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The role of soil fauna in crucial ecosystem services such as nutrient cycling remains poorly quantified, mainly because of the overly reductionistic approach adopted in most experimental studies. Given that increasing nitrogen inputs in various ecosystems influence the structure and functioning of soil microbes and the activity of fauna, we aimed to quantify the role of the entire soil nematode community in nutrient mineralization in an experimental set-up emulating nutrient-rich field conditions and accounting for crucial interactions amongst the soil microbial communities and plants. To this end, we reconstructed a complex soil foodweb in mesocosms that comprised largely undisturbed native microflora and the entire nematode community added into defaunated soil, planted with Lolium perenne as a model plant, and amended with fresh grass-clover residues. We determined N and P availability and plant uptake, plant biomass and abundance and structure of the microbial and nematode communities during a three-month incubation. The presence of nematodes significantly increased plant biomass production (+9%), net N (+25%) and net P (+23%) availability compared to their absence, demonstrating that nematodes link below- and above-ground processes, primarily through increasing nutrient availability. The experimental set-up presented allows to realistically quantify the crucial ecosystem services provided by the soil biota.

We evaluated trends (2005-2013) and patterns of dissolved organic nitrogen (DON) and its ratio with dissolved organic carbon (DOC), DOC:DON in atmospheric deposition and soil solution of five Level II plots of the International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) in Flanders, Northern Belgium. The primary aim was to confirm positive postulated trends in DON levels and DOC:DON under on-going recovery from acidification. The DON concentrations (0.95-1.41 mg L(-1)) and fluxes (5.6-8.3 kg ha(-1)y(-1)) in throughfall were about twice as high compared to precipitation in the open field (0.40-0.48 mg L(-1), 3.0-3.9 kg ha(-1)y(-1)). Annual soil profile leaching losses of DON varied between 1.2 and 3.7 kg ha(-1)y(-1). The highest soil DON concentrations and fluxes were observed beneath the O horizon (1.84-2.36 mg L(-1), 10.1-12.3 kg ha(-1)y(-1)). Soil solution concentrations and fluxes of DON showed significant increasing trends. Temporarily soil solution DOC:DON rose following an exceptionally long spring drought in 2007, suggesting an effect of drying and rewetting on DOM composition. Further research is needed to test the dependence of DON and DOC:DON on factors such as latitude, forest cover, length of the growing season, hydrology and topography. Nonetheless, even with considerable variation in soil type, level of base saturation, and soil texture in the five included ICP Forests Level II plots, all data revealed a proportionally larger positive response of DON flux than DOC to recovery from acidification., (Copyright © 2016 Elsevier B.V. All rights reserved.)

To understand the roles of nematodes in organic matter (OM) decomposition, experimental setups should include the entire nematode community, the native soil microflora, and their food sources. Yet, published studies are often based on either simplified experimental setups, using only a few selected species of nematode and their respective prey, despite the multitude of species present in natural soil, or on indirect estimation of the mineralization process using O2 consumption and the fresh weight of nematodes. We set up a six-month incubation experiment to quantify the contribution of the entire free living nematode community to carbon (C) mineralization under realistic conditions. The following treatments were compared with and without grass-clover amendment: defaunated soil reinoculated with the entire free living nematode communities (+Nem) and defaunated soil that was not reinoculated (-Nem). We also included untreated fresh soil as a control (CTR). Nematode abundances and diversity in +Nem was comparable to the CTR showing the success of the reinoculation. No significant differences in C mineralization were found between +Nem and -Nem treatments of the amended and unamended samples at the end of incubation. Other related parameters such as microbial biomass C and enzymatic activities did not show significant differences between +Nem and -Nem treatments in both amended and unamended samples. These findings show that the collective contribution of the entire nematode community to C mineralization is small. Previous reports in literature based on simplified experimental setups and indirect estimations are contrasting with the findings of the current study and further investigations are needed to elucidate the extent and the mechanisms of nematode involvement in C mineralization.

