- ORCID NUMBER 0000-0002-6084-4972
Biography
Dr Imelda Casey is a University College Cork graduate with a BSc. In Applied Ecology and a PhD in grassland agronomy from Queens University in 2000. The PhD was one of the earlier Walsh Fellowships funded by Teagasc (1995). She has over 25 years’ experience of grassland research and 20 years lecturing experience in agriculture. Research experience at WIT has been mostly on developing more sustainable grassland systems. Research projects have involved studies on agronomy, plant ecology, nitrate and phosphate use efficiency and leaching, carbon emissions from grassland, sward morphology, agricultural botany and plant physiology. She has been employed as a lecturer with the Department of Chemical and Life Sciences, WIT since 2007. She has lectured and led many modules such as agriculture and the environment and quality food production. Prior to this she spent 8 years as a contract researcher (research officer) in the Department of Dairy Husbandry, Teagasc, Moorepark where she was project leader (PI) on several internally funded grassland projects (ARMIS:4467, 4849, 4948,4170, 4236). This involved managing staff and substantial grassland projects and obtaining Teagasc internal funding with a large annual budget. External funding was also awarded to Dr. Casey by the Dairy Levy committee (€600,000) to improve mid season sward quality.
In 2005 she was a lecturer at CIT (MTU) where she lectured on Ecotoxicology and Environmental Science. She has been a lecturer in Agriculture and Agricultural science at Waterford Insitute of Technology since 2007. This has involved lecturing and leading modules such as Integrated Pest Management, Plant Biology, Evironmental Science and Quality Food Production. It also involves developing research in grassland for undergraduates and supervising numerous third and fourth year projects in this area.
Research Interests: Environmentally sustainable grassland systems: Improving fertilizer N management and white clover management, carbon sequestration and loss from grassland, grassland ecology and plant-animal interactions in grazed swards; mid-season sward quality, sward physiology and tillering dynamics.
Recently funded projects.
Dept. Agriculture: RSF (2019)R521 LoCAM: Lowering the carbon and ammonia footprints of pasture based dairy production.main (WIT) collaborator Dr. I. Casery. Total grant €600,00 PI James Humphreys Teagasc
Dept. Agriculture: RSF (2019)R501 FasTEN: Farm sustainability tools for efficient nutrient management (€244,000 WIT) (WIT) collaborators Dr. I Casey and Dr. Nabla Nabla Kennedy. Total grant €1,199,737 PI Dave Wall Teagasc
Vista Milk: (2019): Development and intergration of hygienic and novel processing sensors of incoming milk in a dairy platform. (co supervisor) (€88,000 euros WIT) co supervisor. Dr. Ultan Mc Carthy main WIT supervisor.
INTERREG No.304/2016 (2018-2021): PhD main supervisor (WIT) awarded to Dr. IA. Casey and Teagasc: Propagating innovations for more resilient dairy farming in the Atlantic Area (Dairy-4-Future). PhD supervisor. (collaborator). (€90,000 euros).
Horizon 2020 GA No. 727973 (2017-2021): PhD main supervisor (WIT) awarded to Dr. I. Casey and Teagasc: Transition paths to sustainable legume based systems in Europe (TRUE). PhD supervisor (collaborator) (€88,000 euros).
Teagasc TWF 2017035 (2017-2021) Optimum stocking rate on the grazing platform of fragmented dairy farms.PhD supervisor. (€90,000 euros).
INTERREG IVB NWE 096D (2009-2013) Improving regional prosperity through better resource utilization on dairy farms and stakeholder cooperation (DAIRYMAN). PhD supervisor.(collaborator).(€88,000 euros).
Teagasc staff development: One Phd, one Masters.
Dept. of Agriculture: RSF07 511 (2007-2012) Productivity of clover-based grassland under organic management and nitrate losses to ground water.(collaborator).(260,000 euros). Main WIT collaborator Dr. I. Casey
Research officer Teagasc:1995-2002 Projects were awarded from Dairy Levy funding and were also part funded by the National Development Plan: (Total value €600,000 dairy levy). Others internal projects had substantial budgets also. (Dr. I Casey Project leader: PI).
1.Sward reproductive tillering dynamics at mid-season and their likely impact on sward quality.2.Optimising sward structure and herbage yield for the performance of dairy cows at pasture.3. The effect of cultivar heading date on mid season sward quality ((ARMIS:4467, 4849, 4948,4170, 4236).
