Neither single nor discontinuous hydrological observation data can truly reflect periodic changes in soil moisture under natural conditions or interrelationships between various water sources. Therefore, in this study, precipitation pulse characteristics and variations in the soil water content (SWC) and actual evapotranspiration (ET_a) in relation to pulses are explored through a field multi-water continuous observation system set in desert steppe in Inner Mongolia, China. A comparison between precipitation events in the growing seasons of 2016 and 2017 shows that precipitation events that are greater than 10 mm are the main cause of dramatic interannual precipitation variations in this region. A single small precipitation event has a limited impact on SWC and provides no obvious increase in the SWC within the top 10 cm soil layer. The precipitation interval ratio (P/I) is suitable for comparing water stresses of different drying-wetting cycles, and correlations between soil layers are found to be closer in humid years than in dry years. In this study, three modes of interpulse ET_a in the desert steppe are discussed: a stable ET_a mode under a water-sufficient condition, an attenuation ET_a mode, and a stable ET_a mode under extreme drought conditions.

A sustainable model of combined organic–inorganic fertilizer application for high maize yields and environmental health is important for food security. The short-term combined application of organic and inorganic fertilizers can improve crop yields; however, the effect of different proportions of organic and inorganic fertilizers on the maize yield and nitrogen gas emissions in a long time series has not been reported. In this study, field experiments and DeNitrification-DeComposition (DNDC) model simulations were used to study the long-term effects of substituting inorganic fertilizers with organic fertilizers on crop yields and nitrogen-containing gas emissions. Six treatments were included: no nitrogen (CK); urea (U1); and 25%, 50%, 75%, and 100% of the urea N substituted by organic fertilizers (U3O1, U1O1, U1O3, and O1, respectively). The DNDC model was calibrated using the field data from the U1 treatment from 2018 to 2020 and was validated for the other treatments. The results showed that this model could effectively simulate crop yields (e.g., nRMSE < 5%), soil NH₃ volatilization, and N₂O emissions (nRMSE < 25%). In addition, long-term (26 years) simulation studies found that the U1O1 treatment could considerably increase maize yields and ensure yield stability, which was 15.69–55.31% higher than that of the U1 treatment. The N₂O, NH₃, and NO emissions were in the descending order of U1 > U3O1 > O1 > U1O3 > U1O1, and the total nitrogen-containing gas emissions from the U1O1 treatment decreased by 53.72% compared with the U1 treatment (26 years). Overall, substituting 50% of inorganic nitrogen with organic nitrogen could maintain the high yield of maize and reduce emissions of nitrogen-containing gases, constituting a good mode for the combined application of organic–inorganic nitrogen in this area.

Introduction: The application of biochar is generally considered to enhance soil nutrient availability and improve soil fertility, particularly in saline environments. However, the mechanisms by which biochar pyrolysis temperature influences nitrogen (N) availability and transformation in soils with varying degrees of salinity remain unclear. Methods: In this study, a laboratory incubation experiment was conducted to investigate the effects of biochar produced at different pyrolysis temperatures under three salinity levels (0.78, 1.92, and 2.79 dS m ⁻¹ ). Five treatments were applied: control (CK), conventional nitrogen application (N1), and N1 combined with 1% (w w ⁻¹ ) biochar produced at 300 °C (N1C1), 500 °C (N1C2), and 700 °C (N1C3). Soil microbial biomass, enzyme activities, nitrogen-cycling functional genes, and nitrogen mineralization processes were measured. Results: (1) Under low and moderate salinity, the N1C2 treatment significantly increased soil microbial biomass as well as urease and acid protease activities, whereas under high salinity, N1C3 performed better. Biochar addition also elevated the relative abundance of nitrogen-cycling functional genes, indicating enhanced net nitrogen transformation capacity. (2) Increasing salinity significantly suppressed nitrogen mineralization, while biochar application alleviated this inhibitory effect. Under low and moderate salinity conditions, the N1C2 treatment exhibited higher net nitrification and nitrogen mineralization capacities, whereas under high salinity conditions, the N1C3 treatment showed the most pronounced effect. (3) Soil microbial biomass and the activities of urease and acid protease were key factors influencing nitrogen mineralization across different salinity levels. With increasing salinity, the nitrogen mineralization pathway shifted from one dominated by aerobic mineralization/nitrification to more complex mechanisms involving facultative or anaerobic processes. Discussion: These findings provide valuable insights into nitrogen management in saline soils and underscore the importance of tailoring biochar applications according to pyrolysis temperature and salinity conditions.