C.O.R.N. Newsletter: 2015-35

(Editors note: The following article is being reissued as it appeared in 2011 when we had a very wet fall. The information in it is still relevant today. Unlike 2011 we have had a nice dry fall when we can actually use tillage when it is needed to alleviate compaction, such as ruts left this summer during spraying or over the previous few years. The article also discusses how tillage may also cause damage to the soil instead of making it better.)  

Farmers are eager to harvest soybeans and corn but the fields are very soggy in much of Ohio. The danger of causing soil compaction is therefore high.  Let’s look at ways to increase the resilience of the soil to compaction, to avoid compaction, and ways to alleviate compaction.

1) Make soil more resilient to compaction.

Resilience is a term used by ecologists to describe the ability of an ecosystem to resist perturbation or disturbance by resisting damage and recovering rapidly. Soil can be made to resist compaction by eliminating tillage, increasing organic matter content, and maintaining a living root system in the soil for as much time as possible. Any long-term no-till farmer will testify to the fact that tires do not sink as deep as in tilled soil. Soil that was tilled this spring or even in last year’s spring, will be more susceptible to compaction than a soil that has been in no-till continuously. Increasing organic matter content will also increase the resistance of the soil to compaction, because the spongy humus maintains porosity and also increases aggregate stability. Finally, a living root system at time of traffic would increase the resistance of the soil to compaction. While it is uncommon to see living root systems at harvest time, some exciting work is being done at Penn State University with establishment of cover crops into standing corn or soybean, combined in one pass with herbicide application and side-dressing.  Resilience also includes the concept of kicking back after disturbance. To make soil kick back from the effects of compaction, it is important to try to establish a cover crop after harvest. The roots of the cover crop will help alleviate compaction that has been caused. It is also a practice that helps increase biological activity in the soil – the mycorrhyzae and bacteria growing in the rhizosphere of cover crops produce glomalin and other organic substances that improve aggregation of the soil. If manure is available to give the cover crop a boost and supply additional food for soil microbes that will also be helpful. It should also be noted that without soil disturbance and leaving soil covered with mulch smaller and larger organisms such as nightcrawlers will be much more prevalent and active than if soil is tilled and left bare. Therefore, fall moldboard plowing should be avoided especially, and even chisel plowing in the fall will reduce the activity of these organisms that can help soil kick back from the effects of compaction while also improving drainage of the soil.

2) Avoid compaction

It is advised to stay off the field until conditions are fit for traffic, but sometimes we never reach those conditions! At least, try to avoid creating ruts. If you have different soil types on the farm, start harvest on the better-drained soil types first. Although this is a bit early yet, a little frost in the soil will also help to make the soil much less sensitive to compaction. I assume all of you Ohio farmers are aware of the great importance of increasing tire foot print by using flotation tires, duals and reducing tire pressure because key research in this area was done by Bob Holmes and Randall Reeder at OSU. Their research also showed that tracks can do a very good job as long as the weight of the vehicle is equally distributed along the whole length of the track. The effectiveness of flotation tires is all determined by inflation pressure – inflated at high pressures they will cause much more compaction than at low pressures. Check inflation tables to determine what the minimum allowable pressure is for your tires. If you need to get new tires, ask your equipment representative about tires that cause less compaction. Radial tires have a bigger footprint than bias-ply tires and are therefore recommended to avoid compaction. As far as harvest traffic: Keep those trucks with road tires out of the field. Axle load also plays a role, with axle loads above 10 tons being able to cause subsoil compaction that will be virtually permanent and very difficult to alleviate. Also, try to limit repeated traffic to certain areas of the field. Although these will be more compacted, it will be possible to correct compaction here without having to do remedial action on the whole field.

3) Correct compaction

When compaction has been caused, remedial action may be needed. This is especially the case if ruts have been created. If no ruts are seen it is probably not needed to do tillage – instead plant a cover crop to use the living root system to alleviate compaction. Ruts need to be smoothened out to be able to plant the next crop successfully, however. If ruts are uniformly distributed across the whole field, some type of tillage may need to be done on the whole field. In many cases, however, ruts are localized and only need localized repair. Remember the negative consequences of tillage! It will be necessary to till deeper than the depth of compaction. Shallow ‘vertical tillage’ tools that only do tillage in the top 4 inches will not be sufficient to manage soil compaction. Very tough shanks are needed that will penetrate instead of bounce on top of the compacted layer. New subsoilers can do maximum fracturing without doing much surface disturbance with straight or bent-leg shanks. Parabolic shanks do much more surface disturbance and will need more secondary tillage for seedbed preparation and are therefore not preferred. Deep tillage may be what you could use in the fall, and then come back in the spring to smoothen the field up with a field cultivator or disk harrow. However, it may be tough to find the right soil moisture conditions this fall for deep tillage. Deep tillage should fracture the soil and it therefore needs to be performed in relatively dry soil. With the temperatures coming down now the soil is not likely to dry out sufficiently, and it may be necessary to wait until spring to do deep tillage. Deep tillage can be performed in a living cover crop in the spring – if you use the modern, low disturbance subsoilers.  So let subsoiling not deter you from planting a cover crop. The more tillage you do, however, the more you set yourself up for increased compaction problems in the future.