Short term N2O losses in urine patches: a 15N labelling study

These results show that emission of N2O is greater when N is added as urine compared with mineral N. This can probably be explained by the presence of organic carbon compounds in the urine, which may fuel the N2O production. Moreover, there is a greater exchange of N between the applied urine-N pool and the soil indigenous N-pool compared with the added mineral N-pool and soil indigenous N, which also indicates an increased microbial activity in the urine patches. The urea content of the urine seemed to be of importance for N2O emissions, suggesting dietary regulations of urine N-composition as a N2O mitigation option

Sources of N2O in organic grass-clover pastures.

Organic farming practises, and in particular dairy production systems based on grass-clover pastures are becoming increasingly abundant within Danish agriculture. Grass-clover pastures may provide a mitigation option to reduce grassland nitrous oxide (N2O) emissions (Velthof et al. 1998). The objectives of this work was to examine the relationship between N2O emissions and transformations of inorganic N in organically managed grass-clover pastures of different ages. Results from the project will be used for calibration of the FASSET whole-farm nitrogen transformation model

N2O emission from grass-clover swards is largely unaffected by recently fixed N2

The contribution of biologically fixed dinitrogen (N2) to the nitrous oxide (N2O) production in grasslands is unknown. To assess the contribution of recently fixed N2 as a source of N2O and the transfer of fixed N from clover to companion grass, mixtures of white clover and perennial ryegrass were incubated for 14 days in a 15N2-enriched atmosphere (0.4 atom% excess). Immediately after labelling, half of the grass-clover pots were sampled for N2 fixation determination, whereas the remaining half were examined for emission of 15N labelled N2O for another eight days using a static chamber method. Biological N2 fixation measured in grass-clover shoots and roots as well as in soil constituted 342, 38 and 67 mg N m-2 d-1 at 16, 26 and 36 weeks after emergence, respectively. The drop in N2 fixation was most likely due to a severe aphid attack on the clover component. Transfer of recently fixed N from clover to companion grass was detected at 26 and 36 weeks after emergence and amounted to 0.7 ± 0.1 mg N m-2 d-1, which represented 1.7 ± 0.3 % of the N accumulated in grass shoots during the labelling period. Total N2O emission was 91, 416 and 259 μg N2O-N m-2 d-1 at 16, 26 and 36 weeks after emergence, respectively. Only 3.2 ± 0.5 ppm of the recently fixed N2 was emitted as N2O on a daily basis, thus recently fixed N released via easily degradable clover residues appears to be a minor source of N2O

Kommer der lattergas fra kløvergræsset?

Kløvergræs er et vigtigt element i økologisk mælkeproduktion. Flere undersøgelser har dog antydet at denne driftsform rummer en risiko for uønskede udslip af gasformige kvælstof-forbindelser til omgivelserne. En af de gasformer der er særlig opmærksomhed omkring, er lattergas, der er en kraftig drivhusgas med en væsentlig betydning for den globale opvarmning. Af det samlede danske udslip af drivhusgasser, udgør lattergas mere end 10%, hovedsalig udledt ved landbrugsaktivitet. Biologisk kvælstof-fiksering er en nøgleproces i kløvergræssystemer, men vores viden om processen er endnu ufuldstændig, specielt når det gælder bidraget fra rodbiomassen. Af samme grund eksisterer der heller ingen viden om, hvor meget af det fikserede kvælstof, som atter frigives til atmosfæren som lattergas. Økologisk produktion anses af mange som et initiativ, der kan mindske landbrugets påvirkning af det omgivende miljø, men for at give en nuanceret vurdering heraf er det dog nødvendigt at tilvejebringe yderligere viden om samspillet mellem landbrugsproduktion og miljø. Det er på denne baggrund at Danmarks JordbrugsForskning og Forskningscenter Risø gennemfører et projekt med det formål at bestemme størrelsen, reguleringen og sammenhængen mellem kvælstof-fiksering og lattergasfrigivelse i kløvergræsmarker. Resultaterne fra projektet vil indgå i opbygningen af en model, der beskriver transporten af kvælstof fra stald til mark på den enkelte bedrift. Kvælstof-fiksering er desuden dårligt undersøgt på de mere sandede jorder, som netop indgår i projektet, og resultaterne herfra vil derfor være et værdifuldt bidrag til rådgivningstjenesters beslutningsgrundlag. Resultaterne fra første forsøgsår viser en maksimal kvælstof-fiksering på 185 kg ha-1 i 2. produktionsår faldende 115 kg i 8. produktionsår. I lighed hermed fandt vi at lattergasudslippet var størst i de første produktionsår (235-290 g N ha-1) faldende til 166 g N i 8. år. Samlet set viser disse resultater at tabet af lattergas i kløvergræs udgør en beskeden del af det fikserede N

