Deep Percolation Water Research Articles

Modified Surface Drip Irrigation and Hydraulic Barrier Impacts on Soil Moisture and Water Productivity for Tomatoes in a Greenhouse

Considerable amounts of irrigation water of vegetable crops grown in homogenous sandy soil profiles could be subjected to deep percolation water losses due to inappropriately designed surface or subsurface drip irrigation methods. This study aimed to investigate the combined influence of implementing clay soil layer in homogenous sandy soil profile of low-tech greenhouse ridges and using modified surface drip irrigation (M-DI) on soil moisture distribution and water productivity of tomatoes. In the greenhouse, a 7.5 cm thick clay soil layer was implemented 15 cm from the soil surface of each ridge as a hydraulic barrier. Three irrigation regimes (100%, 70% and 50% of ETo) were imposed with the M-DI on tomato plants and 100%ETo with surface drip irrigation (DI) as control. Regarding economic valuation, viability was preserved for the M-DI and DI methods. The outcome indicated that soil moisture spreads more horizontally than vertically on the sandy soil above the clay soil layer. The combined effect of the homogenous sandy soil profile amendment and full irrigation (100%ETo) with the M-DI irrigation method increased the tomato fruit yield by 64.5%. Furthermore, the combined influence enhanced water productivity by the M-DI to 54.7 kg/m3 compared to 32 kg/m3 by the DI. However, M-DI demonstrated dominance over DI regarding returns, yield, and profit. Economic-wise, the M-DI requires 50% less of the lateral pipelines needed by the DI in low-tech greenhouses. Adopting the M-DI with a hydraulic barrier can improve soil moisture, water productivity, yield, and returns for tomato crops in low-tech greenhouses under sandy soil conditions. Also, the M-DI with the hydraulic clay barriers was an economically viable investment compared to the DI without clay barriers for growing tomatoes in low-tech greenhouses.

Sand-fixing vegetation regulates deep percolation and soil water dynamics in semiarid sandy land: Evidence from a deep percolation recorder and in-situ test

Deep percolation (DP) determines the sustainable utilization of regional groundwater resources and provides large hydrological benefits to ecosystems in semiarid sandy regions. However, studies involving DP variability have rarely conducted in-situ tests with different vegetation coverages (VC) and vegetation types using direct measurements. This study measured soil moisture and DP for four years in five plots, with DP measured using a deep percolation recorder: mobile sand (MS) as the control group; Artemisia ordosica semifixed (AOSF) with VC of 30%–35% and Artemisia ordosica fixed (AOF) with VC of 70%–75% (AOSF and AOF stand ages: 30–40 years), representing different vegetation coverages; and Salix psammophila fixed (SPF) and Pinus sylvestrix var. Mongolica fixed (PSMF) with the same VC of 45%–50% (SPF and PSMF stand ages: 30 years), representing different vegetation types. The effects of sand-fixing vegetation on DP and soil water were evaluated using the relative extractable soil water (RESW) and soil water storage deficit metrics. DP occurrence in MS was closely related to rainfall amounts of > 10 mm and high-intensity rainfall rather than the total annual rainfall. Increases in vegetation coverages and forest selection significantly reduced DP and RESW compared with MS. DP in the shrub plot (SPF) was significantly higher than that in the forest plot (PSMF). Plants utilized water from different sources among the sandy land types: the shallow (0–80 cm) and deep layers (80–200 cm) in PSMF and AOF, and only from the shallow layer in AOSF and SPF. However, compared with MS, soil water storage deficit occurred to varying degrees in each plot. This study can provide a scientific reference for the restoration of the ecology and water cycle in sandy regions.

