Compendium Vol. 2 No. 2: Worthy Miscellany

Compendium Volume 2 Number 2 January 2019 r.1

Direct evidence for microbial-derived soil organic matter formation and its ecophysiological controls, Kallenbach et al. 2016

Although the overall contribution of decaying plants, available substrate, and microbes to the buildup of soil organic matter (SOM) is well recognized, their individual contributions are not as clearly understood. Analytical shortcomings have constrained a thorough study that can distinguish the amount of SOM attributable to plants and the amount attributable to microbes.  Using pyrolysis-GC/MS, the authors investigated the chemistry of carbon and microbe-depleted soils after 18 months, after inoculation by various substrates and with two clays (montmorillonite and kaolinite).

By six months, active microbial communities were present in all inocula save one, and SOM molecular diversity increased across all model soil systems. Soils treated with either sugar or syringol (a structural component of cell walls) contained substantial concentrations of lipids and proteins after 18 months. Soil organic carbon (SOC) also increased over time. Syringol-treated montmorillonite soils accumulated the most carbon, and had lower bacterial and higher fungal abundance than sugar-treated soils. Higher fungal abundance was positively correlated with carbon use efficiency (CUE) across treatments.

The authors concluded that the microbial community may be a stronger driver of SOM development than the soil’s mineralogy. They also found that their sugar- and syringol-treated samples provided a chemical diversity that was as rich as natural soil. This article contributes to an expanding scientific knowledge base regarding soil ecosystems and the critical role of soil microorganisms vis a vis the carbon cycle.  

Global assessment of agricultural system redesign for sustainable intensification, Pretty et al. 2018

This article highlights the relevance of the concept of “sustainable intensification” (SI), wherein farming practices are improved to produce more crops (intensification) while doing no harm to – and possibly even enhancing – the environment (sustainable).

The combination of the two terms was an attempt to indicate that desirable outcomes, such as more food and better ecosystem services, need not be mutually exclusive. Both could be achieved by making better use of land, water, biodiversity, labour, knowledge, and technologies [Pretty 2018: 441].

Having screened hundreds of SI projects/programs worldwide and selected those implemented at a large enough scale to benefit ecosystem services and agricultural objectives across whole landscapes, the authors estimate that 29% of all farms worldwide and 9% of agricultural land have crossed a transformative threshold in their use of SI methods.

Sustainable intensification can be achieved in three non-linear stages of transition: (1) improved efficiency (such as through precision agriculture, which uses sensors to target fertilizer application, thereby wasting less), (2) substitution (such as substituting biological control agents in the place of synthetic inputs), or (3) system redesign. The authors state that of these three stages, only system redesign is capable of “maximizing co-production of both favorable agricultural and environmental outcomes at regional and continental scales” [Pretty 2018: 442].

The authors describe system redesign as follows:

The third stage is a fundamental prerequisite for SI to achieve impact at scale. Redesign centres on the composition and structure of agro-ecosystems to deliver sustainability across all dimensions to facilitate food, fibre and fuel production at increased rates. Redesign harnesses predation, parasitism, allelopathy, herbivory, nitrogen fixation, pollination, trophic dependencies and other agro-ecological processes to develop components that deliver beneficial services for the production of crops and livestock. A prime aim is to influence the impacts of agroecosystem management on externalities (negative and positive), such as greenhouse gas emissions, clean water, carbon sequestration, biodiversity and dispersal of pests, pathogens and weeds. Whereas efficiency and substitution tend to be additive and incremental within current production systems, redesign brings the most transformative changes across systems [Pretty 2018: 442].

We analysed transitions towards redesign in agricultural systems worldwide. We reviewed literature on SI, including meta-analyses and practices, to produce a typology of seven system types that we classify as redesign: (i) integrated pest management, (ii) conservation agriculture, (iii) integrated crop and biodiversity, (iv) pasture and forage, (v) trees in agricultural systems, (vi) irrigation water management and (vii) intensive small and patch systems [Pretty 2018: 443].

By showing that “the expansion of SI has begun to occur at scale across a wide range of agroecosystems” [Pretty 2018: 444], this analysis offers a roadmap for how to transition global agriculture toward systemic ecosystem and community resilience in the face of global warming. The authors emphasize the importance both of social networks and cooperation for the co-creation and sharing of agricultural knowledge, and of state policies to support or at least not undermine SI expansion. The authors suggest that agricultural management may be at a crucial tipping point, where “a further small increase in the number of farms successfully operating re-designed agricultural systems could lead rapidly to re-design of agriculture on a global scale” [Pretty 2018: 445].

For the full PDF version of the compendium issue where this article appears, visit Compendium Volume 2 Number 2 January 2019 r.1