Groundwater uptake and sustainability of Acacia and Prosopis plantations in Southern Pakistan

Farm woodlots or plantations of salt tolerant trees may provide an economic use or reclamation treatment for salt-affected farmland within the irrigation regions of the Indus Valley, but the hydrological impact and sustainability of such plantations are unknown. Detailed measurements of plantation water use, watertable depth and soil conditions were recorded over 2 years in two small plantations with contrasting soil and groundwater salinity at Tando Jam in the Sindh province of Pakistan. The species monitored were Acacia nilotica, A. ampliceps and Prosopis pallida. Annual water use by 3- to 5-year old A. nilotica was 1248 mm on the severely saline site and 2225 mm on the mildly saline site. Water use by the other species was less than 25% of these rates, but this difference is largely explained by their lower density in terms of sapwood area per hectare. Water use by A. nilotica was considerably greater than annual rainfall, implying uptake of groundwater which was confirmed both by piezometric observations and chloride balance modelling to predict vertical water movement through the root zone. Plantation watertables fell from 1.7 m below surface in March to over 2.9 m in September, then rose again during irrigation of the surrounding farmland. Root zone salt concentrations remained high at the more saline site throughout the monitoring period, but at the less saline site there was evidence of increasing root zone salinity as salt accumulated in areas of the profile subject to root water uptake. Salt concentration in the upper profile decreased as the soil dried and water was absorbed from greater depth. Plantations using saline groundwater may be sustainable if occasional leaching and other salt-removing processes are sufficient to maintain root zone salinity at a level which does not excessively reduce tree growth.     

Groundwater uptake and sustainability of farm plantations on saline sites in Punjab province,Pakistan

Productive tree plantations on degraded land within Pakistan’s irrigation areas may help control salinity by extracting shallow groundwater, but their adoption has been limited by a lack of information on tree–water–salt interactions. Tree growth, water use, climate and soil conditions were monitored between 1994 and 1998 in young plantations of Eucalyptus, Acacia and Prosopis at two locations in Punjab province. Eucalyptus camaldulensis on an irrigated, non-saline site near Lahore showed best growth till the age of 5 years, and an annual water use of 1393 mm. Irrigated Eucalyptus microtheca at this site and unirrigated E. camaldulensis dependent on saline groundwater at Pacca Anna also transpired over 1000 mm of water per year. Basal area growth of Acacia ampliceps at the latter site was similar to E. camaldulensis, but its water use was less. Lowest annual water use of 235 mm was shown by an understocked stand of Prosopis juliflora. Canopy conductance decreased with increasing vapour pressure deficit to a species-dependent minimum value. Results of soil sampling, chloride balance modelling and intensive monitoring of soil solution salinity demonstrated accumulation of salt in the root zone of plantations using saline groundwater. The concentration of stored salt varied seasonally as a result of water table fluctuations and redistribution processes within the unsaturated zone. The apparent limitation of salt accumulation by these processes and the continuing satisfactory growth of the plantations justify cautious support of tree growing as a control measure for shallow water tables and salinisation in Pakistan.     

The ionic composition of the streams of the mid-Murrumbidgee River: Implications for the management of downstream salinity

The Murrumbidgee River catchment is a major region of both dryland and irrigated agricultural production in eastern Australia. The salinity of water in the lower reaches of the river is the subject of concern; changing land management upstream is one option to minimise accessions of salt to the river but this must be done in a way that provides an adequate quantity of water for downstream users and the environment.

