Environmental Tradeoffs between Nutrient Recycling and Greenhouse Gases Emissions in an Integrated Aquaculture-Agriculture System.

The sub-project of the project “Minderung von Treibhausgasemissionen im Rapsanbau unter besonderer Berucksichtigung der Stickstoffdungung” of the division Plant Nutrition and Crop Physiology, Department of Crop Sciences of Georg-August University focused on steps in the nitrogen cycle that produce or interfere with N2O emissions from soils. It addressed the question of how the N cycle is modified by a winter oilseed rape – winter wheat – winter barley crop rotation. The focus of the doctoral thesis was put on the post-harvest period and the production of N2O emissions in winter oilseed rape. Several lab and field experiments were conducted: (1) Incubation experiment using oilseed rape and 15N-labelled barley straw; An incubation experiment carried out under controlled conditions aimed at comparing N addition and different straw qualities for their potential to provoke N2O emissions from soil. Treatments consisted of non-treated control soil (CK), 15N labelled barley straw (BST), oilseed rape straw (RST), 15N labelled barley straw + mineral N (BST+N), or oilseed rape straw + mineral N (RST+N). N fertilizer was applied to the soil surface as calcium ammonium-nitrate at a rate of 67.5 mg N kg-1 soil equiv. to 100 kg N ha-1 and soil moisture was adjusted to 80% water-holding capacity. The experiment covered a measurement period of 43 days. Cumulative N2O emissions in this study summed up to 3, 19, 26, 439 and 387µg N2O-N kg-1 soil 43 days-1 for CK, BST, RST, BST+N and RST+N. Application of mineral N fertilizer to the straw amended soils enhanced N2O emissions considerably in BST+N and RST+N treatments masking the effect of straw type. 15N labeling showed that only about 0.72% and 0.46% of the emitted N2O originated from straw-N in the BST and BST+N treatments after 22 days indicating a very low share of straw-borne N to the formation of N2O emissions. In agricultural practice, an N fertilization to soils amended with C-rich residues in the post-harvest period could lead to high N2O emissions. (2) Post-harvest N2O emissions as affected by N fertilizer and straw management – 2 year study at the site Reinshof; Management options to mitigate N2O emissions in oilseed rape cropping were tested in a 2-year field experiment at the field site Reinshof of the Faculty of Agricultural Sciences of Georg-August University of Goettingen. The treatments included a reduced spring N fertilization rate (1/2 of current recommendation), N fertilization of 180 kg N ha-1 and oilseed rape straw removal after harvest. N2O sampling was done from oilseed rape harvest to the beginning of the following growth season. The COUP model (Coupled heat and mass transfer model for the soil-plant-atmosphere system) was employed to uncover possible mechanisms of N2O emissions. In 2013, cumulative August-March N2O emissions ranged between 0.46±0.05 kg N2O-N ha-1 (0 kg N ha-1, with straw removal) and 1.05±0.1 kg N2O-N ha-1 (180 kg N ha-1 with straw application) whereas in 2014 N2O emissions were clearly higher accounting for 4.06±0.34 (90 kg N ha-1, with straw application) und 7.33±0.24 kg N2O-N ha-1 (unfertilized control soil with straw incorporation). There was no statistically significant effect of fertilization (p>0.05), but straw removal compared to straw incorporation slightly increased N2O emissions. In contrast to management measures, soil temperature and soil moisture showed a large influence on the rates of N2O emissions. The modeling approach indicated the importance of decomposition activity. Decomposition accelerated N cycling and in particular denitrification rates with high N2O emissions. (3) Field studies in five regions of Germany in a winter oilseed rape – winter wheat – winter barley crop rotation; For a detailed evaluation of N2O emissions in important oilseed rape cropping regions of Germany, 5 field experimental sites across Germany – Berge, Dedelow, Ihinger Hof, Hohenschulen and Merbitz – were chosen. To allow comparability, the crops were grown simultaneously from December 2012 to October 2015. Various parameters like soil temperature and water-filled pore space (WFPS) were recorded and N2O emissions were measured in the crops oilseed rape, wheat and barley and yield-related N2O emissions were calculated. To assess the impact of abiotic factors and crops, a generalized additive model was set up. The generalized additive model revealed that the abiotic factors drove N2O emissions. The impact of environmental drivers like temperature and WFPS on N2O emissions varied depending on site, but not by crop type. Fertilizer-related N2O emissions across all five sites were 0.76, 0.74 and 0.76% of the applied fertilizer N for oilseed rape, winter wheat and winter barley, respectively. N2O emissions from non-fertilized soils were not considered in this approach. Generally, the thesis demonstrated the dependence of N2O emissions on a set of factors in the post-harvest period. The factor's level of importance changed as they were varying in magnitude. Management options have to be reevaluated and adopted to fit a changing climate.

