granite

We live, above three huge river canyons, on granite which is wonderful for preserving the water table but not so good at forming and maintaining soil.  It floods in winter but 2 inches down is like dusty sand, and nutrients seem to leach through so quickly.  We are adding as much organic matter as we can possibly collect and have swales, berms, ponds and french drains to cope with flooding and draught situations but there still seems to be something missing.  I know neighbours with lush looking vegetable patches have access to herds of cows, whereas our animal dung imput is limited to what we can produce or collect from the lanes.  Is there anything in particular one would recommend to improve a soil of this type?  If it helps, beans and brassicas grow well but grains, root vegetables and onions are troublesome.

Maybe no surprise, but I would use biochar :)
Not by itself, but as part of a mix into Ruth Stout style mulches that compost into carbon rich organic soils that build outward from the mulches.  

Not knowing too much specifics about your plot of land, I am going to give you the following:

Patience: Things take awhile

Earthworks/Swales to help with getting the water deeper than just 2 inches. For now I would cut back on french drains and trying to drain the land, I would maybe touch that in year 7.

Biomass: I would add biochar preferable but any type of carbon is good, woodchip, sawdust, leaf litter, compost, living mulch, chop and drop, bread from the bakery, etc.

Soil Life: this is really where your store of minerals, water, probiotic/good microbes live. So add mushroom slurries, compost, pond water, worm compost, We want everything peeing, pooping, deing/composting in your soil.

Cover Crop: 25%-80% nitrogen fixers, then some from the onion/garlic family, mint/thyme, daikon radish, carrot family and some grass family.

You can also add some mineral amendments, like sea-90.

 

I will echo the comment about cover crops.  Try a mixture of species in a cover crop (as many different species as you can think of and acquire).  Multi-specie cover crops usually perform much better than a single species cover crop and will give you the root exudates and residues that will help build the organic component of your soil the fastest.  

Hi Mandy.

If it's anything like the Canadian Shield here in Ontario, I know the kind of sandy substrate you're talking about. Especially around coniferous copses, rather than deciduous, there seems to be a duff layer of needles, a quarter-inch or so of something like soil, and then sand, and often bedrock immediately thereafter.

If you have so little other than sand that water simply percolates away, I would suggest adding clay to water catchment and control features, in addition to the excellent advice about biochar. Keeping water in the substrate long enough for it to become soil, though, seems of paramount importance to me. I would go heavy on the clay (naturally and locally sourced, if possible) and organic matter amendment, and probably add a full-spectrum mineral amendment like Sea90.

Because of the mineral nature of what you're working with, I would regularly apply actively aerated compost extracts to focus areas, like around water catchment and control areas, so that they act as little oases for soil life, which will work outward, spreading the area of influence as far as reliable hydration extends. I would find out what culinary and medicinal mushrooms will thrive in the root zones of living trees in situ on your property, and enhance those living systems with a little applied mycology.

I have also heard that regularly-spaced compost pits or tubes to the bottom third of the living part of your soil can also act as such oases of spreading soil life.

I would also look at the native pioneer plants that grow where there is hardly any soil. If any of these form wide mats, they could easily be used as groundcover for soil retention. If any have taproots pushing down into the sand or hardpan, these could be used to put organic matter down deep without you having to do much more than gather ripe seeds and spread them where you desire. These might help to prepare the soil so that you can upgrade to the slightly less-hardy, slightly more productive analogs S Bengi mentioned.

But good luck, and keep us posted.

-CK

S Bengi wrote:Not knowing too much specifics about your plot of land, I am going to give you the following:

Patience: Things take awhile

Earthworks/Swales to help with getting the water deeper than just 2 inches. For now I would cut back on french drains and trying to drain the land, I would maybe touch that in year 7.

Biomass: I would add biochar preferable but any type of carbon is good, woodchip, sawdust, leaf litter, compost, living mulch, chop and drop, bread from the bakery, etc.

Soil Life: this is really where your store of minerals, water, probiotic/good microbes live. So add mushroom slurries, compost, pond water, worm compost, We want everything peeing, pooping, deing/composting in your soil.

Cover Crop: 25%-80% nitrogen fixers, then some from the onion/garlic family, mint/thyme, daikon radish, carrot family and some grass family.

You can also add some mineral amendments, like sea-90.

 

Thanks everyone. I am trying many of these. We have a composting toilet so we have a heap for that and another for dog poop. I like the idea of daikon for deep mining, we also grow a great deal of comfrey.  I collect leaves when health permits but I am forbidden by Him Indoors from putting them through the wood chopper. Mushroom slurry? Not sure where I could get that from. But I have just had an idea to contact the chestnut processing plants nearby to see what they do with the hulls. I have just cycled past the street cleaner sweeping all the leaves outside into neat piles and putting them in the bin. Heartbreaking.....

I have used woodchips, leaves, and then added worms to the mix with great results for granite soil. It has taken years though. It sounds like you are on your way.