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Although organic farming was originally promoted as an alternative farming system to address agronomic, environmental and ecological issues, its conventionalisation has led to an intensification and specialisation of production. In the light of this, several studies have questioned the environmental benefits of organic farming as well as its agronomic viability. Thus, there is a need to improve organic vegetable systems to reduce their environmental impact without affecting their productivity. To tackle this challenge, European farmers and researchers have recently started to focus on agroecological service crops (ASCs). However, few studies have simultaneously evaluated the agronomic, environmental and ecological aspects of ASC management under different European pedo-climatic conditions. We evaluated effects of the ASC management strategies—no-till roller crimping (NT-RC) and green manuring (T-GM) on cropping system performance using agronomic, environmental and ecological indicators—to exemplify the need for multidimensional analysis to understand management implications for addressing environmental and agronomic challenges. We combined the results from 11 organic vegetable field trials conducted in seven European countries over a period of 2 years to test for general trends. Our results provide solid evidence that NT-RC management across different pedo-climatic conditions in Europe enhances the activity density of ground and rove beetles and improves both the potential energy recycling within the system and weed control. However, in NT-RC plots, lower cash crop yield and quality, energetic efficiency of production and activity density of spiders were observed compared to T-GM. Synthesis and applications. Multidimensional analyses using agronomic, environmental and ecological indicators are required to understand the implications of agricultural management in agroecosystem functioning. Introducing agroecological service crops combined with the use of no-till roller crimping is a promising strategy for improving agronomic performance (e.g. fewer weeds) and reducing environmental (e.g. increasing the potentially recyclable energy) and ecological (e.g. enhancing the activity density of beneficial taxa such as ground and rove beetles) impacts. However, our study also indicates a need for agronomic and environmental improvements while promoting a wider acceptance of this strategy.

Research on microplastics (MP) in soils is much complicated due to the lack of dedicated (extraction) methodologies and the strong matrix interferences for MP detection, and there is almost no research on the dynamics of the smallest MP in soil. Here we 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. Samples of pure quartz sand, soil with removal of native soil organic matter (SOM), and soil with native SOM still present were amended with fluorescent polystyrene (PS) microparticles (diameter 1.65±0.04 µm) in different concentrations ranging from 0.1 to 0.001%, and after mixing and compaction both the Raman spectra and fluorescence microscopy images were obtained. Characteristic PS Raman peaks (main peak at 1009 cm-1) were visible in quartz sand (all concentrations) and soil without SOM (highest concentration only), but not in the other situations, whereas fluorescence microscopy clearly visualized the MP at all concentrations in all matrices. The possibility of direct and unambiguous fluorescent MP detection in real soil also circumvents the need for lengthy extraction procedures, and opens up new avenues for studying mechanistic aspects of the smallest MP fractions in soil.

Pseudomonas isolates from tropical environments have been underexplored and may form an untapped reservoir of interesting secondary metabolites. In this study, we compared Pseudomonas and cyclic lipopeptide (CLP) diversity in the rhizosphere of a cocoyam root rot disease (CRRD) suppressive soil in Boteva, Cameroon with those from four conducive soils in Cameroon and Nigeria. Compared with other soils, Boteva andosols were characterized by high silt, organic matter, nitrogen and calcium. Besides, the cocoyam rhizosphere at Boteva was characterized by strains belonging mainly to the P. koreensis and P. putida (sub)groups, with representations in the P. fluorescens, P. chlororaphis, P. jessenii and P. asplenii (sub)groups. In contrast, P. putida isolates were prominent in conducive soils. Regarding CLP diversity, Boteva was characterized by strains producing 11 different CLP types with cocoyamide A producers, belonging to the P. koreensis group, being the most abundant. However, putisolvin III-V producers were the most dominant in the rhizosphere of conducive soils in both Cameroon and Nigeria. Furthermore, we elucidated the chemical structure of putisolvin derivatives-putisolvin III-V, and described its biosynthetic gene cluster. We show that high Pseudomonas and metabolic diversity may be driven by microbial competition, which likely contributes to soil suppressiveness to CRRD.

Environmental concerns and rapidly decreasing phosphorus (P) resources caused a renewed interest in improving soil P tests for a more efficient P fertilization. This led to the development of better P fertilizer recommendation systems for major arable crops and grass. Nevertheless, these P fertilizer recommendation systems seem to fail for intensive vegetable crops, with often a very short growing season and limited rooting system. This leads to low P use efficiencies in the horticultural sector. In order to address this problem we set up a study to answer following questions: (1) which soil P test predicts the plant available P content for intensive vegetable crops the best and (2) can new insights, such as combining different soil P tests, improve P fertilizer recommendations for intensive vegetable crops? To this end, bulk samples of 41 soils with very different P status (based on ammonium lactate extractable P) were collected. The plant available P content of these soils was determined using six commonly used soil P tests (P‐CaCl2, P‐water, P‐Olsen, P‐acetate, P‐lactate, and P‐oxalate) and a P fertilizer pot experiment with endive (a very P sensitive vegetable crop) was conducted. Six pots of each soil were planted with endive. Three of these pots received no P fertilization (0P) and three pots received ammonium polyphosphate equivalent to 24 kg P ha−1 (24P). All other factors were kept constant. Relative crop yield of the 0P fertilized plants compared to the 24P fertilized plants was determined. Plotting these relative yields against the P status of the soil per soil P test allowed to fit a Mitscherlich curve through the data. Also the combination of two different soil P tests to predict the relative yield with a Mitscherlich equation was evaluated. The coefficients of variation of the soil P tests, the R2 values and the relative standard errors of the parameter estimates revealed that P‐acetate and P‐water predicted the relative yield of the 0P plants the best and that combining two different soil P tests gave no extra predictive power. This finding may form the basis for the development of a new P fertilizer recommendation system for intensive vegetable crops, leading to an improved P use efficiency in horticulture. In order to develop this new system more data relating soil P test values with RY of intensive vegetable crops should be collected.

