The effects of organic fertilizer on loss risk of nitrogen and phosphorus in paddy ponded water.

There is a great challenge globally for both achieving high crop yields via fertilization and minimizing environmental pollution from nutrient losses. Organic fertilizer (OF) application has been extensively reported to effectively improve arable soil fertility and mitigate nutrient losses. However, few studies are available that accurately quantified the substitution rates of OF for chemical fertilizers (CF) that affect rice yield, the nitrogen/phosphorus in ponded water, and its loss potential in paddy field. Here, an experiment with 5 levels of CF nitrogen substituted by OF nitrogen was performed during the early stage of rice growth in paddy field of Southern China. The results showed that the first 6 days and 3 days following fertilization generally were risky period for N losses and for P losses, respectively, due to corresponding high concentrations in ponded water. Compared to CF treatment, over 30% of OF substitution rates significantly decreased the daily mean TN concentrations by 24.5-32.4%, while TP concentrations unaffected and rice yield maintained comparative levels. OF substitution also improved acidic paddy soils, with the increment of 0.33-0.90 unit for ponded water pH compared to CF treatment. Conclusively, the 30-40% of CF substituted by OF based on N amounts can be considered an ecological fertilization practice for rice production to mitigate environmental pollution due to lower N losses and without significant effect of grain yield. However, the attention also must be paid concerning the rise of environmental pollution risk from NH volatilization and P runoff after long-term OF application.