Deep Seepage Research Articles

Special Seepage Paths Among Nested Groundwater Flow Systems Linking Surface Water Bodies

ABSTRACTA surface water body fed by groundwater is normally known as a terminal place of groundwater flow systems originating from precipitation recharge on highlands. The theory of Tóth predicted that these flow systems form a hierarchically nested structure of groundwater circulation in a composite basin. In this study, we will report new flow paths among groundwater flow systems that were unknown in Tóth's theory, identified as special seepage paths linking different surface water bodies. These seepage paths do not start from the groundwater table but can transmit water between lakes or streams that already serve as discharge zones of traditional local flow systems. As indicated in theoretical models and two real‐world cases, special seepage paths are developed if some parametric conditions are satisfied, especially when surface water bodies cut deeply below the water table or are large enough. Different surface water bodies or different river reaches can directly exchange water, chemicals and heat through deep seepage paths even when both surface and subsurface water divides exist between them. Special seepage paths may play a role in the regional scale hyporheic flow or contribute to inter‐basin groundwater flow. The knowledge of special seepage paths could greatly improve our conventional perception of surface water‐groundwater interaction, groundwater age and geochemical and heat transport at the river basin scale.

Evaluating nitrogen dynamic and utilization under controlled-release fertilizer application for sunflowers in an arid region: Experimental and modeling approach

Traditional nitrogen fertilizers (TNF), such as urea, percolate easily in arid fields, posing low nitrogen use efficiency (NUE) and a high non-point pollution risk. Controlled-release fertilizers (CRF) exhibit significantly lower deep seepage, rendering it a favorable choice in arid fields due to its ability to enhance NUE through slow-release mechanisms. However, current models do not fully account for the soil nitrogen dynamics and crop interactions under controlled-release conditions, and lack quantification. This study improved the APSIM model by adjustment the urea hydrolysis rate to assess the impact of CRF and TNF applications on soil health, crop growth, and water quality. Calibration and validation were conducted through experiments in the Hetao Irrigation District of China from 2019 to 2020, with different nitrogen application rates (135, 225, and 315 kg/ha). The model accurately simulated soil NO3-N concentration (SNC), cumulative NO3-N leaching (CNL), nitrogen uptake (NU), and sunflower yield. During the validation process, R2 and Nash-Sutcliffe efficiency (NSE) values were both above 0.75. Results indicated that the average SNC, NU, and yield under CRF application were significantly higher than those under TNF application, with increases of 38.62%, 44.92%, and 18.38%, respectively. Notably, the proportion of soil nitrogen available (PSNA), a novel metric proposed in this study, was 159.50% higher in the 0–40 cm soil layer with CRF compared to TNF. Additionally, CNL and NO3-N leaching loss rate (NLLR) decreased by 25.76% and 25.77%, respectively. Scenario simulations indicated that the optimal fertilization strategy for this region is to use 180–193.5 kg/ha of CRF with a release period of 80–85.5 d to balance agricultural productivity and ecological protection. This study confirms the significant advantages of CRF in enhancing yield, improving nitrogen management, and promoting environmental sustainability, providing a scientific basis for CRF management strategies and supporting the shift towards more efficient and environmentally friendly agricultural practices.

Mining impacts peatland hydrology reducing discharge and water storage volumes

Peatlands cover about 3% of the Earth’s land surface, but are the largest terrestrial carbon store and are important for freshwater storage. In Australia, nationally protected peatlands (called upland swamps) exist in the catchment headwaters for Sydney’s drinking water supply. In this region, longwall mining of underground coal seams can result in subsurface fracturing, land subsidence, and, potentially, peatland drainage. This study presents the water balance modelling results for an upland peat swamp before and after it was undermined in 2020. Following a detailed field campaign, a conceptual lumped hydrology model was developed to estimate the local water balance, with a Nash Sutcliffe Efficiency of 0.85 for the modelled storage of the intact swamp. After undermining, the water balance of the swamp changed, with higher deep seepage rates and reduced surface water discharge rates. For the first time, these findings detail the hydrologic effects of longwall mining on peatland environments. Based on these findings, broader catchment management initiatives are recommended to prevent or limit further water extraction from upland swamps, including incidental water losses associated with subsidence.

