Effect of increased N use and dry periods on N2O emission from a fertilized grassland

Abstract

To better understand the effects of increased N input and dry periods on soil nitrous oxide (N 2 O) emission, we examined a unique data-set of weather, soil microclimate, N input, and N 2 O emissions (using the eddy covariance method), measured at a fertilized grassland over the period 2003-2008. We found that the N 2 O emission (11.5 kg N ha -1 year -1 ), the ratio of N 2 O emission to N input (3.4), and the duration of elevated N 2 O flux (57 days) in 2003 were about two times greater than those of the following years. 2003 had the highest annual N input (343 kg N ha -1 year -1 ) which exceeded the agronomical requirements for Irish grasslands (up to 306 kg ha -1 year -1 ). In the summer of 2003, the site had a significantly higher soil temperature, lower WFPS and lowest rainfall of all years. Large N 2 O emission events followed rainfall after a long dry period in the summer of 2003, attributed to dominant nitrification processes. Furthermore, in the non summer periods, when temperature was lower and WFPS was higher and when there were prior N applications, lower N 2 O emissions occurred and were attributed to dominant denitrification processes. Throughout the study period, the N input and soil dryness related factors (duration of WFPS under 50%, summer average WFPS, and low rainfall) showed exponential relationships with N 2 O emission and the ratio of N 2 O emission to N input. Based on these findings, we infer that the observed anomalously high N 2 O emission in 2003 may have been caused by the combined effects of excess N input above the plant uptake rate, elevated soil temperature, and N 2 O flux bursts that followed the rewetting of dry soil after an unusually long dry summer period. These results suggest that high N input above plant uptake rate and extended dry periods may cause abnormal increases in N 2 O emissions.

Effects of soil rewetting and thawing on soil gas fluxes: a review of current literature and suggestions for future research

“…Field studies have observed increased soil N 2 O flux following wetting in cropland (Barton et al, 2008), grazed pasture (Kim et al, 2010a), tropical forest (Butterbach-Bahl et al, 2004), grassland (Hao et al, 1988), savannah (Martin et al, 2003), and fen (Goldberg et al, 2010a). Laboratory incubation experiments with cropland (Beare et al, 2009), forest (Dick et al, 2001), grassland , and peatland soils (Dinsmore et al, 2009) have yielded similar results of increased N 2 O flux after rewetting.…”

Response of N 2 O emission to water and nitrogen addition in temperate typical steppe soil in Inner Mongolia, China

“…Both water and N additions significantly increased the peak effluxes in different treatments (P < 0.01), and the interactive effect between water and N addition affected the peak effluxes among the different treatments (P < 0.05). The functions of N and water addition in improving soil N 2 O effluxes are described as follows: (1) N input provides sufficient substrate for the N 2 O generation processes; (2) the drying-rewetting transformation after water addition allows the release of several organic and inorganic substances into the soil, which provides sufficient substrates and energy for nitrification and denitrification (Mummey et al, 1994;Bollmann and Conrad, 1998;Beare et al, 2009); and (3) the variations in soil NO 3 À and NH 4 + contents suggest that water addition facilitates the immediate transfer of fertilizers to mineral N from surface soil to the 0-10 cm soil layer, which also provides ample substrate for nitrification and denitrification (Goldberg et al, 2010;Kim et al, 2010). Short bursts of N 2 O emissions after fertilization were also observed in previous studies (Dobbie and Smith, 2003;Jones et al, 2007); however, the highest effluxes observed in our study was in the lower range relative to the peak values of N 2 O obtained by some other N addition experiments in temperate grasslands abroad (ranged from 100 to 7500 mg m À2 h À1 N 2 O-N) (e.g., Kim et al, 2010;Pinto et al, 2004;Van Beek et al, 2011).…”

“…In late June 2010, when the peaks of N 2 O effluxes were observed, the WFPS was nearly the lowest during the whole growing season; the highest N 2 O effluxes under drought soil water condition (WFPS < 30%) were also observed in previous studies both in fertilized (Zhang and Han, 2008;Peng et al, 2011) and native grasslands (Du et al, 2006;Yao et al, 2010) in Inner Mongolia. The processes of N 2 O production were generally considered depressed in such droughtaffected soil conditions, whereas Kim et al (2010) and Cantarel et al (2011) found that greater N 2 O emissions occurred under drought conditions in the European temperate grasslands. The high soil temperature could contribute to the high N 2 O emission rates during the drought period, both in the current study and in the previous studies with similar results; the N 2 O effluxes during the drought period showed positive correlation with soil temperature (Peng et al, 2011;Kim et al, 2010).…”

“…The processes of N 2 O production were generally considered depressed in such droughtaffected soil conditions, whereas Kim et al (2010) and Cantarel et al (2011) found that greater N 2 O emissions occurred under drought conditions in the European temperate grasslands. The high soil temperature could contribute to the high N 2 O emission rates during the drought period, both in the current study and in the previous studies with similar results; the N 2 O effluxes during the drought period showed positive correlation with soil temperature (Peng et al, 2011;Kim et al, 2010). Furthermore, the N uptake of plants would be reduced during the drought period, and the N threshold for N 2 O generation would be relieved, causing higher N 2 O effluxes (Cantarel et al, 2011).…”

“…Collins et al (2008) proposed a threshold-delay-nutrient dynamics (TDND) model to describe nutrient supply and demand in arid ecosystems, and the model predicted that plants were more sensitive to drought stress than soil microbe because their metabolism was more easily restrained during drought conditions. Kim et al (2010) observed in a 6-years study of fertilized grassland that the N 2 O emission in a drought year was two times higher than those in normal precipitation years because the N uptake of plants reduced during a drought period, and N input was beyond the plant N uptake demand. The experiment performed in the Baiinxile Pasture by Bai (1999) indicated that the positive effects of 10 day precipitation from late June to late August were observed on the primary productivity, which was critical to plant growth in terms of water requirement.…”