The effects of long-term fertilization on rice yields in the red soil region, China: a field meta-analysis

Background Rice is the primary grain crop produced in red paddy soil. However, the effects of different fertilization treatments, inherent soil productivity on rice yield and also the factors that influence the rice yield and inherent soil productivity in this region remain unclear. Methods We here selected 196 cultivated land quality monitoring sites to assess the effects of no fertilizer (CK), chemical fertilizer plus straw return (NPKS) and chemical fertilizer plus manure (NPKM) on rice yield. We also evaluated the soil properties on the rice yield, basic soil productivity contribution rate to rice yield (BSPCR) and fertilizer contribution rate to yield (FCR); furthermore, we assessed the impacts of specific soil properties on BSPCR and FCR. Results The results showed that NPKM and NPKS significantly increased rice grain and straw yield by 82.63% and 83.05%, respectively, compared to CK. NPKM was found to increase yield more than NPKS did. Rice straw and grain yield both increased along with increases in nitrogen fertilizer application and the available nitrogen (AN) content of the soil. In the NPKM and NPKS plots, higher pH levels were associated with a gradual decrease in the rate of yield increase. Compared with CK plots, increased soil organic matter (SOM), available phosphorus (AP), and available potassium (AK) contents in NPKM and NPKS plots were each associated with initial increases in rice grain and straw yield. Soil pH and SOM contents were determined to be the main factors affecting the BSPCR and FCR. Conclusion This study indicated that rice yield benefited more from the application of manure than of returned straw. In the future, improving the acidification and SOM contents of red soil paddy would be the most important measures to improve basic soil fertility, the fertilizer utilization rate, and also the rice yield.