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The Compost Connoisseur 

Compost maturity and stability are not the same 

A mature compost is usually stable, but a stable compost may not be mature.  Yet, both products have their uses.  Though the term“maturity” and “stability” are often used interchangeably to describe compost, they should not be.  

Confused? 

Look at a red and green tomato.  Both are stable and edible.  But the green tomato won’t be mature until it turns red.  This work-in-progress tomato is a bit on the tart side with firmer flesh that holds up when fried.  The mature red one is sweeter, softer, and makes a great sauce. 

As distinct products, mature and immature composts have their specific characteristics and uses, too.  But like red and green tomatoes, they’re definitely not the same. 

Compost maturity and stability 

MATURITY  All organicwill eventually decay until nothing remains but atoms.  The trick is to reach a degradation phase where the easy stuff is gone, leaving only dark, slow-to-degrade, earthy-smelling material behind.  That’s a mature compost. 

Between the raw waste and finished compost, however, are a series of degradation steps that aren’t that beneficial to plants.  In an immature state, compost can release compounds harmful to plants, fight with plants for oxygen, and pull nitrogen out of the soil.  

Compost maturity is best determined by testing, which is a good reason to insist on seeing a recent lab report for the compost under consideration.  Maturity indicators on lab reports include: 

  • C:N ratios  
  • Germination rates  
  • Oxygen uptake  

Maturity assumptions based on curing time are also recognized within the industry, but may not be as reliable as testing. 

STABILITY  If a compost passes the maturity test, it is a stable, market-ready product.  In a mature compost, microbiological activity slows because all the “easy” food has been consumed.  

But there are conditions within the composting mass that can cause product to enter a stable state without reaching maturity. 

Compost that has been dried to remove moisture, for example, makes it lighter for shipping, but can exhibit reduced biological activity, as well.  The same thing happens if the pile is deprived of oxygen. 

Unfortunately, once moisture or air has been reintroduced, microbial colonies can reestablish and return to active feeding.  Pathogens can rebloom and odors resurface as the composting process resumes. 

Germination tests remain one of the best indicators of mature stability.  If the compost exhibits no indications of phytotoxicity in conjunction with good pH ranges and slowed microbial activity, then the product has probably passed into the mature range. 

If trying to evaluate stability while standing next to a pile in a landscape supply yard, look for: 

  • A light, porous, evenly-textured product that encourages good air flow 
  • A compost with sufficient moisture to stick together when squeezed in the palm of the hand without crumbling or dripping water 
  • A pleasant, earthy scent 

Selecting the right product 

In the absence of testing information, the easiest way to gauge a product’s maturity is to smell it.  Compost that smells like soil has likely reached a stable, mature state and is ready for use anywhere and by anyone. 

Product that still retains some pungency isn’t stable or mature.  It’s not quite ready for unrestricted use.  But, provided it has met minimum quality standards for pathogen and vector reductions (as specified by regulations), the compost can be applied in rural areas away from sensitive noses where its higher NPK value is much appreciated by farmers. 

Time and nature will finish the job of product maturation and stabilization. 

What is compost used for?

“What is compost used for?  What’s the difference between compost and manure, or compost and topsoil, or compost and mulch, or compost and…?”

These questions (or some variation thereof) have been posed in Google searches by thousands of McGill Compost website visitors over the years, suggesting a broad lack of understanding on the part of the general public about soil products, in general, and compost products, in particular.

They tell us there’s much more work to be done before compost becomes a solid, steady blip on the soil amendment radar. 

It doesn’t matter whether the compost purveyor is municipal, commercial, or non-profit, or if it’s selling B2C or B2B (or both).   Compost manufacturers, distributors, and retailers can all benefit from marketing programs and advertising campaigns that include a healthy dollop of consumer education along with branding, product descriptions, and price points.

In a recent BioCycle article, Dr. Sally Brown reminds us that “… feel good sayings without quantitative information to back them up doesn’t always help to move the product. To a city engineer, these feel good statements can make you sound like a new age guru pushing a dietary supplement rather than a knowledgeable resource with alternative solutions.

Ouch.  

To be fair to all the OGs out there, in the early days of the composting industry, the only thing we had to peddle was feel good. There was little bona fide research or hard facts that demonstrated compost’s effectiveness to a customer,  just anecdotal evidence and side-by-side field photographs comparing compost and no compost applications.

McGill’s own economic impact studies, conducted in the early 2000s and funded by the state of North Carolina, were among the first to investigate dollar benefits related to compost use.  The research may have been simple by today’s standards, but it validated information our agricultural customers had been telling us for nearly a decade – and provided a solid foundation for the growth of our compost sales program into high-value markets.  (READ: the 2000 and 2001 McGill study reports)

But dollars and cents are only one part of compost’s amazing story that started with fertilizer value, but now just keeps going and going and going to include everything from food waste recycling to stormwater management to carbon storage.

