Fate of 15N-labelled urea as affected by long-term manure substitution

Quantifying the fate of fertilizer nitrogen (N) is essential to develop more sustainable agricultural fertilization practices. However, the fate of chemical fertilizer N, particularly in long-term manure substitution treatment regimes, is not fully understood. The present study aimed to investigate the fate of ¹⁵N-labelled urea in a chemical fertilizer treatment (CF, 240 kg ¹⁵N ha^-1) and N manure 50 % substitution treatment (1/2N + M, 120 kg ¹⁵N ha^-1 + 120 kg manure N ha^-1) in two continuous crop seasons, based on a 10-year long-term experiment in the North China Plain (NCP). The results showed that manure substitution greatly enhanced ¹⁵N use efficiency (¹⁵NUE) (39.9 % vs. 31.3 %) and suppressed ¹⁵N loss (6.9 % vs. 7.5 %) compared with the CF treatment in the first crop. However, the N₂O emissions factor in the 1/2N + M treatment was increased by 0.1 % (0.5 kg ¹⁵N ha^-1 for CF vs. 0.4 kg ¹⁵N ha^-1 for 1/2N + M) compared with the CF treatment, although N leaching and NH₃ volatilization rates decreased by 0.2 % (10.8 kg ¹⁵N ha^-1 for CF vs. 5.1 kg ¹⁵N ha^-1 for 1/2N + M) and 0.5 % (6.6 kg ¹⁵N ha^-1 for CF vs. 2.8 kg ¹⁵N ha^-1 for 1/2N + M), respectively. In which, only NH₃ volatilization presented significantly difference between treatments. It is important to note that in the second crop, the residual ¹⁵N in soil (0-20 cm) remained mostly in the soil for the CF (79.1 %) and the 1/2N + M treatment (85.3 %), and contributed less to crop N uptake (3.3 % vs. 0.8 %) and leached losses (2.2 % vs. 0.6 %). This proved that manure substitution could enhance the stabilization of chemical N. These results suggested that long-term manure substitution effectively increases NUE, suppresses N loss, and improves N stabilization in soil, but negative impacts such as N₂O emissions due to climate change should be investigated further.

Partial substitution of manure reduces nitrous oxide emission with maintained yield in a winter wheat crop

Conventional fertilization of agricultural soils results in increased N₂O emissions. As an alternative, the partial substitution of organic fertilizer may help to regulate N₂O emissions. However, studies assessing the effects of partial substitution of organic fertilizer on both N₂O emissions and yield stability are currently limited. We conducted a field experiment from 2017 to 2021 with six fertilizer regimes to examine the effects of partial substitution of manure on N₂O emissions and yield stability. The tested fertilizer regimes, were CK (no fertilizer), CF (chemical fertilizer alone, N 300 kg ha^-1, P₂O₅ 150 kg ha^-1, K₂O 90 kg ha^-1), CF + M (chemical fertilizer + organic manure), CFR (chemical fertilizer reduction, N 225 kg ha^-1, P₂O₅ 135 kg ha^-1, K₂O 75 kg ha^-1), CFR + M (chemical fertilizer reduction + organic manure), and organic manure alone (M). Our results indicate that soil N₂O emissions are primarily regulated by soil mineral N content in arid and semi-arid regions. Compared with CF, N₂O emissions in the CF + M, CFR, CFR + M, and M treatments decreased by 16.8%, 23.9%, 42.0%, and 39.4%, respectively. The highest winter wheat yields were observed in CF, followed by CF + M, CFR, and CFR + M. However, the CFR + M treatment exhibited lower N₂O emissions while maintaining high yield, compared with CF. Four consecutive years of yield data from 2017 to 2021 illustrated that a single application of organic fertilizer resulted in poor yield stability and that partial substitution of organic fertilizer resulted in the greatest yield stability. Overall, partial substitution of manure reduced N₂O emissions while maintaining yield stability compared with the synthetic fertilizer treatment during the wheat growing season. Therefore, partial substitution of manure can be recommended as an optimal N fertilization regime for alleviating N₂O emissions and contributing to food security in arid and semi-arid regions.

Ammonia mitigation potential in an optimized crop-layer production system

Livestock and crop production are the main sources of ammonia (NH₃) emissions, which are known to degrade the air quality. Numerous studies have been conducted to explore the mitigation potential of various approaches, although few have examined the systematic NH₃ emission mitigation potential when considering both crop and livestock systems based on coherent in situ measurement results. Herein, we design an optimal system wherein coupled crop and layer production systems reveal feasible approaches for significant mitigation potential at each stage of the process. Specifically, these measures involve (i) using a low crude protein (LCP) feed, (ii) composting manure with certain additives, and (iii) substituting manure with optimal fertilization in a summer maize-winter wheat cropping system. The results show that (i) LCP feed leads to a 14 % reduction in NH₃ emissions at the housing stage, (ii) introducing additives during the composing stage reduces NH₃ emissions by 16 %-46 %, and (iii) the NH₃ reduction potential reaches 35 %-44 % at the field application stage. In the overall crop-layer system, the optimal system with the improved management strategy applied at every stage results in a 48 % and 56 % reduction in NH₃ emissions for per unit eggs and grain production, respectively, relative to a traditional production system. This study confirms that NH₃ emissions can be cut in half by implementing optimal crop-livestock systems with appropriate mitigation approaches. This is a feasible model that can be promoted and extended in various agricultural areas, which together with technological, policy, and economic support can enable significant mitigation potential for sustainable agriculture development.