Portsmouth Water and South Downs Farmers discuss cover crop trial

On the 6th of February 2019, Portsmouth Water met with the South Downs Farmers Group to discuss initial results of cover crop trial based on data collected over the 2018/19 winter.

The meeting began at the Barley Mow pub in Walderton, where Susie Holmes presented the nitrate leaching results on behalf of Portsmouth Water. The meeting then moved up the road to reconvene at the farm that hosts the cover crop trial. Here, Portsmouth Water and the Farmers Group discussed the practicalities of establishing cover crops alongside the farmers’ current practices.  

Initial results, as presented by Susie, show an overall declining trend in nitrate concentrations through the winter due to declining temperatures and the slowing down of microbial activity. During this period, nitrate concentrations were lower under the phacelia cover crop but higher under oats when compared to barley stubble. This is potentially related to the amount cover in the plots, which could be taken as an indicator of nitrogen uptake by plants. Oats did not establish well in the dry autumn conditions and hence, the plant cover on these plots was very low. The ensuing discussion focussed on technical aspects, such as how nitrate moves through fissures in the underlying chalk and results in the nitrate spikes measured at the Portsmouth Water abstraction points.

In the afternoon, the group moved to the host farm at West Marden to view the trial itself. The group discussed a number of topics but the practical aspects of establishing cover crops were certainly hot topics. Cover crop species were discussed and the farmers agreed that that a cover crop that could establish well in a range of conditions would be important. This was further supported by the results of the trial where oats had failed to establish properly and nitrate leaching was high. What to do with the cover crop in early spring was also discussed. Amongst others, options such as mulching and ploughing-in were considered. These discussions with farmers, who have a detailed local knowledge, are essential if an ecosystem service buyer or intermediary are to design a successful PES scheme.