The effect of soil fumigation on N mineralization and nitrification needs to be better quantified to optimize N fertilizer advice and predict NO(-)(3) concentrations in crops and NO(-)(3) leaching risks. Seven soils representing a range in soil texture and organic matter contents were fumigated with Cyanamid DD 95 (a mixture of 1,3-dichloropropane and 1,3-dichloropropene). After removal of the fumigant, the fumigated soils and unfumigated controls were incubated for 20 wk and N mineralization and nitrification were monitored by destructive sampling. The average short-term N mineralization rates (k(s)) were significantly larger in the fumigated than in the unfumigated soils (P = 0.025), but the differences in k(s) between fumigated and unfumigated soils could not be related to soil properties. The average long-term N mineralization rates (k(l)) were slightly larger in the fumigated soils but the difference with the unfumigated soils was not significant. Again, the differences in k(l) values could not be related to soil properties. Nitrification was inhibited completely for at least 3 wk in all soils, and an effect on nitrification could be observed up to 17 wk in one soil. An S-shaped function was fitted to the nitrification data corrected for N mineralization, and both the rate constant (gamma) and the time at which maximum nitrification was reached (t(max)) were strongly correlated to soil pH. However, since no correlations were found between the effect of fumigation on N mineralization and soil properties, taking into account the effects of fumigation in fertilizer advice and in the prediction of NO(-)(3) leaching risks will need further research.

In a forest on sandy, metal polluted soil, we examined effects of six tree species on litter decomposition rates and accompanied changes in metal (Cd, Zn) and nutrient (base cations, N, C) amounts. Decomposition dynamics were studied by means of a litterbag experiment lasting for 30 months. The decomposition peak occurred within the first year for all tree species, except for aspen. During litter decomposition, high metal litter types released part of their accumulated metals, whereas low metal litter types were characterized by a metal enrichment. Base cations, N and C were released from all litter types. Metal release from contaminated litter might involve risks for metal dispersion towards the soil. On the other hand, metal enrichment of uncontaminated litter may be ecologically relevant as it can be easily transported or serve as food source. [Copyright &y& Elsevier]

Nitrogen (N) nutrition is a key factor for vegetable growth and yield. However, different rates of nitrogen fertilization may trigger different responses to vegetables. A survey was conducted to investigate the effect of soil fertility management practices on nitrate concentration in vegetables. The survey results were used to plan experiments on the effect of chicken and cattle manures on nitrate levels in Chinese cabbage (Brassica rapa) and amaranthus (Amaranthus cruentus) grown in Tanzania and the patterns of mineral nitrogen in soils under open field conditions. Chicken or cattle manure at 200, 300 kg N ha−1 and 170 250 kg N ha−1 for Chinese cabbage and amaranthus respectively, and control were compared in a randomized complete block design. We observed a higher nitrate content in fertilized Chinese cabbage at day 30 than at day 44 after sowing, ranging from 3243 to 4993 mg kg−1 fresh matter regardless of the N source and rates. Only application of manures at high levels (250 kg N ha−1) induced significantly (p < 0.05) higher nitrate contents in amaranthus at day 28 after sowing, although there was a clear indication of nitrate accumulation even at 170 kg N ha−1 application. Soil NH4+-N + NO3−-N in both Chinese cabbage and amaranthus plots were increased with increasing N application rates and differences between control and amended soils were significant (p < 0.01). There was a positive relationship between NO3− concentration in vegetables and NO3−-N in the rooted top soil layer (0–15 cm). However, higher NH4+ concentrations depressed NO3− build up in crops and a significant negative relationship between soil (NH4+-N)/(NO3−-N) ratio and crop NO3− content was found. It is concluded that low manure application rates result in similar yields to high rates but reduces nitrate accumulation in vegetables and excess mineral nitrogen in soils. [ABSTRACT FROM PUBLISHER]

Crop residues are an important component of N cycling in the agro-ecosystem. In this study, a loam soil was amended with cabbage residues and the N mineralization from soil organic matter and residues, as well as N uptake by Italian rye grass, were investigated. Four mineral fertilizer-residue combination treatments and two application times were tested in micro-plots. For uncropped micro-plots, application of residue resulted in higher soil mineral N content (43 mg N kg-1, 63 days post application) versus 30.5 mg N kg-1 for an unamended soil. Both bulked dry matter production and N uptake by the rye grass decreased in the order full mineral fertilizer > half mineral fertilizer + half residue > full residue applied 3 weeks before sowing > full residue applied at sowing, but the differences were more pronounced in the N uptake. Shoot N recovery from the applied residue (27.5-31.4%) was much smaller than that from the full fertilizer (70.2%), but was still considerable. Apparent net N mineralization from soil organic matter was significantly depressed in the treatments where mineral fertilizer was added. Cropping also reduced apparent net N mineralization, but this effect was reduced when residues were applied 3 weeks before sowing. Results showed that crop residues play an important role in crop production, in terms of obtaining comparable dry matter production to that of full mineral fertilizer application. Moreover, nitrogen supplied as residue is less liable for loss due to leaching during the growing season. The efficiency of crop uptake to residue-derived nitrogen could be increased by earlier application time. [ABSTRACT FROM AUTHOR]

