Spring is around the corner and manure needs to be spread before the corn goes in.

The potential is there to cause serious compaction, as we already alluded to in last week’s Field Crop News. This week I’d like to add a few thoughts on the issue of compaction.

Creating more flexibility to spread manure by diversifying crop rotations.

Diversity in the crop rotation is extremely helpful to manage manure. For example, sorghum, sorghum/sudangrass, or sudangrass can yield very well in Pennsylvania, and are especially suited to droughty soils. These crops can be established later than corn, offering a great opportunity to enlarge the window of manure application. In many cases, ryelage can be harvested, manure applied, and sorghum/sudangrass planted. In a presentation at the Pennsylvania Professional Crop Producers Conference earlier this month a farmer highlighted his success with this system, and the high yields and milk production per acre achieved (very competitive with corn silage). Another worthwhile consideration is to add a small grain to the rotation, opening a great opportunity to spread manure in the summer. I think we have underestimated the value of diversity in the crop rotation for manure management. For one, the storage doesn’t have to be as big. At the same time, one can have smaller manure spreading equipment, and still get the job done on a timely basis. In addition, it is easier to monitor soil moisture conditions, causing less compaction.

The importance of living roots to make soil resist compaction

If a soil is without living vegetation it is much more sensitive to compaction then when it has a good root system in it. There is research available to show this, and there is also the casual observation that we drive on sod if we want to avoid getting stuck. So having a cover crop in the field is a way to make the soil resist compaction better, and to allow for a greater opportunity to spread manure in the spring (or fall).

Measuring soil compaction severity with the penetrometer.

The soil compaction tester, or penetrometer, is used to measure soil compaction. A few tips for its use: In most cases, use the small (1/2”) tip. Check that the tip is not worn or your readings will be low. Use the appropriate reading scale for the tip (usually the inside scale for the small tip). Take 3-4 readings per acre, and record penetration resistance at each 3” interval. If you see spikes in the penetration resistance just below the depth of tillage, that is an indication of a plow pan. You have to realize that penetration resistance varies depending on moisture conditions. The guideline is to measure compaction when the soil profile is at field capacity (48 hours or so after a thoroughly soaking rain). If you measure compaction when the soil is muddy, you will get low readings. More common, if you measure compaction when the soil is dry, you get high readings. So you need to be at field capacity for the numbers to mean anything. Roots of most plant species cannot penetrate soil with a penetration resistance greater than 300 psi, and they are impaired when the resistance is between 200 and 300 psi. These results are true for a soil that has no macro-structure (pulverized soil). In a long-term no-till soil, penetration resistance may not be a helpful measure because of the development of macro-structure with many vertical and horizontal channels that roots will follow. In addition, rocky soils pose a problem for the use of the penetrometer. For more information on how to use the penetrometer and how to interpret the results, go to http://cropsoil.psu.edu/extension/facts/agfacts63.cfm.

Tillage the short-term fix but not the long-term solution

Tillage is a short-term solution to fix severely compacted soils. However, tillage is destructive and does not help to construct a high-quality soil. It is therefore much better to avoid tillage and manage your traffic and crop rotations so you can have a successful no-till system. You will find that, over time, your soil resists compaction better if you use continuous no-tillage, diverse crop rotations, and cover crops.