Can split or delayed application of N fertiliser to grain sorghum reduce soil N2O emissions from sub-tropical Vertosols and maintain grain yields?

Soil Research ◽  
2019 ◽  
Vol 57 (8) ◽  
pp. 859 ◽  
Author(s):  
G. D. Schwenke ◽  
B. M. Haigh
Keyword(s):  
Grain Yield ◽  
N Uptake ◽  
Grain Sorghum ◽  
Yield Response ◽  
N2o Emissions ◽  
Residual Soil ◽  
Soil Mineral N ◽  
Soil Mineral ◽  
Mineral N ◽  
Crop N Uptake

Most soil nitrous oxide (N2O) emissions from rain-fed grain sorghum grown on sub-tropical Vertosols in north-west New South Wales, Australia, occur between fertiliser nitrogen (N) application at sowing and booting growth stage. At three experiments, we investigated the potential for deferring some (split-N) or all (delayed) fertiliser N until booting to mitigate N2O produced without compromising optimum crop yields. N products included urea, 3,4-dimethyl pyrazole phosphate (DMPP)-urea, polymer-coated urea (PCU) and N-(n-butyl)thiophosphoric triamide (NBPT)-urea. For a fourth experiment, the N fertiliser rate was varied according to pre-sowing soil mineral N stocks left by different previous crops. All experiments incorporated 15N mini-plots to determine whether delayed or split-N affected crop N uptake or residual soil N. Compared to urea applied at-sowing, delayed applications of urea, DMPP-urea or NBPT-urea at booting reduced the N2O emission factor (EF, percentage of applied N emitted) by 67–81%. Crop N uptake, grain yield and protein tended to be lower with delayed N than N at-sowing due to dry mid-season conditions. Much of the unused N remained in the soil at harvest. Split-N (33% sowing:67% booting) using urea, reduced EF by 59% compared to at-sowing urea, but maintained crop N uptake, grain yield and protein. Using DMPP-urea or PCU for the at-sowing portion of the split reduced EF by 84–86%. Grain yield was maintained using PCU, but was lower with DMPP-urea, which had more N in vegetative biomass. Using NBPT-urea for the in-crop portion of the split did not affect N2O emissions or crop productivity. Nitrogen budgeting to account for high pre-sowing soil mineral N nullified urea-induced N2O emissions. An N-budgeted, split-N strategy using urea offers the best balance between N2O mitigation, grain productivity and provision of a soil mineral N buffer against dry mid-season conditions. Split-N using DMPP-urea or PCU further enhanced N2O mitigation but there was no yield response to justify the extra expense.

scholarly journals Greenhouse gas (N2O and CH4) fluxes under nitrogen-fertilised dryland wheat and barley on subtropical Vertosols: risk, rainfall and alternatives

Soil Research ◽  
2016 ◽  
Vol 54 (5) ◽  
pp. 634 ◽  
Author(s):  
Graeme D. Schwenke ◽  
David F. Herridge ◽  
Clemens Scheer ◽  
David W. Rowlings ◽  
Bruce M. Haigh ◽  
...  
Keyword(s):  
N Uptake ◽  
Nitrification Inhibitor ◽  
N2o Emission ◽  
N2o Emissions ◽  
Soil Mineral N ◽  
Soil Mineral ◽  
Mineral N ◽  
Before And After ◽  
Ch4 Uptake ◽  
Crop N Uptake

