Conventional Subsurface Drainage Research Articles

Performance of surface, subsurface and trench‐type drainage systems in paddy fields for non‐rice farming

AbstractEffective drainage is a crucial factor in paddy fields, especially in regions with waterlogging or heavy clay soils. Identifying an effective drainage system is essential for the successful removal of excess soil water from paddy fields to prepare them for subsequent crops. This study aimed to evaluate three different drainage systems, shallow surface drainage (shallow ditch), conventional subsurface pipe drainage and trench‐type subsurface drainage (French drain), in paddy fields in terms of drainage water volume, water table depth, drainage intensity, soil moisture and cracks. Experiments were carried out in a physical model capable of simulation with a 7.5 m drain spacing. The findings indicated that trench‐type drainage was more effective in reducing soil moisture due to its higher drainage water volume compared to other systems. The time required for the topsoil to reach its lower plastic limit in the subsurface, trench‐type and shallow surface drainage systems was 14, 11 and 15 h after the depletion of excess water over the soil surface, respectively. Although shallow surface drainage represented faster depletion of excess water, trench‐type drainage eventually proved to be the most effective alternative for providing appropriate qualifications for secondary cultivation. Crack areas on the soil surface were twice as extensive in trench‐type and subsurface drainage systems as in shallow surface drainage systems, indicating their superior performance.

Efficient desalination method using a subsurface drainage pipe with rice husk in paddy fields

The 2011 tsunami from the Great East Japan Earthquake caused severe soil salinization in agricultural lands. Soil salt removal using a subsurface drainage pipe with rice husk has been widely used in many paddy fields. However, desalination was frequently decided based on the expertise of construction contractors in Japan resulting in inefficient desalination methods that led to a significant wastage of freshwater resources and a long duration for agricultural restoration. Previous studies have either simulated conventional subsurface drainage without considering the rice husk zone or focused only on rice husk subsurface drainage systems excluding pipes. However, no quantitative research on a subsurface drainage pipe with rice husk has been conducted using numerical simulations. Accordingly, this study proposes highly efficient desalination methods for reducing freshwater wastage using an indoor experiment and numerical simulation. The indoor experiment of the subsurface drainage pipe with rice husk was set up in a soil tank of 900 × 200 × 900 mm (length × width × height), with reproduced salinization using NaCl solution inundation and soil desalination using freshwater. Thereafter, calibration and validation using HYDRUS-2D confirmed the model's accuracy in reproducing the movement of water and salt in the soil profile. The effects at a ponding water depth of 50–300 mm under various conditions on desalination efficiency and leaching water quantity were simulated. The results suggested that as the same desalination effect is achieved, low ponding water depths with multiple desalting cycles will reduce the quantity of leaching water. Moreover, under low ponding water depth conditions, prolonging the flooding duration will cause a decrease in the desalination effect. In addition, for the same quantity of leaching water, increasing the pipe burial depth is more beneficial to desalination than expanding the rice husk zone width. This study provides theoretical guidance for water conservation and high-efficiency desalination using the subsurface drainage pipe with rice husk for post-disaster early restoration of paddy fields.

Controlled drainage under two climate change scenarios in a flat high-latitude field

Abstract This simulation study focused on the hydrological effects of climate change and controlled drainage operated with subsurface drains and an open collector ditch in an agricultural field. The objective was to understand the potential of controlled drainage and open ditch schemes for managing groundwater levels and field water balance in climate conditions projected to take place in Finland during the 21st century with representative concentration pathways 8.5 and 2.6. A methodological aim was to find ways to condense hourly hydrological results to understand future changes in field hydrology. During the historical reference interval (1970–2005), controlled drainage caused 17–36 cm higher mean groundwater levels and decreased the mean annual drain discharge by 11–23% compared to conventional subsurface drainage. Controlled drainage was projected to increase groundwater levels by additional 1–4 cm in the future compared to its effect on drainage during the reference interval. The effect on annual drain discharge did not change significantly. The open collector ditch lowered groundwater tables and diminished the effect of controlled drainage on groundwater levels in the vicinity of the ditch. Controlled drainage was shown to remain an effective method for countering early summer drought and reducing drain discharge.

Performance Evaluation of Different Combined Drainage Forms on Flooding and Waterlogging Removal

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.

