Water-filled Pore Space Research Articles

Irrigation Combined with Aeration Promoted Soil Respiration through Increasing Soil Microbes, Enzymes, and Crop Growth in Tomato Fields

Soil respiration (Rs) is one of the major components controlling the carbon budget of terrestrial ecosystems. Aerated irrigation has been proven to increase Rs compared with the control, but the mechanisms of CO2 release remain poorly understood. The objective of this study was (1) to test the effects of irrigation, aeration, and their interaction on Rs, soil physical and biotic properties (soil water-filled pore space, temperature, bacteria, fungi, actinomycetes, microbial biomass carbon, cellulose activity, dehydrogenase activity, root morphology, and dry biomass of tomato), and (2) to assess how soil physical and biotic variables control Rs. Therefore, three irrigation levels were included (60%, 80%, and 100% of full irrigation). Each irrigation level contained aeration and control. A total of six treatments were included. The results showed that aeration significantly increased total root length, dry biomass of leaf, stem, and fruit compared with the control (p < 0.05). The positive effect of irrigation on dry biomass of leaf, fruit, and root was significant (p < 0.05). With respect to the control, greater Rs under aeration (averaging 6.2% increase) was mainly driven by soil water-filled pore space, soil bacteria, and soil fungi. The results of this study are helpful for understanding the mechanisms of soil CO2 release under aerated subsurface drip irrigation.

Compost and soil moisture effects on seasonal carbon and nitrogen dynamics, greenhouse gas fluxes and global warming potential of semi-arid soils

PurposeAn 8-week incubation study was conducted to monitor soil inorganic nitrogen (N), dissolved organic carbon (DOC), greenhouse gases (GHG) [CO2, N2O and CH4] and cumulative global warming potential (GWP) in dryland soil.MethodsSoil was amended with variable rates of compost (zero, 15, 30 and 45 dry Mg ha−1) and soil moistures [5% (dry), 7% (normal) and 14% (wet) water filled pore space (WFPS)] and experienced biweekly temperature transitions from 5 °C (late winter) to 10 °C (early spring) to 15 °C (late spring) to 25 °C (early summer).ResultsThe addition of 30 and 45 Mg ha−1 compost enhanced N mineralization with 13% more soil inorganic N (7.49 and 7.72 µg Ng−1 day−1, respectively) during early summer compared with lower compost rates. Normal and wet soils had 35% more DOC in the late spring (an average of 34 µg g−1 day−1) compared to the dry WFPS, but transitioning from late spring to early summer, DOC at all soil WFPS levels increased. Highest rates of compost were not significant sources of GHG with normal soil WFPS, compared with lower compost rates. Carbon dioxide emissions increased by 59 and 15%, respectively, as soil WFPS increased from dry to normal and normal to wet. Soils with normal WFPS were the most effective CH4 sink.ConclusionOne-time application of high compost rates to dryland soils leads to enhanced N and C mineralization under normal soil moisture and warmer temperature of the summer but will not pose significant global warming dangers to the environment through GHG emissions since soils are rarely wet.

Combining no-till with rye (Secale cereale L.) cover crop mitigates nitrous oxide emissions without decreasing yield

No-till (NT) often increases soil carbon (C) sequestration compared with conventional tillage (CT), yet its net effect on N2O emissions is controversial. Cover crops (CCs) adoption is promoted in NT systems because CCs growth curbs nitrate losses via leaching. However, incorporating CC residues into the soil may have positive or negative effects on N2O emissions depending on CC species and agro-ecosystem management. A better understanding of how tillage practices and CC species affect N2O emissions is therefore needed for the development of productive agroecosystems that contribute to climate change mitigation. The objectives of this three-year (2015–2017) field experiment on a Udertic Haplustalf soil in the Po Valley were to compare N2O emissions and crop yield of soybean under NT and CT, and to examine how contrasting residues from two CCs (rye, Secale cereale L. vs hairy vetch, Vicia villosa Roth) affect N2O emissions in NT soybean and maize. We hypothesized that N2O emissions would be lower with NT than with CT and with rye residues than with vetch ones. Nitrous oxide was continuously sampled using automatic chambers during three periods (emergence, N-fixation and maturity) over the soybean-cropping season in 2015 and during the entire cropping maize season in 2017. The DNDC model was calibrated (2015 data) and validated (2017 data), and then used to estimate the annual cumulative N2O emissions in different treatments. Overall, N2O emissions in NT were 40–55% lower than in CT, for both in situ measurements (Period I) and modelled estimations. These differences could be ascribed to the higher water-filled pore space (WFPS) and soil nitrate availability in CT than in NT. No-till also increased SOC content (28%; 0–5 cm) and earthworm abundance (5 times) compared with CT. Within NT systems, N2O emissions were 20–36% lower with rye CC than with vetch CC (P < 0.05), which was a consequence of the lower availability of soil mineral N under rye than under vetch due to the high C/N ratio of rye residues. Yield of soybean and maize under NT was higher with rye CC than with vetch CC. The combination of NT and rye CC that led to the lowest N2O emissions and highest yields should be recommended in the Po Valley region.

