No-Till Gardening
With Minibeds-on-Plastic
(The Glomalin & Mycorrhizal Factor)

Dateline: 11 March 2017

Amazing beauty, on a microscopic level

My new Minibeds-on-Plastic experimental garden will be a no-till vegetable growing system. There will obviously be no tillage under the plastic-covered "ocean" of garden space around the minibeds, but there will also be no tillage in the minibed "islands" themselves. Or, perhaps I should be more precise and say that there will be very minimal tillage.  I see this as a critically important aspect of the Minibeds-on-Plastic system. And I'd like to explain why...

It so happens that tillage of soil does not improve soil tilth, which is to say, it does not improve soil structure. Which is to say, it does not contribute to porosity and aeration of soils. Those physical characteristics are a very important and desirable thing in any garden soil.

In years past, when preparing my soil for spring planting, I rototilled my whole garden until the soil was soft and fluffy. The freshly-tilled earth was beautiful. It was a clean canvass on which to create another garden masterpiece (or so I always hoped). 

I thought that was the right way to prepare a garden. But I am fully persuaded now that such tillage is not a good gardening practice. It is not good for the soil. It is not good for the plants. It is actually counterproductive. Since I stopped the wholesale annual rototilling of my whole garden a few years ago, I have had more productive gardens. I think there is a connection there.

The reason I now believe no-till (or minimal-till) gardening is worlds better is because I have learned about the importance of soil structure and, in particular, the role of mycorrhizal fungi in developing a healthy soil. This deserves some explanation...


The Mycorrhizal Factor

The picture at the top of this page shows a mycorrhizal arbuscle that has invaded the root cell of a plant. It isn't a hostile invasion. It's a mutually beneficial (symbiotic) association that every gardener needs to understand. The plant benefits gained by mycorrhizal fungi are manifold. 

First, you need to know that the plant feeds the fungi. As we all learned in elementary school, plant leaves take sunlight and carbon dioxide from the air and "manufacture" sugars (carbohydrates) in the process of photosynthesis. Some of this photosynthate goes into the plant growth, but not all of it. 

It turns out that plants do not just take from the soil when they grow. They actually leak or pump (two words commonly used, though probably not technically accurate) a surprising amount of their photosynthates into the soil to feed various microbial life forms in the soil, and mycorrhizal fungi is one of the major consumers of these leaking photosynthates. 

So, the tree-like mycorrhizal structure (arbuscle) in the picture above is taking in photosynthates in order to live and grow. In return, the growing mycorrhizal fungi sends out an extensive network of threadlike hyphae into the soil well beyond the plant roots. These hyphae are finding water and nutrients in the soil that the plant's roots can not access and they are feeding these to the plant. 

When you see one of those amazing illustrations of root systems that were painstakingly mapped out by Professor John Weaver in 1927, they don't show the extensive network of mycorrhizal hyphae that may also be at work with those roots. Imagine this Weaver down-view of the root system of a mature corn plant with an equally large, if not larger, network of hyphae acting as root extensions...





Plants that are colonized by mycorrhizal fungi will be better nourished, and better hydrated (drought tolerant) than plants that are not. The difference is clearly visible aboveground.

Mycorrhizal fungi also help defend their host plants from pathogens. And, amazingly, scientists are learning that these fungi are part of a subterranean communications network between plants and soil microbiology.

Aside from helping plants to grow better and be healthier, it turns out that mycorrhizal fungi benefit not just the plant, but the soil structure around it in a profound and very desirable way. This is worth understanding a bit more...


The Glomalin Factor

Mycorrhizal hyphae that spread through the soil produce a substance called glomalin (which was discovered in 1996). Glomalin is a biological glue that helps bind soil particles together. Glomalin-glued soil particles are what gives a soil better tilth. Better aggregation is another way of saying it. 

Aggregation creates large and small pore spaces. In a well aggregated soil structure, water is more freely absorbed and drained down, leaving better aeration, which is conducive to the health of all kinds of good soil micro-biota. You can see this so clearly in the video at the bottom of this post.

