Drain Depth Research Articles

Combining satellite and field data reveals Congo's forest types structure, functioning and composition

AbstractTropical moist forests are not the homogeneous green carpet often illustrated in maps or considered by global models. They harbour a complex mixture of forest types organized at different spatial scales that can now be more accurately mapped thanks to remote sensing products and artificial intelligence. In this study, we built a large‐scale vegetation map of the North of Congo and assessed the environmental drivers of the main forest types, their forest structure, their floristic and functional compositions and their faunistic composition. To build the map, we used Sentinel‐2 satellite images and recent deep learning architectures. We tested the effect of topographically determined water availability on vegetation type distribution by linking the map with a water drainage depth proxy (HAND, height above the nearest drainage index). We also described vegetation type structure and composition (floristic, functional and associated fauna) by linking the map with data from large inventories and derived from satellite images. We found that water drainage depth is a major driver of forest type distribution and that the different forest types are characterized by different structure, composition and functions, bringing new insights about their origins and successional dynamics. We discuss not only the crucial role of soil–water depth, but also the importance of consistently reproducing such maps through time to develop an accurate monitoring of tropical forest types and functions, and we provide insights on peculiar forest types (Marantaceae forests and monodominant Gilbertiodendron forests) on which future studies should focus more. Under the current context of global change, expected to trigger major forest structural and compositional changes in the tropics, an appropriate monitoring strategy of the spatio‐temporal dynamics of forest types and their associated floristic and faunistic composition would considerably help anticipate detrimental shifts.

Developing a new unsteady‐state equation for the design of subsurface drainage systems suitable for the Delta region, Egypt

AbstractThe main goal of this research is to obtain a new unsteady‐state equation for the design of subsurface drainage systems that provides a more combatable solution under conditions in the Delta region, Egypt, while simultaneously avoiding all obstacles, difficulties and points of argument in other unsteady‐state equations. The point of argument in unsteady‐state assumptions is the initial water table shape. Then, the study reached a constant called Csh, which represents the initial water table shape and was proven to depend on drain depth (d.d.). Moreover, the new equation avoids using the drainable porosity of soil (f), which is the greatest restriction in using unsteady‐state equations. The new equation replaces f with another constant called Cs, which can be easily determined by using tables or graphs depending on drain depth (d.d.) and hydraulic conductivity (k). Another new important variable is also used in the new equation: the hydraulic head after 6 days of irrigation (h). Using this parameter with the initial water table (h0) and the water table after t days (ht) ensures more accurate results. Then, the new equation, which can be called the Safaa equation, can result in an optimum solution for the Delta region, Egypt, because it provides spacing between laterals (L), which results in the desired performance with the least cost.

Salt marshes for nature-based flood defense: Sediment type, drainage, and vegetation drive the development of strong sediment beds

In face of sea-level rise and increasing risks for storm impacts on shorelines, there is a growing demand for developing nature-based flood defenses, for example by restoring or creating salt marshes in front of engineered structures such as dikes. However, salt marshes can only optimally provide flood defense if their sediment beds are erosion resistant, even under very high flow velocities. It remains unknown how fast sediment strength develops in marshes restored or created for nature-based flood defense. Therefore, this study investigated how 1) sediment type, 2) tidal drainage depth and duration, and 3) pioneer vegetation species drive the development rate of sediment strength. A controlled experiment was set up with pots filled with two sediment types, which were either left bare or planted with Spartina anglica or Scirpus maritimus, two dominant salt marsh pioneers in NW Europe. All treatments were subjected to four different tidal regimes with different tidal drainage depth and duration. The results showed that sandy mud (with a 37% silt and clay fraction) led to much stronger sediments than fine mud (with a 77% silt and clay fraction). Sediment strength was higher in the treatments with deeper tidal drainage depth and longer drainage duration. The presence of vegetation increased sediment strength and this effect was stronger with Scirpus maritimus than with Spartina anglica. Plant roots increased sediment strength directly, and the presence of vegetation also seemed to increase sediment strength through enhanced evaporation and transpiration. From these results it can be concluded that to restore or create erosion resistant salt marshes for flood defense, it is essential to ensure that marshes can form at relatively high elevations from well-draining sand-mud mixtures, thereby also ensuring vegetation growth.