Variations in hydrological variables using distributed hydrological model in permafrost environment

The Yangtze River Source Region (YaRSR) is located in the third polar region, the most threatened zone by global warming after the Arctic. Permafrost covers eighty percent of the total area of YaRSR, while the rest is seasonally frozen ground. Due to a significant rise in air temperature, degradation of the permafrost could occur. Permafrost coverage in a river basin greatly controls its hydrology. This study focuses on hydrological modeling in this permafrost environment using the Soil and Water Assessment Tool (SWAT). The SWAT model was calibrated (1985–2000) and validated (2001–2015) on a daily time step. The results were also compared on a monthly time scale. An impermeable layer was introduced within the SWAT model to represent the permafrost conditions. The streamflow is strongly dependent on the seasonal variation of precipitation and temperature, and the rising limb of the hydrograph shows the melting of snow, the contribution of soil water, and thawing of permafrost during the spring-summer season. The permafrost layer well restricted the deep percolation of water. During the spring season, streamflow mainly consists of surface runoff because of the frozen soils. Permafrost and frozen ground thawing lead to an increase in the contribution of groundwater flow to streamflow. Ultimately, the frozen ground depletes as the temperature gets close to the freezing point. This study also describes the SWAT model application to better analyze and understand the hydrology of the permafrost/frozen ground with limited data availability.

Study on Nitrogen Loss Rules of Paddy Fields under Different Irrigation and Drainage Modes in Southern China

With the growing problem of agricultural nonpoint source pollution, it is an urgent issue to explore irrigation and drainage modes suitable for rice-growing areas in southern China. Barrel experiments were conducted to study the variation of NH4+-N, NO3−-N and TN concentrations in surface drainage and deep percolation water, as well as the rules of nitrogen runoff losses and leaching losses. Treatments included frequent and shallow irrigation (FSI), drought planting with straw mulching (DPS) and water catching and controlled irrigation (WC-CI). The results showed that the trends of NH4+-N, NO3−-N and TN concentrations in surface drainage were similar, and the N concentration gradually decreased with increasing drainage frequency. The trends of NH4+-N, NO3−-N and TN concentrations in deep percolation water were similar, rising to a peak within 5~7 days after fertilization and then gradually decreasing. NH4+-N loss load was the main form of N loss load in surface drainage and deep percolation water, which accounted for 42.06~89.16%. Compared with FSI, DPS significantly increased surface drainage and N runoff loss loads by 98.67% and 125.86%, respectively, while WC-CI significantly reduced them by 59.21% and 66.38%, respectively. Deep percolation water was reduced by 68.59% and 37.99% for DPS and WC-CI, respectively, and N leaching loss loads were reduced by 74.69% and 43.23%, respectively. Compared with FSI, the total TN loss load was significantly reduced by 76.69% and 43.34% for DPS and WC-CI, respectively, and the pollution control was better for DPS. WC-CI significantly increased rice yield by 7.31%, while DPS decreased by 0.95 % due to long-term water stress. Comprehensively considered, WC-CI has obvious advantages, which can reduce nitrogen loss and maintaining a high yield.

The Effects of Three Furrow Shapes on Water Advance Characteristics, Application Efficiency, Deep Percolation and Tail Water Run-off

The Effects of Three Furrow Shapes on Water Advance Characteristics, Application Efficiency, Deep Percolation and Tail Water Run-off

Potato Yield Response and Seasonal Nitrate Leaching as Influenced by Nitrogen Management

Nitrate leaching is of great environmental concern, particularly with potatoes grown on sandy soils. This 3-year study evaluated the effect of three N rates (100, 150, and 200 kg ha−1) of single applications of polymer-coated urea (PCU) and a 75% PCU + 25% urea mixture, plus a conventional split application of 200 kg N ha−1 of a 50% ammonium sulfate + 50% calcium ammonium nitrate mixture (CONV) on NO3−-N leaching, potato yield, and N uptake under irrigated and non-irrigated conditions on a sandy soil in Quebec (Canada). Fertilizer N application increased growing season NO3−-N leaching only under irrigation. On average, irrigation increased seasonal NO3−-N leaching by 52%. Under irrigated conditions, PCU reduced NO3−-N leaching compared to PCU + urea. However, both PCU and PCU + urea significantly increased NO3−-N leaching compared to the CONV at the equivalent N rate of 200 kg N ha−1. This was attributed to the timing of soil N availability and deep-water percolation. Total (TY) and marketable (MY) yields in the CONV were similar to those in the PCU applied at the equivalent N rate of 200 kg N ha−1. Despite lower plant N uptake, PCU resulted in greater TY and MY compared to PCU + urea. Residual soil inorganic N was greater for PCU and PCU + urea compared to the CONV, providing evidence that PCU products have the potential to increase NO3−-N leaching after the growing season. In this study, PCU was an agronomically and environmentally better choice than PCU + urea. The results also showed that the efficiency of PCU to reduce seasonal NO3−-N leaching may vary according to the timing of precipitation and irrigation.