Yet, the abundance of compost’s benefits seems to be a message that hasn’t been told loud enough or long enough or often enough to reach the ears of the majority.  There are still too many stormwater plans out there that don’t fix the soil as a critical first step,  communities that burn or bury compostables, and farmers who don’t use compost on conventionally-managed fields.

Talking who, what, when, where, and how when promoting compost is good.  But today, when a potential customer, policymaker, or specification writer is searching the web, s/he also wants to know the why — backed up with facts and figures.  Why is compost the right solution for their particular problem?   Why is it a better choice than amendment X, Y, or Z?

What is compost used for?

Adding macro and micro nutrients, building soil organic matter, replenishing and sustaining soil microbes, improving nutrient uptake and plant disease resistance, creating pore space, adjusting pH, absorbing rain impact energy, degrading pollutants, storing carbon —  it’s a lengthy benefits list for a single product that just happens to be “green.” 

Fortunately, unlike decades past, cyberspace is now loaded with scientific studies that provide meaningful data related to compost performance.  This is news the marketplace needs to hear.    

For example, it’s true to say compost alleviates compaction.  But when presenting to engineers, would it not be better to also include a link to or slide of this table that compares compost’s performance to other solutions, showing it among the best?

Or when a city is making decisions about its stormwater management strategy, why not share some comparative costs per gallon retained for various retention solutions discussed in Milwaukee’s Green Infrastructure Plan (see Page 63)?

“Compost will hold 10 times its weight in water” is good for visualization.  But how does it help a stormwater system designer calculate potential water and cost savings for mandating compost use vs. rain gardens or storage tunnels?  

These are the types of statistics a decision-maker needs to see when considering options:

  • A typical compost is about 50% organic matter. 
  • Every 1 percent increase in soil organic matter adds 16,000 gallons of water-holding capacity per acre foot.  
  • At only 2 percent organic matter, soil can hold all the rainfall from a typical rain event — around 1 inch or 27,154 gallons. 
  • A 1 percent increase in topsoil organic matter also stores about 60 tons of carbon per acre.

While specific numbers may vary depending on the study and/or source, the core message — that compost can be the better choice — remains constant. 

Researchers say the majority of today’s buyers do their due diligence and make purchasing decisions before reaching out to vendors for that all-important “first touch.”   If true, it’s more important than ever that brochures, point of sale displays, websites, or other outreach tools make the effort to quantify as well as entice. 

The environmental benefits of compost use are still an important part of the message. But the days of the easy sell to a predisposed customer base are long gone.  Now it’s time to win over everyone else.

Expansion of both B2C and B2B markets depends on the industry’s ability to effectively silence skeptics, motivate fence-sitters, and educate the uninformed — while keeping products (and services) cost-competitive.

Facts and figures will play a big role in that education effort.

Granted, there are lots of challenges ahead, and we do need more research of relevance to compost users to help fill quantitative gaps.

But composting is at an unprecedented place in its own history.  For the first time, the general public is eager to know more about what composting and compost use can do to positively impact a wide variety of issues. 

“What is compost used for?”

For the continued growth and wellness of the industry, research-based numbers need to be part of that all-important answer. 

Can I compost cooking oil and grease?

Is it possible to compost cooking oil and grease?

A lot of cooking fat, oil, and grease (FOG) goes down the kitchen drain.  Commercial kitchens install grease traps to collect the mess before it enters public sewer systems, diverting this waste to alternate disposal.

But the typical home kitchen does not, and the practice can clog pipes and negatively impact wastewater treatment systems.

Yes, it is possible to compost FOG.  But for the home composter, volume reduction and reuse is recommended as the first and best management strategy.  Adopt some of these kitchen practices to reduce and reuse to minimize volumes requiring composting or disposal:

REDUCE   

  • Opt for the oven or air fryer instead of deep or pan frying.
  • Spray oil onto food or into pans to lightly coat before cooking instead of pouring oil into the vessel for significant volume (and calorie) reductions.
  • Wipe cooking vessels with a paper towel before washing to remove excess oil.

REUSE

  • Many fats and oils (bacon, peanut, etc.) can be reused.  Cool and pour through a coffee filter or strainer into an airtight container and store in the fridge for up to a month.  
  • Allow cooking juices to cool.  Skim/remove the fat that congeals on the surface and freeze to use later to flavor veggies, soups, etc.   