Insights on agricultural nitrate leaching from soil block mesocosms.

Quantifying nitrate leaching in agricultural fields is often complicated by inability to capture all water draining through a specific area. We designed and tested undisturbed soil monoliths (termed "soil block mesocosms") to achieve complete collection of drainage. Each mesocosm measures 1.5m ×1.5m ×1.2 m and is enclosed by steel on the sides and bottom with a single outlet to collect drainage. We compared measurements from replicate mesocosms planted to corn (Zea mays L.) with a nearby field experiment with tile-drained plots ("drainage plots"), and with drainage from nearby watersheds from 2020 through 2022 under drought conditions. Annual mesocosm drainage volumes were 6.5-24.6cm greater than from the drainage plots, likely because the mesocosms were isolated from the subsoil and could not store groundwater below the drain depth, whereas the drainage plots accumulated infiltration as groundwater. Thus, we obtained consistent nitrate leaching measurements from the mesocosms even when some drainage plots yielded no water. Despite drainage volume differences, mean flow-weighted nitrate concentrations were similar between mesocosms and drainage plots in 2 of 3 years. Mesocosm annual drainage volume was 8.7cm lower to 16.7cm higher than watershed drainage, likely due to lagged influences of groundwater. Corn yields were lower in mesocosms than drainage plots in 2020, but with irrigation, yields were similar in subsequent years. Mean 2020 surface soil moisture and temperature were similar between the mesocosms and nearby fields. Based on these comparisons, the mesocosms provide a robust method to measure nitrate leaching with lower variability than field plots.

Dynamics of humus in field crop rotations on drained lands

The purpose of the research is to study the influence of different types of field crop rotation, fertilizers, drainage and hydrothermal conditions on the dynamics of humus in reclaimed soil. The studies were carried out on the experimental fields of the All-Russian Research Institute of Reclaimed Lands (reclamation sites “Kuzminskoye Boloto 2”, “Semenovskoye” and “Gubino” in the Tver region). Waterlogged soils were drained using closed drainage (inter-drain distance is 18–20 m, drain depth is 0.9–1.2 m). The soils of the experimental plots are soddy-podzolic, light loamy, gleyic, formed on a moraine or thin binomial. Observations of the dynamics of humus were carried out in the grain-grass-row, grain-grass, grain and grain-row types of crop rotation. The influence of crop rotation on the content of humus in the soil was determined, first of all, by the composition, the structure of the crops grown and agricultural technology of their cultivation. Due to plant residues, 56.6–76.5 % of the volume of mineralized humus were restored in grain-grass-row crop rotation, 51.8 % in grain, 26.4 % in grain-row crop rotation. The most significant qualitative changes in the composition of humus were observed in grain-grass-row crop rotation: with a positive humus balance, the ratio of humic and fulvic acids increased from 0.63 to 0.74. The use of organic and mineral fertilizers significantly changes the balance of humus in the arable layer of the soil. With an organic-mineral fertilizer system, the annual loss of humus (in kg/ha) on the drained plot was 6.8–11.4 times less, on the non-drained plot – 2.1–2.6 times less than in the variant without fertilizers. Drainage of waterlogged soils increases the role of fertilizers in the accumulation of humus, reduces its losses and improves the quality parameters of humus – the ratio of humic and fulvic acids in the composition of humus under the influence of drainage increased from 0.61 to 0.88. The impact on the dynamics of humus of hydrothermal conditions has been established. In years with a dry first half of the growing season, an increase in humus content is observed; in excessively wet years, on the contrary, a decrease is observed. The correlation coefficients of humus content with hydrothermal conditions in May-June were – 0.84 (in 1985–1993) and 0.95 (in 2014–2022).

