Hydraulic and hydro-salinity behavior of skimming wells under different pumping regimes

Skimming wells are meant to extract top fresh water layer in the fresh-saline aquifer. Their development in the Indus basin occurred through private sector in a technological vacuum. As a result, these wells have some technical, environmental and social constraints, which hinder the sustainability of these wells. As an initial step to improve the well technology, the hydraulic and hydro-salinity responses of the fresh-saline aquifer under different pumping regimes need to be monitored. The present paper reports the hydraulic and hydro-salinity behavior of the Indus basin aquifer in Pakistan under field conditions at farmers’ wells. Two sites, having 6- and 16-strainer wells were monitored during July 2000–December 2001. The 6-strainer well was operated for 4 h with single-, 4- and 6-strainer arrangements and the spatial behaviors of specific drawdown were observed under these arrangements. The 16-strainer well was monitored continuously for the above period. The well discharge, pumped water quality and pumping duration was recorded of every pumping event under farmer’s practice to extract groundwater. The rainfall and temporal water table fluctuation was also recorded at this site. The impact of 24 years of well operation on groundwater quality was observed by comparing the hydro-salinity profiles of 1974 and 1998 under 3-strainer well. The results showed that the specific drawdown was higher for single-strainer and it decreased with the increase in number of strainers in skimming wells and hence reduced the chances of saline-upconing. Each strainer in multi-strainer well contributes equally in well discharge provided the horizontal distances among the strainers are equal. The pumped water quality in fresh-saline aquifer was a very sensitive function of fresh water recharge and pumping duration. It was observed that with the increase in daily operation from 2 to 12 h per day, the pumped quality deteriorated three-folds and there was also 30% reduction in well discharge due to high suction lift. It was observed that continuous operation of a 3-strainer well having discharge of 14 lps over the 24 years had raised the fresh-saline interface (iso-concentration line of 1.5 dS/m) to 9 m. Keeping in review the observations, it is recommended that the daily operation of 4–6 h keep the water quality within marginal limit (<1.5 dS/m) and the pumping operation is also cost-effective with only 15–20% reduction in well discharge for the study area.     

Groundwater quality in CR-V irrigation district (Bardenas I,Spain): Alternative scenarios to reduce off-site salt and nitrate contamination

Irrigated agriculture may negatively affect groundwater quality and increase off-site salt and nitrate contamination. Management alternatives aimed at reducing these potential problems were analysed in the 15498 ha CR-V Irrigation District (Spain) by monitoring 49 wells and modelling the hydrological regime in a representative well of the Miralbueno Aquifer. Groundwaters presented low to moderate electrical conductivity (EC) (mean = 0.89 dS/m) and high [NO₃⁻] (mean = 94 mg/L). The groundwater depth (GWD) during the 2001 hydrological year responded to the annual cycles of precipitation and irrigation as well as to the secondary cycles derived from irrigation scheduling. GWD were consistently simulated by the groundwater BAS-A model. Model results indicate that an increase in irrigation efficiency and the pumping of groundwater for irrigation will decrease GWD and aquifer's discharge by 56–70%, depending on scenarios. These recommendations will save good-quality water in the reservoir, will be beneficially economical to farmers, and will minimize off-site salt and nitrogen contamination.     

Simulation of Hydrosalinity Behavior Under Skimming Wells

The movement of underlying saline water inresponse to freshwater abstraction infresh-saline aquifers is dependent uponaquifer properties, well design andoperational plans. The responses of thesefactors under various well configurationsand pumping modes are important forsustainable freshwater abstraction. In thepresent study, three shallow skimming wellswith different well configurations weremonitored under different pumping modes inthe Indus basin of Pakistan. The field datawere used to calibrate MODFLOW and MT3Dmodels for each well system. The resultsshowed that the selected models have thecapability to simulate both the continuousand intermittent pumping operations inskimming wells. The calibrated models wereused to evaluate the sensitivity of variousaquifers, well design, and operationalparameters. Hydrosalinity of the pumpedwater increased with the increase invertical hydraulic conductivity,longitudinal dispersivity, well abstractionrate, well penetration ratio, and pumpingduration; while increase in horizontalhydraulic conductivity, effective porosity,specific yield, freshwater recharge,transverse dispersivity, and number ofboreholes in multi-borehole skimming wellsdecreased the salinity of the pumpedwater.     

