The significance of drilling date and crop cover with reference to soil erosion by water, with implications for mitigating erosion on agricultural land in South East England

Abstract

Early drilling of autumn‐planted cereals is strongly advised in UK government publications targeted at farmers, in part as a measure to combat soil erosion by water. However, in years when rainfall is heavy in early autumn, this strategy is ineffective. Late drilling of autumn‐planted cereals also increases the risk of erosion, but for a different reason: crop cover develops more slowly in cooler weather, resulting in a longer exposure of nearly bare ground. The crucial factor affecting both strategies is the timing of autumn and early winter rainfall. We discuss a conceptual model based on the notion of a ‘window of opportunity’ for erosion, comprising the relationship between drilling date, date of attainment of a sufficiently protective crop cover and the timing of rainfall; variations are presented for different weather conditions and management choices. Of these three factors, only the date of drilling can be chosen by the farmer. The date of attaining a sufficiently protective crop cover can only be predicted approximately. The timing of rainfall cannot be predicted. Thus, erosion control advice to farmers, which is based on choice of date of drilling to minimize erosion during the ‘window of opportunity’, is both difficult to formulate and likely to be ineffective. Sites at risk of erosion need to have better thought‐out mitigation measures in place, rather than relying on a fortuitous temporal pattern of autumn and winter rainfall to minimize the risk of erosion.

Climate impacts on soil erosion and muddy flooding at 1.5 versus 2°C warming

“…The role of timing with respect to rainfall characteristics and land cover is a well‐known cause of soil erosion and muddy flooding and has been reported previously for the same hillslope (Mullan, Vandaele, et al, ). For a more in‐depth discussion of timing with respect to soil erosion, see Boardman and Favis‐Mortlock (), and Burt, Boardman, Foster, and Howden ().…”

Understanding the influence of farmer motivations on changes to soil erosion risk on sites of former serious erosion in the South Downs National Park, UK

“…Early planting (e.g. mid-September) is quite ineffective if heavy rain occurs in early October: the two major erosion events of the last 30 years have occurred on 7 October 1987 and 11 October 2000 (Boardman and Favis-Mortlock, 2014). Buffer strips can be overwhelmed by runoff (see Figure 5) and do little to limit on-site erosion despite being well publicised anti-erosion measures (Natural England, 2010;Rural Payments Agency & Defra, 2009).…”

SMART – Sediment Mitigation Actions for the River Rother, UK

“…Land use consists of arable land covering ca. 28 % of the catchment area with crops of winter wheat, maize, salad vegetables, potatoes and turnips which are all high erosion risk crops (Boardman and Favis-Mortlock, 2014;South Downs National Park Authority, 2015). Prior to the 1950s, the catchment was predominantly under permanent grazing.…”

“…If soils are eroding into waterways it is usually due to an underlying issue with soil health. A reduced rate of water infiltration into the soil, or soil capping, increases the flashiness of surface runoff and increases sediment detachment and transport (Boardman and Favis-Mortlock, 2014). If the soil has a reduced infiltration capacity, excess water can create muddy flows that run across the land and into rivers, thereby increasing flood magnitude (Boardman and Favis-Mortlock, 2014).…”