Seasonal effects reveal potential mitigation strategies to reduce N2O emission and N leaching from grassland swards of differing composition (grass monoculture, grass/clover and multispecies)

Nitrous oxide (N2O) emissions are a major source of gaseous nitrogen loss, causing environmental pollution. The low organic content in the Loess Plateau region, coupled with the high fertilizer demand of maize, further exacerbates these N losses. N fertilizers play a primary role in N2O emissions by influencing soil denitrifying bacteria, however, the underlying microbial mechanisms that contribute to N2O emissions have not been fully explored. Therefore, the research aimed to gain insights into the intricate relationships between N fertilization, soil denitrification, N2O emissions, potential denitrification activity (PDA), and maize nitrogen use efficiency (NUE) in semi-arid regions. Four nitrogen (N) fertilizer rates, namely N0, N1, N2, and N3 (representing 0, 100, 200, and 300 kg ha-1 yr.-1, respectively) were applied to maize field. The cumulative N2O emissions were 32 and 33% higher under N2 and 37 and 39% higher under N3 in the 2020 and 2021, respectively, than the N0 treatment. N fertilization rates impacted the abundance, composition, and network of soil denitrifying communities (nirS and nosZ) in the bulk and rhizosphere soil. Additionally, within the nirS community, the genera Cupriavidus and Rhodanobacter were associated with N2O emissions. Conversely, in the nosZ denitrifier, the genera Azospirillum, Mesorhizobium, and Microvirga in the bulk and rhizosphere soil reduced N2O emissions. Further analysis using both random forest and structural equation model (SEM) revealed that specific soil properties (pH, NO3--N, SOC, SWC, and DON), and the presence of nirS-harboring denitrification, were positively associated with PDA activities, respectively, and exhibited a significant association to N2O emissions and PDA activities but expressed a negative effect on maize NUE. However, nosZ-harboring denitrification showed an opposite trend, suggesting different effects on these variables. Our findings suggest that N fertilization promoted microbial growth and N2O emissions by increasing the abundance of nirS and nosZ denitrifiers and altering the composition of their communities. This study provides new insights into the relationships among soil microbiome, maize productivity, NUE, and soil N2O emissions in semi-arid regions.

Nitrogen fertiliser application represents the largest anthropogenic source of nitrous oxide (N2O) emissions, and the magnitude of these emissions is dependent on the type of fertilisers applied in the agroecosystems. Despite N-P-K compound fertilisers being commonly used in agricultural soils, a lack of information exists regarding their effects on N2O emissions. This study aims at examining the effects of different commonly used N-P-K compound fertiliser formulations with contrasting nitrate to ammonium ratios (0.05 to 0.88) on N2O emissions, yield, and nitrogen use efficiency (NUE) in temperate grassland and to compare these variables with common straight N fertilisers. Compound fertilisers with varying NPK inclusion rates (18-6-12, 10-10-20, 24-2.2-4.5, and 27-2.5-5), and calcium ammonium nitrate (CAN) and urea + N-(n-butyl) thiophosphoric triamide (NBPT) were applied at 80 kg N ha−1 to experimental plots in managed grassland on two occasions in a growing season. Fluxes of N2O during the experiment period, yield and NUE following two harvests were measured. The cumulative N2O emission from urea + NBPT, 18-6-12, 10-10-20, and 24-2.2-4.5 treatments were significantly reduced by 44%, 43%, 37%, and 31% compared with CAN treatment under conducive soil moisture condition. Under the same soil condition, 18-6-12 and 10-10-20 treatments showed higher yield, N uptake, and NUE although did not significantly differ from the other fertiliser treatments. Our results suggest that ammonium-based compound fertilisers have a potential to reduce N2O emissions while maintaining yields. Further long-term study is needed to capture the full magnitude of variations in N2O emissions, including ammonia (NH3) volatilization from nitrate and ammonium-based compound fertiliser applications from multiple soil types and under different climatic conditions.