Vulnerability of groundwater resources from agricultural activities in southern Kuwait

Kuwait is an arid country situated in the northwestern corner of the Arabian peninsula, which suffers from limited natural water resources. Groundwater in Kuwait is mostly saline, except for some freshwater lenses in the northern part and some brackish zones existing in the south and southwest. With an annual average rainfall of 120 mm and evapotranspiration of around 2266 mm, the recharge of aquifers by rainfall is negligible. Fresh groundwater lenses with total dissolved solids (TDS) less than 1000 mg/l are exploited for potable purpose, and brackish groundwater with TDS between 1000 and 5000 mg/l is used for irrigation. The objective of this study was to assess the impact of irrigation on the salinity and the drawdown of groundwater in the Al-Wafra farms area in southern Kuwait. As a result of the gradual increase of the groundwater extraction for irrigation, the quality and quantity of the groundwater in the aquifers have been depleted. Water levels in the southern part of Kuwait have declined and the maximum declination of 20 m was observed at the center of the farm area. About 35% of the irrigated water was lost due to evapotranspiration, and the rest infiltrated back to the aquifer through the vadose zone, resulting in an increase in the TDS level in the groundwater up to 14,000 mg/l. Such an increase was observed at several locations within the farming area. As a part of this study, two numerical models were developed to predict the groundwater quality as well as the drawdown. The relation between the well locations, decline in water levels, variations in groundwater quality and the transmissivity distribution were interpreted, and the results of the numerical simulations were compared and scaled with field observations. It is estimated that, in the next 5 years, if irrigation is continued at the present rate, then only about 20% of the existing wells will have a TDS level of less than 7500 mg/l.     

Nitrate contamination of a rural aquifer and accumulation in the unsaturated zone

Groundwater contamination was studied in a rural setting of the Upper Pantanoso Stream Basin (UPSB) in the southeast of Buenos Aires Province, Argentina, where potential contaminant sources include inorganic fertilizer. Nitrate–N concentrations, greater than accepted level for safe drinking-water of 10 mg l⁻¹ were present in 36% of sampled wells and 67% of samples had nitrate concentrations exceeding the background level of 5 mg l⁻¹. Temporal fluctuation of nitrate concentrations in the groundwater was attributed to seasonal fluctuations in recharge and plant growth. Nitrate concentration was measured in deep soil profiles to determine the extent of leaching. Nitrate accumulation in the unsaturated zone of a soil cropped with potatoes was three times higher than the baseline N concentration found in the pasture. The greatest nitrate concentration in the soil profile occurred under irrigated corn where excessive nitrogen was applied. These results show that high fertilization rates and irrigation lead to increased hazards of groundwater pollution.     

Opening floodgates in coastal floodplain drains: effects on tidal forcing and lateral transport of solutes in adjacent groundwater

The effects of opening tidal barriers (floodgates) upon water table levels and lateral transport of solutes adjacent drains was investigated at two sites on a coastal floodplain. The sites had contrasting geomorphology, soil texture and sediment hydraulic properties. The site with lower hydraulic conductivity (0.3–0.9 m day⁻¹) soils (Romiaka) also had a higher elevation and hydraulic gradients towards the drain. While floodgate opening at Romiaka enhanced the amplitude of pre-existing tidal interaction with adjacent shallow groundwater, altered hydraulic gradients and caused some salt seepage, lateral solute movement from the drain was highly attenuated (<10 m). The site with very high hydraulic conductivity soils (Shark Creek; >125 m day⁻¹) had a lower elevation and seasonally fluctuating hydraulic gradients. The introduction of a tidal pressure signal into the drain by opening the floodgate at Shark Creek caused tidal forcing of groundwater over 300 m from the drain. Floodgate opening at this site also caused changes in groundwater hydraulic gradients, leading to incursion of saline drain water into shallow groundwater over 80 m from the drain. Lateral movement of solutes was relatively rapid, due to macropore flow in oxidised acid sulfate soil horizons, and caused substantial changes to shallow groundwater chemical composition. Conversely, when groundwater hydraulic gradients were towards the drain at this site there was substantial lateral outflow of acid groundwater into drains. This study highlights the importance of assessing the hydraulic properties of soils next to drains on coastal floodplains prior to opening floodgates, particularly in acid sulfate soil backswamps, in order to prevent unintended saline intrusion into shallow groundwater.     