The impact of geomorphology on groundwater recharge in a semi-arid mountainous area

The impact of geomorphological structures on rainwater infiltration and groundwater recharge in the mountainous terrain of a semi-arid region was studied in the southern part of the Judean Western Mountain Aquifer (WMA) in Israel and the Palestinian Authority. The study was conducted in two main typical geomorphological landscape units which include exposed rock outcrops on the hillslope, and human-made agricultural soil terraces in a first-order stream channel. We measured rainwater infiltration through the unsaturated zone in the two geomorphological setups using vadose zone monitoring systems (VMS), that enabled continuous tracking of rainwater percolation and tracer transport through the unsaturated zone with respect to the rain patterns.The results from three years of continuous monitoring of water percolation through the unsaturated zone indicated a quick and intense percolation pattern in the rocky terrain compared to that measured in the deep soil of the terrace. The precipitation patterns, as reflected from the rain distribution and intensities, appeared to have a significant impact on deep water percolation and ultimately on groundwater recharge. In the rocky terrain, rain events of high intensity, even during drought years of low cumulative precipitation, resulted in deep water infiltration, which ultimately turned into groundwater recharge. On the other hand, infiltration through deep soils, as prevailed in terraces, valleys, and high plains, was found to be very limited, subjected to intense evaporation and ultimately result by reduced groundwater recharge. It appears that the value of annual cumulative precipitation is of a lower importance to groundwater recharge while high rain intensity is the most dominant factor responsible for deep water infiltration.Tracer migration patterns in the unsaturated zone revealed that precipitation on the rock outcrops promotes the generation of local runoff that rapidly drains into the subsurface through infiltration hot spots. It has been observed that these hot spots are often marked by prickly burnet shrubs (Sarcopoterium spinosum), which thrive year-round on the water abundancy in the soil pockets beneath the impervious rock on land surface. An important outcome of this study is the suggested strong coupling between geomorphological features and groundwater recharge. Application of variable infiltration functions to the different geomorphological characteristics of each terrain may improve groundwater recharge models. Climate changes in recent years, expected to lead to decreased annual precipitations and increased evaporation in parallel with an increase in rainfall intensities in the semi-arid mountainous areas of the eastern Mediterranean. Yet according to our results, the expected increase in rain intensity may actually result in an increase in groundwater recharge.

Effects of irrigation strategies and soil properties on the characteristics of deep percolation and crop water requirements for a variable rate irrigation system

Reducing deep percolation (DP) across the field is one of the main objectives of a variable rate irrigation (VRI) system under a semi-humid climate. A study was conducted in the North China Plain during the 2016 and 2017 maize growing seasons in a 1.64-ha one-quadrant plot irrigated by a VRI centre pivot irrigation system. The study was designed to quantify and compare the DP dynamics of three irrigation strategies, including soil water balance (SWB), measured soil water content (SWC), and a combination of SWB and rain forecasting for the next three days (RF). The area irrigated by the VRI system was delineated into three management zones (zones 1, 2, and 3) based on the available soil water holding capacity (AWC). Based on the seasonal cumulative DP, the zone-specific crop coefficient (Kc) for each zone was quantified to enhance the accuracy of the SWB method. The results indicated that high daily DP rates occurred during the initial and end growing seasons as well as following rainfall and irrigation events during the mid-season. The delay of DP after an intermittent large rainfall was observed in both seasons. The cumulative DP in zone 2 with a medium AWC and a uniform soil profile was 36% less than the mean values of DP for zones 1 and 3. Compared to the SWC and SWB methods, the cumulative DP for the RF treatment was reduced by 10% and 36%, respectively. During both seasons, the maximum DP values were observed in zones 2 and 3 under the SWB methods. The SWC method tended to increase the risk of DP for a coarse profile, whereas a lower sandy content soil tended to increase the risk for the SWB method. The mean Kc values derived based on DP for the initial, mid-season, and end of the late season stages were 0.86, 0.73, and 0.91 for zones 1, 2, and 3, respectively, with a 7% reduction compared to the Kc without considering DP. The seasonal crop water requirement determined by zone-specific Kc was reduced by 31 mm compared with the uniform Kc in different management zones. Our results suggested that the RF method exhibited promise for reducing DP, and the zone-specific Kc values were helpful to enhance the water savings of the SWB method for a VRI system.

