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Background and aims: Nitrogen fertilization is one of the most important practices for improving of crop yield and soil quality, which also affects soil CO2 emission. CO2 emission is strongly influenced by soil bacterial communities. It is still unknown precisely how nitrogen fertilization affects soil bacterial communities in the semiarid Loess Plateau and how its effects are related to CO2 emissions. Methods: A field experiment was conducted with four nitrogen fertilization rates (0 (N0), 100 (N1), 200 (N2), and 300 (N3) kg N ha–1). Nitrogen fertilization effects soil bacterial communities, CO2 emission, carbon emission efficiency (CEE), and their relationships were investigated. Results: As a result of nitrogen fertilization, soil bacterial abundance increased, and the bacterial community composition and network changed. Soil CO2 emission under N1, N2, and N3 were increased by 17.3%, 24.8%, and 28.9% compared to the N0 treatment, respectively. N2 and N3 exhibited the highest maize grain yield and CEE. CEE under N2 and N3 increased by 96.9%-140.9% compared to the N0 treatment. Soil bacterial abundance had a positive correlation with CO2 emission. CO2 emission were also affected by the bacterial composition and network, which were related to the Actinobacteria. Multiple regression analysis further suggested that CO2 emission was jointly regulated by the abundance, composition, and network modules of the bacterial community. Conclusion: Overall, our results indicated that nitrogen fertilization promoted CO2 emission via increasing bacterial abundance and altering the composition of their community, and provided a new insight into the connection between soil microorganisms and agricultural CO2 emission in the semi-arid region. [ABSTRACT FROM AUTHOR]

Introduction: Improving photosynthetic use efficiency in dryland agroecosystems to sustain high agricultural yields is a key responsibility for ensuring food security. Methods: This study was conducted in the regions on the semiarid Loess Plateau of China during 2018-2020. Dryland maize of Xianyu 335 comprised four modes: basic yield input (CK, plastic film mulching, 37500 plant.ha-1 of plant density and unfertilized), farmer input (FP, plastic film mulching, 45000 plant.ha-1 of plant density and inorganic nitrogen(N) and phosphate(P) fertilizer were 150kg.ha-1 and 90kg.ha-1), high yield and high-efficiency input (HH, full plasticfilm mulching on double furrow, 67500 plant.ha-1 of plant density and N, P and organic manure(M) fertilizer were 230kg.ha-1, 140kg.ha-1 and 1500kg.ha-1), and super high yield input (SH, full plastic-film mulching on double furrow, 9000 plant.ha-1 of plant density and N, P and organic M fertilizer were 300kg.ha-1, 180kg.ha-1 and 7500kg.ha-1). The effects of different cultivation modes on yield, WUE, net photosynthetic rate(Pn), leaf area index(LAI), chlorophyll index(SPAD value) and root index were studied. Results: The results showed that the value average of yield and WUE for CK were 7790kg and 17480kg.ha-1 in three years. SH, HH and FP cultivation modes of yield and WUE was significant higher compared with CK cultivation mode (P<0.05). SH, HH and FP cultivation modes of yield and WUE increased by 34.01%, 48.68%, 56.39% and 34.34%, 47.99%, 57.99%, compared than CK cultivation mode. These differences were observed during the seedling stage, jointing stage, silking stage and filling stage. Year to year variation in performance of applied treatment, this improved in CK cultivation mode significantly enhanced SPAD value, Pn, LAI and the root index than SH, HH and FP cultivation modes. The yield exhibited a positive correlation with the WUE, SPAD value, Pn, LAI. The SH cultivation mode was the highest yields. Discussion: The results indicated that maize yield and WUE could be increased through integrating and optimizing cultivation techniques in maize production on the semiarid western Loess Plateau of China. The SH cultivation mode was the highest yields. The primary factor contributing to the increase in yield and WUE of maize due to increased density, increased fertilizer and covering measures is the augmentation of Pn, LAI, SPAD value, and root index. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N2O) emissions are a major source of gaseous nitrogen loss, causing environmental pollution. The low organic content in the Loess Plateau region, coupled with the high fertilizer demand of maize, further exacerbates these N losses. N fertilizers play a primary role in N2O emissions by influencing soil denitrifying bacteria, however, the underlying microbial mechanisms that contribute to N2O emissions have not been fully explored. Therefore, the research aimed to gain insights into the intricate relationships between N fertilization, soil denitrification, N2O emissions, potential denitrification activity (PDA), and maize nitrogen use efficiency (NUE) in semi-arid regions. Four nitrogen (N) fertilizer rates, namely N0, N1, N2, and N3 (representing 0, 100, 200, and 300 kg ha−1 yr.−1, respectively) were applied to maize field. The cumulative N2O emissions were 32 and 33% higher under N2 and 37 and 39% higher under N3 in the 2020 and 2021, respectively, than the N0 treatment. N fertilization rates impacted the abundance, composition, and network of soil denitrifying communities (nirS and nosZ) in the bulk and rhizosphere soil. Additionally, within the nirS community, the genera Cupriavidus and Rhodanobacter were associated with N2O emissions. Conversely, in the nosZ denitrifier, the genera Azospirillum, Mesorhizobium, and Microvirga in the bulk and rhizosphere soil reduced N2O emissions. Further analysis using both random forest and structural equation model (SEM) revealed that specific soil properties (pH, NO3−-N, SOC, SWC, and DON), and the presence of nirS-harboring denitrification, were positively associated with PDA activities, respectively, and exhibited a significant association to N2O emissions and PDA activities but expressed a negative effect on maize NUE. However, nosZ-harboring denitrification showed an opposite trend, suggesting different effects on these variables. Our findings suggest that N fertilization promoted microbial growth and N2O emissions by increasing the abundance of nirS and nosZ denitrifiers and altering the composition of their communities. This study provides new insights into the relationships among soil microbiome, maize productivity, NUE, and soil N2O emissions in semi-arid regions. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N2O) emissions are a major source of gaseous nitrogen loss, causing environmental pollution. The low organic content in the Loess Plateau region, coupled with the high fertilizer demand of maize, further exacerbates these N losses. N fertilizers play a primary role in N2O emissions by influencing soil denitrifying bacteria, however, the underlying microbial mechanisms that contribute to N2O emissions have not been fully explored. Therefore, the research aimed to gain insights into the intricate relationships between N fertilization, soil denitrification, N2O emissions, potential denitrification activity (PDA), and maize nitrogen use efficiency (NUE) in semi-arid regions. Four nitrogen (N) fertilizer rates, namely N0, N1, N2, and N3 (representing 0, 100, 200, and 300 kg ha−1 yr.−1, respectively) were applied to maize field. The cumulative N2O emissions were 32 and 33% higher under N2 and 37 and 39% higher under N3 in the 2020 and 2021, respectively, than the N0 treatment. N fertilization rates impacted the abundance, composition, and network of soil denitrifying communities (nirS and nosZ) in the bulk and rhizosphere soil. Additionally, within the nirS community, the genera Cupriavidus and Rhodanobacter were associated with N2O emissions. Conversely, in the nosZ denitrifier, the genera Azospirillum, Mesorhizobium, and Microvirga in the bulk and rhizosphere soil reduced N2O emissions. Further analysis using both random forest and structural equation model (SEM) revealed that specific soil properties (pH, NO3−-N, SOC, SWC, and DON), and the presence of nirS-harboring denitrification, were positively associated with PDA activities, respectively, and exhibited a significant association to N2O emissions and PDA activities but expressed a negative effect on maize NUE. However, nosZ-harboring denitrification showed an opposite trend, suggesting different effects on these variables. Our findings suggest that N fertilization promoted microbial growth and N2O emissions by increasing the abundance of nirS and nosZ denitrifiers and altering the composition of their communities. This study provides new insights into the relationships among soil microbiome, maize productivity, NUE, and soil N2O emissions in semi-arid regions.

