The weather is warming, it's spring and you've got the itch to plant your garden. For many, that means it's time to pull out the rototiller and bust up the dirt. But wait! While tilling is an age old response to compacted earth, we now know that it creates far more problems, including the same problems we seek to remedy! Here's 5 reasons to leave that rototiller in the shed.
1. Increases soil compaction. Yes, you read that right, it actually increases compaction by forming a "tillage pan," a layer of compaction at and below the depth of the tiller. That compaction layer discourages root penetration and encourages water to perch there. When water can't filter effectively through the soil, you end up with anaerobic conditions--the kind of conditions that foster diseases and root rot.
2. Destroys soil structure and kills beneficial soil life. Healthy soil is full of diverse beneficial microbes that cycle nutrients continuously and provide necessary structure to soil with their biomass, waste products, and by exuding glue-like substances that bind soil particles while maintaining pore space. Tilling is like putting all of that into a blender and pulverizing it. Fungal strands that could have provided nutrients, water, and disease protection to plant roots are sliced up and destroyed. Diversity and numbers of soil life is drastically reduced. See the video at the end of this post for a demonstration of soil structure and what happens when you have none...
3. Releases carbon into the atmosphere. Tilling initially mixes oxygen into the soil, which supercharges the decomposition of soil organic matter, thereby releasing C02 into the atmosphere. It releases a pulse of nutrient as well, but it is short lived. While it is micro-organisms that perform the decomposition, the number and diversity of those organisms is reduced. The long term reduction of organic matter decreases the soil's ability to hold water and air, and reduces soil life even further. Weeds flourish in these conditions.
4. Reduces the soil's water holding capacity. If you've pulverized the soil, the structure the soil life has provided (as in #2 above) is now pulverized. Good structure keeps water and air suspended around the root zone of plants. Organic matter also holds an enormous amount of water and air, but because of the accelerated decomposition of that organic matter (as in #3 above), there is less of it too. As if that's not enough, pulverized soil has a tendency to crust over, particularly after surface watering or rain, causing greater susceptibility to runoff and erosion. See the video at the end of this post for a demonstration of how water and tilled soils interact...
5. Decreases plant available nutrients. Soil life is responsible for the cycling of nutrients. They consume organic matter, each other, and some fungi even decompose rock. In the process, they convert these things into plant available nutrients on a continuum. In turn, plant roots provide sugars and complex carbohydrates to the microbes that benefit them. Tilling interrupts that cycle and the soil needs to recover in order to function at it's best.
So what's the alternative? In the short term, use a high quality broadfork or digging fork to loosen your soil and incorporate a healthy dose of organic matter. (Cheap tools will make your work exponentially harder, so invest in good tools!) These manual alternatives are much less destructive, and can go deeper than a rototiller anyway. You don't have to kill yourself, just place a layer of compost over your bed and then loosen the soil. Some of the organic matter will mix into the soil. The microbes will do the rest. Keep the soil planted. Always have live plant roots growing to keep the microbes happy and increasing in number. Plant intensively--no bare soil! Plant cover crop in the off season and in bare areas year round. Mulch! Wood chips are particularly attractive to fungi, and our soils could use more fungal life. Your soil will get better and better over time.
Here's a short video demonstrating some of the effects of tilling. Worth a few minutes of your time!