Fertilizing & soil building in winter

Because tree roots go dormant in winter, and soil bacteria are "most active" at temperatures above 40 deg F, what is happening in the soil during winter? None of the books I'm reading are answering this, and whether there's anything one should do to contribute beneficially. In some climates we must be able to make some progress in the slower season.

Heaps continue to compost over winter, especially where temps are often above freezing. Here it's often in the 20s at night but in the 30s or 40s during the day,

I do know that you shouldn't add anything much warmer than the soil itself (a liquid fertilizer/tea kept in a greenhouse is OK) because it will shock the existing microbiology.

Is there any point in urigating over winter? If not, what to do with all that fertilizer that accumulates? That would be a lot of airtight containers...

Under 8 inches of leaf mulch, couldn't one create an oasis for the soil food web to holiday in?

In most states and countries, it is against the law to fertilize in the winter.

I know in Maine it is from Dec 1st through Mar 15th. When I was in Ireland I know they had a similar law.

It makes sense because if you over apply too much fertilizer, even if it is compost tea, or manure, the inability to absorb that manure into the frozen ground means it is going to be shed right off into the local waterbodies. That does not do anyone any good. It does not help the fields, and it does not help the farmer, and it does not help the waterbodies.

A prudent farmer has an impervious area that is designated for manure storage, or for making compost, and is sized right so that they can get through the winter months without resorting to spreading it on frozen ground.

There's an interesting book that acres USA just published recently called "humusphere" and in it the author (who lives and gardens in Norway) talks broadly about building so organic matter. The most interesting suggestions he put forth were using "green mulch" (basically grass clippings and the like) as mulch during the summer and then covering your beds with a thick layer of green mulch (in this case small tree branches that still have their leaves and longer pieces of grass) before the frosts come in earnest.
Exactly like you surmised, he claims it makes a bit of a refuge for school biota and provides some food through the winter. He also recommended blending up your uncooked kitchen waste with enough water to make a slurry and spreading that over the dormant beds.
It's definitely an interesting read for anyone interested in that sort of thing and it aligns broadly with the most common winter garden advice that I see which is basically to mulch heavily. The major difference is that he advocates using green material as opposed to brown

Fredy Perlman wrote:what is happening in the soil during winter?

Well I think it depends on both the type of soil and also the geographic location. Soils in the deep south may frost but rarely begin to freeze to depths with exposure to extended sub freezing temperatures. Indeed fungal and microbial activity can slow to a snails pace when the soil not only gets cold, but also when growing things go dormant and temporarily halt the process of secreting root exudates made from photosynthesis into the soil that feed the soil microbial life. Other things such as some soil chemistry can keep right on occurring in cold soils, with rainwater moving or even leaching mobile minerals that aren't bound to soil particles or organic matters, and cation exchange still happening such as the calcium and magnesium in a fall liming displacing hydrogen ions on soil colloids during winter.

Travis brings up an excellent point regarding frozen soils. Applying conventional water soluble fertilizers or manures is not a good idea on frozen ground or even unfrozen but saturated soils. I believe that applying water insoluble amendments such as rock dusts can be done as long as the soil is not bare or has been left fallow for the winter so the rock dusts don't wash away with rainwater erosion, and the soil isn't so soggy and soft that heavy machinery applying insoluble amendments will rut and tear up soil aggregate structure.

True, without root exudates the soil economy has little currency. (Yucky metaphor.)

And good point that enrichments applied to saturated or frozen soil are probably wasted and sometimes illegal. Even mycorrhizal inoculant is better used at another time.

Liberating, in a sense. I can turn my soil building attention to composting only...but Sluggoo investigations should similarly wait until spring.

Very good information in this thread. I had no idea fertilizer was illegal in some areas.
Here, we sometimes get 3 or 4 days a year where actual snow falls from the sky, and maybe 1 or 2 of those days where it actually sticks to the ground for a few hours. We do sometimes have sleet storms that leave ice on the ground for a day or two, but most of our frozen precipitation occurs at night and melts when the sun comes up.
Now, I wonder if the 6+ inches of wood chips & shredded leaves will break down any during the winter.
How do the soil microbes & roots work when the weather is so variable that it may be 35° night and 75° in the day, then a couple of days with highs in the 30s-40s, then back up to the 60s, etc? A couple of weeks ago we got that arctic blast that dropped us to lows in the mid-20s for a few nights, but now we're back to having days with highs near 80 and lows in the 50s.
I would assume root systems don't have an "on/off" switch to become active/dormant at will (?), and I don't know how the fungi, bacteria, etc would respond to fluctuations.

Kc Simmons wrote:I would assume root systems don't have an "on/off" switch to become active/dormant at will (?), and I don't know how the fungi, bacteria, etc would respond to fluctuations.

Oh very much so! Temperature is everything.

It is very plant dependent too. Like winter rye, that can tolerate a temperature down to 33 degrees and grow and germinate. It does not even kill the plant when it goes well below that, the plant goes dormant, but it does not die, and stays green, even under snow. The second the soil warms to 33 degrees, the plant begins to grow again. But corn does not do that. It germinates at 55 degrees, but can live if the temp is colder than that, but I frost-killed when that occurs. Peanuts are another whole story, that not only requires ground temps of 60 degrees, it requires them for 110 days, something that we never get here in Maine in natural conditions.

