Soil Carbon, Grazing & Cropping Grasslands of Alberta, Canada

114 site study.

Grazing:

  • Grazing increased plant diversity
  • Grazing increased introduced species in higher rainfall (>350mm May – Sept) areas
  • Grazing increased aboveground biomass productivity in high rainfall areas, decreased it in lower rainfall areas.
  • Grazing saw no change in SOC in the 6 study regions.
  • Grazing increased root growth in the top 30cm of soil in high rainfall areas.
  • Grazing increased decomposition of plant litter in high rainfall areas.
  • Grazing lowers CO2/N20 flux.
  • Rotational grazing (High intensity, low frequency) significantly lowered CH4 production.
  • Native grasslands store most carbon.

Conclusion: Rotational grazing native grasslands in high rainfall areas FTW.

Cropping:

root mass.png

  • Perennial grasslands produce higher below ground biomass than above
  • Cultivation leads to a rapid loss 30-60% of soil C
  • Continuous wheat cropping led to 19% loss of C
  • Cropping saw 30-40% C loss after 5 years.
  • Silvopasture (perennial pasture system) produced least CO2
  • Naturally re-vegetated areas failed to recover even after 50 years.

Conclusion: Silvopasture intercropping FTW.

Basically what Colin Seis does with Pasture Cropping native grasses.

skpcap

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

Arthropod Predator Community & Soil Carbon Sequestration

The composition of the arthropod predator community and associated cascading effects on the plant community explained 41% of variation in soil C retention among 15 old-fields across a human land use gradient. We also evaluated the potential for several other candidate factors to explain variation in soil C retention among fields, independent of among-field variation in the predator community. These included live plant biomass, insect herbivore community composition, soil arthropod decomposer community composition, degree of land use development around the fields, field age, and soil texture. None of these candidate variables significantly explained soil C retention among the fields. The study offers a generalizable understanding of the pathways through which arthropod predator community composition can contribute to old-field ecosystem carbon storage.

Predator community composition is linked to soil carbon retention across a human land use gradient. – PubMed – NCBI

Cover Crops May Increase Soil Microbial Biomass 3x More Than Compost

Three to six times more microbial biomass carbon and nitrogen depending on soil type.

These results provide evidence that carbon (C) inputs from frequent cover cropping are the primary driver of changes in the soil food web and soil health in high-input, tillage-intensive organic vegetable production systems.

Fresh is best.

Cover cropping frequency is the main driver of soil microbial changes during six years of organic vegetable production

Microbial communities affected by type of carbon “food” sources

carbontypes.png

A new study has found that:

The type of carbon source affects not only the composition and activity of natural microbial communities, but also in turn the types of mineral products that form in their environment.

“We’ve illustrated that as microorganisms alter their environment, their environment then affects the type of microorganisms that are there and their activity.”

Researchers took anaerobic respiration microbial communities and presented them with one of three carbon sources: glucose, a six-carbon sugar; lactate, a four-carbon compound; or acetate, a simple two-carbon compound.

Their analysis showed that a distinct series of changes occurred consistently when microbes were exposed to lactate or acetate-rich environments. However, in glucose-rich environments, they observed varying patterns of changes.

“We think that, because glucose is a larger, more complex compound that can be broken down into many simpler compounds, this opens up more chemical pathways in the community through which it can be used, and that this diverse metabolic potential accounts for the different patterns we’re seeing,” said O’Loughlin.

Impact of Organic Carbon Electron Donors on Microbial Community Development under Iron- and Sulfate-Reducing Conditions

Coastal wetlands excel at storing carbon

coastal wetlands.jpg

“Coastal wetlands store a lot of carbon in their soils and are important long-term natural carbon sinks, while kelp, corals and marine fauna are not.”

Coastal wetlands outperformed other marine systems in just about every measure. For example, the researchers estimated that mangrove forests alone capture and store as much as 34 million metric tons of carbon annually, which is roughly equivalent to the carbon emitted by 26 million passenger cars in a year. Estimates for tidal marshes and seagrass meadows vary, because these ecosystems are not as well mapped globally, but the total for each could exceed 80 million metric tons per year.

All told, coastal wetlands may capture and store more than 200 metric tons of carbon per year globally. Importantly, these ecosystems store 50-90 percent of this carbon in soils, where it can stay for thousands of years if left undisturbed.

“When we destroy coastal wetlands, for coastal development or aquaculture, we turn these impressive natural carbon sinks into additional, significant human-caused greenhouse gas sources.”

