Articles | Volume 3, issue 1
SOIL, 3, 1–16, 2017
SOIL, 3, 1–16, 2017

Original research article 04 Jan 2017

Original research article | 04 Jan 2017

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

Jonathan Sanderman1,a, Courtney Creamer1,b, W. Troy Baisden2, Mark Farrell1, and Stewart Fallon3 Jonathan Sanderman et al.
  • 1Agriculture & Food, CSIRO, PMB 2, Glen Osmond, SA 5064, Australia
  • 2National Isotope Centre, GNS Science, Lower Hutt, New Zealand
  • 3Australian National University, Canberra, ACT, Australia
  • acurrent address: Woods Hole Research Center, Falmouth, MA 02540, USA
  • bcurrent address: USGS, Menlo Park, CA, USA

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.

Short summary
Knowledge of how soil carbon stocks and flows change in response to agronomic management decisions is a critical step in devising management strategies that best promote food security while mitigating greenhouse gas emissions. Here, we present 40 years of data demonstrating that increasing productivity both leads to greater carbon stocks and accelerates the decomposition of soil organic matter, thus providing more nutrients back to the crop.