The use of agricultural crop residues and animal manure for soil amendment is limited in most part of Ethiopia because of high competition for the uses. However, due to low SOM content in most agricultural soils, there is an urgent need for a sustainable management system of agricultural residues to replenish SOM. Vermicomposting is superior among the most efficient recycling techniques for management of available agricultural wastes. The study aimed to investigate the type of crop residues and animal manure available, determinants for their current use, quantity of residue left for composting and farmer's perception of vermicomposting in three districts of the Benishangul-Gumuz region. Farmers use the largest portion of cereal residue such as sorghum as fuel and tef straw sold at the market and/or as stall-feeding. However, legume residues were consistently preferred for use as a composting material over cereal residues. The average amount of crop residues available for composting was estimated in the range between 0.2 and 0.6 ton year(-1) farmer(-1), across districts. While the quantity of cow manure used for compost production significantly differs between districts and was estimated 1.7, 1.2, and 0.5 ton year(-1) farmer(-1) at Bambasi, Assosa, and Homosha districts, respectively. Unlike other parts of Ethiopia, the mixed farmers in the study region well recognized the benefit of animal manures and did not use them as a source of fuel. Residues were found with varying decomposition characteristics that sorghum (10.08% and 1.65%) and tef (9.16% and 1.43%) residues had higher lignin and polyphenol contents, respectively, than maize, soybean, banana, and haricot bean. In terms of their quantity and quality composition, cow and donkey manures, as well as residues of soybean, banana, and maize are the major organic resources potential for utilization in the vermicomposting process in the region. Moreover, the availability of potential organic residues at the farm level could encourage farmer's motive to adopt high-value vermicompost production.

Purpose Keystone taxa play an important role in soil nutrient cycling and crop growth and can be influenced by soil tillage. We investigated the composition of keystone taxa and their relationships with soil properties under different long-term tillage practices. Methods Four tillage treatments were applied (i.e., CT, conventional tillage; NT, no tillage with mulch; RT, reduced tillage; and SS, subsoiling with mulch), maintained for 21 years. Co-occurrence network (CoNet) was constructed to identify the keystone taxa, and redundancy analysis (RDA) was carried out to explore the relationships between keystone taxa and soil properties under four tillage practices at two growth stages (elongation and grain filling stages) of winter wheat. Results Compared with CT, RT had no significant effect on the microbial community and the keystone microbiome, while NT and SS remarkably altered the microbial community structure and the keystone microbiome at both crop stages. Massilia was the keystone genus under CT and RT, while Sphingomonas , Asanoa and Hoeflea were the keystone genera under NT and SS. RDA results showed that keystone genera were significantly correlated with soil organic carbon (SOC), dissolved organic carbon (DOC) and microbial biomass nitrogen (MBN) at both stages, but especially at the elongation stage. Our results further revealed that the effects of NT and SS on crop growth might be related to the changes in keystone microbiome. Conclusion Our study suggests that NT and SS were suitable conservation regimes and may contribute to the development of sustainable agricultural production in the Chinese Loess Plateau.

Soil organic carbon (OC) levels generally increase with increasing clay and silt content under a similar climatic zone because of increased association of OC to clay minerals and stronger occlusion inside aggregates. Surprisingly though, in Western Europe many silt loam soils actually bear low topsoil OC levels compared to lighter textured soils. Soil texture obviously also strongly controls moisture availability with consequent indirect impact on heterotrophic activity. We hypothesized that with increasingly frequent summer drought: 1) soil microbial activity in sandy soils is more likely impeded due to their limited water holding capacity retention during droughts, while soil OC mineralization in silty soils remain be less drought-limited; 2) capillary rise from sufficiently shallow groundwater would, on the other hand, alleviate the water stress in lighter textures. To test these hypotheses, we established a one-year field trial with manipulation of soil texture, monitoring of soil moisture and maize-C decomposition via 13/12C-CO2 emissions. The upper 0.5 m soil layer was replaced by sand, sandy loam and silt loam soil with low soil OC. Another sandy soil treatment with a gravel layer was also included beneath the sand layer to exclude capillary rise. Soil texture did not affect maize-C mineralization (Cmaize-min) until April 2019 and thereafter Cmaize-min rates were higher in the silt loam than in the sandy soils (P=0.01). θv correlated positively with the Cmaize-min rate for the sand-textured soils only but not for the finer textures. These results clearly highlight that soil texture controlled Cmaize-min indirectly through regulating moisture under the field conditions starting from about May, when soils faced a period of drought. By the end of the experiment, more added Cmaize was mineralized in the silt loam soil (81%) (Pmaize-min in the sandy soil, seemingly because the capillary fringe did not reach the sandy topsoil layer. These results imply that, under future climate scenarios the frequency of drought is expected to increase, the largely unimpeded microbial activity in silty soils might lead to a further stronger difference in soil OC with coarser textured soils under similar management.

Soil organic carbon (SOC) levels generally increase with increasing clay and silt content under similar climatic conditions because of increased physicochemical protection. Surprisingly though, many silt loam soils in Western Europe have low top SOC levels compared to coarser textured soils. Soil texture also strongly controls soil moisture with consequent indirect impact on heterotrophic activity. Especially during periods of prolonged drought, which seem to be occurring more frequently throughout Europe, it could be expected that this soil textural control of moisture retention decisively affects added organic matter (OM) decomposition. We hypothesized that, contrary to expected textural effects on physicochemical protection of OM, the higher moisture availability in silty soils strongly favors added OM mineralization during periodic drought than sandy soils. Moreover, as a secondary objective, we investigated if during prolonged drought, capillary moisture supply could significantly alleviate the water stress on added OM decomposition in sand with rather shallow groundwater table. Therefore, we established a one-year field trial in which the upper 0.5 m soil layer was replaced by sand, sandy loam and silt loam soil with low SOC. In a fourth treatment, a gravel layer was added beneath the sand layer to exclude capillary rise. Maize residues were mixed homogenously with soil in top 25 cm in all plots. Changes in soil moisture and maize-C mineralization (C-maize-min) were measured. We found that soil texture did not affect C-maize-min until after about five months and thereafter C-maize-min rates were higher in the silt loam than in the sandy soils. Moisture content correlated positively with the C-maize-min rate for the sand-textured soils only. Capillary rise did not result in a significant increase in C-maize-min in the sandy soil. After one year, a larger share of added C-maize was mineralized in the silt loam soil (81 +/-& nbsp; 6%) than in the sandy soil (56 +/- 7%). These results clearly highlight that soil texture controlled C-maize-min indirectly through regulating moisture under the field conditions when the study area faced a period of unusual drought. Moreover, our results imply that, under future climate scenarios, more frequent droughts might lead to a lesser SOC depletion in sandy soils compared to in finer textured soils under similar management.

