农业生态环境-气体排放和重金属Agro-ecosystem & Environment—Gas emission & heavy metals
The inhibition of nitrification by mixing nitrification inhibitors (NI) with fertilizers is emerging as an effective method to reduce fertilizer-induced nitrous oxide (N2O) emissions. The additive 3,4-dimethylpyrazole phosphate (DMPP) apparently inhibits ammonia oxidizing bacteria (AOB) more than ammonia oxidizing archaea (AOA), which dominate the nitrification in alkaline and acid soil, respectively. However, the efficacy of DMPP in terms of nitrogen sources interacting with soil properties remains unclear. We therefore conducted a microcosm experiment using three typical Chinese agricultural soils with contrasting pH values (fluvo-aquic soil, black soil and red soil), which were fertilized with either digestate or urea in conjunction with a range of DMPP concentrations. In the alkaline fluvo-aquic soil, fertilization with either urea or digestate induced a peak in N2O emission (60 μg N kg–1 d–1) coinciding with the rapid nitrification within 3 d following fertilization. DMPP almost eliminated this peak in N2O emission, reducing it by nearly 90%, despite the fact that the nitrification rate was only reduced by 50%. In the acid black soil, only the digestate induced an N2O emission that increased gradually, reaching its maximum (20 μg N kg–1 d–1) after 5–7 d. The nitrification rate and N2O emission were both marginally reduced by DMPP in the black soil, and the N2O yield (N2O-N per NO2–+NO3–-N produced) was exceptionally high at 3.5%, suggesting that the digestate induced heterotrophic denitrification. In the acid red soil, the N2O emission spiked in the digestate and urea treatments at 50 and 10 μg N kg–1 d–1, respectively, and DMPP reduced the rates substantially by nearly 70%. Compared with 0.5% DMPP, the higher concentrations of DMPP (1.0 to 1.5%) did not exert a significantly (P<0.05) better inhibition effect on the N2O emissions in these soils (either with digestate or urea). This study highlights the importance of matching the nitrogen sources, soil properties and NIs to achieve a high efficiency of N2O emission reduction.
Ammonia (NH3) emissions should be mitigated to improve environmental quality. Croplands are one of the largest NH3 sources, they must be managed properly to reduce their emissions while achieving the target yields. Herein, we report the NH3 emissions, crop yield and changes in soil fertility in a long-term trial with various fertilization regimes, to explore whether NH3 emissions can be significantly reduced using the 4R nutrient stewardship (4Rs), and its interaction with the organic amendments (i.e., manure and straw) in a wheat–maize rotation. Implementing the 4Rs significantly reduced NH3 emissions to 6 kg N ha–1 yr–1 and the emission factor to 1.72%, without compromising grain yield (12.37 Mg ha–1 yr–1) and soil fertility (soil organic carbon of 7.58 g kg–1) compared to the conventional chemical N management. When using the 4R plus manure, NH3 emissions (7 kg N ha–1 yr–1) and the emission factor (1.74%) were as low as 4Rs, and grain yield and soil organic carbon increased to 14.79 Mg ha–1 yr–1 and 10.09 g kg–1, respectively. Partial manure substitution not only significantly reduced NH3 emissions but also increased crop yields and improved soil fertility, compared to conventional chemical N management. Straw return exerted a minor effect on NH3 emissions. These results highlight that 4R plus manure, which couples nitrogen and carbon management can help achieve both high yields and low environmental costs.
Cadmium (Cd) is one of the most toxic heavy metals in the environment. Atmospheric deposition has been found to be the main source of Cd pollution of soil on a large scale in China, and identification of the relationships between anthropogenic emission, atmospheric deposition, and Cd accumulation in soil is important for developing ways to mitigate Cd non-point pollution. In this study, the relationship between atmospheric emission, atmospheric deposition, and soil Cd accumulation in the Middle-Lower Yangtze Plain in China was investigated using datasets of atmospheric emission, deposition, and soil accumulation from the literatures published between 2000 and 2020. The results showed that the soil Cd accumulation rate in the study area exceeded the national average (4.0 μg kg–1 yr–1) and continued to accumulate in recent decades, although the average accumulation rate decreased from 9.45 μg kg–1 yr–1 (2000–2010 period) to 8.86 μg kg–1 yr–1 (2010–2020 period). The contribution of atmospheric deposition flux to Cd increment in the soil was in the range of 22–29%, with the atmospheric deposition flux decreasing from 0.54 mg m–2 yr–1 (2000–2010) to 0.48 mg m–2 yr–1 (2010–2020), both values being greater than the national average. Atmospheric Cd deposition and emission were highly correlated in a provincial administrative region, which is close to a ratio of 1.0. Emission factors may be in a state of dynamic change due to the influences of new Cd emission control technologies and environmental policies. As the main sources of Cd emissions, dust, and smoke emissions per ton of non-ferrous metal production decreased by 64.7% between the 2000–2010 and 2010–2020 periods. Although new environmental policies have been instigated, atmospheric emission of Cd is still excessive. It was hoped that the findings of this work would provide a scientific basis for the rational control of atmospheric emissions and Cd pollution of soil.
