A Mechanistic Breakdown of Negative Priming of Soil Organic Carbon by pyOM

Silene DeCiucies

Cornell SIPS


Residue Amendment and Soil Carbon Priming for Richer or Poorer

Feed the microbes carbon in C-poor soil and they’ll have a party.
Feed the microbes carbon in C-rich soil and they’ll put it in the C-bank.
This quote is of particular interest, emphasis mine:

The shift of bacterial community composition in response to residue amendment contributes to the sequestration of residue-C in SOC fractions.

Predator-prey carbon sequestration? Sounds similar to the Arthropod predator results. May the shift be with you.

The study:

A 150-day incubation experiment was conducted with 13C-labelled soybean residue (4%) amended into two Mollisols differing in SOC (SOC-poor and SOC-rich soils). …

The amounts of residue-C incorporated into the coarse particulate organic C (POC), fine POC and mineral-associated C (MOC) fractions were 4.5-, 4.3– and 2.4-fold higher in the SOC-rich soil than in the SOC-poor soil, respectively.

Residue amendment led to negative SOC priming before Day 50 but positive priming thereafter.

The primed CO2 per unit of native SOC was greater in the SOC-poor soil than in the SOC-rich soil. This indicates that the contributions of residue-C to the POC and MOC fractions were greater in the SOC-rich soil while residue amendment had stronger priming effect in the SOC-poor soil, stimulating the C exchange rate between fresh and native SOC.

The shift of bacterial community composition in response to residue amendment contributes to the sequestration of residue-C in SOC fractions.

The fate of soybean residue-carbon links to changes of bacterial community composition in Mollisols differing in soil organic carbon

Carbon & Nitrogen Priming of Organic Matter

The Natural Farmer

Awesome to see Jagganath on the land growing again and the Cinghiale (Wild hogs) prevention he’s had to implement to get a keyhole garden going.

In the video he talks about creating another follow up video to discuss solving his nutrient deficient lettuce problems on degraded land, however I wanted to address that here as it sparked a few thoughts and searches while watching.

For my lettuce I’ve currently been soaking straw in mixtures like the Amrut Jal that Jagganath mentions (I use my guinea pig instead of cow) and it has worked well.

Straw alone initially has a slight negative priming effect as Huw found in the following video.

Straw has a C:N of about 80:1 and needs to be brought down to 50:1 or less either naturally or through intervention before the soil carbon building begins and microbes can use that carbon to fix nitrogen.


The figure shows the priming effect of different organic matter C:N ratios, and depending on your environment, reading along the bottom you want to be on the right side of the pink line in the short-term where positive priming occurs, and left of it in the green area for long-term when considering for mulch temperature and moisture management, as well as slow nutrient release. In the blue, carbon mineralization is likely to be limited.

glucose-ammonoium priming.jpg

Priming patterns resulting from different glucose and ammonium inputs to incubations of wood litter (a), leaf litter (b), as well as Oa horizon organic soil (c) and mineral-soil A horizon (d) from a subtropical forest.

One of the other figures in the priming paper[1] that I found most interesting, was this one.

Based on it I just calculated that at least 10 grams of glucose (sugar, molasses etc) to 1 kg of dry straw is needed to prime it, 40 grams (two tablespoons) will accelerate it and so should 2 grams or more of ammonium, which is about 200 ml of human urine.

Guess what I’m making tomorrow and soaking some straw in?

Permie Flix’s Max Prime (+15) Recipe:

  • 4 mL (1 teaspoon) of sugar (unsulfured molasses etc)
  • 200 mL of urine
  • 800 mL of water

My 1L concoction would do about 100 grams of straw. Or if scaled up to a larger 1oL soaking 1kg would be possible.

Permie Flix’s 10 L Max Prime (+15) Recipe:

  • 40 mL of sugar (2 tablespoons)
  • 2.0 L urine
  • 8 L water

Soaking overnight with a weight on top should be enough.

A 20 kg bale? That’s:

  • 800 mL of sugar
  • 40 L urine
  • 160 L water

That’s a lot of piss. I measured mine and I get maybe 800 mL. That’s 50 piss stops or about a month.

For my experiment I only have enough aged urine for my 10L bucket… 🙂

I expect Max Prime would work wonders to kickstart small size heartwood chips and anything with a C:N less than 300:1, while Base Prime (cutting the sugar by a quarter) would be good for less than 150:1 or ramial (branch) chipped wood.

One of the other added benefits if you choose your glucose (sugar) source carefully, is that it can be high in potassium, which fungi love. The low phosphorus in urine is also good for fungi too. Adding manure or high phosphorus material however will upset the fungi, and it’s fungi you want to encourage long-term with a continuous supply of carbon.

[1] Carbon and nitrogen additions induce distinct priming effects along an organic-matter decay continuum https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4726261/

Note to self: Don’t calculate at 4AM.