Research on Automatic Counting of Drill Pipes for Underground Gas Drainage in Coal Mines Based on YOLOv7-GFCA Model

Gas explosions threaten the safety of underground coal mining. Mining companies use drilling rigs to extract the gas to reduce its concentration. Drainage depth is a key indicator of gas drainage; accidents will be caused by going too deep. Since each drill pipe has the same length, the actual extraction depth is equivalent to the number of drill pipes multiplied by the length of a single drill pipe. Unnecessary labor is consumed and low precision is achieved by manual counting. Therefore, the drill pipe counting method of YOLOv7-GFCA target detection is proposed, and the counting is realized by detecting the movement trajectory of the drilling machine in the video. First, Lightweight GhostNetV2 is used as the feature extraction network of the model to improve the detection speed. Second, the (Fasternet-Coordinate-Attention) FCA network is fused into a feature fusion network, which improves the expression ability of the rig in complex backgrounds such as coal dust and strong light. Finally, Normalized Gaussian Wasserstein Distance (NWD) loss function is used to improve rig positioning accuracy. The experimental results show that the improved algorithm reaches 99.5%, the model parameters are reduced by 2.325 × 106, the weight file size is reduced by 17.8 M, and the detection speed reaches 80 frames per second. The movement trajectory of the drilling rig target can be accurately obtained by YOLOv7-GFCA, and the number of drill pipes can be obtained through coordinate signal filtering. The accuracy of drill pipe counting reaches 99.8%, thus verifying the feasibility and practicability of the method.

Comparative Sensitivity Analysis of Hydrology and Relative Corn Yield under Different Subsurface Drainage Design Using DRAINMOD

DRAINMOD is a process-based hydrologic model used to analyze the effectiveness of various drainage systems and management strategies. In this study, a sensitivity analysis of DRAINMOD hydrologic parameters for two different field settings located at Champaign, Illinois, was performed to determine the most sensitive parameters that affect the subsurface flow and relative productivity of corn. Latin-Hypercube One-Factor-at-a-Time (LH-OAT) was used to determine the sensitivity index of 17 parameters for six objective functions for daily flow, water balance, and relative yield for the productivity of corn. The results indicated that flow and yield were highly sensitive to drainage design parameters such as drainage depth and spacing. Winter flow and the water balance were sensitive to soil thermal conductivity parameters; however, they had no impact on the relative corn yield. The significant difference in sensitivity of the two fields was observed in the hydraulic conductivity of soil layers due to varying thicknesses for different soil types. This study highlights the need for more careful calibration of these sensitive parameters to reduce equifinality and model output uncertainty and appropriate drainage design for optimizing crop productivity and drainage outflow.

Effect of Autumn Irrigation on Salt Leaching under Subsurface Drainage in an Arid Irrigation District

Non-growing season irrigation and farmland subsurface drainage play a crucial role in salt leaching and salinization control in arid irrigation areas. This study aimed to investigate the reduction of autumn irrigation quotas and drainage discharge while maintaining soil moisture retention and reducing soil salinization. Field experiments were conducted with different autumn irrigation quotas (160 mm for SD1, 180 mm for SD2, and 200 mm for SD3) combined with subsurface drainage (1.5 m drain depth and 45 m spacing). A control treatment (referred to as CK) without subsurface drainage received 200 mm of irrigation. The results showed that, after 31 days of autumn irrigation, the groundwater depth in all three subsurface drainage plots stabilized to 1.5 m, with the CK being 0.2–0.3 m shallower compared to the SD plots. The mean soil water content in the 0–150 cm soil layer of the SD1, SD2, SD3, and CK after autumn irrigation was 0.36, 0.39, 0.41, and 0.42 cm3cm−3, respectively. The combination of autumn irrigation and subsurface drainage significantly reduced the soil salt content. The mean desalination rates in the root zone (0–60 cm) soil layer were 57.5%, 53.7%, 51.9%, and 45.1% for the SD3, SD2, CK, and SD1, respectively. The mean desalination rate of 60–150 cm was not significantly different between the SD2 and SD3 (p > 0.05), and both were significantly higher than that of the SD1 and CK (p < 0.05). The drainage discharge was 31, 36, and 40 mm in the SD1, SD2 and SD3, respectively. The amount of salt discharge through the drain pipe increased with increasing irrigation quota, which was 1.22 t/ha, 1.41 t/ha, and 1.50 t/ha for the SD1, SD2, and SD3, respectively. Subsurface drainage is an effective way to prevent salt accumulation in the soil, and an autumn irrigation quota of 180 mm is recommended for leaching of salinity in the Hetao Irrigation District. These findings provide valuable insights into optimizing irrigation practices and managing soil salinization in arid regions.