Reducing ammonia (NH3) and nitrous oxide (N2O) emissions have great effects on mitigating nitrogen (N) nutrient loss and greenhouse gas emissions. Controlled release urea (CRU) can control the N release rate, which reduces reactive N loss and increases nitrogen use efficiency relative to conventional urea (CU). However, the crucial factors influencing the responses of NH3 and N2O emissions to CRU relative to CU are still unclear. In this study, we evaluated the responses of NH3 and N2O emissions to CRU based on collected field data with a meta-analysis. CRU reduced the NH3 and N2O emissions by 32.7 and 25.0% compared with CU, respectively. According to subgroup analysis, CRU presented better mitigation of NH3 and N2O emissions in soils with pH 6.5–7.5 (–47.9 and –23.7%) relative to either pH<6.5 (–28.5 and –21.4%) or pH>7.5 (–29.3 and –17.3%), and in the rice season (–34.8 and –29.1%) relative to the wheat season (–19.8 and –22.8%). The responses of NH3 and N2O emissions to CRU increased from rainfed (–30.5 and –17.0%) to irrigated (–32.5 and –22.9%), and then to paddy (–34.8 and –29.1%) systems. In addition, the response of N2O emission mitigation increased with increases in soil total nitrogen (TN); however, soil TN did not significantly affect the response of NH3 volatilization. The reduction in NH3 emission was greater in sandy-textured soil (–57.7%) relative to loam-textured (–32.9%) and clay-textured (–32.3%) soils, whereas soil texture did not affect N2O emission. Overall, CRU was a good option for reducing the NH3 and N2O emissions relative to CU in agricultural production. This analysis improves our understanding of the crucial environmental and management factors influencing the mitigation of NH3 and N2O emissions under CRU application, and these site-specific factors should be considered when applying CRU to reduce reactive N loss and increase NUE.
The combined effects of straw incorporation (SI) and polymer-coated urea (PCU) application on soil ammonia (NH3) and nitrous oxide (N2O) emissions from agricultural fields have not been comprehensively evaluated in Northwest China. We conducted a two-year field experiment to assess the effects of combining SI with either uncoated urea (U) or PCU on soil NH3 emissions, N2O emissions, winter wheat yields, yield-scaled NH3 (INH3), and yield-scaled N2O (IN2O). Five treatments were investigated, no nitrogen (N) fertilizer (N0), U application at 150 kg N ha–1 with and without SI (SI+U and S0+U), and PCU application at 150 kg N ha–1 with and without SI (SI+PCU and S0+PCU). The results showed that the NH3 emissions increased by 20.98–34.35% following SI compared to straw removal, mainly due to increases in soil ammonium (NH4+-N) content and water-filled pore space (WFPS). SI resulted in higher N2O emissions than under the S0 scenario by 13.31–49.23% due to increases in soil inorganic N (SIN) contents, WFPS, and soil microbial biomass. In contrast, the PCU application reduced the SIN contents compared to the U application, reducing the NH3 and N2O emissions by 45.99–58.07 and 18.08–53.04%, respectively. Moreover, no significant positive effects of the SI or PCU applications on the winter wheat yield were observed. The lowest INH3 and IN2O values were observed under the S0+PCU and SI+PCU treatments. Our results suggest that single PCU applications and their combination with straw are the optimal agricultural strategies for mitigating gaseous N emissions and maintaining optimal winter wheat yields in Northwest China.
To understand the CH4 flux variations and their climatic drivers in the rice–wheat agroecosystem in the Huai River Basin of China, the CH4 flux was observed by using open-path eddy covariance at a typical rice–wheat rotation system in Anhui Province, China from November 2019 to October 2021. The variations and their drivers were then analyzed with the Akaike information criterion method. CH4 flux showed distinct diurnal variations with single peaks during 9:00–13:00 local time. The highest peak was 2.15 µg m–2 s–1 which occurred at 11:00 in the vegetative growth stage in the rice growing season (RGS). CH4 flux also showed significant seasonal variations. The average CH4 flux in the vegetative growth stage in the RGS (193.8±74.2 mg m–2 d–1) was the highest among all growth stages. The annual total CH4 flux in the non-rice growing season (3.2 g m–2) was relatively small compared to that in the RGS (23.9 g m–2). CH4 flux increased significantly with increase in air temperature, soil temperature, and soil water content in both the RGS and the non-RGS, while it decreased significantly with increase in vapor pressure deficit in the RGS. This study provided a comprehensive understanding of the CH4 flux and its drivers in the rice–wheat rotation agroecosystem in the Huai River Basin of China. In addition, our findings will be helpful for the validation and adjustment of the CH4 models in this region.