JustinM

Justin Morris
During our Soil for Water premiere, the following question was asked: What kind of tillage do you recommend to improve soil conditions without damaging it?

This is an excellent question. The short answer is that all tillage damages the soil. This is an inescapable fact. But another fact is that not all tillage is equal in its level of destruction. Because tillage is a disturbance, there are at least four dimensions to it. They include: 1) timing, 2) frequency, 3) intensity and 4) depth. Understanding each dimension gives us insight on how to reduce the negative effects of tillage.

Timing

Soil particles sticking together to form aggregates with lots of space between the aggregates are what makes great soil structure. Soil life in conjunction with plants create this structure that allows water to infiltrate and be held in the empty spaces of the soil. Tilling wet soils is a recipe for smashing and tearing apart aggregates as well as causing compaction from the weight of the tillage implement and the tractor pulling it. To minimize damage to the soil, the soil needs to be as dry as possible when tilled.

Frequency

The more frequently a soil is tilled, the longer it takes for soil to begin functioning the way it should because it takes time for soils to begin the re-aggregation process. Disturbances such as tillage can be categorized as being either acute or chronic. The difference between a disturbance that's acute versus one that's chronic is the time between disturbance events or in this case the time between tillage events. The soil ecosystem can recover from an acute disturbance, but it cannot recover from a chronic one. So how do we determine what that amount of time is between acute and chronic? It's the time it takes for soil to recover from the prior tillage event where we see soil aggregation beginning to occur. If soil is able to re-aggregate then the disturbance would be acute, but if the soil can't re-aggregate then the disturbance is chronic. Usually under the most favorable circumstances, it takes at least a few years to get any significant soil aggregation to occur. Tillage occurring every year in the same spot will be counterproductive to building stable soil aggregates and improving water dynamics. If tillage must be done, the frequency must be as low as possible given the cropping sequence. Ideally, a tillage pass happening once every four or more years would be much better than one where tillage occurs annually. A cropping sequence that involves a perennial pasture phase of at least four years would be excellent for restoring soil aggregation. Following the perennial pasture phase, the pasture could be terminated via tillage then planted to annual crops with cover crops in between the annual crops. After three or four years of cropping, the land would be planted back to perennial pasture for another four years. Interestingly, this rotation mimics what our ancestors did pre-WWII when herbicides and chemical fertility were not widely available.

Intensity

This refers to how thoroughly the soil is worked to get the particle size of the soil smaller and smaller. The more intense the soil is worked, the more the soil appears to have a nearly flour-like consistency which also means that soil aggregates are being torn apart - not good. When soil is worked at a very high intensity, this is analogous to your house experiencing a F5 tornado and a 9.0 earthquake all at the same time - total devastation! Multiple passes with a disk harrow to break apart the soil particles so they're finer and finer or running a rotovator/rototiller at full PTO speed with a very slow forward speed destroys soil macro-aggregates by acting like a blender. This prevents water and air from entering the soil while also preventing carbon dioxide from leaving the soil to help drive photosynthesis. To reign back the intensity of tillage, reduce the speed of the spades on the rototiller so that the soil isn't blended and soil aggregate damage is minimized. This can be done by changing the speed of the gearbox so the spades slow down and increasing the forward speed. Rotary spading implements like those from Imants out of the Netherlands don't have horizontal spades that smear the soil surface like a rototiller and therefore when operated correctly do less damage to the soil.

Depth

The greater the depth of tillage, the more invasive and potentially the more destructive the tillage becomes. If the goal is to get more soil organic carbon into the soil, deep tillage unnecessarily exposes certain bacteria called R-strategists to the atmosphere. When these bacteria encounter oxygen, they begin feeding on the glues that bind soil particles together that create stable soil aggregates. These glues are comprised of carbon which means that these bacteria are eating up your organic carbon which is 50 to 58 percent of organic matter. The deeper tillage goes, the greater the number of these bacteria begin eating the carbon that plants placed there. To minimize the damage done by tillage, till at the shallowest depth as possible to accomplish the objective. In situations where there's a root restrictive layer (plow pan) that's several inches thick, I can see where it would be prudent to use a subsoiler or ripper to break through the plow pan. But, if this implement is used, it needs to immediately be followed by a deep-rooting cover crop mixture so that roots can follow the fissure or crack created by the subsoiler. As the crack closes, plant roots can continue growing past the plow pan so that in time the plow pan is somewhat reduced and no longer restricts root growth. If a cover crop mixture isn't planted immediately following the use of a subsoiler, you'll likely have to go back and re-rip the field again and again which is expensive. The goal should be to only use the subsoiler once and then never have to do it again. But the only way for that to work is by planting cover crop mixtures immediately following the subsoiler pass.
 

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