Interactions between microbial-feeding and predatory soil fauna trigger N2O emissions

Dairy production systems represent a significant source of air pollutants such as greenhouse gases (GHG), that increase global warming, and ammonia (NH3), that leads to eutrophication and acidification of natural ecosystems. Greenhouse gases and ammonia are emitted both by conventional and organic dairy systems. Several studies have already been conducted to design practices that reduce greenhouse gas and ammonia emissions from dairy systems. However, those studies did not consider options specifically applied to organic farming, as well as the multiple trade-offs occurring between these air pollutants. This article reviews agricultural practices that mitigate greenhouse gas and ammonia emissions. Those practices can be applied to the most common organic dairy systems in northern Europe such as organic mixed crop-dairy systems. The following major points of mitigation options for animal production, crop production and grasslands are discussed. Animal production: the most promising options for reducing greenhouse gas emissions at the livestock management level involve either the improvement of animal production through dietary changes and genetic improvement or the reduction of the replacement rate. The control of the protein intake of animals is an effective means to reduce gaseous emissions of nitrogen, but it is difficult to implement in organic dairy farming systems. Considering the manure handling chain, mitigation options involve housing, storage and application. For housing, an increase in the amounts of straw used for bedding reduces NH3 emissions, while the limitation of CH4 emissions from deep litter is achieved by avoiding anaerobic conditions. During the storage of solid manure, composting could be an efficient mitigation option, depending on its management. Addition of straw to solid manure was shown to reduce CH4 and N2O emissions from the manure heaps. During the storage of liquid manure, emptying the slurry store before late spring is an efficient mitigation option to limit both CH4 and NH3 emissions. Addition of a wooden cover also reduces these emissions more efficiently than a natural surface crust alone, but may increase N2O emissions. Anaerobic digestion is the most promising way to reduce the overall greenhouse gas emissions from storage and land spreading, without increasing NH3 emissions. At the application stage, NH3 emissions may be reduced by spreading manure during the coolest part of the day, incorporating it quickly and in narrow bands. Crop production: the mitigation options for crop production focus on limiting CO2 and N2O emissions. The introduction of perennial crops or temporary leys of longer duration are promising options to limit CO2 emissions by storing carbon in plants or soils. Reduced tillage or no tillage as well as the incorporation of crop residues also favour carbon sequestration in soils, but these practices may enhance N2O emissions. Besides, the improvement of crop N-use efficiency through effective management of manure and slurry, by growing catch crops or by delaying the ploughing of leys, is of prime importance to reduce N2O emissions. Grassland: concerning grassland and grazing management, permanent conversion from arable to grassland provides high soil carbon sequestration while increasing or decreasing the livestock density seems not to be an appropriate mitigation option. From the study of the multiple interrelations between gases and between farm compartments, the following mitigation options are advised for organic mixed crop-dairy systems: (1) actions for increasing energy efficiency or fuel savings because they are beneficial in any case, (2) techniques improving efficiency of N management at field and farm levels because they affect not only N2O and NH3 emissions, but also nitrate leaching, and (3) biogas production through anaerobic digestion of manure because it is a promising efficient method to mitigate greenhouse gas emissions, even if the profitability of this expensive investment needs to be carefully studied. Finally, the way the farmer implements the mitigation options, i.e. his practices, will be a determining factor in the reduction of greenhouse gas and NH3 emissions.

Identification of nitrous oxide (N2O) and carbon dioxide (CO2) emissions from soils amended with different types of compost is needed for appropriate use of manure in agriculture. This study aimed at investigating the interaction effects of compost type and soil properties and effects of moisture contents on N2O and CO2 emissions, with identification of relative abundances of functional ammonia-oxidizing genes. Laboratory tests were conducted using cattle manure compost (CC) or mixed compost (MC) (cattle, poultry, and swine manure) amended Kochi (from a greenhouse) or Ushimado (from a paddy field) soils (3% by weight) with controls (no compost). Initial moisture contents were adjusted to 60% water-holding capacity (WHC) for Kochi soil and 70% WHC for both soils. The samples were aerobically incubated at 25°C. Emissions of N2O and CO2 and contents of ammonium N (NH4 +-N) and nitrate N in soils were measured continuously until day 42. The abundances of ammonia-oxidizing bacteria (AOB) and archaea genes were estimated to evaluate nitrifying activities. Cumulative N2O and CO2 emissions were significantly higher (p < 0.05) in MC than those in CC treatments probably due to higher NH4 +-N content and lower C/N ratio, which facilitated faster N mineralization and C decomposition. Emissions of N2O and CO2 were higher in compost-amended Kochi soil (70% WHC) with high total C and N, mineral N, and clay contents than those in less fertile Ushimado soil. Interestingly, interactions of compost type and soil properties on N2O emissions were significant (p < 0.05) only in Kochi soil because the addition of decomposition resistant CC increased N2O emissions only from this soil with high C and N contents. Higher soil moisture contents increased N2O and CO2 emissions significantly (p < 0.05) in Kochi soil. Emissions of N2O until day 15 were mainly due to activities of AOB amoA genes (R2 = 0.91). This study suggests that N2O emissions are increased by high NH4 +-N contents and a low C/N ratio in compost and high total C and N, mineral N, and clay contents in soil. The application of compost with less decomposable C increases N2O emissions only from nutrient-rich soil.

