Nitrous Oxide Emissions in a Wheat/Corn Succession Combining Dairy Slurry and Urea as Nitrogen Sources

ABSTRACT: The impact on nitrous oxide (N2O) emissions caused by combining dairy slurry (DS) and urea to supply crops with nitrogen (N) is still not well characterized. The main objective of this study was to compare the differences between N2O emissions in the cases of exclusive use of urea and the combined use of DS and urea as N sources to no-tillage wheat and corn. We also compared N2O emissions between two DS application methods (surface-broadcast vs. injection), as well as the addition of dicyandiamide (DCD) to DS. The experiment was conducted under no-tillage and six treatments were applied at sowing as follows: no fertilization (control), surface-broadcast urea (urea-N), surface-broadcast DS (DSs), surface-broadcast DS with DCD (DSs + DCD), shallow-injected DS (DSi), and shallow-injected DS with DCD (DSi + DCD). Urea was applied at side-dressing in all treatments with DS and urea-N. The N2O emissions were evaluated from the application of the treatments to wheat until 22 days after corn harvest, resulting in a total of 364 days. The partial supply of the N demand of wheat and corn, by DS application at sowing, and the posterior complement of N demand by side-dressing urea increased the annual N2O emissions only when DS was shallow-injected without DCD (DSi). Although the amount of N2O-N emitted from the DSi treatment was 1.04 kg ha-1 (91.2 %) higher than from DSs in corn, the annual N2O-N emissions did not differ between the two methods of DS application to the soil. The emission factors of N2O-N were low, ranging from 0.49 % (DSi + DCD) to 1.27 % (DSi). The results of this study suggest that the combined use of DS with urea in N fertilization of no-tillage wheat and corn (DS applied at sowing and urea at side-dressing) caused no changes in the annual N2O-N emissions compared to crops fertilized exclusively with urea (1/3 at sowing + 2/3 at side-dressing). However, DCD should be added if DS is shallow-injected.

摘要：将奶牛液体粪肥（dairy slurry, DS）与尿素配施以向作物供应氮（nitrogen, N）的措施对一氧化二氮（nitrous oxide, N₂O）排放的影响，目前仍未得到充分表征。本研究的核心目标为对比两种供氮模式下免耕（no-tillage）小麦与玉米田的N₂O排放差异：一是单独施用尿素，二是将DS与尿素配施。此外，本研究还对比了两种DS施用方式（地表撒施（surface-broadcast）与浅施注入（shallow-injected））以及向DS中添加双氰胺（dicyandiamide, DCD）对N₂O排放的影响。
本实验于免耕条件下开展，播种时设置6组处理：不施肥（对照组）、地表撒施尿素（urea-N）、地表撒施DS（DSs）、地表撒施添加DCD的DS（DSs + DCD）、浅施注入DS（DSi）、浅施注入添加DCD的DS（DSi + DCD）。所有施用DS与urea-N的处理均在作物生长期进行尿素追肥（side-dressing）。N₂O排放的监测时段为：从处理施用至小麦生育期，直至玉米收获后22天，总监测时长共计364天。
仅当DS采用浅施注入且未添加DCD（DSi）时，通过播种期施DS部分满足小麦与玉米的氮需求、后续通过尿素追肥补充剩余氮需求的配施模式，才会提升年N₂O-N排放量。尽管玉米季中DSi处理的N₂O-N排放量较DSs处理高1.04 kg·ha⁻¹（增幅91.2%），但两种DS土壤施用方式下的年N₂O-N排放量并无显著差异。N₂O-N排放系数（emission factors）较低，范围为0.49%（DSi + DCD）至1.27%（DSi）。本研究结果表明，在免耕小麦与玉米的氮肥配施中（播种期施DS，生长期尿素追肥），与仅施用尿素的处理（1/3氮肥于播种期施用，2/3于追肥期施用）相比，DS与尿素配施并未改变年N₂O-N排放量。但若采用浅施注入方式施用DS，则应添加DCD以抑制N₂O排放。