Cover crop management during the fallow season may play a relevant role in improving crop productivity and soil quality, by increasing nitrogen (N) and soil organic carbon (SOC) accumulation, but has the possibility of increasing greenhouse gas (GHG) emissions from the soil. A year-long consistency experiment was conducted to examine the effects of various winter covering crops on annual nitrous oxide (N₂O) together with methane (CH₄) emissions in the mono-rice planting system, including direct emissions in the cover crop period and the effects of incorporating these crops on gaseous emissions during the forthcoming rice (Oryza Sativa L.) growing period, to improve the development of winter fallow paddy field with covering crops and to assess rice cultivation patterns. The experiment included three treatments: Chinese milk vetch-rice (Astragalus sinicus L.) with cover crop residue returned (T1), ryegrass (Lolium multiflorum L.)-rice with cover crop residue returned (T2), and rice with winter fallow (CK). Compared with CK, the two winter cover crop treatments significantly increased rice yield, soil organic carbon (SOC) and total nitrogen (TN) by 6.9–14.5%, 0.8–2.1% and 3.4–5.4%, respectively. In all cases, the fluxes of CH₄ and N₂O could increase with the incorporation of N fertilizer application and cover crop residues. Short-term peaks of these two gas fluxes were monitored after all crop residues were incorporated in the soil preparation period, the early vegetative growth period and the midseason drainage period. The winter cover crop residue application greatly enhanced CH₄ and N₂O cumulative emissions compared with CK (by 193.6–226.5% and 37.5–43.7%, respectively) during rice growing season and intercropping period. Meanwhile, the mean values of global warming potentials (GWPs) from paddy fields with different cropping crops were T2 > T1 > CK. Considering the advantages of crop productivity together with environmental safety and soil quality, Chinese milk vetch-rice with cover crop residue returned would be the most practicable and sustainable cultivation pattern for the mono-rice cropping systems.

The large amount of ammonia released during agricultural application of urea fertilizer can result in a partial loss of applied nitrogen, having a detrimental effect on air quality. Although Chamomile recutita has nitrogen transformation inhibitory properties, providing potential agricultural and environmental benefits, the full extent of the effects of the major constituents of this plant on urease activity and NH₃ volatilization in soils is currently unknown. Soil incubation experiments were established using 2-Cyclopenten-1-one and Eugenol, two major constituents of C. recutita, to evaluate their effects on inorganic soil nitrogen pools, urease activity, and NH₃ volatilization in grey desert soil and red soil. An application rate of 0.25 g N kg⁻¹ soil fertilizer was applied as urea with and without additives. An unfertilized treatment was also included as a control. In order to compare results, N(butyl) thiophosphoric triamide (NBPT), a common synthetic urease inhibitor, was also used. NBPT, 2-Cyclopenten-1-one and Eugenol were applied at a rate of 0.00125 g kg⁻¹ soil (equivalent to 0.5% N). The results indicated that the rate of urea hydrolysis was higher in grey desert soil compared to red soil. Soil in the urea-only treatments recorded urea hydrolysis to be almost complete within seven days of application. The rate of hydrolysis was inhibited by the two natural compounds, and higher concentrations of urea were maintained for more than two weeks. Soil amended with the two materials exhibited strong soil urease inhibition in both soil treatments (75.1% in the alkaline grey desert soil and 72.8% in the acidic red soil). The strongest inhibitory effect occurred one to three days after incubation in the Eugenol treatment. Moreover, the inhibitory effects of Cyclopenten-1-one and Eugenol were superior to that of NBPT in the two soils. Cyclopenten-1-one and Eugenol also significantly reduced soil NH₃ emissions by 14.2 to 45.3%, especially in the acidic red soil. Molecular docking studies confirmed inhibition mechanisms, highlighting that natural compounds interacted with the amino acid residues of the urease active center. This action resulted in the urease active pocket being blocked, thereby inhibiting enzyme activity. Overall, our findings suggest that 2-Cyclopenten-1-one and Eugenol are both capable of hindering urease activity and reducing the risk of N loss in the two tested soils. Results highlight their applicability as urease inhibitors and their effect in delaying the release of ammonia nitrogen, thereby increasing fertilizer N use efficiency. However, in order to fully assess N use efficiency and the N balance due to the presence of Chamomile extract in soil-crop systems, further field scale investigations are required.

A nitrification inhibitor is an effective tool that can be used to reduce the loss of nitrogen (N) and improve crop yields. Most studies have focused on the changes in the soil N mineralization process that may influence the dynamics of soil inorganic N and the soil N cycle. However, the effects of the inhibitors on denitrification rates remain largely unclarified. Therefore, in this study, we monitored the dynamics in annual denitrification rates affected by nitrification inhibitors from a maize field for the first time. Treatments included inorganic fertilizer (NPK), cattle manure, a combination of NPK and DMPP (3,4-dimethylpyrazole phosphate), and a combination of manure and DMPP, applied to brown soils in a no-tillage maize field. The findings demonstrated that the denitrification rate and denitrifying enzyme activity (DEA) were highly variable and there were no significant decreases in all treatment groups after the addition of DMPP. Compared to the control soils, the ammonium (NH₄⁺-N) concentration was significantly increased, while the nitrate (NO₃⁻-N) level was significantly decreased in the DMPP-amended soils less than 30 days after treatment application, indicating that nitrification was partially inhibited. The formation of NO₃⁻-N and the nitrification rates could be markedly reduced by DMPP, while NO₃⁻-N availability did not affect the denitrification rates. Complete degradation of DMPP was observed in the soil on day 70 after DMPP addition, and its half-life was 10 days. Our study may ultimately help to clarify the characteristics of denitrification rates affected by nitrification inhibitors from different N fertilizer types applied to soils and explore the influencing factors of the dynamics in annual denitrification rates. However, more field studies evaluating the effectiveness of nitrification inhibitors in reducing denitrification under different sites and climate conditions, and the molecular mechanisms driving denitrification rate changes, need to be performed in the future.

A field micro-plot experiment with nitrogen isotope (¹⁵ N) labelling was performed to study the impacts of the timing of aside-dressed Napplication on urea-¹⁵ N in amaize-soil system. The treatments comprised three application timings, each of which consisted of the identical total rate of N, i.e. 280kg ha⁻¹. In all treatments, 40% of the Nwas used theday prior to sowing, and the rest was used either at the jointing stage (V6) (N1), at the bell stage (V12) (N2) or at the tasselling stage (VT) (N3). The results indicated that the grain yields increased in both the N1 and N2 treatments compared with the N3 treatment. Asplit application of Nat the bell stage significantly raised the percentage of Nderived from fertilizer N(Ndff) compared to the two other side-dressed Napplication timings. The ¹⁵ N recovery efficiencies for the N2 and N1 treatments were 10% greater than the N3 treatment. The possible Nlosses in the N2 treatment were lower than those in the other treatments. Therefore, Nside-dressing at the bell stage is an alternative and sustainable management strategy for maize production and NUE in spring maize cropping systems.