Irrigation efficiency, drain outflow and yield responses to drain depth in the Nile delta clay soil, Egypt

The conventional sub-surface drainage (FD) in the Nile delta clay soil, northern Egypt, results in excessive drainage and low irrigation efficiency (IE). However, a shallower placement of drain might reduce drain outflow and increase IE. The ultimate objective of the present study was to determine the optimum drain depth that minimizes drain outflow and maximizes IE and irrigation water use efficiency (IWUE), while maintaining crop yield and soil salinity. Compared to FD at 120 cm below the soil surface (BSS), the effect of four controlled drain depths (CD) at 40, 60, 80 and 100 cm BSS on drain outflow, IE, salinity buildup, yield and IWUE were investigated for two seasons (2017–18 and 2018–19; wheat-sunflower cropping system). Measurements were conducted for sunflower (as a summer crop). Irrigation was applied based on the soil water content of FD-treatment, thus irrigation depth varied for each treatment. The results showed that decreasing drain depth significantly reduced drain outflow and water input, while IE, seed yield and IWUE were increased. The maximum seed yield and IWUE were obtained at the shallowest drains. Compared with FD at 120 cm, drain depth at 40 cm decreased drain outflow (by 77.20%) and water input (by 29.3%), while increased seed yield and IWUE by 27% and 86%, respectively. Based on water balance, water-uptake from shallow groundwater was maximum for CD-40 cm treatment (31.05% of water-uptake) and was significantly higher than the other treatments. However, by the end of the second season, treatment with drain depth at 40 cm BSS recorded the highest soil salinity (3.6 dS m−1) due to the upward capillary rise of shallow groundwater. Increased soil salinity had no effect on seed yield because it was below the salinity threshold of sunflower. In terms of IE and IWUE, decreasing drain depth to 40 cm BSS is recommended, but with potential salinity buildup. Therefore, drain at 60 cm BSS (had similar seed yield to drain at 40 cm BSS) might lead to significant water-saving (21.8%), while maintaining seed yield and soil quality. In conclusion, modifying the drainage system by reducing drain depth and considering crop water-uptake from shallow groundwater might contribute to water saving. After all, careful water and soil management (e.g., periodic leaching), and suitable cropping systems should be considered for salinity management when decreasing drain depth.

Improvement in canola yield and growth indices and water-use efficiency with subsurface drainage in a humid climate

Improving the productivity of limited land and water resources is necessary to meet the increasing demand for food and feed. A 2-year (2016–18) field study was conducted in a humid climate in the north of Iran to examine the effect of different drainage systems on green water-use efficiency (GWUE), economic water productivity (EWP) and yield and growth indices of winter canola. The treatments consisted of surface drainage (Control) and three conventional subsurface drainage systems. Leaf area index (LAI) and total dry weight were measured randomly during different growth stages. The traits were then used to determine crop growth rate and relative growth rate. Subsurface drainage significantly improved yield and growth indices as well as GWUE and EWP compared with Control, with grater effectiveness under wet season. Yield, GWUE and EWP increase in subsurface drainage systems compared to surface drainage ranged from 460–890 and 825–1090 kg ha−1, 0.13–0.25 and 0.22–0.29 kg m−3 and 0.04–0.08 and 0.07–0.09 US $ m−3 in 2016–2017 and 2017–2018 growing seasons, respectively. Mean LAI in the subsurface drained area was 23–24% and 5–10% more than that in Control in the first and second growing seasons, respectively. The results indicated that an appropriate subsurface drainage system as well as a management strategy is necessary to prevent potential adverse effects of waterlogging in wet seasons and to increase land and water productivity in the study area.

Study on Characteristics of Nitrogen and Phosphorus Loss under an Improved Subsurface Drainage

