Mitigation options for N2O emission from a corn field in Kalimantan,Indonesia

Abstract

Field experiments were designed to quantify N₂O emissions from corn fields after the application of different types of nitrogen fertilizers. Plots were established in South Kalimantan, Indonesia, and given either urea (200 kg ha^?1), urea (170 kg ha^?1) + dicyandiamide ([DCD] 20 kg ha^?1) or controlled-release fertilizer LP-30 (214 kg ha^?1) prior to the plantation of corn seeds (variety BISI 2). Each fertilizer treatment was equivalent to 90 kg N ha^?1. Plots without chemical N fertilizer were also prepared as a control. The field was designed to have three replicates for each treatment with a randomized block design. Nitrous oxide fluxes were measured at 4, 8, 12, 21, 31, 41, 51, 72 and 92 days after fertilizer application (DAFA). Total N₂O emission was the highest from the urea plots, followed by the LP-30 plots. The emissions from the urea + DCD plots did not differ from those from the control plots. The N₂O emission from the urea + DCD plots was approximately one thirtieth of that from the urea treatment. However, fertilizer type had no effect on grain yield. Thus, the use of urea + DCD is considered to be the best mitigation option among the tested fertilizer applications for N₂O emission from corn fields in Kalimantan, Indonesia.     

Nitrous oxide production at different soil moisture contents in an arable soil in China

Abstract

Laboratory incubations were conducted to investigate nitrous oxide (N₂O) production from a subtropical arable soil (Typic Plinthodults) incubated at different soil moisture contents (SMC) and with different nitrogen sources using a 10% (v/v) acetylene (C₂H₂) inhibitory technique at 25°C. The production of N₂O and CO₂ was monitored during the incubations and changes in the contents of KCl-extractable NO^? ₃-N and NH⁺ ₄-N were determined. The production of N₂O increased slightly with an increase in SMC from 40% water-holding capacity (WHC) to 70% WHC, but increased dramatically at 100% WHC. After incubation the NO^? ₃-N content increased even at a SMC of 100% WHC. At a SMC of 100% WHC, the addition of NH⁺ ₄-N promoted the production of N₂O and CO₂, whereas the addition of NO^? ₃-N decreased N₂O production. Compared with the incubation without C₂H₂, the presence of C₂H₂ increased NH⁺ ₄-N content, but decreased NO^? ₃-N content, and there was no significant difference in N₂O production. These results indicate that heterotrophic nitrification contributes to N₂O production in the soil.     

Saccharidic compounds as soil redox effectors and their influence on potential N2O production

Cellulose, xylan, and glucose were compared in waterlogged soil as modifying factors of the redox potential (Eh), of the quantity of reducing equivalents, and of the soil capacity to produce N₂O and CO₂. During the study period (168 h) soils supplied with glucose and xylan showed a higher Eh decrease than the control soil and the soil treated with cellulose. In samples taken after 0, 24, 48, and 168 h, the soils supplied with C showed a higher number of reducing equivalents than the control soil did. These quantities were not correlated with Eh values, nor with N₂O production. N₂O production was increased compared with the control soil over the entire experimental period in the glucose-amended soils but only after 48 h in the xylan-amended soils and not until 168 h in the cellulose-treated soils. The CO₂:N₂O ratio was consistently higher than the theoretical value of 2, suggesting that denitrification and CO₂ production via fermentation occurred simultaneously. Moreover, this ratio was highly correlated with the Eh values. We conclude that more research is needed to explain the role of soil redox intensity (Eh) and capacity (quantity of redox species undergoing reduction) in the expression of soil denitrification-fermentation pathways.     

Methods for measuring N2O flux from water surface and N2O dissolved in water from agricultural land

A new chamber method and a stripping method were developed for field measurements of the rate of N₂O emission from the water surface and for determinations of dissolved N₂O in water from agricultural land.