Effect of shallow groundwater table on crop water requirements and crop yields

Due to the increasing demand for food and fiber by its ever-increasing population, the pressure on fresh water resources of Pakistan is increasing. Optimum utilization of surface and groundwater resources has become extremely important to fill the gap between water demand and supply. At Lahore, Pakistan 18 lysimeters, each 3.05 m × 3.05 m × 6.1 m deep were constructed to investigate the effect of shallow water tables on crop water requirements. The lysimeters were connected to bottles with Marriotte siphons to maintain the water tables at the desired levels and tensiometers were installed to measure soil water potential. The crops studied included wheat, sugarcane, maize, sorghum, berseem and sunflower. The results of these studies showed that the contribution of groundwater in meeting the crop water requirements varied with the water-table depth. With the water table at 0.5 m depth, wheat met its entire water requirement from the groundwater and sunflower absorbed more than 80% of its required water from groundwater. Maize and sorghum were found to be waterlogging sensitive crops whose yields were reduced with higher water table. However, maximum sugarcane yield was obtained with the water table at or below 2.0 m depth. Generally, the water-table depth of 1.5–2.0 m was found to be optimum for all the crops studied. In areas where the water table is shallow, the present system of irrigation supplies and water allowance needs adjustments to avoid over irrigation and in-efficient use of water.     

Management of declining groundwater in the Trans Indo-Gangetic Plain (India): Some options

The average productivity of rice–wheat sequence is quite impressive in the Trans Indo-Gangetic Plain (India) but these gains are over-shadowed due to declining groundwater, particularly in the areas, where groundwater quality is either good or marginal. The groundwater decline can be reversed through artificial groundwater recharge and by adopting suitable land and water management practices. Groundwater recharge is found technically feasible through vertical shafts conducting water from the ground surface directly to aquifers, after it has been passed through a sand-gravel filter. The recharge rate through this system is almost equal to a shallow cavity/filter well yield (about 11 l/s) and its cost is estimated at about INR 10/100 m³ (1 US$ = 45 INR). Further study in the Kaithal and Karnal districts of Haryana for stabilizing watertable within 6–7 m, which permits continuous use of shallow tubewell technology, indicated that the rice area could be supported at 60% of cultivable command area (CCA) and wheat between 65 and 80% of CCA with the existing management practices. The cultivation of wheat crop is sustainable in larger area, mainly due to its medium water requirement, salt resistance characteristics and consistent market demand resulting in assured returns. There is a possibility of supporting rice at a higher level, if part of the area (up to 10%) is left fallow and used for rainwater conservation and recharge. The fallow area may be subsequently put under early rabi (winter) crops like mustard, gram and other pulses. The effect of varying irrigation and fallowing would increase 23% equivalent wheat yield by changing land and water management practices. The analysis further indicated that the adoption of proposed irrigation management practices might stabilize watertable at desired level of 6–7 m in 10–15 years in high (3–4 m), 5 years in medium (5–10 m) and 40 years in deep (>10 m) watertable areas.     

Potential nitrate losses under different agricultural practices in the pampas region,Argentina

Fertilization is an important cause of groundwater contamination with nitrate in agricultural soils. The objectives of the present work were: (i) to quantify the nitrate leaching in two fertilized and irrigated soils of the Pampas Region, Argentina; (ii) to test the ability of the NLEAP model to predict residual and leached nitrate in those soils. The soils were a Typic Hapludoll and a Typic Argiudoll. The treatments were: natural grassland never ploughed or fertilized; maize with a short history of fertilization; maize with a long history of fertilization; irrigated maize with a long history of fertilization. Both sites were sampled after harvest in two consecutive years to a 3 m depth. Residual nitrate and potential losses below 150 cm were estimated by NLEAP model. The average amount of nitrate (NO₃-N), including values of all treatments, in the upper layer (0–1.5 m) was 128 kg NO₃-N ha⁻¹ in the first sampling date and was consistently lower in the second sampling date (38 kg NO₃-N ha⁻¹). In the deeper layer (1.5–3 m) these values were 80 and 28 kg NO₃-N ha⁻¹ for the first and second sampling date, respectively. Differences between the non-fertilized and the fertilized treatments were significantly smaller in the second sampling date. Obtained results suggest that the rainfall previous to the first sampling was not enough to displace nitrate below 3 m depth. The afterwards heavy rainfall leached nitrate previously accumulated in the soil. Complementary irrigation did not affect nitrate movements. Simulated residual and leached nitrate showed a high correlation with observed values. Nitrate leaching was more associated to rainfall regime and crop yields than to soil type. Simulated residual and leached nitrate showed a high correlation with measured values in both soils, which suggests that NLEAP was appropriate to predict soil nitrate leaching under the studied conditions.     

