Crops for increasing soil organic carbon stocks - A global meta analysis

Quantifying the ability of plants to store atmospheric inorganic carbon (C) in their biomass and ultimately in the soil as organic C for long duration is crucial for climate change mitigation and soil fertility improvement. While many independent studies have been performed on the transfer of atmospheric C to soils for single crop types, the objective of this study was to compare the ability of crops, which are most commonly found worldwide, to transfer C to soils, and the associated controlling factors. We performed a meta-analysis of 227 research trials, which had reported C fluxes from plant to soil for different crops. On average, crops assimilated 4.5 Mg C ha(-1) yr(-1) from the atmosphere with values between 1.7 Mg C ha(-1) yr(-1), for barley (Hordeum vulgare) and 5.2 Mg C ha(-1) yr(-1) for maize (Zea mays). Sixty-one percent (61%) of the assimilated C was allocated to shoots, 20% to roots, 7% to soils while 12% was respired back into the atmosphere as autotrophic respiration by plants. Maize and ryegrass (Lolium perenne) had the greatest allocation to the soil (1.0 Mg C ha(-1) yr(-1) or 19% total assimilation), followed by wheat (Triticum aestivum). 0.8 Mg C ha(-1) yr(-1) , 23%) and rice (Oryza Sativa, 0.7 Mg C ha(-1) yr(-1) , 20%). Carbon allocation to the soil positively correlated to C allocation to roots (r = 0.33, P < 0.05), while correlations between shoot and root biomass on the one hand and C allocation to shoots on the other hand were not significant. The question on the long-term stability of the C transferred to soils remains unanswered.