Effect of nitrogen fertilisers on nitrous oxide emission, nitrifier and denitrifier abundance and bacterial diversity in closed ecological systems

In a 3-year microcosm study the nitrous oxide (N2O) emission from an agricultural soil amended with urea, ammonium sulphate or potassium nitrate were examined. Soil samples were taken every year to determine the soil physicochemical properties, the total abundance of bacteria, archaea, nitrifier and denitrifier communities and the changes in the structure and composition of the bacterial community. Gene abundance and biodiversity were estimated using quantitative PCR and pyrosequencing, respectively. The soils were watered weekly to reach 80% water filled pore space and varied from 80 to 62% during that time. N-fertilisation increased the abundance of bacteria and decreased that of archaea. Soils treated with ammonium or urea emitted more N2O than that amended with potassium nitrate and produced yearly increases in the abundance of nitrification genes. Also, the abundance of the denitrification genes gradually increased during the experimental period. N2O emission decreased on a yearly basis and so did the ratio of the genes involved in N2O production and reduction. A non-metric multidimensional scaling plot showed that N2O emission was positively related with the norB gene and negatively with the nosZ. The Shannon and Simpson diversity indices indicated that N-fertilisation reduced the number of operational taxonomic units (OTUs) and that the bacterial community became dominated by a small group of OTUs, respectively. N-fertilisation reduced the number of OTUs whose relative abundance was lower than 1%. We conclude that potassium nitrate reduces N2O emissions and increases the abundance of the N2O reducers. This work also shows that N-fertilisation decreases soil biodiversity and that its response depends on the type of the N-fertiliser.

Oxygen Regulates Nitrous Oxide Production Directly in Agricultural Soils.

Oxygen (O2) plays a critical and yet poorly understood role in regulating nitrous oxide (N2O) production in well-structured agricultural soils. We investigated the effects of in situ O2 dynamics on N2O production in a typical intensively managed Chinese cropping system under a range of environmental conditions (temperature, moisture, ammonium, nitrate, dissolved organic carbon, and so forth). Climate and management (fertilization, irrigation, precipitation, and temperature), and their interactions significantly affected soil O2 and N2O concentrations (P < 0.05). Soil O2 concentration was the most significant factor correlating with soil N2O concentration (r = -0.71) when compared with temperature, water-filled pore space, and ammonium concentration (r = 0.30, 0.25, and 0.26, respectively). Soil N2O concentration increased exponentially with decreasing soil O2 concentrations. The exponential model of N treatments and fertilization with irrigation/precipitation events predicted 74-90% and 58% of the variance in soil N2O concentrations, respectively. Our results highlight that the soil O2 status is the proximal, direct, and the most decisive environmental trigger for N2O production, outweighing the effects of other factors and could be a key variable integrating the aggregated effects of various complex interacting variables. This study offers new opportunities for developing more sensitive approaches to predicting and through appropriate management interventions mitigating N2O emissions from agricultural soils.

Impacts of precipitation, warming and nitrogen deposition on methane uptake in a temperate desert

Desert soils are a significant global sink for methane (CH4). However, it remains unclear how CH4 uptake in temperate deserts could respond to elevated precipitation, nitrogen (N) deposition and warming. An in situ field experiment was conducted to investigate these effects on CH4 uptake in the Gurbantunggut Desert, northwest China, from September 2014 to August 2017. This desert was a weak sink for CH4 (0.83 kg C ha−1 year−1) over this period, with the non-growing season (November–March) accounting for 30.5% of the annual CH4 uptake. Pulse CH4 uptake was found to result from increased water addition (by 30% or 60 mm year−1) and low N deposition (30 kg N ha−1 year−1) which enhanced annual CH4 uptake by 62.3 and 52.6%, respectively. However, no significant impact of high N deposition (60 kg N ha−1 year−1) was found. Warming in open topped chambers (OTCs) had a variable effect on CH4 uptake, which mainly depended on variation in soil moisture. The response in CH4 uptake to the interaction between water and N addition was less than that for the individual factors, except under conditions of warming. In addition, CH4 uptake was significantly positively correlated to water-filled pore space (WFPS), differing from observations in forest and grassland ecosystems. Structural equation modeling indicated that CH4 uptake was significantly enhanced by soil moisture and the underground biomass of ephemerals. Overall, the CH4 sink of this desert was significantly enhanced by increasing precipitation and low N deposition, rather than warming, which may become a feedback for future climate.

