember mixing models to evaluate the contribution of nitrification, denitrification, fungal denitrification to total N2O emissions and to estimate N2O reduction rates. N2O emissions were higher in a dry-seeded + alternate wetting and drying (DS-AWD) treatment relative to water-seeded + alternate wetting and drying (WS-AWD) and water-seeded + conventional flooding (WS-FLD) treatments. In the DS-AWD treatment the highest emissions were associated with a high contribution from denitrification and a decrease in N2O reduction; while in the WS treatments, the highest emissions occurred when contributions from denitrification/nitrifier-denitrification and nitrification/fungal denitrification were more equal. Modeled denitrification rates appeared to be tightly linked to nitrification and NO3- availability in all treatments, thus water management affected the rate of denitrification and N2O reduction by controlling the substrate availability for each process (NO3- and N2O), likely through changes in mineralization and nitrification rates. Our model estimates of mean N2O reduction rates match well those observed in 15N fertilizer labeling studies in rice systems and show promise for the use of dual isotopocule mixing models to estimate N2 losses. [ABSTRACT FROM AUTHOR]

In the Vietnamese Mekong Delta, soil quality and crop yield are steadily declining under rice monocultures with three crops per year. The objective of this study was to evaluate the medium-term effects of rotating rice with upland crops and adding organic amendments on rice yield, and to relate this to soil quality. A field trial with split-plot design including two factors and three replicates was carried out from 2017 to 2020, over the course of nine consecutive cropping seasons. Crop rotations and organic amendments were applied as main-plot and subplot factors, respectively. The rotations were (1) rice–rice–rice (R–R–R), (2) soybean–rice–rice (So–R–R), and (3) sesame–rice–rice (Se–R–R), while organic amendment treatments included (i) no amendment (NO-AM), (ii) compost of rice straw and cow manure (RS+CM), and (iii) sugarcane compost (SGC); the composts were applied at a rate of 2.0 t ha−1. The rotation cycle started with the so-called spring–summer (SS) season, followed by the summer–autumn (SA) season and ending with the winter–spring (WS) season. Rice yield significantly (p < 0.05) increased under organic amendments after nine growing seasons (2019–2020 WS), with an increment of 5.1% for RS+CM (7.07 ton/ha) and 6.1% for SGC (7.14 ton/ha). Contrary to our expectation, rotations with upland crops did not significantly increase rice yield. Rice yield significantly and positively correlated with an integrated soil quality index–SQI (r = 0.85) for the topsoil (0–15 cm), but not for the subsoil (15–30 cm). The increased availability of soil nutrients (Si and marginally also P) and improved soil physical properties probably induced by organic amendments, along with other soil properties under study, cumulatively attributed to enhanced rice yield. Repeated organic amendments thus becomes an effective management practice in improving soil quality under rice-based systems and could be applied to sustain rice yield in rice-producing regions with similar soil types and climatic conditions. Use of a SQI involving several soil quality indicators enables us to quantify the overall importance of soil fertility for rice yield versus other factors, and it provides an effective means of quantifying the integrated effect of improved management. Moreover, integrating a wide range of soil quality indicators in a SQI ensures its applicability across diverse settings, including different crop rotations and various soil types. [ABSTRACT FROM AUTHOR]

