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The secondary drainage channel network, with a linear development of over 12,500 km, has a much higher potential for nitrogen removal via denitrification, estimated in up to 8.5 kt N yr-1 (Soana et al., 2011). Overall, denitrification in surface aquatic habitats within this basin can be responsible for the permanent removal of about 12 kt N yr-1; but the fate of the remaining 28 kt is unknown. We suggest that in this basin groundwater N accumulation and transformation could be an important N sink. In fact, nitrate and nitrous oxide concentrations in springs were high in all sampling campaigns (Figure 1). Nitrate was often above the national value for drinking water (~ 11.2 mg N/L) while nitrous oxide was constantly supersaturated. Significant correlation between nitrous oxide and nitrate were not found, stressing the complexity of the interaction between water pathways and nitrogen cycle in the subsurface.
4. Conclusions A soil system nitrogen budget realized in the Oglio River watershed suggests that net export of this nutrient at the basin closing section represents a minor fraction of the large unbalance between sources and sinks. We provide evidences that groundwater represents a large, temporary site of N accumulation in this basin, that recycles N to the surface via springs and via river-groundwater interactions. Further research should address groundwater N transformations, transfer between surface and deep groundwater and estimate of the time required by groundwater to recover from nitrate pollution if N loads are significantly reduced in the future.
References Nielsen L.P. 1992. Denitrification in sediment determined from nitrogen isotope pairing, FEMS (Federation of European Microbiological Societies) Microbiology Ecology 86, 357-362.
Oenema O., Kros H. and De Vries W. 2003. Approaches and Uncertainties in Nutrient Budgets: Implications for Nutrient Management and Environmental Policies, European Journal of Agronomy, 20 (1-2), 3-16.
Silva S.R., Kendall C., Wilkison D.H., Ziegler A.C., Chang C.C.Y. and Avanzino R.J. 2000. A new method for collection of nitrate from fresh water and the analysis of nitrogen and oxygen isotope ratios, Journal of Hydrology 228, 22-36.
Soana E., Racchetti E., Laini A., Bartoli M. and Viaroli P. 2011. Soil budget, net export and potential sinks of nitrogen in the lower Oglio River watershed (northern Italy), CLEAN- Soil, Air, Water 39(11), 956-965.
Nitrogen Workshop 2012
Nitrous oxide emission from biogas production systems on a coastal marsh soil Techow A.1, Dittert K.2, Senbayram M.2, Quakernack R.3, Pacholski A.3, Kage H.3, Taube F.1, Herrmann A.
Christian-Albrechts-University of Kiel, D-24118 Kiel 1 Institute of Crop Science and Plant Breeding; Grass and Forage Science/Organic Agriculture 2 Institute of Plant Nutrition and Soil Science 3 Institute of Crop Science and Plant Breeding; Agronomy and Crop Science
1. Background & Objectives The marsh regions in northern Germany are characterised by specific soil and climatic conditions (relatively high precipitation and wind speed, moderate temperature, high ground water level, clayrich soils with high water saturation, and low oxygen supply), which bear the risk of high denitrification under intensive N fertilisation. However, the nitrous oxide (N2O) emissions potential of marsh sites has been poorly studied (Jungkunst et al., 2006). As in many other regions throughout Germany, biogas production has expanded substantially in recent years, resulting in high amounts of biogas residues which have to be recycled. The objective of the current study therefore was to (i) quantify the N2O emissions from grassland, and from two cropping sequences of maizewinter wheat and wheat-Italian ryegrass for a typical marsh site, and (ii) to analyse the impact of fertiliser type (biogas residue vs. mineral fertiliser) and N rate (control, optimal, oversupply; N amount dependent on crop) on N2O emissions.
2. Materials & Methods Nitrous oxide emission was monitored from April to December 2009 and from March 2010 to March 2011 on a heavy clay soil (25-30% clay, Fluvimollic Gleysol, pH 7.5) close to the west coast of Schleswig-Holstein, Germany. The measurements were embedded in an ongoing field experiment that was established in 2007 as a randomised complete block design with 4 replicates, where the impact of feedstock production systems for biogas (grassland, maize monoculture, maizewinter wheat-Italian ryegrass), type of N fertiliser (calcium ammonium nitrate (CAN), biogas residue), and N rate (control, optimal, oversupply; N amount dependent on crop) on yield performance and environmental effects (N2O and NH3 emissions) was tested. Measurement of N2O emissions was restricted to the control and oversupply treatments in grassland, and the sequences of maize-winter wheat and wheat-Italian ryegrass. Corresponding N rates were 480 kg N ha-1 for grassland, 240 kg N ha-1 for winter wheat, 200 kg N ha-1 for maize, and 80 kg N ha-1 in Italian ryegrass, split in one to four dressings. Biogas residue was applied by trail hoses. Nitrous oxide emissions were monitored daily after fertiliser applications with successive expansion of the sampling intervals up to one week, using the closed chamber method. The N2O concentrations were determined with a gas chromatograph (Varian). Data on N2O emission were analysed statistically by SAS Proc Mixed and multiple comparisons were conducted by the Tukey-Kramer-Test.