A hydrogeological conceptual model for the groundwater dynamics in the ferricretes of Capão Xavier, Iron Quadrangle, Southeastern Brazil

In the Iron Quadrangle (IQ), southeastern Brazil, ferricretes usually overlie the banded iron formations (BIFs) of the Cauê Formation, rocks that not only host the most important iron ore deposits of this region but are also its major groundwater source. Little is known about the water dynamics in ferricretes and therefore how they influence the recharge of the subjacent aquifer (Cauê aquifer). The objective of this research was to identify ferricrete typologies and investigate their water dynamics in the Capão Xavier region, northwest of IQ. Field work consisted of macroscopic description of ferricretes, infiltration tests and multitemporal electrical resistivity surveys. Two ferricrete typologies were distinguished: structured ferricretes, which are older and occur on top of plateaus, and detrital ferricretes of colluvial-alluvial origin, which were deposited downslope and in topographic lows. The structured ferricretes preserve the medium- to high-angle foliation inherited from the underlying BIFs, whereas the detrital ferricretes constitute thick packs subparallel to the topographic surface and are intercalated with argillaceous layers in areas of karstic depressions. The structured ferricretes are more porous (20.8% to 24.4%) than the detrital ferricretes (14.4% to 17.6%), hence they have higher mean basic infiltration rates (8.3x10-6 m/s) than detrital ferricretes (2.8x10-6 m/s). Despite these low mean basic infiltration rates, infiltration advances thanks to the karstic-fissural porosity (fractures and joints widened by karstification), and superficial cavities that are connected to caves in the interface between the ferricrete and the subjacent, less resistant, transition horizon. Karstification is controlled by the subvertical foliation in the structured ferricretes and subparallel layering in the detrital ferricretes. Some factors that favor infiltration and deep percolation of water are superficial rugosity in structured ferricretes, and karstic depressions in both typologies. The recharge of the Cauê aquifer is diachronic, firstly taking place via the karstic-fissural system and later via the ferricrete matrix.

Remediating the Adverse Effects of Treated Wastewater Irrigation by Repeated On‐Surface Surfactant Application

AbstractThe use of treated wastewater (TWW) has gained recognition as an alternative source for freshwater irrigation, and is steadily expanding worldwide. Despite the benefits of freshwater conservation and nutrient richness, there is mounting evidence of TWW adverse effects on soil, yield, and the environment. Irrigation using TWW has resulted in soil water repellency, in which preferential flow pathways and uneven soil water and chemical distribution occur. These increase deep water percolation and chemical leaching, which can lead to soil and groundwater pollution. This study was conducted in a commercial citrus orchard grown on sandy‐loam soil in central Israel and irrigated with TWW, with the aim of investigating the remediation of these adverse effects, by repeatedly spraying a nonionic surfactant on the soil surface. The surfactant application succeeded to turn the soil wettable, diminishing the preferential flow pathways, and rendering the soil water and dissolved chemicals uniformly distributed. The overall water content in the 0–40 cm layer increased, and deep percolation and chemical leaching substantially decreased. The grapefruit yield increase during the two‐year study period increased the water use efficiency. Electrical resistance tomography scans executed during and after irrigation events for two subsequent years revealed that a “soil memory” phenomenon has been developed for water repellent soils, where water flow takes place through previously developed preferential flow pathways in such soils. This study demonstrates that recurrent surfactant application enables a continuous use of TWW, while eliminating most of its prejudicial effects.

