Greater soil carbon stocks and faster turnover rates with increasing agricultural productivity

Jonathan Sanderman,Stewart Fallon,W Troy Baisden,Mark Farrell,Courtney Creamer

doi:10.5194/soil-3-1-2017

Abstract

Abstract. Devising agricultural management schemes that enhance food security and soil carbon levels is a high priority for many nations. However, the coupling between agricultural productivity, soil carbon stocks and organic matter turnover rates is still unclear. Archived soil samples from four decades of a long-term crop rotation trial were analyzed for soil organic matter (SOM) cycling-relevant properties: C and N content, bulk composition by nuclear magnetic resonance (NMR) spectroscopy, amino sugar content, short-term C bioavailability assays, and long-term C turnover rates by modeling the incorporation of the bomb spike in atmospheric 14C into the soil. After > 40 years under consistent management, topsoil carbon stocks ranged from 14 to 33 Mg C ha−1 and were linearly related to the mean productivity of each treatment. Measurements of SOM composition demonstrated increasing amounts of plant- and microbially derived SOM along the productivity gradient. Under two modeling scenarios, radiocarbon data indicated overall SOM turnover time decreased from 40 to 13 years with increasing productivity – twice the rate of decline predicted from simple steady-state models or static three-pool decay rates of measured C pool distributions. Similarly, the half-life of synthetic root exudates decreased from 30.4 to 21.5 h with increasing productivity, indicating accelerated microbial activity. These findings suggest that there is a direct feedback between accelerated biological activity, carbon cycling rates and rates of carbon stabilization with important implications for how SOM dynamics are represented in models.

Highlights

Sequestration of carbon as soil organic matter (SOM) through shifts in land use and improvements in land management is seen as having the potential to offset a significant fraction of current greenhouse gas (GHG) emissions (Smith et al, 2008; Paustian et al, 2016) and be part of the necessary negative emission technologies that are increasingly believed to be needed to avoid dangerous levels of climate change (Smith, 2016) and as an important stop-gap measure as nations transition to a low carbon economy (Read, 2008)
Only measured in all rotations in 1997 (Baldock, 1998). To overcome this data limitation, we have developed a pedotransfer function using 132 samples from the 1997 dataset, recognizing that since soil texture was similar across the trial, the main variation in Bulk density (BD) will be due to changes in total organic carbon (TOC) content
By 1963, most of the change in soil organic carbon (SOC) stocks had occurred with the exception of the wheat–oat–fallow rotation (WOF) treatment where stocks showed a near-significant (P = 0.08) negative linear trend with time www.soil-journal.net/3/1/2017/

Summary

Introduction

Sequestration of carbon as soil organic matter (SOM) through shifts in land use and improvements in land management is seen as having the potential to offset a significant fraction of current greenhouse gas (GHG) emissions (Smith et al, 2008; Paustian et al, 2016) and be part of the necessary negative emission technologies that are increasingly believed to be needed to avoid dangerous levels of climate change (Smith, 2016) and as an important stop-gap measure as nations transition to a low carbon economy (Read, 2008). J. Sanderman et al.: Greater soil carbon stocks and faster turnover rates and microorganisms in association with this new C because of stoichiometric constraints (Manzoni et al, 2010). Sanderman et al.: Greater soil carbon stocks and faster turnover rates and microorganisms in association with this new C because of stoichiometric constraints (Manzoni et al, 2010) These nutrients are only released upon decomposition of the SOM. Some researchers (e.g., Lam et al, 2013; Kirkby et al, 2014) have gone as far as putting a monetary nutrient cost on SOC sequestration This apparent trade-off is admittedly a bit simplistic because there are other longer-term benefits for hoarding SOC, including improved soil structure, increased water-holding capacity and greater potential to buffer against pH changes (Blanco-Canqui et al, 2013)

Methods

Results

Discussion

Conclusion