3. Results & Discussion In the first experimental year N2O flux pattern mostly followed the fertilisation events in all crops.
Consistently, elevated N2O flux rates were detectable for one to two weeks after fertilisation.
Freeze/thaw events apparently had no effect.
Cumulative N2O emissions in 2009 (Table 1) were characterised by a rather low level compared to other studies (Van Groenigen et al., 2004; Dittert et al., 2009), while the measurements in 2010 resulted in higher N2O emissions. It seems likely that this finding is attributable to low soil moisture conditions during spring and early summer of 2009, which are known to have a great influence on
Nitrogen Workshop 2012
N2O emissions. Senbayram et al. (2009), for instance, found 5-fold higher fluxes at 85% than 65% water holding capacity, and effects of fertiliser type (CAN vs. biogas residue) were significant only at high soil moisture. In accordance, soil moisture content and N2O emissions were higher in 2010.
Table 1. Cumulative N2O emission (kg N2O-N ha-1) monitored from April to December 2009 and from March 2010 to March 2011 for different crops and fertiliser treatments.
Maize denotes the maize-winter wheat cropping sequence, while wheat represents the wheat(*)-Italian ryegrass sequence; (*summer wheat in 2009, since unfavourable conditions in autumn 2008 prevented sowing of winter wheat).
Statistical analysis of the cumulative N2O emission of 2009 revealed a significant effect of the fertiliser treatment (p = 0.002). While no difference was detected between CAN and biogas residue application, both treatments gave higher emission than the control. In 2010, only the mineral N treatment showed significantly higher emissions than the control, although the difference to the biogas residue treatment was marginal. Contrary to our expectations, the crop species caused no significant differences in N2O emissions, whereas Dittert et al. (2009) reported 20 to 30 % higher N2O fluxes for maize compared to a whole crop wheat-grass sequence, which was attributed to the later onset of soil water consumption by transpiration and of later mineral N uptake in maize. Own measurements, however, showed similar soil moisture content in the 0-10 cm layer among the tested crops, whereas ground water level showed considerable spatial and temporal fluctuation.
Overall, the cumulative N2O emissions were well below expectations, probably also due to a low N2/N2O ratio, which is currently being investigated by means of an incubation study.
4. Conclusion Our hypotheses stating that biogas substrate production on a coastal marsh soil will cause high N2O emissions was not confirmed which most likely was due to soil and climatic conditions. A more comprehensive analysis, taking all N flows into account and supplemented by simulation models, is planned for the future and will provide more detailed insights into the underlying processes.
References Dittert K., Senbayram M., Wienforth B., Kage H. and Mühling K.H. 2009. Greenhouse gas emissions in biogas production systems. UC Davis: The Proceedings of the International Plant Nutrition Colloquium XVI.
http://www.escholarship.org/uc/item/18p5q83f (March 2010).
Jungkunst H.F., Freibauer A., Neufeldt H. and Bareth G. 2006. Nitrous oxide emissions from agricultural land use in Germany - a synthesis of available annual field data. Journal of Plant Nutrition and Soil Science 169, 341-351.
Senbayram M., Chen R., Mühling K.H. and Dittert K. 2009. Contribution of nitrification and denitrification to nitrous oxide emissions from soils after application of biogas waste and other fertilizers. Rapid Communications in Mass Spectrometry 23, 2489-2498.
Van Groenigen J.W., Kasper G.J., Velthof G.L., Van den Pol-van Dasselaar A. and Kuikman P.J. 2004. Nitrous oxide emissions from silage maize fields under different mineral nitrogen fertilizer and slurry applications. Plant and Soil 263, 101-111.
