• Effects of over-winter green cover on groundwater nitrate and dissolved organic carbon concentrations beneath tillage land

      Premrov, Alina; Coxon, Catherine E.; Hackett, Richard; Kirwan, Laura; Richards, Karl G. (Elsevier, 13/09/2012)
      Application of over-winter green cover (e.g. cover crops) as a measure for reducing nitrate losses from tillage land has been frequently investigated, especially in the unsaturated zone. Monitoring of groundwater is less common in these studies. Studies on groundwater responses to different land treatments can be challenging because they can be influenced by various conditions, such as recharge, seasonal variations, and aquifer properties, often occurring at different time scales than surface water processes. The aim of this study was to evaluate groundwater nitrate (NO3−single bondN) and dissolved organic carbon (DOC) concentration responses to different over-winter green covers: mustard, natural regeneration and no cover. A field experiment was designed and run for three years on tillage land underlain by a vulnerable sand and gravel aquifer in the south-east of Ireland. Results showed that over-winter green cover growth on tillage land can be an effective measure to reduce groundwater NO3−single bondN concentrations. A significant decrease in groundwater NO3−single bondN concentrations was observed under the mustard cover compared to no cover. All treatments, including no cover, showed a decline in groundwater NO3−single bondN concentrations over time. A significant increase in groundwater DOC was also observed under the mustard cover. Although the overall groundwater DOC concentrations were low, the increased DOC occurrence in groundwater should be accounted for in carbon balances and could potentially enhance groundwater denitrification in cases where aquifer conditions may favour it.
    • Mustard catch crop enhances denitrification in shallow groundwater beneath a spring barley field

      Jahangir, Mohammad M. R.; Minet, E.; Johnston, Paul; Premrov, Alina; Coxon, Catherine E.; Hackett, Richard; Richards, Karl G.; Department of Agriculture, Food and the Marine, Ireland; RSF 06383 (Elsevier, 26/12/2013)
      Over-winter green cover crops have been reported to increase dissolved organic carbon (DOC) concentrations in groundwater, which can be used as an energy source for denitrifiers. This study investigates the impact of a mustard catch crop on in situ denitrification and nitrous oxide (N2O) emissions from an aquifer overlain by arable land. Denitrification rates and N2O-N/(N2O-N + N2-N) mole fractions were measured in situ with a push–pull method in shallow groundwater under a spring barley system in experimental plots with and without a mustard cover crop. The results suggest that a mustard cover crop could substantially enhance reduction of groundwater nitrate NO3--N via denitrification without significantly increasing N2O emissions. Mean total denitrification (TDN) rates below mustard cover crop and no cover crop were 7.61 and 0.002 μg kg−1 d−1, respectively. Estimated N2O-N/(N2O-N + N2-N) ratios, being 0.001 and 1.0 below mustard cover crop and no cover crop respectively, indicate that denitrification below mustard cover crop reduces N2O to N2, unlike the plot with no cover crop. The observed enhanced denitrification under the mustard cover crop may result from the higher groundwater DOC under mustard cover crop (1.53 mg L−1) than no cover crop (0.90 mg L−1) being added by the root exudates and root masses of mustard. This study gives insights into the missing piece in agricultural nitrogen (N) balance and groundwater derived N2O emissions under arable land and thus helps minimise the uncertainty in agricultural N and N2O-N balances.
    • Predicting soil moisture conditions for arable free draining soils in Ireland under spring cereal crop production

      Premrov, Alina; Schulte, Rogier P.; Coxon, Catherine E.; Hackett, Richard; Richards, Karl G. (Teagasc, 2010)
      Temporal prediction of soil moisture and evapotranspiration has a crucial role in agricultural and environmental management. A lack of Irish models for predicting evapotranspiration and soil moisture conditions for arable soils still represents a knowledge gap in this particular area of Irish agro-climatic modelling. The soil moisture deficit (SMD) crop model presented in this paper is based on the SMD hybrid model for Irish grassland (Schulte et al., 2005). Crop and site specific components (free-draining soil) have been integrated in the new model, which was calibrated and tested using soil tension measurements from two experimental sites located on a well-drained soil under spring barley cultivation in south-eastern Ireland. Calibration of the model gave an R2 of 0.71 for the relationship between predicted SMD and measured soil tension, while model testing yielded R2 values of 0.67 and 0.65 (two sites). The crop model presented here is designed to predict soil moisture conditions and effective drainage (i.e., leaching events). The model provided reasonable predictions of soil moisture conditions and effective drainage within its boundaries, i.e., free-draining land used for spring cereal production under Irish conditions. In general, the model is simple and practical due to the small number of required input parameters, and due to model outputs that have good practical applicability, such as for computing the cumulative amount of watersoluble nutrients leached from arable land under spring cereals in free-draining soils.