RECYCLE

  • Check with your public utility to see if there is a FOG drop location in the community.
  • Add cooking grease to the food waste bin if your community composting operation can accept it.

COMPOST AT HOME

  • Small  volumes (up to 1 cup) of plant-based oils are best for home composting.  Simply pour over pile and blend in.  
  • Also compost the paper towels used to wipe oil from pans and kitchen surfaces.      

DISPOSAL

  • Pour waste oil into a non-recyclable can or bottle.  Seal prior to disposal. 

Is it really a good idea to make compostable waste go away and never come back? 

Each year, taxpayers collectively spend millions of dollars to burn or bury compostables.  Much like a tribe of ubiquitous Gollums, they just want garbage — the biodegradable and putrefying fraction of the municipal solid waste stream – to go away and never come back. 

The desire to make disagreeable discards disappear into fiery furnaces or burial mounds is understandable.  But is it wise?  Is it fiscally responsible?  Is it really a good idea to make organic waste go away and never come back? 

Nature recycles everything 

Rocks weather and erode, creating sediment. With heat, pressure, and time, that sediment becomes rock again.  Plants and animals feed and drink from the earth, die, and decompose to replenish the soil that will sustain future generations of flora and fauna.  Water drops from the sky as rain, filters down to aquifers, upwells and evaporates back to the clouds to fall once more. 

In a fantasy land, it may be possible to keep using resources without a thought to replenishment.  But in the real world, organic waste – the decaying residuals of once-living things – must be recycled back to the soil to maintain life-critical soil functions.   

Some seem to think the destruction of organics to make energy is more important than rebuilding soil.  But pushing an organic-waste-to-energy agenda by sacrificing the soil makes no sense. Humans managed to survive for millennia without electricity and centralized energy systems.  Without soil’s life-essential contribution to food and clean water, people face extinction in weeks.  

So, which is more important, energy or soil? 

Make energy and rebuild soil?   

Organic waste from developed societies includes all types of vegetation, food, manures … even compostable plastics.  When turned into a quality compost, these once-lost resources can be used by anyone anywhere to replenish depleted soil.   

Happily, making energy and building healthy soil does not have to be an either/or proposition.  It is possible to extract energy from organic waste without destroying the beneficial properties that make it valuable to soil.   The organic waste streams from these processes can then be used as feedstocks in the manufacture of compost products. 

Unhappily, energy production from biomass is one of the most expensive ways to make energy.  Even solar and wind power can be more cost-effective. 

Furthermore, bioenergy technologies based on anaerobic digestion of organics are still too pricey to be practical in many places.  Where they do exist, the waste stream (digestate) is not always put to highest and best use (i.e. composted).  Instead, residuals may be landfilled or relegated to low-dollar-value reuse. 

But one day, as more communities opt to restore natural soil replenishment cycles and energy generation technologies become more efficient, extracting energy from biomass, followed by composting and compost use, can become the system of choice for organic waste management. 

In the meantime … 

The importance of healthy soil 

Where humans live, topsoil has been scraped away or eroded.  Nutrients are used up.  Compaction has destroyed the pore spaces essential to the transport of air, water, and microbes.  Without a regular infusion of new organic matter to correct these deficiencies, soil dies.   

There are lots of processes for generating energy, but there’s only one way to replenish disturbed soils in developed areas – feed them a good, wholesome diet derived from organic waste converted into compost.   

From farms to lawns to sports fields, soils require periodic applications of compost.  There’s no other way to easily and economically provide soil with everything it requires to retain water, nurture vegetation, and create the type of environment soil microbes need to support nutrient uptake, contribute to disease resistance, and degrade pollutants. 

The best news? In many metropolitan areas, efficient, high-rate composting – the type needed to successfully manage big, urban waste streams – costs no more than landfilling or incineration.  Often, recycling at a modern, industrial composting operation can be more affordable than traditional disposal.   

Composting makes organic wastes go away, but they come back as enriching soil amendments.  Biodegradables need to keep recycling, just like they have since the beginning of time. 

Breaking the natural soil cycle by incinerating or burying compostable waste is a bad idea that should go away and never come back.

VIEW THE SLIDESHARE:  Addicted to convenience

How to make compost fast

The desire to make compost fast can be driven by space restrictions, the need for more product, or simple impatience.   It’s a common goal for composters everywhere, from the backyard to industrial facilities.

Unfortunately, wishing will never make it so.  The speediest course from raw feedstock to finished quality compost is a series of steps controlled by the person doing the composting.  Skip or bungle just one, and biodegradation could slow or even grind to a halt.