Nitrogen Workshop 2012
Nitrous oxide emissions during the decomposition of summer cover crop residue under no-till Giacomini, S.J.a, Weiler, D.A.a, Bastos, L.M. a, Dietrich, G. a, Schmatz, R.a, Aita. C. a a Department of Soil Science, Federal University of Santa Maria, Santa Maria, RS, Brazil.
1. Background & Objectives Some species of legumes, known as summer cover crops (SCC), have satisfactory biomass and N accumulation in a short period of time e.g., between the harvest of summer crops and sowing of winter crops (Creamer and Baldwin, 2000). In Southern Brazil, SCC legumes grown in no-till can be an important source of N for the following winter crops, reducing the cost associated with N fertilizers. However, the addition of N and C with the SCC residues in the soil can increase the emission of N2O to the atmosphere (Baggs et al., 2000). Thus, it is necessary to evaluate the SCC in order to select those species that combine high dry matter (DM) and N addition with low potential to promote N2O emissions. Therefore, the objective of this study was to investigate the temporal patterns and total N2O emissions during decomposition of the SCC residues in no-till with oats.
2. Materials & Methods The experiment was conducted from January to September 2010 on a Typic Hapludalf (60% sand, 30% silt, 10% clay, total C 7.5 g kg-1) at the Department of Soil, Federal University of Santa Maria (29°41’S, 53°48’W), Brazil. The treatments were six SCC: velvet-bean (Mucuna aterrima), pearl millet (Pennisetum americanum), pigeon pea (Cajanus cajan), sunn hemp (Crotalaria juncea), crotalaria spectabilis (Crotalaria spectabilis), jack bean (Canavalia ensiformis) and two fallow plots kept for comparative purposes. Randomized complete block design having four replications and a plot size of 50m2 was used. The SCC were sown in late January and killed with knife rollers at flowering stage in mid-April (80 days of cultivation). After the SCC were killed we carried out direct seeding of oat winter crop in all plots of the experiment. All the plots were fertilized with phosphorus and potassium. However, urea-N (60 kg ha-1) was applied only in one of the two fallow plots. Soil N2O fluxes were measured from April to September after the SCC were killed until the oats reached physiological maturity using static chambers method. The N2O concentrations in the samples were analyzed by gas chromatography (Shimadzu GC-2014 Greenhouse). Daily N2O fluxes (µg N m-2 h-1) were calculated by linear interpolation and the cumulative fluxes (g N ha-1) were calculated by the integration of the daily N2O emissions.
The N2O flux after the SCC residues addition to soil ranged from -1.5 to 1,017 µg N m-2 h-1 (Figure 1). The largest flows of N2O were observed in the first 40 days after the SCC were managed.
During this period, the increase in N2O fluxes coincided with the occurrence of rainfall events which resulted in the elevation of water-filled pore space (WFPS), which favored the anaerobic reduction of NO3-. The largest emissions of N2O were observed 9 days after SCC were managed in velvet bean plots. After 40 days of SCC management, even with the rainfall that caused an increase in WFPS, we observed no increase in the flow of N2O (Figure 1). These results indicated that during this period the lack of NO3- and C limited the activity of facultative anaerobic microorganisms. The cumulative N2O emissions in the SCC treatments exceeded that observed in fallow and ranged from 511 to 987 g N ha-1, corresponding to 0.31-0.70% of the N applied with SCC (Table 1). The percentage of synthetic N fertilizer applied in the oat crop that was emitted as N2O was similar to that observed for the treatments with SCC. The range of emission factors is slightly lower than the emissions predicted by the IPCC (2006) default emission factor of 1% of N applied. The N2O flows and cumulative emissions were not related to the amount of N added with SCC. It is possible that other characteristics of SCC residues, such as polyphenol, also interfere in the N2O emission. The difference in the addition of DM and C among species may also explain this result. The lowest emission factor, considering the amount of N2O emitted per Mg of biomass added by the SCC was observed in the poaceae pearl millet (Table 1). Among the legumes, the highest and lowest emission factor were observed in velvet-bean and sunn hemp plots, respectively.
4. Conclusion This study indicated that among the legumes grown as SCC, sunn hemp fulfilled the requirements of satisfactory N and DM addition to soil with lower N2O emission potential under no-till.
References Creamer N.G.and Baldwin K.R. 2000. An evaluation of summer cover crops for use in vegetable production systems in North Carolina. HortScience 35, 600-603.
Baggs E.M., Rees R.M., Smith K.A. and Vinten A.J.A. 2000. Nitrous oxide emission from soils after incorporating crop residues. Soil Use Manage 16, 82-87.