These methods were used for the measurement of drainage canal water and flooded water of rice fields during the period of June 1982 to January 1983. The results demonstrate that aquatic systems of agricultural land may provide both source and sink for atmospheric N₂O.     

A simple gas chromatographic approach to evaluate CO2 release,N2O evolution,and O2 uptake from soil

Summary We have developed a simple method for the determination of gaseous compounds that reflect microbial activity in soil, as affected by factors such as the presence of an organic amendment (peat) or a variation in soil moisture. The method is based on a gas chromatographic analysis of the headspace of vials containing the soil under examination. A single gas chromatograph can detect up to 10 different gases. As expected, after peat was added to the soil, CO₂ evolution and O₂ uptake increased significantly. Positive relationships were found between the evolution of N₂O, and soil moisture and the amount of peat added to the soil. Both the these variables influenced the CO₂:O₂ ratio. The results given by this method show high reproducibility.     

Application of N2/Ar ratio method for N2 fixation studies in submerged soil

Abstract

Recently there has been developments in the measurement of N₂ fixation due mainly to the C₂H₂ reduction method (1). This method, however, has several disadvantages, especially for submerged soil, and the estimated amount of fixed N₂ on the basis of the C₂H₂ reduction activity is not very reliable. The tracer ¹⁵N₂ technique which gives a reliable estimation of the fixed N₂ is too expensive for common use. Development of an alternative method suitable for submerged soil would therefore be desirable. The present authors expected that the measurement of the ratio N₂/Ar in the soil solution might provide advantages for the estimation of the fixed N₂ in submerged soil.     

Nitrate Transformation and N2O Emission in a Typical Intensively Managed Calcareous Fluvaquent Soil: A 15-Nitrogen Tracer Incubation Study

A 56-day aerobic incubation experiment was performed with 15-nitrogen (N) tracer techniques after application of wheat straw to investigate nitrate-N (NO₃-N) immobilization in a typical intensively managed calcareous Fluvaquent soil. The dynamics of concentration and isotopic abundance of soil N pools and nitrous oxide (N₂O) emission were determined. As the amount of straw increased, the concentration and isotopic abundance of total soil organic N and newly formed labeled particulate organic matter (POM-N) increased while NO₃-N decreased. When ¹⁵NO₃-N was applied combined with a large amount of straw at 5000 mg carbon (C) kg^?1 only 1.1 ± 0.4 mg kg^?1 NO₃-N remained on day 56. The soil microbial biomass N (SMBN) concentration and newly formed labeled SMBN increased significantly (P < 0.05) with increasing amount of straw. Total N₂O-N emissions were at levels of only micrograms kg^?1 soil. The results indicate that application of straw can promote the immobilization of excessive nitrate with little emission of N₂O.     

Denitrification,N2-fixation and fermentation during anaerobic incubation of soils amended with glucose and nitrate

Nitrate and glucose additions were investigated for their role in the C and N dynamics during anaerobic incubation of soil. A gas-flow soil core method was used, in which the net production of N₂, N₂O, NO, CO₂, and CH₄ under a He atmosphere could be monitored both accurately and frequently. In all experiments clayey silt loam soil samples were incubated for 9 days at 25 °C. Addition of nitrate (50 mg KNO₃-N kg^-1 soil) had no effect on total denitrification and CO₂ production rates, while the N₂O/N₂ ratio was affected considerably. The cumulative N₂O production exceeded the cumulative N₂ production for 6 days in the treatment with nitrate addition, compared to 1.2 days in the unamended treatment. Glucose addition stimulated the microbial activity considerably. The denitrification rates were limited by the growth rate of the denitrifying population. During denitrification no significant differences were observed between the treatments with 700 mg glucose-C kg^-1 and 4200 mg glucose-C kg^-1, both in combination with 50 mg KNO₃-N kg^-1. The N₂ production rates were remarkably low, until NO _inf3 ^sup- exhaustion caused rapid reduction of N₂O to N₂ at day 2. During the denitrification period 15–18 mg N kg^-1 was immobilised in the growing biomass. After NO _inf3 ^sup- shortage, a second microbial population, capable of N₂-fixation, became increasingly important. This change was clearly reflected in the CO₂ production rates. Net volatile fatty acid (VFA) production was monitored during the net N₂-fixation period with acetate as the dominant product. N₂-fixation faded out, probably due to N₂ shortage, followed by increased VFA production. In the high C treatment butyrate became the most important VFA, while in the low C treatment acetate and butyrate were produced at equal rates. During denitrification no VFA accumulation occurred; this does not prove, however, that denitrification and fermentation appeared sequentially. The experiments illustrate clearly the interactions of C-availability, microbial population and nitrate availability as influencing factors on denitrification and fermentation.Dedicated to Professor J. C. G. Ottow on the occasion of his 60th birthday     

