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Nitrous oxide (N2O) pulse emissions are detected in soils subjected to freeze–thaw cycles in both laboratory and field experiments. However, the mechanisms underlying this phenomenon are poorly understood. In this study, a laboratory incubation experiment that included freeze–thaw cycles (FTC), freezing (F) and control (CK) treatments was performed on three typical Chinese upland soils, namely, fluvo-aquic soil (FS), black soil (BS) and loess soil (LS). A higher similarity in soil properties and bacterial community structure was discovered between FS and LS than between FS and BS or LS and BS, and the bacterial diversity of FS and LS was higher than that of BS. FTC significantly increased the denitrification potential and the proportion of N2O in the denitrification gas products in FS and LS but decreased the denitrification potential in BS. Accordingly, with the increasing number of freeze–thaw cycles, the bacterial community composition in the FTC treatments in FS and LS diverged from that in CK but changed little in BS. Taxa that responded to FTC or correlated with denitrification potential were identified. Taken together, our results demonstrated that the effects of FTC on N2O emissions are soil-type-dependent and that the shift in the microbial community structure may contribute to the elevated N2O emissions. [ABSTRACT FROM AUTHOR]

Aims: The priming effect (PE) on native soil organic matter induced by exogenous carbon addition influences soil carbon and nutrient cycling across the soil depths. Therefore, this study aimed to explore the effects of exogenous glucose-induced PE on native soil organic carbon (SOC) influenced by soil properties across soil depths, weather factors in different ecosystems and experimental variables. Methods: We conducted a meta-analysis of 1231 experimental comparisons from 41 publications to explore the responses of native SOC to stable or radioactive carbon isotope (glucose) addition in laboratory incubation experiments representing various ecosystems and soil depths on the global scale. Results: Overall, glucose addition had 110% positive PE on native SOC. The PE was higher in deep soil (197%) and lowest in topsoil (99%). Deep soil contains significantly lower SOC, dissolved organic carbon and microbial biomass carbon and a higher soil carbon/nitrogen ratio than topsoil. The PE positively correlated with soil carbon/nitrogen ratio and glucose addition rate but negatively correlated with microbial biomass carbon, dissolved organic carbon, SOC and incubation duration. Furthermore, PE positively related to mean annual temperature and precipitation in cropland while negatively correlated with mean annual precipitation in grassland ecosystem. Conclusions: Low soil nutrients and high carbon/nitrogen ratio is the reason for higher PE in deep soil than topsoil. Furthermore, the experimental variables and weather factors provide a framework for understanding the magnitude and direction of PE on native SOC induced by glucose addition and highlight the need for future integrated approaches of studies on PE. [ABSTRACT FROM AUTHOR]

In sub-Saharan Africa, agriculture can account for up to 66% of anthropogenic greenhouse gas (GHG) emissions. Unfortunately, due to the low number of studies in the region there is still much uncertainty on how management activities can affect these emissions. To help reduce this uncertainty, we measured GHG emissions from three maize (Zea mays) growing seasons in central Kenya. Treatments included: (1) a no N application control (C); (2) split (30% at planting and 70% 1 month after planting) mineral nitrogen (N) applications (Min—100 kg N ha−1); (3) split mineral N + irrigation (equivalent to 10 mm precipitation every three days—MI); (4) split mineral N + 40 kg N ha−1 added as manure (MM—total N = 140 kg ha−1); and (5) split mineral + intercropping with faba beans (Phaseolus vulgaris—MB). Soil CO2 fluxes were lower in season 1 compared to seasons 2 and 3 with fluxes highest in Min (p = 0.02) in season 2 and lowest in C (p = 0.02) in season 3. There was uptake of CH4 in these soils that decreased from season 1 to 3 as the mean soil moisture content increased. Cumulative N2O fluxes ranged from 0.25 to 2.45 kg N2O-N ha−1, with the highest fluxes from MI during season 3 (p = 0.01) and the lowest from C during season 1 (p = 0.03). The average fertilizer induced emission factor (0.36 ± 0.03%) was roughly one-third the default value of 1%. Soil moisture was a critical factor controlling GHG emissions in these central Kenya highlands. Under low soil moisture, the soils were CH4 sinks and minimal N2O sources. [ABSTRACT FROM AUTHOR]

Micro sensors have large potential to measure soil nitrous oxide (N2O) emissions. However, because of its low sensitivity to get the electrical signals on soil with low moisture content, little research has been conducted in semi-arid agro-ecosystem. Moreover, the use of N2O microelectrode studies were largely focused on the marshy fields, paddy fields and waste waters with high soil moisture content. In order to characterize the boundary of the sensor signal (upper and lower), purified water without N2O is usually used as the calibration medium to calibrate the electrode. However, the physical and chemical properties of purified water and soil leaching solutions are very different. In this study, we improved and verified a microelectrode calibration method based on selecting appropriate media and optimal electrolyte concentration. In addition, we applied the improved microelectrode calibration method to continuously observe N2O flux from the soil column in a 30-day-long incubation experiment. The results pointed to noteworthy improvement of the microelectrode calibration compared to the current method, with soil solution validated as a calibration medium at optimal electrolytic concentration of 7:1-8:1, expressed as water/soil ratio. The emission of N2O from soil with different soil fertility were also significantly different. Our research is beneficial to establish the microelectrode calibration method of N2O emission under low moisture conditions from soil microenvironment, and also points on management practices of agro-ecosystem for N2O mitigation strategies. [ABSTRACT FROM AUTHOR]

Various cropping patterns are extensively used on the North China Plain, which greatly alter various soil properties. Although these soil properties respond differently to the different cropping patterns, little is known about the possible effects of cropping patterns on desalinized soils. To assess the effects of the different cropping patterns on soil properties and enzyme activities, a long-term field experiment was conducted at the Nanpi Agro-Ecological Station in Hebei Province, China. The cropping patterns under study were the single-cropping patterns of winter wheat (Triticum aestivum L.), spring maize (Zea mays), and spring cotton (Gossypium hirsutum), and the double-cropping pattern of winter wheat–summer maize (WW–SM), which is the predominant cropping pattern on the North China Plain. Soil samples were collected at a depth of 0–100 cm, depending on the soil properties. Our results indicated that soil available phosphorous (P) and available potassium (K) concentrations at 0–20 cm were greater than those of the subsurfaces. Soil organic matter declined with depth, and WW–SM had the highest amount in the deep levels. The WW–SM cropping pattern also generally showed greater levels of enzyme activities than did the single-cropping patterns, proving that diverse crops can enhance enzyme activities. Soil pH generally increased with depth despite there being no significant differences between the cropping patterns. No significant effects were observed on soil electrical conductivity (EC). However, EC generally increased with depth in spring cotton and winter wheat and declined in spring maize and WW–SM. Winter wheat had a significant aggregate size (<0.053 mm) at 20–40 cm depth and generally showed the lowest amount of nutrients. This study suggests that a fallow period allows the soil to regenerate its structure, whereas WW–SM enhances high soil organic matter in the deep soil layers and promotes increased soil enzyme activities. This indicates that crop rotation could sustainably exploit soil resources without reducing fertility over a long period. There is a need to incorporate different soil management practices for single-cropping patterns to increase their productivity, especially in spring maize, whose organic matter declined the most. Our results also show a need to diversify to different crop rotations to utilize their benefits and enhance soil productivity while increasing crop output. [ABSTRACT FROM AUTHOR]