Depleting soil nutrients through frequency and timing of hay cutting on floodplain meadows for habitat restoration and nutrient neutrality

Floodplain meadows support a high level of botanical diversity because the nutrient inputs from flood sediments are balanced by nutrient offtake via an annual hay harvest, leading to nutrient neutrality. This prevents a buildup of nitrogen (N) and phosphorus (P) and depletes excess nutrients, which mitigates eutrophication in catchment areas and prevents reductions of biodiversity through competitive exclusion. A replicated field trial was undertaken in floodplain meadows in central England, with the aim of comparing the nutrient offtake potential throughout the growing season with a single or a double-cut system, and determining when haymaking should occur to maximise nutrient offtake and nutritional value of the hay. Additionally, farmer perspectives were gathered to investigate the practicality of implementing a second hay cut. The results revealed that a single summer hay cut may be sufficient to balance nutrient inputs. However, a double-cut, where a second harvest replaces autumn grazing, has the potential to actively lower N and P levels, removing 8.69 g m- 2 N and 0.80 g m- 2 P. Maximising time between cuts in a double-cut system provides the greatest opportunity for nutrient removal. Temperature is a key driver of plant growth. The relationship between accumulated thermal time and calendar date in central England has advanced by around two weeks between 1961-1990 and 1991-2020. Delayed hay cutting under agri-environment scheme restrictions may be increasingly detrimental to botanical diversity with advancing seasons, due to lower nutrient removal under a single-cut system, and increased competitive exclusion. Taking a first cut at the mid-summer peak in offtake potential, currently 20-30 June in central England, and a second cut in the autumn offers an opportunity to deplete excess nutrients. Whilst farmers identify practical and financial concerns that may make a second cut prohibitive in some cases, this could be overcome by, e.g., demonstrating the higher-than-expected nutritional value of hay from a second cut.