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Saturday, July 13, 2019

Progression from Raw Desert to Vegetable Crops

This is my foot on top of some raw desert soil in North Las Vegas, Nevada in the Eastern Mojave Desert. Notice the color. It's almost the same color as the rocket came from. There is no organic matter in this soil. Why? Because there wasn't much growing in it to begin with. Why? We get 4 inches of rain in the Mojave Desert when we're lucky and temperatures can reach 120° F (50C)

Desert Soils Are Varied

People think that all desert soils are the same. They are not. They are as varied as non-desert soils. Non-desert soils vary from dark chocolate brown and almost black to light brown chestnuts of the prairies. That brown color is a dead giveaway regarding the amount of organics in the soil, that is dead plant life that is rotten and you can't see it anymore. Just the color remains for the eye to see.
This is raw desert Sandy loam soil. From the color of it you can tell there is extremely little organics in this soil, a.k.a. O M or organic matter. As soil organic matter increases, soils become darker and less like the parent rock it came from. Two ingredients are needed to make this happen: organics and water. The color of this soil is because of a lack in rainfall and a lack of dead plants in the soil. A walk behind trencher was used to cut these trenches in the soil about 30 inches deep. Otherwise you needed a pick. These trenches will be filled with water and compost and then collapsed.

Rainfall Adds Organics to the Soil (Irrigation = rainfall!!!)

The soils in the Sonoran and Chihuahua deserts are vastly different from the Mojave. They are a better quality, they have more organics in them so they are a little darker brown in color, they are lower in salts, a little bit lower in alkalinity and they aren't as problematic as Mojave Desert soils. In other words, you are less likely to run into pockets of toxicity such as boron, sodium and chlorides. Why? The principal reason why is because of rainfall.

Compost and water was added to this soil and the trenches collapsed. The soil was allowed to dry until it was workable with the tractor and implements. The compost added to the soil covered the area 2 to 4 inches deep before it was cultivated as deeply as possible, usually 8 to 10 inches deep.Adding organic matter such as this compost to the soil will do nothing if water isn't applied as well.

Research from Desert Ag Stations

If desert soil was previously in agriculture; that is, irrigation water was applied and plants were grown in it, then of course the organic matter content of that soil will increase year after year until it hits a plateau. Maybe that plateau might be 1% or even 2% but a far cry from the one tenth of 1% found in many of the Mojave Desert soils.Following research performed in previously irrigated desert soils may not give you the same results as planting in raw desert soil.

This is the reason why some of the agricultural experiment stations in the desert come up with some different results when growing plants in desert soil. Knowing it is desert soil is not enough. You must also ask what the organic matter content is to get a good handle on how it will perform and how you must manage it.

Compost is cultivated into the moist soil as deeply as possible, hopefully at least a 12 inches. Once a deep cultivation is done to this rod does soil, the compost is further mixed by using more cultivating tools. Water was added to the soil after the compost was added but it was allowed to dry until it was workable and the tractor and the implements did not compact it. Never ever cultivate a wet soil. That's a big no-no.In small gardens double digging the plot helps in this phase.

Mix Organics Deep and Thoroughly throughout the Soil

Mix organic materials like good quality compost as deeply in the soil as possible. Remember, you will be growing root crops as well as asparagus which needs deep, well-drained soils. Rocks in these soils cause crooked carrots and crooked asparagus spears.The perfect soil for root crops is a Sandy loam with very few rocks in it.

The final mixing of compost into this soil is done with the disc. In home gardens are Rototiller works just fine but don't pulverize the soil. Stop when the organics are mixed and the soil is still "crumby". Over tilling the soil or working the soil too much can cause it to turn to a powder and seal the soil surface making it difficult to irrigate and grow crops.

Shaping the Beds

For high-value crops and at high planting densities it is important to keep plants in separate areas from where people walk. One method is to use raised beds. The least expensive method is to create natural raised beds about three and a half feet wide without constructed side walls. It's easy to do and not expensive. Let the soil maintain the edges of the bed rather than wooden 2 x 8s.

Once the soil has been prepared it can be shaped into three and a half foot wide raised beds with natural sloping sidewalls. Walkways are created with a flat nosed shovel between the beds and throwing the prepared soil from the walkways on top of the raised beds. When the walkways are completed, a lawn rake is used to flatten the surface of the raised beds. For long raised beds I use a landscape rake. People walk in the walkways only unless they are planting or harvesting vegetables from the raised beds. Weeding, fertilizing and irrigation repair is done from kneeling boards with people's tootsies only in the walkways.

Raised Beds with Constructed Sidewalls

Another method is to construct raised beds with sidewalls. Sidewalls can be made from anything but lumber is common. Soil for transplants and seed should be firm but not hard or soft. Walking on top of the raised beds, your feet should sink no more than half inch into the soil when finished. Settle the soil with water from a hose and sprayer.

Here is a constructed raised bed with wooden sidewalls at Viragrow. They test their soil mixes in raised beds and container's before releasing them to the public.
A fabulous job constructing raised beds was done by my friend Chris Alexander. My hat is off to him and the methods he's used in constructing his raised beds.

Thursday, July 11, 2019

Desert Horticulture Podcast: Asparagus Failure, Magnolia Leaf Drop and Apricot Leaf Drop