Temporal variation of SOC storage and crop yield and its relationship - A fourteen year field trial about tillage practices in a double paddy cropping system, China.

Carbon (C) sequestration in agricultural systems is recommended as a beneficial measure for climate change mitigation and food security. Despite much research, the relationship between soil organic carbon (SOC) storage and sustainable crop productivity has not been identified for various agricultural ecosystems, especially in the paddy ecosystem where conservation tillage has been adopted. Thus, a long-term experiment was conducted to evaluate the effects of tillage practices on SOC storage, yield, and their relationship in a double-cropped rice (Oryza sativa L.) paddy in Southern China from 2005 to 2018. Four tillage systems were investigated: no-till with residue retained on the soil surface (NTS), rotary tillage with residue retention (RTS), plow tillage with residue retention (CTS), and plow tillage with residue removed (CT). The SOC accumulation in the 0-20 cm layer in tillage systems included two stages: the rapid accumulation stage (2005-2007) and the slow fluctuation stage (2007-2018), with a tendency for C saturation. After reaching C saturation, the increase in SOC storage was not obvious, even with continued C input, and the SOC storage under different tillage systems was inconsistent. In general, SOC storage under NTS was the greatest. Interannual changes were not significant, while cumulative yield (2005-2018) was highest under CTS (162.13 t ha), followed by RTS (158.46 t ha), NTS (153.99 t ha), and CT (149.70 t ha). Tillage practices had no effect on the yield stability of late rice, but a significant difference in early rice was noticed between CTS and RTS. A non-linear relationship between rice yield and SOC storage was significant (P < 0.0001). With increasing SOC, yields tended to increase first and then decrease. Thus, innovative tillage strategies (such as NTS) could increase SOC storage before it reaches C saturation, but maintaining SOC storage within a reasonable range and optimizing SOC distribution might be more beneficial for crop productivity than a higher SOC storage, especially in C-rich paddy fields.