Effect of controlled-release fertilizer on mitigation of N2O emission from paddy field in South China: a multi-year field observation

There is an ongoing discussion of potential effect of controlled-release fertilizer (CRF) on nitrous oxide (N2O) emission from paddy fields. A four-year field experiment was launched in a major rice cultivation region of China in 2008 and completed in 2011 to explore effects of CRF on N2O emissions from paddy fields. The experimental field followed a water regime pattern typical of China, that is, flooding, mid-season aeration (MSA), reflooding and drying-wetting alternation in sequence. Three treatments, i.e.Treatment CK (no N-fertilizer applied), Treatment U (urea applied), and Treatment C (CRF applied), were laid out in a randomized block design. Over the 4 years, the estimated average of N2O emissions during the rice seasons were 19.5 +/- 5.5, 81.4 +/- 17.8 and 69.6 +/- 18.7 mg N m(-2) in Treatments CK, U and C, respectively. On average, CRF reduced N2O emissions by 13 % and grain yields by 5 %, too, when compared to urea. With normal MSA, Treatment C was 50 %, 11 %, and 25 % lower in N2O emission than Treatment U in 2009, 2010 and 2011 (N) ((N) normal aeration) (p < 0.05), respectively, while the former was 31 % higher (p < 0.05) in 2008 and 7 % lower (p > 0.05) in 2011(D) ((D) delayed aeration) than the latter with delayed MSA. CRF inhibited not only the N2O concentration trapped in the soil pore-water but also the production of N2O during the MSA period. Timing of MSA affected the efficiency of CRF mitigating N2O from the paddy field. The findings suggest that MSA starting around D30 (30 days after rice transplanting), the way the local farmers do, would optimize the effect of CRF mitigating N2O from rice fields in China. However, optimization of rice yield using CRF requires further research.