Agricultural production must produce enough food for almost 10 billion people by 2050 [FAO 2017], and yet a third of all land is degraded [FAO 2015] and nearly all agricultural land has lost significant amounts of SOC (Soil Organic Carbon). So we have a puzzle to solve: how to produce more from less, and in the face of a more chaotic climate system. Between 1960 and 1990, the increased use of synthetic fertilizers, pesticides, irrigation, and modern seed varieties nearly doubled world cereal yield [FAO 1996]. Because of this apparent success, it’s not unreasonable to think the answer to the puzzle involves the same combination.
However, we now face a convergence of extremely dangerous crises – global warming, cascading species extinctions, antibiotic resistance, and ubiquitous chemical and nutrient pollution – all of which are aggravated by the current fossil-fuel-intensive industrial model of agriculture. Indeed, the current food system accounts for nearly 30% of total greenhouse gas emissions [Vermeulen 2012]. Furthermore, nearly half of harvested crops are lost because it is thrown away before being eaten or due to overconsumption (food consumption in excess of nutritional requirements) [Alexander 2017]. In spite of this, 11% of the world’s people are still hungry [FAO 2017].
Yet, for each agricultural problem, there is a known solution. For instance, agriculture has the potential to be a carbon sink. Many scientists have found that implementing various conservation practices can sequester up to 1 ton of carbon per hectare per year (1t C/ha/yr), or an estimated ~20% global emissions offset if such practices were broadly implemented [Smith 2008, Lal 2016]). Yet others have measured sequestration rates upwards of 8t C/ha/yr. While climate and soil type play a role in the variation among sequestration rates, farming practices are a major factor.
Studies with lower sequestration rates tend to isolate just one or two soil-building practices. For example, Minasny et al.  compiled sequestration rates from around the world to assess the viability of the France-led “4 per 1000” initiative (seeking to offset the annual increase in atmospheric CO2 by increasing soil carbon by 0.4% per year). The authors estimate that an annual rate of 0.2-0.5t C/ha/yr “is possible after adoption of best management practices on arable land such as reduced tillage in combination with leguminous cover crops” [Minasny 2017: 61]. However, most of some 40 studies of best management practices assessed only one or two practices, often minimally improved, such as “reduced use of summer fallow,” “rice-rice with NPK,” “inorganic fertilizer,” and “pasture” (without mention of how the pasture was managed) [Minasny 2017: 64]. In other words, the “improved” practices here include even the use of synthetic fertilizer, which can generate more crop biomass and thus more residue, but has also been shown to diminish soil organic carbon [Khan 2007].
By contrast, researchers in New Mexico [Johnson 2017] recorded an annual carbon sequestration rate of 10.7t C/ha/yr from fungal-dominant compost in a 4.5-year trial, and they estimate a potential rate of 19.2t C/ha/yr. Chief investigator David Johnson found that increased plant growth is closely correlated with the fungal to bacterial ratio of the soil. Similarly, Machmuller et al.  measured carbon sequestration rates in the southeastern United States of 8t C/ha/yr following conversion of row crop agriculture to management-intensive grazing, leading to an approximately 75% increase in soil carbon within six years.
The studies showing higher sequestration rates reveal what many farmers already know: that it takes not just one, but multiple regenerative practices, to really build soil organic matter (SOM). California Farmers Paul and Elizabeth Kaiser, for instance, use 5-10 times more compost than average, never till, rotate fields with an extremely diverse mix of vegetable varieties, surround their crops with native trees, shrubs and flowers and have thus built up a thick topsoil containing 10% SOM [Oppenheimer 2015; Kaiser 2017]. North Dakota Farmer Gabe Brown began practicing no-till in 1994. Since then, he has added cover crops (a diverse mix of 70 species), complex crop rotations, orchards, livestock grazing (including cattle, sheep, pork and chicken), vegetable production, and bees. By limiting soil disturbance and favoring biodiversity, Brown reports SOM increased from 1.7% in 1993 to as high as 11% in 2013. Over the same period, rainfall infiltration has increased from ½ inch per hour to more than 15 inches per hour [Brown 2016].
Looking at the big picture, researchers at the Rodale Institute  estimate that if all cropland were converted to a regenerative model, it would sequester 40% of annual CO2 emissions. Adding regeneratively managed pastures to the picture would add another 71%, effectively exceeding the world’s yearly carbon dioxide emissions. Teague et al  came up with similar results, estimating that regenerative conservation cropping and adaptive multi-paddock grazing can turn North American agricultural soils from a carbon source in conventional agriculture into a carbon sink at rate of ~3t C/ha/yr. Key factors include the use of no-till, diversified crop rotation, cover crops, organic soil amendments and reducing use of nitrogen (N) fertilizer.