We examined 30 years of sporadic data on the ionic composition of water for 7 subcatchments contributing to the mid-Murrumbidgee River and for 2 gauging stations on the river itself. Despite the common local presumption that salinity, measured as electrical conductivity (EC), is primarily due to NaCl from cyclic marine salt, we found that NaCl was the dominant salt in only some streams. The presence of HCO₃⁻'s of Ca²⁺ and Mg²⁺ in all streams, and their dominance in 2 streams, indicates that mineral weathering is also a major contributor to the salt load of water in the catchment. However, Ca²⁺ and Mg²⁺ bicarbonates have limited solubility and so their concentrations will not become a cause of osmotic stress when the water is used for drinking or irrigation. Therefore, in our efforts to prioritise lower order catchments of the Murrumbidgee River for changed land management, it will be necessary to examine the nature of the salts they discharge, not just EC. By distinguishing between Cl⁻/Na⁺ dominated streams and Ca²⁺, Mg²⁺/HCO₃⁻ dominated streams we can refine our search for sources of osmotic stress which might potentially worsen with time. This will enable us to target particular land management units so as to obtain the maximum reduction in downstream salinity with a minimal decrease in flow volume and minimal area of land undergoing changed landuse.     

Hydraulics and salinity profile of pitcher irrigation in saline water condition

The hydraulics of pitcher irrigation in saline water condition was studied in laboratory conditions in terms of flow behaviour of pitcher, soil moisture distribution, wetting front advance and distribution of salt concentration in the soil using different pitcher making materials. The Pitcher Type 1 (PT1) made up of local soil and sand yielded the lowest mean hourly depletion ranging from 0.42 to 0.62% depending on salinity of the water used. It was followed by PT2 made up of local soil, sand and resinous material with a mean hourly depletion of 0.51-0.69% and PT3 with local soil, saw dust and sand with a mean hourly depletion of 0.91-1.02%. In all cases, with the increase in salinity level of the water used (ranging from 5 to 20 dS/m), the depletion rate and moisture content in the soil profile were found to decrease.Similarly, it was found that PT1 yielded the lowest wetting front advance and salt movement followed by PT2 and PT3. It was observed that the wetting front advance in the soil decreased with increasing salinity level of the water. The salt concentration in the soil was minimum near the pitcher and maximum at the soil surface and periphery of the wetted zone. In case of PT1, the maximum salt concentration in the soil profile ranged between 1.09 and 3.88 dS/m using water with a salinity ranging from 5 to 20 dS/m, respectively. Similarly, for PT2 the maximum salt concentration in the soil profile also ranged from 1.09 to 3.88 dS/m and for PT3 from 2.30 to 6.07 dS/m. A paired t-test revealed that the moisture as well as the salt distribution of PT3 differed significantly from PT1 and PT2 at α = 0.05. Even, if the salt concentration remained the same and the moisture content remained within field capacity for PT1 and PT2, PT1 is preferred in comparison to PT2 and PT3 as the pitcher material of PT1 is locally economically available.     

Salinity's influence on boron toxicity in broccoli: I. Impacts on yield, biomass distribution, and water use

Research addressing the interactive effects of the dual plant stress factors, excess boron and salinity, on crop productivity has expanded considerably over the past few years. The purpose of this research was to determine and quantify the interactive effects of salinity, salt composition and boron (B) on broccoli (Brassica oleracea L.) fresh head yield, biomass distribution and consumptive water use. A greenhouse experiment was conducted using a sand-tank system in which salinity-B treatment solutions were supplemented with a complete nutrient solution. Chloride-dominated salinity and salinity characteristic of California's San Joaquin valley (SJV), or sulfate-dominated, were tested at ECw levels of 2, 12 and 19 dS m⁻¹. Each salinity treatment consisted of boron treatments of 0.5, 12 and 24 mg L⁻¹. Plant head yield and shoot biomass were significantly reduced by both salinity and boron. Moreover, there was a significant salinity-boron interaction where increased boron was relatively less detrimental under saline conditions. These results occurred regardless of the salt solution composition (chloride or SJV). We found that an ‘interactive model’ better described our growth response than did a ‘single stressor yield model’. Salinity and boron also affected the distribution of shoot biomass. Regardless of salt type, as salinity increased, the fraction of biomass as leaf tissue increased while the biomass fraction as stems and particularly heads, decreased. However, an increase in B at low or high salinity with the SJV composition, decreased the head biomass fraction. This was not observed at moderate salinity, nor on any plants treated with Cl-dominated salinity. Cumulative evapotranspiration (ET) was also reduced by increased salinity but water use efficiency (WUE) was not. WUE was reduced by increased boron, but only at the low and high salinity levels.     