Sterilization (partial or full) is one of the most fundamental tools for studying the ecological roles of soil biota and notably soil fauna, but there is a lack of knowledge on how these techniques affect other soil- inhabiting micro-organisms (non-target), and on their recovery after sterilization. We investigated the effect of a partial soil sterilization with gamma (γ) irradiation (target dose of 6 kGy, proven to selectively remove the entire nematode community and higher soil fauna) on the soil microbial community and its recovery in a microcosm experiment during 12 weeks. We specifically studied the effects, following partial sterilization, of recovery time (4 sampling events after 1, 4, 8 and 12 weeks) on the microbial activity (activities of dehydrogenase and β-glucosidase, and nitrification), microbial biomass and microbial community composition (using PLFA analysis), in two soils of contrasting texture (silt loam and loamy sand). We also studied whether inoculation of finely sieved and homogenized soil powder (SP) from these same soils (containing prokaryotes, fungi and protists, but no metazoan organisms) would stimulate the microbial recovery process. Dehydrogenase activity was strongly reduced by γ-irradiation in the silt loam (and SP did not stimulate its recovery) but not in the loamy sand, whereas there was no effect of γ-irradiation on β-glucosidase activity in either soil. Nitrification was strongly affected in the loamy sand and did not yet recover by the end of the incubation (week12), but the SP inoculation brought nitrification to the level of the unirradiated control by week4. Surprisingly, nitrification rate was not affected by γ-irradiation in the silt loam. The factors "recovery time", "irradiation" and "SP inoculation" affected the microbial community composition (based on PLFA), but the direction of these changes did not seem to follow a clear pattern. These results urge to carefully consider the re-establishment of microbial activity in studies on the roles of micro- and mesofauna following selective sterilization, even after several months. Also, SP inoculation can be a useful way to stimulate the recovery of the nitrification process, which would be crucial in studies of the role of soil fauna in N dynamics. [ABSTRACT FROM AUTHOR]

Historic long-term P application to sandy soils in NW-Europe has resulted in abundant sorption, saturation and eventually leaching of P from soil to the groundwater. Although many studies recognize the control of site-specific factors like soil texture and phosphate saturation degree (PSD), the regional-scaled relevance of effects exerted by single factors controlling P leaching is unclear. Very large observational datasets of soil and groundwater P content are furthermore required to reveal indirect controls of soil traits through mediating soil variables. We explored co-variation of phreatic groundwater orthophosphate (o-P) concentration and soil factors in sandy soils in Flanders, Belgium. Correlation analyses were complemented with an exploratory model derived using ‘path analysis’. Data of oxalate-extractable Al, Fe, P and pH KCl , phosphate sorption capacity (PSC) and PSD in three depth layers (0–30, 30–60, 60–90 cm), topsoil SOC, % clay and groundwater depth (fluctuation) were interpolated to predict soil properties on exact locations of a very extensive net of groundwater monitoring wells. The mean PSD was only poorly correlated to groundwater o-P concentration, indicating the overriding control of other factors in the transport of P to the groundwater. A significant (P < 0.01) positive non-linear relationship was found between groundwater o-P concentrations and pH KCl for all depth layers. Likewise, lower SOC% (P < 0.01) and shallower groundwater level (MHL or MLL) corresponded (P < 0.01) with higher o-P concentrations. Groundwater o-P unexpectedly correlated positively to clay% and path analysis indicated this to be an indirect effect of the groundwater level. Path analysis furthermore indicated an important indirect control of pH on groundwater o-P concentrations and a considerable direct effect of P ox, 0-90 , Al ox, 0-90 and MHL. The fact that groundwater o-P concentration was stronger controlled by soil pH and groundwater table depth than by PSD indicates the likely oversimplification of the latter index to measure the long-term potential risk of P leaching. Accounting for controls on leaching not included in PSD via an alternative index, however, seems problematic as in Flanders for example groundwater o-P turned out to be higher in finer textured soils or soils with higher pedogenic Fe content, probably because of their lower pedogenic Al content and higher soil pH. Path analysis of extensive soil and groundwater datasets seems a viable way to identify prime local determinants of soil P leaching and could be further on used for ‘ground-truthing’ more complex P-migration simulation models. [ABSTRACT FROM AUTHOR]