Now, the problem with typical gardening practices (like rototilling) is that they significantly upset the network of beneficial mycorrhizal fungi, and they destroy glomalin. 

With no-till gardening, glomalin is preserved, soil structure is improved, and garden plants are able to receive the full benefits of naturally-occuring mycorrhizal fungi in the soil.


No-Till With 
Minibeds-on-Plastic

Mycorrhizal fungi and glomalin only work where there are live roots in the soil to interact with. In my Minibeds-on-Plastic gardening concept, much of the garden is covered with black plastic mulch. It is no-till soil under the plastic, but there are no plants with live roots.

This can be viewed as a drawback to the idea, but I am looking at it as a worthwhile compromise. I am forfeiting the maximum benefit to the soil of complete, live-root, no-till in return for easier (much easier) manageability of the whole garden space, with high productivity from focused attention on the minibeds. 

Without the plastic mulch, garden weeds will get ahead of me and take over. That has been my past experience with a large area of garden. It's discouraging and it's not productive. And it's always a hassle getting the garden back in shape after the weeds have taken over. This will not happen with a manageable Minibeds-on-Plastic garden (and I won't have to get my rototiller out to make the clean canvass again).

Since I will not be digging the minibeds, all roots, along with all mycorrhizal hyphae and glomalin will remain undisturbed in the soil. These roots (and hyphae), along with other beneficial microbiology will extend beyond the minibed perimeter.

Also, as part of my minibed no-till approach, I will be rotating root-dense cover crops into the minibeds. Rye, in particular, for fall to spring cover cropping, will put enormous root density into the soil. 

My cover cropping will not be dug into the soil (as a green manure). The top growth will be harvested, chopped up, and used as mulch on the beds, or incorporated into a compost pile.

So that's my concept of no-till gardening with the Minibeds-on-Plastic gardening idea. 

Dan Grubbs has asked about the potential problem of high heat under the black plastic. It may not be an ideal environment for beneficial soil organisms. Yes, that might be a problem, especially in certain growing zones, as I explain in my Minibeds-on-Plastic Report #1 (see Question 15 on page 25). If it turns out to be a problem for me, I will put a layer of wood chips over the black plastic.


Some Fungal Loose Ends

Mycorrhizal fungi are just one of many different kinds of fungi that are in soil. Some fungi work to break down organic matter. Some are pathogenic, but most fungi are good.

Mycorrhizal fungi can and will develop a symbiotic relationship with most plants, but it does not cooperate with the brassicas.

Mycorrhizal fungi are naturally occurring in most garden soils. They will naturally proliferate under the right conditions (no-till).

You can purchase mycorrhizal inoculants for your soil. The effectiveness of these inoculants is questionable.

There are bacteria that also create bio-glues that aggregate soil, on a smaller scale.




Evidence Of 
Good Soil Structure

This video with Ray Archuleta is a powerful testament to the benefits of no-till gardening and farming. You must watch this!




10 comments:

  1. Mr. Kimball - I am a big fan of both of your blogs, although I've been too shy to comment before. Thank you, by the way, for your wonderful work. I have a question. We live in Missouri, and no-till is really catching on in many row-crop farm operations in the Kansas/Missouri area. This is why I am skeptical of it. But I am interested in learning more, and you have further sparked my interest. I'm concerned with how the soil can be amended with compost without tilling. I've always roto-tilled it in, but can you give me some advice on this? Thanks again - Bryan

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    1. Hi Bryan—

      I think many commercial farmers are switching to no-till because they are realizing that their paradigm is financially unsustainable. Many of them are still using herbicides and synthetic chemical fertilizers, but they are using less and saving money while getting good results.

      Surprisingly, the US government, through NRCS people like Ray Archuleta, are really spreading the word about no-till, and for all the right reasons. I'm kind of amazed about that because the chemical conglomerates like Monsanto and Bayer can really pull the strings in Washington. They will lose money if no-till catches on.

      It was Ray Archuleta that really convinced me that no-till is the best thing for soil health, as I wrote about in THIS BLOG POST. And gardening success all rests on soil health. In more ways than we've realized, it's the organisms in a soil that are actually determining the success or failure of any crop planted in the soil.

