Presence Of Shallow Groundwater Research Articles

Role of Soil Compaction on Salt Dynamics in the Presence of Shallow Groundwater: A Combined Experimental and Modeling Study

Role of Soil Compaction on Salt Dynamics in the Presence of Shallow Groundwater: A Combined Experimental and Modeling Study

Assessment of acetochlor use areas in the sahel region of Western Africa using geospatial methods

The goal of this study was to determine the co-occurrence between acetochlor use on crops and potentially vulnerable soils in the Permanent Interstate Committee for Drought Control in the Sahel region of Western Africa. Acetochlor, a pre-emergence herbicide, is used primarily on row crops and has the potential to reach groundwater or surface water following a rain event shortly after application. Off-field transport is often determined by soil properties; therefore, soils within potential use areas were assessed and mapped to establish areas with soils vulnerable to leaching and/or runoff. Corn and cotton production areas were used as surrogate crops for high potential use areas of acetochlor within areas identified using GlobCover land use data and the Spatial Production Allocation Model agricultural statistics data. The geospatial analysis identified approximately 462 million ha of potentially vulnerable soils in the Sahel region of which 65.7 million ha are within agricultural areas. An adjustment for corn and cotton production areas showed that 2.2 million ha or 3.3% of agricultural fields could have potential restrictions for acetochlor use. Approximately 0.159 million ha of soils or 0.24% of agricultural fields are in the presence of shallow groundwater, defined by depth < 9 m. In addition, 0.0128 million ha or 0.02% were determined to be adjacent to surface water bodies. To understand the uncertainty associated with the use of specific land cover datasets, an overlay assessment was conducted using alternative data sources. Overlap between selected land cover datasets in the Sahel region varies and ranges from 24.7% to 75.5% based on a merged 2009 GlobCover and CCI LC datasets. In comparison with the merged 2005 and 2009 GlobCover dataset, the cropland overlaps range from 38.9% to 85.0%. This demonstrates that the choice of land cover dataset can have a significant impact on a spatial assessment. Results from this assessment demonstrate that only a small fraction of vulnerable agricultural soils across the region may be a risk for contamination by acetochlor of groundwater or surface resources, based on product label recommendations. Given the availability of spatial data in a region, the methods contained herein may additionally be used in other localities to provide similar information that can be helpful for water quality management.

Effect of deficit irrigation and different saline groundwater depths on yield and water productivity of quinoa

Water scarcity and salinity are two important limitations for agricultural production. Interaction effects of deficit irrigation and shallow groundwater on crop water use could increase water productivity in arid and semi-arid areas. Quinoa is a traditional Andean seed crop that has been introduced all around the world. However, response of quinoa as a salinity and drought tolerant crop to shallow saline groundwater under deficit irrigation has not been studied. Therefore, the aim of this study was to investigate the influence of saline groundwater depths, GD (0.3, 0.55, and 0.80m) and deficit irrigation, DI (80, 55 and 30% of full irrigation, FI) on growth, yield and water productivity of quinoa and groundwater contribution (GWC) to its water use in lysimeters under greenhouse conditions. Results indicated that 70% reduction of the full irrigation water resulted in only 36% reduction in seed yield (SY) as compared with maximum SY (2.1Mgha−1 at 0.80m GD with 0.80FI), whereas water productivity based on SY (WUEIseed) increased 12%. Shoot dry matter (SDM) is not sensitive to water deficit and reducing the irrigation volume from 0.80FI to 0.30FI resulted in only 8% decrease in SDM in presence of shallow groundwater. It is concluded that at moderate deficit irrigation (0.80FI) shallow groundwater should be maintained at 0.55m or higher to obtained maximum SY; however, in places with shallow groundwater (0.30m), deficit irrigation should be applied in order to achieve higher SY. On average, 27% and 41% reduction in GWC was observed by increasing GD from 0.30 to 0.55m and 0.30 to 0.80m, respectively. GWC/ET ranged from 0.40 to 0.72 for 0.80FI, 0.46 to 0.75 for 0.55FI and 0.51 to 0.80 for 0.30FI. Finally, contour plot was developed to show the combined effect of DI and GD on GWC/ET. The boundary for groundwater contribution to quinoa ET is GD=0.55SWD+1.22 (SWD is the soil water depletion fraction of total available water). Results indicated that 210mm of ET is required to initiate SY production for quinoa in greenhouse conditions and transpiration efficiency (the ratio of SDM to the seasonal transpiration) for quinoa dry matter production is 0.028Mgha−1mm−1. Seed and dry matter yield response factor to water stress indicated that SY is more sensitive to water stress, followed by root dry matter (RDM) and SDM.