Laboratory-Scale Evaluation of the Effects of Water-Filled Pore Space on Emissions of CO2, CH4, N2O, and N2 from Soil-Based Wastewater Treatment

Microbial removal of C and N in soil-based wastewater treatment involves emission of CO2, CH4, N2O, and N2 to the atmosphere. Water-filled pore space (WFPS) can exert an important control on microbial production and consumption of these gases. We examined the impact of WFPS on emissions of CO2, CH4, N2O, and N2 in soil microcosms receiving septic tank effluent (STE) or effluent from a single-pass sand filter (SFE), with deionized-distilled (DW) water as a control. Incubation of B and C horizon soil for 1 h (the residence time of wastewater in 1 cm of soil) with DW produced the lowest greenhouse gas (GHG) emissions, which varied little with WFPS. In B and C horizon soil amended with SFE emissions of N2O increased linearly with increasing WFPS. Emissions of CO2 from soil amended with STE peaked at WFPS of 0.5–0.8, depending on the soil horizon, whereas in soil amended with SFE, the CO2 flux was detectable only in B horizon soil, where it increased with increasing WFPS. Methane emissions were detectable only for STE, with flux increasing linearly with WFPS in C horizon soil, but no clear pattern was observed with WFPS for B horizon soil. Emissions of GHG from soil were not constrained by the lack of organic C availability in SFE, or by the absence of NO3 availability in STE, and addition of acetate or NO3 resulted in lower emissions in a number of instances. Emission of 15N2 and 15N2O from 15NH4 took place within an hour of contact with soil, and production of 15N2 was much higher than 15N2O. 15N2 emissions were greatest at the lowest WFPS value and diminished markedly as WFPS increased, regardless of water type and soil texture. Our results suggest that the fluxes of CO2, CH4, N2O, and N2 respond differently to WFPS, depending on water type and soil texture.

Soil N2O Emissions under Different N Rates in an Oil Palm Plantation on Tropical Peatland

(1) Background: Nitrogen (N) fertilization on drained tropical peatland will likely stimulate peat decomposition and mineralization, enhancing N2O emission from the peat soil. (2) Methods: A field experiment was conducted to quantify the N2O emissions from soil in an oil palm plantation (Elaeis guineensis Jacq.) located in a tropical peatland in Sarawak, Malaysia, under different rates of N fertilizers. The study was conducted from January 2010 to December 2013 and resumed from January 2016 to December 2017. Nitrous oxide (N2O) flux was measured every month using a closed chamber method for four different N rates; control—without N (T1), 31.1 kg N ha−1 yr−1 (T2), 62.2 kg N ha−1 yr−1 (T3), and 124.3 kg N ha−1 yr−1 (T4); (3) Results: Application of the N fertilizer significantly increased annual cumulative N2O emissions for T4 only in the years 2010 (p = 0.017), 2011 (p = 0.012), 2012 (p = 0.007), and 2016 (p = 0.048). The highest average annual cumulative N2O emissions were recorded for T4 (41.5 ± 28.7 kg N ha−1 yr−1), followed by T3 (35.1 ± 25.7 kg N ha−1 yr−1), T1 (25.2 ± 17.8 kg N ha−1 yr−1), and T2 (25.1 ± 15.4 kg N ha−1 yr−1), indicating that the N rates of 62.2 kg N ha−1 yr−1 and 124.3 kg N ha−1 yr−1 increased the average annual cumulative N2O emissions by 39% and 65%, respectively, as compared to the control. The N fertilization had no significant effect on annual oil palm yield (p = 0.994). Alternating between low (deeper than −60 cm) and high groundwater level (GWL) (shallower than −60 cm) enhanced nitrification during low GWL, further supplying NO3− for denitrification in the high GWL, and contributing to higher N2O emissions in high GWL. The emissions of N2O ranged from 17 µg N m−2 hr−1 to 2447 µg N m−2 hr−1 and decreased when the water-filled pore space (WFPS) was between 70% and 96%, suggesting the occurrence of complete denitrification. A positive correlation between N2O emissions and NO3− at 70–96% WFPS indicated that denitrification increased with increased NO3− availability. Based on their standardized regression coefficients, the effect of GWL on N2O emissions increased with increased N rate (p &lt; 0.001). Furthermore, it was found that annual oil palm yields negatively correlated with annual N2O emission and NO3− for all treatments. Both nitrification and denitrification increased with increased N availability, making both processes important sources of N2O in oil palm cultivation on tropical peatland.; and (4) Conclusions: To improve understanding of N2O mitigation strategies, further studies should consider plant N uptake on N2O emissions, at least until the completion of the planting.

