The paddy field is a major source of gaseous carbon and nitrogen emissions, and reducing these emissions is of great significance for mitigating greenhouse effects and non-point source pollution in farmland. Biochar, derived from agricultural waste, possesses a stable structure, large specific surface area, abundant pore structures, and surface functional groups. These characteristics could enhance soil physicochemical properties and microbial activity, thereby facilitating the dual goals of increasing crop yield and reducing emissions. Based on numerous studies, this review summarizes the effects of biochar on the emissions of carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and ammonia volatilization (NH₃), as well as on global warming potential (GWP) and greenhouse gas emission intensity (GHGI). It elucidates the mechanism of emission reduction by biochar amendment from the perspective of carbon and nitrogen conversion processes and soil physicochemical and biological properties. Numerous studies showed the application of 5~40 t ha⁻¹ biochar reduced CO₂, CH₄, N₂O, and NH₃ emissions by 1.64~89.6%, 8.6~89.6%, 10~90%, and 12.27~53%, respectively. A small number of studies found that the application of 5~48 t ha⁻¹ biochar increased CO₂, CH₄, N₂O, and NH₃ emissions by 12~37%, 19.85~176%, 13~84.23%, and 5.47~70.9%, respectively. Most scholars have found that biochar has varying degrees of emission reduction capabilities in different parts of the world. Therefore, future research directions have been suggested for utilizing biochar to reduce carbon and nitrogen emissions in paddy fields.

Understanding the distribution of water and nitrate nitrogen in the soil profile is crucial for the reasonable operation of fertigation, and it is also fundamental for controlling and regulating nitrate nitrogen in the root zone, thereby meeting a crop’s requirements. The application rates of fertilizer and water directly influence this distribution of water and nitrate nitrogen. However, the effects in Aeolian sandy soil, a type of developing soil bordering deserts, remain ambiguous. In this study, field experiments for different drip fertigation treatments in Aeolian sandy soil were conducted to investigate the soil water distribution, as well as that of nitrate nitrogen. A completely randomized experimental design was implemented, encompassing three levels of irrigation amount: low (W1), medium (W2), and high (W3), and three levels of nitrogen application rate: low (F1), medium (F2), high (F3). After the completion of each irrigation treatment, soil samples were extracted at 10–20 cm intervals. The soil water and nitrate nitrogen contents in the profiles of these samples were measured. The experimental results revealed that increasing the nitrogen application rate facilitated the retention of greater amounts of water and nitrate nitrogen in the soil profile. However, with an increase in the nitrogen application rate, both soil water and nitrate nitrogen exhibited a radial tendency to move away from the drip emitter. Some moved upward and accumulated in surface soil near a ridge furrow, while some moved downward and remained in a deeper area approximately 30 cm horizontally from the emitter at depths of 40–60 cm. The uniformity of the water distribution decreased with increasing nitrogen application under low water conditions, with a reversal of this trend observed in medium and high water treatments. The effect of nitrogen application level on the uniformity of the nitrate nitrogen distribution was not significant. There was no significant correlation between the average soil water content and nitrate nitrogen content along the horizontal direction, however, a positive correlation existed in the vertical direction. In the whole profile, increasing the nitrogen application enhanced the correlation under low water conditions, but under medium and high water conditions, this trend was the opposite. This implies that, to avoid nitrate nitrogen leaching or limiting in a specific area, a moderate nitrogen application level is advisable. Under low water conditions, nitrogen application showed a positive effect on the nitrate nitrogen content, and a higher application is recommended. In cases of substantial water irrigation or rainy years, the nitrogen application rate should be decreased.

