How to build soil in a dry climate

A reader's take on the benefits of green manure (left) versus good ol' animal manure.

"It looks like you're already getting good advice, but I do have a comment based on what I saw in the latest post. Amending the soil with organic matter to develop humus is always a great idea for all the reasons we know so well, but you have to be careful how you do it, and the procedure you use depends on the amendment.
What you've done is known as "sheet composting" in most circles. Instead of piling the organic matter in a heap to heat up and digest, you've spread it out as a sheet on the ground. Here in Colorado, I'd generally not recommend adding raw organic matter in any form, except perhaps fresh grass clippings or "green manure" tilled under, without first composting it. Sheet composting is difficult to do well up here. The main reason for this is caused by our dry climate. When I gardened in upstate New York, you could throw anything on the garden in fall, till it under, and by spring it would be well rotted humus. Not so here...the climate does not facilitate such rapid decomposition, mainly because the soils tend not to support large colonies of beneficial fungi, bacteria, and macro-invertebrates (worms...) required for such results.
Furthermore, adding anything with high carbon content causes a temporary nitrogen deficiency in the soil as the few existing microbes go to work and use the available soil nitrogen to digest the carbonaceous material (cellulose, primarily) in the raw amendment. Of all the essential elements in the soil (NPK), nitrogen is the most water soluble and will leach out quickly without humus to retain it. When exacerbated by the rotting effect, it can completely deplete the soil. Eventually, the digestion process is finished and soil nitrogen levels return to normal, and maybe even a bit better than normal because of the newly created humus that helps the soil keep its nitrogen. The faster the microbes can work, the sooner the deficiency returns to normal. As indicated above, unless you can keep your ground really wet, and maintain an artificially high level of the good soil critters, this deficiency will last for quite a while. You can correct this by adding supplemental nitrogen, but then you're just correcting something you caused to need correction. Fresh grass clippings, well tilled in, or a cover crop such as vetch or clover tilled under in spring is not as risky because they're already high nitrogen sources and will rot faster than high carbon additives such as hay, straw, wood shavings, etc. Be careful of herbicides and bad stuff in grass clippings...
Finally, the same dry climate causes soils here to retain sodium chloride (salt...) in the root zone. Salt is a killer to many crops, especially vegetables, so it is a deadly enemy. By using any animal sources of nitrogen (manure especially) you actually increase the amount of salt you're putting on your garden, and it will stay in the upper soil layers for a long time, thus accumulating rapidly to toxic levels. That's too bad, because manure is usually readily available and it's a great source of naturally available nitrogen. Unfortunately, however, we need to be cautious here in Colorado if we use it, and monitor salt levels carefully. I'd simply avoid it and use vegetable-only compost.
And that brings us to my favorite subject: Compost. I've been able to make vegetable-only compost here and get my piles up to 160 degrees. But, we'll save that subject for later.

Best Regards,

Chip