The billion-dollar question, though, remains: can regenerative agriculture feed the world’s ever-expanding population? There is considerable evidence that it can, and in fact the opposite question (can the current model of industrial agriculture feed the world?) deserves at least as much scrutiny, given that so far the answer has been no.
In 2009, a multi-stakeholder team of hundreds of people from every region of the world released the International Assessment of Agricultural Knowledge Science and Technology for Development [IAASTD 2009], which provides a framework for a new global approach to agriculture. It poses the question: how can agricultural knowledge, science and technology (AKST) “be used to reduce hunger and poverty, improve rural livelihoods, and facilitate equitable … sustainable development” [IAASTD 2009: 3] in a global context of mounting social inequity, poverty, human migration, biodiversity loss, and climate change, among other concerns.
Their answer hinges on the concept of multifunctionality of agriculture, or “the challenge … to simultaneously meet development and sustainability goals while increasing agricultural production” [IAASTD 2009: 4]. It calls for a “fundamental shift” in AKST that recognizes “farming communities, farm households, and farmers as producers and managers of ecosystems” [IAASTD 2009: 4], and values both scientific research and traditional and local knowledge. With a focus on multifunctionality,
AKST can contribute to radically improving food security and enhancing the social and economic performance of agricultural systems as a basis for sustainable rural and community livelihoods and wider economic development. It can help to rehabilitate degraded land, reduce environmental and health risks associated with food production and consumption and sustainably increase production [IAASTD 2009: 5].
Thinking of agriculture as multifunctional means valuing agricultural land not only in terms of its capacity for maximum output, but also for its vital role in providing wildlife habitat, sequestering carbon, absorbing and storing rainfall, recycling nutrients, providing for nutritionally balanced diets, and providing the means for an adequate livelihood in farming. And there is abundant evidence that not only do regenerative methods provide these multiple services, they can also be as productive as fossil-fuel-intensive methods, and even more so in times of drought. A 22-year Pennsylvania study [Pimentel 2005] comparing the productivity of conventional versus organic systems showed that while corn yields were comparable overall, during five dry years of the study the organic systems were 28% to 34% more productive than their conventional counterparts.
Thinking of agriculture as multifunctional means valuing agricultural land not only in terms of its capacity for maximum output, but also for its vital role in providing wildlife habitat, sequestering carbon, absorbing and storing rainfall, recycling nutrients, providing for nutritionally balanced diets, and providing the means for an adequate livelihood in farming.
Similarly, a nine-year Iowa study [Liebman 2013] comparing corn and soybean yields in 2-year, 3-year, and 4-year rotations resulted in higher yields from the more diverse 3-yr and 4-yr rotation systems than for the conventional 2-yr system, despite substantial reductions in the use of synthetic N fertilizer, herbicides, and fossil-fuel energy in the longer rotations. The longer rotations also incorporated cover crops and manure fertilizer at planting time, as opposed to the 2-year rotation, which incorporated only synthetic fertilizer, and involved no cover cropping.
These results run counter to other studies that have reinforced the belief that industrial agriculture is necessarily more productive. The authors of the Rodale report offer an explanation for this apparent contradiction:
Meta-analyses of refereed publications show that, on average, organic yields are often lower than conventional. But the yield gap is prevalent when practices used in organic mimic conventional, that is, when the letter of organic standards is followed using an input mentality akin to conventional chemical-intensive agriculture [Rodale 2014: 15].
In other words, a more fundamental commitment to regenerative methods is necessary to bring productivity up to par with that of conventional/industrial methods. Removing the inputs that undergird the success of industrial agriculture will cause the system to falter unless the nutrients and pest resistance provided by those inputs are replaced by that which is proffered through healthy, living soil ecosystems. Indeed, the transition period from industrial system to regenerative system is typically characterized by a drop in yield until the previously damaged soil has come back to life.
