Explore the vast range of titles available.

Hydrological research in humid tropics is particularly challenging because of highly variable hydrological conditions and high socio-economic stresses caused by rapid population increase, as is the case of Nicaragua. The objective of this research is to understand the surface and subsurface runoff generation processes in a poorly gauged coastal catchment in Nicaragua under variable humid tropical conditions. Specifically, it focuses on identifying geomorphological and hydro-climatic controls on catchment response at different spatio-temporal scales and studies the link between hydrological processes and ecosystem conditions.

【Objective】Soil salinization and waterlogging are critical challenges to crop productivity and sustainable agriculture. This study examines the effects of subsurface drainage and biochar application on soil properties and crop growth in coastal saline-alkali soils in the Yellow River Delta.【Method】The field experiment was conducted using sunflower as the model plant. The spacing of the subsurface drain varied from 10 m to 30 m, each having two biochar applications: 0 and 30 t/hm2. During the experiment, we measured soil moisture content and pH, and evaluated how biochar application and drain spacing combined to influence growth, yield components and seed quality of the sunflower.【Result】① Biochar application significantly reduced soil moisture content and increased soil pH. At the flowering stage, the treatment with drain spacing of 30 m reduced soil moisture by 6.82% with biochar application and 16.57% without biochar, compared to the control without drainage and biochar application. ② During the budding and flowering stages, plant height in the treatment with drain spacing of 30 m was significantly higher than that in the control, regardless of biochar applications. At the flowering and maturity stages, biochar addition further increased plant height and stem diameter. Compared to the treatment without biochar application, biochar addition increased single-head grain weight and yield by 10.46%-19.36% and 11.45%-19.35%, respectively. Our results show that 30 m drain spacing combined with biochar application significantly enhanced kernel fat and linoleic acid contents, compared to the control and without biochar.【Conclusion】Subsurface drainage combined with biochar application significantly improves the physicochemical properties of coastal saline-alkali soils, promotes sunflower growth, and enhances yield and quality. This combination can be used as an improved agronomic practice for amelioration of saline-alkali soils and improving crop productivity in coastal regions.

Many engineering construction projects entail excavations into water bearing substrates. The authors explain the drainage techniques required to lower groundwater sufficiently to allow projects to be undertaken with confidence.

【Objective】 Subsurface drain is a drainage system widely used in northwestern China to keep the groundwater below the critical depth and facilitate soil salt leaching. This paper presents an experimental study on the combined effect of drain depth and spacing on soil salt leaching in a representative oasis in Yanqi Basin. 【Method】 The drains were buried at the depth of 1.2 or 1.5 m, with the spacing being 20, 30 or 40 m. Overall, there were six treatments. For each treatment, we measured the spatial changes in soil salt contents before and after the leaching, which were then used to analyze the variation in salt leaching efficiency between different treatments. 【Result】 ① When initial soil moisture was at the field capacity, leaching could quickly saturated the soil and displace the water in the soil above the drains. There were no significant correlations between soil moisture content and the depth and spacing of the drains. ② Salt leaching from the top 0-60 cm soil layer was significantly related to the depth and spacing of the drains. The spacing and depth of the drains combined to affect soil salt removal rate. When the spacing was the same, increasing the burial depth of the drains enhanced salt removal from the 0-60 cm soil layer; when the burial depth of the drains was the same, salt removal rate from the 0-60 cm soil layer was the highest when the spacing was 30 cm (P<0.05). ③ As the leaching elapsed, both cumulative water drainage and soil salt leaching increased steadily and then tended to flatten; the electrical conductivity of the drainage water was relatively stable, correlating positively to soil salt content. The cumulative water drainage and leached salt were impacted significantly by the burial depth of the drains (P<0.05) but insignificantly by the drain spacing (P>0.05). Compared to the burial depth of 1.2 m, the burial depth of 1.5 m considerably improved the drainage efficiency and accelerated soil salt removal. 【Conclusion】 For maximum soil salt removal rate, the optimal depth and spacing of the subsurface drains for the study area was 1.5 m and 30 m, respectively.

