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The effect of stocking rate on nitrate leaching from a free draining dairy farm system in Ireland
J. Mccarthy, D. Hennessy, K. M. Pierce, Luc Delaby, A. Brennan, Brendan Horan
To cite this version:
J. Mccarthy, D. Hennessy, K. M. Pierce, Luc Delaby, A. Brennan, et al.. The effect of stocking rate on nitrate leaching from a free draining dairy farm system in Ireland. Agricultural Research Forum 2014, Mar 2014, Tullamore, Ireland. Agricultural Research Forum, 2014, Proceedings of the Agricultural Research Forum. �hal-01210853�
1
The effect of stocking rate on nitrate leaching from a free draining dairy farm system in Ireland.
J. McCarthy1,2, D. Hennessy1, K.M. Pierce2, L. Delaby3, A. Brennan1and B. Horan1
1Animal and Grassland Research and Innovation Centre, Teagasc Moorepark, Fermoy, Co. Cork;
2School of Agriculture, Food Science & Veterinary Medicine, University College Dublin, Belfield, Dublin 4; 3INRA, AgroCampus Ouest, UMR 1348, Physiologie, Environnement et Génétique pour l'Animal et les Systèmes d'Elevage, F-35590 Saint- Gilles, France.
Introduction
Efficient nitrogen (N) management is critical to the sustainable intensification of Irish dairy farming and the achievement of Food Harvest 2020 targets post EU milk quota abolition. Principle among the environmental impacts, N leaching from the soil profile to groundwater is the main N loss pathway within grass-based milk production systems (Treacy et al., 2008). Although stocking rate (SR; cows/ha) governs milk productivity per ha at grazing (McCarthy et al., 2011), and increased grassland SR is expected post quota abolition, previous studies have indicated that where increased SR’s is achieved based on increased chemical fertiliser N application and increased off-farm supplementary feed importation, N loss to groundwater is increased (Treacyet al.,2008). The objective of this study was to evaluate the effect of three whole-farm SR on nitrate (NO3-) loss from a free draining soil type using modern grazing and nutrient management practices over three full grazing seasons.
Material and Methods
The experiment was conducted over three years (from January 2011 to December 2013) on a permanent grassland site at Curtin’s Research Farm, Teagasc, Animal & Grassland Research and Innovation Centre, Moorepark, Fermoy, Co. Cork. In each year, 138 spring calving dairy cows were randomly assigned to one of three SR treatments, Low (2.51 cows/ha), Medium (2.92 cows/ha) and High (3.28 cows/ha). Each SR group had its own individual farmlet. Concentrate and chemical N fertilizer use were held constant across SR (1,150 kg concentrate DM/ha and 209 kg N/ha, respectively). Slurry produced by the animals while indoors was spread back on each farmlet over the first four months of the year at a rate consistent with the
overall SR of each farmlet. Sixteen ceramic cups were installed to a depth of 1 m within 3 grazing paddocks (representing 18% of each farmlet) to measure total N (TN) loss. Sampling occurred biweekly during the drainage period (September to April) and once per month during the summer (May to August). Samples were analysed for TN content using standard methods.
Total N loss (kg ha−1) was determined annually by multiplying the average TN concentrations (mg L−1) with effective drainage (Schulte et al., 2005; mm). Data were analysed using PROC Mixed in SAS (SAS, 2002). Paddock was included as a random effect while year and SR were included as fixed effects.
Results and Discussion
Average annual rainfall and effective drainage during the three year study period was similar to the 10 year average (966 and 478 mm, respectively). Effective drainage was highest in 2012 (502mm), lowest in 2011 (315mm) and intermediate in 2013 (400mm). There was no significant effect of SR on total annual TN loss during the study (135 kg N/ha) nor was there any interaction between SR and year (Table 1). The lack of difference in TN losses between SR highlights the possibility for sustainable expansion through increased grazed grass utilisation on Irish dairy farms post EU milk quota abolition. The temporal changes in N loss observed within this study suggest that such evaluations should only be considered over a minimum of 3 years.
Conclusions
The results of this study indicate that TN loss to 1 m is not increased where higher overall farm SR are achieved through increased grazed grass utilisation and without added chemical N fertilizer or additional external feed supplementation.
References
McCarthy, B., Pierce, K.M., Delaby, L., Brennan, A., Fleming, C. & Horan, B. (2011)Animal5:5: 784-794.
Schulte, R.P.O., Diamond, J., Finkele, K., Holden, N.M. & Brereton, A.J. (2005).Irish J. Agri. Food Res.
44: 95-110.
Statistical Analysis Systems Institute (2002). Cary, NC, USA.
Treacy, M., Humphreys, J., McNamara, K., Browne, R.
& Watson, C.J. (2008) Irish J. Agri. Food Res. 47:
105-117.
Table 1.Effect of stocking rate1(SR) on total nitrogen (TN) loss (kg N/ha) over three grazing seasons (2011 – 2013).
SR Significance†
TN loss (kg/ha/yr) Low Medium High SEM2 SR1 Y SR*Y
Average 127.8 136.6 141.2 15.10 NS NS NS
2011 129.2 136.8 142.2
2012 144.1 152.9 119.9
2013 110.1 120.0 161.5
†Significance: NS = not significant ;2SEM = Standard error of the mean