Impact of fresh and aged palm shell biochar on N2O emissions,soil properties,nutrient content and yield of Komatsuna (Brassica rapa var. perviridis) under sandy soil conditions

ABSTRACT

Biochar can reduce N₂O emissions and it can be added to the soil once, whereas fertilizers are often applied every cultivation season. The aging of biochar in soil affects its functioning but it is unclear whether palm shell biochar (PSB) could still mitigate N₂O emissions even when additional basal N fertilizers are applied 1 year after the initial biochar application. We studied the impact of fresh and aged PSB (0%, 6%, 12%, and 18% w/w of dry soil) on N₂O emissions, soil properties, nutrient content and yield of Komatsuna (Brassica rapa var. perviridis) under sandy soil conditions. The aged PSB non-significantly reduced N₂O emissions but significantly offset soil acidification, and maintained a high soil nutrient status. Biochar application with fertilizer significantly increased plant tissue K and Ca content but decreased N, P and Mg content compared to the treatments without biochar. At higher application rates, biochar had negative effects on crop yield but as it aged, the negative effects were offset as a result of the similar variation in plant N uptake. Since seasonal N fertilizer application seems to be inevitable in Komatsuna cultivation, addition of biochar could be a possible way of counteracting the effects of excessive fertilizer use. Further research is needed to assess the feasible biochar application rates for Komatsuna fields in various soil types under field conditions.     

Background level of nitrous oxide in the atmosphere in relation to flux from soil

According to Broadbent and Clark (3), there are numerous data indicating that denitrification leads to the emission of N₂O together with N₂, whereby loss of N is developed from soils. Nitrous oxide is also released from soils to the atmosphere during the nitrification of ammonium and ammonium-producing fertilizers under aerobic conditions (1). Relatively few attempts have been made to directly measure N₂O evolution under field conditions (6, 7, 10–12), although a number of laboratory studies have been reported. These studies are essential for determining the N balance between additions and losses of soil N.     