      I used to till in compost but stopped a few years ago. Now I just put compost, mulch and occasional organic fertilizer (kelp meal, primarily) on top of the garden bed. Or I may stir it into the top couple of inches of soil. I'm not disturbing the soil below 2" unless I'm setting a transplant.

      At this point, I'm persuaded that top-dressing of organic matter is superior to putting it under the soil. Top-dressing is the example we see in nature, just like no-till is the example we see in nature. Rain will leach the nutrients into the root zone, and soil biology, like bacteria, fungi, and earthworms will consume and incorporate the top dressing as needed.

      Thanks for the comment and question.

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    2. What an amazing coincidence! I just had the pleasure of hearing Patrice Gros speak on this subject (and more) this past week in West Plains, MO. He's been very successful producing organic vegetables year-round for sale at farmers' markets in Bentonville, AR from his no-till garden beds and high tunnels. My family is planning to give the concept our best try this spring/summer to complement the grass-fed beef that we sell at market. Time will tell, but I would be very happy to retire the tractor and rototiller.

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  2. Thank you for your answer. This makes more sense to me. We used to leave scraps and plant matter on the surface of the garden through the winter months and then till it in in the spring. Doing it this way, we pretty much had to till it in before decomposition would begin. However, if we use a compost pile, the decomposition will already begin through those months, and then we won't have to till it in. We can use that great organic matter/compost as a top-dressing like you said. Thanks again for the advice! -Bryan

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  3. What is the best way to water the garden if it is covered in plastic?

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    1. My Minibeds-on-Plastic gardening system is modeled after Tom Doyle's Plant-and-Pick system, which consisted of a large sheet of black plastic and small planting holes in the plastic. . Mr. Doyle NEVER watered his garden and it thrived through droughts, when his neighbor's gardens dried up. I explain all of this in my Minibeds Report, but the gist of it is that most areas of the country have an enormous reserve of subsoil moisture that is continually rising to the surface by capillarity. The black plastic sheet holds the water from evaporating so the roots can access it. This dynamic, coupled with proper plant spacing means that no watering is necessary—unless you live in an arid region of the country.

      If plant roots are continually watered by artificial means, their root system will be shallow and dependent on the artificial source of water. On the other hand, if seedlings are watered enough to get their tap root established, that root will go deep and the roots will find the water they need in the subsoil. That's what roots are for. If the plants aren't crowded too close together, they will get the water they need on their own.

      I have a well-drained sandy/silty soil and rarely water my garden. When I do, it is only spot watering of fruiting plants in a particularly dry spell. Even then, I think I'm watering more to satisfy myself more than I am watering to satisfy the plant's needs.

      That has been my experience. I'm sure some gardeners will disagree with me. :-)

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  4. I'm in N. Texas where clay or suburban fill is the norm. In principle, would you think this idea would work just as well if I first fill the boxes with good soil and compost. The plastic would kill off the rhizome running grass and I could later amend the clay soil.

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    1. Jim,

      I wouldn't fill the boxes. They will dry out fast. That was my experience with wood-side raised bed gardening. I explain this in my report. And the Rhizome grass will grow right up the insides of your beds. I know that from experience too.

      If I had a rhizome-infected piece of land that I wanted to garden, I would cover it with a big sheet of plastic for a whole year to kill the rhizomes. Then I would lay out the minibeds, keeping them in about 4ft from the perimeter. Then I would plant cover crops in the beds to get live roots and biological activity going on in the soil.

      If the soil is real dense, there are cover crops with powerful roots that will break up the hardpan (this is also discussed in my Report). A sorghum-sudangrass hybrid will grow for you and it will really get your soil in shape. I have only read about the Sorghum-sudangrass, but I just bought some seed from Johnny's and am anxious to plant some.

      Cut the grass low, don't till the soil, and plant into the bed after all of that and I think you will find success on that spot. That's just my opinion, and what I would do based on what you have told me. And it's not a fast solution. :-(

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