what I meant is that the list like the one you linked to are boolean. I.e. a plant is a good accumulator of a given mineral or not. I am wondering if anybody has information on how good a plant is for accumulating a nutrient. For instance, borage could be a 5 out of 10 at accumulating potassium and comfrey a 9.
They create nothing that wasn't there to begin with. If the soil is deficient in any particular nutrient, dynamic accumulators will actually make it more deficient by extracting what little was there. Sure, they can be composted, but will not give back as much as they took...it costs something to grow them. If a soil is deficient in any mineral/nutrient it will need to be supplemented one way or another.
Dynamic accumulators are good for salvaging nutrients before they leach out of the bottom of the soil. Whatever the soil is deficient of cannot be salvaged in any great quantity...it simply doesn't exist in sufficient quantity.
I was under the impression that they could get the necessary minerals from the subsoil...
That is true. One of the things that makes a 'good accumulator' is its ability to get into tough soils.
In a loose sandy soil, a single beet plant can send its roots between 2-10 feet deep. Usually deep enough to find its own nutrients. Put that same plant in a hard clay soil, and it might be lucky to get 6-8". A tougher plant might go 12-24" in that same soil, mining nutrients all the way down. If for example, the plants absorbs 1,000 units of a given nutrient, and it is chopped/dropped there, it will give back some of that nutrient, perhaps 600 units. So your soil has a net loss of that nutrient, but it is now in the top soil, rather than deeper, where the beet couldn't reach.
A monoculture crop usually has little to be gained (mainly because the weed isn't allowed to live long enough to mine the nutrients), but in a good polyculture, it has a dual purpose: as a tough plant is breaking its way deeper, its companion plant's roots are piggy-backing a ride with it deeper than they could have reached on their own, thereby gathering some of the nutrients themselves along the way. Several crops later there won't be any left to mine unless you are adding at least as much as has been consumed.
In a loose, sandy soil, a dynamic accumulator may not really help. If the nutrients have leached deep enough, even it cannot retrieve them.
A deficiency needs to be addressed by importing what is needed, as a dynamic accumulator can only mine it as long as it is in sufficient supply for its needs. After that, soil will turn to dirt as it has in much of the 'heartland'. Dirt blows away in the wind...soil does not.
I use comfrey, rhubarb and horseradish a lot for this reason, it has a very deep root, brings up a lot of food and has huge leaves that make great mulch and can be chopped and dropped pretty much any time of the year without damaging the plant..another good one is swiss chard which will grow for several years under the right conditions, although it is not really a perennial.
I try to use the ones with the largest leaves, even burdock works well in that area..and some weeds also have large leaves and make great mulch..but I wouldn't want them beside my trees.
I gather leaves from things like milkweeds in the fields around my gardens for mulch, I'm always looking for BIG leaves..the more you pile on the more it feeds the soil and keeps in the moisture.
My dynamic accumulators didn't even wilt in our drought
John Polk wrote:
If for example, the plants absorbs 1,000 units of a given nutrient, and it is chopped/dropped there, it will give back some of that nutrient, perhaps 600 units. So your soil has a net loss of that nutrient, but it is now in the top soil, rather than deeper, where the beet couldn't reach.
John - could you please expand a bit more on why only some of the nutrients would be returned? If the nutrient is easily incorporated into volatile compounds such as carbon or nitrogen, I can see why some would be lost in decomposition. Otherwise it seems to me like most minerals would remain after full decomposition of the accumulator.
Adrien Lapointe wrote:There are many lists of dynamic accumulators online and in books, but I haven't seen one that says how well a plant accumulates a given nutrient. I would guess that some plants are superb accumulator for say potassium, but not as good for iron. Anybody has some information on that?
Adrien - I have not seen a source that provides a scale for accumulators in general. There are many studies that have been done on individual plants and individual elements (published in the literature), but it would be great to find some kind of table/chart.
I have also been curious to know what happens for some of these accumulators when the soil is low in minerals that the plant accumulates vs when the plant is grown on soil that has a more moderate level of the mineral. For example, the soil at my location has little to no detectable levels of N/P/K, yet my comfrey grows without supplementation. It doesn't appear nearly as big and beautiful as many photos I have seen of comfrey grown elsewhere, but it does grow. It makes me wonder what the N/P/K and other micronutrient profile of my comfrey plants are compared to those grown at other sites...