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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.

Calculating C:N ratios – hitting the sweet spot when blending multiple feedstocks

Cooking may allow the chef to add a pinch of this and a daub of that to create an incredibly edible meal, but more exact measurements and methodologies are required for successful baking.  That’s because cooking is mostly about building and enhancing flavors.  Baking is about understanding and exploiting science.

Composting is about science, too.  Just as curdled custard and flat cookies are indicative of science gone awry, a sluggish composting process and offensive odors are signs someone failed to adhere to the science.

One of the common culprits of composting-science-gone-bad is getting it wrong when calculating C:N ratios.

C means Carbon.  N stands for Nitrogen.  Together, they influence microbial feeding activities.  C provides energy and microbial cell structure while N is linked to proteins, enzymes and other substances integral to cell growth and other biological functions.

The trick, of course, is to hit the composting “sweet spot” with a carbon-to-nitrogen ratio of about 30:1 for the initial feedstock blend.

Forget about “brown” and “green” for calculating C:N ratios

The ubiquitous brown:green rule of thumb for composting — brown materials are carbon, green are nitrogenous — is often promoted to help the backyard composter recognize differences in materials.  But one cannot categorize feedstocks based on color alone.

Coffee grounds may be brown, but they are rich in nitrogen and can actually serve as a substitute for manure (which is also a brown).  Therefore, coffee grounds are “green.”  Peanut shells, also brown, have a near-perfect C:N ratio for composting of 35:1 without combining with any other carbon or nitrogen.

Adding to the brown-green confusion is a mistaken belief that the ratio relates to volumes of brown material and volumes of green, as in 30 buckets of sawdust to one bucket of cut grass.

It does not.

C and N values are derived from the actual carbon and nitrogen content of the individual blend ingredients, not by feedstock volumes, and those numbers are derived from materials testing or generic charted values based on someone else’s tests.

At a micro-scale, the margin of error associated with color confusion may be small enough to make little difference in odor generation or degradation rate for a home compost pile.  But at industrial-scale, calculating C:N ratios needs to be more precise.

The best method of determining carbon and nitrogen content is feedstock testing.  Then, calculations can be made to determine the mix.  When testing isn’t possible or practical, assumptions can be made based on charts like this one.  Washington State University also makes a Compost Mixture Calculator available online that does the math.

C:N impacts on the composting process

C:N is an indicator of the nutrient content of any given material.  Sometimes, a C:N ratio may be expressed as a single number — i.e., 45, 30, 13, etc. This means 45:1 or 30:1 or 13:1.

A lower “C” number indicates higher nitrogen.  Higher Cs indicate more carbon.

For a composting blend, anywhere in the 25-35:1 range is considered good.

A higher carbon content will slow the biodegradation process.  But if carbon content is too low, odors and anaerobic conditions can become management issues.  Too much nitrogen can also raise pH, killing off desirable microorganisms.

Carbon content will naturally drop during composting as microbes use it for energy.  Carbon is also released as CO2.  Nitrogen, however, gets recycled, so the amount at the end of processing is the same as it was in the beginning.

C:N impacts on compost use

The 30:1 ratio is the Goldilocks Zone for composting, but a typical finished compost might have a ratio of 20-25.  (Soil microbes prefer a C:N ratio of around 24:1.)

When added to the soil, composts with higher numbers can encourage microbes to lock up any available nitrogen for their own use, leaving less for plants. Lower ratios reduce the likelihood for food (nitrogen) competition between plants and microbes, since the feeding microbes will still leave plenty of N for plant growth.  Even at a 10-20:1 ratio, there will still enough carbon and nitrogen to allow plants and microbes to successfully share.

However, when the C:N ratio drops below 10, degradation rate for organic matter becomes very high, negating some of the benefit of compost use.

Soil tests, product tests and a chat with the local agricultural or horticultural extension agent should tell growers what they need to know to maximize yields based on the C:N ratio of finished compost.

LEARN MORE:  Carbon to Nitrogen Ratios in Cropping Systems