To investigate the research hotspots and development trends of subsurface drip irrigation (SDI) over the past 20 years, this study analyzed relevant literature from the Web of Science Core Collection spanning from 2002 to 2022. The data were visualized using CiteSpace, showcasing the publication volume trends, countries, keywords, cited references, authors, and affiliated institutions. Based on 1079 articles, the annual publication volume showed an overall upward trend. The United States had the most extensive research coverage and highest publication volume, whereas China had the fastest growing publication rate in recent years. However, relatively little cooperation occurred among research teams and institutions. Over time, research topics became increasingly diverse, with water conservation and yield increases being the primary research objectives. In addition to improving irrigation and fertilizer use efficiency, SDI has also been applied in research on the safe utilization of unconventional water resources (wastewater and salt water) and the optimization of soil conditions. Among these, aerated irrigation technology—aimed at improving root growth in the rhizosphere—may become a new branch of SDI research. Currently, the main research focus in the field of SDI is the diffusion and distribution of water in the crop root zone, for which Hydrus model simulation is a particularly important method.

Cadmium (Cd) and drought, as abiotic stresses, have long been significant challenges for crop growth and agricultural production. However, there have been relatively few studies conducted on the effects of drought stress on Cd uptake, especially regarding the differences in Cd uptake characterization in varieties with varying Cd accumulation under different drought stress. To investigate the effects of drought conditions on Cd uptake by wheat in different genotypes under specific background levels of Cd pollution, we validated the differences in root absorption characteristics of low- (YM) and high-grain Cd accumulating wheat genotypes (XM) using non-invasive micro-test technology, and we conducted a hydroponic experiment on the Cd addition and different drought levels in a climate-controlled chamber. The biomass, root morphology, Cd uptake, and accumulation were determined under Cd (100 µmol L⁻¹) and different drought levels of 0% (0 MPa), 5% (−0.100 Mpa), 10% (−0.200 Mpa), and 15% (−0.388 Mpa) simulated by polyethylene glycol (PEG-6000). We found that the simultaneous exposure to Cd and drought had a suppressive effect on the total root lengths, root surface areas, and root volumes of XM and YM, albeit with distinct patterns of variation. As the concentration of PEG-6000 increased, the Cd concentrations and the amount of Cd accumulated in the roots and shoots of XM and YM decreased. Specifically, the Cd concentration in the roots exhibited a reduction ranging from 12.51% to 66.90%, while the Cd concentration in the shoots experienced an even greater decrease of 50.46% to 80.57%. The PEG-6000 concentration was significantly negatively correlated (p < 0.001) with Cd concentration of roots and shoots and Cd accumulation in roots, shoots, and the whole plants and significantly negatively correlated (p < 0.05) with the total length, surface area, and volume of roots. This study confirms that drought stress (5% PEG-6000) can decrease the uptake and accumulation of Cd in wheat seedlings without significant inhibition of biomass, and the change of root morphology (root length) and the decrease of Cd concentration in roots may be the main direct pathways for achieving these effects under drought stress. This research provides a new perspective and idea for water management in Cd-contaminated farmland.

Rising freshwater scarcities pose a serious threat to agricultural production. Reclaimed water (RW) is increasingly utilized as one of the alternative resources for irrigation in agriculture. Microbial communities play crucial roles in the soil microenvironment and can be used as effective indicators to assess the ecological influence of RW irrigation in soil. However, there is a lack of research on the effects of RW with different irrigation techniques on soil attributes and microbial communities. The present experiment was conducted in China to investigate the effect of two kinds of water qualities (RW and clean water (CW)), two kinds of irrigation methods (full irrigation (FI) and alternate partial root-zone irrigation (APRI)), and two kinds of irrigation techniques (furrow irrigation (FUI) and subsurface drip irrigation (SDI)) on soil chemical properties, heavy metal concentrations, and bacterial community structure. The APRI treatments received 70% of the irrigation water volume of FI. The results revealed that electrical conductivity (EC), nitrate nitrogen (NO₃⁻-N), and heavy metal (Cu, Cd, Pb, Zn) concentrations in soil irrigated with RW were significantly higher in comparison to the soil irrigated with CW. SDI significantly decreased the contents of TN by 4.88%, the EC by 13.78%, and the heavy metal Cd concentration by 13.14% in soils than that irrigated with FUI treatment. APRI significantly decreased the heavy metal Cu concentration in soils by 6.26% compared to FI treatment. Proteobacteria, Chloroflexi, Acidobacteria, and Gemmatimonadetes in soil irrigated with RW were more abundant than that irrigated with CW. The irrigation water quality, soil moisture content, heavy metal content, TN, and EC under various irrigation techniques and methods significantly affected the structure of soil bacterial communities. In conclusion, we highlight that the SDI-APRI treatment can be an efficient irrigation practice for reducing the EC, heavy metal pollution, and the security risks of soil irrigated by RW.

Aerated irrigation is an emerging and efficient irrigation technique, and the throttle-squeeze releaser (TS releaser) is a commonly used key component in aerated irrigation devices. However, it has issues such as large bubble size, uneven distribution, and low dissolved-oxygen content in the irrigation water. Given these problems, this study optimized the valve chamber and throat structure of the releaser based on the TS releaser, designing three different types of releasers with W-shaped valve chamber, arc-shaped valve chamber, and multi-throat W-shaped valve chamber. The simulation results, obtained using the Fluent module with grid division in ANSYS 2022, show that high-pressure regions are formed inside the releaser with V-shaped and arc-shaped valve chambers that are detrimental to the formation of microbubbles in high-pressure dissolved-air water, while the fluid pressure reduction and energy dissipation are more balanced inside the releasers with a W-shaped valve chamber. Compared to a single-throat design, the multi-throat design allows high-pressure fluid to enter the valve chamber more uniformly, which aids in maximizing the functionality and performance of the valve chamber. To determine the effects of throat size, outlet size, and valve chamber angle on the pressure field, turbulent flow field, velocity field, and air-phase distribution within the multi-throat W-shaped valve chamber releaser, simulation interaction experiments were conducted. The results showed that the optimized releaser performed best when the throat diameter was 1 mm, the outlet size was 2 mm, and the valve chamber angle was 80°. Finally, a comparative performance evaluation between the conventional TS diffuser and the optimized multi-throat W-valve chamber releaser reveals that the latter achieves a maximum dissolved-oxygen content of 6.36 mg/L in the treated irrigation water, representing an approximately 3.5% improvement over the 6.14 mg/L recorded by the traditional releaser. Furthermore, when considering the thresholds of irrigation flow rates above 950 L/h and dissolved-oxygen levels exceeding 5.9 mg/L, the multi-throat W-valve chamber diffuser exhibits a broader operational range characterized by high flow rates and dissolved-oxygen levels.