Drip irrigation with saline water is frequently adopted to realize the sustainable utilization of saline–sodic soil with high water tables, and soil enzyme activities can be used to indicate changes in soil quality. In the current study, spatiotemporal changes in soil urease enzyme (URE), alkaline phosphatase (ALP) and invertase (INV) activities were investigated during consecutive growing seasons. Soil in beds was sampled before planting (0 y) and one, two, three and four years after the growing season (1 y, 2 y, 3 y, 4 y), and these samples were distributed at four horizontal distances from the drip line (0, 10, 20 and 30 cm) and four vertical soil depths (0–10, 10–20, 20–30 and 30–40 cm). The results showed that a distribution pattern of URE and ALP activities formed during the first growing season, while the distribution of INV activity formed until the third growing season. All three soil enzyme activities in the upper soil layers and positions close to the drip line were more greatly affected by planting year. The average URE activity of the soil profile decreased slightly during the first year and increased by about 220% and decreased by 20% after reclamation for two and three years, and finally, it increased to 4.9 μg NH₄⁺·g⁻¹·h⁻¹ at the end of the fourth growing season. ALP activity remained stable during the first two years and rapidly increased in the following years; in particular, in the fourth year, it reached 32.7 μg ph(OH)·g⁻¹·h⁻¹. INV activity increased continually with the number of years after planting and reached 1009.0 μg glu·g⁻¹·h⁻¹ at the fourth season’s end. An analysis of variance indicated that URE, ALP and INV activities varied insignificantly among the time points of 0 y, 1 y, 2 y and 3 y (p < 0.05), while they were significantly higher for 4 y than for 0 y and 1 y. In addition, all three enzyme activities of the soil profile had an exponentially increasing trend with the number of years after planting. These results indicated the soil quality in saline–sodic soils could be improved with time under drip irrigation with local saline groundwater, especially around the drip line.

Accurate irrigation water-use data are essential to agricultural water resources management and optimal allocation. The obscuration presented by ground cover in farmland and the subjectivity of irrigation-related decision-making processes mean that effectively identifying regional irrigation water use remains a critical problem to be solved. In view of the advantages of satellite microwave remote sensing in monitoring soil moisture, previous studies have proposed a method for estimating irrigation water use using the satellite microwave remote sensing of soil moisture. However, the method is affected by false irrigation signals from soil moisture increases caused by non-irrigation factors, causing irrigation water use to be overestimated. Therefore, the purpose of this study is to improve the estimation of irrigation water use in drylands by using irrigation signals from SMAP soil moisture data. In this paper, the irrigation water use in Henan Province is estimated by using the irrigation signals from SMAP (soil moisture active and passive) soil moisture data. Firstly, a method for recognizing irrigation signals in soil moisture data obtained by microwave satellite remote sensing was used. Then, an estimation model of the amount of irrigation water (SM2Rainfall model) was built on each data pixel of the satellite microwave remote sensing of soil moisture. Finally, the amount of irrigation water utilized in Henan Province was estimated by combining the irrigation signals and irrigation water-use estimation model, and the results were evaluated. According to the findings, this study improved the estimation accuracy of irrigation water use by using the irrigation signals in Henan Province. The result of this study is of great importance to accurately obtain irrigation water use in the region.