A modelling approach and module for salinity management in drip irrigation

The article describes a new modelling approach and module for soil salinity management. The two major objectives of the module are to simulate the seasonal course of the salinity of the soil solution in the active root zone of drip-irrigated crops to assist irrigators to optimise irrigation and salt leaching, and to help evaluate the salt fluxes in the deep percolating water for assessing the longer-term salt load of the irrigated crops on the regional ground and surface water resources. The module is based on the solutions of the DIDAS program for quasi-steady water flow and uptake for various drip irrigation scenarios, and on differentiating the applied water to evaporation from the soil surface, uptake by the plant roots, deep percolation through the root zone that leaches salt out of it, and deep percolation outside of the root zone that does not leach salts. After laying out the rationale behind the suggested approach and outlining the expressions used in the module for evaluating the salinity of the root zone, several sample computations, in silico experiments, are performed to illustrate the module functionality and its potential application, and to serve for sensitivity analysis of the system parameters. Additional investigation is needed into the adequacy of the suggested modelling approach and the developed module to simulate soil salinity in the active root zone. • The module evaluates seasonal courses of root zone salinity in drip-irrigated fields. • It simulates root system development but does not predict plant growth and yields. • It is based on modelling quasi-steady water flow and uptake and salt mass balance. • The deep percolating water are partitioned into two fractions. • One that flows through the root zone and leaches salt out of it, and one that flows around it.

Superabsorbent Polymers (SAPs) Hydrogel: Water Saving Technology for Increasing Agriculture Productivity in Drought Prone Areas: A Review

To improve the soil moisture availability, by reducing the evaporation losses and retaining the moisture in effective rooting zone. The soil application of superabsorbent polymers (SAPs) is found to be the promising methodology in drought prone areas. However, very limited research work done in Indian conditions on this aspect. One of such successfully developed product is ‘Pusa hydrogel’ which is first indigenous semi-synthetic superabsorbent technology for conserving water and enhancing crop productivity and thereby increases the water use efficiency. It performs its wetting or drying cycles over a longer period of time, maintaining its very high water swelling and releasing capacity against soil pressure. Consequently evaporation, deep water percolation and nutrient leaching can be avoided. Under rainfed condition, crops can better withstand drought condition without moisture stress by using hydrogel. Systematic field studies under arid and semi-arid conditions of India are needed to develop appropriate dose, frequency and method of application of different polymers to various crops and to assess economics of use of different polymers.

Modelling of Soil Moisture Movement and Solute Transport in Parts of Malaprabha Command

Abstract Infiltration is one of the most important hydrological process through which water enters the soil surface and plays a significant role in controlling soil water storage, crop yields, irrigation efficiency and solute entry into the soil profile. In agriculture fields, generally, the top soils are enriched with high organic matter and clay, particularly in black soils that promotes sorption, biological degradation and transformation of contaminants. During the process some of the chemicals applied to farm land, move down with the deep percolating water from the root zone and there are likely chances to pollute the underlying ground water. Such instances are reported by locals in areas dominated by black soils of Malaprabha command area. In order to understand the extent of groundwater contamination through chemical fertilizers, insecticides and manures, two agricultural plots (sugarcane and banana plantation) have been identified in parts of Malaprabha command area covering parts of Saundatti, Ramdurg (Belagavi district) and Nargund taluks (Gadag district). Hydraulic properties such as infiltration and hydraulic conductivity were determined in the field. Soil samples were collected and analysed in the laboratory for texture and porosity. The study indicated that the soils of the region are layered in structure. Further, it is noticed that the coarse textured loamy soil is present below the fine textured soils (such as silty loam or clayey loam). Due to the presence of fine soils at the top, the irrigated water get accumulated and the evaporation takes place relatively faster and results in the accumulation of excess salt. It is also noticed that the layered soils have obvious effects on solute transport and salt accumulation in the clay rich soil layer at the interface. The average salt accumulation (Total Nitrogen) observed in the study area within soil profile is 18.7g/kg. The maximum salt accumulation (21.38 g/kg) occurred in the top layer of sugarcane plots followed by banana plantation (19.85 g/kg). It is also noticed that there are remarkable changes in the interlayered soils with reference to water infiltration characteristics and salt leaching intensities. Study revealed the fact that the properties of the soil profile with a silty loam interlayer is better than with a silty clay loam interlayer.

