Integrated soil fertility and yield trend in response to long-term fertilisation under the Chinese double rice-cropping systems

Soil fertility is fundamental in determining crop productivity and sustainability in farming systems. A long-term fertiliser experiment in Chinese double rice-cropping systems initiated in 2011 was used in this study to gain an insight into a complete estimating of soil fertility. The six fertiliser treatments included mineral fertiliser (NP, NK, and NPK), combined NPK with farmyard manure (NPKM) or crop straw (NPKS), and no fertiliser application as a control. Results showed that grain yield averaged 5.5-13.0 t/ha/year, and significant increasing trends were observed in the phosphorus-applied plots (NP, NPK, NPKM, and NPKS), but the treatments without phosphorus applied (control and NK) resulted in declining trends in both early- and late-rice yields. After long-term rice cultivation, the contents of total and available phosphorus significantly declined in phosphorus-deficient plots compared to other treatments. Regression analysis showed that the improvement in grain yields was positively correlated with the increased soil fertility over treatments. Relative to the NPK treatment, the NPKM treatment greatly enhanced soil fertility from 0.50 to 0.78, and particularly dramatically increased the content of available soil phosphorus. Therefore, the high grain yield and soil fertility can be simultaneously achieved by long-term balanced fertiliser applications in Chinese double rice-cropping systems.