It doesn’t matter whether you make compost by the tumbler or by the ton.  If you want to make compost fast, follow these steps:

  1. Consider carbon-to-nitrogen (C:N) ratios when mixing every batch.  Base mixes on the C and N percentage of each feedstock, not feedstock volume – it’s not buckets of “brown” to buckets of “green.”   Learn more about calculating C:N ratios.
  2. Get the blend right with uniform particle size, good porosity, no clumps or marbling of feedstocks.  
  3. Maintain a desirable moisture level throughout primary processing.  Don’t expose the composting mass to weather or allow it to dry out.  Add moisture, as needed.   Learn more about composting moisture levels.
  4. Keep air moving through the pile.  This allows microbes to breathe and removes excess heat.  Invest in a temperature probe and adjust air flow to maintain ideal temperatures.       

Master these basics to make compost fast.

Compost is soil’s superhero

Sure, compost adds nutrients. But that might be this soil amendment’s least important function. 

Quite often, articles will mention compost as a replacement for some or all of the nutrients that might be provided to plants through applications of synthetic (man-made) fertilizers.   

That’s certainly true.  Compost delivers the macronutrients nitrogen, phosphorus, and potassium (NPK), plus a slew of plant-essential micronutrients that are missing from most synthesized fertilizer products.  Compost provides plants with a wholesome, well-rounded meal, not the nutritional equivalent of junk food. 

But what these fertilizer-focused articles rarely mention is the fact that the real value in compost use is not related to feeding plants, but to feeding soil … and soil does require a wholesome diet to function as a true soil and not a dead substrate. 

Compost feeds soil

Providing plant nutrients is just one of many soil functions.  Worms and other creatures that live in healthy soils help to physically break down food sources, then microbes take over to convert that food into plant-available form. 

Both physical and microbial conversion depend on a soil environment that can support those lifeforms.  If the soil is chronically too wet, too dry, too compacted  yada, yada  then it can’t support a healthy soil ecosystem.  That plot of ground may not be soil at all, but lifeless dirt. 

To countermand the impacts of human activity, disturbed soils require regular program of replenishment that includes organic matter and microbes.  Compost provides both.  Compost feeds soil.

Then, when it rains, soil retains that water, reducing runoff.  When runoff is reduced, so is erosion, sedimentation, and water pollution.  Because soil microbial activity also degrades pollutants, any stormwater that does run off is cleaner.  

That same microbial activity can help neutralize some soil-borne diseases, too. 

Improving plant nutrition, aiding in disease control, reducing water pollution, and retaining water are all important soil functions. 

But wait, there’s more. 

Compost as a carbon sink 

The build-up of greenhouse gases in the earth’s atmosphere is cause for concern.  As more greenhouse gases flood the atmosphere, temperatures increase. 

This rise in global temperatures influences many things, erratic and extreme weather being one of the most visible.  Subsequent climate shifts can impact people, crops, and livestock for hundreds of years. 

When used to amend soils, compost sequesters carbon.  This means the soil will act as a carbon “sink,” capturing and holding carbon in stasis – but only as long as the soil remains undisturbed.  When the soil is tilled, that carbon is released. 

Extensive use of compost for perennial crops and other long-term application(grasslands, tree farms, utility easements, etc.) can positively impact atmospheric conditions by reducing greenhouse gases.   

At the same time, the addition of compost rebuilds a topsoil layer that has been eroded or scraped away by farming, development, and other human activity.  Since topsoil loss has been identified as a significant threat to planetary health, second only to population growthits restoration is a global priority.   

At a time when nearly a third of the world’s arable land has become unproductive in just a few decades, compost really can be that superhero swooping in to save topsoil, save water, save the atmosphere, and save the planet. 

Comparing costs per gallon retained 

Soil amendment is one of the least expensive ways to collect and manage stormwater 

Manage water where it falls.” 

This sound advice is the foundation of the Milwaukee Metropolitan Sewerage District’s Regional Green Infrastructure Plana program that identified soil amendment as one of the least expensive ways to manage stormwater.  At 28 cents per gallon, improving soil is second only to native plantings in lowest cost per gallon retained. 

Green roofs?  $4.72 per gallon.  Those fancy-schmancy deep storage tunnels?  $2.42 per gallon.  At $1.59 per gallon, even pretty little rain gardens cost more than five times that of simple soil amendment. 

Milwaukee is not alone in promoting soil amendment as a first line of defense for stormwater management  For example: 

  • Denver and GreenleyColorado, require compost use for new landscaping, as does Leander, Texas. 
  • Some state Departments of Transportation (DOTs) now routinely specify compost.  A few years ago, the Texas DOT said it was the largest single market for compost in the U.S. 