Permafrost regions are an important source of greenhouse gases. However, the effects of different permafrost wetland types on greenhouse gas emissions and the driving factors are still unclear in the permafrost region. Here, we selected three typical permafrost wetlands from the Daxing'an Mountains to investigate the effects of permafrost wetland types on greenhouse gas emissions. The cumulative N2O, CO2, and CH4 emissions were 84–122, 657,942–1,446,121, and 173–16,924 kg km−2, respectively. The linear mixed effects model indicated that N2O emissions were significantly affected by the NO3−‐N content, whereas CO2 emissions were mainly driven by soil temperature, water table level, and NO3−‐N content. CH4 emissions were affected by soil temperature and water table level. Permafrost wetland types significantly affected the average and cumulative N2O, CO2, and CH4 emissions. The cumulative N2O emissions were highest in the Larix gmelinii ‐ Carex appendiculata (LC) wetland and lowest in the Betula fruticosa Pall. (B) wetland, driven by NO3−‐N content. The cumulative CO2 emissions were highest in the B wetland and lowest in the L. gmelinii ‐ Ledum palustre var. dilatatum (LL) wetland. The cumulative CH4 emissions from B wetland were significantly higher than those from LL and LC wetlands. The differences in cumulative CO2 and CH4 emissions were driven by the water table level. Our findings indicate that NO3−‐N content affect the spatial‐temporal variation of N2O emissions, whereas water table level influence the spatial‐temporal variation of CO2 and CH4 emissions in the permafrost region of the Daxing'an Mountains.

Adding Corbicula fluminea altered the effect of plant species diversity on greenhouse gas emissions and nitrogen removal from constructed wetlands in the low-temperature season

Intensive vegetable production exhibits contrasting characteristics of high nitrous oxide (N2O) emissions and low nitrogen use efficiency (NUE). In an effort to mitigate N2O emissions and improve NUE, a field experiment with nine consecutive vegetable crops was designed to study the combined effects of nitrogen (N) and biochar amendment and their interaction on soil properties, N2O emission and NUE in an intensified vegetable field in southeastern China. We found that N application significantly increased N2O emissions, N2O–N emission factors and yield‐scaled N2O emissions by 51–159%, 9–125% and 14–131%, respectively. Moreover, high N input significantly decreased N partial factor productivity (PFPN) and even yield during the seventh to ninth vegetable crops along with obvious soil degradation and mineral N accumulation. To the contrary, biochar amendment resulted in significant decreases in cumulative N2O emissions, N2O–N emission factor and yield‐scaled N2O emissions by 5–39%, 16–67% and 14–53%, respectively. In addition, biochar significantly increased yield, PFPN and apparent recovery of N (ARN). Although without obvious influence during the first to fourth vegetable crops, biochar amendment mitigated N2O emissions during the fifth to ninth vegetable crops. The relative effects of biochar amendments were reduced with increasing N application rate. Hence, while high N input produced adverse consequences such as mineral N accumulation and soil degradation in the vegetable field, biochar amendment can be a beneficial agricultural strategy to mitigate N2O emissions and improve NUE and soil quality in vegetable field.

Reducing N2O emissions with enhanced efficiency nitrogen fertilizers (EENFs) in a high-yielding spring maize system.

The burning of agricultural straw is a pressing environmental issue, and identifying effective strategies for the rational utilization of straw resources is decisive for achieving sustainable development. Owing to its high carbon content and exceptional stability, straw biochar produced via pyrolysis has emerged as a key focus in multidisciplinary research. However, the efficacy of biochar in mitigating nitrous oxide (N2O) emissions from paddy soils is not consistent. A 2-year field experiment was conducted and investigated the impact of biochar derived from two feedstocks (rice straw and wheat straw, pyrolyzed at 450°C) on N2O emissions, global warming potential (GWP), greenhouse gas intensity (GHGI), nitrogen use efficiency (NUE), crop yield, and soil quality. The static chamber technique was used for collecting N2O gas samples, and concentrations were analyzed through gas chromatography methods. The treatment combinations included BR0 (control), BR1 (NPK at the recommended dose, 120:60:40kgha-1), BR2 (wheat straw biochar, 5 t ha-1), and BR3 (rice straw biochar, 5 t ha-1). The results exhibited that cumulative N2O emissions from BR2 and BR3 treatments decreased by 10.55% and 13.75% respectively, compared to BR1. Lower GWP and GHGI were observed under both biochar treatments compared with BR1. The highest rice grain yield (3.48Mgha-1) and NUE (76.72%) were recorded from BR3, which also exhibitedthe lowest yield-scaled N2O emission. We observed positive correlations between soil nitrate, ammonia and water-filled pore spaces, while NUE showed negative correlations with N2O emissions. Significant (p < 0.05) improvements in soil quality were also detected in both the biochar treated plots, indicated by increased soil pH, water holding capacity, porosity, and nutrient contents. Overall, the results suggest that applying biochar at a rate of 5 t ha-1 in paddy soil is a viable nutrient management strategy with the potential to reduce reliance on inorganic fertilizers, mitigate N2O emissions, and contribute to sustainable food production.