Pseudomonas isolates from tropical environments have been underexplored and may form an untapped reservoir of interesting secondary metabolites. In this study, we compared Pseudomonas and cyclic lipopeptide (CLP) diversity in the rhizosphere of a cocoyam root rot disease (CRRD) suppressive soil in Boteva, Cameroon with those from four conducive soils in Cameroon and Nigeria. Compared with other soils, Boteva andosols were characterized by high silt, organic matter, nitrogen and calcium. Besides, the cocoyam rhizosphere at Boteva was characterized by strains belonging mainly to the P. koreensis and P. putida (sub)groups, with representations in the P. fluorescens, P. chlororaphis, P. jessenii and P. asplenii (sub)groups. In contrast, P. putida isolates were prominent in conducive soils. Regarding CLP diversity, Boteva was characterized by strains producing 11 different CLP types with cocoyamide A producers, belonging to the P. koreensis group, being the most abundant. However, putisolvin III-V producers were the most dominant in the rhizosphere of conducive soils in both Cameroon and Nigeria. Furthermore, we elucidated the chemical structure of putisolvin derivatives-putisolvin III-V, and described its biosynthetic gene cluster. We show that high Pseudomonas and metabolic diversity may be driven by microbial competition, which likely contributes to soil suppressiveness to CRRD.

There is a wide variety of agricultural waste co- and by-products that could potentially be valorised in high-value applications. One of such products is lignin, the second most abundant organic biopolymer after cellulose. Because of the large amounts of pruning wastes in the Mediterranean regions, lignin extraction can be one of the possibilities for valorisation and sustainable management of agricultural wastes. Research on the application of lignin, particularly lignosulfonates, is limited to its use as a biostimulant for root growth under controlled laboratory conditions and as a complexing agent in micronutrient foliar fertilizer formulations. Little is known about the impacts of lignin extracted from various feedstock on plant growth and soil quality. We investigated the potential of lignin as plant biostimulator and soil conditioner in a pot experiment with fresh soil and lignin extracts obtained from three types of pruning wastes (urban trees, fruit and forest trees) using ryegrass as a test plant, under laboratory conditions. Two doses of lignin extracts (equivalent to 5 and 20 kg lignin-C ha-1) were applied to assess whether the effect on plant growth and soil quality depends on the rate of application. Soil and plant parameters were determined seven weeks after the grass was planted at 17 °C and 16 h photoperiod. Root biomass significantly increased (62-152%) in treatments with lignin addition, particularly lignin from urban and forest pruning wastes compared to the control. However, the increase in root biomass did not result in a simultaneous increase in shoot biomass or N uptake showing the need to apply additional plant nutrient. The microbial biomass C did not significantly respond to the application of lignin. A significantly higher dehydrogenase enzyme activity was recorded in samples with the high dose of lignin extracted from the urban wastes compared to the lower dose. Urban waste lignin extract contains 15-18 times more total N compared to the lignin extracts from forest and fruit trees, which could explain its significant effect on enzymatic activities and root biomass. The findings show that differences in feedstock properties may influence the plant growth stimulating activity of the lignin. Further research is needed to improve the plant growth-stimulating effect of lignin, to investigate the simultaneous application of the major plant nutrients and the response of the microbial community to lignin application.

Predictions of N mineralization are still difficult but maybe this is due to the methodologies. Many soil tests have been proposed to predict N mineralization between field and laboratory experiment. Incubations of soil in the laboratory under controlled environmental conditions are most commonly used to assess N mineralization rates both from SOM and from added organic materials. However, predicting N mineralization due to the methods (the impact of using air-dried and fresh soil) has never been assessed before. If the results differ between the methods commonly used, there is a serious problem. Therefore, the objective of this study was to evaluate the influence of the incubation methods (air-dried vs fresh soil) to predict N mineralization. The N mineralization potential from fifteen agricultural soils in West and East Flanders – Belgium, were determined by aerobic incubation methods used air-dried and fresh soil at (20 – 250C) for 84-days in the laboratory. The results indicated that total mineral nitrogen (NH4+ + NO3-) concentrations and carbon content of microbial biomass (MBC) did not differ significantly between these methods. Nitrogen was mineralized in fresh soil incubations (0.36 mg N. kg-1 soil day -1) while in air-dried soil (0.31 mg N kg-1 soil day -1). Thus, the results generate that it may be conceivable to predict N mineralization by these two methods in controlled conditions.

Diffuse groundwater contamination by intense fertilizer use is a widespread problem in most of the agricultural regions in West-Europe and in many other countries worldwide. As a result elevated nitrate concentrations in groundwater are found, and as groundwater is the source of baseflow into rivers and streams, also surface waters show increased nitrate levels. Flanders in the north of Belgium is no exception and despite restrictions on the fertilizer use and remediation practices initiated in the mid-1990s, and still ongoing, in many stream monitoring points, peak concentrations are measured above the 50 mg/l criterium. In many monitoring stations there is apparently a long delay between the start of the restrictions and effect on water quality. Often this delay is related to high concentrations in the groundwater inflow and long residence and travel times of groundwater feeding the streams. To better understand this behavior and estimate response times a tool was developed that incorporates the main water flows in a typical catchment and considers the effects of varying groundwater ages. This tool is conceived as a parsimonious lumped parameter model, simple and easy enough to be used by many people but still capturing the main mechanisms end processes. In this paper the tool is explained and it is applied on two testcases in Flanders to show its performance.

