Large uncertainty in soil carbon modelling related to method of calculation of plant carbon input in agricultural systems

&NA; The application of dynamic models to report changes in soil organic carbon (SOC) stocks, for example as part of greenhouse gas inventories, is becoming increasingly important. Most of these models rely on input data from harvest residues or decaying plant parts and also organic fertilizer, together referred to as soil carbon inputs (C). The soil C inputs from plants are derived from measured agricultural yields using allometric equations. Here we compared the results of five previously published equations. Our goal was to test whether the choice of method is critical for modelling soil C and if so, which of these equations is most suitable for Swiss conditions. For this purpose we used the five equations to calculate soil C inputs based on yield data from a Swiss long‐term cropping experiment. Estimated annual soil C inputs from various crops were averaged from 28 years and four fertilizer treatments; the average was 3.6 Mg C ha−1 and covered a surprisingly large range from 2.1 to 5.3 Mg C ha−1 year−1 among the five equations. For single crop species, differences reached 6.6 Mg C ha−1 year−1. The variation between estimated soil C inputs depended on crop type and increased with yield. Simulations with the model C‐TOOL showed that calculated SOC stocks were affected strongly by the choice of the allometric equation. With four equations, a decrease in SOC stocks was simulated, whereas with one equation there was no change. This considerable uncertainty in modelled soil C is attributable solely to the allometric equation used to estimate the soil C input. We identify the evaluation and selection of allometric equations and associated coefficients as critical steps when setting up a model‐based soil C inventory for agricultural systems. HighlightsUncertainty analyses in soil C modelling have focused mainly on model parameters and structures.The uncertainty related to estimation of soil C inputs from crop residues was calculated.Simulated soil C stocks and stock changes depend strongly on the method of estimating C input.The method to derive soil C inputs is critical for model‐based soil C inventories.

[1]  Uwe Franko,et al.  Multi-site validation of a soil organic matter model for arable fields based on generally available input data , 2011 .

[2]  A. Fliessbach,et al.  Soil organic matter and biological soil quality indicators after 21 years of organic and conventional farming , 2007 .

[3]  R. B. Jackson,et al.  A global analysis of root distributions for terrestrial biomes , 1996, Oecologia.

[4]  K. Killham,et al.  Carbon distribution within the plant and rhizosphere in laboratory and field-grown Lolium perenne at different stages of development , 1990 .

[5]  J. A. Veen,et al.  Production of root-derived material and associated microbial growth in soil at different nutrient levels , 2004, Biology and Fertility of Soils.

[6]  H. Janzen,et al.  An approach for estimating net primary productivity and annual carbon inputs to soil for common agricultural crops in Canada , 2007 .

[7]  S. Gerber,et al.  Land use change and nitrogen feedbacks constrain the trajectory of the land carbon sink , 2013 .

[8]  T. Kätterer,et al.  Parametrization consequences of constraining soil organic matter models by total carbon and radiocarbon using long-term field data , 2016 .

[9]  D. Dubois,et al.  Soil Fertility and Biodiversity in Organic Farming , 2002, Science.

[10]  G. Buyanovsky,et al.  Carbon cycling in cultivated land and its global significance , 1998 .

[11]  A. Gorissen,et al.  Carbon allocation to roots, rhizodeposits and soil after pulse labelling: a comparison of white clover (Trifolium repens L.) and perennial ryegrass (Lolium perenne L.) , 2004, Biology and Fertility of Soils.

[12]  Martin Körschens,et al.  Simulating trends in soil organic carbon in long-term experiments using RothC-26.3 , 1997 .

[13]  Jørgen E. Olesen,et al.  A flexible tool for simulation of soil carbon turnover , 2002 .

[14]  Jørgen E. Olesen,et al.  Modelling soil organic carbon in Danish agricultural soils suggests low potential for future carbon sequestration , 2016 .

[15]  N. Hansen,et al.  Winter cereal root growth and aboveground–belowground biomass ratios as affected by site and tillage system in dryland Mediterranean conditions , 2013, Plant and Soil.

[16]  Q. Shao,et al.  Convergent modelling of past soil organic carbon stocks but divergent projections , 2015 .

[17]  C. Royo,et al.  Changes in durum wheat root and aerial biomass caused by the introduction of the Rht-B1b dwarfing allele and their effects on yield formation , 2016, Plant and Soil.

[18]  N. H. Ravindranath,et al.  2006 IPCC Guidelines for National Greenhouse Gas Inventories , 2006 .

[19]  Peter J. Gregory,et al.  The fate of carbon in pulse-labelled crops of barley and wheat , 1991, Plant and Soil.

[20]  J. A. Veen,et al.  Assimilate translocation to the rhizosphere of two wheat lines and subsequent utilization by rhizosphere microorganisms at two soil nitrogen concentrations , 1990 .

[21]  J. Liski,et al.  Carbon and decomposition model Yasso for forest soils , 2005 .

[22]  Fusuo Zhang,et al.  Plant carbon partitioning below ground in the presence of different neighboring species , 2008 .

[23]  J. Olesen,et al.  C-TOOL: A simple model for simulating whole-profile carbon storage in temperate agricultural soils , 2014 .

[24]  Y. Kuzyakov,et al.  Carbon input by plants into the soil. Review. , 2000 .

[25]  D. F. Grigal,et al.  Vertical root distributions of northern tree species in relation to successional status , 1987 .

[26]  Eva‐Maria Klimanek.  Bedeutung der ernte‐ und wurzelrückstände landwirtschaftlich genutzter Pflanzenarten für die organische substanz des Bodens , 1997 .

[27]  Christophe,et al.  Rhizodeposition of organic C by plants: mechanisms and controls , 2003 .

[28]  Y. Kuzyakov,et al.  Carbon partitioning and below-ground translocation by Lolium perenne , 2001 .

[29]  H. Oberholzer,et al.  Consequences of Conventional versus Organic farming on Soil Carbon: Results from a 27-Year Field Experiment , 2009 .

[30]  T. Kätterer,et al.  ICBM regional model for estimations of dynamics of agricultural soil carbon pools , 2004, Nutrient Cycling in Agroecosystems.

[31]  Rattan Lal,et al.  Global Potential of Soil Carbon Sequestration to Mitigate the Greenhouse Effect , 2003 .

[32]  N. Batjes,et al.  Total carbon and nitrogen in the soils of the world , 1996 .

[33]  C. Jones,et al.  Development and evaluation of an Earth-System model - HadGEM2 , 2011 .

[34]  A. Lüscher,et al.  An overlooked carbon source for grassland soils: loss of structural carbon from stubble in response to elevated pCO2 and nitrogen supply. , 2006, The New phytologist.

[35]  Peter J. Gregory,et al.  Drought affects the fluxes of carbon to roots and soil in 13C pulse-labelled plants of wheat , 1997 .

[36]  M. Reichstein,et al.  Priming and substrate quality interactions in soil organic matter models , 2012 .

[37]  N. Ramankutty,et al.  Farming the planet: 2. Geographic distribution of crop areas, yields, physiological types, and net primary production in the year 2000 , 2008 .