The occurrence and spread of invasive woody species are a truly global phenomenon, but tropical regions seem to be particularly vulnerable due to high rates of soil degradation in combination with climate change, and limited resources for containment. There is increasing awareness that complete eradication programs are often not effective. The existence of many "controversial species," i.e., species with both negative and positive impacts, renders decision-making processes for management exceedingly complex. By providing a very extensive overview of the current state of knowledge on impacts and containment strategies of invasive woody species, we aim to help underpin such decisions. We discuss both negative impacts and potential benefits of invasive woody species, focusing on the two most important ones, namely animal fodder production and the positive impacts on soil functioning and soil quality. Invasive woody species can positively impact livestock production (1) indirectly by improving pasture quality because of improved soil quality and functioning, and (2) directly by supplying a high-quality protein component for animal fodder. Invasive woody species increase soil carbon sequestration and nitrogen and phosphorus availability depending on the density of the invader, its capacity to fix nitrogen, the quantity and quality of its litter, and the direct interactions between its roots and the soil microbial community. The balance between potential benefits and risks depends to a large extent on the interaction with the local environment (climate, soil, vegetation, and animals) and the socioeconomic context of each region. When an invasion process starts because there is no local predator, then management can target eradication or very strict containment. If the invasion is the result of strong disturbance of the ecosystem, then intensive but well-thought management of the invasive species would be the choice to be made, as this may help to restore the ecosystem. [ABSTRACT FROM AUTHOR]

The addition of exogenous organic matter (EOM) generally stimulates microbial activity and shapes soil structure, likely with stronger effects at a higher application dose. It is not known, however, if and how the application dose of EOM would impact its own mineralisation and that of native soil organic carbon (SOC) by such mediation of soil pore network structure. In 90-day soil incubation experiments, we compared mineralisation of ± 2 cm pieces of 13C-labelled ryegrass as EOM reference at two doses (0.5 g kg−1 vs. 5 g kg−1) and mineralisation of SOC in sandy loam and silt loam soils that were initially subjected to different degrees of disturbance, namely soil sieving at < 2 mm and < 10 mm. We found that the high EOM dose-induced mesoporosity (i.e. vol% increase of pore neck class > 300 μm class by 130% vs. unamended control) and macroporosity (i.e. EOM doses 0.5 g kg−1 and 5 g kg−1 increased the vol% of the 60–100 μm class by 80 and 120% vs. unamended control) formation in the sandy loam soil, whereas the porosity in the silt loam soil remained unaffected. The % of EOM mineralised was independent of EOM dose and therefore did not relate to the changes in soil pore network structure. However, the observed development of meso- and macropores in the sandy loam soil appeared to be associated with stronger stimulation of SOC mineralisation at increasing EOM dose (30% and 71% more SOC mineralisation at low and high dose vs. unamended control). In the silt loam soil, only the high EOM dose-stimulated SOC mineralisation vs. unamended control (28%) but soil pore network structure remained unresponsive to EOM dose. This suggests that stimulation of SOC mineralisation following EOM addition might also be in part linked to the formation of larger pores in the sandy loam soil, and that this stimulation is not always proportional to EOM dose. [ABSTRACT FROM AUTHOR]

Soil nematodes are the most abundant soil fauna, with a potential great impact on soil N mineralization via interaction with soil microorganisms. As a consequence, nematodes likely also influence soil N 2 O production and emission but the very few studies on this matter were carried out in simplified setups with single nematode species and in (highly) disturbed soil conditions. Here we measured soil N 2 O emissions in a 74-day incubation experiment in the presence or absence of the entire soil nematode community with minimal disturbance of the soil microbial community and soil nutrients. This was e.g. evidenced by readily recovery of nitrifiers after the mild and selective sterilization and soil powder inoculation. N 2 O emissions increased in the presence of nematodes, varying between soils +747.7 % in a loamy sand, +55.8 % in a loam, and +51.9 % in a silt loam cropland topsoil, in line with nematode abundance in these soils. In particular, the loamy sand soil showed an atypical N 2 O emission peak at the time of high nematode abundance. Soil nematodes also increased net N mineralization by +8.4, +6.8 and +4.75 %, in these respective soils and to a smaller extent C mineralization as well. The extra soil nitrate buildup and the overall net stimulation of N mineralization by nematodes could not or just slightly explain the observed increased N 2 O emission. This research revealed the important role of soil nematodes in regulating N 2 O emission, and further stresses the need to consider the change in community composition and activity of denitrifiers, and connectivity of soil pores, rather than the stimulation of N mineralization as potential explanations for this role of nematodes. • The effect of soil nematode community on N 2 O emission was tested in realistic soil microcosms. • Nematodes increased N 2 O emissions with organic amendment in loamy sand, loam, and silt loam soil. • Loamy sand soil showed an atypical peak of N 2 O emission with high nematode density present. • Soil nematodes increased N mineralization and to a smaller extent C mineralization. • The enhanced N 2 O emission was not mainly mediated by increased N mineralization. [ABSTRACT FROM AUTHOR]

