Reducing the risks associated with autumn wheeling of combinable crops to mitigate runoff and diffuse pollution: a field and catchment scale evaluation

Abstract

Tramline wheelings are an important management tool for cereals, but their use for autumn spraying also increases the risk and severity of soil compaction and damage, surface runoff, erosion, and nutrient/sediment loss to water bodies (GAEC 5). Recent ADAS research shows most runoff from cereals occurs down these bare, compacted tramline wheelings when soils are wet.

Research evaluated tramline management options over four years at four sites with contrasting soil types and slopes in England and Scotland using replicated hillslope sections. Results showed the most practical cost-effective tramline management options included:
• Correctly-inflated Very Flexible (VF) tyres – operating at half the pressure of conventional tyres 
• A novel self-propelled rotary harrow unit attached to the rear of the crop sprayer in autumn. This punctures the soil in several places across a wheeling, increasing infiltration without affecting traction. It is self-cleaning, easy to use (hydraulically controlled from the cab), has very low (9 hp) draft requirements, and works on both self-propelled and trailed sprayers.
• A novel surface profiler-roller unit attached to the rear of a tractor, and used once after autumn spraying. This creates a convex soil surface which sheds water back into the crop rather than channelling it into the concave tyre imprint usually created by farm traffic.

VF tyres and rotary harrow both proved versatile and cost-effective, significantly reducing (p<0.05) runoff and erosion on a range of soil types (although data on clays was limited). Surface runoff was reduced by up to 75% using VF tyres, 85% using surface profiler-roller and up to 95% using the rotary harrow, compared to control tyres. The surface profiler required a separate pass and so proved less practical in a winter cereal crop situation, although other ADAS research has demonstrated its practicality and cost-effectiveness in row crop systems. For cereals, the slightly greater initial cost of VF compared to conventional tyres was more than offset by their reported longer lifespan, resulting in a net gain of £2/ha across a 300ha farm. The rotary harrow cost £12/ha if applied to only 20% of a 300ha farm (but costs could be lower as allied research confirms efficacy across crop rotations). Supported by this research, capital grants towards tramline management tools are now available under the Higher Tier of Countryside Stewardship in England (RP31).

Other tramline management practices to avoid the risk of compaction, runoff and erosion include:
• Increase tramline spacing (e.g. moving from 18m to 24m or more)
• Correct tyre inflation pressure for the tyre, field operation and axle load (i.e. don’t over-inflate) 
• Careful timing of autumn spraying operations to avoid very moist soil conditions 
• Avoid establishing tramlines on loose “fluffy” seedbeds or when soils are very moist 
• Use an extra headland tramline at the lowest end of the field, and disconnected from the other tramlines, so the area between the two tramlines acts as a buffer strip to most of the field
• Re-orientate crop drilling (and hence spraying) so tramlines do not follow the steepest

However, results showed that drilling tramlines which will be receiving traffic (and spraying using GPS) is not a solution, because soils will still be compacted by sprayer traffic in autumn when soils are often wet and vegetation cover is limited, and so the risk of runoff and erosion remains.