Effects of enhancing soil organic carbon sequestration in the topsoil by fertilization on crop productivity and stability: evidence from long-term experiments with wheat-maize cropping systems in China

Although organic carbon sequestration in agricultural soils hasbeen recommended as a 'win-win strategy' for mitigating climate changeand ensuring food security, great uncertainty still remains inidentifying the relationships between soil organic carbon (SOC)sequestration and crop productivity. Using data from 17 long-termexperiments in China we determined the effects of fertilizationstrategies on SOC stocks at 0-20 cm depth in the North, North East, NorthWest and South. The impacts of changes in topsoil SOC stocks on the yieldand yield stability of winter wheat (Triticum aestivium L.) and maize(Zea mays L.) were determined. Results showed that application ofinorganic fertilizers (NPK) plus animal manure over 20-30 yearssignificantly increased SOC stocks to 20-cm depth by 32-87% whilst NPKplus wheat/maize straw application increased it by 26-38% compared tocontrols. The efficiency of SOC sequestration differed between regionswith 7.4-13.1% of annual C input into the topsoil being retained as SOCover the study periods. In the northern regions, application of manurehad little additional effect on yield compared to NPK over a wide rangeof topsoil SOC stocks (18 - >50 Mg C ha-1). In the South, average yieldfrom manure applied treatments was 2.5 times greater than that from NPKtreatments. Moreover, the yield with NPK plus manure increased until SOCstocks (20-cm depth) increased to ~35 Mg C ha-1. In the northern regions,yield stability was not increased by application of NPK plus manurecompared to NPK, whereas in the South there was a significantimprovement. We conclude that manure application and straw incorporationcould potentially lead to SOC sequestration in topsoil in China, butbeneficial effects of this increase in SOC stocks to 20-cm depth on cropyield and yield stability may only be achieved in the South