Fallow Fields

I was talking with a friend this morning, and she reminded me that I haven't blogged here in a while... so... here goes: Let's talk about land, crops, and water.

The soil in Northern Nevada has very little humus in it... not surprising since it used to be a huge lake bed at one time. It's mostly sandy clay loam. Ok, Margie, just what does that mean?

Soil is made up of particulates. The smaller the particulate, the more compact the soil can get. Clay has very small particulates. Sand is a little bigger. Humus is a different animal altogether: it's more plant than mineral.
The sand doesn't hold much water. Sandy clay will hold some water; but the clay compacts around the sand as it dries. Good ol' desert concrete.
Humus can help fix that.
100 pounds of humus will hold 195 pounds of water. That's 23.4 gallons.
By its nature, humus will swell with water added... which helps break up the clay particulates.

In northern Nevada, I think it's folly to allow fields and gardens lay fallow for any length of time... even over the winter months. Several things can happen by allowing it to just lay:
1. Water erosion - The heavy, fast rains that Nevada often experiences (especially in flash-flood areas) can sweep that precious topsoil right down the gutter.
2. Wind erosion - I don't think there's many places in Nevada that doesn't experience high winds that can whisk away dry humus off the top.
3. You can alternate your crops so the nutrients that one crop takes out, the next crop will put in.
4. By planting a winter crop, you can add even more humus into the soil.
5. The longer it rests, the more susceptible it becomes to weeds.

One year, plant a grain like winter wheat.
The next, plant a brassica like kale.
On the third year, plant a legume like fava beans.
Sow them in the late summer, water them until first frost, then forget about it. Turn it under in the early spring (that warm snap we usually experience in February is ideal). Till it again about two weeks before you intend to plant, and you'll have lots of good humus for the seedling to wrap their filliment-fine roots around.

Each type of wintering crop provides something necessary to the soil (potash, phosphorus, nitrogen, etc)... but the most valuable asset they provide is green-composted humus. One thing to remember is that with most plants, the amount of organic matter you see above ground is about equal to what they've got below the surface.

Knowing all that, why would anyone want to let their soil "rest?"

The concept was developed in monoculture farming. If you were a corn farmer, then that's what you grew. If you were an alfalfa farmer, then that's what you grew.

When you plant the same crop in the same place year after year, you rob the soil of the specific nutrients that the crop uses the most.
Take tomatoes for example: the nutrient they use most is nitrogen. Anyone who's tried to grow tomatoes can tell you that you have to amend the soil with a lot of nitrogen for a good crop.
Now, let's say we decided that we're going to winter some fava beans (or other legume) in the plot where we usually plant our tomatoes. Legumes absorb nitrogen from the air and create nitrogen nodules on their roots, as well as storing some in their vines. Over the winter, we've effectively replaced a lot of the lost nitrogen back into the soil. That's effective land management.

Another reason that monoculture farmers allow fields to lay fallow: the green compost of some crop will retard the growth of the same crop the following year. Take alfalfa for example: it's nearly virtually impossible to harvest an alfalfa crop without losing some leaves onto the ground. The chemical makeup of those leaves retards the growth of alfalfa seed for the next year (or two). That's still no reason to let it lay fallow, though. Because you see, most small grains/grasses or corn will grow just fine in an alfalfa field. Alfalfa is a legume, so the crop following will have the benefit of the nitrogen fixed in the soil.

You can grow one ton of cover crop per acre.
That's 2000 pounds of humus.
That would increase the water retention ability of the soil by 468 gallons per acre... every year.

So, again, why would anyone want to let their land lay fallow?