Bioturbation represents an important pathway controlling soil microplastic bioavailability and fate, yet existing evidence remains qualitative and biased toward earthworm-mediated vertical transport. Here, we quantified horizontal redistribution of small (2–50 µm) fluorescent microplastics by enchytraeids in vitro and in soil microcosms using direct detection of the microplastics. Enchytraeids significantly redistributed microplastics away from hotspots under both conditions, and transported 2 and 10 µm spheres more effectively than 50 µm spheres in vitro . In soil microcosms spiked with 2 µm microplastics (1.28 × 10⁶ ng), enchytraeids relocated 1×10³ ng over an average distance of 33.0 cm during 108 days of incubation. These results reveal a so far overlooked mesofauna pathway of horizontal microplastic redistribution that complements vertical transport in soils.

While several studies have shown that soil nitrogen (N) levels decline by introducing upland crops into paddy rice monoculture, the net effect onto soil N supply remains unclear. The study assessed whether crop rotation could improve soil N availability by enhancing mineralization and releasing fixed NH₄⁺–N under less-reducing conditions. As a secondary aim the effect of extra organic inputs on soil N supply and the N balance was investigated. A field experiment covering 7 growing seasons (2017–2020) was carried out in the Vietnamese Mekong Delta comparing three crop rotations (rice–rice–rice, sesame–rice–rice, soybean–rice–rice) with or without compost. Soil samples (0–15 cm and 15–30 cm) were collected from the third crop onward, and exchangeable NH₄⁺–N, NO₃⁻–N, fixed NH₄⁺–N, and plant N uptake were measured. Crop rotation did not affect exchangeable NH₄⁺–N but increased soil NO₃⁻–N at both depths, raising the risk of N losses. Crop rotation marginally increased fixed NH₄⁺–N, indicating N conservation. Organic amendments enhanced exchangeable NH₄⁺–N but did not affect topsoil fixed NH₄⁺–N. Neither rotation nor amendments alone increased plant N uptake. Overall, the N balance was negative with an imbalance in soil organic N and a gradual net loss of fixed NH₄⁺–N. Introducing upland crops into rice monoculture requires balancing trade-offs between improved N availability for plant uptake and enhanced susceptibility to N losses, emphasizing the need to develop balanced N management strategies in rice-based systems.

Hydrochar, a carbon-rich material derived from hydrothermal carbonization of biomass, has emerged as a promising soil amendment for enhancing carbon sequestration and promoting sustainable agricultural practices. However, the trade-offs between its stability, degradability, and energy inputs during production remain underexplored, particularly across diverse soil types. This study systematically evaluated the effects of hydrochars produced at varying temperatures (150, 180, 200, and 240 degrees C; denoted as H150-H240) on soil carbon mineralization (Cm) and net carbon sequestration in four representative paddy soils from Ningxia (N), Jiangsu (J), Guangxi (G), and Yunnan (Y). Results revealed that low-temperature hydrochars (H150-H180) significantly stimulated Cm (up to 127 %) due to their higher proportion of labile carbon, enhanced microbial biomass, and increased hydrolytic enzyme activities. In contrast, high-temperature hydrochar (H240) showed greater biological stability, with reduced Cm and higher humification coefficients (88-97 %), indicating potential for longterm carbon storage. Energy assessments demonstrated that while lab-scale hydrochar production led to net positive CO2 emissions (57-114 t CO2 ha- 1), scaling up substantially reduced the energy footprint. Notably, application of hydrochar to low-SOC soils (N, J) resulted in net carbon sequestration (up to -6.80 t CO2 ha- 1), whereas in high-SOC soils (G, Y), only high temperature hydrochar contributed to net carbon sequestration. These findings underscore the need to balance hydrochar production conditions and soil characteristics to optimize its climate mitigation potential. This study advances the cleaner production of soil amendments by integrating carbon stability, energy efficiency, and site-specific suitability, contributing to sustainable land management and climate-smart agriculture.