Extensive practice has demonstrated that the continuous pursuit of high yields in the black soil region of Northeast China resulted in imbalances in soil nutrients and declines in both soil quality and water use efficiency. Alternate wetting and drying (AWD) irrigation offers a promising solution for increasing rice yield and maintaining soil fertility. However, the success of this irrigation method largely depends on its scheduling. This study examined the threshold effects of AWD on rice growth, yield, and soil nutrient availability in the Sanjiang Plain, a representative black soil region in Northeast China. A two-year trial was conducted from 2023 to 2024 at the Qixing National Agricultural Science and Technology Park. “Longjing 31”, a local cultivar, was selected as the experimental material. The lower limit of soil water content under AWD was set as the experimental factor, with three levels: −10 kPa (LA), −20 kPa (MA), and −30 kPa (SA). The local traditional irrigation practice, continuous flooding, served as the control treatment (CK). Indicators of rice growth and soil nutrient content were measured and analyzed at five growth stages: tillering, jointing, heading, milk ripening, and yellow ripening. The results showed that, compared to CK, AWD had minimal impact on rice plant height and tiller number, with no significant differences (p > 0.05). However, AWD affected leaf area index (LAI), shoot dry matter (SDM), yield, and soil nutrient availability. In 2023, control had little effect on rice plant height and tiller number among the different irrigation treatments. The LAI of LA was 11.1% and 22.5% higher than that of MA and SA, respectively, while SDM in LA was 10.5% and 17.2% higher than in MA and SA. Significant differences were found between LA and MA, as well as between LA and SA, whereas no significant differences were observed between MA and SA. The light treatment is beneficial to the growth and development of rice, while the harsh growth environment caused by the moderate and severe treatments is unfavorable to rice growth. The average contents of nitrate nitrogen (NO₃⁻-N), available phosphorus (AP), and available potassium (AK) in LA were 11.4%, 8.4%, and 9.3% higher than in MA, and 16.7%, 11.5%, and 15.0% higher than in SA, respectively. Significant differences were observed between LA and SA. This is because the light treatment facilitates the release of available nutrients in the soil, while the moderate and severe treatments hinder this process. Although panicle number per unit area and grain number per panicle in LA were 7.5% and 2.3% higher than in MA, and 10.8% and 2.2% higher than in SA, these differences were not statistically significant. Seed setting rate and thousand-grain weight showed little variation across irrigation treatments. The yield of LA was 10,233.3 kg hm⁻², 9.1% and 14.1% higher than that of MA and SA, respectively, with significant differences observed. Compared with the moderate and severe treatments, the light treatment increases indicators such as the number of panicles per unit area, grains per panicle, thousand-grain weight, and seed setting rate, resulting in significant differences among the treatments. Water use efficiency (WUE) decreased as the control level increased. The WUE of all AWD irrigation treatments was significantly higher than that of the control treatment (CK). Compared with CK, AWD reduces evaporation, percolation, and other water losses, leading to a significant decrease in water consumption. Meanwhile, the yield remains basically unchanged or even slightly increases, thus resulting in a higher WUE than CK. The trends in rice growth, soil nutrient indicators, and WUE in 2024 were generally consistent with those observed in 2023. In 2024, the yield of LA was 9832.7 kg hm⁻², 14.9% and 17.3% higher than that of MA and SA, respectively, with significant differences observed. Based on the results, the following conclusions are drawn: (1) AWD irrigation can affect the growth of rice, alter the status of available nutrients in the soil, and thereby cause changes in yield and WUE; (2) LA is the optimal treatment for increasing rice yield, improving the availability of soil available nutrients, and improving WUE; (3) Both MA and SA enhanced WUE; however, these practices negatively impacted rice growth and the concentration of soil available nutrients, leading to a concurrent decline in yield. To increase rice yield and maintain soil fertility, LA, with an irrigation upper limit of 30 mm and a soil water potential threshold of −10 kPa, is recommended for the Sanjiang Plain region.

Drip irrigation is an effective method to utilize waste saline-sodic land with a high water table. For reasonable and sustainable utilization of saline-sodic soil under such conditions, spatiotemporal changes in total nitrogen (TN), total phosphorus (TP), and soil organic matter (SOM) were investigated during the utilization process. The soil was sampled from newly built raised beds before planting (0 y) and beds in three adjacent plots had been planted with Lycium barbarum L. for one (1 y), two (2 y), and three years (3 y), respectively, at the end of the growing season. Soil samples were obtained at four horizontal distances from the drip line (0, 10, 20, and 30 cm) and four vertical soil depths (0–10, 10–20, 20–30, and 30–40 cm). The results showed that the average TN and TP of the soil profile increased with the planting year and were approximately 0.68 and 1.81 g·kg⁻¹ in the soils of 3 y, approximately 84.9 and 42.4% higher than that of 0 y, respectively. SOM decreased in the first growing season and then continuously increased in the following planting years, reaching 8.26 g·kg⁻¹ in the soils of 3 y, which was approximately 38.2% higher than that of 0 y. TN, TP, and SOM contents were high in soils around the drip line and decreased with distance from the drip line. In both horizontal and vertical directions, TN, TP, and SOM varied slightly in soils of 0, 1, and 2 y, while in soils of 3 y, TN and SOM decreased with increased distance in both horizontal and vertical directions and TP decreased obviously only within 10 cm in both directions. This indicated that the contents and distributions of soil nutrients in such saline-sodic soils could be improved with planting year under drip irrigation with local saline groundwater and especially around the drip line as the soil around the dripper was quickly ameliorated.