The northern Australian grains industry relies on nitrogen (N) fertiliser to optimise yield and protein, but N fertiliser can increase soil fluxes of nitrous oxide (N2O) and methane (CH4). We measured soil N2O and CH4 fluxes associated with wheat (Triticum aestivum) and barley (Hordeum vulgare) using automated (Expts 1, 3) and manual chambers (Expts 2, 4, 5). Experiments were conducted on subtropical Vertosol soils fertilised with N rates of 0–160kgNha–1. In Expt 1 (2010), intense rainfall for a month before and after sowing elevated N2O emissions from N-fertilised (80kgNha–1) wheat, with 417gN2O-Nha–1 emitted compared with 80g N2O-Nha–1 for non-fertilised wheat. Once crop N uptake reduced soil mineral N, there was no further treatment difference in N2O. Expt 2 (2010) showed similar results, however, the reduced sampling frequency using manual chambers gave a lower cumulative N2O. By contrast, very low rainfall before and for several months after sowing Expt 3 (2011) resulted in no difference in N2O emissions between N-fertilised and non-fertilised barley. N2O emission factors were 0.42, 0.20 and –0.02 for Expts 1, 2 and 3, respectively. In Expts 4 and 5 (2011), N2O emissions increased with increasing rate of N fertiliser. Emissions were reduced by 45% when the N fertiliser was applied in a 50:50 split between sowing and mid-tillering, or by 70% when urea was applied with the nitrification inhibitor 3,4-dimethylpyrazole-phosphate. Methane fluxes were typically small and mostly negative in all experiments, especially in dry soils. Cumulative CH4 uptake ranged from 242 to 435g CH4-Cha–1year–1, with no effect of N fertiliser treatment. Considered in terms of CO2 equivalents, soil CH4 uptake offset 8–56% of soil N2O emissions, with larger offsets occurring in non-N-fertilised soils. The first few months from N fertiliser application to the period of rapid crop N uptake pose the main risk for N2O losses from rainfed cereal cropping on subtropical Vertosols, but the realisation of this risk is dependent on rainfall. Strategies that reduce the soil mineral N pool during this time can reduce the risk of N2O loss.

Computer simulation of changes in soil mineral nitrogen and crop nitrogen during autumn, winter and spring

1987 ◽  
Vol 109 (1) ◽  
pp. 141-157 ◽  
Author(s):  
T. M. Addiscott ◽  
A. P. Whitmore
Keyword(s):  
Soil Temperature ◽  
Dry Matter ◽  
N Uptake ◽  
Sowing Date ◽  
Mineralization Rate ◽  
Soil Mineral N ◽  
Soil Mineral ◽  
Soil Mineral Nitrogen ◽  
Mineral N ◽  
Crop N Uptake

summaryThe computer model described simulates changes in soil mineral nitrogen and crop uptake of nitrogen by computing on a daily basis the amounts of N leached, mineralized, nitrified and taken up by the crop. Denitrification is not included at present. The leaching submodel divides the soil into layers, each of which contains mobile and immobile water. It needs points from the soil moisture characteristic, measured directly or derived from soil survey data; it also needs daily rainfall and evaporation. The mineralization and nitrification submodel assumes pseudo-zero order kinetics and depends on the net mineralization rate in the topsoil and the daily soil temperature and moisture content, the latter being computed in the leaching submodel. The crop N uptake and dry-matter production submodel is a simple function driven by degree days of soil temperature and needs in addition only the sowing date and the date the soil returns to field capacity, the latter again being computed in the leaching submodel. A sensitivity analysis was made, showing the effects of 30% changes in the input variables on the simulated amounts of soil mineral N and crop N present in spring when decisions on N fertilizer rates have to be made. Soil mineral N was influenced most by changes in rainfall, soil water content, mineralization rate and soil temperature, whilst crop N was affected most by changes in soil temperature, rainfall and sowing date. The model has so far been applied only to winter wheat growing through autumn, winter and spring but it should be adaptable to other crops and to a full season.The model was validated by comparing its simulations with measurements of soil mineral N, dry matter and the amounts of N taken up by winter wheat in experiments made at seven sites during 5 years. The simulations were assessed graphically and with the aid of several statistical summaries of the goodness of fit. The agreement was generally very good; over all years 72% of all simulations of soil mineral N to 90 cm depth were within 20 kg N/ha of the soil measurements; also 78% of the simulations of crop nitrogen uptake were within 15 kg N/ha and 63% of the simulated yields of dry matter were within 25 g/m2 of the amounts measured. All correlation coefficients were large, positive, and highly significant, and on average no statistically significant differences were found between simulation and measurement either for soil mineral N or for crop N uptake.

scholarly journals Effect of nitrogen fertiliser management on soil mineral nitrogen, nitrous oxide losses, yield and nitrogen uptake of wheat growing in waterlogging-prone soils of south-eastern Australia

Soil Research ◽  
2016 ◽  
Vol 54 (5) ◽  
pp. 619 ◽  
Author(s):  
Robert H. Harris ◽  
Roger D. Armstrong ◽  
Ashley J. Wallace ◽  
Oxana N. Belyaeva
Keyword(s):  
Nitrous Oxide ◽  
Grain Yield ◽  
N Uptake ◽  
Yield Response ◽  
Growth Stages ◽  
N2o Emissions ◽  
Eastern Australia ◽  
Crop N Uptake ◽  
Western Victoria ◽  
N Management