Roller-crimping of cover crops grown during winter may facilitate reduced tillage efforts in organic vegetable production. A one-year field experiment was conducted twice (autumn 2015–2017) in sandy loam soil in Denmark testing two cover crop termination systems, roller-crimping (RC) without tillage before crop planting, and full incorporation by tillage (FI) of mowed cover crops in organic white cabbage (Brassica oleracea L. convar. capitata var. capitata f. alba) production. Three legume species were investigated: winter faba bean (Vicia faba L.), winter pea (Pisum sativum L.), hairy vetch (Vicia villosa Roth), in pure stands or in a mixture with winter rye (Secale cereale L.). Roller-crimping reduced total white cabbage biomass by 31% (2016) and 19% (2017). Marketable white cabbage yield was 100% (2016) or 24% (2017) lower under RC than FI, likely caused by delayed N release from cover crops and reduced soil dehydrogenase activity. White cabbage root growth was reduced by RC following pea/rye, where N availability was low. Despite reduced root growth and yield, RC still had the advantage of reducing weed growth by 63% compared with FI three weeks after cover crop termination in 2017 and of decreasing N leaching risk, indicated by reduced soil mineral N content in 0.5–1.5 m depth in autumn. Marketable yield was 35% higher following legumes compared with legume/rye mixtures in both termination systems in 2017, due to 105 kg N ha−1 higher mineral soil N content in 0–2.5 m depth in the spring and faster N mineralisation from plant material with a lower C/N ratio. This yield increase corresponded with increased root growth following RC legumes. In contrast, legume/rye mixtures had the advantage of decreasing weed growth by 50–68% and N leaching risk by 22 kg ha−1 in 0.5−2 m depth. Although RC demonstrated ecological benefits such as weed suppression and indicated reduced N leaching risk, the trade-off with yield losses could create a barrier to adoption. This trade-off could be mitigated by using pure legume cover crops and by improving management of supplemental N fertility.

The separate and collective role of soil nematodes and protists at community level in soil biogeochemical processes remains poorly quantified due to the lack of appropriate methodologies to study them independently from other soil biota under conditions emulating natural soil. Here we present a methodological exploration for the selective removal of nematodes and protists using gamma irradiation and the subsequent reinoculation with metazoan-free soil powder inoculum that allows reconstructing a complex microbial food web comprising the native microflora and soil protist communities, without other fauna. Nematodes, and culturable flagellates and ciliates were removed from 6 kGy onwards, while a small fraction of the amoebae survived (8% of the entire protist population) at 16 kGy but were totally removed at 27 kGy. Reinoculation with pulverized soil powder successfully established a protist community of similar size and composition as the control soil as assessed by both amplicon sequencing-based detection and microscopic observation after cultivation. A viable native microflora community remained from 6 to 16 kGy doses, but microbial activity was completely inhibited at 27 kGy. We suggest that, in ecological relevant experiments where selective removal of nematodes or other fauna is the purpose and protist community is meant to be kept intact, gamma irradiation needs to be followed routinely by soil powder inoculation in order to restore the suppressed protist community. This experiment also opens up new perspectives for studying the ecological roles of the entire protist community or specific groups thereof (flagellates and ciliates) in real soil and in the presence of a viable native microflora community.

Although the amendment of various forms of exogenous organic matter (EOM) is a common practice in cropland production, it is to date not clear if its mineralisation in soil depends on application rate. Previous research suggested that spatial concentration of EOM in soil positively impacts its degradability. Here, we seek to test these reports and furthermore to investigate if an interactive effect exists with native soil organic carbon (SOC) concentration. We hypothesised that at a low EOM dose, more EOM remains undecomposed in soil and that this effect becomes stronger at lower SOC level. Moreover, as a secondary goal, we explored if priming of native SOC mineralisation depends on EOM dose. Therefore, we set up seventy-day soil incubation experiments with six varying C4-maize residue (δ13C = −12.7‰) doses (0–6 g kg−1) in soil mesocosms of loamy sand subsoils (δ13C = −25.7‰) with three different native SOC levels (i.e. 0.1, 0.5, and 1.0%). Soil CO2 emissions and isotopic signature measurements of CO2 allowed to discern EOM and SOC mineralisation. We found that EOM-derived C mineralisation increased proportionally to EOM dose, refuting the hypothesised relative undecomposed EOM at low concentration. Volumes of larger pore neck size diameter classes (60–100 and >300 μm) almost doubled at high EOM dose, demonstrating formation of macropores. Yet, this apparently did not impact EOM mineralisation, probably because O2 supply was always sufficient to allow unlimited activity of EOM degraders, even at higher EOM doses, as indicated by generally higher measured redox potential. With EOM dose, fungal marker PLFA abundances increased in the 1% SOC soil and protozoan abundances increased in all three soils, but apparently these shifts did not result in an enhanced relative degradation of the EOM. Increasing EOM doses induced negative priming, e.g. EOM ≥1 g kg−1 reduced SOC mineralisation by >43% and >24% compared to the control in the 0.1 and 0.5% SOC soils, respectively; whereas no priming occurred in soil with 1% SOC. These results were largely explained by the amount of added C relative to microbial biomass carbon, and the theorised switch of slow decomposers (so called K-strategists and involved in recalcitrant compound decomposition) from SOM to preferentially decompose EOM at higher doses. We also postulate that at low SOC %, the obvious increased O2 consumption with higher EOM dose more readily results in local anaerobic conditions in finer pores, i.e. where SOC is located and mineralised. We conclude that on the short term, agricultural management for SOM thus does not need to consider EOM doses but only the total amount of EOM.

