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.