Some of the highest nitrous oxide (N2O) emissions arising from Australian agriculture have been recorded in the high-rainfall zone (>650mm) of south-western Victoria. Understanding the association between nitrogen (N) management, crop N uptake and gaseous losses is needed to reduce N2O losses. Field experiments studied the effect of N-fertiliser management on N2O emissions, crop N uptake and crop productivity at Hamilton and Tarrington in south-western Victoria. Management included five rates of urea-N fertiliser (0, 25, 50, 100 and 200kgN/ha) topdressed at either mid-tillering or first-node growth stages of wheat development; urea-N deep-banded 10cm below the seed at sowing; and urea coated with the nitrification inhibitor DMPP (3,4-dimethylpyrazole phosphate) was either topdressed or deep-banded. Pre-sowing soil profile chemical properties were determined before static chambers were installed to measure N2O losses, accompanied by wheat dry matter, crop N uptake and grain yield and quality, to measure treatment differences. N2O losses increased significantly (P≤0.10) where urea-N was deep-banded, resulting in a 2–2.5-fold increase in losses, compared with the nil N control. The high N2O losses from deep-banding N appeared to result from winter waterlogging triggering gaseous or drainage losses before wheat reached peak growth and demand for N in spring. Despite the high losses from deep-banding urea-N, grain yields were largely unaffected by N management, except at Hamilton in 2012, where topdressed wheat growing in a soil with large reserves of NO3–-N, and later experiencing post-anthesis water deficit resulted in a negative grain yield response. All sites had high concentrations of soil organic carbon (>2.8%) and the potential for large amounts of N mineralisation throughout the growing season to supplement low N fertiliser recovery. However, topdressed urea-N resulted in significant enrichment of crop tissue (P≤0.004) and associated positive response in grain protein compared with the deep banded and nil N treatments. 3,4-Dimethylpyrazole phosphate (DMPP)-coated urea provided no additional benefit to crop yield over conventional urea N. Our study highlighted the importance of synchronising N supply with peak crop N demand to encourage greater synthetic N uptake and mitigation of N2O losses.

scholarly journals DETERMINING FERTILIZER NITROGEN NEEDS FOR FRESH MARKET TOMATO IN KENTUCKY

HortScience ◽  
1996 ◽  
Vol 31 (5) ◽  
pp. 759f-760
Author(s):  
R. Terry Jones ◽  
David C. Ditsch
Keyword(s):  
Fruit Size ◽  
Yield Response ◽  
Residual Soil ◽  
Soil Mineral N ◽  
Soil Mineral ◽  
Fresh Market ◽  
Available Nitrogen ◽  
Mineral N ◽  
Significant Difference ◽  
Petiole Sap

Tomato fertility trials (1992–94) showed no yield response to fertigation N rates between 101–393 kg·ha–1. In 1995, soil Cardy NO3-N readings taken just prior to fertigation showed 53 kg NO3-N/ha in the top 30 cm. Laboratory test on the same sample showed 72.4 kg/ha (NO3 + NH4-N). Forty percent of the available nitrogen was NH4-N, which is not detected by Cardy meters. Soil mineral N levels were measured at fourth injection, second harvest, and 9 days after last harvest. On these dates the 0 kg N/ha treatment had 28, 24, and 8 mg N/kg available in the top 15 cm of soil, similar to the N fertigation treatments. As the growing season progressed, soil mineral N levels decreased, and 9 days after the last harvest residual soil N levels were close to those seen initially. Tomato petiole sap Cardy NO3-N readingsshowed a significant difference between the 0 kg·ha–1 treatment and those (84, 168, and 252 kg·ha–1) receiving N (512 ppm vs. 915, 1028, and 955 ppm NO3-N, respectively). Treatments receiving fertigation N gave petiole sap NO3-N readings higher than those listed by Hochmuth as sufficient for tomatoes. While the data showed a clear separation between the three N treatments and 0 N rate, no significant difference in yield of US #1 or US #2 large fruit occurred. This suggests that adequate N fertility was provided from O.M. mineralization. The highest N rate also had significantly more US #1 small and cull tomatoes than the other treatments. Some Kentucky soils have adequate residual N capable of producing commercial fresh-market tomato crops with little or no additional N. In addition to potential ground water pollution, overfertilization of tomatoes may decrease fruit size and reduce fruit quality by causing NH4-K + ion competition, as well as increase the risk of certain fungal and bacterial diseases.