Soil surface N balances and soil N content in a clay-loam soil under Irish dairy production systems

This study evaluated the effect of a dairy system involving grazing over the winter on a soil surface N balance (SSB) and soluble N content in a clay loam soil in comparison with early spring calving systems. The SSBs were calculated for each paddock within three dairy systems for 2 years. Inputs included N entering the soil in fertilizer, slurry, excreta, atmospheric deposition and biological N fixation. Outputs consisted of N leaving the soil in harvested and grazed herbage. Nitrogen surplus was calculated as a difference between N inputs and outputs. Soluble N was assessed in soil extracts at three depths to 0.9 m. The management of the systems resulted in N surplus from 113 to 161 kg N ha−1 year−1 and N use efficiency of the soil component from 63 to 72 % without significant variation between the systems. The dairy system had no effect on soil N content as its variation was likely buffered by inherent soil properties (heavy texture, high C, pH) and the presence of shallow groundwater. The biochemical anaerobic reduction processes (i.e. denitrification) likely ensured soil oxidised N consistently low (<20 kg ha−1). Consequently, the system involving grazing over the winter on these soils did not create an additional environmental pressure via N losses to groundwater and N2O emissions compared with early spring calving systems. The size of soil inorganic N pools was mainly controlled by the hydrological factors and soil temperature, which are the most important factors controlling microbial activity, biochemical processes and leaching.

Survival and growth of perennial halophytes on saltland in a Mediterranean environment is affected by depth to watertable in summer as well as subsoil salinity

Farmers need methods for assessing the capability of saltland for productive use based on characteristics that are readily measurable at the paddock scale. We conducted experiments on saltland transects with gradients of salinity and depth to watertable at three sites in south-western Australia. Each was planted with five perennial species with at least some salt tolerance: samphire (Tecticornia mellaria K.A.Sheph.), river saltbush (Atriplex amnicola Paul G.Wilson), small leaf bluebush (Maireana brevifolia (R.Br.) Paul G.Wilson), saltwater couch (Paspalum vaginatum Sw.), and Rhodes grass (Chloris gayana Kunth). Survival and growth of species was related to depth to watertable in summer and average subsoil (0.25–0.50 m depth) electrical conductivity of the saturation extract (ECe). It has been hypothesised that plant zonation on land affected by dryland salinity is affected by the level of salinity and waterlogging on sites. While plant survival ≥60% could be associated with particular ranges of depth to watertable and soil salinity, our data suggest that the most important factor affecting survival and growth was the presence of shallow groundwater in summer. The range of depths to watertable in summer associated with ‘good survival’ (≥60%) was 0.7–1.0 m with samphire, 0.7–1.6 m with saltwater couch, 0.8–1.5 m with Rhodes grass, 0.7–2.4 m with river saltbush, and 0.9–2.4 m with small leaf bluebush. The subsoil ECe (95% confidence interval) associated with ‘good survival’ was 5–14 dS/m for Rhodes grass, 6–11 dS/m for small leaf bluebush, 7–11 dS/m for river saltbush, 6–16 dS/m for saltwater couch, and 27–65 dS/m for samphire. Growth of the perennial grasses was strongly affected by the presence of a shallow watertable in summer; the size of saltwater couch and Rhodes grass increased many-fold as watertable depths decreased from ~1.3 to 0.9 m from the soil surface.

Simple physics-based models of compensatory plant water uptake: concepts and eco-hydrological consequences

Abstract. Many land surface schemes and simulation models of plant growth designed for practical use employ simple empirical sub-models of root water uptake that cannot adequately reflect the critical role water uptake from sparsely rooted deep subsoil plays in meeting atmospheric transpiration demand in water-limited environments, especially in the presence of shallow groundwater. A failure to account for this so-called "compensatory" water uptake may have serious consequences for both local and global modeling of water and energy fluxes, carbon balances and climate. Some purely empirical compensatory root water uptake models have been proposed, but they are of limited use in global modeling exercises since their parameters cannot be related to measurable soil and vegetation properties. A parsimonious physics-based model of uptake compensation has been developed that requires no more parameters than empirical approaches. This model is described and some aspects of its behavior are illustrated with the help of example simulations. These analyses demonstrate that hydraulic lift can be considered as an extreme form of compensation and that the degree of compensation is principally a function of soil capillarity and the ratio of total effective root length to potential transpiration. Thus, uptake compensation increases as root to leaf area ratios increase, since potential transpiration depends on leaf area. Results of "scenario" simulations for two case studies, one at the local scale (riparian vegetation growing above shallow water tables in seasonally dry or arid climates) and one at a global scale (water balances across an aridity gradient in the continental USA), are presented to illustrate biases in model predictions that arise when water uptake compensation is neglected. In the first case, it is shown that only a compensated model can match the strong relationships between water table depth and leaf area and transpiration observed in riparian forest ecosystems, where sparse roots in the capillary fringe contribute a significant proportion of the water uptake during extended dry periods. The results of the second case study suggest that uncompensated models may give biased estimates of long-term evapotranspiration at the continental scale. In the example presented here, the uncompensated model underestimated total evapotranspiration by 5–7% in climates of intermediate aridity, while the ratio of transpiration to evaporation was also smaller than for the compensated model, especially in arid climates. It is concluded that the parsimonious physics-based model concepts described here may be useful in the context of eco-hydrological modeling at local, regional and global scales.