Microplastics and biochar interactively affect nitrous oxide emissions from tobacco planting soil

Reclamation of coastal wetland to paddy soils alters the role of bacteria and fungi in nitrous oxide emissions: Evidence from a 53-year reclamation chronosequence study

Increased N2O emissions by the soil nematode community cannot be fully explained by enhanced mineral N availability

Many plant species possess structures on their leaves that often harbour predatory or fungivorous mites. These so‐called domatia are thought to mediate a mutualistic interaction; the plant gains protection because mites decimate plant pathogenic fungi or herbivores, whereas the mites find shelter in the domatia. We tested this hypothesis using two species of coffee (Coffea spp.) plants that posses domatia consisting of small cavities at the underside of the leaves, and which often harbour mites. We assessed densities of domatia, of the predatory mite Iphiseiodes zuluagai Denmark and Muma (Acari: Phytoseiidae) and of herbivorous mites Oligonychus ilicis (McGregor) (Acari: Tetranychidae) and Brevipalpus phoenicis (Geijskes) (Acari: Tenuipalpidae) on Coffea arabica L. (Rubiaceae) and Coffea canephora Pierre in the field. Over a period of 50 days, C. arabica harboured on average 7.5 times more predatory mites and 0.4–0.66 fewer prey mites than C. canephora. Hence, the higher density of predatory mites on C. arabica could not be explained by higher densities of prey. However, the density of domatia on C. arabica was on average 1.65 times higher than on C. canephora, and within each species, leaves with higher densities of domatia also harboured more predators. This suggests a positive effect of domatia on predatory mites. In the laboratory, survival of adult female predatory mites on leaves of C. arabica with open domatia was indeed significantly higher than on leaves with closed domatia. Hence, predatory mites benefited from the domatia. However, plants with higher densities of domatia did not harbour fewer herbivores. Taken together, our study only provides partial evidence for a mutualistic interaction between coffee plants and predatory mites, mediated by domatia.