scholarly journals Maize root and shoot litter quality controls short-term CO<sub>2</sub> and N<sub>2</sub>O emissions and bacterial community structure of arable soil

2020 ◽  
Vol 17 (4) ◽  
pp. 1181-1198 ◽  
Author(s):  
Pauline Sophie Rummel ◽  
Birgit Pfeiffer ◽  
Johanna Pausch ◽  
Reinhard Well ◽  
Dominik Schneider ◽  
...  
Keyword(s):  
Bacterial Community ◽  
Bacterial Community Structure ◽  
Litter Quality ◽  
Maize Root ◽  
N2o Emissions ◽  
Soil Mineral N ◽  
Soil Mineral ◽  
Mineral N ◽  
Root Litter ◽  
C And N

Abstract. Chemical composition of root and shoot litter controls decomposition and, subsequently, C availability for biological nitrogen transformation processes in soils. While aboveground plant residues have been proven to increase N2O emissions, studies on root litter effects are scarce. This study aimed (1) to evaluate how fresh maize root litter affects N2O emissions compared to fresh maize shoot litter, (2) to assess whether N2O emissions are related to the interaction of C and N mineralization from soil and litter, and (3) to analyze changes in soil microbial community structures related to litter input and N2O emissions. To obtain root and shoot litter, maize plants (Zea mays L.) were cultivated with two N fertilizer levels in a greenhouse and harvested. A two-factorial 22 d laboratory incubation experiment was set up with soil from both N levels (N1, N2) and three litter addition treatments (control, root, root + shoot). We measured CO2 and N2O fluxes, analyzed soil mineral N and water-extractable organic C (WEOC) concentrations, and determined quality parameters of maize litter. Bacterial community structures were analyzed using 16S rRNA gene sequencing. Maize litter quality controlled NO3- and WEOC availability and decomposition-related CO2 emissions. Emissions induced by maize root litter remained low, while high bioavailability of maize shoot litter strongly increased CO2 and N2O emissions when both root and shoot litter were added. We identified a strong positive correlation between cumulative CO2 and N2O emissions, supporting our hypothesis that litter quality affects denitrification by creating plant-litter-associated anaerobic microsites. The interdependency of C and N availability was validated by analyses of regression. Moreover, there was a strong positive interaction between soil NO3- and WEOC concentration resulting in much higher N2O emissions, when both NO3- and WEOC were available. A significant correlation was observed between total CO2 and N2O emissions, the soil bacterial community composition, and the litter level, showing a clear separation of root + shoot samples of all remaining samples. Bacterial diversity decreased with higher N level and higher input of easily available C. Altogether, changes in bacterial community structure reflected degradability of maize litter with easily degradable C from maize shoot litter favoring fast-growing C-cycling and N-reducing bacteria of the phyla Actinobacteria, Chloroflexi, Firmicutes, and Proteobacteria. In conclusion, litter quality is a major driver of N2O and CO2 emissions from crop residues, especially when soil mineral N is limited.

Five years of straw incorporation and its effect on growth, yield and nitrogen nutrition of sugarbeet (Beta vulgaris)

1995 ◽  
Vol 125 (1) ◽  
pp. 61-68 ◽  
Author(s):  
M. F. Allison ◽  
H. M. Hetschkun
Keyword(s):  
Field Experiments ◽  
Nitrogen Nutrition ◽  
N Uptake ◽  
Growth Yield ◽  
Soil Mineral N ◽  
Soil Mineral ◽  
Mineral N ◽  
Fertilizer Use ◽  
Experimental Station ◽  
Straw Incorporation

SUMMARYIn 1990–92, field experiments were performed at Broom's Barn Experimental Station to study the effect of 5 years' repeated straw incorporation on sugarbeet. Straw incorporation had no effect on plant population density. Processing quality was reduced by incorporated straw but N had a much larger effect. The effect of incorporated straw on the mineral N content of the soils and N uptake by beet was inconsistent, and this may be related to the amount of soil mineral N present when the straw was incorporated. The efficiency of fertilizer use was unaffected by straw incorporation. On Broom's Barn soils when straw was incorporated, the optimal economic N dressing was c. 120 kg N/ha, and in unincorporated plots it was c. 100 kg N/ha. At the optimal economic N rate, incorporated straw increased beet yields.