Abstract: Twenty-two long-term measurements of direct N2O emissions from soils in an intensive agricultural area were used for the validation of the process-based DNDC model (version 8.3P). Model simulations were evaluated for temporal patterns of N2O, NH4 +, NO3 − and water-filled pore space (WFPS) and total N2O emissions. Several soil and crop input parameter adjustments to the model were evaluated but only the recalculation of the WFPS at wilting point and at field capacity, using pedotransfer functions, resulted in a clear improvement of the simulated variables (WFPS in all cases, N2O in some cases). Therefore, only this adjustment was made to DNDC 8.3P. This change, however, resulted for some cases (both cropland and grassland) in retardation of nitrate leaching and to a lesser extent of NH4 + to the deeper soil layers. The goodness of fit of the simulated temporal pattern of N2O varied considerably between sites. The total simulated N2O emissions from cropland showed a good agreement with the measurements, although there was a systematic overestimation of 7.4kgN2O-Nha−1. Grassland soils, in contrast, gave a low agreement between total simulated and measured N2O losses. On the basis of all measured data a regional emission factor of 3.16 with a 95% confidence interval of −0.89 to 7.21 could be calculated. DNDC simulations resulted in an emission factor of 6.49 with a 95% confidence interval of 4.04–8.93. The overall outcome of the N2O emission measurements and DNDC simulations were compared with several empirical regression models, which may be applicable for a temperate climate system. All of the tested regression models showed reliable results up to a N2O emission of 10kgN2O-Nha−1. Higher emissions, however, were systematically underestimated. Though DNDC both under- and overestimated specific sites, the general agreement, over the whole range between measurements and simulations of total N2O losses (simulations=0.82×meas.+6.2), was better than for the different regression models. [Copyright &y& Elsevier]

Degradability of organic matter (OM) in soil depends on its spatial location in the soil matrix. A recent breakthrough in 3D-localization of OM combined dual-energy X-ray CT-scanning with OsO4 staining of OM. The necessity for synchrotron-based µCT and the use of highly toxic OsO4 severely limit applications in soil biological experiments. Here, we evaluated the potential of alternative staining agents (silver nitrate, phosphomolybdenic acid (PMA), lead nitrate, lead acetate) to selectively enhance X-ray attenuation and contrast of OM in CT volumes of soils containing specific mineral soil particle fractions, obtained via lab-based X-ray µCT. In comparison with OsO4, administration of Ag+ and Pb2+ resulted in insufficient contrast enhancement of OM versus fine silt (< 20 µm) or clay (< 2 µm) mineral particles. The perfusion procedure used in this work induced changes in soil structure. In contrast, PMA staining resulted in a selective increase of OM's attenuation contrast, which was comparable to OsO4. However, OM discrimination from other soil phases remained a challenge. Further development of segmentation algorithms accounting for grey value patterns and shape of stained particulate OM may enable its automated identification. If successful in undisturbed soils, PMA staining may form an alternative to OsO4 in non-synchrotron based POM detection. [ABSTRACT FROM AUTHOR]

