Sequestering carbon in grassland soils (Score 2, Informative)

Grasslands can sequester enormous amounts of carbon in the form of soil organic matter, especially humus. Unless disturbed by plowing or poor land management, humus can remain stable for hundreds or thousands of years. Healthy grasslands can sequester considerably more carbon than forests, because grasslands can keep growing soils indefinitely. This is how grassland soils 1-4 meters (3-12 feet) thick -- the agricultural soils of today -- got built over much of the temperate zone.

Advantages of sequestering carbon with grasslands:

1. Carbon sequestration in grassland soils can be done inexpensively, using existing technology that is available everywhere in the world -- see below for details.
2. The amount of carbon that can be sequestered is enormous -- often 10-20 metric tonnes/hectare (4-9 tons/acre) per year of organic matter, which is about half carbon by weight (56%).
3. The amount of land available to do this on is also enormous. Grasslands occupy 20-25% of Earth's land area. There are also huge areas of desertified land that were grassland 50 to 5000 years ago, such as South Africa's Karoo (a grassland 300 years ago, mostly desert now), much of North Africa and the Middle East, and large portions of the western U.S.
4. Crops can be planted in grasslands, using a method called pasture cropping (see http://www.grainandgraze.com.au/ColinSeis.htm). Most farmed soil loses organic matter (and therefore carbon) to the atmosphere and erosion. Pasture-cropped land can grow soil.
5. The same management that increases carbon sequestration also generates other benefits, such as increasing soil's ability to capture water (thus reducing floods and droughts, and increasing groundwater recharge), improving habitat for wildlife, and increasing biodiversity.

Let's do some calculations:

• Earth's land area is, conservatively, 148,300,000 km2, or 14,830,000,000 hectares
• Grasslands cover 1/5 of that, about 300,000,000 ha.
• Sequestering 7 tonnes/ha/year on that land absorbs 2.1 Gt/year, which is 1/3 of the 6.5 Gt emitted annually by burning fossil fuels and making concrete. It won't do the whole job, but it's a start.

How do grasslands sequester carbon? Here's how it works:

1. Perennial grasses use atmospheric carbon to build their tissues. (Most of the dry weight of a plant is atmosphere-derived carbohydrates such as cellulose; very little comes from the soil.) About half a perennial grass plant's mass is roots below ground.
2. Grazing animals eat the plants' leaves, and then move elsewhere, as wild herds moved in nature.
3. The grass plants pull nutrients out of some of their roots to grow new leaves, and shed the excess roots. These roots feed soil organisms, which convert a large portion of them to soil humus.
4. The grasses regrow their leaves. At this point they have still not regrown completely, and further grazing would damage them.
5. The plants regrow their roots.
6. At this point the plants have completely recovered from grazing, and can be grazed again.

This is how grasslands and grazers evolved to function. This type of "pulsed grazing" can sequester enormous amounts of carbon, and grow 10-30 mm of new soil per year.

Animal behavior is crucial

The trick to making this work is the behavior of the grazing animals. Grazers must behave in the ways grass plants are adapted to. That means moving onto the land in a tightly bunched herd (as wild grazers did because of predation), grazing and trampling intensively, then moving on and giving plants adequate time to recover before they get grazed again.

If grazer behavior is correct, the grasses don't much care whether they are grazed by bison, kangaroos, or cattle. If the behavior is incorrect (too-frequent grazing that weakens plants that are not yet fully recovered, or too-infrequent grazing that weakens plants by allowing standing dead growth to accumulate and shade the plant's growth points), even wild grazers can cause severe damage. Damage caused by specific, unnatural grazer behaviors is what's given grazing a bad name. Grasslands and grazers evolved together, and eacth depends on each other.

Most of the world no longer has enough wild grazers to maintain healthy grasslands, and what wild grazers remain no longer behave naturally because of fencing, elimination of their natural predators, etc. So most of the work of regenerating the world's grasslands is going to have to be done with livestock, at least for now. That means that solving the world's atmospheric carbon problem is going to create a lot of rural jobs, because good grazing management requires managing the animals, not just sticking them in a pasture season-long.

The methods to manage grasslands for maximum health and high soil carbon sequestration have been around for about 25 years, and have been proven to work worldwide in seasonally dry climates -- the places where grasslands naturally grow.

More information:

"How to build new topsoil" by soil scientist Christine Jones
http://managingwholes.com/new-topsoil.htm

"Grazing management for healthy soils" by Christine Jones
http://managingwholes.com/grazing-soils.htm

"How can grazing heal land?" by Wilma Keppel
http://managingwholes.com/grazing-heals-land.htm

Environmental restoration success stories, done with regenerative grazing:
Western U.S.:
http://www.ecoresults.org/
Worldwide:
http://managingwholes.com/--environmental-restorat ion.htm

Carbon Coalition Against Global Warming
http://www.carboncoalition.com.au/

Carbon Farmers of America
http://www.carbonfarmersofamerica.com/

How managing the soil surface can reduce floods and droughts, and increase groundwater capture(Flash slide show):
http://managingwholes.com/flash/wcSlideshow.htm