Project Leader: James Humphreys

Introduction

A considerable amount of information indicates that tight grazing favours the clover content of swards (Frame and Boyd, 1987; Acuña and Wilman, 1993; Schils and Sikkema (1999). In general cutting to 4 cm increased clover yield by 30% to 35% and combined grass and clover yield by in the region of 16 to 20%. Cutting to 8 cm at intervals of 4 weeks resulted in a severe reduction in clover content, almost eliminating it from the sward over a three-year period. However, grazing to approximately 4 cm is known to depress intake of herbage and lower milk yield and composition (Mayne et al., 1987; Maher et al., 2003). The objective of this experiment was to evaluate the impact of grazing intensity on the clover content, herbage production and milk production from cows grazing grass-clover swards.

Materials and Methods

There were three treatments involving three different post-grazing heights (PGH) maintained throughout the grazing season (February to December; Fig. 1). Each treatment received annual fertilizer N input of 100 kg/ha and was stocked at 2.0 cows/ha.

There were 27 cows per treatment. Cows were divided into four main groups on the basis of lactation number (1, 2, 3 & ³4) and then sub-divided into sub-groups of three on the basis of calving date. From within each sub-group one cow was randomly assigned to each herd. Herds were randomly assigned to each treatment. Milk production in the third whole week of lactation was used as covariate in analysis of variance. Mean calving date was 22 February. Clover stolon production was measured in February, May, August and November.

Results and Discussion

There were no (P >0.05) differences in production of milk, fat, protein or lactose, although each of these tended to decline with lower PGH (Table 1). Likewise there were no (P >0.05) differences in live-weight or body condition score (BCS) at the end of lactation (Table 1).

There were no (P >0.05) differences in stolon mass between PGH treatments. There were differences (P <0.001) between sampling dates (s.e.m. = 57.0) with stolon dynamics showing typical annual cyclicity: lowest masses in spring and highest in the late autumn. Low masses in February 2007 compared to February 2008 can be attributed to one-third of the paddocks on each treatment containing no clover at the start of the experiment. Grazing to 4 cm increased herbage production and, hence, carrying capacity by 12%.

Conclusions

Lowering PGH from 6 to 4 cm did not increase stolon mass and clover content of swards and did not have a detectable impact on milk output or on cow live-weight or BCS although there were trends towards lower milk production and lower live-weight and BCS associated with lower PGH. This needs further investigation.

(kg/cow)

Project Leader: James Humphreys

Project Abstract

This project aims to quantify the change in greenhouse gas (GHG) emissions from Irish dairy production when mineral fertilizer N (MFN) is replaced by white clover-biologically fixed N (BFN). This will be quantified using lifecycle assessment (LCA) on a whole farm basis, initially using existing data sets of N flows within both MFN-based and white clover-BFN-based systems of dairy production measured over the last four (2003-2007) years at Teagasc Research Farm at Solohead. Gaps in existing knowledge in terms of nitrous oxide and ammonia emissions will be filled by on-site measurements and compared with model predictions. An appropriate LCA methodological framework will be developed and questionnaire detailing the key inputs needed to conduct the LCA of dairy farms will be drawn up. This questionnaire, which will include indicators of economic performance, will be used in the collection of data from approximately 20 farms on a range of soil types around the country that have switched from MFN-based to white clover-BFN-based grassland in recent years. This will give a broad-based interpretation of the likely change in GHG emissions associated with the wider use of white clover for dairy production that can be linked into the national emissions inventory. This study may provide justification for payments for white clover in rural environment protection schemes.

Start date: 01/11/07

Completion date: 31/01/11

Collaboration: Bioresources Research Centre, UCD School of Agriculture, Food Science and Veterinary Medicine Earlsfort Terrace, Dublin 2: Nick Holden. Teagasc, Johnstown Castle, Wexford: Gary Lanigan Civil and Environmental Engineering, University College Cork: Paul Leahy

Funding Agency: Department of Agriculture and Food

Project Leader: James Humphreys

Project Abstract

Manufacturers of fresh organic dairy products offer a price premium of 157% to dairy producers that supply >55% of their milk during the winter. Grazing cows on clover-based grassland is a key component of profitable organic milk production. Ireland’s climate is conducive to production from clover swards over a long growing season. Organic systems of production operate at low stocking rates compared with conventional systems. Low stocking rates offer the potential to extend the grazing season throughout the autumn, winter and early spring. This project aims at substantially lowering the cost of feed for organic winter milk production by supplying a large proportion (>50%) of the diet from grazed clover swards during the autumn and winter. However, grazing during the winter, albeit at low stocking rates, carries the risk of losses of nitrate to groundwater. One objective of this project is to investigate the productivity of white clover-based grassland under different management regimes for dairy production: (i) conventional spring calving; (i) simulated organic non-fertilizer-N (NFN) spring calving; (iii) NFN winter production, with particular emphasis on autumn-winter production from clover-based swards. The other objective is to measure the impacts of these three systems on nitrate losses to groundwater.

Sub-project: Aspects of the survival of white clover in grassland

The objective is to study the impacts of shading and hoof-damage during the autumn and winter on clover abundance measured in terms of clover stolon mass and clover herbage content of sward herbage DM. These factors will be examined in two experiment: (i) sward canopy structure during the autumn and winter, abundance of clover stolon and sward productivity and (ii) Hoof-damage during the autumn and winter and clover stolon survival and abundance. Experiment (i) will be a plot-scale experiment where different canopies of herbage of grass-clover swards will be established by different harvesting regimes during the autumn and winter. Canopies will be described in terms of sward height and herbage mass. The extent of shading will be determined by light interception at the base of the sward recorded using an Accupar® Lp-80 ceptometer. These measurements will be used to establish a relationship between light interception at the base of the sward during the autumn and winter and clover stolon abundance during the following spring and summer. Experiment (ii) examine the impact of hoof-damage on clover stolon abundance within system-scale experiment examining different systems of milk production, including one system involving grazing during the winter. There will be six paddocks per system. Within each paddock stolon abundance will be determined in strips (1 m x 20 m) that are either unprotected or protected from hoof-damage. The effect of hoof-damage in each strip will be assessed using (a) ground-scoring index, (b) photographs analysed using Photoshop® and (c) a ground penetrometer.

Start date: 01/11/07

Completion date: 31/04/11

Collaboration: Department of Chemical & Life Sciences, Waterford Institute of Technology Cork Road, Waterford. Eddy Fitzgerald and I.A.Casey.

Funding Agency: Department of Agriculture and Food