Deficit irrigation combined with reduced N-fertilizer rate can mitigate the high nitrous oxide emissions from Chinese drip-fertigated maize field

Agricultural soils are major sources of the greenhouse gas N2O, particularly under maize with high nitrogen (N) inputs and excessive irrigation. To determine how N and water management can mitigate N2O emissions from drip-irrigated maize fields, a field study was carried out in the North China Plain during the maize growing season. The objective of the study was to investigate the individual and combined effects of irrigation level and N input on N2O emissions and grain yields, as well as N and water use efficiency (WUE), under drip-fertigation management. The main treatments were two irrigation levels: 50 mm/event (sufficient irrigation, WH) and 25 mm/event (limited irrigation, WL), with four N application rates: 0 (N0), 90 (N1), 180 (N2), and 270 (N3) kg N ha−1. Pulses of N2O emissions were recorded every 2–3 d following each irrigation or fertigation (irrigation + fertilization) event. N input, irrigation, and their interactions all significantly influenced N2O emissions. A significant exponential relationship (P < 0.05) was observed between N application rate and cumulative and yield-scaled N2O emissions in both irrigation treatments. The cumulative N2O emission fluxes from the N0, N1, N2, and N3 levels of fertilizer with WL were 11.4, 13.8, 27.2, and 58.8% lower, respectively, than those from the same N levels with WH; this occurred because high pulses of N2O were avoided during low irrigation conditions. Under WH, denitrification was the likely source of the high amounts of N2O, whereas nitrification was likely the main source of N2O emissions under WL. The variations in the water-filled pore space (WFPS) between the two irrigation treatments may explain these results. The effect of N fertilizer on grain yield and WUE depended on the availability of soil water. Based on the available soil water content, the regulation of N fertilizer application can increase yield and also reduce cumulative and yield-scaled N2O emissions.

Dissolved organic matter and inorganic N jointly regulate greenhouse gases fluxes from forest soils with different moistures during a freeze-thaw period

ABSTRACT Antecedent soil moisture before freezing can affect greenhouse gases (GHG) fluxes from soils during thaw, but their critical threshold values for GHG fluxes and the underlying mechanisms are still not clear. By using packed soil-core incubation experiments, we have studied nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4) fluxes from a mature broadleaf and Korean pine-mixed forest soil and an adjacent white birch forest soil with nine levels of soil moisture ranging from 10 to 90% water-filled pore space (WFPS) during a 2-month freezing at −8°C and the following 10-day thaw at 10°C. The threshold values of soil moisture ranged from 50 to 70% WFPS for CH4 uptake and from 70 to 90% WFPS for N2O and CO2 emissions from the two soils during the freeze-thaw period. Under the optimum soil moisture condition, fulvic-like compounds with high bioavailability contributed more than 60% of dissolved organic matter (DOM) in the soil. Cumulative N2O emissions from forest soils during the freeze-thaw period were greatest when the concentration ratio of nitrate-N to dissolved organic carbon (DOC) was 0.04 g N g−1 C. Cumulative soil CO2 emissions and CH4 uptake during the freeze-thaw period were both regulated by the interaction between soil DOC and net N mineralization. The activities of β-1,4-glucosidase and β-1,4-N-acetyl-glucosaminidase, microbial biomass C and N, and the microbial biomass C-to-N ratios, were all significantly correlated to the soil N2O, CO2, and CH4 fluxes. Overall, upon a freeze-thaw period with different soil moistures, GHG fluxes from forest soils were jointly regulated by inorganic N and DOC concentrations, and related to the labile components of DOM released into the soil, which could be strictly controlled by the related microbial properties.

