We are have begun to augment our acreage in north easter Arizona. (Approx 40 acreas). We have really really deep sand. Its like a beach honestly, but much finer sand. Its river bottom, in an area where a river used to be many moons ago. Our acreage is up high in the hills with amazing views. Basically we are beginning to shape the property one acre at a time. We have pinion pine and lots and lots of juniper.
We have lots of cattle roaming in the area and we collect all of the manure as we can. Our plan so far is to add a very very thick layer of manure into the the sand by discing it in lightly. Then adding a great deal of straw that we put through the hopper part of our chipper. We then want to add lots more of organic matter as well, likely in the form of bulk compost soil bought by the truckload from a nearby place that makes it. To top that we want to bed down more straw and let it all just do its thing with daily watering. We also plan on adding wood chips super finely chipped since its a potential resource right on the property.
Thoughts on this plan? We don't want to add chems, but we need to get soil going instead of this sand that holds no water or nutrients because those things have no organic matter to be stored in.
We have sooooo much dry downed juniper wood all over the property as well that we will lilely do some hugelbeds as borders for pathways and along terraces.
My experience with sand and digging in stuff to try to convert the sand to soil was a complete failure. I'm at the beach in Florida, and since it never really gets cold here, the stuff I mixed in got devoured by the ceaseless organisms in the earth. Top dressing has worked much better for me. You can probably do some good using wood for hugelkultur beds, or perhaps some biochar mixed in the soil, but I would try to use most of the organic matter on top.
There are a few reasons why I think top dressing has worked better for me. You mention the sand not holding water or nutrients. With the nutrients, if you bury stuff then it is just that much further down to be washed below the root zone. Also, the sand has a lot of thermal mass, which means all sorts of problems with watering. If you can use organic matter on top (which has much less thermal mass) then it shields the sand from the sun. Sun baked sand can evaporate moisture well after the sun has gone down. Because water moves through the sand easily, it can wick up moisture from below and cause further water loss which can slow down soil building. Having the organic matter there to shield and hold in the moisture means more root growth and increased soil biology. You can't transform sand in to soil, but you can increase root zones and soil biology so the sand makes up a much smaller percentage of the soil. Also, more soil moisture means less irrigation and less nutrients being washed away.
Top dressing and cover crops, along with chop and drop methods can also help protect evaporation via the wind. Of course if things are extremely windy there would be an issue of keeping your organic material in place. In that instance you might be better off just using cover crops as a living mulch, and perhaps knocking it down or cutting the tops vs chopping everything down. If the wind isn't that extreme regularly then it should stay in place and retain moisture that could otherwise be lost to the wind and sun.
Another thing I noticed with sand is that once it gets so hot and dry, it repels water! You would think something so loose wouldn't have this issue. I have seen people stand with a hose for several minutes on one sun baked spot and virtually all of the water runs off and pool in low spots, eventually sinking in the ground in those spots several minutes later. I could walk right up to where they were watering, stick my finger in the ground, and get dry sand just a small fraction of an inch down. My hypothesis is when the sand gets below 10% humidity it gets a static charge that repels the polarized water. This is another critical reason to protect the sand from the sun, especially if you do raised rows or beds. The water can easily run off and do little good for your plants. When I start building up a new area, I will lightly water over the entire area, generally in the evening when the sun isn't hitting the sand, and then wait 10 minutes before irrigating. The sand will much more readily take the water with far less run off. Water running off also causes erosion, so anything you can do to avoid that will save you labor down the road. An organic layer on top will more readily accept water, even after baking in the sun, and will have far less erosion issues than sand.
I don't remember exactly where it was said, but I remember Paul saying something to the effect of "If you have enough mulch to cover an area with 4" of mulch, or half as much space with 8" of mulch, you will get happier plants with 8" of mulch." OK, so I haven't actually tried putting down a full 8" of mulch, but I believe he was completely right. I tried various methods when I first started my garden, from digging things in, to a little digging and a little top dressing, to top dressing with mulch, compost teas, and more. When I did one area from bare sand to top dressing with compost + mulch over 3" thick was when I started to see a real difference. The other areas that I kept adding stuff to did eventually start to perform well as I increased life and moisture in the soil, and compost teas did help speed that up, but getting a thick layer on top did the best at converting bare, nearly dead beach sand in to soil plants could thrive in for the first season instead of several seasons of slowly building things up.
My method I use now is to figure out how large an area I want to work with in the end, figure out how much volume of material I can get to cover the sand, and make mulch islands. Covering at least a few square feet per island, I can grow stuff in the mulch to build up the soil. As the moisture levels increase, the hydrostatic pressure will force some of the moisture between the mulch islands, slowly making the sand more hospitable to life. Native plants and others that I have found to work well for my area can easily start to take hold. Eventually things will grow, I will accumulate more stuff to chop and drop, yard debris, and compost to start filling in between until I get the whole area much more plant friendly. This is not something I do in late spring or summer as it is just way too brutal in the sun at that time. I let my sweet potatoes and watermelons run wild then as they seem the best at being able to spread and cover ground for me when it is that hot. Fall, winter, and early spring are more like summer in the north and I have much better luck growing at those times. Observing your local conditions and utilizing native plants can help a lot. Instead of spreading all of your resources evenly, you can do more localized intensive soil rehabilitation, which in turn makes it easier for those areas to have a positive influence on the entire ecosystem. As the areas in between mulch islands improve, the native plants will jump at the chance to live better. You can encourage this by selecting seeds of native plants you would prefer to have around and spread them. Often this takes nothing more than a little time and water. They can act as a cover crop and start to protect the sand from the sun in those areas not yet covered by other means.