Inherently low soil fertility and costly chemical fertilizers contribute to low maize yield and food insecurity among rural smallholder farmers in sub-Saharan Africa. The use of fertilizer trees such as Faidherbia albida (Faidherbia) to improve the soil fertility and yield of maize is recognized by many as a good practice. This study examined the litterfall pattern, quantity, and nutrient deposition from 8-, 15- and 22-year old Faidherbia trees at two locations in Zambia before and during the 2014/15 and 2015/16 rainy seasons. Litterfall including its nutrient content was estimated using nylon mesh litter traps erected under three randomly selected representative Faidherbia trees of each age. Further, we assessed the yield levels of maize grown under 8-, 15- and 22-year old Faidherbia trees. All trees started dropping litter before the onset of the rains in both seasons. The leaf litterfall averages of the two seasons were 1.6, 1.7 and 3.8 t DM ha−1 from 8-, 15- and 22-year-old trees, respectively. These litterfall quantities translate to potential carbon and nutrient deposition of 0.7–1.6 t C ha−1, 34–83 kg N ha−1, 1.8–4.3 kg P ha−1 and 10–26 kg K ha−1 per year. The yield levels of maize for the two growing seasons under Faidherbia tree canopy were 7–12 times higher than from outside the canopy, and these yield differences were much more pronounced in the driest year (2015/16 growing season). The large nutrient deposition through litterfall and increase in maize yield under Faidherbia tree canopies show the potential of these trees to contribute to food security and mitigate the risk of crop failure on resource-poor smallholder farmers’ fields, especially in drought years.

Despite massive efforts over the past twenty-five years to reduce nitrogen (N) losses, too high nitrate (NO3−) concentrations in surface and groundwater from agricultural sources remain a major environmental concern, especially in field grown vegetable production areas. A strict restriction of the N fertiliser application rates is accepted to be the best N management strategy to minimise NO3− leaching losses to surface and groundwater. We analysed Flemish field experiments on lettuce, spinach, leek, carrots, cauliflower and Brussels sprouts with various N fertiliser application rates (2009–2016) with a view to fine-tune the N fertiliser application rates where possible. To find an economic and ecological optimum we considered both yield quantity, quality (leaf colour and uniformity for all vegetables, and nitrate concentration for leafy vegetables) and residual soil mineral N (RSMN) to rooting depth at harvest in function of crop available N. Even at relatively high crop available N, NO3− concentrations in lettuce and spinach remained below the legal maximum concentration. Contrary to some farmers’ perception, low RSMN can be obtained without a low score for quality parameters leaf colour and uniformity, except for the un- and underfertilised plots. When crop available N exceeds the optimum, RSMN increased steeply (i.e. a breakpoint) for all considered vegetables, except carrots, implying an increased risk of NO3− leaching. The results indicate that N fertilisation advices and maximum allowed N fertiliser application rates can be reduced, at least for some vegetables, without a risk of decreasing the marketable yield quantity and quality. As N uptake continues to increase, to a variable extent, after the maximum marketable yield has been obtained, N fertiliser application rates obviously should be based on marketable yield rather than total yield.

Soil phosphorus (P) leaching is one of the major causes of diffuse P losses towards the environment in north-west Europe. In order to cut back these P losses over the long term, soil P stocks need to be drastically reduced. Greenhouse experiments have shown that a rapid reduction of the plant available P pool is attained by reducing the P fertilizer input to zero while cropping, but field trials confirming these findings are rare. Moreover, important additional questions arise in any P mining strategy: (i) to what extent will crop performance be affected in high P soils under 0 P fertilization, (ii) which crops reduce soil P stocks most efficiently and (iii) how can soil organic carbon (SOC) levels be maintained when organic fertilizers are no longer applied. In order to address these questions we set up two 0 P fertilization field trials at sites with a very high initial soil P status (i.e. a P saturation degree > 30%). On each site, we compared the effect of 0 P fertilization on crop yield, soil P status and SOC level to a business as usual scenario, for two crop rotations. At the first site, a comparison was made between a mixed crop rotation with or without the inclusion of a catch crop. At the second site, a comparison was made between an arable/grass and a vegetable crop rotation. Four consecutive years of 0 P fertilization had no effect on neither the crop yield nor the crop P uptake. Further, English ryegrass, silage maize, celeriac and Chinese cabbage made the largest contribution to P removal. Although 0 P fertilization reduced the P balance at field level with 102–121 kg P ha-1 over four years, this had no significant (measurable) effect yet on the soil P stocks. Continuation of these experiments over a longer time will thus be needed to allow to see any such effects. Simulations of the evolution of the SOC levels over a thirty-year period showed that the use of grass as green manure or as main crop only allows to partially maintain the SOC levels in the absence of any organic fertilizers. These results indicate that P mining is a challenging task, that will take a long time to reduce the soil P stocks and that will come at a cost for the farmer.

Nitrogen (N) depositions in Europe are decreasing, but this could not explain faster than expected improvement of N saturation indicators in temperate forests. Alongside there were local signs of initial recovery from acidification during the past three decades and enhanced leaching of dissolved organic carbon and nitrogen (DOC, DON). These two global change processes both affect total dissolved nitrogen (TDN) levels and often occur simultaneously, hence complicating mechanistic explanations for changing European forest N status. We aimed to test the hypothesis that forest N status in northwest Europe has started to improve. If this hypothesis is confirmed, we wanted to investigate to what extent such improvement is due to reduced N deposition. We evaluated the evolution of multiple N saturation indicators in five ICP Forests Level II plots in northern Belgium, using long-term soil solution and foliage datasets. The DON:TDN ratio (molar) in soil solution increased overall in the O horizon (mean 0.279–0.463, slope 0.023–0.037 yr −1 ) and in the mineral soil (mean 0.134–0.78, slope 0.007–0.051 yr −1 ) between 2005 and 2014. The DOC:NO 3 − ratio (molar) in soil solution increased in three plots in the O horizon (mean 6.84–22.15, slope 0.58–1.92 yr −1 ) and in four plots in the mineral soil (mean 2.07–25.32, slope −0.06–5.76 yr −1 ) between 2002 and 2014. The ratio of N and phosphorus (P) concentrations in foliage (mg g −1 ) and the ratio of base cations (Bc = Ca + K + Mg) and N concentrations in foliage (molar) remained unaltered between 1999 and 2013. Changes in the soil solution chemical composition thus confirmed an improvement in forest N status, despite sustained high NO 3 − concentrations, but biotic recovery appeared to be lagging behind. This demonstrates that insight in forest recovery from N saturation requires a multiple indicator approach, and further monitoring of tree nutritional status alongside soil processes is needed to monitor the evolution of European forest N status.

