Adding compost on top of mulch?

Hi all

I would like to know what people's opinions are when managing and maintaining soil fertility.

I have in many of the ornamental gardens I manage for business decided to use permaculture/organic principles. I have top dressed bare soil with compost/mushroom compost, and then with woodchip mulch from my arborist contact.

Now, that woodchip mulch is going to take years to break down (despite containing some leaves and needles as well as bark/wood), but for fertility reasons want to be adding roughly 10mm - 20mm of compost each year for the next few years to increase nutrient content and soil organic matter (both active and passive organic matter).

I'm wondering if I can do a Paul Gauche and just top dress a fine layer of compost/manure over the woodchip mulch and water it well, or if this would rob the compost/manure of all of its nitrogen due to nitrogen drawdown.

I understand in a forest garden using fallen leaves rather than woodchips, then nitrogen drawdown isn't as big a problem, but woodchips can have a 500:1 carbon:nitrogen ratio, compared to 50:1 for leaves.

Some of these gardens are large and I don't know how possible it will be to move the mulch out the way before composting annually/biannually.

Kind regards,
Tom

I wouldn't expect it to be a problem unless you don't have a continuous source of woodchips. What I've noticed with woodchips and compost is that once you start adding that biology the woodchips start to disappear faster and faster

It seems to me that rain would wash some of that compost into the wood chips, spreading the microbes and feeding them very well, resulting in an explosion of microbe life. Sounds like a good thing to me.

Have you seen Dr. Redhawk's Soil Series?

Thanks for the responses guys, i'm going to give it a go. I'm not too familiar with the nitrogen drawdown mechanism, won't the mulch underneath rob the compost or manure of all of it's nitrogen?

The clients are well off and able to pay the $150 AUD for 15m3 arborist mulch from my contact so running out of mulch breaking down quickly is not a problem.

I have done this before and agree with the comments above. It will probably make your results from the compost/manure additions slower but longer lasting, generally a good thing long term. If you wanted more immediate benefits from the nitrogen in the manure, you could take the chips aside but I’d just water it through the woodchips. It will also break the chips down faster. I have also always seen good results with manure/compost teas watered in through the chips. The woodchips also make it easier to water more assertively, as I can use a much stronger stream from an open ended hose and the chips disperse it and prevent compaction/erosion. I generally make a fairly strong compost tea, add a modest amount around any garden beds I want fertilized/inoculated, then water that in through my woodchip mulch.

Just saw your last response, and yes manure mixed with wood chips will gas off nitrogen when on the surface together. However, nitrogen is basically free, as it’s about 4/5 of our atmosphere. We just need to help the soil fixate this N, and the manure and woodchips will be the perfect habitat for fungal inoculation, which can be as proficient at N fixation as any legume. You could let nature do its thing or inoculate the woodchips with king stropharia or blue oyster mushrooms, which inhabit a wide range of wood. I’d also grow legumes in almost any bed, and strongly recommend Scarlet Runner Bean if in zone 7+ where it can be perennial.

Maybe you can help the nitrogen problem by stealth. Darron Williams has a post here that suggests ways to add nitrogen organically. Here is a direct link to Wild Homesteading with the correct range of water to urine you would need. Much better than creeping onto the properties at night for target practice.

Tom Clarke Armstrong wrote:Thanks for the responses guys, i'm going to give it a go. I'm not too familiar with the nitrogen drawdown mechanism, won't the mulch underneath rob the compost or manure of all of it's nitrogen?

The clients are well off and able to pay the $150 AUD for 15m3 arborist mulch from my contact so running out of mulch breaking down quickly is not a problem.

My understanding is that the nitrogen is tied up in the bodies of microorganisms who use the nitrogen as a fuel source to help consume the carbon in the woodchips. My observations tell me that it is a very narrow band (like several cm at most) right against the surface of the wood. The biological activity can create heat that could damage the fine roots and also volatalize additional nitrogen. My experience with this effect.has been that it is problematic (or rather, can be) when you are working with dirt that doesn't have a robust biological community cycling nutrients so the bound up nitrogen ends up representing a significant portion of all available nitrogen. Once the community is in swing that bit of nitrogen that is temporarily bound up is well worth the carbon that it is helping to liberate into the soil.