Uncertainty in the Management of Tropical Peatlands for Oil Palm Plantations due to Drainage Practices

The conversion of tropical peatlands to oil palm plantations has affected the long-term storage stability of water and carbon. The conversion requires a drainage system that results in land subsidence and, in turn, reduces the carrying capacity of water storage and carbon stocks. This study aims to analyze subsidence from long-term observations (2004-2020) to obtain an appropriate water management measure for three scenarios of drainage depths at the oil palm plantations in Jambi Province. It is found that the reduction is quite variable depending on the level of drainage depths. The subsidence was 55 cm, 49 cm, and 34.7 cm for deep, moderate, and shallow drainage conditions. The groundwater level was deeper than 100 cm, which is far below the threshold of 40 cm, as stated in the government regulations. However, the regulations are still debated since subsidence must occur in drained peatlands regardless of the water level. The observed large subsidence implies that better water management in a new site is crucial and necessary to reduce the impact of peatlands degradation relative to current conditions and that high rates of land subsidence should be accepted as an inevitable change from the conversion of tropical peatlands to oil palm plantations.

Formation of groundwater levels of drained lands in the natural and climatic conditions of the Novgorod region

Studies on the formation of groundwater levels have been carried out on open and closed drainage systems in the natural and climatic conditions of the Novgorod region for more than 30 years at 2 pilot production sites. On the first site there are 4 structures of closed drainage: shallow with a depth of 70 cm; medium-deep drainage (drainage depth 110 cm) with various options for filling the drainage trench-wood chips and sand-gravel mixture; two-tier drainage (drainage depth 110 and 60 cm). On the second site there are four open drainage structures: channels; hollows – without hydro-reclamation structures; with drainage along the bottom-tubular and strip-free. The average long-term data on groundwater regimes on experimental structures were obtained and conclusions were drawn that the average seasonal groundwater level formed by closed drainage systems is 18 cm lower compared to open drainage systems; the most favorable groundwater regime is formed by drainage systems of two-tier drainage. The dependences of groundwater levels formed during the most intense periods of operation of drainage systems (May – 1st decade of June) on the amount of precipitation for previous periods are analyzed. It was revealed that the closeness of the relationship between groundwater levels and the amount of precipitation in the open drainage variants is less close (r2 = 0.01-0.30) compared with the closed drainage variants (r2 = 0.02-0.54). The closest relationship on closed drainage systems is observed between the groundwater level of the third decade of May and precipitation for May: during this period, with an increase in precipitation by 1 mm, groundwater rises by 0.3 cm – in the variant with chip filling and by 0.6 cm – in the variants of shallow and two-tier drainage.

A Drain Spacing Tool That Estimates the Optimum Subsurface Drain Spacing for Maximum Profit

Highlights An empirical equation was embedded in a user-friendly tool to estimate the site-specific design drainage rate. The site-specific design drainage rate was based on the local soil, weather, and economics of the area of interest. The tool uses the site-specific design drainage rate to estimate the optimum drain spacing. The optimum drain spacing maximizes the economic return on investment. Abstract. Properly estimating the subsurface drain spacing is critical to optimizing crop production. The Hooghoudt equation can be used in humid climates to approximate the drain spacing. However, the application of this equation has been limited due to site-specific data requirements and because it is a complicated process that is not usually practical for practitioners. Traditionally, drainage contractors have chosen a drain spacing without using the Hooghoudt equation. The objective of this article is to develop a user-friendly decision-support tool that estimates the site-specific optimum drain spacing for maximum economic return on investment. We developed the Drain Spacing Tool for the Midwest USA based on the Hooghoudt equation and site-specific inputs. The tool automatically acquires the site-specific equivalent saturated hydraulic conductivity of the soil profile and depth to the restrictive layer from the gSSURGO database, and the user manually enters the desired drain depth. The site-specific input of design drainage rate (DDR), that is required in the Hooghoudt equation, is estimated from an empirical equation that was developed from a DRAINMOD modeling study. The site-specific inputs for the empirical equation include site-specific 30-year average growing-season rainfall, drain depth, equivalent saturated hydraulic conductivity, and depth to the restrictive layer, all of which are automatically acquired from gSSURGO, except for the rainfall data, which was acquired from the PRISM Climate Group. The site-specific DDR value from the empirical equation was then used in the Hooghoudt equation to estimate the optimum drain spacing that maximizes economic return on investment. In conclusion, the tool estimates the site-specific optimum drain spacing based on the local soil, weather, and economics of the area of interest. Keywords: Decision-support tool, Design drainage rate, DRAINMOD, Farm profitability, Tile drainage.