Rational application of nitrogen is an important strategy for increasing yield while reducing environmental pollution due to nitrogen. Pot experiments were conducted to study the effects of different application times on maize yield and soil N2O emission under conditions of equal nitrogen content, and to explore the relationship between the abundance of nitrogen conversion functional genes and N2O emission. Four treatments were used, namely a control (CK, no urea), one-time application (S1, one application of 0.5 g·kg-1 urea+nitrification inhibitor), two separate applications ［S2, two applications of 0.5 g·kg-1 urea (40% and 60% respectively)］ and three separate applications (S3, 0.5 g·kg-1 urea was divided into three different applications: 20%, 40% and 40% respectively). The results showed that: ① nitrogen application promoted soil acidification, and the degree of soil acidification varied significantly with different application times. More applications of nitrogen led to stronger soil acidification. Nitrogen application significantly increased the ear yield and stem biomass of fresh table maize, but different nitrogen application times may alter soil pH, leading to differences in the degree of nitrogen uptake and utilization in plants. While the S3 treatment significantly reduced soil pH, it also reduced the cumulative nitrogen uptake and utilization in the plants, resulting in a high cumulative N2O emission. Compared with the S3 treatment, the yield was 40.21% and 42.55% higher in the S1 and S2 treatments, and the cumulative N2O emission decreased by 79.4% and 20.9%, respectively. ② N2O emission was positively correlated with the abundance of AOB and nirK genes, which were the main contributors to N2O emission. S1 significantly decreased the abundance of AOB and nirK genes and N2O emissions, while S2 and S3 significantly increased the abundance of nirK and nirS genes and decreased the abundance of nosZ genes after fertilization, promoting N2O emissions. Nitrogen application times affect the functional genes of the nitrogen transformation process, and thus affect N2O emissions. In conclusion, a one-time application of urea combined with DCD only guarantees high maize yield and improves the efficient use of nitrogen, but also reduces greenhouse gas emissions. Thus, it is the recommended nitrogen fertilization mode for the cultivation of fresh corn in Hainan.

Long-term application of controlled-release urea reduced ammonia volatilization, raising the risk of N2O emissions and improved summer maize yield

Nitrous oxide (N2O) is a potent greenhouse gas primarily emitted from agricultural soils through microbial nitrogen transformation processes. Different nitrogen application rates and fertilizer types influence soil nitrogen transformation pathways, thereby affecting N2O production and emissions. Reclaimed water (RW), due to its chemical composition, may further modulate these processes. In this study, a disturbed soil incubation experiment was conducted using two irrigation water types [RW and deionized water (CW)], three nitrogen fertilizer forms [ammonium sulfate (NH4+), potassium nitrate (NO3−), and sodium nitrite (NO2−)], and two nitrogen application rates (200 and 400 mg N kg−1) to examine the dynamics of soil N2O emissions. The study found that, compared to CW, high fertilization levels (400 mg N kg−1) of NH4+ under RW treatment significantly increased cumulative soil N2O emissions by 25.04%, primarily by enhancing the abundance of the ammonia monooxygenase gene in ammonia-oxidizing archaea (AOA-amoA), the ammonia monooxygenase gene in ammonia-oxidizing bacteria (AOB-amoA), and the nitrite reductase gene (nirS). However, at low fertilization levels (200 mg N kg−1) of NH4+, there is no significant differences in cumulative N2O emissions. Under NO3− treatment, although RW increased the abundance of AOA-amoA and AOB-amoA, it did not lead to higher soil NO or N2O emissions at either high or low NO3− concentrations. In contrast, under NO2− treatment, RW increased the abundance of AOA-amoA and AOB-amoA compared to CW, significantly enhancing cumulative soil N2O emissions by 27.56% and 39.25%, respectively. In conclusion, RW irrigation does not elevate soil N2O emissions with nitrate-based fertilizers. However, careful management of nitrification rates is required with ammonium-based fertilizers, including the use of nitrification inhibitors and improved soil aeration, to minimize NO2− accumulation and related environmental risks.