A new look at an old concept: using &amp;lt;sup&amp;gt;15&amp;lt;/sup&amp;gt;N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O isotopomers to understand the relationship between soil moisture and N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O production pathways

Abstract. Understanding the production pathways of potent greenhouse gases, such as nitrous oxide (N2O), is essential for accurate flux prediction and for developing effective adaptation and mitigation strategies in response to climate change. Yet there remain surprising gaps in our understanding and precise quantification of the underlying production pathways – such as the relationship between soil moisture and N2O production pathways. A powerful, but arguably underutilized, approach for quantifying the relative contribution of nitrification and denitrification to N2O production involves determining 15N2O isotopomers and 15N site preference (SP) via spectroscopic techniques. Using one such technique, we conducted a short-term incubation where N2O production and 15N2O isotopomers were measured 24 h after soil moisture treatments of 40 % to 105 % water-filled pore space (WFPS) were established for each of three soils that differed in nutrient levels, organic matter, and texture. Relatively low N2O fluxes and high SP values indicted nitrification during dry soil conditions, whereas at higher soil moisture, peak N2O emissions coincided with a sharp decline in SP, indicating denitrification. This pattern supports the classic N2O production curves from nitrification and denitrification as inferred by earlier research; however, our isotopomer data enabled the quantification of source partitioning for either pathway. At soil moisture levels &lt; 53 % WFPS, the fraction of N2O attributed to nitrification (FN) predominated but thereafter decreased rapidly with increasing soil moisture (x), according to FN=3.19-0.041x, until a WFPS of 78 % was reached. Simultaneously, from WFPS of 53 % to 78 %, the fraction of N2O that was attributed to denitrification (FD) was modelled as FD=-2.19+0.041x; at moisture levels of &gt; 78 %, denitrification completely dominated. Clearly, the soil moisture level during transition is a key regulator of N2O production pathways. The presented equations may be helpful for other researchers in estimating N2O source partitioning when soil moisture falls within the transition from nitrification to denitrification.

Impact of tillage and N fertilization rate on soil N2O emissions in irrigated maize in a Mediterranean agroecosystem

In irrigated Mediterranean conditions there is a lack of knowledge about the best combination of tillage and N fertilization practices to reduce soil nitrous oxide (N2O) emissions while maintaining maize productivity. The aim of this work was to investigate the effects of different soil management practices and synthetic N fertilization rates on soil N2O emissions and their relationship with maize grain yield to determine the best management system to reduce yield-scaled N2O emissions (YSNE) in a semiarid area recently converted to irrigation under Mediterranean conditions. A long-term tillage and N rate field experiment established in 1996 under barley (Hordeum vulgare L.) rainfed conditions, was converted to irrigated maize (Zea mays L.) in 2015. After the transformation to irrigation, the field experiment maintained the same tillage treatments and N fertilization rates. Three types of tillage (conventional tillage, CT; reduced tillage, RT; no-tillage, NT) and three mineral N fertilization rates (0, 200, 400 kg N ha−1) were compared during three years (2015–2017) in a randomized block design with three replications. Soil N2O emissions, water-filled pore space, soil temperature, mineral N content (as NH4+ and NO3−), denitrification potential and maize grain yield and above-ground N uptake were quantified. Moreover, the emission factor (EF) and YSNE were calculated. The results showed that the combination of NT and the highest rate of N fertilization led to greater N2O emissions. Furthermore, the lowest N2O fluxes were observed in CT when WFPS was below 40% and the highest N2O fluxes were seen in NT when WFPS was above 60% coinciding with the greatest denitrification potential. Cumulative N2O emissions in 2017 and 2015 followed the order 400 > 200 > 0 kg N ha−1, while in 2016, rate of 400 and 200 kg N ha−1 showed greater cumulative N2O emission compared to the control. Only RT showed differences between growing seasons on cumulative N2O emissions, with greater values in 2017 compared to 2015, and intermediate values in 2016. In all treatments, the N2O EF was much lower than the default IPCC emission factor (1%). NT and RT increased the grain production compared to CT which was affected by severe soil crusting causing water deficit. Likewise, N fertilizer treatments significantly affected the YSNE, increasing with increasing fertilizer N application rate in the first year of study. Our data show that the use of NT or RT does not lead to more yield-scaled N2O emissions than CT in Mediterranean agroecosystems recently converted to irrigation.

