Brackish water has been widely used to irrigate crops to compensate for insufficient freshwater water supply for agricultural use. The goal of this research was to determine an efficient brackish water use method to increase irrigation efficiency and reduce N₂O emission. To this end, we conducted a field experiment with four salinity levels of irrigation water (1.1, 2.0, 3.5, and 5.0 g·L⁻¹ with drip irrigation) at Hetao Irrigation District (Inner Mongolia, China) in 2017 and 2018. The results show that irrigation with 3.5–5.0 g·L⁻¹ water salinity increased the soil salinity compared with irrigation using 1.1–2.0 g·L⁻¹ water salinity. The soil water content with 5.0 g·L⁻¹ brackish water irrigation was significantly higher than with 1.1–3.5 g·L⁻¹ water salinity due to the effect of salinity on crop water uptake. The overall soil pH increased with the increase in irrigation water salinity. Saturated soil hydraulic conductivity decreased with the increase in irrigation water salinity. These results indicate that brackish water irrigation aggravates the degree of soil salinization and alkalization. The soil N₂O cumulative flux resulting from irrigation with 5.0 g·L⁻¹ water salinity was 51.18–82.86% higher than that resulting from 1.1–3.5 g L⁻¹ water salinity in 2017, and was 32.38–44.79% higher than that resulting from 1.1–2.0 g·L⁻¹ in 2018. Irrigation with brackish water reduced maize yield, and the reduction in yield in 2018 was greater than that in 2017, but irrigation with 2.0 g·L⁻¹ brackish water did not significantly reduce maize yield in 2017. These results suggest that reducing the salinity of irrigation water may effectively reduce soil N₂O emission, alleviate the degree of soil salinization, and increase crop yield.

Reclaimed water (RW) is widely used in agricultural systems; however, it affects soil properties and the surrounding environment, thus influencing soil nitrogen transformation and increasing N₂O and NO emissions. Understanding the influencing mechanism of N₂O production in RW-irrigated soil is very important for water resource utilization and environmental protection, but it is rarely studied. This study investigated the impact of three nitrogen ions (NH₄⁺, NO₃⁻, NO₂⁻) on the nitrogen transformation process and non-biological processes affecting NO and N₂O emissions from soil under multiyear RW-irrigated conditions. The results showed that RW effectively increased the abundance of nitrifying and denitrifying functional genes, leading to a significant increase (p < 0.05) in soil NO and N₂O emissions under ammonium treatment. Furthermore, RW can reduce the cumulative NH₃ emission by 19.11% compared to deionized water (DW). In nitrate treatment, RW can significantly increase (p < 0.05) the nitrate conversion rate by increasing the abundance of denitrifying genes, but not significantly enhance N₂O and NO emissions. In NO₂⁻ oxidation, RW could increase the abundance of nitrifying genes (AOA-amoA, AOB-amoA), thereby promoting the progression of nitrifier denitrification and leading to a substantial increase (p < 0.05) in soil N₂O production. In summary, RW irrigation primarily increases N₂O emissions from soil by enhancing soil autotrophic nitrification and heterotrophic nitration. To effectively control soil N₂O emissions under agricultural irrigation with RW, it is crucial to carefully manage soil nitrification and adjust the ratio of ammonium and nitrate in the soil.

Alternative irrigation between saline water and groundwater can alleviate shortages of available agricultural water while effectively slowing the adverse effects of saline water on the soil-crop system when compared with continuous irrigation with saline water and blending irrigation between saline water and groundwater. In 2018, we tested the effect on soil CO₂ and N₂O emissions by two types of irrigation regimes (alternating groundwater and saline water (GW-SW), and alternating groundwater, followed by two cycles of saline water (GW-SW-SW)) between groundwater and three levels of salinity of irrigation water (mineralization of 2 g/L, 3.5 g/L, and 5 g/L), analyzed the correlation between gas emissions and soil properties, calculated comprehensive global warming potential (GWP), and investigated the maize yield. The results show that, with the same alternate irrigation regime, cumulative CO₂ emissions decreased with increasing irrigation water salinity, and cumulative N₂O emissions increased. Cumulative CO₂ emissions were higher in the GW-SW regime for the same irrigation water salinity, and cumulative N₂O emissions were higher in the GW-SW-SW regime. The GW-SW-SW regime had less comprehensive GWP and maize yield as compared to the GW-SW regime. The 2 g/L salinity in both regimes showed larger comprehensive GWP and maize yield. The 3.5 g/L salinity under the GW-SW regime will be the best choice while considering that the smaller comprehensive GWP and the larger maize yield are appropriate for agricultural implication. Fertilizer type and irrigation amount can be taken into consideration in future research direction.

