Higher maize yields and lower ammonia emissions by replacing synthetic nitrogen fertiliser with manure in the North China plain

Ammonia (NH 3 ) emitted from synthetic nitrogen (N) fertiliser applications to farmland leads to air pollution and terrestrial acidification. Previous studies have indicated that replacing urea-based N fertilisers by manure may reduce NH 3 emissions and enhance crop yield. However, the long-term effects of replacing urea N fertiliser by manure on crop yield and NH 3 emissions have not been sufficiently quantified. The objective of the field study presented here was to examine the effects of three treatments (i.e., 100% synthetic fertiliser N application (NPK); 50% synthetic fertiliser N +50% manure N application (50%MNS); and 100% manure N application (100%MNS)) on NH 3 emissions and maize grain yields over a 3-year period in a long term (13 years) study site in the North China Plain. Results showed that the NH 3 emissions in the NPK treatment ranged from 9.7 to 11.7 kg ha − 1 during the three maize growing seasons. Replacement of urea fertiliser by manure significantly decreased the NH 3 emissions by 22–54% in the 50% MNS treatment and by 47–71% in the 100%MNS treatment. Maize grain yields were 14–30% higher in the 50%MNS treatment and 17–45% higher in the 100% MNS treatment, compared to the NPK treatment (8.1–8.8 t ha − 1 ). The NH 3 emission factor for the NPK treatment ranged from 4.1 to 4.8%. Additional 15 N labelling work established that 83% of NH 3 emissions originated from the urea fertiliser in the NPK treatment. Manure treatments had a higher maize N uptake and soil organic matter content, and a lower soil pH than the NPK treatment. This study highlights that replacing synthetic N fertiliser with manure on farmland in the North China Plain has long-term beneficial effects on maize yield and N uptake, NH 3 emission mitigation and soil carbon storage.