What is soil tillage and what are the effects of it on soil? What does Zero Till mean? And how do I know if I should till or not?
What is Tillage?
Tillage is “the manipulation of the soil into a desired condition by mechanical means.” (1) Tillage can happen in your flower pot, raised garden bed, or on a commercial field. Tillage usually happens using tools. In the garden this can be with a hoe, rake, “the claw,” or gas powered tiller, to name a few. Tillage tools that are often used on a commercial field are harrows, vertical tillage tools, and cultivators. Tillage is used to kill weeds, mix plant materials or fertilizer into the soil and to prepare the soil for seeding.
Effects of Tillage
The biggest benefit of soil tillage is mixing plant material into the soil where microbes can break it down. I grew up on a commercial grain farm and we knew it was important for plant residue to ‘break down’ in the soil to provide fertilizer, but did not know about the microbes consuming it. We didn’t talk much about what we were going to do to promote the microbe population but feeding microbes is essential to maintaining your soil’s health. Those critters need that food. The minerals in the straw are also returned to the soil where they can be used by the next crop.
Weeds are killed by tillage. Conventional “modern” agriculture suggests that we could kill the weeds by using herbicides instead of tillage. These herbicides will also kill many microbes in your soil and pollute it with heavy metals and salts. While tillage has a minor detrimental effect on microbes, not tilling and spraying chemicals to kill the weeds is far worse in the long term.
Fungal roots, called hyphae, are broken up by tillage. Yes, fungal networks need to reestablish after tillage but their hyphae fragments are actually an inoculant for future fungal growth.
Proper tillage techniques bring Calcium to the surface of the soil. Calcium is fairly heavy and moves down in the soil over time. Your soil test can show that there is much Calcium in the soil but that test will not show where it is. Most often it is down five to six inches or deeper. This is far below the typical aerobic zone where plant roots cannot get at it. Tillage can keep Calcium up in the aerobic zone. Some farmers plow their fields every few years which flips over a 6” layer of soil, bringing that Calcium back up to the top!
What is Zero Till?
Zero Till is a practice of not tilling fields that emerged in America in the 1940s. It was a response to the Dust Bowl which happened after the breaking up of grasslands in a semi-arid region in the United States. This region typically received little rain but the deep rooted grasses there held the soil during the dry and windy seasons. When the land was plowed up it was no longer protected by these grasses. It dried up and blew up into huge dust storms.
The No Till practice that developed after the Dust Bowl was different than the practices used before modern tillage came about in the 1800s. Modern Zero Tillage includes the use of herbicides to control weeds and these have a massive detrimental effect on soil and microbes. To name a few, herbicides kill LOTS microbes, increase soil salinity, and lead to weeds developing tolerances to these chemicals effectively rendering them useless for weed control.
Since Zero Till does not mix plant material into the soil microbes cannot break it down so they’re going hungry. Since the straw stays on the soil surface, the sun shines on it and UV light breaks it down. The minerals in the straw oxidize and enter the atmosphere. Over half of the minerals in your straw will leave your field/garden in this form if you leave your straw on the soil surface.
Straw left on the soil surface in Zero Till also plays a role in reducing the natural movement of air in and out of the soil. Soil microbes breathe in oxygen and breathe out carbon dioxide. If they cannot get what they need, they suffocate just like you and I would.
Most fields and gardens are depleted of Calcium. Due to this they are not well flocculated and the soil gets hard. I have a neighbor who does some herbicide application for someone who practices zero till. This neighbor says the sprayer drives so easily over those fields because they are packed so hard!
Should we till the soil?
In one word: Yes. After years of research, we’ve learned that No Till is terrible for soil. But so is over-tilling. You should lightly till in spring and fall, but no deeper than 1” below the aerobic zone. You will be helping your microbes get the food they need, and reincorporating nutrients for another crop. If you need to protect your soil from winds, plant a cover crop and/or cultivate in a way that prevents wind erosion. You will be holding down your soil and the plants will be feeding your microbes too.
If in the garden you would like to break up the soil a bit without completely pulverizing it you could use a tool called a broadfork.
There is a great article about straw decomposition at MeatChefTools. https://meatcheftools.com/how-long-does-it-take-for-hay-straw-to-decompose/
Notes
- Tillage – https://www.britannica.com/topic/tillage
Leave a Reply