Long term responses of olive trees to salinity

Water demand for irrigation is increasing in olive orchards due to enhanced yields and profits. Because olive trees are considered moderately tolerant to salinity, irrigation water with salt concentrations that can be harmful for many of fruit tree crops is often used without considering the possible negative effects on olive tree growth and yield. We studied salt effects in mature olive trees in a long term field experiment (1998-2006). Eighteen-year-old olive trees (Olea europaea L.) cv. Picual were cultivated under drip irrigation with saline water composed of a mixture of NaCl and CaCl₂. Three irrigation regimes (i. no irrigation; ii. water application considering soil water reserves, short irrigation; iii. water application without considering soil water reserves and adding a 20% more as a leaching fraction, long irrigation) and three salt concentrations (0.5, 5 or 10 dS m⁻¹) were applied. Treatments were the result of the combination of three salt concentrations with two irrigation regimes, plus the non-irrigated treatment. Growth parameters, leaf and fruit nutrition, yield, oil content and fruit characteristics were annually studied. Annual leaf nutrient analyses indicate that all nutrients were within the adequate levels. After 8 years of treatment, salinity did not affect any growth measurement and leaf Na⁺ and Cl⁻ concentration were always below the toxicity threshold of 0.2 and 0.5%, respectively. Annual and accumulated yield, fruit size and pulp:stone ratio were also not affected by salts. However, oil content increased linearly with salinity, in most of the years studied. Soil salinity measurements showed that there was no accumulation of salts in the upper 30 cm of the soil (where most of the roots are present) because of leaching by rainfall at the end of the irrigation period. Results suggest that a proper management of saline water, supplying Ca²⁺ to the irrigation water, using drip irrigation until winter rest and seasonal rainfall typical of the Mediterranean climate leach the salts from the first 0-60 cm depth, and growing a tolerant cultivar, can allow using high saline irrigation water (up to 10 dS m⁻¹) for a long time without affecting growth and yield in olive trees.     

Estimating potential costs and gains from an aquifer storage and recovery program in Australia

Artificial recharge of aquifer storage can provide water during drought periods, reverse falling groundwater levels and reduce water losses associated with leakage and evaporation, as compared with surface water storage. We examine the technical and economic potential of artificial storage and recovery for drought mitigation in the Murrumbidgee Region of New South Wales, Australia. Potential locations for infiltration basins and injection/recovery wells are identified according to criteria such as water availability, aquifer suitability, recharge potential, and potential to provide a usable resource. The estimated annual artificial recharge potential is 180,000 ML through a combination of injection wells and infiltration basins. The cost estimates for artificial recharge vary from AU$ 62 ML⁻¹ to AU$ 174 ML⁻¹ depending on the choice of recharge method. Underground storage capacity can be developed at less than half the cost of surface storage facilities without undesirable environmental consequences or evaporation losses. The estimated benefits of artificial storage and recovery through infiltration basins are three to seven times the costs, during low allocation years.     

Community attitudes towards water management in the Moore Catchment,Western Australia

The Moore Catchment, which lies to the north of Perth in Western Australia, suffers from a number of problems related to water management. Farmers want to manage salinity and waterlogging problems through the use of drains, but this has possible negative off-farm impacts on both the environment and flood risk. Views on responsibilities for managing water within the catchment differ between farmers, local communities and government agencies. This paper reports the results from surveys of attitudes towards catchment management, for two community groups: residents of Perth and residents of rural towns in the catchment. These surveys elicited general attitudes towards the environment and agriculture, and views on responsibilities for managing the catchment. It also included a choice modelling section, where the attributes under consideration included the area of land under salt and trees, ecological risks to off-farm wetlands and risk of flooding, farm incomes and personal financial contributions to a management fund. Preliminary results indicate that residents of both rural towns and Perth are willing to pay to avoid damage to the natural environment, both on and off-farm, as well as the risk of flooding. Perhaps more surprisingly, whether farmers’ incomes were being negatively affected in a choice set has a very strong impact on the choice made.     