Micro- and nanoplastics (MNP) pose an emerging threat to soil ecosystems, with particular concern for small MNP (≤10 µm). Although small fluorescent MNP are widely used to track MNP distribution and transport in aquatic environments and organisms, analyses of small fluorescent MNP in soil remain qualitative. Here, we present the first direct quantification approach for MNP ≤2 μm in soil using fluorescence microscopy, with recoveries calculated from fluorescence area ratios between MNP in filtered soil suspensions and pure water. Direct detection yielded rapid and reliable quantification with recovery rates (49.1–53.1%) comparable to magnetic separation (60.4–61.7%) and about 7 times higher than conventional separation (6.8–7.5%). We established a robust calibration line (R² = 0.988) converting fluorescence area ratios to MP concentrations across a wide range (0.01–1000 mg/kg) in loamy sand, with systematic underestimation corrected through linear calibration. Under more realistic conditions (MP mixed with larger amounts of soil and incubated for 15 d), quantification yielded an average symmetric mean absolute percentage error ranging from 15% to 39%. The calibration curve was applicable across diverse soil types (R²= 0.979-0.998) and MNP sizes down to 500 nm (R²=0.961). This direct detection method provides a highly efficient, robust tool to advance mechanistic understanding of MNP behaviour and environmental hazards in soils.

Soil microbial carbon use efficiency (CUE), defined as the fraction of assimilated organic carbon allocated to microbial biomass, plays a central role in soil carbon cycling. In paddy soils, irrigation regime and exogenous organic carbon (EOC) amendment jointly alter oxygen availability and substrate supply, which are expected to shift microbial carbon allocation between growth and respiration. However, how these management practices influence microbial CUE via microbial physiological processes remains poorly understood. In this field experiment, straw and hydrochar were applied to paddy fields under flooding irrigation (FI) or controlled irrigation (CI) to assess their effects on dissolved organic carbon (DOC), microbial biomass carbon and nitrogen (MBC, MBN), microbial respiration (Rs), microbial growth and turnover, microbial community structure (PLFAs), and microbial CUE based on microbial growth measured by 18O-DNA incorporation. CI significantly increased soil MBC, MBN and DOC, accompanied by increases in Rs (33–47

Long-term compost addition often increases soil organic carbon (SOC) and improves soil structure, yet its effect on nitrous oxide (N2O) emissions remains uncertain. This study investigated N2O emissions from a 13-year compost amendment experiment with 11 Mg compost ha−1 year−1 on a sandy loam in Belgium. Emissions from a treatment with (Com) and without (NCom) compost addition were monitored over an entire year using static chambers. In year 13 since the start of the experiment, annual N2O emissions were slightly higher under Com than under NCom (5.361 vs. 4.835 kg N2O-N ha−1), but this difference was not statistically significant. Variation in soil mineral nitrogen content (Nmin) and water filled pore space (WFPS) through time strongly shaped the temporal emission pattern. During the potato growing season under a ridge-furrow system, emissions were monitored separately for each of these field positions. Cumulative emissions from both positions did not differ significantly, likely because higher Nmin in the ridge was counterbalanced by lower WFPS, while the opposite was observed in the furrow position, showing lower Nmin and higher WFPS. Potato yield was not significantly affected by compost application. These findings suggest that long-term compost addition does not substantially increase annual N2O emissions, and that although ridges and furrows show different Nmin and WFPS, these shifts may not translate into significant differences in cumulative N2O emissions.

Substantial input of exogenous organic matter (EOM) may be required to offset the projected decline in soil organic carbon (SOC) stocks in croplands caused by global warming. However, information on the effectivity of the EOM application dose in preserving SOC stocks is surprisingly limited. Therefore, we set up a 90 d incubation experiment with large soil volumes (sandy loam and silt loam) to compare the mineralization of EOM (13C-labelled ryegrass) and SOC as a function of three EOM application doses (0.5, 1.5, and 5 g dry matter kg−1 soil). The percentage of mineralized EOM was expected to increase linearly with a higher EOM dose in sandy loam soil and to level off in silt loam soil due to the limited O2 supply in order to maintain aerobic microbial activity. In the sandy loam soil, the percentage of mineralized EOM was not affected by EOM dose, while SOC mineralization increased proportionally with an increasing EOM dose (+49.6 mg C g−1 EOM). Likewise, the formation of microbial biomass carbon was proportional to EOM dose, suggesting no reduction in microbial growth efficiency at a higher C concentration. In the silt loam soil, a decreasing tendency in the percentage of mineralized EOM was apparent but could not be confirmed statistically. We therefore conclude that, as in the sandy loam, the proportion of EOM mineralization was not affected with an increasing EOM dose, while SOC mineralization increased at a higher rate than in the sandy loam soil (+117.2 mg C g−1 EOM). Consistently with this lack of response in the proportion of EOM mineralization to EOM dose, soil EH did not decrease with an increasing EOM dose, indicating no O2 limitations. In both soils, an increasing EOM dose possibly supplied energy for microbial growth and enzyme production, which, in turn, stimulated mineralization of native SOC (i.e. co-metabolism). The observed stimulation of soil macroporosity at higher EOM doses in the silt loam soil might have contributed to sustaining the aerobic conditions required for SOC mineralization. In sum, this experiment and our previous research suggest that EOM mineralization is mostly independent of EOM dose, but EOM dose modulates the mineralization of native SOC. Provisional C balances compared to unamended controls indicated that, at low doses, less C remained than when EOM was added at normal or high doses in sandy loam soil, while no effect was found in silt loam soil. These findings tentatively indicate that using larger EOM doses could help preserve more added EOM-C, but longer-term confirmation in the field will firstly be required before we can draw any conclusion for soil C management.