Optimizing Urban Mobility: Innovative Sloped Road Design for Fuel Efficiency and Safety

In this paper, an urban road design concept is proposed that introduces gentle slopes along straight roads to optimize fuel efficiency between signalized intersections. These calculated inclines leverage gravitational forces, reducing vehicle fuel consumption. At signal crossings, a deliberate reversal of slope mitigates depth accumulation concerns, promoting safe intersection navigation. Smooth transition zones enhance road stability and drain depth adjustments accommodate stormwater management. Collaborative efforts with experts and public awareness initiatives are vital for successful implementation. This innovative concept combines technical precision, safety considerations, and environmental sustainability, offering a holistic approach to urban road design for enhanced efficiency and user experience.

Horizontal well dewatering systems in mining: Experience and prospects

Almost all mineral deposits being currently mined occur in the zones of risk governed by difficult geology, geomechanics, hydrogeology and engineering geology. The main complication factor is often groundwater. The choice of a dewatering system depends on the natural conditions and mining technology at each specific deposit. The article addresses issues of waterproof at an open pit mine of AGD Diamonds; the critical point here is pitwall rock mass dewatering. The performance of a horizontal well dewatering system as the internal pit drainage facility is described. The scope of the analysis embraces the current technology used in construction of horizontal wells of the optimized ‘telescopic’ structure and the size of stricken water influxes. The visual effectivity of pitwall drainage using the horizontal dewatering wells consists in the reduced seepage of groundwater on the pitwall and in the decreased gravity moisture of overburden rocks. The horizontal dewatering wells create conditions for the controllable groundwater removal from the Pandun rock mass at the drainage depth to 150–200 m, which greatly reduces the overall number of flowing water sources on pitwall in the test surface mine of AGD Diamonds. The concept is formulated for the efficient use of the horizontal well dewatering system as the permanent water protection of ultimate pitwall. The horizontal dewatering wells can be used as independent drainage elements and can be included in more complex systems generating an extended horizontal drainage at a certain depth from ground surface.

Experimental and modeling evaluation of siphon-type subsurface drainage performance in flooding and waterlogging removal

Agricultural subsurface drainage is necessary for crop production in humid, poorly drained regions with frequent rainfall. Flooding and waterlogging have become more widespread and frequent in recent years, and effective measures should be adopted to increase the subsurface drainage capacity and alleviate flooding and waterlogging disasters after short-term heavy rainfall. However, subsurface drainage focused on the layout parameters (drain depth, drain spacing, etc.) in previous studies, and these measures were limited and cumbersome in the improvement of the flow rate of subsurface drainage. Thus, we aimed to alleviate the flooding and waterlogging threats to farmland and innovatively proposed a new method to increase the flow rate of subsurface drainage, namely siphon-type subsurface drainage. The paper evaluated the performance of the siphon-type subsurface drainage by the indoor sand tank test and the HYDRUS-2D model. Three factors were considered during the experiments: conventional and improved subsurface drainage; shallow, medium, and deep drain depth; and the outlet elevation, including the outlet elevation of the drain pipe under the non-siphon drainage and the outlet elevation of the siphon pipe under the siphon drainage. The results indicated that the siphon-type subsurface drainage performed better under the conditions of steady-state ponding and ponding subsided. The flow rate of the siphon-type subsurface drainage was 27.1–45.7%, 41.8–89.8%, and 39.3–50.5% higher than that of conventional, thin-improved, and thick-improved subsurface drainage with non-siphon drainage under steady-state ponding, respectively. It also had a significant advantage when the outlet elevation was the same. The siphon-type subsurface drainage could increase the flow rate during ponding subsided and reduce the flow rate attenuation degree before the ponding disappears. The flooding removal effect of the siphon-type subsurface drainage was significantly better than that of non-siphon subsurface drainage. The water head and flow rate were used to calibrate and validate the HYDRUS-2D model. The results indicated that the simulated values of flow rate matched well with the measured ones and the relative errors were less than 10%. The influence range and absolute values of the negative water head increased with the decrease of outlet elevation, and the increase effect of flow rate increased with the decrease of the water head. The siphon-type subsurface drainage has more control distance than the non-siphon. The advantages of siphon-type subsurface drainage are not only prominent in quart sand but also applicable to field soil. The results of this study could provide technical support for the application of flooding and waterlogging removal in areas where waterlogging is prone to occur and could improve the ability of agricultural production to address waterlogging disasters.