Salinity's influence on boron toxicity in broccoli: II. Impacts on boron uptake, uptake mechanisms and tissue ion relations

Limited research has been conducted on the interactive effects of salinity and boron stresses on plants despite their common occurrence in natural systems. The purpose of this research was to determine and quantify the interactive effects of salinity, salt composition and boron on broccoli (Brassica oleracea L.) performance, particularly, element accumulation, ion interactions and boron uptake processes. A greenhouse experiment was conducted using a sand tank system where salinity-B treatment solutions were supplemented with a complete nutrient solution. Chloride-dominated salinity and salinity characteristic of California's San Joaquin valley (SJV), or sulfate-dominated, were tested at ECw (electrical conductivity of the irrigation water) levels of 2, 12 and 19 dS m⁻¹. Each salinity treatment consisted of boron treatments of 0.5, 12 and 24 mg L⁻¹. Salinity, regardless of salt composition, reduced shoot boron concentration at very high boron concentration (24 mg L⁻¹). However, increased salinity increased shoot boron concentration when external boron concentration was low (0.5 mg L⁻¹). Tissue Ca, Mg, Na, K, S and Cl concentrations were also affected by salinity level, chloride or sulfate salinity composition, and in some cases by substrate boron concentration. Calcium concentrations in shoots were greater for chloride-treated salinity as compared to SJV salinity-treated plants; magnesium concentrations trended opposite and were greater in those treated with SJV salinity. Chloride and sodium shoot concentrations both increased with salinity. Shoot chloride was greater with chloride substrate salinity and shoot sodium was greater with SJV substrate salinity. Using stable isotope analysis of solutions to separate transpiration from evapotranspiration (ET), we found that boron uptake and accumulation in the shoot was not simply the product of mass flow (solution concentration × cumulative transpiration), and the vast majority of the water lost from the tank system was by transpiration (>90%) regardless of treatment. Under low substrate boron, the levels of boron in broccoli shoots could be not accounted for by simple passive uptake and transport in the transpiration stream, which suggests that some energy-dependent process was also occurring. However, under high boron treatments, broccoli plants exhibited a mechanism that restricted boron uptake, transport and accumulation in the shoot.     

Corn crop response under managing different irrigation and salinity levels

Non-uniformity of water distribution under irrigation system creates both deficit and surplus irrigation areas. Water salinity can be hazard on crop production; however, there is little information on the interaction of irrigation and salinity conditions on corn (Zea Mays) growth and production. This study evaluated the effect of salinity and irrigation levels on growth and yield of corn grown in the arid area of Egypt. A field experiment was conducted using corn grown in northern Egypt at Quesina, Menofia in 2009 summer season to evaluate amount of water applied, salinity hazard and their interactions. Three salinity levels and five irrigation treatments were arranged in a randomized split-plot design with salinity treatments as main plots and irrigation rates within salinity treatments. Salinity treatments were to apply fresh water (0.89 dS m⁻¹), saline water (4.73 dS m⁻¹), or mixing fresh plus saline water (2.81 dS m⁻¹). Irrigation treatments were a ratio of crop evapotranspiration (ET) as: 0.6ET, 0.8ET, 1.0ET, 1.2ET, and 1.4ET. In well-watered conditions (1.0ET), seasonal water usable by corn was 453, 423, and 380 mm for 0.89EC, 2.81EC and 4.73EC over the 122-day growing season, respectively. Soil salt accumulation was significantly increased by either irrigation salinity increase or amount decrease. But, soil infiltration was significantly decreased by either salinity level or its interaction with irrigation amount. Leaf temperature, transpiration rate, and stomata resistance were significantly affected by both irrigation and salinity levels with interaction. Leaf area index, harvest index, and yield were the greatest when fresh and adequate irrigation was applied. Grain yield was significantly affected in a linear relationship (r² ≥ 0.95) by either irrigation or salinity conditions with no interaction. An optimal irrigation scheduling was statistically developed based on crop response for a given salinity level to extrapolate data from the small experiment (uniform condition) to big field (non-uniformity condition) under the experiment constraints.     