In an urban environment, opportunities for soil amendment abound.  City parks, athletic fields, planters, urban lawns, highway medians and easements, foundation backfill – anywhere there’s soil, there’s opportunity for inexpensive water retention. 

Every 1 percent increase in soil organic matter (SOM) content adds an additional 16,000 gallons of water-holding capacity per acre foot.  A site managed to maintain soil organic matter at only 2 percent can hold all the water of a typical rain event (1 inch or less), which is 27,154 gallons per acre.     

In fact, at 5 percent SOM, the soil can retain the water equivalent of nearly 3-inches of rainfall.  In some regions, this equal95 percent of all storm events. 

Soil amendment may not solve all rainfall issues, especially in downtown areas.  But managing water where it falls can be the most sensible, efficient, environmentally- and economically-prudent strategy for “first line of defense” stormwater management.   

Can compost and perennial food crops save the planet?

A match made in food science heaven has the potential to forever change agriculture’s environmental impact.

Long ago, humans abandoned the hunter-gatherer lifestyle in favor of agriculture. They tweaked deep-rooted perennial grasses, turning them into shallow-rooted annual grain crops with higher yields.

But farming came at a price.  Domestication of wild edibles set off a destructive cycle of soil depletion.

Seasonal tilling loosened soil particles. Wind and rain carried topsoil away. With it went the earth’s ability to store water and sequester carbon.

In the last 200 years alone, the top 2 meters of the earth’s soil have lost 133 billion tons of carbon.

Soil loss has turned into a big problem for today’s humanoids. Topsoil is at a fraction of historic levels.  Storage capacity is dwindling.  Greenhouse gases are building, and global temperatures are rising.

No-till agriculture was once thought a solution to soil loss. By planting in the rubble of the previous crop, farmers didn’t need to plow the soil.  But many no-till farmers rely on heavy doses of chemicals to control weeds. This, we now know, generated its own set of problems.

But no-till put agriculture on the right track.

Perennial crops like orchard fruit, tree nuts, berries, and asparagus produce food.  Because the soil remains undisturbed season to season, these crops are also no-till.

Through photosynthesis, they sequester carbon in the soil for many years.  By adding carbon-rich compost before planting and throughout the crop’s lifecycle, carbon storage becomes even more significant.

But from maize to melons, most of today’s plant-based foods are annuals. These dead-within-a-year plants constitute 85 percent of human calorie intake.  Yet they offer no long-term carbon sequestration and require tillage year after year.

Compost application may boost soil productivity on annual cropland. But much of its carbon is released with the next tilling, too.

So scientists began to ask:

Is it possible to revert more crops, especially grains, to perennial form? Could agriculture meet this goal without sacrificing yields?

Back to the future with Kernza®

The answer appears to be a resounding … could be. Probably … yes. A cautious … quite likely.

Researchers have gone back through time to marry the characteristics of two crops. One is an ancient perennial wheat-like grass. The other is a modern, annual wheat.

Together, they have produced a perennial wheat with the trademarked name, Kernza. This year, General Mills’ Cascadian Farms plans to produce 6,000 boxes of a breakfast cereal featuring the grain as a research fund-raiser. Though total acreage is still small, other commercial applications for Kernza include bread and beer.

In photographs, Kernza kernels look more like a wild rice (a grass) than a wheat berry. But it is considered flavorful and can be harvested using conventional farming equipment.

Deep-rooted (10-20 ft.), this intermediate wheatgrass grows from a rhizome.  It is planted in the fall (in Minnesota).  Most growers plant in rows, but solid seeding is also used.  Weeds are not a big issue, because as the rhizomes spread, they choke out weeds.

The problem is that the kernel is small, like the yield per acre.  Conventional milling equipment doesn’t work.  And, currently, Kernza growers reap a meager 500 pounds per acre. Their conventional wheat-growing counterparts get an average of 2,856 pounds in the U.S.

After a few years, those thick, horizontal stems can run out of expansion space, too. Yields decrease.  As a result, some growers replant every 3-5 years. At least one farmer is experimenting with chisel plow strips to extend productivity to lengthen the time between replanting.  (More cultivation information:  Farmers voice their experience growing intermediate wheatgrass for grain)

The importance of deep root systems and perennial food crops

Worldwide, several annual food crops, including rice, have become the focus of similar research.  Perennials for biofuel production are being studied, too.

Minimizing soil disturbance is one reason. The benefits that come with deep-rooted crops is another.