Kilovis af N omsættes dagligt i kløvergræs

Gennem de seneste årtier har der været stigende opmærksomhed omkring udledningen af drivhusgasser i forbindelse med landbrugsproduktionen, og megen forskning har været rettet mod at identificere de væsentligste kilder og mulige afværgeforanstaltninger. I forbindelse med planteproduktion er det især anvendelsen af kvælstof(N)-holdige gødningstyper, mineralske såvelsom husdyrbaserede, som bidrager til udslip af den vigtige drivhusgas lattergas

Afgrøderester og sædskifte har stor betydning for udledning af lattergas

Lattergas udgør en del af det atmosfæriske tab af kvælstof fra dyrkningsjorden. Målt i kg kvælstof er mængderne små, men fordi lattergas er en meget kraftig drivhusgas, er gassens betydning for landbrugets samlede udledninger stor

Technical Note: Mesocosm approach to quantify dissolved inorganic carbon percolation fluxes

Dissolved inorganic carbon (DIC) fluxes across the vadose zone are influenced by a complex interplay of biological, chemical and physical factors. A novel soil mesocosm system was evaluated as a tool for providing information on the mechanisms behind DIC percolation to the groundwater from unplanted soil. Carbon dioxide partial pressure (<i>p</i>CO₂), alkalinity, soil moisture and temperature were measured with depth and time, and DIC in the percolate was quantified using a sodium hydroxide trap. Results showed good reproducibility between two replicate mesocosms. The <i>p</i>CO₂ varied between 0.2 and 1.1%, and the alkalinity was 0.1–0.6 meq L⁻¹. The measured cumulative effluent DIC flux over the 78-day experimental period was 185–196 mg L⁻¹ m⁻² and in the same range as estimates derived from <i>p</i>CO₂ and alkalinity in samples extracted from the side of the mesocosm column and the drainage flux. Our results indicate that the mesocosm system is a promising tool for studying DIC percolation fluxes and other biogeochemical transport processes in unsaturated environments

BioConcens: Biomass and bioenergy production agriculture – consequences for soil fertility, environment, spread of animal parasites and socio-economy

The research programme called “international research cooperation and organic integrity” was commenced for a period 2006-2010. It is coordinated by DARCOF (The Danish Research Centre for Organic Farming). The whole programme, with acronym DARCOF III, consists of 15 projects (http://www.darcof.dk/research/darcofiii/index.html). One of them is BIOCONCENS - Biomass and bioenergy production in organic farming – consequences for soil fertility, environment, spread of animal parasites and socio-economy (http://www.bioconcens.elr.dk/uk/). The production of bioenergy in organic agriculture (OA) can reduce its dependency of fossil fuels and decrease green house gasses emission; consequently it will increase sustainability of organic farms. Biorefinery concept based on co-production of biogas, bioethanol and protein fodder in organic farming will be developed within the BIOCONCENS project and the background for the project and the different work packages will be presented in this paper

Decrease in heathland soil labile organic carbon under future atmospheric and climatic conditions

Characterization of the impacts of climate change on terrestrial carbon (C) cycling is important due to possible feedback mechanisms to atmospheric CO2 concentrations. We investigated soil organic matter (SOM) dynamics in the A1 and A2 horizons (~0–5.1 and ~5.1–12.3 cm depth, respectively) of a shrubland grass (Deschampsia flexuosa) after 8 years of exposure to: elevated CO2 (CO2), summer drought (D), warming (T) and all combinations hereof, with TDCO2 simulating environmental conditions for Denmark in 2075. The mean C residence time was highest in the heavy fraction (HF), followed by the occluded light fraction and the free light fraction (fLF), and it increased with soil depth, suggesting that C was stabilized on minerals at depth. A2 horizon SOM was susceptible to climate change whereas A1 horizon SOM was largely unaffected. The A2 horizon fLF and HF organic C stocks decreased by 43 and 23% in response to warming, respectively. Organic nitrogen (N) stocks of the A2 horizon fLF and HF decreased by 50 and 17%, respectively. Drought decreased the A2 horizon fLF N stock by 38%. Elevated CO2 decreased the A2 horizon fLF C stock by 39% and the fLF N stock by 50%. Under TDCO2, A2 horizon fLF C and N stocks decreased by 22 and 40%, respectively. Overall, our results indicate that shrubland SOM will be susceptible to increased turnover and associated net C and N losses in the future