Monday, November 2, 2009

Soil Scars and Dressing your Dirt
No dig methods for growing veg

Part I: It's not just you

Believe it or not, common folk are not the only people interested in no/low dig gardening. Agricultural scientists have been looking into ways of lessening the use of the plow to preserve the health of the little 'e' earth, which will help feed us in farther futures than generally we pursue with these types of advancements. Disheateningly, as weeding is one of the things accomplished in big farm frequent tilling, a commonly suggested alternative is nuking the ground with Rounduptm and of course planting rows with the requisate Rounduptm ready crops.

This post does not recommend the use of death-icides for normal gardening or agricultural practices (or at all really).

What is it exactly that Big-Agri is trying to prevent by no/low tilling? Soil, like water or air, is a natural resource required for our life, and the biosphere as we know it, and therefore should be preserved. Good agricultural soil is a complex 3D structure stuffed with both floral and faunal organic materials. It has a porous structure that allows for the movement of both water and nutrients, as well as root penetration. When you till the soil, you break up the structure, alter its ecosystem and bring humus (broken down vegetable matter or the manna of soil) to the surface where it breaks down more quickly. Essentially you start to degrade and use up your soil. Overworked ground is tired. Bare dirt is exposed to the ravages of wind and water runoff.

In the backyard gardening world, no-till is commonly referred to as no-dig, including methods such as lasagna gardening, and topdressing. Instead of double digging and ammending the soil in the spring, compost etc... are spread on the surface and garden beds become strict no step areas to prevent soil compaction. In annual vegetable growing, disease causing plant remains, are removed from the garden and hot composted to kill off the organism, or removed entirely. Yearly (or more) addition of more organic matter is generally required to keep a thick surface mulch.

Like anything in life, it is not all rosy as there are some problems with this method so let's address them quickly.

The Problems

1. It promotes the growth of perennial weeds - Turn this around into, it prevents the growth of weeds, many of them annual that are typically found on disturbed ground such as lamb's quarters as these seeds need some light (to be brought close to the surface) to germinate. Tilling constantly rotates this seed bank to the surface for sprouting. Agricultural researcher Hida Manns,* writes about this fascinating succession of annual to more mixed weed growth in her technique where she does not only askew most digging, but also uses heavy mulching and weed management. Instead of pulling, she keeps the weeds at a lower height between the rows (to prevent sun competition I imagine). These meadow strips create an ecosystem of bug and pest busters between her vegetables. Her findings have been that crop yeilds are similar but the losses are from different reasons. A weedy garden probably suffers from some root competition but suffers fewer losses from diseases. The biggest advantages, beyond labour saving, is the lack of death-icides, as well as the preservation of the soil.

If you are concerned about perennial weeds, especially if they are difficult ones like couch grass, etc... you can try smothering with layered cardboard in heavily infested areas. Remember to pull as soon as you see them too. A little bit of digging to get out the tap roots is a-okay with me.

2. It slows the warming up of soil in the spring. Bare soil bakes faster to be sure and if you have a muddy field in a foggy land, I can see the attraction of getting a headstart. An alternative might be to raise your beds as well as to continue to topdress organic matter to the soil in order to lighten the texture. Slanting the garden toward the south when first shaping beds or planting on a southerly slope can create a warmer microclimate. Plasticulture such as mulching with clear plastic, cloches and row covers may also help to raise soil surface. If you heavily mulch, you may consider moving back the top layer of mulch that is not broken down to reveal your planting rows and once the seeds have germinated, move the mulch back.

3. It increases disease or pest problems. Ultimately, I don't believe this criticism. I can see how it applies to the agricultural practice of leaving crop debris on the soil to prevent erosion. However, heavy mulch can make an niche for certain pests such as slugs and mice even as it prevents others such as cucumber beetle from heavy infestation.

4. It robs the soil of nitrogen. Okay, this one originates from methods that start with a heavy unbroken down floral matter such as straw, leaves and the like. In the beginning of the composting process, nitrogen levels can fall as the soil organisms sequester it. Adding materials with high nitrogen such as manures, should help balance this problem. As reassurance, I have never noticed this in my garden but I use a variety of different mulch materials such as grass and other green clippings, autumn leaves, manures, and compost. Too much of any one thing may be problematic. This method can be compared to surface composting so add your greens with your browns.

Part II - I wanna try - realizing your no-dig dream
Coming next week


* Looking for info on Hida Manns, contact me, and I'll try to help, she's not easy to google.

Excellent Wiki entry on No Till Agriculture

Scientific America article (a 'innovation' friendly mag, with dubious green credility at times)

1 comment:

Dawn said...

I only just learned about not digging and totally agree. I was shocked at the weeds that appeared in my last year in my nice clean raised beds when I used my garden claw. This year, no digging allowed. I'll just spread on a layer of compost and or peat moss before planting.