Abstract: The concentration of dissolved organic matter (DOM) in the soil solution is predominantly determined by sorption processes to mineral surfaces. We compared four models describing DOM sorption isotherms to mineral soil material using the results of batch experiments for dissolved organic carbon (DOC) and nitrogen (DON) sorption to different horizons of a podsol. The Initial Mass and modified Langmuir isotherms could be fit to the data points in all cases. The three curvilinear models (Langmuir, Freundlich and exponential models) were found to result in similar goodness-of-fit and parameter estimates. We found that the most widely used, linear model (the Initial Mass isotherm) could be used for horizons with very small sorption capacity and horizons almost saturated with DOM, but failed to describe sorption in the deeper, DOM-unsaturated horizons characterized by a curvilinear shape of the sorption isotherm. The modified Langmuir isotherm was found to describe DOM sorption to mineral soil best and gave realistic parameter estimates, including a measure for maximum sorption capacity of the soil. Comparing the results of the sorption experiments with DOM concentrations in soil solution in the field indicated that the sorption isotherms can serve as a basis for larger DOM leaching models. [Copyright &y& Elsevier]

At the moment, Hungarian agriculture is confronted with a certain duality as far as nutrients are concerned. On the one hand, national soil nutrient balances show substantial deficits, and on the other hand, agricultural nutrient use is responsible for a part of the nitrogen (N) and phosphorus (P) losses to the environment. To understand this duality and help optimize farm nutrient management, the farm gate N and P balances of 12 farms, representing a variety of Hungarian agriculture, were calculated for the year 2002. The farm gate N and P surpluses/deficits in the east of the country were lower than in the west. This was correlated with a lower fertilization rate. The low soil fertility level due to a prolonged period of low fertilization in combination with continuing nutrient deficits can lead to possible future reduction in crop yields. [ABSTRACT FROM AUTHOR]

Several ecosystem processes such as nitrogen mineralization are mainly controlled by complex multitrophic interactions in which nematodes play major roles. Despite the abundance and diversity of these nematodes, studies on their contribution to N mineralization have been limited to a few selected species and often in completely sterilized media. Such simplified experiments are unrealistic and usually give inaccurate results as part of the interaction is missed. Therefore the contributions of nematodes to N mineralization need to be quantified more accurately in realistic conditions where native microbes, nematodes and plants interact. To do this, we set up a microcosm incubation experiment in which the whole nematode communities were extracted from fresh soil and reinoculated into the soil defaunated by 5 kGy dose gamma irradiation that leaves the microbial community largely intact. Three treatments namely control, +Nem (with nematodes) and −Nem (without nematodes), with or without plants were incubated for 86 days. In bare microcosms, +Nem cores increased total mineral nitrogen with 32% compared to −Nem. However, no significant (p > 0.05) differences were observed on total mineral nitrogen and plant N uptake between +Nem and −Nem treatments in planted microcosms. Nematode abundances and community structures were significantly changed over time and differed in bare and planted microcosms. Bacterivores dominated in bare, while herbivores dominated in planted soils throughout the incubation period. This could explain the contrasting effects of nematodes in N mineralization in bare and planted microcosms. Optimization of gamma irradiation technique is required to further reduce its side effects on nutrient flush and non-targeted organisms. [ABSTRACT FROM AUTHOR]