Farmland in southern China is prone to flooding and waterlogging alternation after short-term heavy rainfall. Single drainage form cannot meet the requirements of the farmland flooding and waterlogging removal. Drainage measures and layout forms should be explored to alleviate flooding and waterlogging threat and improve crop yield. So, based on an indoor sand tank experiment, this paper presents a combined drainage form: conventional subsurface drainage as an auxiliary drainage measure and is alternatively combined with open ditch (OD), filter drainage (FD), conventional (CD) and improved subsurface drainage (ID), respectively, under equal and unequal drain depth. The performance of different combined drainage forms and the effect of auxiliary drainage measures are discussed for stable ponding and receding water. During the experiment, two factors—drainage measure and drain depth—are considered. The results indicate that compared with the conventional subsurface drainage alone, the flow rates of the open-ditch, thin-improved, and thick-improved subsurface drainage combined with conventional subsurface drainage can be increased by 22.4–32.3%, 10.6–16.2%, and 29.8–32%, respectively, under equal drain depth in stable ponding water. Among the four combined drainage forms, the flow rate of shallow–deep combination is 8.1–17.1% higher than that of the shallow–shallow combination. Compared with a single drainage form, the flow rates of the combined drainage have the same change characteristics over time. Additionally, the use of auxiliary, conventional, subsurface drainage can improve the flooding and waterlogging removal efficiency in farmland. For the combined drainage forms, the contribution degree of the open-ditch and thin-improved subsurface drainage is 51.3–56.7%, while the thick-improved subsurface drainage is approximately 61.0%, under equal drain depth conditions in the flooding removal process. Moreover, open-ditch and thick-improved subsurface drainage combined with conventional subsurface drainage have significant advantages in flooding and waterlogging removal, which were 11.5–38.1% and 37.1–48.6% faster than conventional subsurface drainage in flooding removal time, 14.3–157.1% and 14.3–44.4% faster than conventional subsurface drainage in the waterlogging removal time. The synergistic application of shallow–deep and medium–medium combinations can be carried out by exploiting the advantages of each drainage measure. The experimental flow rate observation is in good agreement with the theoretically calculated value, with a relative error of less than 5%. These research findings could provide technical support for the increased application of combined drainage forms in areas prone to flooding and waterlogging.

A two-year (2024–2025) field experiment was conducted in southern Xinjiang to alleviate soil compaction and severe salinization in saline–alkali soils and to evaluate the combined effects of tillage depth and subsurface drain spacing on soil improvement. Six treatments were established with three deep tillage depths, 70 cm (W1), 50 cm (W2), and 30 cm (W3), and two subsurface drain spacings, 20 m (S1) and 40 m (S2). Treatment effects on soil water–salt dynamics, soil physical properties and structure, ionic composition, and subsurface drainage and salt removal were analyzed. This study provides mechanistic and practical evidence that coupling deep tillage with subsurface drainage creates a more effective leaching–drainage pathway than either measure alone and enables robust optimization of design parameters (drain spacing × tillage depth) for saline–alkali land improvement in arid regions. Deep tillage in combination with subsurface drainage significantly increased soil profile water content, total porosity, and cumulative subsurface drainage and salt export, all of which reached their maxima under S1W1; it also significantly reduced bulk density, total salinity, and the concentrations of Na+, K+, Mg2+, Ca2+, Cl−, and SO42−, which reached their minima under S1W1. After two spring irrigation–leaching events (in 2024 and 2025), surface salt accumulation in the soil profile was markedly alleviated, and the mean salinity in the 0–20 cm layer decreased by 45.68% across treatments. The S1W1 treatment achieved the best desalinization performance in both leaching events, with reductions of 41.36% and 44.68%, respectively. Pearson correlation analysis indicated that the desalinization effect was significantly negatively correlated with porosity and significantly positively correlated with bulk density and ionic concentrations. Overall, coupling deep tillage with subsurface drainage effectively reduced soil salinity and harmful ions, improved soil structure, and enhanced drainage-mediated salt removal, with the 70 cm tillage depth combined with a 20 cm drain spacing delivering the best performance.

Subsurface drainage and organic fertilizer application are two important measures for improving saline–alkali soils, while the effects of different drainage spacings combined with organic fertilizer application amounts on alfalfa growth and coastal saline soil properties have seldom been evaluated. This study designed subsurface drainage pipes at four spacing distances, including 0 m (CK, without subsurface drainage), 6 m (S1), 12 m (S2), and 18 m (S3), and three organic fertilizer application amounts, including 3000 kg/ha (N1), 4500 kg/ha (N2), and 6000 kg/ha (N3), to observe the effects of different combinations of subsurface pipe spacings and organic fertilization amounts on alfalfa yield, quality, soil salinity, and nutrients. The results showed that the yield of alfalfa increased with higher fertilization amounts and smaller spacing between drainage pipes. The highest yield occurred in the S1N3 treatment, and the three batches reached 1268.5 kg/ha, 3168.0 kg/ha, and 2613.3 kg/ha, respectively, significantly (p < 0.05) higher than CK for all three batches. The increase in organic fertilizer amount resulted in an increase of 0.5–9.3% in the crude protein content, a decrease of 1.8–3.4% in the neutral detergent fiber content, and a decrease of 1.3–5.5% in the acid detergent fiber content for alfalfa plants. Under CK, the contents of quality indicators in alfalfa were the highest. For the drainage treatments, the quality indicator contents were overall at a higher level under S3. Subsurface drainage had a reduction effect on the salinity of all the 0–80 cm soils. For the surface soil, it was detected that smaller spacing was beneficial for reducing soil salt content, while higher fertilization amounts increased the salt content. S1 reduced the soil salt content by 36.3–46.1% compared to CK; however, N3 increased the salt content by 7.0–16.2% compared to the other two fertilization treatments. In addition, smaller spacing between the subsurface drainage pipes generally reduced the soil’s available nitrogen, and total nitrogen increased the C/N ratio but had no significant effect on the organic matter. It was concluded that the spacing between subsurface drainage pipes and the application amounts of organic fertilizer have remarkable impacts on alfalfa yield and quality, mainly by changing the soil salinity and nutrient status.