Six PhDs One Master completed (main supervisor). Currently supervising: 6 PhDs one Masters. Total scientific journals 26. 3 accepted.
Work Experience
2007-present: Waterford Institute of Technology, Lecturer agriculture/research environmentally sustainable grassland systems
2005 Cork Institute of Technology, lecturer environmental science
1996-2002 Teagasc, Dairy Production Research Centre, Moorepark, Fermoy, Co. Cork.
Research Officer leading research on sward management, mid-season sward quality and pasture intake
1995 :Crossnacreevy Plant Breeding Station, Department of Agriculture, Northern Ireland
1994: Teagasc, Dairy Production Research Centre, Moorepark, Fermoy, Co. Cork.
Research assistant on mid-season sward quality and pasture intake
Coelho, J.J., Hennessy, A., Casey, I., Woodcock, T. and Kennedy, N., (2020) Biofertilisation withAnaerobic Digestates: Effects on the Productive Traits of Ryegrass and Soil Nutrients. Journal of Soil Science and Plant Nutrition, pp.1-14.https://doi.org/10.1007/s42729-020-00237-7
Coelho, J.J., Hennessy, A., Casey, I., Bragança, C.R.S., Woodcock, T. and Kennedy, N., (2020). Biofertilisation with anaerobic digestates: A field study of effects on soil microbial abundance and diversity. Applied Soil Ecology, 147, p.103403. https://doi.org/10.1016/j.apsoil.2019.103403
Coelho, J.J., Hennessy, A., Casey, I., Woodcock, T. and Kennedy, N., (2019). Responses of ryegrass, white clover, soil plant primary macronutrients and microbial abundance to application of anaerobic digestates, cattle slurry and inorganic N-fertiliser. Applied Soil Ecology, 144, pp.112-122.https://doi.org/10.1016/j.apsoil.2019.07.011
Coelho, J.J., Prieto, M.L., Hennessy, A., Casey, I., Woodcock, T. and Kennedy, N., (2019). Determination of microbial numbers in anaerobically digested biofertilisers. Environmental Technology, pp.1-11.https://doi.org/10.1080/09593330.2019.1645214
Coelho, J.J., Prieto, M.L., Dowling, S., Hennessy, A., Casey, I., Woodcock, T. and Kennedy, N., (2018). Physical-chemical traits, phytotoxicity and pathogen detection in liquid anaerobic digestates. Waste Management, 78, pp.8-15. https://doi.org/10.1016/j.wasman.2018.05.017
Humphreys J., Phelan P., Li D., Burchill W., Eriksen J., Casey I., Enriques-Hidalgo D. and Soeegaard K. (2017) White clover supported pasture-based systems in north-west Europe, pages 139-156. In: Legumes in Cropping Systems. D. Murphy-Bokern, F.L. Stoddard and C.A. Watson (Eds.). CAB International 2017.
Mihailescu, E., Ryan, W., Murphy, P. N. C., Casey, I. A., and Humphreys, J. (2015) “Economic aspects of nitrogen and phosphorus management on nineteen intensive grass-based dairy farms in the South of Ireland”, Agricultural Systems; 132, 121-132
Mihailescu E., Murphy P. N. C., Ryan W., Casey I. A. and Humphreys J.* (2014) Phosphorus balance and use efficiency on twenty-one intensive grass-based dairy farms in the south of Ireland. Journal of Agricultural Science (Cambridge), in press.
Mihailescu E., Murphy P. N. C., Ryan W., Casey I. A. and Humphreys J.* (2014) Nitrogen balance and use efficiency on twenty-one intensive grass-based dairy farms in the south of Ireland. Journal of Agricultural Science (Cambridge), doi:10.1017/S0021859614000045.
Phelan P., Casey I.A. and Humphreys J.* (2013) The effect of target post-grazing height on sward clover content, herbage yield and dairy production from grass-white clover pasture. Journal of Dairy Science, 96 (3), 1598-1611.
Necpálová M., Casey I. and Humphreys J.* (2013) Effect of ploughing and reseeding of permanent grassland on soil N, N leaching and nitrous oxide emissions from a clay loam soil. Nutrient Cycling in Agroecosystems, 95: 305-317.