Soil water migration under three tree species in response to water stress and extreme rainstorms

In arid and semi-arid areas, plant growth and survival are directly related to the soil water content. The soil water content is an important parameter for monitoring land degradation. A better understanding of how forests use soil water is crucial for the quantification how the terrestrial hydrologic cycle adapts to forestry practices and regional climate anomalies in these areas. This study investigated the variation of the water balance under different precipitation patterns (including soil water redistribution patterns under water stress and extreme rainstorms) under three common tree species in a mountainous area of Beijing were investigated. The results showed that soil water storage in the 80–150 cm layer played an important role for the ability of Platycladus orientalis (L.) Franco and Quercus variabilis Blume to survive drought during a dry season. Compared to P. orientalis and Q. variabilis, the duration of water stress was shortest for Pinus tabulaeformis Carr. (15 months). P. tabulaeformis had a higher ability to utilize top soil water but showed a less balanced use of soil water in each soil layer. It also had the strongest ability to replenish groundwater through deep seepage. P. tabulaeformis may resist drought by transferring water to deeper soil horizons, where it is less susceptible to evaporation and where moisture can be temporarily stored. P. orientalis and Q. variabilis are more dependent on soil water storage in response to water stress conditions.

Chinese Violet Cress (Orychophragmusviolaceus L.) Yield and Nitrogen Balance in Response to Coupling Effects of Water–Nitrogen Application—A Case Study Using 15N Tracing Technique

The accurate and efficient management of water and nitrogen is of significance for the intensive production of field-cultivated flowers. To investigate the effects of different irrigation and nitrogen application modes on the growth, development, and nitrogen use of Orychophragmus violaceus, three nitrogen application doses of 120, 160, and 200 kg/ha and three irrigation treatments of 50 + 30 mm (overwintering water and regreening water), 75 + 45 mm, and 100 + 60 mm were implemented. The 15N isotope tracing technique was used to investigate the fertilizer nitrogen use, soil nitrogen residue, and nitrogen balance of Orychophragmus violaceus, and the entropy weight coefficient evaluation model was employed to optimize the water and nitrogen strategy. Results showed that after the application of water and nitrogen, the fresh yield of Orychophragmus violaceus increased by 21.4–49.3%, W2N3 possessed the most obvious effect on promoting yield increase, and the fresh yield reached 31.1 t/ha. The highest plant nitrogen use efficiency (39.1%) was detected in W2N2, but no significant (p > 0.05) difference of nitrogen use efficiency was found between W2N2 andW3N2. After the peak flowering period, 23.8–39.1% of the fertilizer nitrogen was absorbed by the plants, 44.3–59.2% remained in the soil, and 13.7–21.6% was lost via deep seepage, a gaseous state, or other unknown ways. A higher application amount of water or nitrogen increased the risk of nitrogen loss. Among the treatments, W2N2 treatment has the highest entropy weight coefficient evaluation value of 0.905, indicating that W2N2 was the water–nitrogen coupling mode with optimal comprehensive benefits. It was recommended that 75 mm of overwintering water and 45 mm of regreening water combined with a 160 kg/ha nitrogen application amount is the suitable water and nitrogen regulation scheme for Orychophragmus violaceus.

Water Budget of Urban Turf Field and Optimal Irrigation Schedule Simulation in an Ecotone between Semi-Humid and Semi-Arid Regions, Northern China