Long-term field experiments have confirmed belowground plant carbon (C) to be two to three times more efficient precursor of soil organic carbon (SOC) than aboveground plant residues. But it remains elusive just when this belowground biomass is relatively stabilized against mineralization: during the initial fast degradation, or on the longer term? A one-year field experiment was set up with biweekly follow-up of the in-situ mineralization of maize (Zea mays L.) C-inputs, either above- or belowground biomass based on soil δ13C resolved CO2 emissions. In addition, a treatment with maize roots and post-harvest remnant rhizodeposited-C left undisturbed in the field was included as well as a corresponding control that was physically disturbance as in the other treatments. We found that most maize-C was mineralized within a year with peaks in late fall and spring, i.e. 1 and 8 months after incorporation. Shoot-C decomposed only 1.4 times faster than root-C though statistically insignificant, which shows that on the short term (i.e. within a single year) the 2–3 fold stability of belowground biomass C is not manifested. Total maize-derived CO2 emissions of soil amended with only roots and with roots and post-harvest rhizodeposits were equal, likely because the rhizodeposited-C had already degraded quickly. A much smaller share of root- and rhizodeposited-C (43%) was mineralized when soil was not disturbed after harvest. We hypothesize that such a delayed physical disturbance, which in practice would only occur in early spring, could be key in stabilizing belowground biomass C in the field. Overall, our findings show a limited difference in degradability of roots and shoots under field conditions on the short term, and a large effect of tillage timing.

Acidification of manure, digestate and their processed derivatives has been proposed as a technique to, amongst others, mitigate ammonia emissions related to application in the field. The current study investigated whether acidification of (1) pig slurry (PS), (2) liquid fraction of pig slurry (LFPS), (3) digestate (DIG), and (4) liquid fraction of digestate (LFDIG) increases their nitrogen (N) fertilizer replacement value (NFRV) as compared to non-acidified counterparts, a synthetic N fertilizer (calcium ammonium nitrate; CAN) and an unfertilized control. Product performance was evaluated from the perspective of (1) crop development (yield, nutrient uptake, and crop quality assessment) via a pot experiment with Lactuca sativa L. and (2) soil N dynamics [net N release (Nrel,net) and net N mineralization] via a soil incubation experiment. Crop yield of pots receiving bio-based fertilizers performed ‘on par' with CAN as compared to unfertilized control, implying that bio-based fertilizers derived from digestate or manure could potentially play a role in replacing synthetic N fertilizers. However, our findings also suggest that acidification did not result in an increased use efficiency of applied N. NFRVs of acidified products were below those of non-acidified products and CAN, with crop yield on average 6–13% and 11–18% lower compared to non-acidified products and the CAN treatment, respectively. A possible explanation for lower performance as compared to non-acidified products could be an inhibitory delay in the Nrel,net, which in our experimental design proved to be negative for crops with short production cycles. This pattern was revealed in the incubation experiments in which Nrel,net in acidified products remained below that of non-acidified, in this study tentatively attributed to immobilization of mineral N. However, this negative effect on N availability should be reaffirmed in crops with longer production cycles. Finally, some interesting findings with regard to plant composition also warrant further in-depth investigation, e.g., Zn uptake by lettuce in acidified treatments was significantly higher than that of non-acidified treatments. This implies that product pre-treatment may play a future role in biofortification and amelioration of (trace) element composition of crops (arguably for crops with longer production cycles). Improving crop nutritional value by increased uptake of micronutrients is receiving increasing attention.

High rainfall intensity is major factor governing leaching process, where leaching is often the most important process of N loss from the field and lead to agricultural environmental pollution. In order to measure the movement of mineral-N in soil profile, a field research had been conducted in two sites of center vegetable farming area with six farmer cooperators in Central Java, Indonesia. Regular soil sampling was done from Improve Practice (IP) and Farmer Practice (FP) treatment for three planting seasons during 2007. Almost all treatments FP applied higher rate of N fertilizer compare to IP, but it was not reflected in N profile. Comparison of predicted and measured mineral N content was simulated using Burns α model, then the closeness of the estimation and measured calculated using Coefficient of Residual Mass (CRM) calculation as an indicator with 0 as ideal value. Out of 9 measurements of IP and FP treatment, eight and seven measurements had negative CRM representinga slight overestimation. The NO3-N loss estimated using the Burns α model for IP and FP was in average of 67% for IP and 71% for FP of total N fertilizer added or 67% for IP and 76% for FP of total-N surplus, respectively. The calculation of potential nitrate concentration (PNC) at 1 m soil depth at the end of the third season showed a high concentration with significant different of IP and FP having mean value of 59.8 and 82.5 mg N L-1. From the gathered data it was obvious that over N fertilization had negative effect to agricultural environment.

The few available studies on maize biomass in soil of field experiments have shown that belowground maize biomass resides more than twice as long as aboveground residues. Our principal objective was to investigate the effect of maize crop residue incorporation on the long-term dynamics of soil organic carbon (SOC) for a selection of croplands with sandy to sandy loam texture in Flanders, Belgium. After a period of more than 20 years, we resampled 31 and 29 parcels that had either silage maize (MS, only belowground biomass input) or grain maize (MG, both above- and belowground biomass input) dominated crop rotations. Changes in maize-derived SOC (Cmaize) of MS and MG systems between 1993 and 2018 were evaluated by detecting SOC content and its δ13C value. In addition, a 140-day incubation experiment (at 20.5 °C) was carried out to compare the stability of Cmaize and the related nitrogen (N) mineralization between the MG and MS fields. After two decades, δ13C raised 2.4 and 2.6‰, while Cmaize increased 1.6 and 2.2 g kg−1 in MS and MG systems, respectively. The estimated average humification coefficient over this period of maize-C was 0.11 for the MS system, about twice as that of the MG system (0.06). This reconfirms findings of stronger contribution of belowground biomass versus aboveground residues to stabilized SOC pools over the medium to long term. By the end of the incubation, on average 10.4% and 11.6% of Cmaize had been decomposed in the MS and MG soils, respectively. These Cmaize mineralization rates were statistically equal for the two systems, which indicates that mainly belowground biomass remained in the soils. Also, net N mineralization was indifferent to the crop rotations (MS: 58.8 mg N kg−1 and MG: 52.6 mg N kg−1). To reconcile the two main observations in this study, we hypothesize that the lower preservation of shoot-C could be manifested on a shorter term. Detailed research is needed to determine the time scale of increased stabilization of root-C versus shoot-C under field conditions.