Necpálová M., Phelan P., Casey I. and Humphreys J.* (2013) Soil surface N balances and soil N content in a clay-loam soil under Irish dairy production systems. Nutrient Cycling in Agroecosystems, 96:47-65.
Necpálová M., Li D., Lanigan G., Casey I.A., Burchill W. and Humphreys J.* (2013) Changes in soil organic carbon in a clay loam soil following ploughing and reseeding of permanent grassland under temperate moist climatic conditions. Grass and Forage Science, doi: 10.1111/gfs.12080.
Phelan P., Casey, I.A. and Humphreys, J.* (2013) The effects of simulated summer-to-winter grazing management on herbage production and white clover persistence in a grass-clover sward. Grass and Forage Science, DOI: 10.1111/gfs.12041.
Phelan P., Keogh, B., Casey, I.A., Necpalova, M. and Humphreys, J.* (2012) The effects of treading by dairy cows on soil properties and herbage production in white clover based grazing systems on a clay loam soil. Grass and Forage Science, DOI: 10.1111/gfs.12014.
Humphreys J.*, Mihailescu E. and Casey I. A. (2012) An economic comparison of systems of dairy production based on N fertilized grass and grass-white clover grassland in a moist maritime environment. Grass and Forage Science, 67 (4) 519-525.
Necpalova M., Fenton O., Casey I.A., Humphreys J.* (2012) N leaching to groundwater from dairy production involving grazing over the winter on a clay-loam soil. Science of the Total Environment, 432:159-172.
Humphreys J.* Casey I.A. and Laidlaw A.S. (2009) Comparison of milk production from clover-based and fertilizer N-based grassland on a clay loam soil under moist temperate climatic conditions. Irish Journal of Agricultural and Food Research, 48, 189–207.
Humphreys J.* Casey I.A. Darmody P. O’Connell K. Fenton, O. and Watson C. J. (2008) Soil mineral N and nitrate-N losses to groundwater from four grassland-based systems of dairy production on a clay-loam soil under moist temperate climatic conditions. Grass and Forage Science, 63, 481-494
Humphreys J.* O’Connell, K. and Casey I.A. (2008) Nitrogen flows and balances in four grassland-based systems of dairy production on a clay-loam soil in a moist maritime environment. Grass and Forage Science, 63, 467-480.
Invited papers to international conferences
Humphreys J., Casey I.A. and Laidlaw A.S. (2009) Comparison of milk production from clover-based and fertilizer N-based grassland on a clay loam soil under moist temperate climatic conditions. In: Forage Legumes in Temperate Pasture-based Systems. Silver Springs Hotel, Cork, 15-16 October 2009 (Published in the Irish Journal of Agricultural and Food Research).
Humphreys J. Casey I.A. and Carton O.T. (2004) Meeting Environmental Objectives and Potential Constraint on Dairy Production in Ireland. In: Bos, J., Aarts, F., Vertès, F. and Pflimlin, A. (eds.): Nutrient Management at Farm Scale: Attaining Policy Objectives in Regions with Intensive Dairy Farming. Quimper (France) 23 to 25 June 2003, Plant Research International, 145-164.
Humphreys J. and Casey I.A. (2002) Grassland renovation in Ireland. In: Conijn, J.G., Velthof, G.L. and Taube, F. (Eds.): Grassland Resowing and Grass-Arable Rotations. Wageningen (The Netherlands) 18 and 19 April 2002. Plant Research International, Report 47, 79-91.
Papers contributed to international conferences
Humphreys J., Mihailescu E. and Casey I. A. (2012) An economic comparison of dairy production on N fertilized and white clover grassland. Grassland Science in Europe, 17, 774-776.
Phelan P., Casey I. and Humphreys J. (2012). Predicting N-fixation in a grass-clover sward. Grassland Science in Europe, 17, 154-156.
Necpalova M., Li, D., Lanigan, G., Casey I.A., Fitzgerald E., Burchill, W., Humphreys J. (2012) Changes in soil organic carbon in clay-loam soil under permanent and cultivated grassland under temperate moist climatic conditions Grassland Science in Europe, 17, 583-585.
Necpalova M., Phelan P., Casey I.A. and Humphreys J. (2012). Effect of non-fertilized winter grazing dairy production on soil N balances and soil N dynamics. Proceedings of the 63rd EAAP Annual Meeting. Bratislava, Slovak Republic, 150.
