More Is Not Always Better
Apr 19, 2009
Is it a "guy thing" that we always take things too far? Tell a farmer to torque a bolt to 100 pound-feet and he'll always twist it to 110 lb.ft. Give a farmer a way to firm soil around fresh-planted seed and he will leave the seeds in the black dirt-equivalent of a paved parking lot.
Corn planting is maybe 25 percent complete in our area, and once again I'm finding a lot of planters with the gauge wheel down pressure settings too heavy and the closing wheel down pressure handles one notch too strong. Soil conditions are wet and cool. When I dig behind planters with my little pocket screwdriver I often flip up chunks of packed dirt the size of golf balls. On a sunny day there are smooth, shiny strips alongside the closing wheel marks, where the seed unit gauge wheels have pressed so firmly against the soil that they've left packed strips. And the marks from the closing wheel tires are an inch or more deep, with a one-inch or higher ridge of soil squeezed up between them.
The only reason for down pressure on seeding units is to keep the units from bouncing as they move across tilled fields, or in no-til fields where the disk openers need a little help in slicing into the undisturbed soil. Any additional down force applied by gauge wheels packs the dirt alongside the seed furrow and makes it difficult for seedling roots to grow normally. Closing wheels should merely pinch the seed furrow closed---packing the soil over seeds complicates seedling shoot emergence.
There are no discrete recommendations on pounds/square foot of down pressure, or which notch in the adjuster to use. It all depends on the soil in each field. But in general, with the planter lowered and in planting position, you should be able to twist a guage wheel 1/4 turn, with effort. If you can turn it easily you need to increase down pressure. If you can't turn it at least 1/4 turn, you've got too much down pressure on that row unit. Closing wheel down pressue should be just enough to close the seed furrow. Deep closing wheel tracks or a high center ridge hint of too much down pressure.
A definitive test is to dig. In an unplanted part of the field, dig to planting depth. Note how hard you have to dig and the consistency of the soil at seeding depth. Compare that to the soil around seeds you have just planted. The planting process will naturally firm the soil to some degree, but if you have to dig and jab to get down to seed depth, and the soil pops out in chunks, then it's time to control your testosterone and take a kinder, gentler approach to setting your planter.
Scroll to the bottom of this post for a photographic example of the effects of too much down pressure.
In this photo of knee-high corn, the wall of the over-compacted seed furrow is still visible as the vertical surface marked by the screwdriver. Note that all the critical primary seedling roots are running parallel with the seed furrow--they haven't been able to penetrate the compacted seed furrow wall. All the moisture and fertility between the rows is unavailable to that plant, due to too much down pressure on the planter's row unit gauge wheels.