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Too much plant mulch = risk of overfertilisation?  RSS feed

 
Posts: 67
Location: Lake Geneva, Switzerland, Europe
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Is there an upper limit to how much compost or ramial wood chips can be applied? i.e. If I apply say 15cm of wood chips and leaves ,might there be a risk of having too much of, say, potassium or phosphate in the soil in the long run? I am not turning them in but will plant into/through them.

My understanding was that as compost or wood chips don't release their nutrients (NPK etc) as easily as, say, manures as the process is more one of stimulating micro-organisms in the soil which provide the plants with nutrients. Manure' s nutrients being water-soluble can lead to leaching and overfertilisation. Is this correct?

Is there any  research on the topic?
 
pollinator
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Location: Massachusetts, Zone:6/7, AHS:4, Rainfall:48in even Soil:SandyLoam pH6 Flat
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Short Answer:
Finished Compost or Raminal Compost, you will not have any problem with too much. And the soil life and plant root will take care of everything.

Long Answer:
Regular green leaves are "balanced" unlike say leaves that trees drop in the fall that have had "all" minerals except K removed.

Raminal woodchip is "balanced" and will be fine.
Raminal woodchip will get hot and start steaming so which might be physically too hot vs in the usually sense of it being chemically (nitrogen) too hot.

Unfinished "Compost" will also steam up too, so not good, and if all the "manure" is at the bottom next to tree root, not good. Manure is not balanced it has way too much Nitrogen and will burn affect plants.

When you transplant trees you have to make sure that you don't leave roots hanging out and that you don't bury it too deep with the truck covered. So if you add compost/woodchip to the point where you have the trunk covered with compost/soil. Then it will be bad for the plant.

There is also slugs and other critters, you will have to plan for these too, but it isn't really a big thing.

The most I have done is 12inches green/fresh woodchip (not composted), nothing died.
6inches seems perfect and it last for a few years. I had so many new mushroom + slime mold show up.
3inches and it is gone in one season.
 
gardener
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Yes there is an upper limit for depth of mulching, this is because the soil needs access to air.
6 inches is more than enough to block out sunlight and keep all the moisture in the soil, deeper than that and you will create anaerobic conditions at the soil surface, this is not a good thing.

There are times when you can go deeper, usually this is done with pure wood chip that is fungal active already, you can grow lots of vegetables (not root vegetables) directly in these types of chips.
In England, I've read papers from two gardeners doing experiments on garden plots where they laid down 12 inches of decaying wood chips, planting most of their beans, cabbages, etc. directly into the wood chips, no added soil, and they produced quite well.
One other person has 6 inches of wood chips on her plot and the first year she separated the chips to plant, the second year she planted directly into her replenished to 6 inch depth plot and out produced her first year.
Her third year she again replenished to 6 inch depth and again out produced her second year.

The key to these systems great performance was that all were already decomposing through fungal activity.

Manures indeed release their nutrients faster into the soil and these products need to be either well aged (at least a year) or composted prior to use in a garden for best results with least possibility of pathogens being present.

There are mounds of research papers out there, just do a search on scientific sites that have agriculture, horticulture or biology sections (all will have at least two of these).

Redhawk
 
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It is not a rule that mulch locks moisture.This happens only when you already have a strong soil full of life and lots of rain.
Lots of mulch and lots of compost actually can dehydrate the top layer of the soil. When you experience drought ,the wood acts as a spongue
draining the moisture out of the top layer.If you have minimal rain and lots of mulch,the rain will not even reach the soil layer to hydrate it.
It seems that a small layer of mulch and trying to boost soil life would be the best bet.Of course cover crops are so natural looking and you build soil via chopping and dropping
the upper part and leaving the roots to compost.Look at nature ,how much biomass do fall leaves or weeds bring back to the soil.It is a gradual small layer,not creating mulch towers.
That being said if you build soil life with wood chips,then because the soil organisms have a lot of moisture you counteract the wood acting as a spongue and draining the soil.
To me it seems that soil roots activate the soil,so whatever you do try to plant and plant and plant.
 
Susan Wakeman
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Location: Lake Geneva, Switzerland, Europe
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I have no doubt that mulch builds soil life.

However the question is coming from a farmer who is worried that the soil might be "high" in an element such a s Ph, P, Na etc. in the long term as a result of mulching. He has guidelines for his fields where he cannot exceed a certain quantity of compost. What am I to tell him?

My argument has been as that I don't till, the mulching is similar to what happens in the forest in the fall, and forest soil is balanced. And that compost from plant sources does not release its nutrients as quickly as manures do.

I think he is looking for some proof of this.

Dr. Redhawk, I'd love a thread with some coaching in finding relevant scientific information for those of us that don't know how to start...
 
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