Necpalova M., Phelan P., Casey I.A., Humphreys J. (2012) Effect of non-fertilized winter grazing dairy production on soil N balances and soil N dynamics in a clay-loam soil. In: Proceedings from 17th international Nitrogen Workshop, 26-29 June 2012.
Necpalova M., Casey I.A., Humphreys J. (2012) Effect of ploughing and reseeding of permanent grassland on N leaching to groundwater and nitrous oxide emissions from a clay-loam soil. In: Proceedings from 17th international Nitrogen Workshop, 26-29 June 2012.
Necpalova M., Fenton O., Casey I.A., Humphreys J. (2012) Effect of organic winter grazing dairy production system based on clay-loam soil on N leaching to groundwater. In: Proceedings from 17th international Nitrogen Workshop, 26-29 June 2012.
Mihailescu E., Murphy P., Casey I.A, and Humphreys J. (2012) “Nitrogen use efficiency on dairy farms”. In: Proceedings of the 17th international nitrogen workshop (Eds. K. G. Richards, O. Fenton, C. J. Watson), 26-29th June 2012, Wexford, Ireland, 352-353.
Mihailescu, E., Casey I. A., and Humphreys J. (2011) “Nitrogen and phosphorus use on dairy farms”, In: Proceedings of the Agro-Environment conference, Athlone, Ireland, 10th November 2011, 29-30.
Necpalova M., Li, D., Lanigan, G., Casey I.A., Fitzgerald E., Burchill, W., Humphreys J. (2011) Changes in soil organic carbon in clay-loam soil under permanent and cultivated grassland under oceanic climatic conditions. In: Proceedings of the British Grassland Society 10th Research Conference in Belfast 20- 21.
Phelan P., Keogh B., Fitzgerald E., Casey I.A. and Humphreys J. (2011). The effect of trampling by dairy cows on a rotationally grazed grass-clover sward. Proceedings of the British Grassland Society 10th Research Conference. Belfast. p7.
Humphreys, J. Keogh, B., Phelan, P. and Casey, I. A., 2010. Post-grazing height and productivity of white-clover based dairy production. Nordic Association of Agricultural Scientists Seminar 432, Hvanneyri, Iceland, 20- 22 June, 137 – 140.
Humphreys, J. Keogh, B., Phelan, P., Necpalova, M., Fitzgerald, E. and Casey, I. A., 2010. Dairy production from clover-based grassland under different management strategies. Nordic Association of Agricultural Scientists Seminar 432, Hvanneyri, Iceland, 20- 22 June, 117 – 120.
Phelan, P. Keogh, B. Casey I.A. Fitzgerald E. and Humphreys J. (2010) Cutting height and interval in autumn and annual herbage production in a white clover-grass sward. Nordic Association of Agricultural Scientists Seminar 432, Hvanneyri, Iceland, 20- 22 June,125 – 128.
Phelan P., Keogh B., Casey I.A., Fitzgerald E. and Humphreys J. (2010). Impacts of autumn cutting height and interval on annual productivity of white clover-grass sward. Grassland Science in Euorpe, 15, 985-987.
Humphreys, J., Keogh, B. Phelan, P., and Casey, I.A. (2010) Post grazing height and productivity of white clover-based systems of dairy production. Grassland Science in Euorpe, 15, 958-960.
Keogh, B., Humphreys, J., Phelan, P., Necpalova, M., Casey, I. and Fitzgerald, E. (2010) Organic management strategies and its effect on clover-based grassland production. Advances in Animal Biosciences, 1, pp 147
Phelan, P., Keogh, B., Casey, I.A., Fitzgerald, E. and Humphreys, J. (2010). The effects of autumn rotation length and cutting height on a perennial ryegrass-white clover sward. Advances in Animal Biosciences p. 320.
Keogh B., Humphreys J., Phelan P., Necpalova M., Casey I.A. and Fitzgerald E. (2009) Organic management strategies and its effect on clover-based grassland production. Irish Journal of Agricultural and Food Research, 48, p267.
Phelan P., Keogh B., Casey I.A. and Humphreys J. (2009) The effects of rotation length and cutting height in autumn on the productivity of a perennial ryegrass-white clover sward. Irish Journal of Agricultural and Food Research, 48 (2), p140.
