Avoid compaction from large harvest machinery

Last fall was wet during and following harvest, so more soil compaction than has been common in recent years occurred on many fields in Iowa. This past spring, most areas again experienced many rainy periods and compaction occurred during secondary tillage or planting or both. It was very common in June to see the field cultivator’s pattern across fields. Likewise, it was not uncommon to see

Avoid compaction from large harvest machinery

Last fall was wet during and following harvest, so more soil compaction than has been common in recent years occurred on many fields in Iowa. This past spring, most areas again experienced many rainy periods and compaction occurred during secondary tillage or planting or both. It was very common in June to see the field cultivator’s pattern across fields. Likewise, it was not uncommon to see the planter wheel’s pattern across fields.

Both of these are outcomes of compaction. A third cause of compaction we saw this year was from excessive down pressure on the row units of the planter. The down pressure needs to be adjusted to a level that gives a nice uniform planting depth. In wet years, it is easy to use too much down pressure, resulting in compaction in the row. When that happens, roots are severely restricted until they manage to get out of the compaction area. More on that in a moment.

Often when on field calls this past spring, I was asked what caused the unevenness of plant height. We could push a flat-bottom spade in the ground with one smooth push of the leg, and it would stop at the depth of compaction. In the case of the secondary tillage, such as a field cultivator, the spade stopped at the same depth as the tillage. In the case of the planter wheels, it was common for the spade to stop at just an inch or two deep where the planter wheels carried the weight of the planter in soil that wasn’t quite dry enough to bear that weight. In those cases, moving the spade over a little resulted in deeper penetration of the spade.

In the case of the row unit down pressure, pushing the spade in the ground in the row showed a compaction layer just an inch or two deep. By moving over to between the rows, we could push the spade in about 5 inches before stopping.

Avoiding the problem

How are these three causes of compaction avoided? Before doing secondary tillage, dig down to the depth of the tillage. In the case of a field cultivator for instance, dig down to where the tip of the shovel will be. See if that soil is fit to work. Often it can be fit to plant but not yet dry enough to till. If that is the case, you have two choices: either wait until it is fit below, or skip the tillage and begin planting.

In the case of the planter wheel causing excessive compaction, do some checking behind the planter wheels. If the wheels are causing excessive compaction, you could either hold off or at least carry less seed, and fertilizer or pesticides for a half day or so until the soil has drained the excess water to a deeper level.

In the case of the planter row unit’s down pressure, do some digging behind the row. If it is difficult to dig the area and seed is consistently placed at a uniform depth, back off the down pressure until you can dig easier and still maintain uniform seed depth. If that is not possible, the field is not fit to plant.

What about this fall? We need to be aware of how much heavier our equipment is today than 50 years ago. I saw this comparison by a farmer last December regarding combines. It makes you think.

The farmer compared an older John Deere model 45 built 55 years ago with a newer 2010 model 9670 STS. The newer combine is considerably larger. To provide some specs on dimensions and capacities, the table below summarizes the data from the owners’ manuals of the two machines. You can see just how much things have changed in half a century.

Pay particular attention to the weight, the combine’s grain tank capacity and the fuel capacity. The weight difference of the two machines is 26,567 pounds. Add to that about 21,000 pounds of grain in a full grain tank and nearly another ton of fuel. The modern machine is nearly 25 tons heavier. Both era machines are going down two rows.

Consider how all that extra weight is impacting soil structure on each pass across the field. Then add in a grain cart holding anywhere from say 600 to 1,500 bushels, which is 33,600 to 84,000 pounds. Maybe emptying the combine on each end of the field when possible makes sense.

Multi-season compaction

What can we do about compaction from last fall, this spring and this fall? If the upper soil is wet, I suggest limiting fall tillage to the bare minimum. Freeze and thaw cycles over the winter will break up compaction in the top 4 to 5 inches of soil.

If there is compaction deeper than that, before you do any deep ripping, be sure the soil being disturbed is down to field capacity for moisture content. If the soil at point of tillage is too wet, the tillage will do more harm than good. It needs to be dry enough for the tillage to shatter the compaction. If soil is too wet, the tillage will smear and put compaction in, causing more problems than if the soil were left untilled.

Johnson is the ISU Extension field agronomist for central Iowa. Contact him at [email protected]

55 years of combine evolution

Model number

45

9670 STS

Cutting width

10 feet

35 feet

Grain tank cap

40 bushels

400 bushels

Weight

6,100 pounds

32,667 pounds

Length

22 feet w/ platform

34 feet, 3 inches

Height

12 feet, 9.5 inches

14.9 feet

Width

7 feet, 2 inches

17 feet, 6 inches

Wheel base

10 feet, 4 inches

11 feet, 6 inches

Rear track

3 feet

10 feet, 3 inches

Horsepower

42 hp

305 hp

Engine displacement

188 cubic inches

549 cubic inches

Fuel capacity

25 gallons

250 gallons

Comparing a Deere model 45 combine manufactured around 1960 with a Deere model 9670 STS combine built in 2010.

This article published in the September, 2015 edition of WALLACES FARMER.

All rights reserved. Copyright Farm Progress Cos. 2015.

Field Conservation Maintenance/Practices

Harvest Management

Harvesting Equipment

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