Effect of drip irrigation on squash (Cucurbita pepo) yield and water-use efficiency in sandy calcareous soils amended with clay deposits

Water research studies in Saudi Arabia clearly showed sever depletion of groundwater. Therefore, the scientifically applied research program related to water saving and conservation in agriculture is essential, where agricultural activities account for more than 85% of the total water consumed. This study aims to investigate the effect of four irrigation levels, two irrigation methods and three clay deposits on water-use efficiency (WUE) of squash and the distributions of salts and roots in sandy calcareous soils. A field experiment was conducted at the college experimental station in 2002 and 2003. It consists of three clay deposits, three rates (CO = 0, C2 = 1.0 and C3 = 2.0%), four irrigation levels (T₁ = 60, T₂ = 80, T₃ = 100 and T₄ = 120% of Eto) using surface (IM1) and subsurface (IM2) drip irrigation.Results indicated that squash fruit yield was significantly increased with the increase in irrigation water level for each season. Generally, WUE values were increased as linearly with applied irrigation water and decreased at the highest irrigation level. Types of clay deposits significantly affected fruit yields compared with the control. The yield increase was 12.8, 8.35 and 6.4% for Khulays, Dhruma and Rawdat clay deposits, respectively. The differences between surface and subsurface drip on fruit yields and WUE were also significant. Results indicated that moisture content of subsurface-treated layer increased dramatically, while salts were accumulated at the surface and away from the emitters in subsurface drip irrigation. Intensive root proliferation is observed in the clay-amended subsurface layer compared with non-amended soil. The advantages of subsurface drip irrigation were related to the relative decrease in salt accumulation in the root zone area where the plant roots were active and water content was relatively higher.     

Modelling the effect of groundwater depth on yield-increasing interventions in rainfed lowland rice in Central Java,Indonesia

Because of drought and nutrient stress, the yields of rainfed lowland rice in Central Java, Indonesia, are generally low and unstable. Variation in groundwater depth can contribute to experimental variability in results of yield-increasing interventions. To test this hypothesis, we used the crop growth simulation model ORYZA2000 to explore the impacts of groundwater depth on the effect of sowing date, tillage, fertiliser-N application and supplementary irrigation on the yield of lowland rice at Jakenan, Central Java, Indonesia. ORYZA2000 was first parameterized and evaluated using data from eight seasons of field experiments between 1995 and 2000. The model adequately simulated the soil water balance, crop growth and grain yield. With shallow to medium groundwater depth (less than 0.5 m deep), rainfed rice yields are close to potential yields with timely sowing in the wet season. With groundwater tables fluctuating mostly between 0.5 and 1.5 m, rainfed yields are 0.5–1 Mg ha⁻¹ lower than potential yields with timely sowing. The decrease in yield with late sowing sets in earlier and proceeds faster with deeper groundwater depths. Deep tillage and supplementary irrigation increase yield more with deep groundwater tables than with shallow groundwater tables, but N fertilisation increases yield more with shallow than with deep groundwater tables. Groundwater depth should be taken into account in the selection of yield-increasing interventions.     

Shallow groundwater contribution to pistachio water use

Pistachio can be grown in the central desert of Islamic Republic (I.R.) of Iran with adverse conditions such as shallow saline groundwater tables. The contribution of water from shallow, saline groundwater to crop water use may be important in such conditions. The objectives of this study were to determine the contributions from shallow, saline groundwater to water use of pistachio seedlings, and how this contribution was affected by groundwater depth, salinitiy, and irrigation conditions. The results indicated that an increase in groundwater depth resulted in significant increase in root depth and significant decrease in seasonal evapotranspiration (ET), transpiration, and groundwater contribution to the plant water use. Non-saline shallow (30–120 cm depth) groundwater under irrigated and non-irrigated conditions contributed 72.4–89.7% and 90.7–100.0% of plant water use, respectively. However, these contributions were 57.2–74.8% and 79.3–100.0% for irrigated and non-irrigated conditions, respectively for saline shallow (30–120 cm depth) groundwater. The effect of groundwater depths (D, cm) on groundwater contributions (q, %) was found to be influenced by the salinity levels of the groundwater (EC, dS m⁻¹). The linear multiple regression equations were q = 97.5 − 1.24(EC) − 0.194(D) and q = 105.9 − 0.48(EC) − 0.154(D) for irrigated and non-irrigated conditions, respectively. The maximum reductions in relative plant dry weight of 80.3% and 44.8% were occurred under non-irrigated condition and saline groundwater depth of 30 cm and non-saline water depth of 60 cm, respectively. Root depth analysis indicated that vertical root growth caused the root to reach a moist layer near the groundwater. A very close to 1:1 relationship between relative reduction in top dry weight (1 − y/y_m) and relative reduction in transpiration (1 − T/T_m) was obtained.     

