Friday, April 1, 2011

Garden Cover Crop Field Trial - Results

As I posted a few times last year, topsoil is a scarce commodity at the City Farm.  Partly because it's on a slight hill, but mostly because few or no gardeners undertake any soil conservation practices.  I guess with a 10' x 30' plot, it's easy enough to neglect. 
I also knew that I worked really hard to establish good soil in my first season there (2010), and there's no way I'm giving it away to the creek (where it ends up).  So I tried two fall-sown cover crops - Austrian Field Peas and Mammoth Red Clover - and planted each one two different ways.  All plantings got a shot of Royal Peat legume innoculant (to start the nitrogen fixing bacteria on their way).

Trial 1: Austrian Field Peas: planted and innoculated in rows

Trial 2: Austrian Field Peas: broadcast w/innoculum, worked into upper topsoil

Trial 3: Mammoth Red Clover: planted & innoculated in deep topsoil

Trial 4: Mammoth Red Clover: broadcast over compacted soil, gently worked into upper topsoil.

Trial 5: Soil opened for seeding by weeds

When the snow melted in late February, it was pretty clear that the Field Peas won the day. A month later, at 8" tall, it was even more clear.  The clover is still struggling to beat 1", and (I'd propose) has done little to nothing to protect the soil from raindrop impact or runoff over the winter.  Which, after all, was the goal of this field trial.  I was pretty surprised that the clover even grew on the compacted soil, but it eventually took.  It's interesting to compare all of these to the unplanted bed, which grew almost no weeds over the winter, but lost a fair amount of soil by flooding out under the raised bed. 
Another key component of this cover crop experiment, since I selected two types of legumes, was to increase organic matter and fixed nitrogen in the soil.   While I'll leave grams and calories to the real scientists out there, it's clear that the field peas accumulated root mass and nitrogen nodules over the winter (all of which will be turned under), while the clover did significantly less work below ground.
The third and least important component of this cover crop experiment was to determine which plant would provide more compost or "green manure" when cut or tilled under this spring.  It's not super important to me because I will probably compost it all at home with the rest of our leaves, table scraps, etc.  Nonetheless, the results are pretty obvious.

Between the two planting methods for field peas I didn't see a huge difference.  For comparison:
Planted in rows

Broadcast and worked into topsoil

It's rare that I experiment with anything in the outdoors and get obvious results (other than obviously bad ones).  I guess this is the exception and I'll be ordering twice as many Austrian field peas this summer! 

If you are new to this whole concept and would like to learn more, take a look at this NRCS-funded guide to cover crops.  Or this Purdue University guide to selecting a cover crop.  Oregon State University wrote this up for you about Austrian Field Peas.  And Penn State U. would like you to read their notes on Red Clover.  Most cover crop seed is available seasonally at your local farm supply store by the pound (or 50lb bag), and small amounts (even less than a pound!) are often available at high end garden centers, especially from August to October.

Remember that your soil is a resource and that soil conservation is a wise (and in my opinion, patriotic) thing to pursue.  Your soil doesn't belong downstream.  Why would you give away your land?  The fish don't want it, and God knows, taxpayers don't want to pay to dig it back up out of the river. So plant some cover.


Michael J. Budd said...

How big is your garden overall, is it 10x30. My wife and I want to start a community garden in Crossett. She came up with the perfect spot and I need to start mapping out plot locations and how many folks (gardens) the site can hold.

On another note, I built a big veggie box that I'll unveil on my blogsite soon. When I started piecing it together using pressure treated lumber, my brother-in-law had a good question: "Aren't you worried about the chemicals used in the pressure treating process leaching into your soils and ultimately your plants, especially the first couple years while the wood is still drying". Any thoughts on this? with enough soil, it shouldn't be a problem.

Kirk Mantay said...

Hey Mike. Mine is 10x30, but a lot of the plots are 10x20. 20x30 would be ideal for me, but that's also because I plant a lot of wildflowers for the bees. You need a grassed or mulched walkway every other row, and a very wide exterior grassed/mulched walkway. Other important consideration is water. Can you get it there?

The "new" treated lumber is not literally carcinogenic like the old stuff was, but the "new mix" (CCA) still contains arsenic. This article found that after three years, elevated arsenic levels were only found in the soil right up against the wood.

But as you know, anywhere south of PA & Michigan, you'll have to choose between natural wood + termites (and replacing the lumber every 5-7 years - maybe less in Arkansas) or the arsenic (wood should last 12+ years).

If your beds are at least 4x4, I would guess that contamination isn't a realistic issue. Mine are 4x8 (4 beds), with 2 beds at 4x2.5. I used natural wood because it was cheap, and I had some on hand.

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