How does soil compaction alter nitrous oxide fluxes? A meta-analysis

Agricultural soils represent a source of N2O and CO2 which are the major greenhouse gases and should be reduced to diminish global warming. The increase of organic matter in soils, which can be reached by the long-term application of organic fertilizer, is an important factor to improve soil quality and to bind atmospheric CO2. However, the influence of long-term organic fertilization on trace gas emissions is not well understood. Therefore, the aim of the present study was to compare the emissions of N2O and CO2 in different long-term field experiments with addition of organic and mineral or no fertilizer. The key question of this thesis is whether N2O emissions, which are produced during the microbial processes of nitrification and denitrification, increase due to higher organic C stocks. On the one hand higher C stocks can increase microbial activity which in turn depletes the oxygen in the soil. This leads to optimal conditions for denitrification. On the other hand C is used as a substrate for heterotrophic nitrification and denitrification. During this thesis the following four studies were performed to investigate the influence of organic fertilization on N2O emissions. The first experiment was a laboratory incubation with the sandy soil from a long-term fertilization experiment at Darmstadt. The effects of long-term fertilization (organic vs. mineral) on N2O emissions were determined at different soil moisture levels. Further, these long-term effects were compared with the short-term emissions following the application of different fertilizers (KNO3, farmyard manure and biogas waste). The second study was another incubation experiment, which was performed with soils from three different long-term experiments with similar fertilization history, but different texture and C stocks. The question underlying this study was whether different soil types lead to different C stocks and whether they have a different impact on N2O emissions. For this experiment, emission rates of N2O and CO2 were measured at a constant soil moisture content of 60% water-holding capacity, following the application of different fertilizers (KNO3 vs. farmyard manure from cattle) and after simulation of a heavy rainfall event, which increased soil moisture to field capacity. The third experiment was a two-year field study, which was conducted to determine the effect of increased organic C stocks on N2O emissions under field conditions. Gas fluxes were measured weekly with closed chambers on the sandy soil at the Darmstadt long-term fertilization experiment. In the fourth study a validation and calibration approach was tested to describe the field experiment at Darmstadt using the DNDC model. The results showed that increased C stocks only play a minor role in terms of N2O emissions. Two of the three soils investigated in the second study showed slightly increased N2O emissions when incubated at 60% water-holding capacity. However, the effect of fertilization history and increased organic carbon contents on N2O emissions was small. Moreover, these effects were not detectable anymore following the application of fertilizers, which resulted in large emissions independent of the fertilization history. On the sandy soil from the Darmstadt site, the higher organic C stocks did not affect N2O emissions, neither during the laboratory incubation (first study) nor during the field experiment (third study). This was attributed to the sandy soil texture and low soil moisture content during the incubation and during the field experiment. During the laboratory study, short-term emissions after fertilization were much more pronounced. Especially the application of biogas waste was followed by very high N2O emissions. Tillage combined with fertilization led to the highest emissions in the field. The second laboratory incubation showed much higher emissions from a soil which was depleted of organic matter due to the lack of fertilization for 25 years. This indicates that a sustainable soil humus management is necessary to regulate N2O emissions. Modelling C and N dynamics using the DNDC model indicated that the model was useful for a prediction of N2O emissions after site-specific cal! ibration when the same fertilizer type was used at a different rate. However, the model failed when a different fertilizer type was used. Summing up, organic C stocks can influence N2O emissions but only to a small extent and under certain conditions. On sandy soils, where soil moisture tends to be low, the risk of increased N2O emissions at higher organic C stocks is probably low. Further, short-term effects like fertilization events influence emission dynamics to a much higher extent. Finally, it appeared that a balanced nutrient and humus management can even avoid N2O emissions by it positive effects on soil structure. Our results indicate that feedback mechanisms of soil carbon sequestration on N2O emissions have to be considered when discussing options to increase soil carbon stocks.

The application of urea in agricultural soil significantly boosts nitrous oxide (N2O) emissions. However, the reason for nitrite accumulation, the period of nitrite-oxidizing bacteria (NOB) suppression, and the main NOB species for nitrite removal behind urea fertilization have not been thoroughly investigated. In this study, four laboratory microcosm experiments were conducted to simulate urea fertilization in agricultural soils. We found that within 36 h of urea application, nitrite oxidation lagged behind ammonia oxidation, leading to nitrite accumulation and increased N2O emissions. However, after 36 h, NOB activity recovered and then removed nitrite, leading to reduced N2O emissions. Urea use resulted in an N2O emission rate tenfold higher than ammonium. During incubation, Nitrobacter-affiliated NOB growth decreased initially but increased later with urea use, while Nitrospira-affiliated NOB appeared unaffected. Chlorate suppression of NOB lasted longer, increasing N2O emissions. Urease inhibitors effectively reduced N2O emissions by slowing urea hydrolysis and limiting free ammonia production, preventing short-term NOB suppression. In summary, short-term NOB suppression during urea hydrolysis played a crucial role in increasing N2O emissions from agricultural soils. These findings revealed the reasons behind the surge in N2O emissions caused by extensive urea application and provided guidance for reducing N2O emissions in agricultural production processes.