Healthy, carbon-rich soil is a powerful engine for plant growth, thanks in large part to the presence of billions of microorganisms working in concert with plants. This includes bacteria living in the roots of leguminous plants that fix plant-available nitrogen, other bacteria defending plants against disease, hyphae-forming fungi attaching to the end of roots and effectively extending those roots deeper into the soil to retrieve micro-nutrients. There are fungi that mine otherwise unavailable soil phosphorus and deliver it to plants, and fungi that help to build the structure of the soil by binding clumps of soil together in aggregates. This aggregation, in turn, facilitates soil aeration and water-holding capacity, while also holding soil organic carbon in place.
It is ironic that in the process of delivering synthetic inputs to feed plants and prevent disease, industrial methods destroy the microorganisms and soil structure that would otherwise serve these purposes. However, for soil to perform these functions in the context of agricultural production requires thoughtful management aiming to protect soil and recycle nutrients. Harvesting a crop removes nutrients from a system, which then need to be replaced. In a wild ecosystem, nutrients consumed are generally replaced by plant litter and animal waste. Nutrients are also made available to plants in healthy, undisturbed soils, by microbial action on mineral particles and rocks. Regenerative agricultural systems mimic this nutrient cycling through compost and manure application, cover cropping, and no-till (which protects the soil, allowing microorganisms to flourish). Moreover, regenerative agriculture mimics wild systems by striving for biodiversity, which improves the stability and productivity of ecosystems.
Also challenging is the fact that a majority of researchers demonstrating climate mitigation through better agricultural conservation practices (Minasny 2017, Zomer 2017, Grimson 2017, Lal 2016, Smith 2008, West & Post 2002, for example) stop short of considering carbon sequestration from a full suite of conservation practices representing a more fundamental commitment to regenerative agriculture. Making only minimal conservation improvements while maintaining the same industrial system tends to result not only in minimal sequestration outcomes, but also lower yields. As noted above, this in-between approach to agriculture risks sacrificing the strengths tendered by a full suite of practices, whether from the industrial or the ecological model.
Murmurings from every corner of the globe reveal that many already acknowledge the imperative, especially for wealthy countries, to radically change our way of living, including the design of our agricultural systems. The vision for societal change varies from cutting fossil fuel emissions to zero within a decade; to building a commons-oriented de-growth economy that values life and sharing over the hoarding of material wealth; to transitioning to a community-based, equitable, agro-ecological food-system.
Specifically responding to the question of how to feed more people with less, like a riddle from the Sphinx, requires thinking outside the box and acknowledging our imperative to radically change ourselves. It’s not enough simply to improve the current industrial agricultural model if, at best, that merely slows progress toward climate tipping points (when the positive feedback loops accelerate global warming beyond our control). Tweaking the current system with small improvements toward inadequate goals is what Margaret Klein Salamon calls “climate gradualism.” For all its political practicality, this approach is like putting a band-aid on a severed limb, and is irrational from the perspective of preserving human civilization in the face of climate breakdown.
In our technophilic society, it may come as a surprise that building biologically active, carbon-rich soil is the answer both to the climate crisis and to the question of how to feed more with less. While protecting and rehabilitating wild ecosystems are also essential, rebuilding the soil in agricultural lands through a regenerative, multifunctional approach is arguably the key to protecting human civilization.
In our technophilic society, it may come as a surprise that building biologically active, carbon-rich soil is the answer both to the climate crisis and to the question of how to feed more with less.
The articles that follow are a small sampling of many recent studies examining various aspects of agricultural ecosystems and food production in the face of climate breakdown. Each provides a glimpse into the range and depth of nature-based tools at our fingertips to transform agriculture into a wellspring of planetary resilience.
Compilation of agriculture articles
Natural climate solutions, Griscom 2017
This is one of the most comprehensive mainstream studies to date of a broad spectrum of natural climate solutions by thirty-two co-authors and supported by The Nature Conservancy. The report examines “20 conservation, restoration, and/or improved land management actions that increase carbon storage and/or avoid greenhouse gas emissions across global forests, wetlands, grasslands, and agricultural lands.” The authors “find that the maximum potential of NCS [Natural Climate Solutions] —when constrained by food security, fiber security, and biodiversity conservation—is 23.8 petagrams of CO2 equivalent . . . This is ≥30% higher than prior estimates, which did not include the full range of options and safeguards considered here.” [Griscom 2017: 11645]. The study seeks to assess both the potential emissions from land use as well as the carbon-sequestration potential.