Water security in the ecotone between semi-humid and semi-arid regions (EHA) is very vulnerable and sensitive to climate change and human interferences. Urban turf irrigation is a primary consumer of urban water resources in the EHA, which places huge pressures on water security by substantial irrigated water use due to the expansion of urban turf planting. Based on a 2-year (2020–2021) turf experiment in Zhangjiakou City, a typical water-deficit city in the EHA of northern China, the water budget for turf was measured and analyzed. Furthermore, the Root Zone Water Quality Model (RZWQM2) was employed to evaluate the optimal irrigation scheme for turf. The results showed that the average volumetric water content in the 0–40 cm soil layer was maintained above 23% in 2020–2021. The evapotranspiration in growth period of turf accounted for more than 70% of the annual evapotranspiration, and the deep seepage in turf soil accounted for 49.67% and 60.28% of the total precipitation and irrigation in 2020 and 2021, respectively, during the vigorous growth period of the turf from May to September. The calibrated RZWQM2 showed a robust ability to simulate the water changes in turf. The d-values (consistency index) between the simulated and observed volumetric water contents and evapotranspiration were both greater than 0.90. In the aspects of irrigation scenarios, the T60%-12 scenario (TA-B, where A is 100%, 80%, 60% or 40% of the total irrigation amount and B is the number of irrigation events corresponding to A) was determined as the best irrigation schedule in our study area because of lower evapotranspiration, seepage and higher turf soil water storage under this irrigation scenario, also resulting from the comparison of different irrigation scenarios using the entropy-weight-TOPSIS method. In such an optimal scenario, T60%-12 irrigation treatment reduced the irrigated water requirement of turf by 40% (142.06 mm) and the seepage amount by 28.07% (39.05 mm), and had the lowest negative impacts on the turf growth.

Effect of Irrigation Scheduling Methods on Maize Grain Yield and Nitrate Leaching in Central Minnesota

Highlights Four irrigation scheduling methods were compared for maize yield vs nitrate-N losses. Yield was similar with SM, CB, and EPIC, and lower for IMA irrigation scheduling. Nitrate-N leaching losses were highly dependent on precipitation as well as on the rate and frequency of irrigation. IMA and EPIC methods should be adopted with further calibration. ABSTRACT. Coarse-textured soils in the Great Lakes states have limited water holding capacity, which makes irrigation essential to obtain optimum yields for maize; however, excess irrigation has the potential to contaminate ground and surface water resources through deep seepage of applied fertilizers, making irrigation management critical. The objective of this study was to evaluate the impact of different strategies for agricultural irrigation water management on maize grain yield and nitrate leaching losses. In this three-year study (2019-2021), the following four irrigation scheduling strategies were compared under continuous maize cropping systems at two sites in Central Minnesota, Becker and Westport: (1) soil moisture monitoring using soil moisture sensors (SM), (2) checkbook method of irrigation scheduling (CB), (3) irrigation management assistant tool (IMA), and (4) EPIC model auto-irrigation (EPIC). Overall, in comparison to the CB method (highest irrigation method), the SM, IMA, and EPIC methods recommended 2.58%, 51.05%, and 9.27% less water in irrigation, respectively. In terms of grain yield, no significant differences were observed between irrigation treatments at the Becker site. The average maize grain yield at the Becker site was 12.02, 11.97, 11.76, and 10.62 Mg/ha, for SM, CB, EPIC, and IMA treatments, respectively. However, in the drier 2021 season, a grain yield loss of 30%, 27%, and 21% was observed under IMA when compared to SM, CB, and EPIC methods, respectively, at the Becker site. At the Westport site, on average, no significant difference in yield was obtained between SM, CB, and EPIC, however, yield under IMA treatment was significantly lower (12%) than CB. The results suggest that nitrate leaching losses can be significantly reduced by altering the rate and frequency of irrigation. IMA treatment resulted in significantly lower nitrate leaching (62%) than the CB method, reducing nitrate leaching from 35.86 kg/ha to 13.71 kg/ha at the Westport site. No significant differences in nitrate leaching were observed at the Becker site because the impact of precipitation superseded the impact of irrigation. Results from this study can aid in the adoption and further development of less labor-intensive and more accurate methods of irrigation scheduling in coarse-textured soils of Great Lakes states. Keywords: Coarse textured soils, Crop evapotranspiration, Irrigation scheduling methods, Maize grain yield, Nitrate-N leaching, Water quality, Water quantity.