Agricultural drainage plays an effective role in preventing waterlogging and salinity disasters and also is the main transport pathway for agricultural non-point source pollutants into rivers and lakes. Hence, the water quality of agricultural drainage should be a point of focus. In this paper, nitrogen and phosphorus loss under improved subsurface drainage with different filter materials (gravel, layered sand-gravel, mixed sand-gravel, straw) were studied by a three-year field experiment (2016–2018) compared with the conventional subsurface drainage. The pH values, total nitrogen, ammonia nitrogen, nitrate nitrogen, total phosphorus and soluble reactive phosphate were considered. The results showed that the nitrogen and phosphorus concentrations of drain outflow under improved subsurface drainage with gravel filter were larger than that with layered sand-gravel filter and mixed sand-gravel filter. The improved subsurface drainages with layered sand-gravel filter and mixed sand-gravel filter had an effect on reducing the ammonia nitrogen, total phosphorus and soluble reactive phosphate concentrations of the outflow. Meanwhile, the characteristics of nitrogen and phosphorus loss under the improved subsurface drainage with straw filter were different from that with layered sand-gravel filter and mixed sand-gravel filter. For the improved subsurface drainage with layered sand-gravel filter outflow, the ammonia nitrogen, total phosphorus, and soluble reactive phosphate concentrations were about 13%–78%, 38%–63%, 40%–68% less, and total nitrogen, nitrate nitrogen concentrations were 24%–80%,18%–96% more than that under conventional subsurface drainage. Meanwhile, for the improved subsurface drainage with straw filter outflow, compared with conventional subsurface drainage outflow, the percentage changes of the total nitrogen, nitrate nitrogen, ammonia nitrogen, total phosphorus and the soluble reactive phosphate concentrations were about −76%–62%, −77%–78%, −152%–−274%, −103%–−400% and −221%–−291%, respectively. Additionally, in the outflow of all subsurface drainage patterns, there were much higher total nitrogen and nitrate nitrogen concentrations which should be focused on and the agricultural water management should be adopted.

Evaluating Drainmod‐s to Predict Drainage Water Salinity and Groundwater Table Depth During Winter Cropping in Heavy‐Textured Paddy Soils

AbstractSimulation models can quickly and cost‐effectively describe various aspects of management practices in newly reclaimed agricultural soils. In this research, the capability of the DRAINMOD‐S model was evaluated to predict the salinity of the subsurface drainage effluents in a newly subsurface drained paddy field during winter cropping. Measurements of groundwater table depths and drainage water salinity were taken in three conventional subsurface drainage systems at the Sari Agricultural Sciences and Natural Resources University, northern Iran, during three canola growing seasons (2011–2012, 2015–2016 and 2016–2017). The data were used to calibrate and validate the model. The model provided better predictions of groundwater table depths in shallower drainage systems. Measured and simulated drainage water salinities varied, respectively, from 620 to 1580 and 790–1430 mg l−1 in the calibration process and from 441 to 1640 and 656–1820 mg l−1 in the validation process. The differences between measured and simulated salt loads were in the range of 59–174 and 43–586 kg ha−1 in calibration and validation, respectively. The results indicated that DRAINMOD‐S can be used as a management tool to diminish environmental issues in heavy paddy soils from the viewpoint of salt load. © 2019 John Wiley & Sons, Ltd.

Field and numerical experiment of an improved subsurface drainage system in Huaibei plain

New requirements are put forward for agricultural drainage system due to frequent floods and cultivated land shortage in Huaibei plain, China. The improved subsurface drainage is a more efficient drainage system by laying high permeability materials as filter above the drains based on conventional subsurface drainage whose function is limited by soil hydraulic conductivity. Field experiments was used to evaluate the performance of the improved subsurface drainage preliminarily and numerical experiments was used to explore the capacity of the improved subsurface drainage deeply. Based on calibration and validation by field experiment data, HYDRUS model was used to evaluate the impacts of design parameters of filter hydraulic conductivity, filter width and height, drain spacing and depth on improved subsurface drainage discharge with constant ponding depth. Then, water table depths at different distances from the pipe drain for improved and conventional subsurface drainage were simulated under initial conditions of saturated soil and no surface ponding. Besides, the daily water balance under improved subsurface drainage had been also studied. The result of field experiment showed that the discharge of improved subsurface drainage was about 1.9 times of the conventional subsurface drainage discharge under conditions of same surface ponding depths. The results of numerical experiments indicated that the improved subsurface drainage had a real-time drainage function for the reason that cumulative outflow increased by about 87% than conventional subsurface drainage within 12h after beginning draining. The improved subsurface drainage lowered water table to an appropriate depth faster than conventional ones, which could provide a more favourable soil moisture condition for crop growth. Furthermore, through daily water balance analysis of improved and conventional subsurface drainage with different rainfalls and initial water table depths, the results showed that subsurface drainage could reduce surface runoff effectively, especially for improved subsurface drainage. Good drainability of the improved subsurface drainage was beneficial to decrease the amount of soil water storage after rainfall and helpful to shorten subsequent draining time of water table drawdown. The research results could provide scientific basis for improved subsurface drainage design and lay a good foundation for its application. Meanwhile, it would be beneficial to enrich agricultural drainage technologies and promote development of agricultural drainage in China.

