Wednesday, September 30, 2015

Regenerative Organic Agriculture and Climate Change: A Down-to-Earth Solution to Global Warming

Book Review: Regenerative Organic Agriculture and Climate Change: A Down-to-Earth Solution to Global Warming – by Rodale Institute

This is actually a white paper put out by Rodale Institute. See the link to the pdf below:

According to the authors, regenerative organic agriculture, which includes methods such as crop rotation, cover crops, composting, and reduced tillage, can sequester quite large amounts of carbon compared to typical commercial agriculture. This report puts the max safe temp rise at 1.5 deg C which is lower than IPCC’s 2 deg C. The authors here suggest that 100% of annual carbon emissions could be sequestered if these organic regenerative agricultural and pasture management techniques were widely adopted. I doubt that but it is certainly worth taking a more detailed look. Soil-carbon sequestration does indeed have potential. They do acknowledge here that it will take decades, perhaps quite a few, to de-carbonize the economies of the world. 

The authors see regenerative organic agriculture (ROA) as a shelf-ready short-term method of geoengineering for climate change mitigation that has already been successful in small trials. They state that most agricultural soils have lost 30-75% of their original carbon stores. Modern farming also emits N2O and grazing and rice paddy farming emits significant amounts of methane. In farming the main culprits of soil-carbon loss are synthetic nitrogen fertilizer, tillage, mono-cropping, and yield-based management systems. They note that agricultural emissions are about 10% of ghg emissions and they have been increasing about 1% per year. The food system as a whole, they note, accounts for a whopping 30% of emissions. ROA utilizes “closed nutrient loops, greater diversity in the biological community, fewer annuals and more perennials, and greater reliance on internal rather than external resources.” This is akin to methods of “agroecology” the world over. If all crop land utilized such management techniques, that could sink 60% of annual carbon emissions with the rest and more sinkable through regenerative pasture management practices, they say. They think that if even half of all cropland shifted to ROA without any pasture management that would be enough to keep temp rise below 1.5 deg C.

Techniques used as a part of ROA include cover crops, residue mulching, composting, crop rotation, and conservation tillage. Low or no-till practices have yet to take hold in organic agriculture but are vital to ROA. According to Stewart Brand no-till has been used quite successfully with certain GMO crops, which may be more amenable to it.

Exposed soil yields carbon-rich topsoil that is ready to be eroded by wind and water. There is no biomass accumulation happening. Soil aggregates begin the breakdown leading to loss of carbon to the atmosphere. Tillage inhibits the growth and network of mycorrhizal fungi which aid soil aggregation.

Conservation tillage is very important for conserving and fixing carbon. It is best used with organic ag methods in this respect since nitrogen fertilizer adds N2O to the atmosphere and increases microbial respiration of CO2. Phosphorous fertilization suppresses the growth of root symbiotic fungi which is important for long-term soil-carbon storage.

Heavy cover cropping for weed suppression can complement no-till agriculture and increase carbon sequestration rates through time, say the authors. Cover crops can be of several types: ground cover between cash crops, perennial mulching, overwintering cover, and nutrient catch-crops. These have many benefits: erosion reduction, water retention, better root systems in the perennials, better soil structure, better water infiltration, weed reduction, and atmospheric nitrogen fixation.

Enhanced crop rotation, in this case replacing ‘monocropping with fallow’ with ‘polycropping with no fallow’ is recommended. Continuous cover is the goal as soil bacteria and fungi remain in the root zone. Perennial grasses with well-developed root systems are good choices.

No-till systems conserve crop residues of cover crops rather than to burn them or collect them to make biofuels as is common now. Cover crops can also be wholly or partially composted, which refers to controlled aerobic decomposition of the residues. Composting has many known benefits. Composted manure is particularly effective. It has been shown to be superior to nitrogen fertilization in building good soil structure and in sequestering carbon.

The authors emphasize the “holistic interaction of management practices, soil conditions, and climatic circumstances.” They do note that sequestration rates vary according to soil type: clay soils sequester carbon longer than sandy ones. More needs to be discovered about the soil-carbon sequestration potentials of various regional soil types.

Mycorrhizal fungi are root-associated fungi that fix carbon. Generally the more mycorrhizal fungi the more carbon fixing potential. They fix it for longer periods by aiding the process of soil aggregation. Boreal forests are known to have vast networks of MF and fix carbon for very long-periods of time. Soils can also be inoculated with MF, especially damaged soils from tilling.

Interestingly, carbon at depths just below typical till depths tends to be older and more amenable for long-term storage. The authors recommend compost tea, earthworm abundance, and deep-rooted cover crops as ways to introduce more carbon to depths below tillage for longer storage potential. They note trials in both tropical and desert areas to have been very effective in increasing carbon retention in very short time periods. They also note that it is likely that different soils have different unique carbon saturation thresholds that need to be evaluated.

The section on yields is less clear. Mega-studies usually have shown that conventional (fertilizer and pesticide intensive) farming has shown higher yields than organic agriculture. High yields are touted as necessary to feed a growing population. The gap in yields could well be closed with ROA as Rodale evidence suggests. Others have noted that combining successful GMOs with agroecological methods like ROA could be the key to maintaining soil fertility and increasing yields. Clearly there is a need to maintain soil fertility and structure. Yields need to be worked out so that conventional can transition. 

The authors note a clear and pressing need for more trials of agroecology and ROA. They mention a tropical one begun in 2013 in Costa Rica. These practices have so many benefits that it makes sense to pursue them and seek yield and profit parity with conventional systems. If they are even close to conventional yields and profits they should be pursued in a widespread fashion for the numerous other benefits compared to conventional.

 While I think land restoration and reclamation through such methods as these and better grazing practices can go a long way toward keeping carbon from escaping the land I think their optimism and claims of stopping global warming with it are perhaps a bit exaggerated. However, the myriad benefits of such practices need to be further considered. In any case, it is valuable information. It would obviously be better if implemented on the commercial level rather than on the small farm level as that would not be enough. One problem is going to be convincing commercial interests of the value of such practices. This is where science comes in with more and multiple trials in different regions and in different soil types. I heard a talk at a conference recently that attempted to promote similar things with land reclamation and grazing practices and it was received with mixed reactions.  

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