Climate Change in a Semi-Arid Environment: Effects on Crop Rotation with Dairy Manure Applications

Highlights Spring wheat yields increase with high temperatures and the minimal impact of increased CO2. At high temperatures and increased CO2, spring barley yields increase; yields decrease at only high temperatures. Potato and sugarbeet yields decrease with climate change. Climate change had little impact in soil nitrogen processes. Abstract. Agricultural crops grown in the irrigated semi-arid region of southern Idaho account for almost two-thirds of the median household income in the region. The impacts of climate change on cropping systems and the availability of water for irrigation would be a serious challenge for the state's economic dependence on agriculture. The objective of the study was to simulate the future impact of climate change on a crop rotation of spring wheat-potato-spring barley-sugarbeet grown in the semi-arid region of southern Idaho using conventional management practices and a high dairy manure application. The Root Zone Water Quality Model (RZWQM2) simulations used bias-corrected and spatially disaggregated projections from the World Climate Research Program’s coupled model inter-comparison project phase 5 to generate 40 GCM projections for the time from 2071-2099. The 28-yr scenarios were designed to simulate the impact of temperature and CO2 regimes on crop production, soil nitrogen mineralization, nitrogen seepage, deep seepage of water, and nitrous oxide emissions. Data from a field experiment in southern Idaho with conventional fertilizer practices and annual applications of 52 Mg ha-1 dairy manure with a crop rotation of spring wheat-potato-spring barley-sugarbeet were used in the RZWQM2 simulations. Results were compared to a baseline scenario of conventional management practices, historical weather data, and ambient CO2. Spring wheat yield increased by 22% and 16% for manure and fertilizer treatments, respectively, compared to the baseline scenario. Using the same comparison, potato tuber yield decreased by 65% and 60% in the manure and fertilizer treatments, respectively, for the highest temperature and CO2 increase scenarios. Spring barley produced a 33% higher yield with increased temperature and CO2. However, yield decreased when temperature increased, but CO2 remained unchanged. Sugarbeet yields decreased by 16% and 18% for manure and fertilizer treatments, respectively, compared to the baseline scenario. Nitrogen mineralization, N seepage from the profile, and nitrous oxide emissions were strongly influenced by the manure applications, and there was little simulated impact of climate change on these processes. These simulation results indicate that genetic enhancements or alternative management will be needed to maintain potato and sugar beet production levels in semi-arid areas, while spring barley and wheat yields may increase, assuming adequate irrigation water supplies are available. Keywords: Nitrogen Mineralization, Potato, RZWQM2, Spring Barley, Spring Wheat, Sugarbeet.

Research on water seepage detection technology of tunnel asphalt pavement based on deep learning and digital image processing

To improve the safety of road tunnel pavement, the research established road tunnel pavement water seepage recognition models based on deep learning technology, and a water seepage area extraction model based on image processing technology to finally achieve accurate detection of water seepage on tunnel pavements. First, the deep learning models EfficientNet water seepage recognition model and MobileNet water seepage recognition model were built, the models were trained with the self-collected pavement seepage data set, and the F1 score was introduced to evaluate the accuracy and comprehensive performance of the two models in predicting different categories of water seepage characteristics. Then three grayscale processing methods, the cvtColor function, mean method and maximum method, six global threshold segmentation methods, Otsu thresholding method, THRESH_BINARY, THRESH_BINARY_INV, THRESH_TRUNC, THRESH_TOZERO and THRESH_TOZERO_INV, three filtering methods, namely Gaussian filtering, median filtering and morphological open operation, as well as small connected domain removal, were used to reduce the noise of the images. Finally, the seepage area image calculation method was proposed based on the processed images to predict the actual pavement seepage area. The results show that the recognition accuracy of the EfficientNet water seepage recognition model is 99.85% and 97.53% in the training and validation sets respectively, which is 2.85% and 0.76% higher than the 97% and 96.77% of the MobileNet model. The average F1 score of the EfficientNet model is 95.22%, which is 5.05% higher than that of the MobileNet model, for the four types of seepage feature images: point seepage, line seepage, surface seepage and no seepage. The cvtColor function for grayscale processing, THRESH_BINARY for threshold segmentation and a combination of median filtering and morphological open operation for image noise reduction can effectively extract the seepage features. The area calculation is performed by the seepage area image calculation method, and the average error between the predicted value and the actual seepage area is 8.30%, which can better achieve the accurate extraction of the seepage area.

