Greenhouse gas fluxes over managed grasslands in Central Europe

Abstract

Central European grasslands are characterized by a wide range of different management practices in close geographical proximity. Site-specific management strategies strongly affect the biosphere-atmosphere exchange of the three greenhouse gases (GHG) carbon dioxide (CO ), nitrous oxide (N O), and methane (CH ). The evaluation of environmental impacts at site level is challenging, because most in situ measurements focus on the quantification of CO exchange, while long-term N O and CH flux measurements at ecosystem scale remain scarce. Here, we synthesized ecosystem CO , N O, and CH fluxes from 14 managed grassland sites, quantified by eddy covariance or chamber techniques. We found that grasslands were on average a CO sink (-1,783 to -91 g CO m year ), but a N O source (18-638 g CO -eq. m year ), and either a CH sink or source (-9 to 488 g CO -eq. m year ). The net GHG balance (NGB) of nine sites where measurements of all three GHGs were available was found between -2,761 and -58 g CO -eq. m year , with N O and CH emissions offsetting concurrent CO uptake by on average 21 ± 6% across sites. The only positive NGB was found for one site during a restoration year with ploughing. The predictive power of soil parameters for N O and CH fluxes was generally low and varied considerably within years. However, after site-specific data normalization, we identified environmental conditions that indicated enhanced GHG source/sink activity ("sweet spots") and gave a good prediction of normalized overall fluxes across sites. The application of animal slurry to grasslands increased N O and CH emissions. The N O-N emission factor across sites was 1.8 ± 0.5%, but varied considerably at site level among the years (0.1%-8.6%). Although grassland management led to increased N O and CH emissions, the CO sink strength was generally the most dominant component of the annual GHG budget.

Plant diversity effects on forage quality, yield and revenues of semi-natural grasslands

“…Furthermore, less fertilizer application would allow maintaining high plant diversity over longer time 56,57 , and in turn maintaining the plant diversity effect. Moreover, any reduction in management can also entail other ecosystem benefits, such as increasing whole-ecosystem biodiversity (beside solely plant diversity) or decreasing greenhouse gas emissions 58,59 . Considering all our findings, altering plant diversity even in more intensively used grasslands appears to be a valuable management tool to farmers.…”

Grassland Management Affects Delivery of Regulating and Supporting Ecosystem Services

“…In Central Europe, ecosystem CO 2 , N 2 O, and CH 4 fluxes were quantified using eddy covariance or chamber techniques from 14 grassland sites under a wide range of management treatments (Hörtnagl et al, 2018). Grasslands were on average a CO 2 sink (−1783 to −91 g CO 2 m −2 yr −1 ), but a N 2 O source (18,640 g CO 2 -equivalent m −2 yr −1 ), and either a CH 4 sink or source (−9 to 488 g CO 2 -equivalent m −2 yr −1 ).…”

Management matters: testing a mitigation strategy for nitrous oxide emissions using legumes on intensively managed grassland

“…For a more targeted comparison, here we considered only the non-restoration site years and excluded 2012, which showed high N 2 O emissions particularly related to grassland restoration. The Hörtnagl et al (2018) study covered the years 2010-2013 for our site but used a different gap-filling method. The high emissions from our site were explained by warm temperatures (∼ 20 • C), combined with moist to wet soil moisture conditions after fertiliser events, and therefore particularly favourable conditions for N 2 O production compared to conditions at other sites.…”

“…Processes producing and consuming N 2 O are numerous and their complex interactions and dependencies on biotic and abiotic factors are generally known but not yet fully understood (Butterbach-Bahl et al, 2013). Nevertheless, it is known that N 2 O emissions in grasslands strongly depend on management practices (Hörtnagl et al, 2018;Li et al, 2013;Snyder et al, 2009), and reducing N 2 O emissions while maintaining yields can thus contribute to climate smart agriculture (CSA) (Lipper et al, 2014). For mitigating N 2 O emissions from soils, a range of options (e.g.…”

“…Moreover, grass-legume mixtures are beneficial to fodder composition as they are characterised by higher protein contents than grass swards, and show well-balanced feeding values (Phelan et al, 2015). Legume-rich fodder has high crude protein (CP) contents and was shown to increase voluntary intake by 10 %-20 % (Dewhurst et al, 2003) and to increase milk production (Dewhurst et al, 2003;Huhtanen et al, 2007).…”