Urine from dairy cattle grazing pastures with high crude protein (CP) concentrations is a major source of N lost in drainage water from New Zealand farms. This paper provides predictions of urinary N leaching losses for a range of stocking rates and levels of supplementation

Brookes, I. M.

Horne, D. J.

English

University of Kentucky

 XX International Grassland Congress 748Modelling urine nitrogen production and leaching losses for pasture-based dairying systems I.M. Brookes and D.J. HorneCollege of Sciences, Massey University, Private Bag 11 222, Palmerston North, New Zealand, Email:I.Brookes@massey.ac.nzKeywords: dairy production, nitrogen losses, pasture feeding, supplementary feeds Introduction  Urine from dairy cattle grazing pastures with high crude protein (CP) concentrations is a major source of N lost in drainage water from New Zealand farms. This paper provides predictions of urinary N leaching losses for a range of stocking rates and levels of supplementation.  Method  Urinary outputs (kg N/ha) were estimated for dairy herds on notional 100 ha farms stocked at 2.35 (L), 3.00 (M) or 5.00 (H) cows/ha. Farm L was assumed to grow 13,000 kg pasture dry matter (DM)/ha annually. For farms M and H, 100 and 200 kg fertiliser N/ha were applied, to give annual pasture yields of 14,080 and 15,160 kg DM/ha, respectively. A feed budget identified periods when pasture (P; 20% CP) required supplements of either maize silage (MS; 7% CP) or pasture silage (PS; 16% CP) to maintain at least 1,700 kg grass DM/ha. Supplements were fed from Feb. to Sept. on farm M and in all months on farm H, accounting for 16% and 47% of the total DM intakes. Urinary N outputs were estimated by the Cornell Net Carbohydrate and Protein System model (Fox et al., 2004), and leaching losses by the Nitrogen Leaching Estimation (NLE) model of Di & Cameron (2000). Table 1  Annual N intake, urine N output and N leached Stocking rate/Supplement L MMS MPS HMS HPSDietary CP  (% DM) 20.0 17.9 19.1 13.9 17.4Dietary N intake  (kg/cow) 150 136 145 107 135Urine N output  (kg/cow) 72 58 67 39 59(kg/ha) 169 174 200 196 296N in urine patches* (kg/ha) 889 725 833 490 740N leached  (kg/ha) 7 16 21 23 44* Assumes urine from a cow covers ~ 0.08 of the area2004006008001000A S O N D J F M A M J Jg N/haL MMS MPSHMS HPSFigure 1  Monthly urine N outputs per ha Results  Dietary CP %, urinary N outputs and N leaching losses are given in Table 1 and Figure 1. Although the CNCPS model is reported to under-predict the ratio of urinary to faecal N, the results described here are supported by Mulligan et al. (2004), who showed a positive linear relationship between urinary N output and N intake, in cows fed supplements with high or low CP%. They also observed a decrease in the proportion of urinary N in the total excreta N when the supplement CP% concentration was reduced. Replacing pasture with a supplement of lower CP% can reduce the concentration of N under urine patches. On farm M, this occurs mainly in early spring and autumn, as no supplements were required in late spring and summer. The extent of N leaching was related to N fertiliser use and N concentration in the urine patches. Despite a two-fold increase in stocking rate and the higher N fertiliser usage, N concentration under urine patches was 50% lower on farm H with MS than on farm L. The reduction in urinary N production per cow and the increased area of urine deposition on the HMS farm results in N leaching losses that are not much greater than those for the M systems. However, when pasture silage was fed on farm H, N leaching losses were much higher.  Conclusions  This analysis suggests that where increases in stocking rate are accompanied by the use of maize silage, intensification may not pose an increased risk of nitrogen leaching from dairy farms.  There is a need for quantification of urine N output on farms as affected by stocking rate and diet, and for measurement of the exact area occupied by urine patches.    References Di, H.J. & K.C. Cameron (2000).  Calculating nitrogen leaching losses and critical nitrogen application rates in dairy pasture systems using a semi-empirical model. N Z Journal of Agricultural Research, 43, 139-147. Fox, D.G, L.O.Tedeschi, T.P.Tylutki, J.B.Russell, M.E.Van Amburgh, L.E.Chase, A.N.Pell & T.R.Overton (2004). The Cornell Net Carbohydrate and Protein System model for evaluating herd nutrition and nutrient excretion. Animal Feed Science and Technology, 112, 29-78. Mulligan, F. J., P. Dillon, J.J. Callan, M. Rath & F.P. O'Mara (2004). Supplementary concentrate type affects nitrogen excretion of grazing dairy cows. Journal of Dairy Science, 87. 3451-3460.