Research on microplastics (MP) in soils is much complicated due to the lack of dedicated (extraction) methodologies and strong matrix interferences for MP detection, and there is almost no research on the dynamics of the smallest MP in soil. In our research we first compared the possible detection of the smallest MP fraction (1-2 µm) by µ-Raman spectroscopy and fluorescence microscopy in matrices of highly varying complexity. Subsequently, we have demonstrated that it is possible to use fluorescent MP to monitor and measure the rate of the leaching process of small MP in soils under field conditions.In a first experiment, samples of pure quartz sand, soils with variable texture (sandy loam, silt loam, clay loam) and removal of native soil organic matter (SOM), and a sandy loam soil with native SOM still present were amended with fluorescent polystyrene (PS) microparticles (diameter 1.7 µm) in different concentrations ranging from 0.1 to 0.001%. After mixing and compaction both the Raman spectra and fluorescence microscopy images were obtained. Characteristic PS Raman fingerprint peaks (main peak at 1001 cm-1) were visible in quartz sand (all concentrations) as well as in sandy and silt loam soils without SOM (some concentrations), but not in the other situations, whereas fluorescence microscopy clearly visualized the MPs at all concentrations in all matrices.In a second experiment, fluorescent PS microparticles were amended under field conditions to a sandy loam soil on a small surface area (circles of ± 0.2 m diameter), to a depth of 3 cm and at a rate of 70 mg kg-1 soil. At regular time intervals, samples were taken up to a depth of maximally 100 cm. The results of the experiment demonstrate the fast process of downward transport of the MP, reaching a depth of 30 cm after only 40 days and subsequently moving further through the vadose zone to get into range of the fluctuating groundwater table. Unambiguous fluorescent MP detection in real soil thus opens up new avenues for monitoring the vertical redistribution of the smallest MP fractions in the soil profile.

With climate change expected to intensify the occurrence and severity of droughts, the impacts of the groundwater table (GWT) depth and capillary rise on topsoil moisture may become critical drivers of biological activity. Consequently, the GWT depth could influence topsoil carbon (C) mineralization. In this study, undisturbed 200 cm long soil columns with three different textures (loamy sand, sandy loam and silt loam) were subjected to two artificial GWT depths (−165 and −115 cm) in the laboratory. We examined (1) upward moisture flow by capillary action along the soil profile, specifically into the top 20 cm of soil, and (2) the effect of the GWT on the decomposition of an added 13C-enriched substrate (ryegrass) over a period of 10 weeks, with limited wetting events representing a dry summer. A 50 cm difference in the GWT depth (−165 vs. −115 cm) resulted in different topsoil moisture values for the sandy loam (31 % vs. 38 % water-filled pore space – WFPS) and silt loam (33 % vs. 43 % WFPS) soils. In the loamy sand soil, GWT-induced moisture differences appeared only up to 85 cm above the GWT. The expected acceleration of the mineralization of the added ryegrass under a shallower GWT was not confirmed. In contrast, CO2 efflux pulses after some of the wetting events were even higher for the drier −165 cm GWT than for the −115 cm GWT across all three soil textures. Additionally, a model fitted to cumulative ryegrass mineralization showed a lower mineralization rate for the stable Cryegrass pool in the silt loam soil with the shallowest GWT, where capillary rise contributed most significantly to topsoil moisture, compared with other combinations of soil texture and GWT depth. These findings suggest that the upward capillary moisture flow, along with the resulting increase in topsoil moisture and the anticipated enhancement of biological activity and ryegrass mineralization, might have been counteracted by other processes. One possible explanation could be that rewetting may have triggered a stronger mineralization response, commonly known as the Birch effect, in drier topsoils compared with conditions in which the soil remained consistently wetter with a shallower GWT level. Based on our findings, inclusion of the process of texture-specific capillary supply from the GWT is required to adequately simulate moisture in the topsoil during droughts as they occurred over the past summers in northwestern Europe, depending on the GWT–texture combination. However, the net effect on topsoil C mineralization is complex and warrants further investigation, including the integration of processes related to fluctuations in soil moisture following rewetting.