Soil moisture and activity of nitrite- and nitrous oxide-reducing microbes enhanced nitrous oxide emissions in fallow paddy soils

Although cumulative N2O emissions are greater in the winter fallow season than in the rice-growing period, the mechanisms by which the emissions affect fallow paddy fields remain unclear. We aimed to identify N2O flux characteristics and illustrate how key nirS-, nirK- and nosZ-containing denitrifiers affect N2O emission levels in acidic fallow paddy soil. Five water-filled pore space (WFPS) levels were set at 25%, 50%, 75%, 100% and 125%, respectively. During the 48-h-long, high-flux incubation period, the N2O flux was the highest in soil samples with 75% WFPS, followed by those with 100% WFPS. The size of nirS-containing denitrifier community was more sensitive to the shifts in soil moisture and showed a stronger correlation with N2O flux than that of nirK-containing denitrifiers, whereas higher N2O concentrations induced an increase in the levels of nosZ-containing bacteria. After incubation for 48 h, nirK- and nosZ-denitrifying bacterial composition varied remarkably under 50%, 75%, and 100% WFPS treatments. However, the composition of nirS-containing denitrifying bacterial community gradually varied with an increase in soil moisture from 25% to 100% WFPS. Certain dominant OTUs of nirK- nirS- and nosZ-containing denitrifiers were highly abundant, especially under treatments of 50%, 75% and 100% WFPS, which were closely associated with the N2O flux. Thus, nirK, nirS and nosZ-containing denitrifiers respond to soil moisture differently, and enriched species might mainly be involved in controlling N2O flux in fallow paddy soils via denitrification, while the abundance of nirS-containing denitrifiers might affect N2O emission levels more significantly than that of nirK-containing denitrifiers.

Impacts of irrigation methods on greenhouse gas emissions/absorptions from vegetable soils

Recently, N2O, CO2, and CH4 have been gaining attention as major greenhouse gases (GHGs) that contribute to global warming. Agricultural water-saving irrigation technology has become more and more important and is widely applied to the arid areas. These influences have important and strategic significances for reducing greenhouse effects. However, there is limit information regarding the influence of irrigation methods on soil gases emissions. We investigated the effect of mulched drip irrigation (MDI), drip filtration irrigation (DFI), and conventional irrigation (CK) on N2O, CO2, CH4 emissions, affecting factors and their correlations in a greenhouse soil. Observations were performed from April to August in 2015 on the entire tomato growth season. We monitored the flux of GHG emissions by the static chamber-gas chromatograph method under three irrigation conditions: mulched drip irrigation (MDI), drip filtration irrigation (DFI), and conventional irrigation (CK). To investigate the effects of affecting factors on soil GHG emissions, we also measured soil temperature (5 cm), soil moisture, and air temperature. Compared with the cumulative emission of GHGs (N2O and CH4 calculation in the form of CO2), we created the concept of the ratio of yield and gas (crop yield and soil accumulated GHG emissions). Tomato yield of MDI and DFI is significantly higher than CK. Soil moisture is the main factor affecting N2O emissions and CH4 exchange during the tomato-growing season. N2O emission fluxes have an extremely significant correlation with water-filled pore space (WFPS) at suitable temperatures. CO2 emissions demonstrated a significant correlation with environment temperature (soil and air). CO2 emissions gradually increased and had seasonal variations with rising temperatures and plant growth in each irrigation method. CH4 exchange fluxes showed a significant correlation with WFPS. MDI obtains high yields, is cost-efficient, conserves water, and produces the least amount of integrated GHGs. It helps to mitigate global warming and it would be the best irrigation method.

Long-term loblolly pine land use reduces methane and net greenhouse gas emissions in a subtropical Cambisol, despite increasing nitrous oxide

In loblolly pine land use of 17–32 years following forest clearing, CH 4 consumption and N 2 O emission diminished by 17 years, due to high soil moisture (~ 80% WFPS, N 2 O into N 2 ), but increased by 32 years, where medium moisture favoured methanotrophy and denitrification into N 2 O. Soil greenhouse gases (GHG) emission was positive by 17 years, but negative by 32, when soil sequestered carbon. Much of the role of planted forests in the gaseous soil-atmosphere exchanges in the subtropics remains to be evaluated. To assess the impacts of loblolly pine (Pinus taeda L.) on soil nitrous oxide (N2O) and methane (CH4) fluxes in a subtropical Cambisol. Fluxes were monitored over 1 year with static chambers, in forest stands under natural forest (NF) and pine plantation for 17 (P17) and 32 years (P32). The NF soil showed the lowest N2O emission and the highest CH4 consumption, because of the lowest water-filled pore space (WFPS, < 40%) and highest soil macroporosity. In P17, N2O emission was still low, but CH4 consumption diminished sixfold, possibly because of the predominance of methanotrophy, favoured by the highest WFPS (~ 80%) and lowest macroporosity that together with low mineral N concentration also did not favour the formation of N2O. In P32, the improved soil mineral N, macroporosity and intermediate WFPS (~ 60%) increased CH4 consumption and also N2O emission, in an environment supposedly favourable to methanotrophy and also to N2O production. Considering soil organic carbon (SOC) from a concurrent study, the net GHG emission (Mg Ceq ha−1 year−1) was 2.8 in P17 and − 1.1 in P32. Soil under pine plantation is the source of GHG in the first rotation (17 years), because of the low CH4 consumption and SOC losses, but soil becomes C sink in the second rotation (32 years), by sequestering SOC and consuming more CH4, despite emitting more N2O.