The study posits a target of <2o C as the conventionally agreed-upon safe limit:
Warming will likely be held to below 2 °C if natural pathways are implemented at cost-effective levels . . . and if we avoid increases in fossil fuel emissions for 10 y and then drive them down to 7% of current levels by 2050 and then to zero by 2095 [p. 11647]
The authors state that their estimates are intentionally conservative because (1) they do not include potential benefits of payments for high-money-value ecosystem services in stimulating NCS efforts; (2) they exclude various management practices where data were not “sufficiently robust for global extrapolation,” e.g., no-till, adaptive multi-paddock grazing, etc.; and (3) significant additional investment would be required to keep warming at 1.5o C. [Griscom 2017: 11648]
Detail is provided on contributions of specific mitigation pathways, such as forests, wetlands, grasslands, etc., and on challenges as well. For example, “Despite the large potential of NCS, land-based sequestration efforts receive only about 2.5% of climate mitigation dollars.” [Griscom 2017: 11648] This observation is consistent with our observations of limited available resources for the most basic NCS education. Other challenges include deforestation for farming and animal husbandry, losing high carbon sequestration benefits of wetlands due to reclamation, and impacts of climate feedbacks such as fire, drought, temperature increases, etc.
We applaud Griscom et al. for an excellent and comprehensive analysis and review of many of the factors in natural climate solutions. We do, however, believe that (1) the potential of nature’s solutions is far greater than Griscom et al. estimate, and (2) that the temperature limits (1.5o – 2o C) are too high and too dangerous – considering that natural processes are already changing, drastically and for the worse, with an average global temperature increase of barely 1o C (see Appendix A: Urgency of the Biodiversity and Climate Crisis).
The differences between the perspectives of Griscom et al. and those adopted in this Compendium are paradigmatic. Griscom et al. acknowledges that their estimates are conservative, looks at a set of studies that tends toward the mainstream and is primarily based on established and widespread practice. This is perfectly reasonable in the process of what Thomas Kuhn calls “normal science” (see Compendium Vol. 1 No. 1 for an extensive discussion of Kuhn’s landmark work). Unfortunately the process of normal science for accepting new thinking and discoveries usually takes decades, and we are currently in the throes of an extinction, and an emergency with respect to biodiversity, and climate change. Therefore we have to accelerate our response. Accordingly, Bio4Climate searches for studies that tend to examine positive variants, i.e., examples of what is possible beyond current conceptual boundaries. We emphasize goals to strive for, even if the data are not yet “sufficiently robust for global extrapolation.” The robustness of such data will increase with more intentional focus.
An interesting side effect of the paradigm difference is that numerous sources that we cite, many from the scientific literature, don’t appear in NCS references (for example, Richard Teague [Teague et al. 2016], Gabe Brown [Brown 2016], Tom Goreau [Goreau 2015], Rebecca Ryals and Whendee Silver [Ryals and Silver 2013], David Johnson [Johnson 2017], Paul and Elizabeth Kaiser [Kaiser 2017], Terry McCosker [McCosker 2000], Carol Evans and Jon Griggs [Evans et al., 2015], to name just a few). Nor are there discussions of permaculture or agroforestry, two of the more promising areas of research and practice in land management that lead to climate-positive results.
Unfortunately the process of normal science for accepting new thinking and discoveries usually takes decades, and we are currently in the throes of an extinction, and an emergency with respect to biodiversity, and climate change. Therefore we have to accelerate our response. Accordingly, Bio4Climate searches for studies that tend to examine positive variants, i.e., examples of what is possible beyond current conceptual boundaries. We emphasize goals to strive for, even if the data are not yet “sufficiently robust for global extrapolation.” The robustness of such data increases with intentional focus.
Drawdown, Hawken, ed. 2017
Edited by innovator and entrepreneur Paul Hawken, Drawdown is a remarkable and comprehensive work presenting eighty well-vetted solutions and twenty promising “coming attractions” to remove carbon from the atmosphere and restore planetary health. Hawken engaged numerous scientists, modellers, advisers, artists and writers, resulting in a beautifully illustrated and comprehensive exploration of possibilities for reversing global warming.
The impact of the book as a whole is as important as each solution: Drawdown presents a universe of actions that go far beyond what we can imagine if we consider only emissions reductions and alternative energy. It leads to an entirely different climate conversation from the one we’re used to, and offers many threads of hope.
Drawdown has something for everyone, covering sectors of Energy, Food, Buildings and Cities, Land Use, Transport, and Materials. Near the top of the list is Women and Girls, whose education has dramatic effects on population and is one of the most important climate positive steps we can take. Of course technology offerings abound, but they are amply balanced by discussions of biology and social change, often sorely missing in debates on global warming. Of particular interest in this Compendium are biological strategies; we’ll mention just three of them here.
