No-Till Gardening

To the left is a picture of a beautiful cover crop, ready to be incorporated into the soil.  If you mow it, then till it in, it will be ready to plant in a few weeks, at which point the clock will be ticking.  Cover crops reach their highest nutrient density just as they begin to flower. Conventional wisdom has this as the moment they are to be mowed down and tilled into the soil in order to build organic matter. What happens is that as the lush green cover crop begins to decay in the soil, the microbe population explodes.  A flush of nitrogen is released into the soil and a flush of carbon dioxide is released into the air.  If you’ve just planted a new crop of seeds or put in transplants, they will start off with a big flush of nitrogen-induced growth. But, there is more nitrogen available than the small plants can use. As time goes on, the food source (your decaying cover crop) will be used up and the microbes begin to die off. Your new planting begins to slow its growth as the nitrogen release fades.  Four to six weeks later as your crop heads towards flowering and seed formation, the nutrient release from the cover crop is long gone.  The crop languishes until you add more nitrogen as a side-dress or liquid.

If instead the cover crop is killed by putting a tarp over it, the decay process is slowed down.  Before covering with a tarp, the cover crop can be mowed down with a string trimmer, which leaves fairly large pieces of the above ground plant parts on the surface of the soil.  The tarp excludes light and is left on several weeks until the plants die.  The root mass begins to decay in the soil while the above ground plant mass begins to decay on the surface. Now the surface organic matter decays more slowly since it is out of reach of most soil organisms except worms and fungal mycelia. When we lift the tarp we find a huge amount of earthworm activity on the surface.

And pleasantly enough, the area that has been tarped doesn’t grow weeds easily.  Weed seeds are no longer brought to the surface with tillage or buried with tillage.  A fine mulch is left on the surface which helps to conserve soil moisture and tilth for the next crop, and continues to release nitrogen into the soil.  The overwhelming microbe party associated with tillage never happened. In our loamy sand soil, the seedbed is ready to plant. For those with heavier soil, a tarped bed may require loosening with a broadfork occasionally to bring in air to the bottom of the bed. In that case, the soil is not turned over, but is just gently loosened from the top by rocking the fork back and forth.

Tarping works so well for us that now our BSC tiller remains quietly in the garage.  We can now build up fungal populations in our light soil.  There is no disturbance of earthworm tunnels.  When we add the few minerals that are required annually in our soil (boron and gypsum) we can just add them to the surface and allow the rain and occasional overhead irrigation to carry them down. The only time we need to disturb the soil is if we want to incorporate something into the entire top six inches as we might do if we were starting a new planting bed or incorporating biochar.  In general we try to avoid disturbing the soil as much as possible.

***Fast forward three years***

We practiced a sort of No-Till vegetable gardening here for 3 years. I wanted to get some charged biochar deeper into the soil, so I abandoned No-Till, and began forking a bed in preparation for onion transplants.

This is what I found (see picture at right).

In 10 feet of bed I found tree roots to cover two folded shopping bags. Our trees are not particularly close, but they did find their way into the moist and fertile garden. Please consider if you might want to explore for invasive roots while adding minerals.

It is generally better to dig amendments into the soil if doing a major re-mineralization.

Mineral amounts are directly proportional to the depth of the beds. We figure an amount for no-till that is equivalent to digging the amendments in 6″ deep. If you have a 9” bed and are willing to dig the minerals in, multiply the amounts by 1.5. For a 12” bed, multiply by 2.

Growers have different ideas of what no-till means. When I pull weeds, I often insert a fork, and gently rock the soil without turning it. If you do this, you may be able to mineralize to the full depth of the beds while watering in (as described below). For the purposes of this paper, we do not consider using a fork (even to loosen weeds) as No-Till.

There are application work-arounds for most of elements using strict No-Till methods. Lime needed to raise the pH is an exception. It needs to be dug in. Phosphorus can be applied as a high P liquid fish every 7-10 days throughout the growing season. This is obviously much more work than establishing a phosphorus reserve in the soil. But, the phosphorus in soft rock phosphate is immobile in the soil and needs to be dug in.

Some minerals are mobile in the soil, and some are not. This is crucial information for mineralizing a strict No-Till field. The chart on this page is for minerals in their elemental form. All the minerals are mobile in their sulfate form, though some are more mobile than others. The mobility of the sulfates is proportional to their salt index. Gypsum, for instance, has a salt index of 6 on a scale of 100, so although it will move in the soil it is not easy. Magnesium sulfate (Epsom salts) has a salt index of 53. Potassium Sulfate is about 43. The salt index also tells us how easy the sulfates will dissolve in water.

Some minerals, Nitrate-N, Boron, and Sulfur are quite mobile in the soil. They generally need to be replaced for every crop. These should be applied close to transplanting or seeding in the spring. If growing a fall cover crop it is generally worthwhile applying sulfur (usually as gypsum) and boron close to seeding the cover crop. The amounts required are quite small, and they can be re-applied in the spring.

The other minerals can be applied anytime. Some are better applied in the fall; elemental sulfur (if required to lower the pH) and lime (if required to raise the pH).

Here is a general guideline for No-Till mineral applications:

• It is best to have no plants growing in the area to be mineralized. If this is not possible, wash the leaves when done to remove any mineral dusts.
• Remove any mulch.
• Consider whether you want to check for tree roots in the soil. If there are tree roots, consider digging the bed to remove them and at the same time apply the amendments.
• If the bed is deeper than 6” and you are going to dig in the minerals, increase the mineral amounts (see above).

All the minerals (except lime, oyster shell flour or rock phosphate) can be cast on the surface and watered in at the same time. Add a couple drops of ivory soap or other surfactant to help the water penetrate the soil. Do not water to the point of runoff.