Modelling Projected Changes in Soil Water Budget in Coastal Kenya under Different Long-Term Climate Change Scenarios

The possible impacts that climate change will have on soil water budget and specifically on deep percolation, runoff and soil water content have been investigated using HYDRUS, a methodology based on numerical modelling simulations of vertical water movement in a homogenous soil column on a flat surface. This study was carried out on four typical soil types occurring on the Kenyan coast and the adjacent hinterlands of up to an elevation of 200 m above sea level (m a.s.l.) covered by five weather stations (two dry and three wet stations). Results show that deep percolation and runoff are expected to be higher in 2100 for both Relative Concentration Pathways (RCPs) 2.6 and 8.5 scenarios than they were for the reference period (1986–2005). The average deep percolation is expected to increase by 14% for RCP 2.6 and 10% for the RCP 8.5, while the average runoff is expected to increase by 188% and 284% for the same scenarios. Soil water content is expected to either increase marginally or reduce depend in the same scenarios. The average soil water content is also expected to increase by 1% in the RCP 2.6 scenario and to decrease by 2% in the RCP 8.5 scenario. Increase in deep percolation through clay soil is expected to be the largest (29% in both scenarios), while sandy and sandy clay soil are expected to be the least influenced with an average increase of only 2%. Climate change is expected to impact runoff mostly in sandy soils, whereas the least affected would be clay loam soils. These results further support the assertion that the change in climate is expected to impact the recharge of aquifers by triggering an increase in infiltration under both scenarios.

Effects of irrigation and nitrogen fertilization management on crop yields and long-term dynamic characteristics of water and nitrogen transport at deep soil depths

Appropriate irrigation and nitrogen (N) management practices should be implemented to obtain high grain yields while considering the influence of water and N leaching on groundwater in the intensively cropped winter wheat (Triticum aestivum)-maize (Zea mays L.) rotation system. The calibrated RZWQM2 model was used to explore long-term (1984–2017) effects of irrigation and N fertilization on crop yield, water and nitrogen use efficiency, deep percolation water (DPW), N leaching loss (NLL), and their effects on deep soil layers (2−30 m) in this rotation system in the Jinghui Canal irrigation area of the Guanzhong Plain in China. Results showed that crop yields increased with increasing N rate. The critical N application rates of 140 and 240 kg N ha−1 coupled with 75 and 90 mm of irrigation for maize and wheat, respectively, resulted in high yields (7535 and 8977 kg ha−1), water use efficiency (2.22, 2.07 kg m-3), and nitrogen use efficiency (44.56, 40.78 kg kg−1). The simulated DPW values were 69 and 110 mm for maize and wheat, respectively, and NLL values were 25.36 and 25.47 kg ha−1. Crop yield and NLL for wheat were more sensitive to N application timing than maize yield and NLL, indicating that split N applications of two application times and three application times for maize and wheat, respectively, could be a more effective way of applying N fertilizer. DPW fluxes increased from 0.021-0.024 (varied over the 2−30 m depth) to 0.107-0.110 mm d−1 for irrigation ranging from 60 to 135 mm. The response times for DPW to be observed at the groundwater depth of 30 m could range from one year to more than two years, with DPW velocities of 0.034 and 0.077 m d−1 for 60 and 135 mm irrigation application amounts, respectively. NLL flux increased with added irrigation and N application rate, while decreasing exponentially with soil depth. Annual recharge of NO3-N to the groundwater (0.15–6.2 kg N ha−1) with lower irrigation amounts (60−90 mm) could be neglected, but higher irrigations (≥105 mm) even with lower N application rates could cause groundwater contamination. Therefore, comprehensively considering the effects of irrigation and fertilization practices on grain yields and groundwater could improve the sustainability of the agro-hydrological environment and agricultural production.

