Brisbane Local Food

Growing local

Mel Landers posted this in Soil4Climate:

I read it a few times and loved the argument.

Mulch versus Compost - Why I choose mulch –Experience, Observation and Research

I have answered so many questions about this that I am going to post this response for everyone.

Experience:

When I was a toddler, my mother had a highly productive garden while we lived in the state of Washington where the weather was mostly cloudy with light rains. So the soil stayed moist.

I began gardening at the age of nine in Central Texas where the weather was full sun, hit temperatures and little rain. The soil was always hot dry and hard and my plants suffered.

In my teens, I mulched the soil with stones. This maintained soil moisture much better than my bare soil and plants grew better. I now realize that this also provided habitat for invertebrates and microbes that did not exist in the hot dry soil.

In my twenties, in Colorado, I tried applying compost, which soon disappeared and I was left with the same conditions I knew in Texas, except that one summer it was too cold to harvest ripe tomatoes. Then I read Ruth Stout’s recommendations and decided to do a trial and I began cutting the grass and weeds for mulch material off the flood plain next to my house

Observation:

I grew the same crops in beds covered with as deep a mulch as I could manage, without covering up my plants and I planted them in beds to which I applied compost. The plants protected by the mulch did not suffer from drying despite less irrigation and they were not infected with leaf, stem and fruit rot like the plants which by that time were in bare soil; after the compost disappeared. The plants in the mulch grew larger and produced more that those with compost. Also, I noticed that the beds covered with mulch did not suffer erosion like those with compost.

In my thirties, on my own farm, I did not produce any compost. I had learned my lesson in Colorado. But, some friends of mine who farmed organically produced large quantities of compost and purchased rock dust, bone meal, etc. Their plants thrived, but they needed to apply organic mulches to many of their crops to prevent them from suffering, despite a drip irrigation system.

I developed a seven year rotation in which I began with a deep mulch and planted different crops as the biomass decayed;
1. Beginning with potatoes planted a foot or so above the soil in the midst of deep hay.
2. The second year, I planted sweet potatoes in the rounded pile of hay that was left.
3. Then I made holes in the hay the third year to plant squash.
4. The fourth year, I planted maize, beans and small leaved squash.
5. By the fifth year, the mulch was the consistency of compost, but was two to three inches deep. Into this, I planted peanuts.
6. In the sixth year I planted tomatoes, peppers and basil with a thinner layer of new mulch.
7. The seventh year was dedicated to root vegetables like carrot, onion, beets, turnips, radishes and kohlrabi. I reapplied mulch for this between the rows.
8.
This is how I learned to grow crops in thinner layers of mulch which still
• stop the compactive and erosive force of the rain,
• prevent wind erosion,
• shade the soil to keep it cool and moist,
• feed the earthworms, arachnids, fungi, bacteria and other organisms,
• provide habitat for some of these,
• deliver minerals from deep in the soil,
• reduce weed growth, etc. (although weeds provide more mulch)

Research:

In my mid-fifties, I studied paleo-climatology and discovered the danger posed by various Greenhouse gasses. I knew from previous study that the composting process is oxidative (like fire) and produces greenhouse gas emissions just like burning does. So, I decided to see what contribution composting makes to the greenhouse effect. Although it is not substantial today, production of compost does contribute much to the greenhouse effect; with home composting contributing a lower percent than large scale composting.

If compost were to be used as a replacement fertilizer for petrochemicals, it would become a major source of both methane and Nitrous Oxide which are much more potent than carbon dioxide; not that the carbon dioxide emissions would not also be substantial if thousands of farms switched to that strategy for organic production.

Then I asked the question about the difference between mulch and compost for soil microbes. It turns out that compost does increase the number of fungi in the soil. But, there is much less hyphal generation and elongation in compost treated soils in comparison with soils protected by mulch. Thus the vital mycohrrizal associations are improved in mulched soils. This, soil moisture levels and earthworm biomass are constant regardless of the thickness of the mulch. Also, Carbon availability is the limiting factor for most soil microbes. So, gassing off the carbon in the composting process leads to less microbial growth than with the biomass being used as mulch.

I discovered that worm manure increases soil enzymatic activity in proportion to the number and size of the earthworm population in the soil. Worms need to eat. Mulch provides them with much greater quantities of food than does compost. Their greater numbers also yields better soil structure. In addition, if there is enough food to keep them fed continually, rather than for a short time, they will completely turn the topsoil twice a year in soils that do not freeze. They also transport the carbohydrates from decaying mulch deep into the soil where it becomes labile and/or stable humus. For all of this, worms need organic mulch over the soil.

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Replies to This Discussion

Interesting stuff - thanks for the info Dave.

Good discussion Dave.  It got people talking! 

Oh, I no longer feel guilty about greenhouse gas from my compost.  Having thought it through, I think this way:  I make waste. It's unavoidable I reckon.  I can either ship that waste to the tip where it creates greenhouse gas but isn't used, or I can compost it which avoids me shipping it, yes it creates greenhouse gas when it breaks down but then I use the compost (which also avoids me having to ship in a heap of soil).  

I happily throw small cuttings etc on the garden but the grass was a product of my own experience out the front on the building site garden.  Yes, it doesn't last there for ever but I swear it stopped the water getting in.  

I didn't know how coffee rock developed, I thought it was from volcanic action.  The sugar cane mulch we get has less poison than most as they are the tops of the cane just before the rest is cut.  They actually class it as organic though that is hard to prove.  

All you can do in live is try to get stuff that has not had too much human interference.

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