Soil autotrophic bacteria play a crucial role in regulating CO2 fixation and crop productivity. However, the information is limited to how fertilization amendments alter soil autotrophic bacterial community, crop yield, and carbon emission efficiency (CEE). Here, we estimated the impact of the structure and co-occurrence network of soil autotrophic bacterial community on maize yield and CEE. A long-term field experiment was conducted with five fertilization treatments in semiarid Loess Plateau, including no amendment (NA), chemical fertilizer (CF), chemical fertilizer plus commercial organic fertilizer (SC), commercial organic fertilizer (SM), and maize straw (MS). The results showed that fertilization amendments impacted the structure and network of soil Calvin–Benson–Bassham (CBB) (cbbL) gene-carrying bacterial community via changing soil pH and NO3–N. Compared with no amendment, the cbbL-carrying bacterial diversity was increased under the SC, SM, and MS treatments but decreased under the CF treatment. Soil autotrophic bacterial network contained distinct microbial modules that consisted of closely associated microbial species. We detected the higher abundances of soil cbbL-carrying bacterial genus Xanthobacter, Bradyrhizobium, and Nitrosospira. Structural equation modeling further suggested that the diversity, composition, and network of autotrophic bacterial community had strongly positive relationships with CEE and maize yield. Taken together, our results suggest that soil autotrophic bacterial community may drive crop productivity and CEE, and mitigate the atmospheric greenhouse effect.

Soil autotrophic bacteria play a crucial role in regulating CO2 fixation and crop productivity. However, the information is limited to how fertilization amendments alter soil autotrophic bacterial community, crop yield, and carbon emission efficiency (CEE). Here, we estimated the impact of the structure and co-occurrence network of soil autotrophic bacterial community on maize yield and CEE. A long-term field experiment was conducted with five fertilization treatments in semiarid Loess Plateau, including no amendment (NA), chemical fertilizer (CF), chemical fertilizer plus commercial organic fertilizer (SC), commercial organic fertilizer (SM), and maize straw (MS). The results showed that fertilization amendments impacted the structure and network of soil Calvin–Benson–Bassham (CBB) (cbbL) gene-carrying bacterial community via changing soil pH and NO3–N. Compared with no amendment, the cbbL -carrying bacterial diversity was increased under the SC, SM, and MS treatments but decreased under the CF treatment. Soil autotrophic bacterial network contained distinct microbial modules that consisted of closely associated microbial species. We detected the higher abundances of soil cbbL -carrying bacterial genus Xanthobacter , Bradyrhizobium , and Nitrosospira. Structural equation modeling further suggested that the diversity, composition, and network of autotrophic bacterial community had strongly positive relationships with CEE and maize yield. Taken together, our results suggest that soil autotrophic bacterial community may drive crop productivity and CEE, and mitigate the atmospheric greenhouse effect. [ABSTRACT FROM AUTHOR]

The farming practice of alternating ridges–furrows with plastic film mulching is widely used to improve field productivity of most staple crops such as maize and wheat in the semiarid Loess Plateau, but whether the technology has similar benefits on oil crops such as linseed flax ( Linum usitatissimum L.), still remains unknown. From 2012–2013, a 2–year field experiment was carried out to evaluate the effects of different ridges–furrows mulching patterns on soil hydrothermal parameters, linseed yield performance, water use efficiency and economic benefit at a rainfed semiarid site of the Loess Plateau. Four different treatments were designed as: i) alternating small and large ridges with full film mulching (RFM), ii) alternating ridges and furrows with plastic film mulching only on the ridges (RM), iii) flat planting with fully film mulching (FM) and iv) conventional flat planting without mulching (CK). Local widely cultivated variety Tianya 9 was used as testing cultivar. The results indicated that soil water storage during early growing stage was increased by 7.1%, 0.6% and 6.3% in RFM, RM and FM, respectively, compared with that of CK across two growing seasons. After harvesting, soil water storage in RFM was recovered to higher level than that of CK. Average soil temperature at seedling stage was 3.1 °C and 2.1 °C higher in RFM and FM than that of CK. In addition, film mulching generally accelerated crop development during early vegetative period, leading to a shorter growing season in RFM and RM. Particularly, both linseed yield and water use efficiency were enhanced by 116.2% and 154.8% in RFM, 50.3% and 72.4% in RM, 87.5% and 84.2% in FM across two growing seasons, respectively, compared with those of CK. Critically, the greatest net income and output to input ratio were achieved in RFM across both growing seasons. Present results clearly suggest that the practice of alternating small and large ridges with full film mulching provide an innovative option to optimize soil hydrothermal conditions, thereby boosting the productivity and profitability of dryland linseed flax in rainfed semiarid environment. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N 2 O) emissions are a major source of gaseous nitrogen loss, causing environmental pollution. The low organic content in the Loess Plateau region, coupled with the high fertilizer demand of maize, further exacerbates these N losses. N fertilizers play a primary role in N 2 O emissions by influencing soil denitrifying bacteria, however, the underlying microbial mechanisms that contribute to N 2 O emissions have not been fully explored. Therefore, the research aimed to gain insights into the intricate relationships between N fertilization, soil denitrification, N 2 O emissions, potential denitrification activity (PDA), and maize nitrogen use efficiency (NUE) in semi-arid regions. Four nitrogen (N) fertilizer rates, namely N0, N1, N2, and N3 (representing 0, 100, 200, and 300 kg ha -1 yr. -1 , respectively) were applied to maize field. The cumulative N 2 O emissions were 32 and 33% higher under N2 and 37 and 39% higher under N3 in the 2020 and 2021, respectively, than the N0 treatment. N fertilization rates impacted the abundance, composition, and network of soil denitrifying communities ( nirS and nosZ ) in the bulk and rhizosphere soil. Additionally, within the nirS community, the genera Cupriavidus and Rhodanobacter were associated with N 2 O emissions. Conversely, in the nosZ denitrifier, the genera Azospirillum , Mesorhizobium , and Microvirga in the bulk and rhizosphere soil reduced N 2 O emissions. Further analysis using both random forest and structural equation model (SEM) revealed that specific soil properties (pH, NO 3 - -N, SOC, SWC, and DON), and the presence of nirS -harboring denitrification, were positively associated with PDA activities, respectively, and exhibited a significant association to N 2 O emissions and PDA activities but expressed a negative effect on maize NUE. However, nosZ -harboring denitrification showed an opposite trend, suggesting different effects on these variables. Our findings suggest that N fertilization promoted microbial growth and N 2 O emissions by increasing the abundance of nirS and nosZ denitrifiers and altering the composition of their communities. This study provides new insights into the relationships among soil microbiome, maize productivity, NUE, and soil N 2 O emissions in semi-arid regions., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Fudjoe, Li, Anwar, Shi, Xie, Wang, Xie and Yongjie.)

The cropland-to-apple orchard conversion is expanding in the semiarid Loess Plateau, yet its impacts on deep soil moisture and nitrate are poorly documented. This study was conducted in Luochuan, typically the best area for apple planting in China, where fifteen 6-m-deep soil profiles were sampled from each cropland (as the control), as well as 8-, 17- and 25-yr apple orchards, to investigate the vertical distributions of soil moisture and nitrate and their storage. Results showed that the 8-yr apple orchards were comparable to cropland in soil moisture content (SMC), soil water storage (SWS), soil nitrate concentration (SNC) and residual soil nitrate (RSN). In contrast, 17- and 25-yr apple orchards, caused serious SWS deficits, of 140 mm and 150 mm, and substantially increased RSN, by 4270 and 7250 kg N ha−1, respectively, when compared with cropland. Notably, RSN in deep soils was strongly enhanced by the stand age of apple orchard, which was primarily associated with accumulated N fertilizer inputs. Similar SNCs in the 540–600 cm layer among land use types implied a 6-m-deep soil profile might be robust for evaluating NO 3 − dynamics following cropland-to-orchard conversion in the study region. Regression relationships between RSN and SWS were significantly positive in the 100–300 cm soil layer under cropland but significantly negative in the 0–100 cm and 100–300 cm layers under 8-yr apple orchards, indicating distinct hydrological processes of NO 3 − under differing land uses. In conclusion, converting cropland to apple orchards could result in soil moisture decline and nitrate accumulation in the 6-m profile that may threaten the Loess Plateau's sustainability. Therefore, integrated water and N management should be practiced to mitigate the unfavorable impacts and develop sustainable apple production in China and other semiarid areas of the world. • The 17- and 25-yr apple orchards decreased soil moisture in soils deeper than 3 m. • NO 3 − accumulation in deep soil layers increased with stand age of apple orchard. • A 6-m-deep soil profile was robust for evaluating vertical patterns of soil NO 3 −. • 8-yr orchard may be an optimal age avoiding soil water decline and NO 3 − accumulation. • Converting cropland to apple orchard may threaten the Loess Plateau's sustainability. [ABSTRACT FROM AUTHOR]