Compaction effects on CO2 and N2O production during drying and rewetting of soil

The effects of compaction on soil porosity and soil water relations are likely to influence substrate availability and microbial activity under fluctuating soil moisture conditions. We conducted a short laboratory incubation to investigate the effects of soil compaction on substrate availability and biogenic gas (CO₂ and N₂O) production during the drying and rewetting of a fine-loamy soil. Prior to initiating the drying and wetting treatments, CO₂ production (−10 kPa soil water content) from uncompacted soil was 2.3 times that of compacted soil and corresponded with higher concentrations of microbial biomass C (MBC) and dissolved organic C (DOC). In contrast, N₂O production was 67 times higher in compacted than uncompacted soil at field capacity. Soil aeration rather than substrate availability (e.g. NO₃⁻ and DOC) appeared to be the most important factor affecting N₂O production during this phase. The drying of compacted soil resulted in an initial increase in CO₂ production and a nearly two-fold higher average rate of C mineralization at maximum dryness (owing to a higher water-filled pore space [WFPS]) compared to uncompacted soil. During the drying phase, N₂O production was markedly reduced (by 93-96%) in both soils, though total N₂O production remained slightly higher in compacted than uncompacted soil. The increase in CO₂ production during the first 24 h following rewetting of dry soil was about 2.5 times higher in uncompacted soil and corresponded with a much greater release of DOC than in compacted soil. MBC appeared to be the source of the DOC released from uncompacted soil but not from compacted soil. The production of N₂O during the first 24 h following rewetting of dry soil was nearly 20 times higher in compacted than uncompacted soil. Our results suggest that N₂O production from compacted soil was primarily the result of denitrification, which was limited by substrates (especially NO₃⁻) made available during drying and rewetting and occurred rapidly after the onset of anoxic conditions during the rewetting phase. In contrast, N₂O production from uncompacted soil appeared to be primarily the product of nitrification that was largely associated with an accumulation of NO₃⁻ following rewetting of dry soil. Irrespective of compaction, the response to drying and rewetting was greater for N₂O production than for CO₂ production.     

The effect of growing soybean (Glycine max. L.) on N2O emission from soil

A pot experiment was conducted to investigate the effect of growing soybean on N₂O emission from soil. When soybean was growing in pots, the cumulative N₂O emission during the growing season was 2.26 mg N pot⁻¹, which was 5.9 times greater than that from the identical but unplanted pots (CK). However, the difference in N₂O fluxes between the two treatments was not significant until the grain-filling stage. Of the total N₂O emission, 94% took place during the period from grain-filling to ripening. Premature harvesting of the aerial parts of the plants at various growth stages substantially stimulated N₂O emission from the soil. These results implied that the process of symbiotic N fixation per se does not stimulate N₂O production or emission, but rather senescence and decomposition of the roots and nodules in the late growth stage. Therefore, additional N₂O would be emitted from the soil after harvesting of soybean with roots, litter, and residues left in situ.     

Estimating N2 fixation by field-grown lupins (Lupinus angustifolius L.) using soil and plant 15N enrichment

Summary Biological N₂ fixation was estimated in a field experiment following the addition of NH₄Cl or KNO₃ to unconfined microplots (1.5 m²) at 2.5 g N m^-2 (10 atom% ¹⁵N). A model of total N and ¹⁵N accumulation in lupins and decreasing ¹⁵N enrichment in the KCl-extractable soil-N pool (0–0.15 m depth) was used to estimate the proportion of N in lupins derived from biological N₂ fixation. Estimates of N₂ fixation derived from the model were compared with ¹⁵N isotope-dilution estimates obtained using canola, annual ryegrass, and wheat as nonfixing reference plants. Biomass, total N accumulation, or ¹⁵N enrichment in the lupin and reference crops did not differ whether NH _inf4 ^sup+ or NO _inf3 ^sup- was added as the labelled inorganic-N source. The decrease in soil ¹⁵N enrichment was described by first-order kinetics, whereas total N and ¹⁵N accumulation in the lupins were described by logistical equations. Using these equations, the uptake of soil N by lupins was estimated and was then used to calculate fixed N₂. Estimates of N₂ fixation derived from the model increased from 0 at 50 days after sowing to a maximum of 0.79 at 190 days after sowing. Those based on the ¹⁵N enrichment of the NO _inf3 ^sup- pool were 10% higher than those based on the mineral-N pool. ¹⁵N isotope-dilution estimates of N₂ fixation ranged from 0.37 to 0.55 at 68 days after sowing and from 0.71 to 0.77 at 190 days after sowing. Reference plant-derived values of N₂ fixation were all higher than modelled estimates during the early states of growth, but were similar to modelled estimates at physiological maturity. The use of the model to estimate N₂ derived from the atmosphere has the intrinsic advantage that the need for a non-fixing reference plant is avoided.     

