Tuesday, May 6, 2008

Raging controversy over soil amendment

So I'm faced with the issue of what to do about the soil, which is sandy, compacted, or both, and in several places, like near the cottage, is actually subsoil that is almost pure sand.  

All I really want to grow is clover (nitrogen-fixing drivable groundcover) and other soil-building cover crops, but the soil is in such bad shape I fear even these won't take.  

For compaction Jacke & Toensmeier recommend: "Amend with organic matter and till.  Thoroughly incorporate organic matter through depth of compaction.  Compost and Compost Tea."  They give a reference:  Harris, Clark, and Matheny, Arboriculture:  The integrated management of landscape trees, shrubs, and vines.  3rd edition.  Prentice Hall 1999.
For soil-too-sandy J&T recommend: "Add organic matter:  Mulch, Compost and Compost Tea, Cover Crops, green and brown manures."

As I understand it there are two kinds of Organic Matter - decomposable and nondecomposable.  Fresh animal manure, dead leaves and other mulch, kitchen scraps, etc, are decomposable.  The nondecomposable remainder is called humus, which helps the soil retain water and the plant nutrients released when the decomposing microbes finish and die.  If I am understanding this correctly, Compost is a mixture of humus and and these plant nutrients (fertilizer.)

Solomon explains very well how there is good compost and bad compost, according to how much fertilizer ends up in it, and how making really good compost is as subtle an art as making good beer or wine.  

Here at the cottage I surmise the soil is lacking in both humus and nutrients.  I really wish I could at least give it a massive humus infusion.  It dries out so quickly.  I feel like if only I could increase the water retention and cation exchange, that would give my forage crops a big jumpstart.

One form of Organic Matter that we can get a honking lot of is old, partly rotted sawdust.  There are also the sawdust berms that were scraped off the site a couple of years ago.  My dear friends Flora and Pigpen, both trained biologists, are in total disagreement as to whether this would make a good  soil amendment.  The issue seems to have to do with its carbon/nitrogen ratio and humus content.

The books say fresh sawdust is extremely high-carbon, and Pigpen is convinced it must still be too high, so that applying it would freak out the soil microbes and cause them to flare off all the soil nitrogen into ammonia gas, or something like that.   Flora is convinced it has become a lot like peat moss and should therefore make a good soil amendment.

At the meeting we agreed to send a sample out for lab testing.

In the meantime, I started an experiment on the ground.

The photo below shows the 4x4 foot patches I made, which have different soil amendments, but are all seeded with dutch white clover.  The seed is preinoculated with the nitrogen-fixing bacteria.

The site is pad 2, one of the built-up subsoil areas, which had a house-trailer on it all last year.

  • The lower left patch just has the seed raked shallowly into the surface with no amendment. You can see the soil is gravelly sand.
  • The upper left patch has an inch of the rotted sawdust raked shallowly into the surface.
  • The upper right patch has an inch of composted humanure raked shallowly into the surface. This compost has a lot of sand in it as the humanure was composted with sandy soil as the bulking material. Pigpen thinks this is well-finished compost.
  • The lower right patch was loosened one spade deep and about half the dirt removed and replaced with four inches of the rotted sawdust. Some of the underlying soil was turned up into it and raked to a uniform mix.  I have to say it was moderately difficult getting the shovel in.
The idea with all of these treatments is to simulate something we could do on the broader scale with the bobcat, so no fussy topdressing.  

I have this vague notion that even if the sawdust amendment is too-high in carbon,  since all I'm trying to do is grow a nitrogen-fixing cover crop, maybe it won't care so much if decomposing microbes are hogging up all the pre-existing nitrogen while they are decomposing the sawdust. 

I'd love to hear from you pro-am composters out there, how you think this will turn out.

As I write it has begun to rain, the first hard rain of the season.  I hope my experiment does not wash away.

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