Nitrogen (N) is a main parameter affecting crop growth and yield. However, when variable rate N fertilization (VRNF) is adopted, a main question arises of whether to add more on the highly fertile zone or on the less fertile zone. This study aimed to compare two map-based VRNF treatments, e.g., variable-rate 1 (VRNF1) with the application of recommended rate (RR) of N fertilizer plus 40-50% to the high fertility zones, RR to the medium-fertility zones and RR minus 40-50% to the least fertile zones, and VRNF2 following the opposite scenario to that of VRNF1. Recommendations for both VRNF treatments were derived from the fusion of soil data and crop data, e.g., normalized difference vegetation index (NDVI) and historical yield and were compared with traditional uniform rate (UR) application. Online soil measurement was carried out in two fields in Belgium, using a multi-sensor platform that collects high-resolution data on key soil properties using a fiber type visible and near-infrared (vis-NIR) spectrophotometer. The vis-NIR sensor was calibrated using a partial least squares regression (PLSR) to predict pH, organic carbon (OC), moisture content (MC), calcium (Ca), sodium (Na), magnesium (Mg), phosphorous (P) and potassium (K). The predicted soil properties were fused with NDVI and historical yield data to delineate management zone (MZ) maps with different fertility classes. A cost-benefit analysis was carried out using the cost of fertilizer applied as input cost and the price of barley and wheat in 2019. Results showed that the VRNF2 treatment was more profitable compared to both VRNF1 (11.55 and 19.52 EUR ha-1) and UR (16.40 and 148.78 EUR ha-1). The VRNF2 treatment maintained or increased crop yield by up to 10.4% and reduced the amount of N fertilizer applied by up to 19.4%, compared to the traditional UR. Because of the lower amount of N fertilizer used compared to the other two treatments, the VRNF2 would reduce the negative environmental impact by reducing the amount of N fertilizer applied. Therefore, we recommend the VRNF2 based-on data fusion of soil and crop parameters as the best approach to manage N fertilization site specifically.

Soil texture is well known to directly affect bioavailability of organic matter to heterotrophs, but it also steers their activity by moderating soil moisture fluctuation. Disentangling these direct and indirect textural controls is, however, not trivial and attempts to do so are very scarce. Most attention has just gone to the stimulation of soil carbon (C) mineralization by soil moisture fluctuation per se. To quantify the indirect moisture-mediation control of soil texture on C mineralization, we monitored maize straw degradation in various soil texture/moisture regime combinations. Moisture levels were firstly kept fixed at 32% WFPS (experiment Fixed32) in a sand, sandy loam and silt loam soil or allowed to fluctuate between 20% and 50% water-filled pore space (WFPS, Dry-wet20-50). Total maize-C (Cmaize) mineralized was highly similar between these three textures and thus the direct textural control was minor. On the contrary with the fluctuating moisture level, around threefold more added Cmaize was mineralized (P

Catch crops may strongly reduce nitrate leaching during autumn and winter in temperate climates. Authorities therefore aim to stimulate farmers to place catch crops in their rotations by allowing them to apply more nitrogen (N) to their fields. Furthermore, some regulations make it possible to fertilize catch crops after harvest of specific crops such as winter cereals, even if catch crops are sown during late summer. Some farmers claim that this practice is essential for a good development of the catch crop. However, it is not sure whether this summer fertilization to catch crops could result in any additional nitrate leaching, compared to nitrate leaching under non-fertilized catch crops. We therefore designed field experiments including four different catch crop species, each of them sown after harvest of winter cereals at two different dates, and each of them receiving two different doses of pig slurry or receiving no fertilizer at all. Experiments were installed on sites with different soil textures in northern Belgium. Based on the results of soil mineral N and N uptake, we assessed the risk of additional nitrate leaching caused by fertilization of catch crops. We found that the apparent uptake of N released from pig slurry was rather limited but sufficient to avoid additional nitrate leaching on sandy soils, mainly due to supplementary immobilization of the applied N occurring during mineralization of the cereal crop residues. It is critical to mention the limiting conditions that we found to be adequate from our results: catch crops were to be sown in good circumstances before September and could only receive the smallest dose of pig slurry, which was approximately 60 kg N ha−1. On silty soils, however, we found even under these conditions a few indications of small amounts of additional nitrate leaching. As fertilization did not seem mandatory to develop an effectively functioning catch crop and as there was no indication of reduced nitrate losses due to this practice, we would rather discourage fertilization of catch crops to exclude any environmental risk. However, fertilization significantly increased the catch crop yield, so the decision to fertilize or not may also be seen as a trade-off between minor amounts of additional nitrate leaching and enhanced biomass-related effects, such as the additional input of organic carbon into the soil.

In Cote d’Ivoire, smallholder farmers cultivate cassava on poor, highly weathered soils without improved varieties or fertilizer inputs. Land pressure combined with high demand result in premature harvests and low yields. Furthermore, subsistence agriculture limits the adoption of input-intensive technologies. This study aimed at identifying integrated soil fertility management systems for increasing cassava productivity and profitability in two locations in southern Cote d’Ivoire. The integrated technical interventions included improved cassava genotypes and modified spacing, legume intercropping, and application of fertilizer at moderate doses. Overall, an improved cassava variety (Yavo) generally out-yielded the other varieties at both sites. Legumes performed better at the higher soil fertility site and gave higher grain yield and biological nitrogen fixation in a 2 × 0.5 m cassava spacing compared to 1 × 1 m. The response of cassava to nutrient amendments varied between sites, suggesting the ...