Deep Drainage Lowers Methane and Nitrous Oxide Emissions from Rice Fields in a Semi-Arid Environment in Rwanda

Few studies have explored greenhouse gas (GHG) emissions from arable land in sub-Saharan Africa (SSA), and particularly from rice paddy fields, which can be a major source of methane (CH4) and nitrous oxide (N2O) emissions. This study examined the effect of drainage on CH4 and N2O emissions from rice fields in Rwanda under shallow drainage to 0.6 m, with the drain weir open four times per week, and deep drainage to 1.2 m with the weir open four times or two times per week. CH4 and N2O fluxes from the soil surface were measured on nine occasions during rice flowering and ripening, using a closed chamber method. Measured fluxes made only a minor contribution to total GHG emissions from rice fields. However, drainage depth had significant effects on CH4 emissions, with shallow drainage treatment giving significantly higher emissions (~0.8 kg ha−1 or ~26 kg CO2-equivalents ha−1) than deep drainage (0.0 kg) over the 44-day measurement period. No treatment effect was observed for N2O fluxes, which ranged from low uptake to low release, and were generally not significantly different from zero, probably due to low nitrogen (N) availability in soil resulting from low N fertilization rate (in the region). Overall, the results suggest that deep drainage can mitigate CH4 emissions compared with traditional shallow drainage, while not simultaneously increasing N2O emissions.

Effects of different drainage conditions on nitrogen losses of an agricultural sandy loam soil

Prolonged waterlogging in agricultural fields has severe consequences for the crop development and growth, and could potentially lead to higher N losses. In this study, a 3.93 ha agricultural field in Denmark was separated into two parts of well-drained (WD) and poorly-drained (PD) based on the installation depth of the tile drains. The field was continuously monitored for drainage, soil water dynamics, nitrogen leaching through the drains, and grain dry matter and nitrogen yields in a 4-year period (2017–2020). Furthermore, denitrification potential of the top 1 m of the soil at both parts of the field was measured through the denitrifying enzyme activity assay, and a 1D Daisy model was utilized to capture the differences between water and nitrogen balances at WD and PD. Results indicated that on average over the 4 years, annual harvested nitrogen in the crops at PD was 14% lower compared to WD, with a significant reduction of 33% in 2017–2018, that coincided with the longest period of waterlogging at PD. Moreover, greater losses of nitrogen through leaching from drainage and other pathways were measured at the PD (109 kg N ha−1 ya−1) compared to the WD (95 kg N ha−1 ya−1). Based on the simulations, losses through preferential flow pathways to the drains dominated at PD and most of the denitrification is expected to occur within the topsoil. Future studies could significantly benefit from monitoring the redox dynamics in the top 30 cm of the PD soils, and increasing the depth of tiles drains by redrainage could reduce the N losses of poorly drained agricultural soils.

