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

Production of N2O in grass-clover pastures

In organic as well as conventional dairy farming, grass-clover pastures is an important component of the cropping system. This is because grass-clover is an excellent cattle fodder, and because clover has the ability of fixing atmospheric N2. When budgets for N2O emissions are made accord-ing to the IPCC guidelines it is assumed that 1.25 % of added nitrogen is emitted as N2O. This emission factor is used for all nitrogen inputs although the factor relies on experiments with fertilizer and manure, only. The emission factor for biological fixed nitrogen may be lower than 1.25 %, because nitrogen is released only slowly into the soil. However knowledge is very sparse. On the other hand, when the effect of grazing cattle is added the situation might be different. In Denmark organic cattle are supposed to be on grazing fields for at least 150 days a year. Nitrogen returned to the system in urine and dung is likely to locally exceed the needs of the plants and is therefore at risk of being lost as N2O. Thus far, however, there have only been a few detailed estimates of total N2O emissions from grassland livestock productions, and understanding of the factors controlling N2O emissions remains unsatisfactory

Biologically fixed N2 as a source for the N2O production in a grass clover mixture, measured by 15N2

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 growth cabinet with 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, which accounted for 2.1 ± 0.5 % of the total N2O-N emission. Thus, recently fixed N released via easily degradable clover residues appears to be a minor source of N2O

Greenhouse gas emissions from cultivation of energy crops – is it important?

Replacing fossil fuel-derived energy with biomass-derived energy is commonly emphasized as a means to reduce CO2 emissions. However, our study highlights the risk of large greenhouse gas emissions when wastes from bioenergy production are recycled as fertilizer for energy crops. Crop management affects the magnitude of these emissions, which in some cases negate a considerable fraction of the global warming savings associated with biofuels

Production of N2O in grass-clover pastures

In organic as well as conventional dairy farming, grass-clover pastures is an important component of the cropping system. This is because grass-clover is an excellent cattle fodder, and because clover has the ability of fixing atmospheric N2. When budgets for N2O emissions are made accord-ing to the IPCC guidelines it is assumed that 1.25 % of added nitrogen is emitted as N2O. This emission factor is used for all nitrogen inputs although the factor relies on experiments with fertilizer and manure, only. The emission factor for biological fixed nitrogen may be lower than 1.25 %, because nitrogen is released only slowly into the soil. However knowledge is very sparse. On the other hand, when the effect of grazing cattle is added the situation might be different. In Denmark organic cattle are supposed to be on grazing fields for at least 150 days a year. Nitrogen returned to the system in urine and dung is likely to locally exceed the needs of the plants and is therefore at risk of being lost as N2O. Thus far, however, there have only been a few detailed estimates of total N2O emissions from grassland livestock productions, and understanding of the factors controlling N2O emissions remains unsatisfactory

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