Water and salt balance at irrigation scheme scale: A comprehensive approach for salinity assessment in a Saharan oasis

Salt balance methods are generally applied in the root-zone and at local scales but do not provide relevant information for salinity management at irrigation scheme scales, where there are methodological impediments. A simple salt balance model was developed at irrigation scheme and yearly time scales and applied in Fatnassa oasis (Nefzaoua, Tunisia). It accounts for input by irrigation, export by drainage and groundwater flow, and provides novel computation of the influence of biogeochemical processes and variations in the resident amount of salt for each chemical component in the soil and shallow groundwater. Impediments were overcome by limiting the depth of the system so that the resident amount of salt that remained was of the same order of magnitude as salt inputs and allowed indirect and reliable estimation of groundwater flow. Sensitivity analyses as partial derivatives of groundwater salinity were carried out according to non-reactive salt balance under steady-state assumption. These analyses enabled the magnitude of the salinization process to be foreseen as a function of hydrological changes linked to irrigation, drainage, groundwater flow and extension of the irrigated area. From a salt input of 39 Mg ha⁻¹ year⁻¹ by irrigation, 21 Mg ha⁻¹ year⁻¹ (54%) and 10 Mg ha⁻¹ year⁻¹ (26%) were exported by groundwater flow and drainage, respectively. 7 Mg ha⁻¹ year⁻¹ (18%) were removed from groundwater by geochemical processes, while a non-significant 2 Mg ha⁻¹ year⁻¹ were estimated to have been stored in the soil and shallow groundwater where the residence time was only 2.7 years. The leaching efficiency of drainage was estimated at 0.77. With a water supply of 1360 mm by irrigation and 90 mm by rainfall, drainage, groundwater flow and actual evapotranspiration were 130, 230, and 1090 mm, respectively. The current extension of date palm plantations and salinization of groundwater resources are expected to significantly increase the salinity hazard while the degradation of the drainage system is expected to be of lesser impact. The approach was successfully implemented in Fatnassa oasis and proved to be particularly relevant in small or medium irrigation schemes where groundwater fluxes are significant.     

Evapotranspiration, crop coefficient and growth of two young pomegranate (Punica granatum L.) varieties under salt stress

Pomegranate (Punica granatum L.) is a drought-hardy crop, suited to arid and semi-arid regions, where the use of marginal water for agriculture is on the rise. The use of saline water in irrigation affects various biochemical processes. For a number of crops, yields have been shown to decrease linearly with evapotranspiration (ET) when grown in salt-stressed environments. In the case of pomegranate, little research has been conducted regarding the effect of salt stress. Our study focused on the responses of ET, crop coefficient (K_c) and growth in pomegranate irrigated with saline water. Experiments were conducted using lysimeters with two varieties of pomegranate, P. granatum L. vars. Wonderful and SP-2. The plants were grown with irrigation water having an electrical conductivity (EC_iw) of 0.8, 1.4, 3.3, 4.8 and 8 dS m⁻¹. Plants were irrigated with 120% of average lysimeter-measured ET. Seasonal variation in ET, crop coefficient (K_c) and growth were recorded. Variation in daily ET was observed 1 month after initiation of the treatments. While significant seasonal ET variation was observed for the EC-0.8 treatment, it remained more stable for the EC-8 treatment. Salinity treatment had a significant effect on both daily ET (F = 131, p < 0.01) and total ET (F = 112.68, p = 0.001). Furthermore, the electrical conductivity of the drainage water (EC_dw) in the EC-8 treatment was five times higher than that of the EC-0.8 treatment in the peak season. Fitting the relative ET (ET_r) to the Maas and Hoffman salinity yield response function showed a 10% decrease in ET per unit increase in electrical conductivity of the saturated paste extract (EC_e) with a threshold of 1 dS m⁻¹. If these parameters hold true in the case of mature pomegranate trees, the pomegranate should be listed as a moderately sensitive crop rather than a moderately tolerant one. Fitting 30-day interval ET_r data to the Maas and Hoffman salinity yield response function showed a reduction in the slope as the season progressed. Thus using a constant slope in various models is questionable when studying crop-salinity interactions. In addition, both of the varieties showed similar responses under salt stress. Moreover, the calculated value of K_c is applicable for irrigation scheduling in young pomegranate orchards using irrigation water with various salinities.     