Agricultural subsurface drainage can be an important conduit of nitrate from agricultural fields to streams. This study focused on understanding the variability in nitrate concentrations and loads, exported by subsurface drains, into a small, north-central Iowa stream. Ninety-three subsurface drains in this watershed were sampled up to 5 times between 2006 and 2008. Additionally, 2 subsurface drains and the stream draining the study area (South Fork Iowa River near Blairsburg, IA, USA) were sampled frequently during the growing seasons in 2007 and 2008. Spatial variability analysis revealed no distinct spatial pattern in nitrate concentrations. The median nitrate concentrations were not significantly different when the drain outlets were characterized by diameter (17–23 cm, 27–48 cm, 60–108 cm). The eight large subsurface drains (part of the public drainage network) had less variability in nitrate concentration than the smaller drain sizes and generally contributed 70–87% of the total water and nitrate loads exported by subsurface drains to the stream. During high-discharge events, the medium-sized (27–48 cm) subsurface drains discharging to the stream became more important by contributing a higher discharge and nitrate load. The temporal variability examined in this study found that discharge and nitrate loads were influenced by the amount of precipitation that had occurred over the previous months. This paper demonstrates the spatial and within-season homogeneity of nitrate delivery to a stream from an intensely agricultural landscape that has subsurface drainage.

Subsurface drainage pipes covered with filters and geotextiles are the key to preventing clogging and ensuring efficient drainage. To improve the salt discharge efficiency of these subsurface drainage pipes, different layers of geotextiles were set outside the pipes with the aid of uniform gravel filters. This paper reports our findings from laboratory simulation of subsurface drainage pipes and experiments. The study examined the influence of different layers of geotextiles on the drainage efficiency, salt discharge effects of subsurface drainage pipes, and the effect of superimposed geotextiles on the salt drainage efficiency as well as the anti-clogging effect of subsurface drainage pipes. The results are as follows: (1) The geotextile and filter material wrapped around the subsurface pipe facilitated the movement of water towards the subsurface pipe, which could promote the salt discharge of the subsurface pipe. However, in the single leaching experiment, the reduction in soil pH was not significant for different scenarios. (2) The salt removal rate of the geotextile-wrapped subsurface pipes was more than 95%. The salt removal rate of the double-layer geotextile scenario was the highest (96.7%), and the total salt content of soil profiles was 8.3% and 31.3% lower than those of the single-layer and triple-layer geotextile scenarios, respectively. The drainage efficiency of the double-layer geotextile scenario was the highest, and the salt distribution in the 0–60 cm profile was relatively uniform, ranging from 2.3 to 3.0 g∙kg−1. (3) The clogging in the triple-layer geotextile scenario was caused by the geotextile, i.e., a dense filter cake layer formed on the surface of the geotextile. The clogging in the single-layer and double-layer geotextile scenarios was the clogging of the geotextile itself, i.e., soil particles retained in the fiber structure of geotextiles. (4) In the case of the single-layer and double-layer geotextile scenarios, the soil particles failed to completely clog the selected geotextiles, and there were still a large number of pores retained. The double-layer geotextiles integrate filtration, clogging prevention, and drainage promotion to provide the best salt drainage with the subsurface pipe. This study reveals the influence of the filter on soil water salt and salt discharge and provides a theoretical explanation and technical justification for the application of the subsurface pipes salt discharge technology in saline soil ameliorate.

Subsurface pipes covered with geotextiles and filters are essential for preventing clogging and ensuring efficient drainage. To address low salt discharge efficiency due to subsurface drainage pipes (SDPs) clogging easily, sand gravel, straw, and combined sand gravel–straw were set above SDPs, respectively, within a setting of uniform geotextiles. The influences of different filter materials on the drainage efficiency and salt discharge effect of the SDPs, as well as the effects of different filter materials on the salt drainage efficiency and anti-siltation effect of the SDPs were studied by performing simulation experiments in a laboratory. The results confirmed the following: (1) The salt removal rates of the SDPs externally wrapped with materials exceeded 95%. The subsurface pipe treated with the sand gravel filter material had the highest desalting rate (93.69%) and soil profiles with total salt contents that were 17.7% and 20.5% lower than those treated with the straw and combined sand gravel–straw materials, respectively. (2) The soil salinity of the sand gravel filter material around the SDPs was between 1.57 and 3.6 g/kg, and the drainage rate (R) was 0.97, so its salt-leaching effect was the best. (3) The sand gravel filter material increased the characteristic particle size of the soil above the SDP by 8.4%. It could effectively intercept coarse particles, release fine particles, and facilitate the formation of a highly permeable soil skeleton consisting of coarse particles, such as sand particles surrounding the soil. (4) The use of the straw filter material produced dense filter cake layers on the upstream surfaces of the geotextiles. When the sand gravel and combined sand gravel–straw filter materials were used, soil particles remained in the geotextile fiber structure, and a large number of pores were still retained. Therefore, the sand gravel filter material was the most suitable for the treatment of Yinbei saline–alkali soil in Ningxia Hui Autonomous Region.