What Agriculture Can Learn from Native Ecosystems in Building Soil Organic Matter: A Review

Abstract

Over the last century, researchers and practitioners with diverse backgrounds have articulated the importance of improving soil organic matter (SOM) contents in agricultural soils. More recently, climate change scientists interested in CO 2 sinks, and agroecologists interested in ecological intensification have converged on the goal of building SOM stocks in croplands. The challenge is that agriculture itself is responsible for dramatic losses of SOM. When grassland or forest ecosystems are first converted to agriculture, multiple mechanisms result in SOM declines of between 20% and 70%. Two of the most important mechanisms are the reduction in organic matter inputs from roots following the replacement of perennial vegetation with annual crop species, and increases in microbial respiration when tillage breaks open soil aggregates exposing previously protected organic matter. Many agricultural practices such as conservation tillage and integration of cover crops have been shown to achieve some degree of SOM improvement, but in general adoption of these practices falls short of accumulating the SOM stocks maintained by grasslands, forests or other native ecosystems that agriculture replaced. Two of the overarching reasons why native terrestrial ecosystems have achieved greater soil organic matter levels than human agroecosystems are because they direct a greater percentage of productivity belowground in perennial roots, and they do not require frequent soil disturbance. A growing body of research including that presented in this review suggests that developing perennial grain agroecosystems may hold the greatest promise for agriculture to approach the SOM levels that accumulate in native ecosystems. We present calculations that estimate potential soil organic carbon accumulation rates in fields converted from annual to perennial grains of between 0.13 and 1.70 t ha −1 year −1 .

Strategies, Advances, and Challenges in Breeding Perennial Grain Crops

“…Numerous papers have been published over the last decade describing predicted improvements in soil carbon balance, nutrient retention, soil water uptake efficiency, soil microbiome functions, and weed suppression, as annual crops that require soil disturbance and/or frequent exposure to maintain are replaced by perennial crops that require minimal soil disturbance or periods of exposure [1][2][3][4][5][6][7]. Other papers have addressed questions of why humans originally domesticated annual grain crops and what strategies make sense for domesticating new perennial grain crop species [8][9][10][11].…”

A preview of perennial grain agriculture: knowledge gain from biotic interactions in natural and agricultural ecosystems

“…2). Many studies indicate that changes in biological and chemical soil characteristics such as soil organic matter accumulation, biodiversity, and biomass of various soil organisms as well as food web complexity in the transition from rotational to perennial crops are long-term processes (Culman et al 2010, Henneron et al 2015, Coulibaly et al 2017, Crews and Rumsey 2017, Scott et al 2017). Hence, it can be expected that potential benefits of soil conservation mediated by species interactions are only reached after several years, and effects of soil interventions such as crop replanting remain unclear.…”

Perennial Grain Legume Domestication Phase I: Criteria for Candidate Species Selection

“…Lastly, the large rooting systems of perennial legumes function to increase soil organic C by reducing erosion, reducing microbial respiration (via lack of tillage) and by adding large amounts of C back into the system. As a result, nutrients are retained in the cropping system for use by the current and subsequent crops [20,112]. Preferred legume candidates will have one or more of these nutrient acquisition and/or retention strategies, will maintain and build the soil fertility in the field where it is grown, and thus, will improve the productivity for the subsequent rotational species.…”

“…Perennial grain legumes retain the natural synchronicity of N supply and demand during grain fill and have small rates of N loss in the cropping system [17]. In annual cereal grain systems with an annual legume cover crop, the legume may fail to meet the cereal grain's N requirements because the rhizobia-symbiosis exists for only a fraction of the growing season, because using tillage to terminate the legume cover crop can change the carbon-nitrogen balance, because loss of N from the soil occurs due to its volatility and mobility and because complete synchronicity of the legume N supply and the cereal grain N demand is extremely difficult to achieve for maximum productivity [20][21][22].…”