The rising demand for feed and food has put an increasing pressure on agriculture, with agricultural intensification as a direct response. Notwithstanding the higher crop productivity, intensive agriculture management entails many adverse environmental impacts. Worldwide, soil organic carbon (SOC) decline is hereby considered as a main danger which affects soil fertility and productivity. The life cycle perspective helps to get a holistic overview when evaluating the environmental sustainability of agricultural systems, though the impact of farm management on soil quality aspects is often not integrated. In this paper, we introduce an indicator called Agricultural Biomass Productivity Benefit of SOC management (ABB_SOC), which, relying on natural resource consumption, enables to estimate the net effect of the efforts made to attain a better soil quality. Hereby the focus is put on SOC. First, we introduce a framework to describe the SOC trend due to farm management decisions. The extent to which remediation measures are required are used as a measure for the induced SOC losses. Next, ABB_SOC values are calculated as the balance between the natural resource consumption of the inputs (including remediation efforts) and the desired output of arable crop production systems. The models RothC and EU-Rotate_N are used to simulate the SOC evolution due to farm management and the response of the biomass productivity, respectively. The developed indicator is applied on several rotation systems in Flanders, comparing different remediation strategies. The indicator could be used as a base for a method to account for soil quality in life cycle analysis. [ABSTRACT FROM AUTHOR]

Both herbivorous and bacterivorous microfauna have been shown to influence root development, soil nitrogen (N) mineralization, and plant productivity. However, our knowledge of these effects is limited as multitrophic interactions remain largely unexplored. We investigated whether and how herbivorous nematodes (Pratylenchus zeae) and bacterivorous nematodes (Poikilolaimus oxycercus), alone and in combination, affect plant biomass (Lolium multiflorum) through root traits and/or soil N mineralization. Bacterivorous nematodes increased, whereas herbivorous nematodes decreased, plant productivity. We found that root trait coordination in response to soil microfauna was consistent with the concept of root economics space. The negative interaction between herbivorous and bacterivorous nematodes on plant productivity at high herbivorous nematode infestation could be explained by reduced N mineralization and variation in the root nitrogen concentration-root tissue density (RNC-RTD) axis aligned with increased herbivory intensity. This study revealed that herbivorous and bacterivorous nematodes moderated each other's effect on plant productivity via root trait coordination and N mineralization, and suggests, for the first time, the value of the root economics space concept for interpreting phenotypic root plasticity and functioning in response to local biotic factors. • We investigated whether and how microfauna interactively affect plant productivity. • Herbivorous and bacterivorous nematodes had a negative interaction on plant biomass. • The negative interaction was due to variation in N mineralization and root traits. • Root traits influenced by microfauna were in line with the root economics space. [ABSTRACT FROM AUTHOR]

Paddy soil indigenous N supply is often poorly related to N status and our aim was to assess its linkage to reduction of Fe 3+ and Mn 4+ , primary terminal electron acceptors in submerged soils. Transplanted rice was grown in the greenhouse in four Bangladeshi paddy soils with distinct SOC to Fe ox ratio (1.6 to 4.9) for 72 days firstly under continuous and then intermittent flooding. Solution buildup rates of Fe 2+ and Mn 2+ in the first 2–3 weeks of flooding correlated negatively with soil organic carbon (SOC) to NH 4 -oxalate extractable Fe (Fe ox ) and Mn (Mn ox ) ratios (p < 0.01). Mössbauer analysis detected ferrihydrite and goethite in all soils and with Mn 3 O 4 these are the likely source minerals. An electron (e − ) balance calculated from soil C-emission rates suggested reductive Fe and Mn dissolution to relevant e − -accepting processes, probably responsible for no >50% of e − capture, though. Reduction of abundantly present octahedral Fe 3+ in chlorites and vermiculite and their interstratified forms in these floodplain silty Inceptisols is hypothesized to also support microbial activity. Notwithstanding, a close temporal synergy existed between solution Fe and soil mineral N and their build-up rates were correlated (r: 0.77 to 0.90; p < 0.01) and with that of dissolved OC (DOC) (r: 0.84 to 0.96; p < 0.01), C emission rate (r: 0.99; p < 0.01) and SOC:Fe ox (r: −0.71; p < 0.01). These correlations suggest Fe 3+ reduction to be a relevant intermediary step in soil N mineralization, possibly through release of associated DOC, N or both. After switching to intermittent flooding dissolution of Fe, Mn and DOC were decoupled from mineral N release but since Eh remained in the Fe 3+ -reduction range in three out of four soils, possibly clay-Fe 3+ alternated with O 2 as e − -acceptor. Most importantly, in all soils N release slowed or halted after only 2 weeks of flooding but recommenced with intermittent flooding. As a next step, field experiments could verify if indigenous soil N supply also benefits from non-continuous irrigation management. Lastly, experimental proof is pending for release of clay-bound N and interlayer NH 4 + following reduction of octahedral Fe 3+ with consequent increased negative charge or structural destabilization, possibly an important process in floodplain paddy soils in Bangladesh. [ABSTRACT FROM AUTHOR]