Irrigation management and hydrosalinity balance in a semi-arid area of the middle Ebro river basin (Spain)

The analysis of irrigation and drainage management and their effects on the loading of salts is important for the control of on-site and off-site salinity effects of irrigated agriculture in semi-arid areas. We evaluated the irrigation management and performed the hydrosalinity balance in the D-XI hydrological basin of the Monegros II system (Aragón, Spain) by measuring or estimating the volume, salt concentration and salt mass in the water inputs (irrigation, precipitation and Canal seepage) and outputs (evapotranspiration and drainage) during the period June 1997–September 1998. This area is irrigated by solid-set sprinklers and center pivots, and corn and alfalfa account for 90% of the 470 ha irrigated land. The soils are low in salts (only 10% of the irrigated land is salt-affected), but shallow (<2 m) and impervious lutites high in salts (average EC_e=10.8 dS m⁻¹) and sodium (average SAR_e=20 (meq l⁻¹)^0.5) are present in about 30% of the study area.The global irrigation efficiency was high (Seasonal Irrigation Performance Index=92%), although the precipitation events were not sufficiently incorporated in the scheduling of irrigation and the low irrigation efficiencies (60%) obtained at the beginning of the irrigated season could be improved by minimising the large post-planting irrigation depths given to corn to promote its emergence. The salinity of the irrigation water was low (EC=0.36 dS m⁻¹), but the drainage waters were saline (EC=7.5 dS m⁻¹) and sodic (SAR=10.3 (meq l⁻¹)^0.5) (average values for the 1998 hydrological year) due to the dissolution and transport of the salts present in the lutites. The discharge salt loading was linearly correlated (P<0.001) with the volume of drainage. The slope of the daily mass of salts in the drainage waters versus the daily volume of drainage increased at a rate 25% higher in 1997 (7.6 kg m⁻³) than in 1998 (6.1 kg m⁻³) due to the higher precipitation in 1997 and the subsequent rising of the saline watertables in equilibrium with the saline lutites. Drainage volumes depended (P<0.001) on irrigation volumes and were very low (194 mm for the 1998 hydrological year), whereas the salt loading was moderate (13.5 Mg ha⁻¹ for the 1998 hydrological year) taking into account the vast amount of salts stored within the lutites. We concluded that the efficient irrigation and the low salinity of the irrigation water in the study area allowed for a reasonable control of the salt loading conveyed by the irrigation return flows without compromising the salinization of the soil’s root-zone.     

Effect of water-saving irrigation on rice yield and water use in typical lowland conditions in Asia

With decreasing water availability for agriculture and increasing demand for rice, water use in rice production systems has to be reduced and water productivity increased. Alternately submerged–nonsubmerged (ASNS) systems save water compared with continuous submergence (CS). However, the reported effect on yield varies widely and detailed characterizations of the hydrological conditions of ASNS experiments are often lacking so that generalizations are difficult to make. We compared the effects of ASNS and CS on crop performance and water use, at different levels of N input, in field experiments in China and the Philippines, while recording in detail the hydrological dynamics during the experiment. The experiments were conducted in irrigated lowlands and followed ASNS practices as recommended to farmers in China. The sites had silty clay loam soils, shallow groundwater tables and percolation rates of 1–4.5 mm per day.Grain yields were 4.1–5.0 t ha⁻¹ with 0 kg N ha⁻¹ and 6.8–9.2 t ha⁻¹ with 180 kg N ha⁻¹. Biomass and yield did not significantly differ between ASNS and CS, but water productivity was significantly higher under ASNS than under CS in two out of three experiments. There was no significant water×N interaction on yield, biomass, and water productivity. Combined rainfall plus irrigation water inputs were 600–960 mm under CS, and 6–14% lower under ASNS. Irrigation water input was 15–18% lower under ASNS than under CS, but only significantly so in one experiment. Under ASNS, the soils had no ponded water for 40–60% of the total time of crop growth. During the nonsubmerged periods, ponded water depths or shallow groundwater tables never went deeper than −35 cm and remained most of the time within the rooted depth of the soil. Soil water potentials did not drop below −10 kPa. We argue that our results are typical for poorly-drained irrigated lowlands in Asia, and that ASNS can reduce water use up to 15% without affecting yield when the shallow groundwater stays within about 0–30 cm. A hydrological characterization and mapping of Asia’s rice area is needed to assess the extent and magnitude of potential water savings.     