Living plants remove carbon dioxide (CO2) from the air. They keep some of the carbon (C) and release the rest, along with the oxygen (O2), back to the atmosphere. The retained carbon resides in stems, leaves, and roots. Plants use water and light to turn that carbon into sugars to fuel growth. When plants die and decompose, the carbon becomes a constituent of soil organic matter (SOM).

Deep roots extend the rhizosphere, the zone where roots, soil, and microbes interact. Microbes aid in the transfer of carbon from plants to soil.  Researchers say increasing this area could raise soil carbon storage.

Deep-rooted crops are a tool of what has become known as “carbon farming.”  The goal is carbon sequestration — removing excess from the atmosphere and storing it in the soil, instead.

Moisture and temperature increases could speed up carbon release at lesser depths.   But research suggests deeper soils buffer that carbon from climatic change.

If true, consider the carbon impact of a 20-ft. Kernza root compared to the typical agricultural plant (~3 ft. root depth).  To better understand the potential, this article includes an image comparing perennial Kernza and annual wheat root systems.

Assessing carbon storage potential of perennial food crops

Estimates of the carbon storage potential of “perennialized” annuals are sketchy, at best. None of the new grains have yet to hit their commercial stride.

Research on deep-soil carbon storage is a bit thin, too. It’s difficult to find sequestration estimates that consider all possible impacts like:

  • Reductions in fossil fuel extraction and use
  • Conversion of annuals to perennial crops+
  • Capture of all organics for composting and reuse

But as food for thought, here are some numbers from recent articles and research papers:

  • The soil carbon storage from improved root growth in agricultural crops could offset human-caused environmental emissions for the next 40 years.
  • Reuters: The U.S. emits around 5 billion tonnes of carbon dioxide per year. Better soil management could boost carbon stored in the top layer of the soil by up to 1.85 gigatonnes each year. This is about the same as the carbon emissions of transport globally.
  • Peak Prosperity: A 1 percent increase in SOM stores approximately 10 tons of carbon per acre. Doing the math: There are about 130 million U.S. acres in major annual grain crops. If converted to perennial varieties, carbon storage potential equals 1.3 billion tons.  That’s roughly 1/5 of the U.S. carbon pollution.
  • Bulletin of Atomic Scientists: Devote 5 percent of the world’s cropland to plants bred for carbon storage. Capture ~50 percent of current global CO2 emissions.  (That’s an area about the size of Egypt.)
  • USEPA: In 2015, about 38 million tons of food waste were burned or buried. Only 2 million tons went to composting. Doing the math: Composting all 40 million tons would produce ~20 million tons of soil amendment. This would cover roughly 600,000 acres in 1/2 inch of compost. Its ~11 million tons of carbon (20 million tons of compost @ 54 percent carbon) could go to deep-soil storage under perennials.
  • Life Cycle Assessment (LCA) of landfilling organic waste vs. composting and recycling estimated a net greenhouse gas mitigation benefit of 23tCO2eq/ha over a 3-year period when organics were composted. That’s 23 tonnes (1 tonne = 1,000 kilograms) of carbon dioxide equivalent per hectare — about 25 tons spread over 57 acres.  As little as a 1.3 cm (about a half inch) topdressing of compost resulted in “substantial” increases in carbon storage on rangeland, too, attributed to better water retention and improved grass productivity.

 Economic benefits add up, too

Looks like there’s yet one more reason to bank on perennials — economics.

Agricultural investors say annualized income for perennials rose ~13 percent over 10 years. Income from annual cropland stagnated at about 4 percent during the same period.

And in a few spots, Kernza is generating more profit than the more traditional corn and soybeans. In addition, Kernza leaves and stems remain green at ripening, making its hay more valuable than wheat straw.

Commercialization of annual-to-perennial food crops is a tantalizing possibility.  The day may come when “perennial food” labels sway consumer purchases, just like organic, gluten-free, and other profitable food-niche certifications.

But most enticing is this factoid — at $0-$100 per ton, soil carbon sequestration is the cheapest carbon mitigation tool currently available.

It should be noted that soils can eventually reach a point where no additional C can be absorbed.  Sequestration is not a miracle cure.  People still need to work on reducing CO2 generation.

But in the interim, agriculture offers one opportunity to reduce the human carbon footprint.  And compost under foot makes this challenge easier.

Can compost use impact deep-soil carbon storage?

Atmospheric carbon dioxide (CO2) levels have reached a 3-million-year high.  The overload has been building up since the Industrial Revolution hit its stride about 200 years ago.  One culprit is conventional farming, which releases stored soil carbon, (C) relies on synthetic input, and degrades soils.  The use of fossil fuels — which adds even more carbon to the air — is another major contributor to the increase. 

Impacts include reduction in carbon storage capacity due to topsoil loss, pollution, and climactic changes linked to global warming.