Nitrous oxide emissions are highly episodic and to accurately quantify them annually, continuous measurements are required. A tower-based micrometeorological measuring system was used on a commercial cattle farm near Cô teau-du-Lac, (QC, Canada) during 2003 and 2004 to quantify N2O emissions associated with the production of edible peas. It was equipped with an ultrasonic anemometer and a fast-response closed-path tunable diode laser. Continuous measurements of N2O fluxes were made during the spring thaw following corn cultivation in summer 2002, then during an edible pea growing season, followed by cattle manure application, cover crop planting and through until after the next spring ploughing. The cumulative N2O emissions of 0.7 kg N2O-N ha-1 during the initial snowmelt period following corn harvest were lower than expected. Sustained and small N2O emissions totalling 1.7 kg N2O-N ha-1 were observed during the growing season of the pea crop. Solid cattle manure applied after the pea harvest generated the largest N2O emissions (1.9 kg N2O-N ha-1 over 10 d) observed during the entire sampling period. N2O emissions associated with the cover crop in the fall were mostly influenced by manure application and totalled 0.8 kg N2O-N ha-1. For the subsequent spring thaw period, N2O emissions were 0.8 kg N2O-N ha-1. This represents approximately 15% of the annual emissions for the edible pea-cover crop system, which totalled 5.6 kg N2O-N ha-1 over the measuring periods. There was little difference in spring thaw N2O emissions between the two growing seasons of corn and edible pea-cover crop. Key words: Nitrous oxide emissions, legumes, snowmelt, dairy manure, tunable diode laser, flux tower

Literature reports on N2O and NO emissions from organic and mineral agricultural soil amended with N-containing fertilizers have reached contradictory conclusions. To understand the influence of organic manure (OM) and chemical fertilizer application on N2O and NO emissions, we conducted laboratory incubation experiments on an agricultural sandy loam soil exposed to different long-term fertilization practices. The fertilizer treatments were initiated in 1989 at the Fengqiu State Key Agro-ecological Experimental Station and included a control without fertilizer (CK), OM, mineral NPK fertilizer (NPK), mineral NP fertilizer (NP), and mineral NK fertilizer (NK). The proportion of N emitted as NO and N2O varied considerably among fertilizer treatments, ranging from 0.83% to 2.50% as NO and from 0.08% to 0.36% as N2O. Cumulative NO emission was highest in the CK treatment after NH 4 + -N was added at a rate of 200 mg N kg−1 soil during the 612-h incubation period, whereas the long-term application of fertilizers significantly reduced NO emission by 54–67%. In contrast, the long-term application of NPK fertilizer and OM significantly enhanced N2O emission by 95.6% and 253%, respectively, compared to CK conditions. The addition of NP fertilizer (no K) significantly reduced N2O emission by 25.5%, whereas applications of NK fertilizer (no P) had no effect. The difference among the N-fertilized treatments was due probably to discrepancies in the N2O production potential of the dominant ammonia-oxidizing bacteria (AOB) species rather than AOB abundance. The ratio of NO/N2O was approximately 24 in the CK treatment, significantly higher than those in the N-fertilized treatments (3–11), and it decreased with increasing N2O production potential in N-fertilized treatments. Our data suggests that the shift in the dominant AOB species might produce reciprocal change in cumulative NO and N2O emissions.

Application of feedlot manure (FLM) to cropping and grazing soils could provide a valuable N nutrient resource. However, because of its high but variable N concentration, FLM has the potential for environmental pollution of water bodies and N2O emission to the atmosphere. As a potential management tool, we utilised the low-nutrient green waste compost (GWC) to assess its effectiveness in regulating N release and the amount of N2O emission from two Vertisols when both FLM and GWC were applied together. Cumulative soil N2O emission over 32 weeks at 24°C and field capacity (70% water-filled pore space) for a black Vertisol (Udic Paleustert) was 45 mg N2O m−2 from unamended soil. This increased to 274 mg N2O m−2 when FLM was applied at 1 kg m−2 and to 403 mg N2O m−2 at 2 kg m−2. In contrast, the emissions of 60 mg N2O m−2 when the soil was amended with GWC 1 kg m−2 and 48 mg N2O m−2 at 2 kg m−2 were not significantly greater than the unamended soil. Emission from a mixture of FLM and GWC applied in equal amounts (0.5 kg m−2) was 106 mg N2O m−2 and FLM applied at 0.5 kg m−2 and GWC at 1.5 kg GWC m−2 was 117 mg N2O m−2. Although cumulative N2O emissions from an unamended grey Vertisol (Typic Chromustert) were only slightly higher than black Vertisol (57 mg N2O m−2), FLM application at 1 kg m−2 increased N2O emissions by 14 times (792 mg N2O m−2) and at 2 kg m−2 application by 22 times (1260 mg N2O m-2). Application of GWC did not significantly increase N2O emission (99 mg N2O m−2 at 1 kg m−2 and 65 mg N2O m−2 at 2 kg m−2) above the unamended soil. As observed for the black Vertisol, a mixture of FLM (0.5 kg m−2) and GWC (0.5 or 1.5 kg m−2) reduced N2O emission by >50% of that from the FLM alone, most likely by reducing the amount of mineral N (NH 4 + –N and NO 3 − –N) in the soil, as mineral N in soil and the N2O emission were closely correlated.