Soil N and salinity leaching after the autumn irrigation and its impact on groundwater in Hetao Irrigation District,China

Soil water and salinity are crucial factors influencing crop production in arid regions. An autumn irrigation system employing the application of a large volume of water (2200–2600 m³ ha⁻¹) is being developed in the Hetao Irrigation District of China, since the 1980s with the goal to reduce salinity levels in the root zone and increase the water availability for the following spring crops. However, the autumn irrigation can cause significant quantities of NO₃⁻ to leach from the plant root zone into the groundwater. In this study, we investigated the changes in soil water content, NO₃–N and salinity within a 150 cm deep soil profile in four different types of farmlands: spring wheat (F_W), maize (F_M), spring wheat–maize inter-planting (F_W–M) and sunflower (F_S). Our results showed that (1) salt losses mainly occurred in the upper 60 cm of the soil and in the upper 40 cm for NO₃–N; (2) the highest losses of salt and NO₃–N could be observed in F_W, whereas the lowest losses were found in F_W–M.NO₃–N concentration, pH and electrical conductivity (EC) in the groundwater were also monitored before and after the autumn irrigation. We found that the autumn irrigation caused the groundwater concentration of NO₃–N to increase from 1.73 to 21.6 mg L⁻¹, thereby, exceeding the standards of the World Health Organization (WHO). Our results suggest that extensive development of inter-planting tillage might be a viable measure to reduce groundwater pollution, and that the application of optimized minimum amounts of water and nitrogen to meet realistic yield goals, as well as the timely application of N fertilizers and the use of slow release fertilizers can be viable measures to minimize nitrate leaching.     

Performance of temperate aerobic rice under different water regimes in North China

Since the late 1990s, aerobic rice varieties have been released to farmers in the North China Plain to grow rice as a supplementary-irrigated upland crop to cope with water scarcity. Little is known about their yield potential, water use, water productivity (WP), and flood tolerance. In 2001–2002, experiments with aerobic rice varieties HD502 and HD297 and lowland rice variety JD305 were conducted under aerobic and flooded conditions. Under aerobic conditions, five irrigation treatments were implemented. Under flooded conditions, JD305 yielded up to 8.8 t ha⁻¹, HD502 up to 6.8 t ha⁻¹, and HD297 up to 5.4 t ha⁻¹. Under aerobic conditions, the aerobic varieties yielded higher than the lowland variety. HD502 produced 3–3.5 t ha⁻¹ with 450–500 mm total water input and 5.3–5.7 t ha⁻¹ with 650 mm water input and more. HD297 produced 3–3.5 t ha⁻¹ with 450–500 mm total water input and 4.7–5.3 t ha⁻¹ with 650 mm water input and more. The water productivity of aerobic rice under aerobic conditions was higher or on a par with that of the lowland variety under flooded conditions, reaching values of 0.6–0.8 g grain kg⁻¹ water. The relatively high yields of the aerobic varieties under aerobic soil conditions were obtained under “harsh” conditions for growing rice. The soil contained more than 80% sand, was permeable, and held water above field capacity for a few hours after irrigation only. The groundwater table was deeper than 20 m, the soil moisture content in the rootzone was mostly between 50 and 80% of saturation, and soil moisture tension went up to 90 kPa. We conclude that the aerobic rice varieties HD502 and HD297 are suitable for water-scarce environments, and can stand being periodically flooded.     