The Nitrification Inhibitor Vizura® Reduces N2O Emissions When Added to Digestate before Injection under Irrigated Maize in the Po Valley (Northern Italy)

The agricultural area in the Po Valley is prone to high nitrous oxide (N2O) emissions as it is characterized by irrigated maize-based cropping systems, high amounts of nitrogen supplied, and elevated air temperature in summer. Here, two monitoring campaigns were carried out in maize fertilized with raw digestate in a randomized block design in 2016 and 2017 to test the effectiveness of the 3, 4 DMPP inhibitor Vizura® on reducing N2O-N emissions. Digestate was injected into 0.15 m soil depth at side-dressing (2016) and before sowing (2017). Non-steady state chambers were used to collect N2O-N air samples under zero N fertilization (N0), digestate (D), and digestate + Vizura® (V). Overall, emissions were significantly higher in the D treatment than in the V treatment in both 2016 and 2017. The emission factor (EF, %) of V was two and four times lower than the EF in D in 2016 and 2017, respectively. Peaks of NO3-N generally resulted in N2O-N emissions peaks, especially during rainfall or irrigation events. The water-filled pore space (WFPS, %) did not differ between treatments and was generally below 60%, suggesting that N2O-N emissions were mainly due to nitrification rather than denitrification.

Stimulation of heterotrophic nitrification and N2O production, inhibition of autotrophic nitrification in soil by adding readily degradable carbon

This study aimed to test the hypothesis that readily degradable Carbon (C) has contrasting effect on soil N autotrophic and heterotrophic nitrification, can stimulate nitrous oxide (N2O) emission. The knowledge can improve our understanding of the effect of readily degradable C on soil N nitrification and the related N2O emission. 15N tracing technique along with acetylene inhibition was used to determine the effect of different doses of glucose-C addition on the rates of total nitrification (ntot), autotrophic nitrification (na), heterotrophic nitrification (nh), and N2O production in two soils. Soils were collected from Glenormiston (GN) and Terang (TR), Victoria, Australia and incubated at soil moisture content of 60% water-filled pore space (WFPS) and at 25 °C. The addition of mixed C and N substrates with wide C/N ratio (> 25) promoted heterotrophic nitrification by 2.84- to 3.33-folds but inhibited autotrophic nitrification by 30.4–54.8%, thereby resulting in high ntot and NO3− accumulation compared with the soil samples under the control treatment. The mechanism of glucose inhibition of na might be caused by increasing the microbial immobilization of NH4+ and not by affecting the gene copy numbers of ammonia-oxidizing archea and ammonia-oxidizing bacteria. The glucose addition stimulated N2O production in soil, which might be caused by promoting heterotrophic nitrification and denitrification. The stimulating effect of degradable C application on the contribution of heterotrophic nitrification to total nitrification, NO3− accumulation, and N2O production should be considered, especially in soils with low pH and high organic C content.

Presence of spring-thaw N2O emissions are not linked to functional gene abundance in a drip-fertigated cropped soil in arid northwestern China