Exploring optimal irrigation and nitrogen fertilization in a winter wheat-summer maize rotation system for improving crop yield and reducing water and nitrogen leaching

Irrigation and nitrogen (N) fertilization play important roles in grain yield. However, amounts supplied in excess of crop demand are responsible for water and N leaching during intensive agricultural production. A three-year winter wheat (Triticum aestivum L.)-summer maize (Zea mays L.) rotation experiment involving varied irrigation and N fertilization treatments was conducted in the Jinghui Canal irrigation area of Guanzhong Plain in China. To develop a more sustainable agroecosystem taking into account crop yields, deep percolation and N leaching, the RZWQM2 model was used to simulate crop production. Various irrigation and N fertilization strategies were simulated to obtain high crop yields and to reduce water and N leaching in different precipitation years, using long-term historical weather data spanning 57 years (1961–2017). The simulated soil water and NO3-N content, grain yield, water and nitrogen use efficiencies (with nRMSE values ranging from 5.3–25.1 %), and the simulated crop biomass and N uptake (with RE values ranging from -16.4–18.3 %) were in good agreement with observed data. Simulated LAI values were acceptable (with RMSE ranging from 0.31 to 1.68 and index of agreement, d, ranging from 0.28 to 0.94), with the poorer simulations occurring with water and N stress. Maize seedling stage and wheat jointing stage were the phases most sensitive to water deficit, and optimal irrigation schedules could be adjusted according to variable precipitation and other climate changes. The best irrigation strategies for maize in the Guanzhong Plain were irrigation applied at the seedling stage in wet and normal years, and two irrigations applied at the seedling and jointing stages in dry years. The best irrigation strategies for wheat were two, three, and four irrigations applied in wet, normal, and dry years, respectively. Irrigation at different crop growth stages significantly influenced N leaching and nitrogen use efficiency. Increasing N input led to greater water use efficiency and less deep percolation water. Considering the interactive effects of water and N input on yield, deep percolation, and N leaching, the most appropriate N application rates in all precipitation years were 140 kg N ha-1 for maize and 240 kg N ha-1 for wheat, coupled with the recommended irrigation strategies. Improving water and N management can significantly reduce deep percolation of water and N leaching while maintaining agricultural productivity and environmental sustainability.

Modeling soil water balance and irrigation strategies in a flood-irrigated wheat-maize rotation system. A case in dry climate, China

Demand for irrigation water has been steadily increasing in arid regions where intensification of crop production is supported by flood-irrigation. An assessment of irrigation performance, water productivity, and irrigation schedules is critical to water conservation in dry climates. In this study, we conducted a field experiment to compare soil water balance in a flood-irrigated wheat-maize rotation system during the growing season of 2015–2016. We then modeled the soil water balance and improved irrigation strategies by coupling Hydrus-1D with the CROPWAT model, and using evapotranspiration calculated from climatic data. The calibrated Hydrus-1D model was used to simulate the temporal and spatial variation of evapotranspiration and deep percolation based on measured soil water distribution of soil profiles in the unsaturated zone. Results showed that using soil hydraulic parameters from inversion modeling can simulate soil water flow in multi-layer soil during a crop growing season. Simulation results indicated that about 36.6 and 40.6% (478.6 and 680.1 mm) of total water input in 2015 and 2016, respectively, was consumed by evapotranspiration. Furthermore, simulated deep percolation amounted for approximately 32.3 and 42.9% (403.9 and 696.6 mm) of the total amount of irrigation water in 2015 and 2016, respectively. These results indicated that only a small proportion of irrigation water was used by crops for transpiration. In addition, irrigation performance indicators such as relative water supply, relative irrigation supply, depleted fraction, and overall consumed ratio values indicated poor performance of irrigation practices in the study area. Particularly, crop yields did not increase with increases in irrigation water in flood-irrigated fields during the last ten years. Results of the CROPWAT model indicated that combinations of a fixed irrigation depth and timing, of 40 mm every 10 days, and 50 mm every 10 days were reasonable for wheat and maize, respectively, given the sandy soil in the study area. The improved irrigation strategies will limit water irrigation loss to 20% without significant effects on crop yields. This study provides an alternative approach for estimating deep percolation and crop water requirements supporting management efforts in water conservation in dry climates.