Coastal wetlands excel at storing carbon

Clarifying the role of coastal and marine systems in climate mitigation – Howard – 2017 – Frontiers in Ecology and the Environment

Biochar to Terra Preta aka “Black Soil”

Wikipedia tells us Terra Preta is said to have a minimum proportion of 2.0-2.5% organic matter at 50cm depth as the photo below of field-based Terra Preta indicates.

Since most naturally occurring fertile soil becomes anaerobic at about this depth 60cm (2 feet), I wanted to try and emulate Terra Preta levels down to that depth.

It’s important to note that as opposed to field sites, Terra Preta amongst village areas appears much deeper and laden with clay pottery shards that may have originally been buried humanure waste vessels.

terra preta 60cm.jpg

My aim is then 60cm (2 feet) of at least 2.5% biochar.

I have created my back of the envelope calculations based on a soil that has an existing 0.5% in the top 10cm, and I’m using the cheapest charcoal available locally which happens to be this lump charcoal.

I’ve also calculated the lump charcoal bulk density and estimated it’s skeletal density and plugged that information into my biochar spreadsheet.

lump-charcoal-10kg

What I calculated is that to achieve an average of 2.5% organic carbon in that 60cm profile requires approximately three 29 litre boxes of this 10kg lump charcoal in raw form per square meter, or 9.5kg when micronised.

Biochar2TerraPreta.png

Notice the 8% carbon target in the top 10cm in my spreadsheet. Each subsequent 10cm layer is a linear halving of this that when all added up results in 15% total organic carbon distributed through the soil profile. When averaged over the 6 layers this results in the magical 2.5% that Terra Preta is said to have at 50cm.

As I’ve previously written, that 8% is similar to the amounts in biochar field trials that achieve highest yields. While the 2.5-3.0% appears to be the tipping point where plants are sequestering the most amount of carbon into the soil.

There’s your reason Terra Preta is so productive.

Add 15% or 9.5kg of the above micronised charcoal per square meter into the top soil, and you’re gold. Less if your charcoal has a higher bulk density. Over time and under continuous cropping without fallow land the plants roots and microbes in the subsoil will build the soil down two foot, and probably at an accelerated rate in the tropics and high rainfall zones. At over 8% the ecosystem begins to dissolve that carbon and leach it deeper into the soil profile building the soil from top down.

This may be how Terra Preta is said to grow back after mining the top soil and leaving 20cm of it to regrow at pace in the tropics, especially if the micronised charcoal is well mixed with the soil profile.

Mixing that 15% evenly into the two feet for an average of 2.5% carbon, the point where plants then sequester the most soil carbon and build soil, may be another, potentially slower option. The plants will have to build it up to 8% in the top soil for most productivity, at which point dissolved organic carbon is increased and begins to leach through the profile finding an equilibrium.

At a bare minimum to get an existing 0.5% SOC soil to a 2.5% in the topsoil and a 4% total SOC, then about 2.5kg micronised charcoal is needed, or 8.3kg of the above lump charcoal. 2.5kg when micronised.

Biochar2TerraPretaMinimum.png

This is all speculation on my part from my learnings.

And please note: I am yet to implement decreasing air and water volume as the depth increases into the model so take what I’ve written with a grain of biochar.

Native forest soils also tend to decline in a more non-linear manner compared to the linear grasslands when it comes the to soil carbon soil profile used in my model, so the choice of crops may affect the building of soil and the maximising of photosynthesis for a given area.

And remember that because the charcoal is pyrolyzed it is longer lasting in the soil, whereas carbon sequestered by plants tends to oxidise, why we may not see this natural process occurring in all high carbon soils.

End Over Out.

Building Soil.

I’m a firm believer that inputs drive the microbial community. For without regular water, food, shelter and play area, organisms don’t thrive. The best inputs do all of those and more.
Living plants do all these things and more, but sometimes they can use a helping hand to maximise the rate of soil production. What builds soil? Carbon life forms. Without the life forms, soil is called dirt.
The most productive soil to date appears in a protected bay growing sea grass, it has the highest natural soil organic carbon recorded so far. All because when the grass dies it gets buried in the anaerobic sediment and stays there a long time aided by the fact the bay is well protected and nutrients aren’t washed out to sea. The edge effect in action. Other ecosystems that are highly productive are low lying grasslands that receive nutrient run-off from higher elevations. Many of these are in high rainfall areas and actually store more soil carbon than forests. Grasslands tend to create a linear soil carbon profile down to about two foot, whereas forests tend to have a lot up top but less as you go deeper. The key with grasslands is the long, thin and deep rooted perennials that maximise photosynthetic area and can penetrate subsoil. The deeper you go, the less air, the less oxidation, the longer living the soil carbon.