Vermicomposting has recently been shown to be an efficient recycling technology that would improve the quality of the final product by stimulating the microbial community. However, the efficacy of vermicomposting process, as well as the microbial biomass and community structure during this bioconversion process, depend on earthworm species and type of substrate ingested. Therefore, this study investigated the potential of native (Eudrilus eugeniae) and exotic (Eisenia fetida and Eisenia andrei) earthworms in Ethiopia on nutrient transformation and microbial dynamics and enzymatic activity during vermicomposting of substrates from mixed agricultural wastes. Earthworm inoculation transformed the wastes into a nutrient-rich humified vermicompost with a significant reduction in pH, TOC and C:N ratios (twofold reduction compared to non-composted substrates). An increase in worm growth and cocoon production were shown in substrates of cow manure mixed with soybean and banana residues (CM + SB) after gut transit through Eudrilus eugeniae and Eisenia fetida. Cow manure mixed with maize and soybean residues (CM + MS) were found suitable for Eisenia andrei. The same substrate and earthworm species resulted in the highest nutrient concentrations (N, P, K, and S) and higher C loss (up to 77% of the initial C) with lower N loss (<9%) compared to non-composted substrates. A considerable increase in microbial biomass, β-glucosidase and dehydrogenase activity (two times more than control) was obtained in substrates of CM + SB using Eudrilus eugeniae. The PLFA analysis indicated that earthworms increased Gram-positive and Gram-negative bacteria, actinomycetes, AMF, fungi18:1, and protozoan population, while they reduced fungal community (fungi18:2 and fungi18:3) compared to uninoculated control. In conclusion, vermicomposting earthworms could potentially valorize substrates from agricultural wastes into nutrient-rich and microbially improved vermicomposts. [Display omitted] [ABSTRACT FROM AUTHOR]

Soil mesofauna play an essential role in soil functioning. However, in studies on the impact of agricultural management on soil quality, the overall abundance of soil mesofauna and specific groups thereof has not been widely used as an indicator in developing countries. Here, we used soil mesofauna as a soil quality indicator compared to more traditional soil chemical, physical, and microbial indicators, in a comparison of the impact of three diverse agricultural management systems in Central Cuba: state (CSt), conventional private (CPr), and organic private (OPr) farms. We sampled the top 20 cm of soil of 30 fields from 12 farms and 1 natural reference site (NR) and analysed a number of soil chemical, physical, and microbial soil parameters as well as mesofauna (Acari and Collembola, further subdivided into Mesostigmata–Prostigmata–Oribatida–Astigmata and Isotomidae–Entomobryidae, respectively). Differences in soil properties between agricultural fields and natural soil were observed (especially in the multivariate analysis), but no significant differences were observed between agricultural systems, probably due to a lack of differences in soil organic carbon (SOC) content. The mesofauna differed strongly between the NR and the two conventional management practices (CSt and CPr), both in total numbers and in group numbers for most groups and in both rainy and dry seasons, whereas there were almost no significant differences between NR and OPr. Principal component analysis based on mesofauna clearly distinguished NR from all farming systems and OPr from CSt and CPr. Differences in soil mesofauna were mainly attributed to the use of synthetic pesticides. We conclude that in this context, without clear differences in SOC content between agricultural fields, mesofauna is a superior soil quality indicator. Our results indicate that simple counts of total abundance are as useful as counts of specific mesofauna groups irrespective of the sampling period (dry or wet season). [ABSTRACT FROM AUTHOR]