This is my first post, but I've been watching your for a couple of years now. My woman and I have recently purchased some land in south central Montana, and I figured it was time to ask some questions.
So here is our situation: we own an acre with permission to cultivate an additional three. The land is nearly perfectly flat. We have access to an irrigation ditch which is slightly brackish. The soil isn't the best, but the location suits us perfectly. We've done some soil tests, and concluded that it's pure or nearly pure silt, it's alkaline, sodic, and deprived of organic matter and structure.
My plan is pretty simple: this fall I will be ravaging the nearby towns and stealing all of their leaves. Muahaha. I will place them in my zone 1 beds to breakdown a bit this winter, and in spring till them in with compost, sand, gypsum and rock dust. This will be my one and only tilling, after which I'll sheet mulch it and treat it as a no till bed. I'll be mulching with pine woodchips that I can get for cheap from a nearby sawmill. I am going to construct a wetland to filter the irrigation before I use it, likely using woodchips as the growing media for reeds and cattails, as I've read that fungus can bind some salt. After the primary filtration, I plan on using drip irrigation to help keep the salt imports low. Neighbors nearby have bare spots with salt crusting on the surface, which I assume is partially from irresponsible irrigation, partially from the fact that the water table is relatively high and the capillary action with evaporation tends to bring salts up to the surface, and mostly from the fact that the bulk of our soils are made from ground shale from the glaciers way back when. Anyhow, salt is obviously a big issue here.
Does it seem like I'm overlooking anything? Short of evaporation or reverse osmosis, is there any way I can desalinate my irrigation water? With the exception of alfalfa and Russian Olive (which is invasive here and not an option), it seems most legumes are very sensitive to salt. What other kinds of pioneer species could I use that might tolerate it better? Obviously I won't be able to give all of my land this much love in the first season, and I'd like to implement pioneer species to help out until I can mulch over the whole property. My backup plan is to seal off the lower soil and just do raised beds with a soil that I build/import, but I'd like to work with what I have if I can, especially because I want to put in a lot of trees.
Joe Ouldhouse: Welcome. Great to have a place of your own to work with. When I put organic matter on top of silty soil in the fall/winter, it's a muddy gumbo mess come spring. It generally can't be tilled until things really dry out in about mid-June. By then, it's too late in my climate to be planting a garden. Leaves tilled into the soil in the fall work really well in my silty soil.
I'd like to suggest (in the further away zones) that rather than constantly fighting the soil to turn it into something that it isn't, that you focus on selecting species and varieties that grow well in the existing conditions. Sure, grow some of your favorite vegetables in pots if you want to. The ground has been the way that it currently is for perhaps 10,000 years. Any surface applications that you might apply seem to be only skin-deep: sure some shallow rooted plants will really appreciate the organic matter you add. I expect the underlying structure of the soil, and the irrigation water to remain the same as they have been since time immemorial.
I had some success in high pH soil by keeping a duff layer on top of the soil around a fruit tree. The tree got (some of) the nutrients it needed from interface between the duff and the underlying soil. It was hard for me to maintain consistently, so the tree eventually died.
Do you know if your salts are sodas or chlorides? It might make a difference how you deal with them... Sodas can be neutralized by acids, chlorides can only be washed away.
Is Russian Olive not an option because you face jail time for growing it? Or would you only face peer-pressure? To find pioneer species that can tolerate your soil, look at what is already growing there and in the nearby areas with similar soils. Perhaps there are closely related species that might be more palatable. Tamarisk is another small tree that loves growing near salt flats.
The main problem you state is lack of humus. Conifer trees have acidic needles so using these for mulch will both protect the soil and reduce the pH to better levels, spent coffee grounds are also acidic and most folks have some every day.
To add deep humus to your soil, Daikon radish and Rape are good things to grow, and they will grow in the fall as well as in the spring. Chopping the tops off after they have had a couple of months to grow naturally adds humus via the rotting root.
If you plan to till once, it would be better to double dig and add compost, ground up leaves, etc. at that time then once you have completed the double dig, spread a layer (or lasagna style layers) of mulch and plant winter crops through this.
There are many methods for you to experiment with and all will be beneficial to your soil. Silt by the way is usually really good as a starting base. We had 100 feet of silt soil when I lived in Sacramento, CA. everything grew wonderfully once I got the humus levels up.
Mycoremediation will help a lot with the salts issue.
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