Seedbed: The three tillage tools misused most often

Monday, August 9, 2010

The mouldboard plow, smooth roller and subsoiler all have their uses in specific situations. But they can also cause soil damage if used inappropriately

by Keith Reid

As I am writing this, the spring seeding is just finishing up, so the cumulative impact of all the various tillage implements is obvious across the landscape.

My first reaction to what I am seeing is that there are some tillage tools we would be better off without. But then I realized that I, myself, have recommended each of these implements for specific situations. The problems arise where they are used too often, too aggressively or in the wrong place. 

My rogue's gallery, therefore, are the three implements that I see misused most often – the mouldboard plow, the smooth roller, and the subsoiler.

Rogue #1: Mouldboard Plow. The challenge facing John Deere as he was inventing the self-scouring plow was that the tough prairie sod defeated all the available implements of the day.

His new plow really opened up the prairie to farming, and there is still no better implement for breaking a heavy sod. The added advantage at the time was that buryingall of the residue allowed the shoe or hoe-type openers on seed drills to operate without plugging. 

The drawback to the plow is that it leaves no residue on the soil surface, so there is no protection from wind or water erosion. The uneven soil surface left after plowing also requires more secondary tillage passes than other systems, causing greater degradation of soil structure.

Few situations generate enough yield increase over the alternatives, particularly in an annual crop rotation, to justify the extreme soil disruption of the mouldboard plow. It's a bit like the commuters with their SUVs driving down Highway 400, because they want to be prepared for extreme road conditions. A wide range of alternative tillage tools are available, including offset disks, chisel plows, vertical tillage tools and strip till units, for those situations where no-till is not a viable option.

Rogue #2:  Smooth Roller. Packing the soil following planting helps to ensure good seed-soil contact, so there are continuous pores to carry moisture to the seed. This is particularly important in a dry spring. It also breaks down clods, pushes stones down into the soil and provides a smooth surface to allow the combine header to shave the ground at harvest. 

The smooth roller does all this, but too well. The fine, firm surface that is desirable in dry conditions rapidly forms an impenetrable crust when it rains, leading to increased emergence problems. The perfectly smooth surface encourages rapid runoff, leading to increased erosion by water. There is also nothing to disrupt air movement over the surface, so the powdery soil is more subject to wind erosion.

The first consideration should be whether you really need the packer, before it gets hitched up behind the drill or planter. Most modern seeding equipment already does a good job on its own of firming the soil around the seed. If fields need packing routinely, that could be an indication of too many secondary tillage passes.

Finally, if a field does need to be packed, a corrugated packer will do a better job of breaking down clods while leaving indentations in the soil surface to slow down and catch runoff during rainfall. 

Rogue #3: Subsoiler. Compaction below the normal tillage depth can restrict root growth and prevent drainage of excess water from the root zone, leading to reduced crop growth and increased surface runoff. In most fields, frost action or cracking due to soil drying, combined with deep root growth, will alleviate soil compaction over time – one of the advantages to farming in Ontario rather than the southern United States. There are some situations, however, where breaking up a compacted layer with tillage is the most expedient option. 

Trouble arises when the subsoiler is used without checking first if soil compaction is actually limiting crop growth in a particular field, or if it is used at the wrong depth or when soil conditions are inappropriate. Most often, the result is only unnecessary wear and tear on equipment and excessive black smoke, but occasionally the misuse of a subsoiler will actually damage soil structure to the point that it hurts crop yields.

The first rule in dealing with soil compaction is always to avoid the damage rather than trying to fix it afterwards. If there has been unavoidable compaction from, for example, a wet harvest season, check with a tile probe or compaction meter for where and how severe the compacted layer is.

If mechanical intervention is necessary, set the depth of the implement just below the bottom of the compacted layer for maximum effectiveness. BF

Keith Reid is soil fertility specialist with the Ontario Ministry of Agriculture, Food and Rural Affairs, based in Stratford. Email: keith.reid@ontario.ca