Transitioning from standard to minimum tillage: Trade-offs between soil organic matter stabilization, nitrous oxide emissions, and N availability in irrigated cropping systems

Few studies address nutrient cycling during the transition period (e.g., 1–4 years following conversion) from standard to some form of conservation tillage. This study compares the influence of minimum versus standard tillage on changes in soil nitrogen (N) stabilization, nitrous oxide (N₂O) emissions, short-term N cycling, and crop N use efficiency 1 year after tillage conversion in conventional (i.e., synthetic fertilizer-N only), low-input (i.e., alternating annual synthetic fertilizer- and cover crop-N), and organic (i.e., manure- and cover crop-N) irrigated, maize–tomato systems in California. To understand the mechanisms governing N cycling in these systems, we traced ¹⁵N-labeled fertilizer/cover crop into the maize grain, whole soil, and three soil fractions: macroaggregates (>250 μm), microaggregates (53–250 μm) and silt-and-clay (<53 μm). We found a cropping system effect on soil N_new (i.e., N derived from ¹⁵N-fertilizer or -¹⁵N-cover crop), with 173 kg N_new ha⁻¹ in the conventional system compared to 71.6 and 69.2 kg N_new ha⁻¹ in the low-input and organic systems, respectively. In the conventional system, more N_new was found in the microaggregate and silt-and-clay fractions, whereas, the N_new of the organic and low-input systems resided mainly in the macroaggregates. Even though no effect of tillage was found on soil aggregation, the minimum tillage systems showed greater soil fraction-N_new than the standard tillage systems, suggesting greater potential for N stabilization under minimum tillage. Grain-N_new was also higher in the minimum versus standard tillage systems. Nevertheless, minimum tillage led to the greatest N₂O emissions (39.5 g N₂O–N ha⁻¹ day⁻¹) from the conventional cropping system, where N turnover was already the fastest among the cropping systems. In contrast, minimum tillage combined with the low-input system (which received the least N ha⁻¹) produced intermediate N₂O emissions, soil N stabilization, and crop N use efficiency. Although total soil N did not change after 1 year of conversion from standard to minimum tillage, our use of stable isotopes permitted the early detection of interactive effects between tillage regimes and cropping systems that determine the trade-offs among N stabilization, N₂O emissions, and N availability.     

Dinitrogen emissions and the N2:N2O emission ratio of a Rendzic Leptosol as influenced by pH and forest thinning

Reduction of nitrous oxide (N₂O) to dinitrogen (N₂) by denitrification in soils is of outstanding ecological significance since it is the prevailing natural process converting reactive nitrogen back into inert molecular dinitrogen. Furthermore, the extent to which N₂O is reduced to N₂ via denitrification is a major regulating factor affecting the magnitude of N₂O emission from soils. However, due to methodological problems in the past, extremely little information is available on N₂ emission and the N₂:N₂O emission ratio for soils of terrestrial ecosystems. In this study, we simultaneously determined N₂ and N₂O emissions from intact soil cores taken from a mountainous beech forest ecosystem. The soil cores were taken from plots with distinct differences in microclimate (warm-dry versus cool-moist) and silvicultural treatment (untreated control versus heavy thinning). Due to different microclimates, the plots showed pronounced differences in pH values (range: 6.3–7.3). N₂O emission from the soil cores was generally very low (2.0 ± 0.5–6.3 ± 3.8 μg N m⁻² h⁻¹ at the warm-dry site and 7.1 ± 3.1–57.4 ± 28.5 μg N m⁻² h⁻¹ at the cool-moist site), thus confirming results from field measurements. However, N₂ emission exceeded N₂O emission by a factor of 21 ± 6–220 ± 122 at the investigated plots. This illustrates that the dominant end product of denitrification at our plots and under the given environmental conditions is N₂ rather than N₂O. N₂ emission showed a huge variability (range: 161 ± 64–1070 ± 499 μg N m⁻² h⁻¹), so that potential effects of microclimate or silvicultural treatment on N₂ emission could not be identified with certainty. However, there was a significant effect of microclimate on the magnitude of N₂O emission as well as on the mean N₂:N₂O emission ratio. N₂:N₂O emission ratios were higher and N₂O emissions were lower for soil cores taken from the plots with warm-dry microclimate as compared to soil cores taken from the cool-moist microclimate plots. We hypothesize that the increase in the N₂:N₂O emission ratio at the warm-dry site was due to higher N₂O reductase activity provoked by the higher soil pH value of this site. Overall, the results of this study show that the N₂:N₂O emission ratio is crucial for understanding the regulation of N₂O fluxes of the investigated soil and that reliable estimates of N₂ emissions are an indispensable prerequisite for accurately calculating total N gas budgets for the investigated ecosystem and very likely for many other terrestrial upland ecosystems as well.     