Are northern German Scots pine plantations climate smart? The impact of large-scale conifer planting on climate, soil and the water cycle

Increasing temperatures and rising atmospheric vapor pressure deficits are exposing forests around the globe to increasing drought and heat stress, demanding a shift to climate-smart forestry for increasing the stress resistance and resilience of production forests and to enhance their climate change mitigation potential. Based on measurements in paired pine and beech forests and the review of literature data, we analyse the biophysical consequences and the carbon cycle impact of large-scale Scots pine (Pinus sylvestris L.) plantations in northern Germany in the face of a warming and aridifying climate. We quantified canopy surface albedo and surface temperature, evapotranspiration and deep seepage, carbon (C) storage in biomass and soil and annual C sequestration, and soil acidification of pine plantations in comparison to beech forests (Fagus sylvatica L.), the natural forest vegetation. We find that near-infrared (NIR, 700–3000 mn) canopy surface albedo is higher by 5.2 percentage points during summer over beech as compared to pine forest, resulting in a 9 % higher net radiation and a 0.6 K higher surface temperature of the pine canopy. Deep seepage is on average by 68 mm yr−1 smaller under pine than beech forest (66 mm yr−1 vs. 134 mm yr−1) due to the higher evapotranspiration of pine. C storage in biomass and soil is by ∼ 48 Mg C ha−1 higher in beech than pine forests, reflecting the higher productivity of beech, demonstrating an unfavorably low C sequestration potential of Scots pine plantations. We conclude that the large-scale Scots pine plantations in northern Germany (>1.7 million ha) are neither environmental-friendly nor climate smart, given their enhancement of climate-warming, low climate change mitigation potential, and negative effect on groundwater recharge. Replacing pine plantations by beech (or other hardwood) forests in northern Germany and adjacent regions is urgently needed for achieving the goals of climate-smart forestry.

Soil salt balance in a cotton field under drip irrigation and subsurface pipe drainage systems

AbstractSoil salinization is a vital factor limiting crop yield in dryland oasis cropland. A film‐mulched drip irrigation and subsurface pipe drainage (MDI‐SPD) system has been proved to be highly efficient at mitigating salination globally. However, the soil salt balance in time and spatial dimension is unclear in this system. A MDI‐SPD experiment was conducted for 4 yr (2015–2019) in a field in Manas River Basin, western China. The subsurface drainage pipes were installed at a depth of 1 m with a space of 15 m. Three long‐term observation points were set at 0, 5, and 7.5 m horizontal from the subsurface pipe and served as long‐term observation points in 0‐to‐20‐, 60‐to‐80‐, and 180‐to‐200‐cm soil layers. Results after 4 yr indicated that the total salt output in the irrigated area was 260 t, with 103 t of salt drained by the subsurface pipe (40% of the total salt output in the irrigation area), and the seed cotton yield increased by 52%. Soil salt balance indicated desalination. The electrical conductivity (EC) of subsurface pipe drainage was positively correlated with drainage flow and salt discharge and negatively correlated with drainage discharge and time (P < .05). If salt leaching stops, soil EC at the 0‐to‐200‐cm depth could reach 15 dS m–1 in 8 yr. Thus, two or three uses of MDI‐SPD measures in the next 8 yr should suffice to maintain the soil salt at a low concentration. An increase in shaft drainage would also reduce the deep seepage of salt.

The slow and steady salinization of Sparkling Lake, Wisconsin

The concentrations of conservative solutes in seepage lakes are determined by the relative inputs of precipitation vs. groundwater. In areas of road salt application, seepage lakes may be at high risk of salinization depending on groundwater flow. Here, we revisit a 1992 analysis on the salinization of Sparkling Lake, a deep seepage lake in Northern Wisconsin. The original analysis predicted a rapid increase in chloride concentrations before reaching a steady steady of 8 mg L−1 by 2020. Forty years of monitoring Sparkling Lake show that rather than reaching a dynamic equilibrium, chloride concentrations have steadily increased. We update the original box model approach by adding a soil reservoir component that shows the slow steady rise in chloride is the result of terrestrial retention. For freshwater rivers and lakes, chloride retention on the landscape will both delay chloride impairment and prolong recovery and must be considered when modeling future chloride contamination risk.