Humphreys J. Darmody P. O’Connell K. Casey I.A. and Watson C.J. (2004) Reducing nitrogen inputs to grassland-based dairy production. Proceedings of the 20th General Meeting of the European Grassland Federation - Land-Use Systems in Grassland-Dominated Regions. Luzern (Switzerland) 21-24 June, 2004, 747-749.
Humphreys J. Lawless A. O’Connell K. and Casey I.A. (2002) Reducing nitrogen inputs to grassland-based dairy production. In: Profitable Grass and Forage: Meeting the Needs of the Farmer and Society. Proceedings of the British Grassland Society, Stafford (UK) 27 and 28 November 2002, 19-24.
Paper/Summary in Proceedings of National Conferences
Mihailescu E., Casey I.A. and Humphreys J. (2012) Nitrogen use efficiency on commercial dairy farms. The Agricultural Research Forum. Tullamore, Ireland. 84.
Mihailescu E., Casey I.A. and Humphreys J. (2011) Nitrogen and Phosphorus use on dairy farms. Proceedings Teagasc Agri-Environment Conference, Hudson Bay Hotel, Athlone, 29-30.
Phelan P., Keogh B., Fitzgerald E., Casey I.A. and Humphreys J. (2011). Effect of seasonal grazing system on productivity of a grass-clover sward. The Agricultural Research Forum. Tullamore, Ireland. p84.
Phelan P., Keogh B., Fitzgerald E., Casey I.A. and Humphreys J. (2011). Predicting Nitrogen fixation in grass-clover pastures. Proceedings of the Waterford Institute of Technology Research Forum. Waterford, Ireland. p103 - 104.
Necpalova M., Casey I.A., Fitzgerald E., Humphreys J. (2011) Changes in soil organic C in a clay-loam soil under permanent and cultivated grassland. In: Book of abstracts of the Research day 2011, Waterford Institute of Technology, 13. April 2011, Waterford, Ireland, p. 99.
Phelan P., Casey I.A. and Humphreys J. (2011). Grazing management of white clover in grassland. Proceedings of the Teagasc Walsh Fellowship Seminar. Royal Dublin Society (RDS), Dublin. p55.
Mihailescu, E., Casey, I.A., Fitzgerald, E. and Humphreys, J. (2011). An economic comparison of white clover-based and N-fertilized grassland-based dairy systems under moist temperate climatic conditions. Agricultural Research Forum, Tullamore, Ireland, 144.
Necpalova, M., Casey, I.A., Fitzgerald, E. and Humphreys, J. (2011). Changes in soil organic C in a clay-loam soil under permanent and cultivated grassland. Agricultural Research Forum, Tullamore, Ireland, 28.
O’Connell K. Humphreys J. Watson C.J. and Casey I.A. (2002) The impact of urine deposition on soil mineral-N concentrations in soils under grazed pasture swards. Agricultural Research Forum, 13.
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Coelho, J.J., Hennessy, A., Casey, I., Woodcock, T. and Kennedy, N., (2020) Biofertilisation withAnaerobic Digestates: Effects on the Productive Traits of Ryegrass and Soil Nutrients. Journal of Soil Science and Plant Nutrition, pp.1-14.https://doi.org/10.1007/s42729-020-00237-7
Coelho, J.J., Hennessy, A., Casey, I., Bragança, C.R.S., Woodcock, T. and Kennedy, N., (2020). Biofertilisation with anaerobic digestates: A field study of effects on soil microbial abundance and diversity. Applied Soil Ecology, 147, p.103403. https://doi.org/10.1016/j.apsoil.2019.103403
Coelho, J.J., Hennessy, A., Casey, I., Woodcock, T. and Kennedy, N., (2019). Responses of ryegrass, white clover, soil plant primary macronutrients and microbial abundance to application of anaerobic digestates, cattle slurry and inorganic N-fertiliser. Applied Soil Ecology, 144, pp.112-122.https://doi.org/10.1016/j.apsoil.2019.07.011
Coelho, J.J., Prieto, M.L., Hennessy, A., Casey, I., Woodcock, T. and Kennedy, N., (2019). Determination of microbial numbers in anaerobically digested biofertilisers. Environmental Technology, pp.1-11.https://doi.org/10.1080/09593330.2019.1645214
Coelho, J.J., Prieto, M.L., Dowling, S., Hennessy, A., Casey, I., Woodcock, T. and Kennedy, N., (2018). Physical-chemical traits, phytotoxicity and pathogen detection in liquid anaerobic digestates. Waste Management, 78, pp.8-15. https://doi.org/10.1016/j.wasman.2018.05.017
Humphreys J., Phelan P., Li D., Burchill W., Eriksen J., Casey I., Enriques-Hidalgo D. and Soeegaard K. (2017) White clover supported pasture-based systems in north-west Europe, pages 139-156. In: Legumes in Cropping Systems. D. Murphy-Bokern, F.L. Stoddard and C.A. Watson (Eds.). CAB International 2017.