New ley legumes increase nitrogen fixation and availability and grain crop yields in subtropical cropping systems

2017 ◽  
Vol 68 (1) ◽  
pp. 11 ◽  
Author(s):  
Lindsay W. Bell ◽  
John Lawrence ◽  
Brian Johnson ◽  
Mark B. Peoples
Keyword(s):  
N2 Fixation ◽  
Farming Systems ◽  
Grain Sorghum ◽  
Soil N ◽  
Soil Mineral N ◽  
Soil Mineral ◽  
Forage Legumes ◽  
Mineral N ◽  
Forage Sorghum ◽  
Grain Crops

Several new and existing short-term forage legumes could be used to provide nitrogen (N) inputs for grain crops in subtropical farming systems. The fixed-N inputs from summer-growing forage legumes lablab (Lablab purpureus), burgundy bean (Macroptilium bracteatum) and lucerne (Medicago sativa) and winter-growing legume species snail medic (Medicago scutellata), sulla (Hedysarum coronarium) and purple vetch (Vicia benghalensis) were compared over several growing seasons at four locations in southern Queensland, Australia. Available soil mineral N and grain yield of a following cereal crop were compared among summer-growing legumes and forage sorghum (Sorghum spp. hybrid) and among winter-growing legumes and forage oats (Avena sativa). In the first year at all sites, legumes utilised the high initial soil mineral N, with <30% of the legume N estimated to have been derived from atmospheric N2 (%Ndfa) and legume-fixed N <30 kg/ha. In subsequent years, once soil mineral N had been depleted, %Ndfa increased to 50–70% in the summer-growing legumes and to 60–80% in winter-growing legumes. However, because forage shoot N was removed, rarely did fixed N provide a positive N balance. Both lablab and burgundy bean fixed up to 150 kg N/ha, which was more than lucerne in all seasons. Prior to sowing cereal grain crops, soil nitrate was 30–50 kg/ha higher after summer legumes than after forage sorghum. At one site, lablab and lucerne increased the growth and yield of a subsequent grain sorghum crop by 1.4 t/ha compared with growth after forage sorghum or burgundy bean. Of the winter-growing legumes, sulla had the highest total N2 fixation (up to 150 kg N/ha.year) and inputs of fixed N (up to 75 kg N/ha), and resulted in the highest concentrations of soil N (80–100 kg N/ha more than oats) before sowing of the following crop. Wheat protein was increased after winter legumes, but there was no observed yield benefit for wheat or grain sorghum crops. New forage legume options, lablab, burgundy bean and sulla, showed potential to increase N supply in crop rotations in subtropical farming systems, contributing significant fixed N (75–150 kg/ha) and increasing available soil N for subsequent crops compared to non-legume forage crops. However, high soil mineral N (>50 kg N/ha) greatly reduced N2 fixation by forage legumes, and significant N2 fixation only occurred once legume shoot N uptake exceeded soil mineral N at the start of the growing season. Further work is required to explore the impact of different management strategies, such as livestock grazing rather than harvesting for hay, on the long-term implications for nutrient supply for subsequent crops.

Organic amendment effects on tuber yield, plant N uptake and soil mineral N under organic potato production

2008 ◽  
Vol 23 (03) ◽  
pp. 250-259 ◽  
Author(s):  
Derek H. Lynch ◽  
Zhiming Zheng ◽  
Bernie J. Zebarth ◽  
Ralph C. Martin
Keyword(s):  
N Uptake ◽  
N Availability ◽  
Residual Soil ◽  
Soil Mineral ◽  
Soil Mineral Nitrogen ◽  
Mineral N ◽  
Total N ◽  
Available N ◽  
Organic Potato ◽  
Certified Organic