Spring-thaw represents a significant source for nitrous oxide (N2O) emissions from fertilized croplands in temperate regions. In this study, we present surface N2O fluxes, soil-profile N2O concentrations at 5, 15, 30 and 60 cm depths along with the abundance of nitrifiers and denitrifiers over the winter and spring-thaw periods in an arid, drip- fertigated cotton field, which had received spring application of 240 kg N ha−1 as urea alone (Urea), polymer-coated urea (ESN), and urea plus urease and nitrification inhibitors. Nitrous oxide emissions from December to April were generally unaffected by fertilizer treatments with a cumulative average of 186 g N ha−1, accounting for 39% of the annual N2O emissions. Emission peaks occurred at spring-thaw and coincided with increasing soil-profile N2O concentrations at all depths, suggesting the burst in N2O fluxes was due to new N2O production, rather than a physical release of N2O trapped in the soil profiles over winter. The abundance of nitrifier and denitrifier genes changed over the winter and spring-thaw periods but was not affected by fertilizer treatments from the previous spring, suggesting the abundance of N2O-producing microorganism was more controlled by environmental conditions than N sources applied in the previous spring. The daily N2O flux rate from December to April was positively correlated with soil temperature, water-filled pore space, and denitrifying enzyme activity, but not with the gene copy number of AOA, AOB, narG, nirS, nirK and nosZ, indicating that variation in the abundance of these genes was not contributing to the N2O emissions. These results suggest that N2O emissions in spring-thaw are substantial for drip-fertigated croplands in the arid regions and should be considered in the annual budgets. The environmental factors such as soil temperature and moisture are likely more important than the copy-numbers of N2O-producing functional genes in driving the variability in spring-thaw emissions.

Effect of soil tillage and N fertilization on N2O mitigation in maize in the Brazilian Cerrado.

The management system of soils and nitrogen application can cause impacts on the N2O emissions produced by the agricultural sector. In the establishment of practices of greenhouse gas mitigation for this sector, the objective of this study was to evaluate the effect of soil tillage, with and without N fertilization, on N2O emissions from Oxisols under rainfed maize in the Brazilian Cerrado region. The managements were of monoculture maize under conventional tillage (CT) and no-tillage (NT), with (1) and without (0) application of N fertilizer (0 and 257 kg N ha-1). From November 2014 to October 2015, gas emissions were measured. The soil and climate variables were measured and related to the N2O fluxes. In the N-fertilized treatments, N2O fluxes were higher (P < 0.01), ranging from -21 μg m-2 h-1 to 548 μg m-2 h-1 N2O under conventional tillage and from -21 μg m-2 h-1 to 380 μg m-2 h-1 N2O under no-tillage, compared with -6 to 93 μg m-2 h-1 N2O from systems without N application. There was a combined effect of mineral N and water-filled pore space for most N2O fluxes. The emission factors of N2O during maize cultivation were lower than the standard factor (1%) established by the International Panel of Climate Change. During the plant crop cycle, 30% less N2O was emitted from the N-fertilized no-tillage than from the conventional tillage. For the total cumulative N2O (crop cycle + fallow), the N2O emissions from NT1 and CT1 were not different, but 10× higher than those from the respective crops without N fertilization. To the emissions per unit of grain yield, CT1 and NT1 emitted 769 and 391 mg N2O kg-1 grain produced, respectively, and NT1 was most efficient in fertilizer-into-product conversion. Under maize cultivation, the soil acted as N2O source, regardless of the management.

Exotic Spartina alterniflora invasion alters soil nitrous oxide emission dynamics in a coastal wetland of China

Exotic Spartina alterniflora invasion resulting from anthropogenic activities significantly affects microbial nitrogen (N) transformation and associated nitrous oxide (N2O) emission in coastal wetland soils. However, the responses of soil N2O emission dynamics to plant invasion remain unclear. This study assesses the effects of S. alterniflora invasion on soil N2O potential production and consumption processes. We used natural isotope tracing technique to investigate potential N2O production and consumption rates in S. alterniflora invaded and native saltmarsh zones (Phragmites australis, Scirpus mariqueter and bare mudflat) in the Yangtze Estuary. Soil potential net N2O production rates in summer were lower in S. alterniflora stands than in S. mariqueter and bare mudflat stands, but no significant differences among these saltmarsh habitats occurred during winter. Potential gross N2O production and consumption rates were higher in S. alterniflora and P. australis stands compared to S. mariqueter and bare mudflat stands. The gross consumption proportion in S. alterniflora and P. australis stands was higher, which affected net N2O production. Hydroxylamine (NH2OH) oxidation and nitrifier denitrification contributed 4.52–12.62% and 13.87–21.58% of soil N2O source, respectively, but denitrification was the dominant pathway (69.83–80.09%). S. alterniflora invasion increased the contributions of NH2OH oxidation and nitrifier denitrification to N2O source slightly, but decreased the contribution of denitrification to N2O source. Soil potential N2O production and consumption processes were influenced by water-filled pore space, pH, sulfide, and carbon and N substrates. Exotic S. alterniflora invasion affected soil N2O dynamics by increasing substrates and altering microenvironments, thus mediating N2O emission from coastal saltmarsh soils.