Mihailescu, E., Ryan, W., Murphy, P. N. C., Casey, I. A., and Humphreys, J. (2015) “Economic aspects of nitrogen and phosphorus management on nineteen intensive grass-based dairy farms in the South of Ireland”, Agricultural Systems; 132, 121-132
Mihailescu E., Murphy P. N. C., Ryan W., Casey I. A. and Humphreys J.* (2014) Phosphorus balance and use efficiency on twenty-one intensive grass-based dairy farms in the south of Ireland. Journal of Agricultural Science (Cambridge), in press.
Mihailescu E., Murphy P. N. C., Ryan W., Casey I. A. and Humphreys J.* (2014) Nitrogen balance and use efficiency on twenty-one intensive grass-based dairy farms in the south of Ireland. Journal of Agricultural Science (Cambridge), doi:10.1017/S0021859614000045.
Phelan P., Casey I.A. and Humphreys J.* (2013) The effect of target post-grazing height on sward clover content, herbage yield and dairy production from grass-white clover pasture. Journal of Dairy Science, 96 (3), 1598-1611.
Necpálová M., Casey I. and Humphreys J.* (2013) Effect of ploughing and reseeding of permanent grassland on soil N, N leaching and nitrous oxide emissions from a clay loam soil. Nutrient Cycling in Agroecosystems, 95: 305-317.
Necpálová M., Phelan P., Casey I. and Humphreys J.* (2013) Soil surface N balances and soil N content in a clay-loam soil under Irish dairy production systems. Nutrient Cycling in Agroecosystems, 96:47-65.
Necpálová M., Li D., Lanigan G., Casey I.A., Burchill W. and Humphreys J.* (2013) Changes in soil organic carbon in a clay loam soil following ploughing and reseeding of permanent grassland under temperate moist climatic conditions. Grass and Forage Science, doi: 10.1111/gfs.12080.
Phelan P., Casey, I.A. and Humphreys, J.* (2013) The effects of simulated summer-to-winter grazing management on herbage production and white clover persistence in a grass-clover sward. Grass and Forage Science, DOI: 10.1111/gfs.12041.
Phelan P., Keogh, B., Casey, I.A., Necpalova, M. and Humphreys, J.* (2012) The effects of treading by dairy cows on soil properties and herbage production in white clover based grazing systems on a clay loam soil. Grass and Forage Science, DOI: 10.1111/gfs.12014.
Humphreys J.*, Mihailescu E. and Casey I. A. (2012) An economic comparison of systems of dairy production based on N fertilized grass and grass-white clover grassland in a moist maritime environment. Grass and Forage Science, 67 (4) 519-525.
Necpalova M., Fenton O., Casey I.A., Humphreys J.* (2012) N leaching to groundwater from dairy production involving grazing over the winter on a clay-loam soil. Science of the Total Environment, 432:159-172.
Humphreys J.* Casey I.A. and Laidlaw A.S. (2009) Comparison of milk production from clover-based and fertilizer N-based grassland on a clay loam soil under moist temperate climatic conditions. Irish Journal of Agricultural and Food Research, 48, 189–207.
Humphreys J.* Casey I.A. Darmody P. O’Connell K. Fenton, O. and Watson C. J. (2008) Soil mineral N and nitrate-N losses to groundwater from four grassland-based systems of dairy production on a clay-loam soil under moist temperate climatic conditions. Grass and Forage Science, 63, 481-494
Humphreys J.* O’Connell, K. and Casey I.A. (2008) Nitrogen flows and balances in four grassland-based systems of dairy production on a clay-loam soil in a moist maritime environment. Grass and Forage Science, 63, 467-480.