Simulation of Flow and Agricultural Non-Point Source Pollutant Transport in a Tibetan Plateau Irrigation District

Flow and transport processes in soil and rock play a critical role in agricultural non-point source pollution (ANPS) loads. In this study, we investigated the ANPS load discharged into rivers from an irrigation district in the Tibetan Plateau and simulated ANPS load using a distributed model. Experiments were conducted for two years to measure soil water content and nitrogen concentrations in soil and the quality and quantity of subsurface lateral flow in the rock and at the drainage canal outlet during the highland barley growing period. A distributed model, in which the subsurface lateral flow in the rock was described using a stepwise method, was developed to simulate flow and ammonium nitrogen (NH4+-N) and nitrate nitrogen (NO3−-N) transport processes. Sobol’s method was used to evaluate the sensitivity of simulated flow and transport processes to the model inputs. The results showed that with a 21.2% increase of rainfall and irrigation in the highland barley growing period, the average NH4+-N and NO3−-N concentrations in the soil layer decreased by 10.8% and 14.3%, respectively, due to increased deep seepage. Deep seepage of rainfall water accounted for 0–52.4% of total rainfall, whereas deep seepage of irrigation water accounted for 36.6–45.3% of total irrigation. NH4+-N and NO3−-N discharged into the drainage canal represented 19.9–30.4% and 19.4–26.7% of the deep seepage, respectively. The mean Nash–Sutcliffe coefficient value, which was close to 0.8, and the lowest values of root mean square errors, the fraction bias, and the fractional gross error indicated that the simulated flow rates and nitrogen concentrations using the proposed method were very accurate. The Sobol’s sensitivity analysis results demonstrated that subsurface lateral flow had the most important first-order and total-order effect on the simulated flow and NH4+-N and NO3−-N concentrations at the surface drainage outlet.

Deep seepage of per- and polyfluoroalkyl substances through the soil of a firefighter training site and subsequent groundwater contamination

Per- and polyfluoroalkyl substances (PFASs) are utilized in specific firefighting foams. The objectives of this study were i) to map PFAS distribution in the soil and groundwater of a firefighter training site active for more than 3 decades, ii) to locate the main points of entry of PFASs into the aquifer and iii) to identify which PFASs seeped most deeply into the soil. A total of 44 soil cores and 17 groundwater samples were collected. Perfluorooctane sulfonate (PFOS), 6:2 fluorotelomer sulfonic acid (6:2 FTSA) and 6:2 Fluorotelomer sulfonamide alkylbetaine (6:2 FTAB) were the most predominant PFASs in surface soil. The highest total PFAS concentrations (up to 357 μg/g) were measured in two areas. Both areas were considered as potential points of entry of PFASs into the aquifer since PFASs were detected in soil 15 m below the surface, despite the presence of clay layers. The highest total PFAS concentrations were recorded in the monitoring wells located in the perimeter of the firefighter training site and in the spring located downgradient in the direction of groundwater flow. They ranged from 300 to 8300 ng/L. The fluorotelomer 6:2 FTAB was quantified in 6 monitoring wells, suggesting that this FT can reach a water table 20 m below the ground's surface.

Gatun Dam—megastructure of the Panama Canal

Abstract The kingpin structure of the American scheme to construct a ship canal across Panama in 1907–1914 was an earthen dam of unprecedented scale and scope at Gatun, to retain the aggregate flow of the Chagres River and its principal tributaries. Upon this structure alone, the entire plan rested, because it created the man-made lake rising 85 ft (25.9 m) above sea level, which allowed ships to cross the 550 ft (167.6 m) continental divide between the Atlantic and Pacific Oceans. Everything about Gatun Dam was enormous. Its dimensions were without precedent: a crest length of 8,200 ft (2,500 m) and a maximum width of 2,300 ft (701 m). With a height of 105 ft (32 m) above sea level, it stored sufficient water to maintain an operating pool covering 164 mi2 (425 km2). At its center was the most critical structure, a mass concrete spillway capable of passing flood flows of the unpredictable Chagres River. The biggest problem with the site was the underlying geology, which included two deepley incised paleo-channels. The massive embankments were placed over these paleo-channels, which were up to 258 ft (78.6 m) deep. The channel infill of the upper 50 ft (15.2 m) was of relatively low permeability, mostly sandy silts and clay. There were more pervious sands and gravel lying beneath these, which allowed deep seepage cutoffs to be precluded.