Response of safflower (Carthamus tinctorius L.) to saline soils and irrigation: I. Consumptive water use

Salt-tolerant crops can be grown with saline water from tile drains and shallow wells as a practical strategy to manage salts and sustain agricultural production in the San Joaquin Valley (SJV) of California. Safflower (Carthamus tinctorius L.) was grown in previously salinized plots that varied in average electrical conductivity (EC_e) from 1.8 to 7.2 dS m⁻¹ (0–2.7 m depth) and irrigated with either high quality (EC_i<1 dS m⁻¹) or saline (EC_i=6.7 dS m⁻¹) water. One response of safflower to increasing root zone salinity was decreased water use and root growth. Plants in less saline plots recovered more water on average (515 mm) and at a greater depth than in more salinized plots (435 mm). With greater effective salinity, drainage increased with equivalent water application rates. Seed yield was not correlated with consumptive water use over the range of 400–580 mm. Total biomass and plant height at harvest were proportional to water use over the same range. Safflower tolerated greater levels of salinity than previously reported. Low temperatures and higher than average relative humidity in spring likely moderated the water use of safflower grown under saline conditions.     

Drainage water salinity of tubewells and pipe drains:: A case study from Pakistan

Drainage water salinity data from 71 public deep tubewells and 79 pipe drainage units near Faisalabad, Pakistan, were studied. Drainage water salinity of the tubewells and the pipe drains remained approximately constant with time. This was attributed to the deep, highly conductive, unconfined aquifer underlying the area, which facilitates lateral groundwater inflow into the drained areas. Tubewells alongside surface drains showed average electrical conductivity, sodium adsorption ratio, and residual sodium carbonate values of 3.2 dS m⁻¹, 17.2 (meq l⁻¹)^0.5, and 6.4 meq l⁻¹, respectively. For pipe drains, which are situated in areas with comparable conditions, the corresponding values were 2.5 dS m⁻¹, 12.2 (meq l⁻¹)^0.5, and 3.7 meq l⁻¹, respectively. Tubewells have an inferior drainage water quality because they attract water from greater depths, where the water is more saline.     

Water conservation practices for a river valley irrigated with groundwater

Water conservation strategies for center pivot and furrow irrigation in the Central Platte Valley of Nebraska were evaluated using computer simulation. Irrigation requirements, grain yield, return flow and net depletion (gross irrigation minus return flow) of groundwater were simulated for a period of 29 years for Hord and Wood River silt loam soils. Grain yields were simulated for a typical corn variety for non-limiting water supplies (maximum attainable yield), for two levels of deficit irrigation (irrigation limited to certain growing periods), and for dryland conditions. Additional simulations were performed for a short-season corn, grain sorghum, and soybeans. The impacts of tillage practices on water conservation were also investigated.Center pivot irrigation on the Hord silt loam required 75–125 mm/year less water application than furrow irrigation. For the Wood River silt loam, water applications were the same for both irrigation systems. Applied water depths were reduced by an additional 75–125 mm using deficit irrigation with only a small reduction in yield. Return flow to the groundwater was small for well-managed pivots but high for some furrow irrigation systems based on the assumption that all deep percolation returns to the aquifer in the Central Platte Valley. Net depletion (gross irrigation minus return flow) of the groundwater for a center pivot with LEPA was 50 mm (17%) less than a center pivot with impact sprinklers. Ridge till had a net depletion 50 mm (25%) less than conventional tillage (double disk, plant) for furrow systems.     

Irrigation based on a nomogram using soil suction measurements

Pivot-irrigation was managed with tensiometers on a field cropped with sugarcane at Analaiva (west coast of Madagascar). The volumes of water delivered by the pivot were 20 mm or less (expressed in terms of equivalent rain), depending on the stage of the crop. These applications were made when suctions at certain depths attained fixed values: a single value of 500  hPa in the top layer of the soil in the installation and growth stages of the crop, double values (600 hPa at 50 cm, 400 hPa at 150 cm) at the ripening stage.To characterize water movement in the soil, lines of isoflux were calculated from the hydrodynamic properties of the soil, and plotted so that the flux of water determined by the Darcy–Buckingham law would be read on the profile of hydraulic head. Maps of two-dimensional water movement were drawn independently from the data collected by an array of 30 tensiometers crossing a cane row. Before the rainy season, the water consumed by the crop corresponds to the irrigation water. At the ripening stage, an upward flux from the deep layer of the soil (wetted during the previous months of rains) is obtained by the strict management of irrigation.