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A total of 30 storm runoff events were sampled between 2017-2020. In March 2020, data collection ceased due to the Covid-19 pandemic. On that basis, our results are reported for individual monitoring years spanning April – March, rather than the more conventional water year for the northern hemisphere. This reporting period also aligns better with the farm management year for grassland systems wherein fertilisers for encouraging grass growth are applied in spring and fodder maize is also sown.

Water samples were collected using an Envitech SampSys autosampler. A total of 24 samples could be collected from each replicate plot, with millivolt readings from the level sensor used to trigger the initiation of sampling on a 10 mV staging basis. Sampling periods were established via Meteorological Office weather forecasts, with a delayed start via the internal clock of the SampSys used to gain samples from both the rising and falling limbs of the hydrograph of any individual sampled storm runoff event.