Agroforestry in Burkina Faso
After terrible droughts in the 1980s resulted in a 20% reduction in rainfall and millions of deaths by starvation, farmer Yacouba Sawadogo enhanced a traditional practice of digging rain-capturing pits by adding manure. There were seeds in the manure and as a result trees began to grow, holding soils together with roots, protecting plantings from wind gusts that before had required frequent re-sowing, and opening channels that moved water into the soils and raised water tables. This foray into agro-forestry spread across the rural countryside to widespread beneficial effect.
Of great significance is that the expertise, invention and community organizing were native and local, required no foreign aid or expensive soil inputs, and in terms of money cost nothing. This is what sustainability can look like. [Hawken 2017: 118-120]
In 1979, after a devastating fire destroyed his two-thousand acre farm in Australia, Colin Seis began to question why crops and animals couldn’t be profitably raised on the same land, effectively doubling output. Persisting through a difficult transition, Seis saw water retention improvements, decreased input costs, a virtual end to insect infestation, and measures of soil fertility and carbon content go up along with profits. Today, pasture cropping is practiced on over two thousand Australian farms and is spreading throughout the world. [Hawken 2017: 175]
Silvopasture, the most common form of agroforestry, is the practice of combining trees and woody shrubs with pasture grasses. The result is healthier plant and animal growth, including sequestering a respectable one to four tons of carbon per acre. It is currently practiced on over one billion acres worldwide.
For remarkable next steps enter the intensive part of silvopasture, starting with a quickly growing, edible leguminous shrub, Leucaena leucocephala in Australia and Latin America (different species of shrubs are suitable in different ecosystems). Water retention improves, biomass increases, species biodiversity doubles, animal stocking rates almost triple, ambient temperatures decrease by 14 to 23 degrees F in the tropics, meat production increases by a factor of 4 to 10, and perhaps most strikingly, soil carbon sequestration rates have exceeded 10 tons per acre (conventional agriculture can claim 1 ton of carbon per acre or less, or even net carbon loss to the atmosphere). [Hawken 2017: 181]
Intertidal resource use over millennia enhances forest productivity, Trant 2016
Abstract: Human occupation is usually associated with degraded landscapes but 13,000 years of repeated occupation by British Columbia’s coastal First Nations has had the opposite effect, enhancing temperate rainforest productivity. This is particularly the case over the last 6,000 years when intensiﬁed intertidal shellﬁsh usage resulted in the accumulation of substantial shell middens. We show that soils at habitation sites are higher in calcium and phosphorous. Both of these are limiting factors in coastal temperate rainforests. Western red cedar (Thuja plicata) trees growing on the middens were found to be taller, have higher wood calcium, greater radial growth and exhibit less top die-back. Coastal British Columbia is the ﬁrst known example of long-term intertidal resource use enhancing forest productivity and we expect this pattern to occur at archaeological sites along coastlines globally [Trant 2016: 1].
Although focused on forests and not farmland, this study shows that, as in the Amazon, where indigenous people created SOM-rich terra preta soil (akin to biochar-enhanced soil), human populations can increase soil quality and ecosystem productivity beyond what the potential would have been absent human activity.
This is an interesting point with respect to global potential for soil carbon sequestration. Scientists often refer to an equilibrium point, up to which soils can regain carbon previously lost through exploitive human activity. Equilibrium is generally seen as being the point at which new SOC levels are equivalent to or somewhat less than what they were prior to human exploitation of the soil, and never greater than the original amount. While Trant et al.  have found evidence of calcium and phosphorus (not carbon) enrichment due to human activity, their findings raise questions about the extent to which intentionally building soils through all the methods we know to maximize carbon storage could increase various soils’ presumed equilibrium points.
Human occupation is usually associated with degraded landscapes but 13,000 years of repeated occupation by British Columbia’s coastal First Nations has had the opposite effect, enhancing temperate rainforest productivity [Trant 2016: 1].