Of course we can manipulate ground temperatures by using plastic to heat the soil and get unconventional crops for the area to grow, or start plants in a greenhouse and transplant outside at a later date, or grow in greenhouses year around.

Plants are VERY sensitive to temperature. There is only 1 degree difference between 32 degrees, and 33 degrees, and yet winter rye knows the difference. This is why farmers here chop their corn in October, then immediately plant winter rye. All winter it s preventing erosion, and soil building with organic matter, and will be turned under in the spring when the temps allow corn to be planted again. In that sense, farmers are building soil all winter, and on a grand scale.

And the manure for the fields, that too is at work in some degree now that I think about it. That is being dumped into massive tanks where the solids are being settled out, and the water keeps the nitrogen from escaping into the air. In the spring, the lagoon is stirred up, the nitrogen goes into the water, and then that compost tea is spread across the fields.

I add organic amendments to the mulch all winter long. I try to get it down before rain is anticipated.

I like dry coffee grounds, kelp puree, alfalfa, and stuff like that.
I scavenge whatever I can.

Not so much soil building as preparing for soil building, but winter is an excellent time to start making your charcoal for next spring's biochar.  It works especially well if you have animals and can add it to their bedding, but if not, it can easily be added to your compost in the early spring.

Trace Oswald wrote:Not so much soil building as preparing for soil building, but winter is an excellent time to start making your charcoal for next spring's biochar.  It works especially well if you have animals and can add it to their bedding, but if not, it can easily be added to your compost in the early spring.

I'm not any kind of biochar expert, but I've been trying different things with the charcoal leftover from when my neighbor burned some brush in his pasture. I put some in the compost pile, some in the keyhole bed compost, and also soaked some in urine before adding it to the deep wood chips mulch I put in the forest/annual gardens this fall. I figured even if it doesn't do a lot of good, it at least won't hurt to have it in there.

[quote=Travis Johnson]Oh very much so! Temperature is everything.[/quote]

Thank you, Travis. That's what I thought about annual/herbaceous roots.

I should have been more specific, but I was wondering more about trees & woody perennials.
For instance, my pecans, some fruit trees, most NFTs, and various shrubs all dropped leaves and went dormant after the big cold front last month, and will most likely stay dormant above the ground until late Feb. But, would the last few weeks of highs in the 50s-70s and lows in the high 30s-50s result in the roots/microbial life waking up and continuing to work as usual? Or do they mirror the aboveground parts of the tree/shrub and generally stay dormant until the typical "wake up" time?

It makes sense for the top half of the tree to stay dormant until the spring arrives & days get longer since it costs a lot of stored energy to push new foliage; just to have it freeze back in a few weeks and the shorter days not allowing enough sunlight to regain what's been spent.
But I would think the roots wouldn't have as much trouble since they aren't necessarily pushing a lot of new growth and, instead, could take advantage of the warm autumn rains to uptake water & nutrients to better prepare for the foliage push next spring.

The Best Way To Build Organic Matter Fast During The Winter

https://www.advancingecoag.com/soil-amendment-program

No, they act pretty instantly I would say.

I say that going by the Sugar Maple. Their best producing days are when it is cold at night, and warm during the day. That cycle really gets them to pump the sap out of them as they waffle back and forth between being dormant (night) and active again. If it is always cold, or always warm, sap season is nowhere near productive.

That may just be the Sugar Maple though. The Yellow Birch pumps out sap constantly, but it is much later in the season, and when it does flow, it REALLY flows constantly.

To what degree does the freeze-thaw cycle work to create space for springtime fertility by breaking down otherwise inert or inorganic material?

I mulch heavily in the fall, and even though the top layer doesn't have much activity (I live in Oklahoma so we freeze and thaw tens of time over the winter months.) things break down rather quickly and thoroughly in the mechanical sense.

Jordan Mathis wrote:To what degree does the freeze-thaw cycle work to create space for springtime fertility by breaking down otherwise inert or inorganic material?

I mulch heavily in the fall, and even though the top layer doesn't have much activity (I live in Oklahoma so we freeze and thaw tens of time over the winter months.) things break down rather quickly and thoroughly in the mechanical sense.

Jordan, Good point.  I use that very thing to break up my charcoal that doesn't get crushed enough by my truck tires.  By spring, the larger blocks break down to some degree.  Since I incorporate biochar into all my compost, as well as broad forking it in at times, I would think the same would happen underground.  

Jordan Mathis wrote:To what degree does the freeze-thaw cycle work to create space for springtime fertility by breaking down otherwise inert or inorganic material?

I mulch heavily in the fall, and even though the top layer doesn't have much activity (I live in Oklahoma so we freeze and thaw tens of time over the winter months.) things break down rather quickly and thoroughly in the mechanical sense.

I have excellent luck using the spent mushroom block material in the winter. The mold infested wood appears to stay fairly active during the nightly freezes and breaks down quickly.