Abstract: Crop rotations in Western Europe contain crops that seem not suitable for reduced tillage (RT) agriculture because they often include beets and potatoes, resulting in a high disturbance of the soil at the formation of the ridges and at harvest. Therefore, the short- and long-term effects of RT on the stratification and stock of total nitrogen (TN) in the 0–40cm depth layer and the nitrogen (N) mineralization in the upper 15cm depth layer of silt loam soils was evaluated. For doing so, 10 fields at seven locations representing the important types of RT systems in Belgium, applied for a different number of years, and eight fields under conventional tillage (CT) with comparable soil type and crop rotation were selected. Despite the presence of root and tuber crops in these rotations, the stratification of the percentage of TN and of the carbon to nitrogen ratio was more pronounced under RT than CT fields. The TN stock in the RT fields worked with a cultivator or soil loosener was comparable to CT fields, even after 20 years. No trend could be found in the change in TN stock of reduced tillage by direct drilling compared to CT. The N mineralization rate in undisturbed soil cores under controlled conditions in the laboratory was on average 0.20±0.08mgNkg−1 dry soil day−1 for RT fields compared to an average of 0.13±0.05mgNkg−1 dry soil day−1 for CT fields. This increase in N mineralization rate was correlated with a higher microbial biomass nitrogen content. [Copyright &y& Elsevier]

Abstract: The farm gate nutrient balance approach has improved nutrient management in Western-European countries by re-examining the routine agricultural practices. This paper reports on the farm gate nitrogen (N) and phosphorus (P) balances of typical Hungarian arable and mixed farms calculated for 2002–2004. The farm gate nutrient surpluses/deficits varied a great deal between the farms within 1 year and between the different years for one farm. This could partly be explained by the stock changes. The N and P balances calculated hypothetically (assuming increased or decreased purchase instead of an increase or decrease of stock of roughage, concentrates, manure, mineral fertilizers and seeds and presuming increased or decreased sales instead of an increase or decrease of stock of animals, animal products and plant products) clearly reflected the lower grain crop yields in 2003 due to the dry weather circumstances, especially for the arable farms. The east–west divide in Hungarian agriculture was shown in the total inputs and surpluses of N. The low farm gate P surpluses or even deficits of most selected farms indicate soil mining and are a warning for possible future crop deficiencies and yield reduction. [Copyright &y& Elsevier]

Gamma irradiation is becoming a potential tool in soil ecological studies as it gives a possibility to vary a dose that selectively kills the target organism. It makes minimum changes in soil biochemical properties as compared to autoclaving and freezing. Although gamma irradiation has often been used in studying the roles of nematodes on nutrient cycling, the recommended doses to eliminate nematodes still lead to a nutrient flush, and are less reproducible. Given that the indirect effect of gamma irradiation is through radiolysis, the same dose might have a different effect on the soil biochemical properties as the soil moisture content changes. Thus, an optimal dose that eliminates nematodes needs to be determined taking the moisture content of the soil sample at the time of irradiation into consideration. We conducted an incubation experiment for about three months during which the effects of a range of low gamma irradiation doses (0, 1, 3 and 5 kGy) at different moisture content (air dried, 50% water filled pore space (WFPS), 80%WFPS) were tested on nematode abundance and selected soil biochemical properties. Leaching with water immediately after irradiation at 50%WFPS, was used to assess to what extent it would remove N from the flush. The results showed that as the moisture content of the soil increases from 50%WFPS to 80%WFPS, nematode abundance, enzyme activities and total mineral N concentrations decreased during most of the incubation period at each irradiation dose. Increasing the moisture content, however, did not make significant changes in total phospholipid fatty acid concentrations in all levels of irradiations except at 3 kGy. These findings indicate the effects of gamma irradiation on soil biological and chemical properties vary depending on the moisture content of the soil at the time irradiation. Moreover, the moisture content of the soil at the time of gamma irradiation need to be considered during optimizing gamma irradiation as a tool in selective sterilization or defaunation. In the current experimental set up, the application of 3 kGy at 80%WFPS at the time of irradiation eradicated nematodes and left a comparable microbial abundance and community structure to the unirradiated CTR. Leaching the 50%WFPS samples irradiated at 5 kGy dose immediately after irradiation generally significantly reduced both NH 4 + -N and NO 3 − -N concentrations, but NH + 4 -N concentration remained higher compared to the unirradiated CTR. This indicates that leaching with water only partly reduced the nutrient flush and underlines the need to test additional methods to reduce the nutrient flush further. [ABSTRACT FROM AUTHOR]