SOIL CONDITIONER EFFECT ON SOIL WETTING PATTERNS UNDER PULSED DRIP IRRIGATION SYSTEM

Optimal drip irrigation design and management depend on soil wetting patterns where, sandy soil under continuous drip irrigation was the depth of wetting pattern is relatively higher than the width that leads to increase deep percolation beyond root zone. Therefore, the study aim to improve drip irrigation efficiency using soil conditioners with pulse drip irrigation. An empirical mathematical model was used to describe soil wetting patterns. The laboratory experiments were conducted on sand soil using soil conditioners named commercially by Composite that contains mixed materials in the rate of 5:1 from local Aswan Clay and Hydrogel (super absorption polymer, SAP) with pulsed drip irrigation at cycle ratio equal 0.5 for different cycles times P (20, 30, 40 and 60 minutes). And also, an empirical model by Al-Ogaidi, et al., (2016) was used to estimate the wetted radius of dripper at the soil surface and at the depth of the wetting pattern. Results demonstrated that using composite with pulse flow technique in sand soil led to increase both soil moisture distribution, moisture percent, and the wetting front advances in horizontal direction more than vertical direction. Percentage of the surface and maximum wetted radius to wetted depth under dripper were increased. Also, the percentage of the soil surface wetted radius for all treatments compared to continuous flow without soil conditioner was increased. Predicted and observed values were compared well to test model applicability in laboratory conditions on the basis of model performance parameters. The result shows the advantage of soil conditioner with pulsed flow method for reducing the deep percolation of water under the root zone, while obtaining a wide horizontal spread of wetting.

Landscape and organismal factors affecting sagebrush‐seedling transplant survival after megafire restoration

Larger and more frequent disturbances are motivating efforts to accelerate recovery of foundational perennial species by focusing efforts into establishing island patches to sustain keystone species and facilitate recovery of the surrounding plant community. Evaluating the variability in abiotic and biotic factors that contribute to differences in survival and establishment can provide useful insight into the relative importance of these factors. In the western United States, severe degradation of the sagebrush steppe has motivated substantial efforts to restore native perennial cover, but success has been mixed. In this study, we evaluated survival of more than 3,000 sagebrush seedlings transplanted on 12 patches totaling 650 ha within a 113,000 ha burn area, and related the survival to organismal and subtaxonomic traits, and to landscape variables. Big sagebrush has high intraspecific diversity attributed to subspecies and cytotypes identifiable through ultraviolet (UV)‐induced fluorescence, length:width of leaves, or genome size (ploidy). Of these organismal traits, survival was related only to UV fluorescence, and then only so when landscape variables were excluded from analyses. The most significant landscape variable affecting survival was soil taxonomic subgroup, with much lower survival where buried restrictive layers reduce deep water infiltration. Survival also decreased with greater slope steepness, exotic annual grass cover, and burn severity. Survival was optimal where perennial bunchgrasses comprised 8–14% of total cover. These soil, topographic, and community condition factors revealed through monitoring of landscape‐level treatments can be used to explain the success of plantings and to strategically plan future restoration projects.

Effect of Soil Texture on Water Movement of Porous Ceramic Emitters: A Simulation Study

Choosing reasonable design parameters for ceramic emitters used in subsurface irrigation is important for reducing the deep percolation of water and improving the water use efficiency. Laboratory experiments and numerical simulations with the HYDRUS-2D software were carried out to analyze the effect of soil texture on the infiltration characteristics of porous ceramic emitters used for subsurface irrigation. HYDRUS-2D predictions of emitter discharge in soil and wetting front are in agreement with experimental results, and the HYDRUS-2D model can be used to accurately simulate soil water movement during subsurface irrigation with ceramic emitters in different soil textures. Results show that soil texture has a significant effect on emitter discharge, soil matrix potential around the emitter, and wetting front. For 12 different soil textures, the aspect ratio of the wetting front is basically between 0.84–1.49. In sandy soil, the wetting front mainly appears as an ellipse; but in the clay, the wetting front is closer to a circle. As irrigation time increases, emitter discharge gradually decreases to a stable value; however, emitter discharge in different texture soils is quite different. In order to improve the crop water use efficiency in sandy soil, soil water retention can be improved by adding a clay interlayer or adding water retention agent, reducing the risk of deep percolation and improving the water use efficiency.