The study of microplastics (MP) in soils presents significant challenges due to the absence of standardized extraction techniques and the strong matrix interferences that complicate MP detection, particularly for the smallest particle sizes. As a result, little is known about the behavior and dynamics of these minute MP in soil environments. In this study, we assessed and compared the direct detection of fluorescently labelled small MP (1-2 μm) using Raman and fluorescence microscopy across matrices with varying complexity. We introduced fluorescent polystyrene (PS) microparticles (1.71 ± 0.03 μm in diameter) into different substrates-pure quartz sand and soils with distinct textural properties (sandy loam, silt loam, and clay loam). The soils were analyzed both with and without prior removal of native soil organic matter (SOM). MP were added at concentrations ranging from 0.1 % to 0.001 % (corresponding to a range of natural concentrations), after which their detection was evaluated using μ-Raman and fluorescence microscopy. Raman analysis successfully identified characteristic PS peaks (notably at 1001 cm-1) in quartz sand at all tested concentrations and, to some extent, in sandy loam and silt loam. However, detection failed in clay loam and in all soil samples still containing the native SOM. In contrast, MP across all concentrations and soil types were consistently visualized by fluorescence microscopy. Furthermore, fluorescent PS particles were directly observed via fluorescence microscopy in field samples collected from an experiment where MP downward transport was monitored, whereas detection was challenging with Raman microscopy. The ability to directly and unequivocally identify fluorescent MP in complex soil matrices eliminates the need for time-intensive extraction methods and offers new opportunities for investigating the movement and behavior of the smallest MP fractions in soil.

Ubiquitous microplastics (MP) have emerged as a global environmental concern. However, limited attention has been given to the migration and distribution of small-sized MP (< 10 μm) due to the challenges associated with separating MP. Here, we show that magnetic labelling of MP greatly increases the efficiency of MP extraction from soil using a magnetic field. Magnetic labelling was achieved by exploiting the glass transition of polystyrene MP sphere. By heating MP (4 µm), to induce a surface transition to rubbery state in a suspension containing Fe3O4 magnetic nanoparticles (MNS), the MNS were adsorbed onto the MP surface. Subsequent cooling to room temperature, led to fixation of the MNS into the MP surface layer enabling MP extraction using a magnet. Incubating MP and MNS at 90°C for 2.5 h gave the highest MP recovery rate of 92 % in water. The same MP were added to sandy soil to optimize labelling and extraction. Optimized parameters included dispersant type, organic matter digestion, and MNS size, concentration, and storage time. Compared to conventional MP detection methods, the MP recovery using magnetic extraction improved from 26 % to 93 %. To the best of our knowledge, this research represents the first successful quantitative extraction of MP < 10 μm from soil.

Intensified droughts under future climate are threatening agricultural production in Western Europe. As a consequence, there is a growing interest in soil amendments that have the capability to enhance the water storage capacity of soils, increasing their resilience against drought. Chitin is a natural biopolymer known to hold potential to improve soil moisture retention. Considering the variable success of compost on soil hydrological properties documented in literature, enriching compost with a soil amendment such as chitin could potentially improve the functioning of the compost. An eight-week pot experiment with lettuce as test crop was set up under greenhouse conditions where multiple treatments consisting of a sandy loam soil mixed with 1 g kg-1 or 2 g kg-1 of crude chitin in its pure form, mixed with compost as chitin-enriched compost, and three types of pure compost were tested under two water regimes. The addition of crude chitin without compost, after this referred to as pure chitin significantly increased the readily available water defined as the macro-mesoporosity (30 mu m-3 mu m) and the plant available water after this referred to as the mesoporosity (30 mu m-0.2 mu m) under water regime 1, which comprised a sudden, dry period halfway the growing period of the crop. Under this water regime, the treatment with chitin-enriched compost resulted in a significant improvement in macro-mesoporosity and mesoporosity, when compared to the unamended compost. A different trend was obtained under the second water regime, featuring a cyclic pattern of dry periods, which points to the importance of the environmental conditions with regard to the functioning of chitin. These results highlight the potential of chitin-based amendments to enhance soil water retention properties, with their effectiveness strongly influenced by the prevailing water regime.