Simulating the effects of different potassium and water supply regimes on soil water content and water table depth over a rotation of a tropical Eucalyptus grandis plantation

Although large amounts of potassium (K) are applied in tropical crops and planted forests, little is known about the interaction between K nutrition and water supply regimes on water resources in tropical regions. This interaction is a major issue because climate change is expected to increase the length of drought periods in many tropical regions and soil water availability in deep soil layers is likely to have a major influence on tree growth during dry periods in tropical planted forests. A process-based model (MAESPA) was parameterized in a throughfall exclusion experiment in Brazil to gain insight into the combined effects of K deficiency and rainfall reduction (37% throughfall exclusion) on the water used by the trees, soil water storage and water table fluctuations over the first 4.5 years after planting Eucalyptus grandis trees. A comparison of canopy transpiration in each plot with the values predicted for the same soil with the water content maintained at field capacity, made it possible to calculate a soil-driven tree water stress index for each treatment. Compared to K-fertilized trees with undisturbed rainfall (+K+W), canopy transpiration was 40% lower for K deficiency (−K+W), 20% lower for W deficit (+K−W) and 36% lower for combined K deficiency and W deficit (−K−W) on average. Water was withdrawn in deeper soil layers for −W than for +W, particularly over dry seasons. Under contrasted K availability, water withdrawal was more superficial for −K than for +K. Mean soil water content down to 18 m below surface (mbs) was 24% higher for −K+W than for +K+W from 2 years after planting (after canopy closure), while it was 24% lower for +K−W and 12% lower for −K−W than for +K+W. The soil-driven tree water stress index was 166% higher over the first 4.5 years after planting for −W than for +W, 76% lower for −K than for +K, and 14% lower for −K−W than for +K+W. Over the study period, deep seepage was higher by 371 mm yr−1 (+122%) for −K than for +K and lower by 200 mm yr−1 (−66%) for −W than for +W. Deep seepage was lower by 44% for −K−W than for +K+W. At the end of the study period, the model predicted a higher water table for −K (10 mbs for −K+W and 16 mbs for −K−W) than for +K (16 mbs for +K+W and 18 mbs for +K−W). Our study suggests that flexible fertilization regimes could contribute to adjusting the local trade-off between wood production and demand for soil water resources in planted forests.

Soil water transformation regularity of farmland for typical crop in Beijing-Tianjin-Hebei region: Experimental and simulating analyses

The transformation process of soil water plays an important role in the hydrological cycle, and is a link to other water processes. Study on the regularity of soil water transformation under agricultural plantation is favorable to understanding the influence of human activities on soil water conversion. Typical crop was selected in Beijing-Tianjin-Hebei(BTH) region and the study on regularity of field-scale soil water transformation was carried out by means of crop-soil water field experimental observation combined with model simulation. In the field experiment, testing and observation of irrigated and rainfed maize were simultaneously carried out in the adjacent fields respectively to form a comparative experimental study. The experimental observation data were used to establish the soil water model, which is calibrated in many aspects, such as field water content change during the maize growth period, the soil profile water content distribution at different moments, maize leaf area index and plant height. The results show that this model has an efficient simulation effect. Quantitative study on field evapotranspiration regularity, field soil water flux under irrigated and rainfed modes, impact mechanism of soil water deep seepage during maize growth period was achieved through the simulation of soil water process, and related reference conclusions were also proposed for water resources management and conservation in BTH.

Optimizing Irrigation Rates for Cotton Production in an Extremely Arid Area Using RZWQM2-Simulated Water Stress