The ecology of soil carbon: pools, vulnerabilities, and biotic and abiotic controls, Jackson 2017
This review examines “the state of knowledge for the stocks of, inputs to, and outputs from SOM around the world” [Jackson 2017: 422], with a view toward developing better understanding of processes that stabilize SOM. It explains the biological processes involved in carbon cycling and storage, finding that “root inputs are approximately ﬁve times more likely than an equivalent mass of aboveground litter to be stabilized as SOM” [Jackson 2017: 420]. Litter input can either increase or decrease SOM, despite the assumption in most carbon models that there is a linear relationship between litter input and transformation of carbon into more stable forms. This finding suggests that perennials and other deep-rooting plants have an important role to play with respect to carbon sequestration. As the author puts it:
Managing carbon inputs and relative allocation, for instance, through selection for deep roots or for greater belowground allocation in crops (Kell 2011), has been suggested as a way to increase SOM formation and stabilization in such systems (Bolinder et al. 2007, Eclesia et al. 2016). However, plant breeding has traditionally selected for aboveground yields alone; therefore, potential trade-offs between yield and root production must be carefully evaluated (DeHaan et al. 2005). New tools for monitoring root systems and in situ SOM in the ﬁeld are needed (Molon et al. 2017) [Jackson 2017: 422]. . . .
The importance of root inputs for SOM formation is likely attributable to both their chemical composition and, almost certainly, their presence in the soil; upon death, they immediately interact with soil minerals, microbes, and aggregates. Roots tend to be characterized more by aliphatic compounds that are readily sorbed to mineral surfaces, and their composition (and that of root exudates) can increase microbial carbon use efﬁciency (CUE), deﬁned as the ratio of microbial growth to carbon uptake, more than litter can. High CUE promotes microbial growth and carbon stabilization in mineral-associated soil pools, and low CUE favors biomass respiration (Manzonietal.2012a) [Jackson 2017: 423]. . . .
Soils hold the largest biogeochemically active terrestrial carbon pool on Earth and are critical for stabilizing atmospheric CO2 concentrations. Nonetheless, global pressures on soils continue from changes in land management, including the need for increasing bioenergy and food production [Jackson 2017: 420].
. . . plant breeding has traditionally selected for aboveground yields alone; therefore, potential trade-offs between yield and root production must be carefully evaluated [Jackson 2017].
National comparison of the total and sequestered organic matter contents of conventional and organic farm soils, Ghabbour 2017
An analysis of hundreds of soil samples collected from organic and conventional farms around the US shows higher average percentages both of total SOM and of humic substances – a measure of carbon sequestration – for organic farm soils compared to conventional farm soils. The mean percent humification (humic substances divided by total SOM) for organic soils is 57.3%, compared to 45.6% for conventional soils.
Agroforestry strategies to sequester carbon in temperate North America, Udawatta & Jose 2012
This meta-analysis estimates total carbon sequestration potential in the US from various agroforestry practices to be 530 TgC/year (530 million metric tons), equivalent to about 1/3 of annual US carbon emissions from fossil fuel combustion. Based on their literature review, the authors estimate per-hectare sequestration rates (based on aboveground and belowground carbon accumulation) for each practice as follows: 6.1t C/ha/yr (silvopastoral), 3.4t C/ha/yr (alleycropping), 6.4t C/ha/yr (windbreaks), 2.6t C/ha/yr (riparian buffer).
Compost, manure and synthetic fertilizer influences crop yields, soil properties, nitrate leaching and crop nutrient content, Hepperly 2009
A sequestration rate of 2.363t C/ha/yr was demonstrated where compost made of dairy manure and leaves was applied to fields in a three year rotation of corn-vegetable-small grain, with leguminous cover crops. The same rotation treated with chemical fertilizer instead of compost resulted in a net loss of -0.317t C/ha/yr.
Legume-based cropping systems have reduced carbon and nitrogen losses, Drinkwater 1998
This study compared three corn-soybean cropping systems: (1) conventional 2-yr rotation with chemical inputs, and residues returned to soil; (2) a longer (than 2 years), organic rotation with grass/legume hayed and returned to soil in manure; and (3) a longer (than 2 years) organic rotation with grass/legume turned back into the soil directly. Even though the conventional system returned more total residue to the soil, carbon sequestration was significantly lower for the conventional system than for the two organic, legume-based systems. Authors suggest that this is due to greater temporal plant diversity from the longer rotations, and higher quality residue (greater N:C) in the two legume-based organic systems. Furthermore, CO2 emissions were lower in the legume-based organic systems due to 50% lower energy use.
Even though the conventional system returned more total residue to the soil, carbon sequestration was significantly lower for the conventional system than for the two organic, legume-based systems. Authors suggest that this is due to greater temporal plant diversity from the longer rotations, and higher quality residue (greater N:C) in the two legume-based organic systems. [Drinkwater]
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