While some say CO2 levels are a non-issue, others believe the opposite and are working to reduce atmospheric carbon by cutting greenhouse gas emissions and sequestering more carbon.

Proposed solutions include ideas like basalt rock injection and ocean storage.   But one of the simplest and most cost-effective options already in play is to simply return carbon to soils.

But there is a catch.  Since soil disturbance releases carbon, farmland dedicated to annual crops offers little to no upper layer storage potential.  Unless the farm — organic or conventional — has adopted no-till practices, the soil is disrupted every year during planting.  Therefore, acres that will remain undisturbed for long periods of time are the best candidates for long-term carbon storage, a.k.a. carbon farming.

This translates into a need for conversion of annual grains and other crops to perennials to maximize soil carbon storage potential.  But developing high-yielding perennial grains is a process that will take time.

Applying compost to both annual and perennial acres is something that can be done now.

Long-term soil carbon storage has two primary pathways — plant-based via deep-rooted perennials (like some trees and grasses) and soil amendment.  Compost leads the pack as the amendment of choice, offering a plethora of soil- and crop-enhancing benefits in addition to carbon storage.

The carbon sequestration benefit of compost use is two-fold.  It adds compost’s inherent carbon content to the soil.  But it also improves soil productivity, increasing above- and below-ground biomass, which stores more carbon.  This positive impact can persist for many years from just one compost application.

Microorganisms and insects like earthworms and ants also influence carbon storage.

Current research emphasis seems to focus on C storage potential in agriculture.  That’s because worldwide, farmers crop 4.62 billion acres — a treasure-trove of carbon storage potential.

But it should be noted there are many more non-ag acres that can offer long-term, deep-soil carbon storage, too.  No need to wait for researchers to develop new perennial grains or convince farmers to make the switch from annuals to perennials.

In the U.S. alone, millions of acres could take and store compost-applied carbon today:

  • 40 million acres of lawns
  • 50 million acres of managed turf including 700,000 athletic fields and 17,000 golf courses
  • 7 million acres of public lands under the jurisdiction of the Bureau of Land Management (FY 2017)
  • Umpteen million acres in government-controlled roadside easements, utility rights-of-way, local and state parklands, and other managed greenspace, both public and private.

Just a 1% increase in soil organic matter (about 20 tons of compost per acre or a 1/4-inch application depth) can store 10 tons of carbon per acre

While it may not be practical or possible to add compost to all those acres, the potential for long-term, compost-based carbon storage in the U.S. alone is … well … pretty big.  And the deeper the storage, the longer the retention time.  Even annually tilled acres can offer C sequestration if that carbon can find a pathway to deeper soils below the plow layer.

But how does compost-applied carbon migrate from upper soil levels to deep-soil storage?

Below the plow layer — deep-soil carbon storage

A “plow layer” is the layer of soil disturbed when a plow (plough) is dragged through a field.  Depending on the type of plow used and its settings, the layer depth can range from a typical 8 inches to 20 inches or more.

The trick is to facilitate the movement of carbon from the plow layer to deeper soils where it can lie locked up and undisturbed for centuries.

Typically, the root systems of trees and perennial grasses grow deeper than annuals.  As the root systems of plants bury themselves in soil, they do more than just carry carbon in their tissues.

Downward growth also creates passageways for water and a transportation route for microbes.

Critter burrows create pathways for water and microbes, too.  Well below the plow line, termite colonies can be found as deep as 6 meters.  Some types of ants live at depths of 3-4 meters.  (1 yard = .91 meters)

Nightcrawlers will work their way down several meters into the soil, bringing organic matter with them.  Their castings (excreta) have a carbon-to-nitrogen ratio of 12-15:1 and include beneficial microbes.  A healthy soil layer above ensures plenty of available carbon for below-the-plow-layer earthworm storage.

C storage depends on many factors

It is important to remember neither the C cycle nor microbial metabolic processes operate in isolation. These functions are influenced by many factors like:

  • Nutrients
  • Temperature
  • Moisture
  • pH

Climate plays a role, too.  Globally, cool-wet regions tend to have the highest concentrations of soil carbon and deserts the lowest.  One of the more disturbing aspects of a warming planet is that more soil-bound carbon may be released to atmosphere as temperatures rise.

Effective solutions will require wholistic approaches, but compost use continues to rank among the top options due to its affordability, universal applicability, ease of use, and immediate availability.

Bottom line:  The potential for deep-soil carbon storage exists, even on annually tilled cropland, through management programs designed to improve soil health and encourage symbiotic facilitators like nightcrawlers.

