Project code: D-39-08

Duration    1 year commencing March 2007 

Team and Leader  A. Dale, C.Ferris, S.Mayne, P. Frost

Organisations involved AFBI                                            

Background and Summary                

The improvement of efficiency at farm level will be crucial for the dairy industry moving forward.  Increases in grain prices coupled with improvements in global milk prices  highlights the necessity to maximise milk from grazed grass.  

Furthermore, this is all happening during a period that has seen intense pressure to improve nutrient use and nutrient efficiency from animal manures, with legislative and economic pressures being the main drivers. Knowledge has been building in recent years in relation to improving use of slurry nutrients, and the ability of slurry nutrients to replace inorganic N, P and K is evident. However, previous studies focused predominately on silage cutting simulations, with only a small number of studies incorporating this technology into a grazing scenario (eg. IGER 2002).

With legislative restrictions on inorganic fertiliser inputs, a greater focus must be placed on efficiently utilising the forage that is grown. Traditionally, a high grass allowance was perceived to be the optimal way to maximise grass intake by the dairy cow and therefore maximise profitability at grazing. However, this concept is being challenged by New Zealand research, which has demonstrated a significant lift in whole farm profitability by adopting a very tight grazing system. This research indicates that by lifting grass quality (ME in particular), the energy intake of the animals can be sustained or even improved, thus animal performance can be maintained. With restrictions on milk production  (milk quotas) being removed, the area available for grazing will become one of the biggest restrictions for farmers, and thus maximising output/ha will become the main driver for many.

The higher stocking rates required to graze swards to a low residual throughout the season will inevitably lift output/ha. However, it is important to quantify if the improvement in grazing efficiency is achievable in unison with improvements in slurry nutrient use, particularly in relation to the ability to graze swards out cleanly when slurry is applied between grazings.

This project aims to examine the opportunities to integrate slurry nutrients into a rotational grazing system managed at two stocking rates, and potential effects on animal and sward performance.


This study will take place during the 2007 grazing season and will include 60 spring calving dairy cows. The study will include 4 treatments:

T1. All fertiliser N at a stocking rate of 5.5cows/ha in early season (normal SR)
T2. A combination of slurry and fertiliser N at a stocking rate of 5.5 cows/ha in early season (normal SR)
T3. All fertiliser N at a stocking rate of 6.6cows/ha in early season (20% higher than normal SR)
T4. A combination of slurry and fertiliser N at a stocking rate of 6.6cows/ha in early season (20% higher than normal SR)

Slurry will be applied to each paddock on four occasions during the season. The slurry will be applied to all the core 22 paddocks within the same grazing rotation. By applying the slurry in two applications per grazing cycle, the maximum interval between slurry application and grazing will be 11 days. The slurry will be applied on every other grazing rotation (i.e. 1st, 3rd, 5th and 7th cycle), with fertiliser N being applied across all treatments on the other cycles. During the slurry spreading cycles, the fertiliser application will be delayed to match the slurry application date, so that the paddocks on all treatments receive N on the same day. Details of the fertiliser and slurry applications are given in Table 1, and the total fertiliser N replaced by slurry will be 152kg/ha. The measurements taken will include animal performance, sward parameters (grass growth, pre- and post-grazing height, farm cover) and herbage quality.

Table 1. Target fertiliser application (assuming 27.5%N) and target slurry application rates (assuming 1.2kg available N/m3)
Target kgN/ha
Target fertiliser application rate
Target slurry application rate
½ bag urea/acre
1st cycle
1.8 bags/acre
2nd cycle
3rd cycle
4th cycle
5th cycle
6th cycle
7th cycle
Total N (kg/ha)



The industry has until January 2010 before the Nitrates Directive becomes fully activated, and therefore in the three year interim period this study will provide some of the answers to the questions that farmers will have at this stage. The availability of alternative spreading technology to farmers across Northern Ireland remains limited, but an increased interest from farmers could see contractors adopting this technology in greater numbers.

Related documents

The effect of applying cattle slurry within rotational grazing systems using trailing-shoe technology on dairy cow and sward performance - Technical Report (D-35-07 and D-39-08) - Agrisearch

Effect of spreading slurry during the grazing season on cow performance (D-39-08) - Agrisearch

FileDescriptionFile size
Download this file (slurry.pdf)slurry.pdfEnd of Project Techincal Report - Effect of applying slurry within grazing systems on cow performance475 kB
Download this file (Booklet_19.pdf)Improving Grass EfficiencyImproving the efficiency of grass and nutrient use from slurry under rotational grazing by dairy cows D-39-08171 kB