Nitrous oxide (N2O) flux measurements from an Irish spring barley field managed under conventional and reduced tillage and different N fertilizer rates at the Teagasc Oak Park Research Centre were made for two consecutive seasons. The aims were to investigate the efficacy of reduced tillage, reduced N fertilizer and climate change on N2O fluxes and emission factors and to study the relationship between crop yield and N-induced fluxes of N2O. The soil is a sandy loam with a pH of 7.4 and organic carbon and nitrogen content at 15 cm of 19 and 1.9 g kg-1 dry soil, respectively. Three climate scenarios, a baseline of measured climatic data from a nearby weather station and a high and low temperature sensitive scenarios predicted by the Hadley Global Climate Model were investigated. The Field-DeNitrification DeComposition (DNDC) was tested against measured nitrous oxide flux from the field, and then used to estimate future fluxes. Reduced tillage had no significant effect on N2O fluxes from soils or crop grain yield. Soil moisture and soil nitrate are the main significant factors affecting N2O flux. The derived emission factor was 0.6% of the applied N fertilizer. By reducing the applied nitrogen fertilizer by 50 % compared to the normal field rate, N2O emissions could be reduced by 57% with no significant decrease on grain yield or quality. DNDC was found suitable to estimate N2O fluxes from Irish arable soils however, underestimated the flux by 24%. Under climate change, using the high temperature increase scenario, DNDC predicted an increase in N2O emissions from both conventional and reduced tillage, ranging from 58 to 88% depending upon N application rate. In contrast annual fluxes of N2O either decreased or increased slightly in the low temperature increase scenario relative to N application (-26 to +16%). Outputs from the model indicate that elevated temperature and precipitation increase N mineralisation and total denitrification leading to greater fluxes of N2O. Annual uncertainties due to the use of two different future climate scenarios were significantly high, ranging from 74 to 95% and from 71 to 90% for the conventional and reduced tillage respectively.

Tea gardens, being a key agroecosystem type, are an important source of nitrous oxide (N2O) emissions. However, main factors that regulate N2O emissions following urea and organic matter amendments have yet to be clarified. To investigate the influence of different fertilization management measures on N2O emissions in tea garden soil, a 50-day laboratory incubation experiment was conducted. Five treatments were designed for this experiment: control (CK), urea (U), rapeseed cake (R), urea + rapeseed cake (2:1, UR1), and urea + rapeseed cake (1:2, UR2). N2O emission flux in the R treatment peaked at 14.12 μg kg−1 h−1 on day 19, which occurred later than the UR1, UR2, and U treatments. Cumulative N2O emissions from the R and UR2 treatments were 6073 and 4296 μg kg−1, respectively, which were greater by a factor of 11.2 and 7.9, respectively, compared to the U treatment. Moreover, N2O emissions of the UR1 and UR2 treatments were significantly lower than the R treatment. Additionally, N2O emissions were also significantly positively correlated to pH levels and microbial biomass carbon (MBC) content. MBC content had the most direct and greatest influence on soil N2O emissions, indicating that MBC could be the key limiting factor for N2O emissions in this experiment. A single application of rapeseed cake caused an increase in N2O emissions, whereas the combined application of rapeseed cake and a synthetic N fertilizer (urea) caused a decrease in N2O emissions. Results from this study offer potential strategies to mitigate soil N2O emissions from tea garden agroecosystems through improved field fertilization management.

N2O emissions from a fertilized humid grassland near Cork, Ireland were continuously measured during 2003 using an eddy covariance system. For most of the year emissions were close to zero and 60% of the emissions occurred in eight major events of 2–20 days’ duration. Two hundred and seven kg ha−1 of synthetic N and 130 kg ha−1 organic N were applied over the year and the total measured annual N2O emission was 11.6 kg N ha−1. The flux data were used to test the prediction of N2O emissions by the DNDC (DeNitrification – DeComposition) model. The model predicted total emissions of 15.4 kg N ha−1, 32 % more than the observed emissions. On this basis the model was further used to simulate (a) background (non-anthropogenic) N2O emissions and (b) the effect on N2O emissions of future climate perturbations based on the Hadley Center model output of the IS92a scenario for Ireland. DNDC predicts 1.7 kg N ha−1 year−1 of background N2O emissions, accounting for 15% of the observed emissions. Climate shifts will increase total annual modeled N2O emissions from 15.4 kg N ha−1 to 22.4 kg N ha−1 if current levels of N applications are maintained, or to 21.2 kg N ha−1 if synthetic N applications are reduced to 170 kg N ha−1 to comply with recent EU water quality legislation. Thus the projected increase in N2O emissions due to climate change is far larger than the decrease expected from reduced fertilizer applications.

Effects of moisture on emissions of methane, nitrous oxide and carbon dioxide from food and garden waste composting

Simulation of a spark ignited hydrogen engine for minimization of NOx emissions

Climate factors affect N2O emissions by influencing the migration and transformation of nonpoint source nitrogen in an agricultural watershed