Oil palm (Elaeis guineensis) plantation on tropical peatland in South East Asia: Photosynthetic response to soil drainage level for mitigation of soil carbon emissions

While existing moratoria in Indonesia and Malaysia should preclude continued large-scale expansion of palm oil production into new areas of South-East Asian tropical peatland, existing plantations in the region remain a globally significant source of atmospheric carbon due to drainage driven decomposition of peatland soils. Previous studies have made clear the direct link between drainage depth and peat carbon decomposition and significant reductions in the emission rate of CO2 can be made by raising water tables nearer to the soil surface. However, the impact of such changes on palm fruit yield is not well understood and will be a critical consideration for plantation managers. Here we take advantage of very high frequency, long-term monitoring of canopy-scale carbon exchange at a mature oil palm plantation in Malaysian Borneo to investigate the relationship between drainage level and photosynthetic uptake and consider the confounding effects of light quality and atmospheric vapour pressure deficit. Canopy modelling from our dataset demonstrated that palms were exerting significantly greater stomatal control at deeper water table depths (WTD) and the optimum WTD for photosynthesis was found to be between 0.3 and 0.4 m below the soil surface. Raising WTD to this level, from the industry typical drainage level of 0.6 m, could increase photosynthetic uptake by 3.6 % and reduce soil surface emission of CO2 by 11 %. Our study site further showed that despite being poorly drained compared to other planting blocks at the same plantation, monthly fruit bunch yield was, on average, 14 % greater. While these results are encouraging, and at least suggest that raising WTD closer to the soil surface to reduce emissions is unlikely to produce significant yield penalties, our results are limited to a single study site and more work is urgently needed to confirm these results at other plantations.

Heterogeneity of nitrate reduction indicators across a tile drained agricultural catchment in East Jutland, Denmark

Detailed knowledge of the nitrate (NO3−) attenuation capacity of different landscapes is essential to support current aspirations of locally differentiated fertilizer nitrogen (N) regulation for protection of aquatic ecosystems. In this context, we studied the spatial heterogeneity of NO3−, ammonium (NH4+), and total N concentrations in pore water collected in an artificially drained sub-catchment and complemented this with measurements of apparent electrical conductivity (ECa), potential denitrification rates, and basic soil physico-chemical properties. Piezometer nests were installed in transects to represent a range of ECa and slopes in the sub-catchment and were then categorized according to predetermined classifications to delineate the different redox environments. Water samples were collected (February to August 2017) from piezometers that were installed in nests with screen depths at 25–75 cm, 85–115 cm and 125–165 cm. For transects with an average ECa higher than 20 mS m−1, NO3− concentrations were <5 mg N L−1 at the depth slightly above the drainage depth, whereas transects with an average ECa of <20 mS m−1 had NO3− concentrations ranging from 0.2 to 15 mg N L−1. Transects with ECa higher than 20 mS m−1 had the highest average clay content and estimated water contents and, possibly, higher macropore connectivity across the soil profile, which could enhance NO3− transport and the potential for development of anaerobic microsites facilitating microbial denitrification. Potential denitrification rates correlated with the presence of amorphous and poorly crystalline iron (Fe) oxides, yet the results were inconclusive regarding the possible role of Fe(II) mediated NO3− reduction. By categorizing the piezometer transects according to their average ECa values, patterns of N concentrations were found that reflected differences in nitrate attenuation capacity, thereby supporting the further pursuit of ECa as a simple and operational tool for mapping the variability in nitrate reduction patterns in the unsaturated zone on a sub-catchment scale.