Experiment and analysis on flow rate of improved subsurface drainage with ponded water

An improved subsurface drainage with characteristics of less land occupied and reasonable flow rate drained was presented to overcome the disadvantage of small flow rate of conventional subsurface pipe drainage and adapt to the new challenge of agricultural drainage. Based on soil column experiment, the performance of improved subsurface drainage was discussed in saturated and unsaturated soil. During the experiment, five factors of filter width, soil medium, surface ponding depth, outflow condition and groundwater depth were considered. Then, drainage equation for improved subsurface drainage flow rate under conditions of surface ponding and homogeneous saturated soil was first proposed. The results indicated that improved subsurface drainage performed better in both saturated and unsaturated soil with surface ponding. Flow rates of improved subsurface drainage equaled to 2–3 times of that in conventional subsurface pipe drainage when filter width varied from 2cm to 6cm in completely saturated fine-sand medium. In addition, the greater the hydraulic conductivity gaps between filter and soil in a specific range, the more effective the improved subsurface drainage is. Besides, in case of large groundwater depth, improved subsurface drainage was still effective. When groundwater depth was 2 times of drain depth, improved subsurface drainage flow rate was comparable to 2 times of that in conventional subsurface pipe drainage in saturated fine-sand medium. The calculated flow rates matched well with the observed ones. The research results can provide technical support to the application of improved subsurface drainage. Meanwhile, it will be beneficial to enrich agricultural drainage technologies in China, which is of practical significance to ensure food safety and promote sustainable development of irrigated areas.

Influence of Controlled Drainage on the Groundwater Nitrogen and Phosphorus Concentration at Jointing-Booting Stage of Wheat

The effect of controlled drainage on nitrogen (N) and phosphorus (P) emission at jointing-booting stage of winter wheat was studied in 2007-2008. The conventional subsurface drainage was taken as the control (T5). The groundwater depth was naturally drained to 400 mm and 800 mm below the soil surface within 3 days at the jointing-booting stage, after the water level was kept at 100 mm for 1 day (T1, T2) and 3 days (T3, T4) from the soil surface. Results showed that controlled drainage could significantly reduce the concentration of P and N in groundwater. Compared to T5, the four controlled treatments could significantly decrease the concentration of TP,NH4+-N, andNO3--N. The highest concentration reduction for TP andNO3--N was observed under T4 and T1, which reached 64.9% and 73.2%, respectively. As for the concentration ofNH4+-N, the highest reduction was obtained under T2. The change of TP concentration was significantly affected by the interaction of submergence time and drain depth, while the influence of controlled drainage onNH4+-N concentration was not significant. The submergence time, drain depth, and the interaction of submergence time and drain depth had significant effect on the change of concentration ofNO3--N.

Ammonia and nitrous oxide gas loss with subsurface drainage and polymer-coated urea fertilizer in a poorly drained soil

Gaseous nitrogen (N) loss from denitrification and ammonia (NH₃) volatilization from poorly drained soils in corn (<i>Zea mays</i> L.) production can be significant, diminish production, and lead farmers to apply a high rate of N. Nitrous oxide (N₂O), a greenhouse gas that is emitted during denitrification, has a high global warming potential that contributes to climate change. Reducing gaseous N loss from poorly drained soils through drainage and N management in corn production is essential to minimizing the environmental impact and maintaining high yields. The objective of the study was to determine how subsurface tile drainage and applications of polymer-coated urea (PCU) affect soil N₂O emissions and N fertilizer-induced NH₃ volatilization loss from a claypan soil. Drainage water management treatments consisted of conventional subsurface tile drainage, managed subsurface tile drainage, and no-drainage in combination with N fertilizer source (noncoated urea [NCU] and PCU). Subsurface drainage treatments did not significantly (<i>p</i> ≤ 0.05) affect cumulative soil N₂O emissions and NH₃ volatilization loss compared to no-drainage. Averaged over 2010 to 2013, cumulative soil N₂O emissions from PCU was 2% of applied N, and NCU was 4% of applied N. Yield-scaled soil N₂O emissions were reduced 53% with PCU compared to NCU. The percentage fertilizer loss from NH₃ volatilization was significantly (<i>p</i> ≤ 0.05) reduced from 2.8% with NCU to 0.8% with PCU. These results suggest that use of PCU may assist in reducing cumulative losses of N₂O and NH₃ from poorly drained claypan soils, but drainage systems operating under this study9s environmental conditions did not affect gaseous N losses.