Knowing this, I like to think about what different inputs put into the soil by way of the nutrients, structure, and biology, to change it. I also like to think about what houses and holds onto those nutrients in the soil and builds fertility. Components of soil like the sand, silt, clay, and the succession of these towards structured organic matter. The structure that is formed by carbon-based lifeforms creating the soil mucilages, exudates and porous structures as those lifeforms feed on nutrients and swim and burrow though soils.
How do different farming practises compare at creating these microbial community structures and soil carbon?
Distinct soil microbial diversity under long-term organic and conventional farming
FYM=Farm Yard Manure, CONMIN=Conventional Mineral, BIOORG=Bioorganic, BIODYN=Biodynamic
ismej2014210f1
There is now Direct evidence for microbial-derived soil organic matter formation and its ecophysiological controls.
Basically that means microbes fed glucose can build soil structure without any added plant matter aka humus. Glucose is just carbon, oxygen and hydrogen, and these all exist in the air that plants and some microbes then photosynthesise into sugars. The organisms that can’t, like mycorrhizal fungi, rely on photosynthesising hosts.

When I see just how often carbon appears in the below image, it reminds me of its importance. Carbon beats out nitrogen by 4 atoms and it also forms the sugar phosphate backbone.

So along with carbon, nitrogen, and oxygen, if you just add nitrogen from the air and phosphorous from the soil then you’re ready to spin the spiral staircase and begin to churn the primordial soup.
dna-rna-structure

As a result, carbon is responsible for so much diversity.
Soil organic carbon (SOC) appears to be correlated with microbial diversity and abundance.
Bacterial abundance and diversity appears to increase linearly, at least to 4% SOC.
Fungal abundance also increases linearly, however diversity appears to taper off up to 4% SOC, or it could just be that there isn’t enough data on high carbon soils.
microbialsoc
I’ve read that “Higher soil pH values were consistently associated with higher bacterial diversity indices.”
I’ve also read the same of fungi and that Soil-available potassium was positively correlated with mycorrhizal colonization and species richness.
There’s also the Bacterial:fungal ratios are of limited utility for understanding soil processes that goes against some people beliefs.

One subject kept popping up in my soil carbon learnings, and that was just how important soil moisture is in keeping microbes active and not dormant or dead. Increasing aridity reduces soil microbial diversity.

Biocrusts are an amazing example at one end of the extreme. They can wake at a drop of rain landing on hydrophilic hairs on their surfaces, yet sleep an age during the dry times. Sleeping because without that rain the protein folding within cells doesn’t happen. The fine hairs on their surfaces even harvest atmospheric water, it’s that important.
A large Australian Soil Carbon study showed that soil moisture was correlated with 76% of SOC. That pH and soil bulk density were also important, but after that, not much else. The better the soil bulk density is, the better the soil/air exchange, while pH makes for happy microbes that breathe that air. It’s not a coincidence that soil carbon tends to buffer pH then.
Higher levels of soil carbon also increase soil moisture holding and reduces soil bulk density.
Another Brazilian forests study found 86% of soil nitrogen correlated with SOC.
I watched a Terra Preta documentary the other day. They were harvesting the high carbon black soils and trucking it out. The land owner claimed that if he left 20cm of the soil, that the deep black soil “grew back” over time. Fact or fiction? Are there microbes in the soil somehow creating long lasting soil carbon or are the soils simply at a tipping point with the 20cm and it’s enough to create or hold shorter-term carbon that may oxidise over time? Beats me. I do however know there are different forms of soil carbon and not all are equal.

Why I really love the notion of a Soil Carbon Continuum, it’s never ending. 🙂
Carbon and nitrogen additions induce distinct priming effects along an organic-matter decay continuum
srep19865-f1

As for adding biology to soils, there is a lot to consider. I wrote about Bokashi and Natural Farming in this thread recently. The results at the bottom of that post seem to indicate it works, but is that the ingredients or biology or a combination? Work With Nature on YouTube and his friend are performing a trial where they boil a compost tea and compare with a biologically active tea. I’m interested to see their results.