The resource potential of in-situ shallow ground water use in irrigated agriculture: a review

Shallow ground water is a resource that is routinely overlooked when water management alternatives are being considered in irrigated agriculture. Even though it has the potential to provide significant quantities of water for crop use under the proper conditions and management. Crop water use from shallow groundwater is affected by soil water flux, crop rooting characteristics, crop salt tolerance, presence of a drainage system, and irrigation system type and management. This paper reviews these factors in detail and presents data quantifying crop use from shallow ground, and describes the existing state of the art with regard to crop management in the presence of shallow ground water. The existing data are used to determine whether in-situ crop water use from shallow ground water is suitable for a given situation. The suggested methodology uses ratios of ground water electrical conductivity to the Maas–Hoffman yield loss threshold values, the day to plant maturity relative to plant growth period, and the maximum rooting depth relative to the nearly saturated zone. The review demonstrates that for in-situ use to be feasible there has to be good quality ground water relative to crop salt tolerance available for an extended period of time. Shallow ground water availability is one area that can be managed to some extent. Crop selection will be the primary determinant in the other ratios.

Managing subsurface drip irrigation in the presence of shallow ground water

A 3-year project compared the operation of a subsurface drip irrigation (SDI) and a furrow irrigation system in the presence of shallow saline ground water. We evaluated five types of drip irrigation tubing installed at a depth of 0.4 m with lateral spacings of 1.6 and 2 m on 2.4 ha plots of both cotton and tomato. Approximately 40% of the cotton water requirement and 10% of the tomato water requirement were obtained from shallow (<2 m) saline (5 dS/m) ground water. Yields of the drip-irrigated cotton improved during the 3-year study, while that of the furrow-irrigated cotton remained constant. Tomato yields were greater under drip than under furrow in both the years in which tomatoes were grown. Salt accumulation in the soil profile was managed through rainfall and pre-plant irrigation. Both drip tape and hard hose drip tubing are suitable for use in our subsurface drip system. Maximum shallow ground water use for cotton was obtained when the crop was irrigated only after a leaf water potential (LWP) of −1.4 MPa was reached. Drip irrigation was controlled automatically with a maximum application frequency of twice daily. Furrow irrigation was controlled by the calendar.

Water Quality as Design Criterion in Drainage Water Management Systems

In the past, irrigation and drainage systems were designed and managed as separate entities. As water supplies become scarce and environmental restrictions increase, there will be a demand for the integrated design and management of irrigation and drainage systems. This type of system will make optimum use of existing water supplies and should reduce the impact of return flow on the environment. Modifications in current drainage design practice are presented that will facilitate integrated management. Recommended modifications include changing the design minimum water table depth from 1.2 to 0.9 m and the depth of drains from 2.4 to 1.5 m. These changes, coupled with either improved irrigation management or the incorporation of crop water use from shallow ground water, will result in approximately the same drain spacings as calculated using the USBR transient design procedure. Adopting the new drain depth criterion should result in less drain water and lower salt loads being discharged. These concepts were demonstrated with simulations using a drainage system designed for a cotton crop growing in the presence of shallow ground water.

Managing irrigation and drainage systems in arid areas in the presence of shallow groundwater: case studies

Two field studies were conducted on the west side of the San Joaquin Valley of California to demonstrate the potential for integrated management of irrigation and drainage systems. The first study used a modified cotton crop coefficient to calculate the irrigation schedule controlling the operation of a subsurface drip system irrigating cotton in an area with saline groundwater at a depth of 1.5 m. Use of the coefficient resulted in 40% of the crop water requirement coming from the groundwater without a loss in lint yield. The second study evaluated the impact of the installation of controls on a subsurface drainage system installed on a 65 hectare field. As a result of the drainage controls, 140 mm less water was applied to the tomato crop without a yield loss. A smaller relative weight of tomatoes classified as limited use, was found in the areas with the water table closest to the soil surface.