AbstractThe market for certified organic potatoes in Canada is growing rapidly, but the productivity and dynamics of soil N under commercial organic potato systems remain largely unknown. This study examined, at two sites in Atlantic Canada (Winslow, PEI, and Brookside, NS), the impacts of organic amendments on Shepody potato yield, quality and soil mineral nitrogen dynamics under organic management. Treatments included a commercial hog manure–sawdust compost (CP) and pelletized poultry manure (NW) applied at 300 and 600 kg total N ha−1, plus an un-amended control (CT). Wireworm damage reduced plant stands at Brookside in 2003 and those results are not presented. Relatively high tuber yields (~30 Mg ha−1) and crop N uptake (112 kg N ha−1) were achieved for un-amended soil in those site-years (Winslow 2003 and 2004) when soil moisture was non-limiting. Compost resulted in higher total yields than CT in one of three site-years. Apparent recovery of N from CP was negligible; therefore CP yield benefits were attributed to factors other than N availability. At Winslow, NW300, but not NW600, significantly increased total and marketable yields by an average of 5.8 and 7.0 Mg ha−1. Plant available N averaged 39 and 33% for NW300 and NW600, respectively. Soil (0–30 cm) NO3−-N at harvest was low (&lt;25 kg N ha−1) for CT and CP, but increased substantially both in season and at harvest (61–141 kg N ha−1) when NW was applied. Most leaching losses of NO3−-N occur between seasons and excessive levels of residual soil NO3-N at harvest, as obtained for NW600, must be avoided. Given current premiums for certified organic potatoes, improving yields through application of amendments supplying moderate rates of N or organic matter appears warranted.

scholarly journals Regulation of N<sub>2</sub>O emissions from acid organic soil drained for agriculture: Effects of land use and season

2019 ◽  
Author(s):  
Arezoo Taghizadeh-Toosi ◽  
Lars Elsgaard ◽  
Tim J. Clough ◽  
Rodrigo Labouriau ◽  
Vibeke Ernstsen ◽  
...  
Keyword(s):  
Pyrite Oxidation ◽  
Acid Volatile Sulfide ◽  
Organic Soils ◽  
N2o Emissions ◽  
N Availability ◽  
Soil Mineral N ◽  
Soil Mineral ◽  
Mineral N ◽  
Total Reduction ◽  
Reduction Capacity

Abstract. Drained organic soils are extensively used for cereal and high-value cash crop production or as grazing land, but emissions of nitrous oxide (N2O) are enhanced by the drainage and cultivation. A study was conducted to investigate the regulation of N2O emissions in a raised bog area drained for agriculture. The area has been classified as potentially acid sulfate soil, and we hypothesised that pyrite oxidation was a potential driver of N2O emissions. Two sites with rotational grass, and two sites with a potato crop, were equipped for monitoring of N2O emissions, as well as sub-soil N2O concentrations at 5, 10, 20, 50 and 100 cm depth, during spring and autumn 2015. Precipitation, air and soil temperature, soil moisture, water table (WT) depth, and soil mineral N were recorded during weekly field campaigns. In late April and early September, intact cores were collected to 1 m depth at adjacent grassland and potato sites for analysis of soil properties, which included acid volatile sulfide (AVS) and chromium-reducible sulfur (CRS) to quantify, respectively, iron monosulfide (FeS) and pyrite (FeS2), as well as total reactive iron (TRFe) and nitrite (NO2−). Soil organic matter composition and total reduction capacity was also determined. The soil pH varied between 4.7 and 5.4. Equivalent soil gas phase concentrations of N2O ranged from around 10 µL L−1 at grassland sites to several hundred µL L−1 at potato sites, in accordance with lower soil mineral N concentrations at grassland sites. Total N2O emissions during 152–174 days were 3–6 kg N2O-N ha−1 for rotational grass, and 19–21 kg N2O-N ha−1 for potato sites. Statistical analyses by graphical models showed that soil N2O concentration in the capillary fringe was the strongest predictor for N2O emissions in spring, and for grassland sites also in the autumn. For potato sites in the autumn, nitrate (NO3−) availability in the top soil, together with temperature, were the main controls on N2O emissions. Pyrite oxidation coupled with NO3− reduction could not be dismissed as a source of N2O, but the total reduction capacity of the peat soil was much higher than explained by the FeS2 concentration. The concentrations of TRFe were also much higher than pyrite concentrations, and potentially chemodenitrification could have been a source of N2O during WT drawdown in spring. The N2O emissions associated with rapid soil wetting and WT rise in autumn were consistent with biological denitrification. Soil N availability and seasonal WT changes were important controls of N2O emissions.

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