PhD student and MAGLUE researcher Amanda Holder discovers how digging holes can help inform policy decisions.

Amanda Holder, a PhD student at Aberystwyth University and part of MAGLUE Work Package 1 provides an update of work carried out so far and how with the interaction of the MAGLUE project field studies can be transformed into policy recommendations.

Posted on 18 June 2017.

After 18 months of PhD work at least 750 soil samples have been taken/holes dug in order to investigate changes in greenhouse gas emissions and hydrology that arise from land use change from grass pasture to the bio-energy crop Miscanthus (Miscanthus x giganteus).

Monthly soil cores to be analysed for ammonium (NH4+) and nitrate (NO3-) have been taken across experimental plots over the last year. This is to compliment fortnightly ground surface gas sampling for emissions of nitrous oxide (N2O). N2O emissions showed an initial spike over the cultivation period (from 0 up to 1 mg m-2 hr-1), but retuned to pre-cultivation levels after 3 months. The soil cores will help to assess the contribution to soil N2O fluxes of soil nitrification or denitrification processes.  Sampling is to continue over the second growing season to investigate any changes, particularly in comparison to sheep grazed grass pasture control plots.

Mini-rhizotron tubes (clear tubes inserted into the soil to enable observations of root growth) were installed into field plots of Miscanthus in February 2017 and once a fortnight a camera is sent down the tubes to photograph the roots (Picture left). Analysis of these pictures will help to obtain root to shoot proportions used in yield and hydrology modelling as well as in considering carbon stocks.

Investigations into soil carbon changes are also taking place at a trial site with 12 year old Miscanthus.  60 soil cores have been taken from 20 plots to determine soil carbon changes over the long term (Picture below right).

Interaction with the MAGLUE project will enable data obtained from these and other samples to inform and validate the ECOSSE computer model used to simulate and analyse greenhouse gas emissions.

Changes to hydrology are an important environmental consideration and soil holes varying from 5cm to over 1m in depth have been used to help understand the impacts of a commercial scale Miscanthus crop.

Small wells (to a maximum depth of 1.3m) have been created within a Miscanthus plantation and in adjoining grass pasture fields. These will be used to monitor changes to ground water levels. At the other extreme small 5cm deep holes have been used with a mini-tensiometer to take spot measurements of top soil water potential. This data will be combined with top soil moisture maps taken before and 4 years after planting, in-situ soil moisture probes and eddy covariance atmospheric monitoring, to examine the impacts of the Miscanthus crop on soil moisture.

 A study was also completed last year investigating the role of the Miscanthus canopy in reducing rainfall reaching the soil. This revealed an interception of precipitation by the canopy of 24% (from the period June 2016 to March 2017) in a mature, commercial scale crop situated in west Wales.

These surveys are continuing throughout the 2017 growing season and when combined with the other MAGLUE work packages can be used to improve modelled outputs and allow for optimisation of different land use transition options and management practices. With the benefit of MAGLUE stake-holder input results will be moved forward to provide policy relevant recommendations.

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