Long-term growth, water consumption and yield of date palm as a function of salinity

Actual measurements of water uptake and use, and the effect of water quality considerations on evapotranspiration (ET), are indispensable for understanding root zone processes and for the development of predictive plant growth models. The driving hypothesis of this research was that root zone stress response mechanisms in perennial fruit tree crops is dynamic and dependent on tree maturity and reproductive capability. This was tested by investigating long-term ET, biomass production and fruit yield in date palms (Phoenix dactylifera L., cv. Medjool) under conditions of salinity. Elevated salinity levels in the soil solution were maintained for 6 years in large weighing-drainage lysimeters by irrigation with water having electrical conductivity (EC) of 1.8, 4, 8 and 12 dS m⁻¹. Salinity acted dynamically with a long-term consequence of increasing relative negative response to water consumption and plant growth that may be explained either as an accumulated effect or increasing sensitivity. Sensitivity to salinity stabilized at the highest measured levels after the trees matured and began producing fruit. Date palms were found to be much less tolerant to salinity than expected based on previous literature. Trees irrigated with low salinity (EC = 1.8 dS m⁻¹) water were almost twice the size (based on ET and growth rates) than trees irrigated with EC = 4 dS m⁻¹ water after 5 years. Fruit production of the larger trees was 35-50% greater than for the smaller, salt affected, trees. Long term irrigation with very high EC of irrigation water (8 and 12 dS m⁻¹) was found to be commercially impractical as growth and yield were severely reduced. The results raise questions regarding the nature of mechanisms for salinity tolerance in date palms, indicate incentives to irrigate dates with higher rather than lower quality water, and present a particular challenge for modelers to correctly choose salinity response functions for dates as well as other perennial crops.     

Effect of brackish water irrigation and straw mulching on soil salinity and crop yields under monsoonal climatic conditions

Fresh water shortages are severally restricting sustainable agriculture development in the North China Plain. The scarcity of fresh water has forced farmers to use brackish water from shallow underground sources, which helps to overcome drought and increase crop yields but also increases the risk of soil salinization. To identify safe and effective ways of using brackish water in this region, field experiments were conducted to evaluate the effect of brackish water irrigation and straw mulching on soil salinity and crop yield in a winter wheat-summer maize double cropping system. The experiment was in a split-plot design. Six rates of straw mulching (0, 4.5, 6.0, 7.5, 15.0 and 30.0 Mg/ha) were assigned to the main plots and two irrigation water qualities (i.e. brackish water with salt content of 3.0-5.0 g/L and fresh water with only 1.27 g salt/L) were applied to subplots. The brackish water irrigation significantly increased the salt content at different soil depths in the upper 1 m soil layer during the two growing seasons. Straw mulching affected the vertical distribution of salt in the brackish water irrigation plots and the average salt content of straw mulch treatments (4.5, 6.0, 7.5, 15.0 and 30.0 Mg/ha) within the 0-20, 20-40 and 0-100 cm soil depths was 10.2, 14.0 and 1.8% lower than that without straw mulch (A₀). No salt accumulation occurred to a depth of 1 m in the brackish water irrigation plots and there was no correlation between the value of SAS (salt accumulated in 1 m of soil) and straw mulch rate. In 2000 and 2001, the salt content within the 0-40 cm soil layer in brackish water irrigation plots increased due to high evaporation rates during April-June, and then decreased up to September as salts were leached by rain. For the fresh water irrigation plots, the salt content remained relatively stable. Straw mulching affected the salt content in the 0-40 cm soil layer in brackish water irrigation plots in different periods of 2000 and 2001, but no correlation between salt content and straw mulch rates was observed except in September of 2000. Unlike for wheat, the yield of maize increased as the straw mulch rate increased according to the equation, y = 0.1589x + 5.3432 (R² = 0.6506). Our results would be helpful in adopting brackish water irrigation and straw mulching in ways that enhance crop yields and reduce the risk of soil salinization. However, long-term effects of brackish water irrigation and straw mulching on soil salinity and crop yield need to be further evaluated for sustainability of the system.     

