BEHIND THE CULTIVATOR
by Greg Stewart, OMAF Corn Specialist

Independent pull-behind harrows/packers/conditioners may allow for greater flexibility in meeting secondary tillage needs

The value of a "fine, firm seedbed" in corn production is more than anecdotal. In years of tillage research, seedbed fineness has been a reasonably good indicator of the potential yield from a tillage system. Making a fine seedbed is the main reason most growers run some sort of harrow, crumbier, packer or roller behind the field cultivator as part of the secondary tillage operation. Reason number two is most likely to create a more level seedbed in order to improve uniformity of seeding depth and seed-to-soil contact of the planter unit especially if planting speeds are on the high side. Reason number three in many areas will be to push stones back down to allow for smoother harvesting both in this years corn and next years no-till beans.

From a dollars per acre perspective, these devices are probably a good investment. The warning however about seedbed fineness is centered on the tilth or structure of your soil. Soils with low organic matter and poor structure that are left with a very fine aggregate are more prone to crust. Also, research by Dr. Tony Vyn while at the University of Guelph showed that in addition to plant residue cover, aggregate stability can have a significant impact on soil erosion potentials. The art of tillage becomes the ability to strike a balance between a seedbed which is fine enough to promote high yields and a seedbed where tillage has reduced aggregate size and stability to the point were the risks of crusting and erosion are too high. As a leveling tool, my perspective is that what you put on the back of the cultivator is very limited in what it can accomplish. If the soil has been left uneven after fall tillage, your field cultivation in the spring becomes overly focused on getting the gullies and mounds leveled and less on creating a relatively fine seedbed. In these cases, pulling packers or harrows behind the cultivator while you are trying to level the field may result in a finer, less stable seedbed than desired. The distinct preference here is to do a much more uniform, level job of fall tillage. One of my particular hang-ups is with fall tillage that leaves the field far too rough for secondary tillage to be able to smooth it out in less than 2, or in some cases 3, passes.

Aggressive harrow/crumbler units behind the cultivator may allow for superior seedbeds with fewer tillage passes

The twisted shovel chisel plow is often the culprit and efforts should be taken to leave the soil more uniform in the fall than is often the case with this tool. Remember that residue cover on the soil surface is considerably more important than soil roughness in preventing soil erosion. Achieving a more level profile may mean switching to sweeps, a combination of shovels and sweeps, putting leveling devices on the back of the chisel plow, or moving to some alternative form of primary tillage. Leaving the soil rough in the fall also makes it more difficult to ensure that the cultivator is not working the soil too deep - and consequently too wet -in places.

As far as spring options go, having a harrow/rolling harrow that is able to be easily lifted (mounted units), or removed (separate pull-type units) from the cultivator enhances your options of doing the correct amount of tillage in a range of conditions. Why pound the aggregates to death while what you are really trying to do in the first pass is get the field leveled up?

When pushing rocks down is the priority, then large diameter drum rollers have become more the tool of choice and in many cases can often accomplish a significant amount of aggregate size reduction at the same time.

Consider the five pillars of corn planting in light of your seedbed preparation: f) Correct Density (for the hybrids and field you are planting), 2) Uniform Emergence (no plants that are more than one leaf stage behind their neighbours), 3) Planting Depth (into moisture and usually in the 1.5 to 2.0 inch depth range), 4) Uniform Nodal Root Development (avoid root systems that do not explore the soil volume uniformly in all directions), and 5) Uniform Spacing (much of this will come as a result of getting the density correct, plants can compensate for a fair bit of spacing variation but large gaps can hurt). Fine tuning your management, and in some cases increasing your investment in the tool behind the cultivator may be an important step towards accomplishing corn planting excellence.