Sustainable agriculture requires the careful optimization of the use of organic amendments to improve soil fertility while minimizing any harmful environmental effects. To understand the events that occur in soil after the addition of different organic amendments, we evaluated the nitrogen (N) mineralization dynamics in soil after adding organic amendments, and evaluated changes in the microbial population. The four organic amendments were fresh dairy cattle manure, fresh white clover, vegetable, fruit, and yard waste compost, and poplar tree compost. The N mineralization potential of each organic amendment was determined by analyzing total mineral nitrogen during a 97-day laboratory incubation experiment. Soils amended with clover released 240 μg N g −1 soil during the 97-day incubation, more than twice as much as that released from soils amended with manure or composts (76–100 μg N g −1 soil). At the end of the incubation, the net N mineralization in clover-amended soils was 54%, more than five times higher than that in soils amended with composts or manure (4%–9%). Nitrogen was mineralized faster in clover-amended soil (1.056 μg N g −1 soil day −1 ) than in soil amended with composts (0.361–0.417 μg N g −1 soil day −1 ). The microbial biomass carbon content was higher in clover-amended soil than in the soils amended with manure or composts. We monitored changes in the microbial population in amended soils by a phospholipid fatty acid (PLFA) analysis. On day 97, there were higher concentrations of total PLFAs in soils with organic amendments (e.g., 14.41 nmol g −1 in clover-amended soil) than in control soil without amendments (9.84 nmol g −1 ). Bacteria (Gram-positive and Gram-negative), actinomycetes, and fungi were more abundant in clover-amended soils than soils amended with manure or composts. The N mineralization potential varied among the four organic amendments. Therefore, the timing of application and the type of organic amendment should be matched to the nutrient needs of the crop.

Biochar addition to soils is heralded to reduce N2O emissions, but still, the explanatory mechanisms have not been resolved. Moreover, it is uncertain whether N2O emission reductions would persist after prolonged biochar incorporation in the field. In this study, we incorporated four biochar types in a loam textured cropland field and intact soil cores were sampled to investigate the physical control of biochar on denitrification after 7 months. During a first incubation experiment, we measured N2O emissions from undisturbed and disturbed (i.e. sieved (2 mm) and grounded) soil cores. Both in the disturbed and undisturbed soil cores biochar at water filled pore space (WFPS) of 80% reduced the N2O emissions by 50–90%, refuting the hypothesis that biochar exerts an indirect physical control over soil denitrification several months after incorporation. Secondly, we hypothesized that biochar creates denitrification ‘hotspots’ in soil, where complete reduction of N2O to N2 is promoted compared to non-amended soil. In these hotspots biochar particles could act as microlocations with local anaerobic conditions and local higher pH, stimulating in this way complete denitrification. Via the acetylene inhibition method we did not observe a reduction in the N2O/(N2O + N2) ratio, which could suggest that biochar did not promote the reduction of N2O to N2. Manipulations likely to promote labile C bioavailability, here either by glucose addition or by soil particulate OM disclosure after disruption of soil aggregates, resulted in the most prominent biochar-induced N2O emission reductions.

SUMMARYIn order to intensify cassava production in southern Côte d'Ivoire, multiple farmers’ field trials were carried out in two important cassava-producing areas (Dabou and Bingerville). The effectiveness of an Integrated Soil Fertility Management (ISFM) approach as intensification pathway was evaluated for poor sandy soils. Overall, ISFM-based systems outperformed the local cultivation system. The average cassava yield was 14.5 and 6.5 t ha−1 and 12.6 and 5.7 t ha−1 for the ISFM and traditional systems, in Dabou and Bingerville, respectively. The average profitability of ISFM systems was ca. 2500 Euro ha−1, whereby 66% was generated by cowpea intercrop, which yielded on average 3.1 t ha−1. Taking into account the limited farmer's resource endowment and poor soil fertility, ISFM is a crucial component for sustainable intensification of cassava production and poverty alleviate in southern Côte d'Ivoire.

N fertilization is often viewed as a cheap insurance against yield loss in vegetable production because of the generally large added value, resulting in application of fertilizer N often in excess of actual crop demand. In combination with the low fertilizer N recovery by many vegetable crops and the often excessive irrigation, this may lead to both health and environmental risks related to high nitrate concentrations in water leaving the root zone. In this review, we discuss the decisive factors in the overall N balance of field vegetable production systems and the different tools at hand to increase fertilizer use efficiency and consequently reduce N losses to the environment. Based on this, we identify areas of research and technology transfer where further work is required. Only an integration of the different methods and strategies for N management may really mitigate the risk of nitrate leaching and maintain crop yields while enhancing the environmental sustainability of vegetable production systems.

In north-west Europe, agricultural diffuse P losses are a major cause of eutrophication problems in surface waters. Given that the Water Framework Directive (WFD) demands fast water quality improvements and most of the actual P mitigation strategies tend to work on the long run, new short-term mitigation measures are urgently needed. We here report on the entire process of developing small scale field filters to remove P at the end of tile drains, starting from the screening of potential P sorbing materials (PSM): iron coated sand (ICS), acid pre-treated natural minerals (biotite, glauconite and olivine) and bauxite. Initial batch (ad)sorption experiments revealed following order in both, P sorption capacity and speed: ICS > bauxite > glauconite > olivine = biotite. Because of the presence of significant amounts of lead and/or nickel, we excluded bauxite and olivine from further experiments. Subsequent lab scale flow through systems were conducted with P filters containing mixtures of ICS and glauconite (100/0, 90/10, 80/20, 70/30 and 60/40%, respectively, on weight basis). We found a significant relationship between Ksat and the filter mixtures particle size distribution and bulk density, and a significant effect of the filter mixture composition on P removal efficiency and stability of Ksat. During the 10 week field trials, the pure ICS filters were capable of processing all drainage discharge rates (up to 6 m3 day−1) with a P removal efficiency of ≥74%. The 90/10 ICS/glauconite filters could process up to 4 m3 water day−1 with a P removal efficiency of 57%. As saturated ICS filters can easily be replaced and recycled for other applications, this is a promising sustainable technique to drastically cut back diffuse P losses and to tremendously improve surface water quality in the short term.