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Soil erosion on arable land in lowland Britain has been the subject of field‐based surveys, which have assessed the volumes or masses of soil transported in channels across farmers’ fields. These surveys provide a unique database on the extent, frequency and rates of soil loss by water. This study synthesizes the key findings from those surveys and underscores the implications for soil erosion modelling. Rill erosion occurs in a small number of fields (consistently <10%). Over ~5 yr, a considerable proportion of the farmed landscape will suffer from rill erosion, but mostly in fields that erode only once. Mean erosion rates for lowland arable landscapes are much less than mean erosion rates for individual eroded fields within that landscape. These observations pose important challenges for modelling. Rainfall and cropping vary from year to year so that risk of wash or rill erosion in the same field also varies. Due to the infrequent occurrence of rill erosion, loss rates of eroding fields cannot be spatially extrapolated across the landscape, except in the case of wash erosion which takes place a number of times in almost all fields every year. A consistent pattern of increasing wash erosion, in terms of spatial extent, is emerging in lowland Britain. Resulting losses of fine silt and clay‐sized particles are small in amount and possibly insignificant in terms of loss of soil as a resource, but have significant implications for contaminant concentrations and pollution of water courses.

Summary 22We describe the development of a manual of methods for mitigating diffuse water pollution 23 from agriculture and its important influence on policy and practice in England and Wales. The 24 objective of the 'User Manual' was to provide policy makers and those implementing policies 25 with information about the cost, effectiveness and applicability of potential methods in a form 26 that would be readily understood by non-specialists. The 'User Manual' was based on earlier 27 reports synthesising available research data and, where data were unavailable, used expert 28 elicitation. The outcome generated 44 potential methods (under the broad categories of land 29 use, soil management, livestock management, fertiliser management, manure management 30 and farm infrastructure) and described the simultaneous impact of applying each method on 31 losses of nitrate, phosphorus and faecal indicator organisms relative to baseline losses. 32Estimates of cost and effectiveness were presented at the whole-farm level for seven model 33 farm types. Methods differed widely in their cost-effectiveness and applicability to the 34 different model farms. Advantages and limitations of the approach are discussed and 35 subsequent developments of the original 'User Manual' are described, together with the 36 opinions of catchment officers who have used the 'User Manual' to implement mitigation 37 methods on farms. 38

Management rules for integrating manure applications into arable crop rotations have generally been developed from short-term studies. The aim of this experiment was to test whether they would apply to frequent applications across an entire crop rotation. The hypothesis was that by avoiding autumn manure applications and adjusting fertilizer inputs to account for manure nitrogen (N) inputs, frequent manure applications could be made to a rotation without increasing N leaching compared with a control that received inorganic fertilizer according to the recommended rates. Four separate manure management strategies with varying manure types (pig slurry vs. pig farmyard manure), timing (autumn/winter vs. spring) and frequency (4-7 applications in 7 yrs) were superimposed on the rotation and compared with a treatment that received no manure. The rotation comprised cereals, potatoes, sugar beet and fallow and was undertaken on a retentive marine silt soil in Eastern England. The results demonstrated that by reducing fertilizer N inputs (by 14-54%, depending on manure type and application frequency) to account for manure N and by avoiding autumn applications of slurry, applications could be made as regularly as 6 yrs in seven without increasing N leaching, compared with an inorganic fertilizer control. Yields were at least the same as the inorganic fertilizer control from all manure treatments. This result contrasts with previous work which demonstrated that less frequent manure applications were necessary on a sandy soil. Soil type is therefore an important consideration when developing guidelines. The message is generally positive: fertilizer savings, similar or better yields and no extra leaching can be achieved over a rotation by careful manure management.