Really excellent reply there from Daniel. Especially this:
Daniel Schmidt wrote:Instead of spreading all of your resources evenly, you can do more localized intensive soil rehabilitation, which in turn makes it easier for those areas to have a positive influence on the entire ecosystem.
My biom is also hot and sandy-and I used to live in Arizona. I would just emphasize the following:
1.Water harvesting: I remember those annual flood rains in Arizona. You need to come up with earth works and reservoirs to take catch every drop.
2. Cover, cover, cover. 8 inches sounds about right. My most successful garden bed this year was a core of brush wood, sprinkled with soil, covered with a few layers of compost and mulch material--basically a compost pile on top of brush wood. This plot held water and produced great! It's so labor intensive though you really have to start small so as not to get discouraged. Once one of these beds are established though, they're easy to keep adding to with mulch and compost for revolving crops.
3.Grey water--use every drop! This can grow a lot of vegetation right around your house for a cooling effect. I grow papayas and bananas and chaya with mine, as well as squash and gourds over some arbors for shade.
I forgot to mention, grey water is also the perfect place to produce mulch in a hot climate, that will in turn build soil wherever you want. My favorites for mulch are banana, moringa and pigeon pea. Pigeon pea is great for nitrogen (as well as the delicious peas! ) and moringa leaves have a growth hormone in them that will really stimulate your garden--as well as being really nutritious to eat. You can plant pigeon pea and Moringa really close in a leach bed and cut it quite frequently. The both grow really fast in the heat.
That looks like pretty harsh growing conditions. You mention that you are on an old dry river bed. Do you get season water flowing through? Is landscaping an option to build swales and texture to
As has been discussed, I would look to get lots of organic material into the soil, but given the conditions I would probably focus on concentrating it in beds rather than trying to amend the whole area. Much of your nutrients will be being lost to the deep sand by leeching as it breaks down. If you have the capability to make biochar I think that would be a useful project. Char traps moisture and nutrients like a sponge and lasts effectively indefinitely.
I am not familiar with your climate. Do you get hard frosts? If not then vetiver grass is potentially of great use for you. It has deep roots, produces tonnes of biomass and can be planted on contour to make natural terraces as the soil and biomass collects up hill of it.
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I think a lot of good points have been raised. I have some more, hopefully as good.
I would build intensively managed, slightly sunken beds, and use those as your islands of fertility that nurture the soil life. I would look at your property and decide where the wind usually blows from, and go to that edge of your property. If there are any on site, I would consider building a low wall on the bed's windward side out of any rocks you can scrounge, and building your slightly sunken bed in its shelter. It will likely act as an airwell, if there are air spaces sufficient to the task, and that will harvest water for your bed.
I would plant trees in this bed, probably something that fixes nitrogen and sheds its leaves, or that will coppice/pollard, such that you can harvest its biomass without losing the benefits of the tree as shelter. Food trees are an option as well, but obviously, choose based on your conditions.
Whatever trees and shrubberies you choose for this bed will slow the dessicating wind, transpire moisture into the air, leaving less carrying capacity to rip moisture away from the rest of your property. The shelter belt guild should also be designed to spread itself with minimal assistance, such that the sheltering effect keeps growing, making your work easier over time.
As to choice of species, I have read that deeply taprooted trees have been used in desert regreening projects where there is a deep watertable, as once the taproot reaches that water, it will thrive without watering, and depending on the species, will pull water up for the rest of the bed. Up north where I am, Sugar Maples perform hydraulic lift, raising the water table locally for themselves and those plants growing around them. Ideally, this is what your choice of tree would do.
Once the shelter bed is established, it will provide shelter for plantings downwind of it, and so on, and so forth.
Water harvesting is pretty key. I would keep in mind the downpours you can get seasonally, as mentioned by Nathaniel, I think, and think about making water harvesting depressions on-contour, rather than swales less-suitable for large volume rain events.
Honestly, if I was being minimalist about the rest of the project, I would put in the water harvesting features (long, shallow basins on contour) and then hill up rows of straw on the downslope side to trap sediment. In areas of increased rates of water flow, I would actually stake small rectangular bales on contour, especially in river beds that tend to look like rivers in rain events.
I think vetiver would be really awesome in rows on contour. If not that, then pretty much anything else that will survive in your climate, planted on contour (preferably on the downslope sides of your water capturing landforms) will hold the soil and sand in place, and nurture those soil critters that do all the actual soil-building work.
I think it crucial to think about not just water harvesting, but also the trapping of sediment from the wind and rain. The vetiver rows on contour (or whatever you choose that works in your area) would act as perfect sediment traps, but just laying some of that mesquite down on contour downslope of water harvesting features would result in sediment building up on the windward and waterward sides.
I also wonder if anyone in the position of turning lots of sand into soil has used bentonite clay or some other hydrophilic powdered clay as amendment to hold water longer and to break up the homogeny of nothing but sand. This in itself should make it easier for soil life to expand outside of the islands of fertility that your beds will represent. Covering that sand outside of your beds with whatever mulch you can, even just enough to block the sun from baking the sand, will reduce the heat island effect.
And as to that, I like Nathaniel's idea about sweet potatoes and watermelon. Anything termed "living mulch" like giant-leaved curcurbits will shade out the soil, too, and provide biomass after harvest. I would build a hot-season guild focusing on sweet potatoes, okra (they are complimentary in the garden), and watermelon, for starters. I would plug in as many companions to those as will fit without getting in eachothers' ways. I have included the link for the List of companion plants that I go to most often. I figure that groups of plants that support eachother will only make your job easier.
All the best to you in your endeavours. Keep us posted, and good luck!
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