Substitution of chemical fertilizer with organic manure reduces ammonia volatilization in maize farmland in North China Plain

Objectives  Ammonia volatilization in farmland contributes to the atmospheric ammonia, thus the need and methods for reducing ammonia volatilization in farmland have become part of the trending international research topics. Substitution of chemical fertilizers with organic fertilizers is a widely recognized method for reducing ammonia volatilization in farmland. The impact of inter-annual climate change on emission reduction capacity of organic fertilizers was studied in this paper.

Methods  This study was conducted in a long-term experimental maize field in North China Plain. The experiment commenced in 2007, and ammonia volatilizationmonitoring was conducted in three consecutive years (2017–2019). There were four treatments in the experiment, as: no N fertilizer (PK), single chemical fertilizer (NPK), half of the organic N replacing chemical fertilizer N (HONS), full amount of organic N replacing chemical fertilizer N (FONS).

Results  The substitution of chemical fertilizers with manure increased the maize yield. Compared with NPK treatment, HONS and FONS treatments increased the maize yield by 20.7% and 30.9%, respectively. The partial N productivity of the different treatments ranged from 35.6 to 46.7 kg/kg. Compared with NPK treatment, HONS and FONS treatments increased the partial N productivity by 20.8% and 30.9%, respectively. The ammonia volatilization pattern among years and treatments was the same, with the peak ammonia volatilization appeared in 2–4 days after fertilization, and then gradually decreased and stabilized within 9 days. About 70.1% and 63.7% of the total ammonia volatilization occurred in the first 9 days after basal application and topdressing of fertilizer, respectively. Compared with NPK treatment, HONS and FONS treatments reduced ammonia volatilization by average of 33.5% and 58.7%, respectively. The inter-annual change in ammonia volatilization in HONS and FONS treatments were significantly higher than that of chemical fertilizer. The ammonia volatilization in NPK treatment was 12.3% higher in 2018 than that in 2019, while volatilization in HONS and FONS treatments were higher (91.2% and 105.0%, respectively) in 2018 than that in 2019. The corresponding reduction rates in HONS and FONS treatments were higher in 2019 than 2018 (54.3% vs. 22.1% and 71.1% vs. 47.2%, respectively). Principal component analysis showed that the variations of air temperature and soil moisture were the main reasons for the differences in ammonia volatilization.

Conclusions  Compared with sole application of chemical fertilizers, the replacement of chemical fertilizers with organic fertilizers can increase crop yields. Full-scale replacement of chemical fertilizers with organic fertilizers has a stronger potential to improve crop yields over time than partial replacement. More importantly, results of this study suggest that the substitution of chemical fertilizers with organic fertilizers could effectively reduce ammonia volatilization in North China Plain, but the reduction rate could vary among years.