Can organic waste help green the Sahara for carbon storage?

It has been suggested devoting 5 percent of the earth’s land mass to plants bred for carbon storage could capture about half of global CO2 emissions.

That’s an area about the size of Egypt, a country that has already embarked on a program to reclaim some of the Sahara.  Project drivers are linked to food production, not climate change.  But the Land of the Pharaohs has not had an easy time of it, and some question the plan’s chances for long-term success.

Yet, as agricultural acreage declines worldwide and so many global minds focus on ways to feed a growing earth population, the Egyptian effort does beg the question:

Can reclaimed deserts store carbon and grow food?  More to the point, could composted organic waste help green up deserts like the Sahara or the Kalahari or the Sonoran?

Search the web for successful desert reclamation projects.  The use of compost is integral to all and has been referred to as “fertility priming.”

Capturing and composting organics would be the easy part. Unfortunately, there are major hurdles between barren sand and arable acres:

  • Tilling releases carbon. Unless the crops planted are perennial, some of that applied carbon will be lost.  In Egypt’s case, the goal is more annual grains like wheat and corn, perennials.  However, it should be noted, soil sampling at two of Egypt’s desert farms suggest carbon supplied from organic soil amendments will accumulate, even in oft-tilled fields.
  • While compost holds water, that water has to come from somewhere — if not rain, then rivers and aquifers or, as a last resort, desalination. But river water can be diverted by projects upstream.  Fossil aquifers, like those under northern Africa, are not replenished and will, eventually, dry up.  Desalination is still considered an expensive solution.  This means water availability will continue as the most critical factor to project success.
  • Desert soils tend to be salty, too, which creates unfavorable growing conditions. Fortunately, one permaculture specialist has reported a de-salting effect from building a living soil in the desert.

There seems to be a wealth of anecdotal material out there on desert reclamation, but not much peer-reviewed, scientific research.  Some “research” is based on calculations, not long-term field testing/studies.

In addition, the reclamation farms tend to be smaller “niche” operations — organic, biodynamic, permaculture, etc. — and not large, conventionally managed acreage.

That said, by simply looking at photos and videos, it’s obvious that desert reclamation is possible.  Whether or not it can also be profitable on a large scale remains to be seen.

But if these issues could be resolved, resulting in a clear path for resurrecting vast expanses of sandy soil, how much compost would it take to green a desert?

Most desert soils contain less than 1 percent organic matter.  To make the calculation easy, assume that number to be zero and add enough compost to boost organic matter content (OM) to the recommended 5 percent.

Based on this example,  a 1 inch application requires 135 cubic yards or 54 tons of compost per acre.  This assumes a 60 percent organic matter content, a bulk density of 800 lbs./cubic yard, and 30 percent moisture.

The author of this article about raising soil organic matter (SOM) levels says bumping SOM 1 percent “requires an additional 20,000 lbs. (10 tons) of soil organic matter or 11,600 lbs. (5.8 tons) of carbon, as soil organic matter is roughly 58 percent of carbon.”

The article further calculates stover and root mass from a no-till wheat cover crop system can only be expected to add about 0.1 percent of organic matter to soil.  Obviously, though that percentage might fluctuate a bit depending on the crop and cropping system, one of the fastest ways to build soil organic matter content is not through plants, but through compost use.

At 3.6 million square miles or about 2.3 billion acres, the Sahara is roughly the size of the United States.  It would take billions of tons to make those acres productive.

But balancing out CO2 emissions only requires a couple of plots the size of Egypt.  That’s about 500 million acres.  It sounds like a daunting task until considering there are nearly twice that many farm acres — more than 900 million as of the 2017 agricultural census — in the U.S. alone.

This is doable.  And the best news?  Nary an ounce of waste or compost needs to be hauled to Egypt.  Those 500 million acres can be divvied up and spread across the globe.  From tenders of 10,000-acre ranches to diggers of 100 sq. ft. gardens, anyone can contribute to carbon sequestration.

Of course, playing with numbers is just that — play.   A tremendous amount of effort, plus a megadose of dollars, would be required to convert all world organics to compost.  But rough numbers and real-world economics suggest sequestering carbon through compost use is possible.  (View the SlideShare title: Compost to the Rescue)

And as the World Bank expects the global waste stream to grow by 70 percent by 2050, it sounds like there will be plenty of organics available to get the job done.

Bottom line:  We have the know-how.  We have the technology.  We have the organics.  Costs to produce compost are competitive with landfilling and WTE/incineration.  And whether existing farmland, greenspace, or desert, whether Africa, Asia, or the Americas, we have the acreage needed to clear the air.  The only thing missing? The will to do so.