Responses of soil organic and inorganic carbon to organic and phosphorus fertilization in a saline - alkaline paddy field

There is evidence of increased soil organic carbon (SOC) and inorganic carbon (SIC) under fertilization in dry croplands of arid and semi-arid areas. However, not much is known about the responses of SOC and SIC in coastal saline - alkaline paddy soils that undergo flooding - draining cycles. Here, we assess the impacts of various combinations of organic and phosphorus fertilization on SOC and SIC and other soil properties in a saline - alkaline paddy field of the Yellow River Delta. Our study showed that organic fertilization resulted in an increase of SOC by 11.9% over 0 - 20 cm and 13.3% over 20 - 100 cm (i.e., 140 - 250 g C m(-2)y(-1) over 0 - 100 cm) whereas phosphorus fertilization only led to a significant increase of SOC in subsoils (or similar to 75 g C m(-2)y(-1) over 0 - 100 cm). There were little differences in SIC over 0 - 20 cm among the treatments; but SIC showed a significant decrease over 20 - 100 cm under organic fertilization combined with lower rate of phosphorus fertilization. However, high rate of phosphorus fertilization combined with organic amendment led to an increase in SIC stock, but a decrease in SOC stock in the subsoil. There was a significant negative relationship between SIC and SOC stocks in this paddy soil. This study demonstrated that fertilization practices could have complex influences on SOC and SIC in saline - alkaline paddy fields due to the flooding - draining cycles that lead to changes in soil conditions.