Industry-driven mitigation measures can reduce GHG emissions of palm oil

Tropical peatland stores a large amount of carbon. In the last 20 years, drainage of Asian peat soil has increased to satisfy the demand of land for plantation agricultures. Industrial oil palm plantations occupy large areas of peatland in Indonesia and Malaysia, with associated GHG emissions and biodiversity loss, here referred to as nature occupation impact. This study performs a detailed Life Cycle Assessment (LCA) of 1 kg of palm oil for two case studies: PT SMART's Hanau and Sungai Rungau facilities in Central Kalimantan, Indonesia. The objective is to quantify the reduction in GHG emissions and nature occupation that has been achieved by implementing the following industry-driven measures: reducing the area of cultivated peat soil, reducing the peat drainage depth, and setting aside part of the land-bank for nature conservation. The results show that 1 kg of palm oil causes 2.72 and 2.25 kg CO 2 -eq./kg palm oil from Hanau and Sungai Rungau facilities respectively. These are 20%–34% lower than average RSPO certified palm oil and 49%–58% lower than average non-certified palm oil. Sungai Rungau achieves the reduction mainly due to a completely peat soil-free supply base. Hanau's peat emissions are instead 0.28 kg, compared to the 0.77 and 2.36 kg CO 2 -eq for RSPO certified and non-certified palm oil respectively, due to a very low drainage depth (18–25 cm compared to 57–73 cm in average of RSPO certified and non-certified respectively) and an overall lower share of oil palms on peat land. The impact on nature occupation is 24%–43% lower in Hanau and Sungai Rungau compared to non-certified oil and 4%–29% lower compared to RPSO certified respectively. About 8% of the total land bank of the Hanau supply-base has been set aside for nature conservation, reducing GHG emissions by 2% and nature occupation by 9%. Both Hanau and Sungai Rungau could also significantly reduce GHG emissions in the palm oil milling stage, by implementing biogas capture in palm oil mill effluent (POME) treatment. • Avoiding the cultivation of peat soil reduces the GHG emissions of palm oil production. • When oil palms are on peat soil, reducing the peat drainage depth reduces the GHG emissions. • Nature conservation initiatives reduce GHG emissions and nature occupation of palm oil production. • Capturing the biogas produced in palm oil mill effluents (POME) treatment reduces GHG emissions. • Using the captured biogas in boiler or biogas engine further abates the GHG emissions of palm oil.

Simulation and evaluation of soil water and salt transport under controlled subsurface drainage using HYDRUS-2D model

Controlled drainage is an important measure to improve salinized soil in arid and semi-arid areas. However, free drainage during the growth period leads to excessive water loss, and crops lack water in the later growth period, resulting in crop yield reduction. Therefore, in arid and semi-arid areas, soil salts should be leached during the non-growing period, and drainage should be controlled during the growing period to ensure that crops have adequate water absorption and utilization, improve soil water availability for optimal water supply and salinity control. In this study, through field trials in 2020 and 2021, 3 treatments were set up. The depth of free drainage (FD) is common subsurface pipe drainage and the controlled drainage in the growth period were 40 cm (CWT1) and 70 cm (CWT2), respectively, and the drainage depth in the non-growing period was 100 cm. Using the HYDRUS-2D model to simulate the dynamic changes of soil water and salts in the 0–100 cm range, the calibration and validation of the HYDRUS-2D model were performed using the measured soil water and salt content values of 2020 and 2021. The results showed that the simulated soil water and salt contents agreed well with the measured contents. Controlled Drainage (CD) is a new agricultural drainage management practice that involves periodically increasing the outlet elevation of subsurface drainage pipes, CD significantly increased the water content of the 0–100 cm soil layer—especially at 0–40 cm depth—after growth stage irrigation. Under FD, CWT1, and CWT2, the 2-year mean soil water content of the 0–40 cm soil layer after growth stage irrigation in 2020 and 2021 was respectively 0.263, 0.278, and 0.267 cm3 cm−3, with the latter two values being higher by 5.70 % and 1.52 % than the former value, respectively. Soil water uptake by sunflower after irrigation mainly occurred in the 0–40 cm soil layer, which contributed 55.88–78.51 % of the total soil water uptake. Soil re-salinization occurred in the late growth stage (the flowering stage) under different treatments, with a mean re-salinization rate (relative to the period before spring irrigation) of 29.29 %, 33.48 %, and 30.34 % under FD, CWT1, and CWT2, respectively. Although the re-salinization rate was relatively high under CWT1 and CWT2, it had a low effect on crop growth as well as crop yield. HYDRUS-2D simulation was performed to compare different drain depths in the growth stage in order to determine the optimal drain depth for sunflower in moderately saline soils. To this end, the following metrics were considered for the main root zone (0–40 cm): soil water content, soil salt content, soil de-salination rate during spring irrigation, and soil re-salination rate in the late growth stage. Reduce soil salt content during spring irrigation, increase soil water content after irrigation during growth period, and minimize soil salt return rate in late growth stage, that is, to provide suitable water conditions for crop growth and minimize salt stress. The optimal drain depth during the growth stage was ultimately determined to be 50 cm.