Abstract. Quantifying crop water demand and optimizing irrigation management practices are essential to water resource management in arid desert oases. Agricultural systems modeling can serve to develop a better understanding of the hydrologic cycle under various irrigation and climate conditions. RZWQM2-simulated water stress can be used as an indicator for irrigation scheduling but has not been applied to extremely arid zones. The objectives of this study were to (1) evaluate the performance of RZWQM2 in simulating soil moisture content and crop production in an extremely arid area and (2) develop an optimal irrigation strategy using model-simulated crop water stress. In this study, RZWQM2 hybridized with DSSAT was calibrated and validated against soil moisture, cottield, and development stage data collected from 2006 to 2013 in a flood-irrigated cotton field located in an extremely dry oasis in Cele, situated in Xinjiang, China (mean annual precipitation 37 mm). The simulated water balance was analyzed to determine the actual crop water consumption, crop water requirements, and seepage loss. Subsequently, an optimal irrigation scheme was developed using RZWQM2 by averting crop water stress from planting to 90% open boll. In comparison to similar studies, the accuracy of soil moisture content simulations was deemed acceptable based on percent bias (PBIAS < ±15%), coefficient of determination (0.378 = R2 = 0.636), Nash-Sutcliffe model efficiency (0.130 = ME = 0.557), and root mean squared error (0.022 m3 m-3 = RMSE = 0.031 m3 m-3). The model performed well in simulating cotton yield (R2 = 0.79, ME = 0.75, RMSE = 417.0 kg ha-1, and relative RMSE (rRMSE) = 12.5%). Model-simulated plant emergence dates were generally six days late because of the model’s lack of a component for mulching after seeding. Other phenological dates were closely matched, with a mean difference of ±4 days. On average, over eight years, the simulated growing season (planting to 90% open boll) water balance showed that the cotton crop consumed 532 mm year-1 of water under current irrigation practices, while 109 mm of water was lost through deep seepage. However, based on simulated PET, the crop water requirement was 641 mm year-1, suggesting water stress under current irrigation practices. Under these conditions, water stress occurred mainly during the late stages of cotton growth. The model-simulated actual evapotranspiration (ET) is comparable to the calculated ET using the water balance method, with percent error of -1.3%, indicating the rationality of applying model-simulated results in a water stress-based irrigation scheduling method. On average, the water stress-minimizing RZWQM2 irrigation schedule resulted in an apparent irrigation water savings of 32 mm year-1 (4.9%) and an annual yield increase of 527 kg ha-1 (16.3%). RZWQM2 was shown to be suitable for simulating soil hydrology and crop development in an agricultural system implemented in an extremely dry climate. Rescheduling of irrigation using a water stress-based method can be used to optimize irrigation water use and cotton production. Keywords: Cotton production, Optimum irrigation, RZWQM2, Soil water content, Water stress, WS-based regime.

Erratum to “Disentangling the Effects of Land Management and Soil Heterogeneity on Soil Moisture Dynamics”

The following three passages and the respective references were not included in the published version. They should have been added to the paragraphs specified below. 4 studied the effects of different land management practices on deep seepage and solute leaching based on soil water content and tension time series measured in 3 m soil depth. The field experiment was designed to study the effects of land use and land management on deep seepage and solute leaching (3; 1). Time series of soil moisture and soil water tension were continually measured in high temporal solution, and soil water samples were taken in different soil depths down to 3 m. The measurements started in 1994 and continue today. Our findings about the small functional heterogeneity at the experimental site confirmed the basic assumption by 2 that relative soil moisture dynamics at different positions in the deep vadose zone are very similar. They developed and tested a field method for quantifying deep seepage and solute leaching based on tension and water content measurements and applied it successfully at 40 plots in northeast Germany (3; 4).

Advanced Soil Hydrological Studies in Different Scales for Sustainable Agriculture

Abstract A comprehensive study of interactive processes between soil, water, plant, animal and atmosphere to protect the natural resources requires knowledge of parameters and processes in different scales. Soil hydrological studies in North-East Germany were carried out in different scales, starting with laboratory, lysimeter measurements and in the field. The measurements of soil hydrological properties were executed with the Extended Evaporation Method (EEM) and the HYPROP device. A method for quantifying deep seepage and solute leaching under field conditions was developed, tested and applied at more than 40 soil hydrological field plots in NE Germany. The hypothesis was confirmed that arable land constitutes the main source of deep drainage and groundwater recharge in Northeast Germany. Deep seepage was strongly reduced under forest. For decision support on landscape renovation and land rededication by afforestation in NE Germany the seepage reduction under forest is to be taken into consideration, especially with respect to the conservation or restoration of wetlands in regions with negative climatic water balance. The EEM and the soil hydrological field method so called “virtual lysimeter” have the potential for the improvement of soil hydrological studies in Asia as a whole.