Soil aggregates play a pivotal role in soil organic carbon dynamics and microbial activity. However, their influence on the pressing issue of microplastic (MP) contamination in soils remains poorly understood. This lack of attention may be attributed to the inherent complexity and heterogeneity of soil, which renders plastic isolation and identification in soil is particularly challenging. This study aims to investigate MPs redistribution among soil aggregate fractions during the process of soil aggregation. Two soil textures (silt loam and sandy loam) were amended with organic matter (OM) to promote aggregation during a two-month incubation period, with 0.1 % microplastics powder added to the soils. A self-made pristine and aged LDPE and PET microplastics (

ABSTRACT To accurately predict soil organic carbon (SOC) stocks under a changing climate, models must properly integrate soil hydrological controls. In Northwest Europe, prolonged droughts are expected, during which capillary moisture transport may help maintain topsoil moisture. At present, the importance of capillary moisture supply for topsoil moisture during dry summers remains uncertain, and so it is not clear if account thereof during SOC stock simulation is needed. This study aimed to determine whether a ~2‐m deep groundwater table supplies moisture to topsoil during a dry summer and its effect on SOC mineralisation in six croplands across common textures (loamy sand, (sandy) loam and silt loam) in Flanders. We adopted a novel approach by installing repacked topsoil columns in situ within the plough layer, with or without a gravel layer below to act as a hydraulic barrier. In the loamy sand and (sandy) loam soils, groundwater tables of up to 2.3‐m depth appeared too deep to affect topsoil through capillary moisture transport in our setup since topsoil was even slightly wetter in the gravel treatment, likely due to impeded downward water redistribution following rainfall. This artefact could be avoided with deeper barrier placement. In contrast, in the silt loam fields with groundwater tables up to 2‐m depth, soil at a 15‐cm depth was significantly wetter (25% volumetric water content (VWC) and a matric suction of −405 cm water height (WH)) when upward water transport was unobstructed compared to when it was blocked by the gravel barrier (18% VWC and −445 cm WH) during a 1‐month drought period with very limited rainfall (5.8 mm). Surprisingly, this moisture increase via capillary rise did not enhance C mineralisation. Apparently, in these silt loam soils, C mineralization did not strongly depend on moisture, whereas in the coarser loamy sand soil, temporal moisture fluctuations had a greater impact on C mineralisation. This suggests that if capillary rise were to reach the topsoil, for instance with shallower groundwater, it could potentially influence C mineralisation. However, further research is needed to confirm this effect. Overall, whether groundwater moisture supply significantly impacted topsoil moisture and C mineralisation could only be evaluated in the silt loam croplands. Nonetheless, the proposed hydraulic barrier, with a recommended deeper installation, offers a promising tool for further testing conditions where capillary wetting may influence SOC dynamics.

Hydrochar is proposed as a climate-friendly organic fertilizer, but its potential impact on greenhouse gas (GHG) emissions in paddy cultivation is not fully understood. This two-year study compared the impact of exogenous organic carbon (EOC) application (rice straw and hydrochar) on GHG emissions, the net ecosystem carbon budget (NECB), net global warming potential (net GWP), and GHG emission intensity (GHGI) in a rice pot experiment using either flooding irrigation (FI) or controlled irrigation (CI). Compared with FI, CI increased ecosystem respiration by 23 - 44 % and N2O emissions by 85 - 137 % but decreased CH4 emissions by 30 - 58 % (p < 0.05). Since CH4 contributed more to net GWP than N2O, CI reduced net GWP by 16 - 220 %. EOC amendment increased crop yield by 5 - 9 % (p < 0.05). Compared with CK, hydrochar application increased initial GHG emission, net GWP and GHGI in the first year, while in the second year, there was no significant difference in net GWP and GHGI between CI-hydrochar and CK. Compared with straw addition, hydrochar amendment reduced net GWP and GHGI by 20 - 66 % and 21 - 66 %; and exhibited a lower net CO2 emission when considering the energy input during the hydrochar production. These findings suggest that integrated CI-hydrochar practices would be a sustainable and eco-friendly way for organic waste management in rice production as it holds potential to enhance the NECB and SOC sequestration of rice production, while also offsetting the extra carbon emissions from organic inputs.