Modelling Urine Nitrogen Production and Leaching Losses for Pasture-Based Dairying Systems

University of Kentucky UKnowledge International Grassland Congress Proceedings XX International Grassland Congress Modelling Urine Nitrogen Production and Leaching Losses for Pasture-Based Dairying Systems I. M. Brookes Massey University, New Zealand D. J. Horne Massey University, New Zealand Follow this and additional works at: https://uknowledge.uky.edu/igc  Part of the Agricultural Science Commons, Agronomy and Crop Sciences Commons, Plant Biology Commons, Plant Pathology Commons, Soil Science Commons, and the Weed Science Commons This document is available at https://uknowledge.uky.edu/igc/20/satellitesymposium4/80 The XX International Grassland Congress took place in Ireland and the UK in June-July 2005. The main congress took place in Dublin from 26 June to 1 July and was followed by post congress satellite workshops in Aberystwyth, Belfast, Cork, Glasgow and Oxford. The meeting was hosted by the Irish Grassland Association and the British Grassland Society. Proceedings Editor: D. A. McGilloway Publisher: Wageningen Academic Publishers, The Netherlands © Wageningen Academic Publishers, The Netherlands, 2005 The copyright holder has granted the permission for posting the proceedings here. This Event is brought to you for free and open access by the Plant and Soil Sciences at UKnowledge. It has been accepted for inclusion in International Grassland Congress Proceedings by an authorized administrator of UKnowledge. For more information, please contact UKnowledge@lsv.uky.edu.  Utilisation of grazed grass in temperate animal systems 1942004006008001000A S O N D J F M A M J Jg N/haL MMS MPSHMS HPSFigure 1  Monthly urine N outputs per ha Modelling urine nitrogen production and leaching losses for pasture-based dairying systems I.M. Brookes and D.J. Horne College of Sciences, Massey University, Private Bag 11 222, Palmerston North, New Zealand, Email: I.Brookes@massey.ac.nz  Keywords: dairy production, nitrogen losses, pasture feeding, supplementary feeds  Introduction  Urine from dairy cattle grazing pastures with high crude protein (CP) concentrations is a major source of N lost in drainage water from New Zealand farms. This paper provides predictions of urinary N leaching losses for a range of stocking rates and levels of supplementation.   Method  Urinary outputs (kg N/ha) were estimated for dairy herds on notional 100 ha farms stocked at 2.35 (L), 3.00 (M) or 5.00 (H) cows/ha. Farm L was assumed to grow 13,000 kg pasture dry matter (DM)/ha annually. For farms M and H, 100 and 200 kg fertiliser N/ha were applied, to give annual pasture yields of 14,080 and 15,160 kg DM/ha, respectively. A feed budget identified periods when pasture (P; 20% CP) required supplements of either maize silage (MS; 7% CP) or pasture silage (PS; 16% CP) to maintain at least 1,700 kg grass DM/ha. Supplements were fed from Feb. to Sept. on farm M and in all months on farm H, accounting for 16% and 47% of the total DM intakes. Urinary N outputs were estimated by the Cornell Net Carbohydrate and Protein System model (Fox et al., 2004), and leaching losses by the Nitrogen Leaching Estimation (NLE) model of Di & Cameron (2000).  Table 1  Annual N intake, urine N output and N leached  Stocking rate/Supplement L MMS MPS HMS HPSDietary CP  (% DM) 20.0 17.9 19.1 13.9 17.4Dietary N intake  (kg/cow) 150 136 145 107 135Urine N output  (kg/cow) 72 58 67 39 59 (kg/ha) 169 174 200 196 296N in urine patches* (kg/ha) 889 725 833 490 740N leached  (kg/ha) 7 16 21 23 44* Assumes urine from a cow covers ~ 0.08 of the area  Results  Dietary CP %, urinary N outputs and N leaching losses are given in Table 1 and Figure 1. Although the CNCPS model is reported to under-predict the ratio of urinary to faecal N, the results described here are supported by Mulligan et al. (2004), who showed a positive linear relationship between urinary N output and N intake, in cows fed supplements with high or low CP%. They also observed a decrease in the proportion of urinary N in the total excreta N when the supplement CP% concentration was reduced. Replacing pasture with a supplement of lower CP% can reduce the concentration of N under urine patches. On farm M, this occurs mainly in early spring and autumn, as no supplements were required in late spring and summer. The extent of N leaching was related to N fertiliser use and N concentration in the urine patches. Despite a two-fold increase in stocking rate and the higher N fertiliser usage, N concentration under urine patches was 50% lower on farm H with MS than on farm L. The reduction in urinary N production per cow and the increased area of urine deposition on the HMS farm results in N leaching losses that are not much greater than those for the M systems. However, when pasture silage was fed on farm H, N leaching losses were much higher.   Conclusions  This analysis suggests that where increases in stocking rate are accompanied by the use of maize silage, intensification may not pose an increased risk of nitrogen leaching from dairy farms.  There is a need for quantification of urine N output on farms as affected by stocking rate and diet, and for measurement of the exact area occupied by urine patches.     References Di, H.J. & K.C. Cameron (2000).  Calculating nitrogen leaching losses and critical nitrogen application rates in dairy pasture systems using a semi-empirical model. N Z Journa lof Agricultural Research, 43, 139-147. Fox, D.G, L.O.Tedeschi, T.P.Tylutki, J.B.Russell, M.E.Van Amburgh, L.E.Chase, A.N.Pell & T.R.Overton (2004). The Cornell Net Carbohydrate and Protein System model for evaluating herd nutrition and nutrient excretion. Animal Feed Science and Technology, 112, 29-78. Mulligan, F. J., P. Dillon, J.J. Callan, M. Rath & F.P. O'Mara (2004). Supplementary concentrate type affects nitrogen excretion of grazing dairy cows. Journal of Dairy Science, 87. 3451-3460.  

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Modelling Urine Nitrogen Production and Leaching Losses for Pasture-Based Dairying Systems

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