Effects of nutrient management techniques on nitrogen fertilizer efficiency and carbon emission of maize in a Mollisol

Objectives The yield, nitrogen (N) fertilizer use efficiency and carbon emission in maize production system were studied under different fertilizer management practices, in order to reduce the cumulative carbon emissions and increase fertilizer use efficiency in northeast China.

Methods A field maize experiment was conducted in a typical black soil type in Heilongjiang Province for two years under the recommended fertilizer rate application (RF), recommended N rate+ organic N replacing 20% chemical nitrogen fertilizer (MRF), recommended fertilizer rate + straw returned (SRF), farmers’ fertilizer rate (TF), and no nitrogen fertilizer (CK). Based on life-cycle assessment method, the grain yield, N agronomy efficiency, N partial productivity, and carbon footprint were evaluated.

Results Compared with TF, RF treatment, MRF and SRF treatments increased (P<0.05) maize yield by 1.3%, 6.2% and 7.6%; agronomic efficiency of N fertilizer by 31.3%, 82.6% and 50.3%; and nitrogen partial productivity by 29.0%, 69.0% and 37.0%, respectively. Compared with CK treatment over the two-year experimental period, the RF, MRF, SRF and TF treatments significantly increased carbon emission by 37.6%, 24.0%, 38.5%, 63.6%(P<0.05), respectively, and MRF treatment had the lowest carbon emission among the N fertilizer treatments each year. N fertilizer input and nitrogen loss (N₂O+NH₃+NO₃^–) were the main contributory factors, contributing more than 70% of the total carbon footprint during the maize life cycle, followed by pesticide and fuel consumption, which contributed 10.2% and 13.6%, respectively. Phosphorus and potassium fertilizer accounted for the lowest percentage of C emission, with contribution rate of less than 3%. Compared with TF treatment, the carbon footprint of RF, MRF and SRF treatments were significantly reduced by 16.0%, 24.7% and 16.4% (P<0.05), respectively, and the carbon footprint in MRF treatment was decreased by 9.9% and 10.4% in comparison with RF and SRF treatments, respectively.

Conclusions In black soil region of northeast China, 70% carbon footprint was contributed by N fertilizer and N loss, while phosphorous and potassium fertilizers accounted for less than 3%. Decreasing N and P input with an increase in K input will not affect maize yield, while replacing 20% of chemical N with organic fertilizer will not only increase maize yield, but also improve N-use efficiency and reduce N loss more effectively than recommended fertilization and straw returning, thus organic N replacing 20% chemical nitrogen fertilizer produce a significantly lower carbon footprint, and is beneficial to achieve sustainable development in agriculture.