Sustainable cropland management requires preservation of soil organic matter (SOM). In spite of in depth understanding gained from ample field and laboratory studies, we have a poor understanding of landscape scale spatial variation of fresh organic matter (OM) decomposition and its conversion into soil organic carbon (SOC). Particularly, local topographic position may be expected to co-control these processes via soil hydrology. In this study, we sought to identify if such control is significant by setting up a field experiment with two contrasting positions across 10 gently sloping cropland fields covering three different soil texture groups, i.e. loamy sand, (sandy) loam and silt loam. We wanted to link OM decomposition to within-field differences in soil moisture, whilst keeping variation in other soil and management factors minimal. Specifically, mesocosms with 13C enriched ryegrass (the OM source) were incorporated in the fields for ten weeks and afterwards, soil was separated into > 500 mu m, 53 - 500 mu m and < 53 m sized fractions. Overall, we found that lower located positions were wetter than higher positions with average differences of 11 %, 20 % and 16 % in water-filled pore space for the loamy sand, (sandy) loam and silt loam soil, respectively. Mineralization of added OM was surprisingly independent of landscape position, even though moisture conditions appeared wetter than optimal at the low but not at the high landscape positions. Remaining ryegrass residues > 500 mu m did follow local topography-driven gradients in soil moisture with higher amounts in low landscape positions. In other words, drier conditions at high landscape positions improved coarse OM decomposition, with consequently more ryegrass-carbon (C) ending up in finer soil fractions (< 500 m). Additionally, soil texture affected decomposition of the smallest fraction (< 53 m) with a stabilizing effect for finer-textured (silt loam) soils. We conclude that, despite significant contrasts in moisture conditions between landscape positions, within-field spatial variability of OM mineralization was overall limited during the observed wet summer period. Nevertheless, landscape position affected the quality of remnant unmineralized C, with relatively more conversion of freshly added OM into OM associated with silt and clay at the drier higher positions, potentially improving the long-term stability of SOM. Likewise observations under different weather conditions are needed to evaluate the necessity of precise modelling of local soil hydrology for predicting SOC stock evolution on the landscape scale.

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.

Soil nematodes, being the most abundant soil fauna, can significantly impact soil N mineralization via interaction with soil microorganisms. As a consequence, nematodes likely also influence soil N2O production and emissions 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 N2O 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. N2O 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 N2O 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 N2O emissions. This research revealed the important role of soil nematodes in regulating N2O emissions, 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.

Manure is used as a source of nutrients and organic matter for agricultural lands, but its unbalanced use has unfortunately made nitrogen (N) and phosphorous (P) leakage to the environment quite common in Western Europe. One way to optimize the use of manure is variable rate (VR) application, wherein within field spatial variability of soil nutrient provision is accounted for. This work evaluated the economic and environmental benefits of a P-based VR manure application and compared it to an N-based uniform rate (UR) application. An on-line visible and near-infrared spectroscopy sensor was used to collect on-line spectral data from soils in two fields of 7.9 and 5.1 ha with barley and wheat, respectively, in Belgium. A calibration model to predict extractable P (P) in soil was developed by partial least squares regression. Based on the locally predicted P level, the P-fertilizer application rate was calculated. According to P2O5 content in manure, manure application rates were set based on the level of soil P measured with the on-line soil sensor. Based on application maps, a strip experiment was conducted to compare the efficiency of VR and UR treatments. The results showed that P-based VR manure application resulted in almost the same yield as the UR treatment; however, it saved the environment by reducing N by 44 kg/ha and 29 kg/ha, and P2O5 by 18 kg/ha and 12 kg/ha, when applied in the two fields. Since farmers received compensation from the manure providers for allowing the manure to be applied in their fields, the P-based VR manure application using less manure has resulted in a smaller gross margin than the N-based UR method, by which more manure was applied. However, if farmers had to pay for this application (as is the case in some European countries), a P-based VR manure application would result in positive gross margins. It is encouraged to adopt VR manure applications in arable crop production, as both economic and environmental benefits are feasible.