Enterische methaanemissie van melkvee in relatie tot (vers) graskwaliteit: Jaarrapport 2: 2021: Resultaten van een meerjarige beweidingsproef naar methaanemissie bij weidegang, zomerstalvoedering en het voeren van graskuil

The Climate Agreement describes strict reduction targets to reduce methane (CH4) and ammonia (NH3) emissions simultaneously. The goal of this multiannual research is to explore the reduction potential for CH4 and NH3 in the dairy sector via (fresh) grass management. In two consecutive years containing three periods per year (April/May, June/July and August/September) the same experiment has been performed were enteric CH4 of dairy cows was measured receiving grass silage, fulltime grazing or zero-grazing (cut-and-carry system). The results found in the second year were in comparison with the first year, having the lowest CH4 emission on fulltime grazing in spring. Overall, regardless of year or period, the average CH4 yield of cows on fulltime grazing was 17.2 g CH4/kg DM, on zero-grazing 18.3 g CH4/kg DM and on grass silage 21.0g CH4/kg DM. CH4 yield of fresh grass differed between periods. Growth stadia had an effect as well, emission was lower on short grass compared to long grass. Based on these two years, no year effect was found. The measured variance in CH4 emission shows potential for reducing enteric CH4 using grassland management. Additionally, the study showed the importance of adjusting the emission factor of fresh grass based on grass quality.