The fate of ^{\sf\sl{15}}N from dairy cow urine under pasture receiving different rates of N fertiliser

$^{15}$N-labelled urine was used to study the fate of N applied as urine in spring, summer and autumn on ryegrass receiving two different fertiliser rates (100 and 300 kg N $\cdot$ ha$^{-1}$ $\cdot$ yr$^{-1}$) in Brittany (France). Ammonia volatilisation of labelled urine N was less than 4% and immobilised urine N represented 21–31% of the applied $^{15}$N. Recovery of labelled N in plants ranged from 30 to 65% of N input as urine, showing a decrease in autumn for the highest fertiliser nitrogen treatment. The plant recovery of urine N was relatively high in autumn (49%) when urine was deposited on ryegrass receiving a fertiliser rate of 100 kg N $\cdot$ ha$^{-1}$ $\cdot$ yr$^{-1}$. Lower N fertiliser regimes can therefore lower the leaching potential of urine N in pastures.Devenir de l'azote des pissats de vache émis sur une prairie recevant différents niveaux de fertilisants azotés. De l'urine de vache laitière marquée au $^{15}$N a été utilisée pour étudier le devenir de l'azote urinaire apporté au printemps, en été et à l'automne sur un ray-grass anglais fertilisé à 2 doses d'azote (100 et 300 kg N $\cdot$ ha$^{-1}$ $\cdot$ an$^{-1}$). La volatilisation d'ammoniac est toujours inférieure à 4 % de l'azote apporté et l'azote immobilisé dans le sol sous forme organique représente 21 à 31 % de l'apport. Le coefficient réel d'utilisation de l'azote par les plantes varie de 30 à 65 %, diminuant à l'automne pour le traitement 300. Le CRU de l'apport d'automne demeure cependant relativement élevé pour la prairie ne recevant que 100 kg N $\cdot$ ha$^{-1}$ $\cdot$ an$^{-1}$ (49 %). Cela peut conduire à un risque de lessivage de l'azote urinaire plus faible dans les régimes de fertilisation modérée

Long-term maintenance of grasslands on dairy farms is associated with redesign and hybridisation of practices, motivated by farmers' perceptions

Despite a constant decline in grassland areas between the 1970s and 2010 at the regional and national scale in France, in particular on lowlands, grasslands have been maintained locally. This raises questions about long-term changes on the farms involved in these dynamics, particularly with regard to the relation between the evolution of the role of grasslands in production processes, and farmers' perceptions of fodder systems within production systems. Our research concerned three peri-urban cantons in Brittany, where we examined grassland practices over the long term and farmers' perceptions of grasslands in a sample of 15 farms within the area where grasslands were maintained. First, we modelled pathways of the place and roles of grasslands on farms, based on criteria of quantitative presence, management, and valorisation. Second, we characterised the farmers' perceptions of grasslands and the fodder system. We then performed combined analysis of these pathways and perceptions. The maintenance of grasslands was found in a diversity of pathways in which grasslands were used to a medium and large extent in the fodder systems. These changes occurred either through a complete redesign of the fodder system or through hybridisation of practices aimed at obtaining dairy systems that were more intensive yet more agri-ecological. The pathways that gave a new place to grasslands in the fodder system were related to farmers' perceptions marked by a fading opposition between grasslands and maize farming. They attributed additional value - in terms of animal welfare, economics, or agronomy - to grasslands in a mixed maize/grassland fodder system