Groundwater management of acid sulfate soils using controlled drainage, by-pass flow prevention, and subsurface irrigation on a boreal farmland

Sulfide-bearing anoxic sediments are found in coastal regions around the world including Australia and the Baltic. Upon lowering of the groundwater by drainage, they are oxidized and form acid sulfate soils (pH < 4) that mobilize plenty of potentially toxic metals into watercourses with serious environmental consequences. Being highly valued for their excellent crop yields, there is an urgent need to find management solutions that minimize the oxidation. In this study, possibilities to manage the groundwater with controlled subsurface drainage (CD) and subsurface irrigation (CDI), which included a vertical plastic sheet to prevent by-pass flow into the main drain, was examined on a Boreal farmland in Western Finland. During a 3-year study, the groundwater in the reference field (Ref) with conventional subsurface drainage pipes at 1.1–1.4 m depth typically dropped down to almost 2 m in the end of summers (September) due to evapotranspiration exceeding precipitation. CD delayed the groundwater drop, shortening the time of oxidation. In CDI system, the groundwater could be kept at c. 1 m or shallower throughout the summers, thereby preventing oxidation of critical sulfide horizons in the lower subsoil. Differences in total discharge and soil geochemistry features were small during the course of the study period. Salt accumulation seemed to be a small risk for crop growth but the capillary rise of acidity to the surface horizon may be increased in CDI, possibly increasing the need for surface liming. A “floating groundwater antenna,” indicating groundwater fluctuations, proved to be an easy and reliable tool to farmers for proper management of controlled drainage.

Effect of subsurface drainage on water balance and water table in poorly drained paddy fields

The hydrological effects of different drainage systems were investigated as a pilot study in 4.5ha of paddy fields of Sari Agricultural Sciences and Natural Resources University, located at Mazandaran province, Northern Iran (36.3°N, 53.04°E), during two successive growing seasons of rice and canola from July 2011 to May 2012. Experimental treatments were: three conventional subsurface drainage systems including drainage system with drain depth of 0.9m and drain spacing of 30m (D0.9L30), drain depth of 0.65m and drain spacing of 30m (D0.65L30), and drain depth of 0.65m and drain spacing of 15m (D0.65L15); a bi-level subsurface drainage system with drain spacing of 15m and drain depths of 0.65 and 0.9m as alternate depths (Bilevel), and surface drainage system (Control). Water balance components were determined in both rice and canola crop seasons. Measurements of water table depth and subsurface drainage discharge were made daily during drainage periods. In the rice season, the total water supply was 754.6mm, of which 61.7% was lost by evapotranspiration and 16.2–19.1% was lost by deep percolation (DP). In the canola season, the treatments of D0.9L30, Bilevel, D0.65L30 and D0.65L15 were discharged, respectively, 44%, 51.5%, 43% and 60.5% of the total rainfall from the soil profile. Shallow drains were more effective in controlling water table compared with deep drains so that, average of measured water table depths in the representative observation wells of D0.9L30, Bilevel, D0.65L30, and D0.65L15 were 2.1, 15, 24.1, and 32.4cm, respectively. Also, values of SEW30 (sum of excess water) were 3461, 1498, 1038 and 450cm for D0.9L30, Bilevel, D0.65L30 and D0.65L15, respectively. Based on the results, water management through a subsurface drainage system could provide winter cropping condition in the study area.

Subsurface Drainage and Subirrigation Effects on Water Quality in Southeast North Dakota

