Overview: Reduced or minimum tillage requires soils to be in good condition for an efficient and effective transition from more conventionally tilled situations. Promoting healthy, biologically active and aerobic soil conditions is key to all forms of successful farming, and especially important where such activity, allied to vigorous crop root development and growth, can result in improved levels of soil resilience. Such resilience is becoming ever more important as our weather conditions become more extreme in both the wet and dry sense.
Important factors to consider when transitioning to reduced, or zero tillage: Soil type is important, along with the status of the soil itself. Biological activity, for example, will have been influenced by past and current cropping and cultivations. Naturally free-draining and self-structuring (calcareous) soils are likely to make a transition faster, and more efficiently than slowly permeable soils with a slumping-prone nature (silt is a key fraction here, especially in clay soils), or those where previous cultivations have been very intensive. Low soil organic matter levels (as a result, or where straw is removed, or no FYM or biosolids have been returned) also imply the need for care when looking to make such a transition. Other factors of critical importance include the following.
Drainage: Having aerobic soil biology is critical. A rapid return back from saturation to field capacity after high levels of rainfall will help. The capability to pass water through the soil profile efficiently – having a good level of vertically connected pores in a stable, well aggregated structure – is key to unrestricted water passage. Porosity levels also should be roughly 50% of the total soil mass. These pores can then hold onto water and air in balanced amounts, and provide pathways for such, along with plant roots and a home for the soil biology.
A fast return from saturation (all pores full) to 50% full of water at field capacity is driven by stable, resilient soil structure and effective drainage where this is needed for water to leave the field. On heavier soils needing drainage, yield improvements of circa 1 tonne/Ha of cereals crops is common, once the scheme has bedded in, and soil has begun to repair itself. New schemes are costly, so it is vital to ensure current schemes are functioning to their best before considering further investment:
- Ensure ditches are free of obstructions, and outfalls are clear, and above the bottom of the ditch. This also includes allowing water off the farm holding, onto the next by such means.
- Following heavy rain when soils are already damp, drains should start to run quickly, and slow down equally fast once surplus water has been removed by drainage.
- Mole drainage on appropriate subsoils (at appropriate moisture levels – the soil must be plastic at depth and drier nearer the surface for traction) should supplement under-drainage if indicated on drainage maps. This fissuring action above the mole can also help maintain subsurface structure when it is at appropriate moisture levels.
- Other considerations for effective mole drainage include proper mole channel formation – these need time to “cure” so avoid moling immediately before forecast heavy rainfall where soils at depth are near field capacity. Back-fill gravel above drainage pipes also ensures mole channels can vent efficiently and minimises risk of premature collapse.
Attempting to direct drill poorly drained and poorly structured soils is a recipe for disaster.
Soil Structure: This also determines free root, water, and air passage. Barriers, if found, should be removed so effective rooting (and yield) can result. Soil structure resilience improves with biological and root activity, so significant compromises to yield (and crop rooting) will prolong the transition process, and have negative effects on the business bottom line. The spade is essential here to determine the degree of damage, if present, and actions then needed.
Soil loosening by low disturbance “soil profile stretching” should be considered if this improves rooting, and shallow drainage.
- In many cases, such structuring can be done by a tine based drill – for example when establishing a cover crop. Having the capability to drill seed slightly shallower than loosening depth can be good – as the BTT opener examples seen on Clive’s Sprinter drill.
- An option to use a loosener ahead of the drill can also be effective, where needed.
- Such loosening can often be timed ahead of a break crop such as WOSR or beans, allowing its effect to benefit the following first wheat also.
- Deeper structure issues are often confined to known areas (turning headlands, & on less stable soils) where a controlled “stretching” of the profile will usually then allow effective root development and drainage. This process is NOT subsoiling, and can be done by a “sward lifting” approach in conjunction with growing roots through the profile.
- Where this loosening action is needed, ensuring structured “columns” remain between the loosened zones will further stabilise the structure and help maintain the biology present. The benefit to yield in the example previously outlined was just over 1 tonne per hectare of spring barley where the compacted headland was restructured.
Cropping: Growing crops with effective root systems normally drives further, higher yielding crops to then follow. Such crops and roots support positive soil biology, soil resilience, and also sequester Carbon most effectively. Avoid leaving land fallow and without some form of a growing crop whenever possible will maximise the building of soil resilience.
Prevention before cure: Prevention, or mitigation of trafficking damage helps to minimise unnecessary cultivations, accelerating the transition.
- Controlling and managing traffic limits areas of damage – Controlled Traffic Farming principles apply.
- Minimising axle loads, and ground pressures resulting, is a key factor to consider when transitioning. Many disc based direct drills do not use eradicators, and in any event, keeping ground pressures to levels of 0.7b or below will minimise adverse yield effects in these trafficked zones. Yield effects from ground pressure vary, and can lead to yield reductions of 40% or more, compared to where not trafficked, when drilling direct.
Above: typical crop yields (compared to where untrafficked) in drill tractor trafficked areas: a mean of 4 seasons of work across 2 soil types (light & heavy) where cereal crops have been direct drilled.
