Grass/clover silage field trial

Title of Experiment: Grass/clover silage field trial

Date started: May 2013

Contact: Prof Dave Chadwick; Prof Davey Jones; Dr Prysor Williams

Funding source: EBLEX, HCC, DairyCo., QMS

Location: Henfaes Research Centre (lowland site)

Experimental Aims:

  • To compare the performance of a grass/clover sward receiving no nitrogen fertilisation with a pure grass sward receiving nitrogen fertilisation
  • To assess the effects of clover density on greenhouse gas (N2O) emissions and soil nitrogen dynamics in comparison to grass only swards receiving synthetic fertiliser
  • To monitor actual nitrogen fixation by clover relative to quoted values and to assess accuracy of fertiliser recommendations
  • To test novel real-time in situ soil nitrate sensors and microdialysis technology
  • To examine the difference in greenhouse gas emissions from ‘urine patches’ from sheep on a diet of grass ± clover to assess the environmental impacts associated with sward composition


Brief description

The trial is located at the Bangor University Henfaes Research Centre in the lowland part of the farm. An old pasture that has been ploughed and reseeded is used as the experimental plot. The experiment is a randomized block design with five treatments and four replicates (see diagram below).

Each plot measures 25m2 in area. The treatments are: 1) a control, 2) a grass/clover sward with 10% clover cover, 3) a grass/clover sward with 50% clover cover, 4) a grass only sward applied with the amount of synthetic N that the Defra Fertiliser Manual (RB209) hypotheses will match biological nitrogen fixation (BNF) from the clover density in the second treatment, 5) a grass only sward applied with the amount of synthetic N that RB209 hypothesises will match BNF from the clover density in the third treatment.

Nitrous oxide (N2O) fluxes are measured by a closed static chamber technique. The chambers are made of polypropylene and fitted into polyethylene collars, which are inserted 5cm into the soil at least 24 hours before gas samples are taken. Two chambers are assigned to each plot, with 3 additional chambers allocated to a reference plot. Sampling is conducted weekly with an increase in frequency following N application. On each sampling day, flux measurements are conducted between the times 09:00 and 12:00. N2O emissions from urine treated plots are also measured to simulate urine deposition from sheep fed the biomass from a particular plot.

Gas samples are analysed using a gas chromatograph (GC) fitted with an electron capture detector (ECD). N2O concentrations at 0, 20, 40, and 60 min are used to estimate N2O fluxes (g N ha-1 d-1) for each chamber. Ancillary soil measurements are also made on each sampling date to get an overall picture of different N forms.


The people working on this trial are John Hyland, Rory Shaw, Karina Marsden, Dave Chadwick, Davey Jones and Prysor Williams. The trial is funded by the agricultural levy boards EBLEX, HCC, DairyCo., and QMS. We welcome collaboration on this trial by interested parties from the UK and overseas. The contact details are listed at the top of the page.

Photographs of the trial

Figure 1. Greenhouse gas collection during (top) and following (bottom) the establishment of grass ± clover.