Rising water tables, increased soil salinity, and poor trafficability have prompted rapid expansion of subsurface drainage in the Red River Valley of the North in eastern North Dakota and northwestern Minnesota. A conventional subsurface drainage (CD) and subirrigation (SI) field study was conducted in southeast North Dakota from 2008 to 2010 to investigate drainage and subirrigation effects on water quality. Water samples were collected biweekly from a sump pump structure (used as the water inlet and outlet) and 16 observation wells within the field. Water quality variables included chloride (Cl-), electrical conductivity (EC), total dissolved solids (TDS), sodium adsorption ratio (SAR), sodium (Na+), orthophosphate (PO4-P), ammonium (NH4-N), nitrite and nitrate (NOx-N), Kjeldahl nitrogen (TKN), and total nitrogen (TN). A three-factor partially nested design and a general linear model with random effects were employed to compare the effects of water management treatment, distance to drain, and well locations (soil heterogeneity) on water quality. The most significant water quality difference was found at the outlet structure, where a significant difference (p < 0.001) between the CD and SI water was found for all ten variables. The water quality of the drainage water was better than the subirrigation water from the aquifer, except for the NOx-N, EC, and TDS concentrations. Well water Cl- concentrations inside the field were significantly greater in SI compared with CD water; EC, TDS, SAR, and Na+ were not. In contrast, EC, TDS, SAR, and Na+ were significantly higher at two well locations, indicating that soil heterogeneity affected the water quality. Due to SI practice, a significant difference for Cl-, SAR, and Na+ was found between the locations closest to and farthest from the drains during the SI practice, which implies that the SI process may cause soil properties to change in the future. Overall, well locations significantly affected PO4-P, NOx-N, and TN, indicating that the soil physical and chemical properties affected the water quality, and these effects could overcome the difference due to different water treatments.

Examination of nitrate concentration, loading and isotope dynamics in subsurface drainage under standard agricultural cropping in Atlantic Canada

Intensive agricultural farming practices have the potential to cause high levels of nitrate-nitrogen (NO(3)(-)-N) to be released from tile drainage systems. A better understanding of the temporal dynamics of NO(3)(-)-N loading, δ(15)N and δ(18)O from standard drainage systems is needed, in order to improve our understanding of NO(3)(-)-N transport and transformation processes; particularly, with regards to the imperfectly drained agricultural soils found within Atlantic Canada. Three conventional subsurface drainage plots (48×48m) placed at a 0.80m soil depth were monitored over a seven month period on sandy loam soil in Onslow, Nova Scotia. Each plot received similar applications of both organic and inorganic fertilizer. Water samples were obtained and analyzed for NO(3)(-)-N concentrations and isotopic signatures of δ(15)N and δ(18)O for NO(3)(-)-N. Maximum NO(3)(-)-N loads were observed in the winter and fall, when both discharge and concentration of the NO(3)(-)-N were highest. Mean isotope values in NO(3)(-) ranged from 3.1 to 8.5‰ for δ(15)N and-3.2 to 17.7‰ for δ(18)O. Results suggest that NO(3)(-)-N from the drainage water was derived from organic sources (i.e. manure and soil organic matter) and that loss via denitrification does not impart an identifiable signature upon the NO(3)(-)-N pool. The dual isotope approach examined here provides insight into N source and transformation processes which may be contributing to the NO(3)(-)-N found within the drainage water.

Experimental study on the distribution of soil nitrate and ammonium nitrogen under controlled drainage

A field experimental project was set up to assess the effects of controlled drainage on the distribution and concentration of nitrogen in the soil at the Irrigation and Drainage Experimental Station under Four-Lake Engineering Administration of Jingzhou City, Hubei Province. Two plots drain runoff by controlled drainage system, with an area of 0.1 hm2 (20 m×50 m) each. The third one with an area of 0.04 hm2 (8 m×50 m) has a conventional subsurface drainage system. Under this experimental condition, the study draws the following conclusions: ① The controlled drainage system has a remarkable effect on the diminishing ratios of nitrate nitrogen between neighboring layers. It is presented that the diminishing ratio increases with the raising height of drain outlet. Controlled drainage system also reduces the transference of nitrate nitrogen in topsoil. ② Different from nitrate nitrogen, the concentration of ammonium nitrogen is stable along the longitudinal section of soil, which is little affected by the controlled drainage system. It indicates that the concentration of ammonium nitrogen decreases according to the lowering of controlling height of the drain outlet.