Use of 15N isotope dilution for quantification of N2 fixation associated with roots of kallar grass (Leptochloa fusca (L.))

Summary Leptochloa fusca (L.) Kunth (kallar grass) has previously been found to exhibit high rates of nitrogen fixation. A series of experiments to determine the level of biological nitrogen fixation using ¹⁵N isotopic dilution were carried out in nutrient solution and saline soil. In the nutrient solution, E. coli inoculated plants were taken as non-nitrogen-fixing control. It was observed that nearly 60%–80% of the plant N was derived from atmospheric fixation. Estimations based on the N difference method gave much lower values (18%–35%). In experiments with saline soil which was initially sterilized with chloroform fumigation, a mixed culture of N₂-fixing rhizospheric isolates from kallar grass roots was inoculated and planted to kallar grass. Uninoculated treatments were regarded as controls. The soil was previously labelled with ¹⁵N by adding cellulose and (¹⁵NH₄)₂SO₄. The results of these studies showed fixation values of 6%–32% when estimated by ¹⁵N dilution, whereas by the N difference method 54% of the plant N was estimated to be derived from fixation. This discrepancy is due to the increase in root proliferation due to inoculation, which results in greater uptake of soil N. The distribution of ¹⁵N in different fractions of the soil-N indicted isotopic dilution due to bacterial fixation of atmospheric N₂.     

Assay system for measurement of denitrification-N loss from ornamental plants potted in peat substrate

An assay system was evaluated for denitrification measurement with potted ornamental plants cultivated in peat substrate (Pelargonium zonale, Euphorbia pulcherrima). Flow-through chambers only enclosing the pot of the plants were considered best for denitrification measurement. Loss of N₂O from the chambers by transport through the plant shoot was negligible with both species. To determine (N₂O + N₂)-N loss, C₂H₂ was applied to inhibit reduction of N₂O. Experiments were conducted with unplanted substrate in closed incubation systems to determine optimum C₂H₂ concentration and pre-treatment duration. Complete inhibition of N₂O reduction in peat substrate was achieved using 1 vol% C₂H₂. However, a concentration of 5 vol% C₂H₂ was chosen for further experiments because C₂H₂ concentrations in flow-through chambers varied. The duration of C₂H₂ pre-treatment (0, 2, 12, 24 h) showed no clear effect on (N₂O + N₂)-N accumulation. However, a pre-treatment duration of 2 h was chosen to guarantee immediate inhibition of N₂O reductase at the start of experiments. Exposure to C₂H₂ gas proved to affect plants of both species. During C₂H₂ exposition in flow-through chambers, the leaves of P. zonale became chlorotic (48 h) and necrotic (72 h). E. pulcherrima showed no chlorosis but did exhibit leaf epinasty (24 h) and wilting (96 h). Transpiration of P. zonale and C availability in the growing medium of both species were not affected by 52 h and 24 h treatments with C₂H₂, respectively. As N emissions usually ended within 38 h of C₂H₂ treatment, it was concluded that side effects of C₂H₂ did not affect denitrification measurements.