Soil erosion and the consequent loss of nutrients have consistently been significant factors contributing to land degradation and nonpoint source pollution. While runoff serves as the primary carrier for nutrient loss, the hydraulic processes governing the mechanisms of nutrient loss remain not entirely clear. This paper aims to investigate the impacts of rainfall intensity and the slope gradient on hydraulic parameters, soil loss rates, and ammonia nitrogen loss rates, with the objective of determining the optimal hydraulic parameters for more accurate predictions of soil erosion and nutrient loss rates. A series of simulated rainfall experiments with three rainfall intensities (25, 50, and 75 mm min⁻¹) and four slope gradients (8.7%, 17.6%, 26.8%, and 36.4%) were conducted on a 5 m × 10 m slope. The results indicated that the flow velocity, shear stress, stream power, unit stream power, and unit energy all increased with the increase in slope gradient or rainfall intensity. The water depth decreased with an increase in the slope gradient but increased with an increase in the rainfall intensity. Laminar flow occurred in all experiments (Reynolds number < 500). Only the overland flow under a 25 mm h⁻¹ rainfall intensity and 8.7% slope gradient was subcritical flow (Froude number < 1). Hydraulic parameters, the soil loss rate, and ammonia nitrogen loss rate could be all expressed as the product of rainfall intensity and slope power function, with R² ranging from 0.949 to 0.997. The average soil loss rate and process soil erosion rate could both be fitted using the power function of hydraulic parameters, with the optimal fitting parameter being stream power (R² = 0.980 and 0.909). The average ammonia nitrogen loss rate exhibited a linear relationship with the hydraulic parameters, and the optimal fitting parameter was also stream power (R² = 0.933). However, there were relatively low correlations between hydrodynamic parameters and the ammonia nitrogen loss rate (R² = 0.450–0587). Our results contribute to a deeper understanding of the hydraulic processes involved in nutrient loss.

A experiment was conducted at the Jiangxi Province Center Station of Irrigation Experiment from 2019 to 2021 to study the water and nitrogen balance under water and fertilizer regulation modes. The study aimed to propose a recommended mode for paddy fields that could save water, control pollution, reduce gas emission, and improve fertilizer use efficiency. This study examined the impact of different irrigation methods and nitrogen application levels on water saving and emission reduction in paddy fields. The experiment included six treatments, which involved two irrigation methods (intermittent irrigation and flooding irrigation, referred to as W1 and W0, respectively) and three application rates of nitrogen fertilizer (0 kg/ha, 135 kg/ha, 180 kg/ha, referred to as N0, N1 and N2, respectively). The study found that irrigation methods had a significant effect on the amount of irrigation, drainage, leakage, nitrogen load from drainage, soil nitrification potential, and ammonia volatilization. The results showed that compared to flooding irrigation, intermittent irrigation reduced the amount of irrigation, drainage, leakage and nitrogen load from drainage by an average of 25.98%, 16.03%, 8.43% and 10.86%, respectively. However, the study also found that the nitrification potential and ammonia volatilization increased by an average of 6.45% and 4.32%, respectively. Fertilization levels had a significant effect on drainage nitrogen load, early soil nitrification potential and ammonia volatilization. Compared with the treatment of N2 (180 kg N/ha), the drainage nitrogen load under the treatment of N1 (135 kg N/ha) decreased by 10.86% on average, while nitrification potential and ammonia volatilization increased by 38.74% and 3.33%, respectively. In terms of nitrogen output, the amount of nitrogen absorbed by crops was the largest, followed by the nitrogen load from field drainage, then ammonia volatilization, and then denitrification. Considering the goals of water saving, emission reduction, and the efficient utilization of water and fertilizer in paddy fields, the optimal water and fertilizer regulation mode was the W1N1 mode (intermittent irrigation combined with reduced nitrogen fertilizer application rate, 135 kg N/ha).

Soil salinization is a pressing issue that needs to be addressed in current agricultural production. In this study, we utilized novel materials, unfunctionalized multi-walled carbon nanotubes (MWCNT) and functionalized multi-walled carbon nanotubes (MWCNT-OH), to explore the effects of soil carbon and nitrogen cycles in saline soil. We set up four treatments, which were exposed to two exposure doses of 1 g/kg and 1 μg/kg and two MWCNT types of functionalized MWCNT-OH and unfunctionalized MWCNT. Our results demonstrate that exposure of saline soil to 1 g/kg functionalized MWCNT-OH significantly increased the soil inorganic nitrogen (p < 0.05), while also promoting the soil microbial biomass. This exposure can also potentially enhance greenhouse gas emissions from saline soil. Moreover, exposure to MWCNTs significantly increased the proportion of Actinobacteria and Proteobacteria, two dominant phyla (p < 0.05), which in turn improved their contribution to the carbon and nitrogen cycling processes within saline soil. High exposure dose treatments (1 g/kg) significantly increased the abundance of functional genes associated with carbon metabolism, carbon fixation, methane metabolism, and nitrogen cycling processes within saline soil. In contrast, low exposure dose treatments (1 μg/kg) had no significant effect on the abundance of functional genes related to nitrogen cycling, but significantly increased the abundance of special functional genes related to carbon cycling. Redundancy analysis revealed that the microbial community composition within saline soil was significantly impacted by the soil total carbon, total nitrogen, and nitrate nitrogen content. Furthermore, it was observed that over 80% of the carbon and nitrogen cycling processes within the saline soil were contributed by the dominant phyla. In summary, our research confirms the potential applicability of MWCNTs within saline soil. Notably, exposure of saline soil to 1 g/kg functionalized MWCNT-OH exhibited the most significant promoting effect on the carbon and nitrogen cycles.