Salt Uptake by Acacia biflora Saplings from Saline Root Zone

Waterlogging and subsequent soil salinization are the two major causes of degradation of irrigated agricultural lands. Subsurface Drainage Technology (SSDT) is an effective control measure for both. However, this technology is expensive and has an associated problem of safe disposal of the drainage effluents. These features have limited its large-scale adoption in India. Biodrainage is considered by some as an alternative, in which water and salt tolerant plant species are grown to remove the salt solutions from saline and waterlogged lands in an eco-friendly and economical manner. A pot experiment was conducted with saplings of Acacia biflora to determine the plant's salt uptake capacity from the root zone that was made saline by irrigation with water of different salt concentrations for a period of 6 months. The consequent plant sap salinity was measured and salt balance analysis was carried out to ascertain salt migration from the soil to the plant. The study revealed that the plants irrigated with the water of highest salinity removed 28.7 g of salt in comparison to the plant under control, which removed 8.4 g of salts. Even the highest salt removal by Acacia biflora saplings was negligible as compared to that by conventional subsurface drainage system. To portray bio-drainage as a land reclamation option, confirmation of salt uptake from saline lands having established plantation needs to be carried out.

Effects of controlled drainage on N and P losses and N dynamics in a loamy sand with spring crops

The effects of controlled drainage on N and P losses from soil were examined in a 4-year field drainage experiment on a loamy sand in Southern Sweden. Of the three plots (0.2 ha each), one was drained by conventional subsurface drainage (CD), and two by controlled drainage (CWT1 and CWT2). The groundwater level in the CWT plots was naturally drained to at least 70 cm below the soil surface during the vegetation period between early spring and harvest but allowed to rise to 20 cm below the soil surface during the rest of the year. Measurements of precipitation, drain outflow, weir depths and air and soil temperatures were carried out hourly. Groundwater levels were measured and samples of drain outflow for analyses were collected twice a month. Mineral N contents in soil were measured three times a year and grain yields and N uptake in crops after harvest. Controlled drainage significantly lowered N and P loads in drain outflow and altered N dynamics in soil. The relative decrease in N and P loading in drain outflow from CWT plots, compared with CD, was of the same magnitude as the reduction in drain outflow rate (60–95%). The high-risk periods for N losses coincided with periods of high outflow rates and high mineral N content in soil, for all years and for all treatments. Positive correlations in N concentrations in drain outflow were found between drainage systems. In contrast, high-risk periods of P losses from CD did not exclusively occur in months with highest outflow rates. In 3 out of 4 years, peak P loads occurred in late winter and P concentrations were positively correlated to soil temperature. In CWT, peak P loads coincided with highest outflow rates and no correlations were found between P concentrations and soil temperature. CWT plots, compared to CD, improved N efficiency for applied fertiliser due to lower N loads in drain outflow and higher N uptake by crop. The yields in CWT were 2–18% larger and the crop uptake of N increased by 3–14 kg ha −1. The net changes of N (changes in mineral N content in soil, NO 3-N loading in drain outflow, N fertiliser application, N uptake in crops) showed a surplus during autumn in all plots, with the highest surplus in CWT due to higher mineralisation rates and lower N loads. During the winter season, a surplus in measured net changes of N was found in CD in all years. In contrast, the net changes of N in CWT showed a deficit, probably due to a lower mineralisation rate and non-measured N sinks such as denitrification, immobilisation and deep seepage loads.

The effects of controlled drainage on subsurface outflow from level agricultural fields

AbstractDaily outflow frequencies and recession curves were used to identify differences in storage–outflow relationships between two different drainage systems, conventional and controlled drainage. A three‐year (1996–1999) field drainage experiment was carried out on a loamy sand soil in southern Sweden. Plots with an area of 0·2 hectares were drained by conventional subsurface drainage (CD) or by controlled drainage (CWT1 and CWT2). The controlled drainage system allowed the groundwater level in the soil to be varied during the year. It was kept at least 70 cm below the soil surface during the growing season but allowed to rise to a maximum of 20 cm below the soil surface during the rest of the year. Measurements were performed to record precipitation, drain outflow and groundwater levels. Daily values of outflow were divided into 10 categories, based on the size of outflow. Recession curves of hourly measurement of outflow were selected. They behaved like single reservoirs and a linear storage–outflow model was applied. Least squares estimates of the parameters initial outflow, initial storage volume and retention constant were calculated.Controlled drainage had a significant effect on total drain outflow and outflow pattern during the three years of measurement. The total drain outflow was 70% to 90% smaller in CWT than in CD. The analysis revealed that the initial outflows were higher, the retention constant and the temporary storage lower in CWT. The hydrological impacts of the reduction in temporary storage were higher peak flow, shorter lag time and shorter recession time and these effects increased with an increased groundwater level. Copyright © 2003 John Wiley &amp; Sons, Ltd.