Seed Bed: What tillage system is right for you?
Thursday, December 3, 2009
Drainage, crop rotation and the condition of your soil can all influence
how well no-till works on your fields
by KEITH REID
The growing season of 2009 has been, for many parts of Ontario, cooler than normal and frequently plagued by wet soil conditions that interfered with field operations. The result has been a challenging year for all crop producers, but the perception (and sometimes the reality) is that no-till suffered more than other tillage systems.
At the same time, rill and gully erosion has been obvious on many conventionally tilled fields to a greater extent than any time in the past couple of decades. This has some farmers rethinking their tillage programs, so it is worthwhile to step back and consider what conditions will favour the choice of a particular tillage system.
As an aside, I find it interesting that growers who have lower yields on their no-till fields are quick to blame the tillage system, while growers who suffer yield losses from
too much or inappropriate tillage – and I see many of those fields as well – either blame some other factor (usually the weather) or else just keep quiet at the coffee shop. I guess this means that no-till is still not considered to be part of normal practice by the majority of Ontario farmers.
A number of factors influence how successful a tillage system is going to be in a given field. Some of the challenges with no-till are undoubtedly due to the weather, but we can put at least some of the blame on ignoring the lessons from 20 years ago.
Soil texture, structure and organic matter. The number one and two challenges for no-till in Ontario are getting the soil dry enough in the spring that the crop can be planted without smearing, and maintaining enough air-filled porosity in the soil. Both of these are directly affected by the interactions among texture, structure and organic matter.
Sandy soils dry out quickly, so they have been easy to manage in no-till as long as they didn't get packed too tightly by frequent traffic. Clay soils take longer to dry out, and smear more easily when wet, so they have demanded far greater patience for no-till management. High organic matter contents will create a stable soil structure that is more forgiving of field activities when the soil is not quite dry enough.
The most challenging soil texture for no-till is silty clay loam, where the high silt content weakens the soil structural stability.
These same factors affect the soil's response to tillage. Fine textured soils need the winter to break down the clods created by primary tillage, so are not good candidates for spring plowing. Medium and coarse textured soils, on the other hand, will respond very well to being left undisturbed over winter and tilled just before planting.
Drainage and compaction. Part of the goal of tillage is to create an open, porous soil structure. In no-till, we depend on natural processes to perform this same task.
These processes tend to be slower than a cultivator operating at eight miles per hour, so set-backs to these natural processes have a much greater impact in no-till than in tilled systems.
Successful no-till farmers make sure there is adequate drainage, so they don't have to travel over the field when the soil is wet, and are extremely diligent about reducing the number of field passes and limiting the weight of equipment to avoid soil compaction. This also avoids the creation of ruts, which interfere with the proper placement of seed by no-till planters.
Soil fertility. There are fewer opportunities to mix nutrients with the soil in no-till than when the soil is regularly being mixed by tillage. This has little impact if the soil fertility levels are adequate, but infertile fields can suffer significant yield loss from nutrient deficiency. No-till equipment should always have the provision for banded fertilizer application. Acid soils need to be limed before switching to no-till, since lime needs to be thoroughly mixed with the soil to be effective.
Crop rotation. When any crop is grown continuously, pests and diseases specific to that crop build up, and in no-till those pests are on the surface rather than buried in the soil. Recent research has also found that plant roots will follow the old root channels of a different plant, but avoid the old root channels of the same crop, so a rotational crop can extend its roots out into the soil much more easily than a second-year crop. Both of these factors help to explain why crop rotation has a much greater benefit in no-till systems.
Crop rotation is also important in managing the residue cover that must be planted through. Alternating crops that produce large and small amounts of residue can help to avoid a situation where the layer of surface mulch prevents the soil from drying in the spring, or impedes the ability of planting equipment to actually place the seed through the residue.
Weed control. Weeds reduce crop yields in any tillage system, but the mix of weed species and the nature of weed control changes in no-till. Growers who haven't adapted to these shifts become proof of the axiom that "good weed control gets better in no-till, and poor weed control gets worse." BF
Keith Reid is soil fertility specialist with the Ontario Ministry of Agriculture, Food and Rural Affairs based in Stratford. keith.reid@ontario.ca