Ameliorative effects of inoculation with the plant growth-promoting rhizobacterium Pseudomonas sp. DW1 on growth of eggplant (Solanum melongena L.) seedlings under salt stress

The objective of this work was to evaluate the effect of inoculation with the plant growth-promoting rhizobacterium Pseudomonas sp. DW1 on eggplant (Solanum melongena L.) growth, mineral uptake and activities of the antioxidant enzymes including superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) of plant leaves under salinity stress. The study was conducted in pot experiments using eggplant (S. melongena L., cv. Yinjia) and a coastal soil. The NaCl concentration of the coastal soil was 0.57 g (kg soil)⁻¹. Four NaCl levels were tested: 0.57, 1.0, 2.0, and 3.0 g NaCl (kg soil)⁻¹, by adding NaCl to soil, respectively. Pseudomonas-inoculated seeds had an increase in the germination percentage over its non-inoculated seeds under salinity. Salinity negatively affected growth of eggplant; however, plants inoculated with Pseudomonas sp. DW1 grew to a significantly greater extent than plants that were not treated with this bacterium. Salinity significantly decreased K⁺ concentration, increased Na⁺ concentration, and did not significantly decrease Ca²⁺ content in shoots of eggplants. Inoculating with Pseudomonas sp. DW1 increased shoot Ca²⁺ of eggplant compared to the non-inoculating eggplant plants under salinity. Inoculating treatments with Pseudomonas sp. DW1 had no effect on shoot Na⁺ concentration in 0.57 and 1 g (kg soil)⁻¹ NaCl, but there were significant decreases in inoculated treatments than in non-inoculated ones at 2 and 3 g (kg soil)⁻¹ NaCl. Salinity decreased SOD activities and increased POD activities, and inoculated Pseudomonas sp. DW1 had an increase effect on SOD activity in the leaves of eggplants. Alteration of mineral uptake and increase in the antioxidant enzyme activities may be two mechanisms for the alleviation of salt stress. Based on the results of the experiment reported herein, the use of the plant growth-promoting rhizobacterium treatment may provide a means of facilitating plant growth under salt stress.     

Water allocation practices among smallholder farmers in the South Pare Mountains, Tanzania: The issue of scale

The impact of ambitious water sector reforms, that have been implemented in many countries, has not been uniform, especially in Africa. It has been argued that the disconnect between the formal statutory reality at national level and what is happening on the ground may have widened rather than shrunk. There is, therefore, a renewed interest in local water allocation arrangements and how they function. This study looks at water sharing practices and agreements among smallholder farmers in Makanya catchment (300 km²), which is part of Pangani river basin (42,200 km²) in northern Tanzania. Existing water sharing agreements have been studied in the Vudee sub-catchment (25 km²), which has about 38 irrigation furrows of which 20 have micro-dams. Five micro-dams are located at the downstream side of the sub-catchment. At the outlet of the Makanya catchment, farmers practice spate irrigation, using the residual flows from the highlands to irrigate.Based on interviews with smallholder farmers and supported by hydrological data water sharing agreements were found to exist among irrigators using the same furrow, among furrows using the same river and at sub-catchment scale. Some agreements date back to the 1940s. They mostly specify water sharing on a rotational basis at all three scales. No water sharing agreements were found at catchment scale, such as between the water users in Vudee sub-catchment and Makanya village.The study concludes that, as a result of the increase in demand for a diminishing resource, tradeoffs between upstream and downstream water uses have emerged at an increasingly larger spatial scale. At the catchment scale, downstream water users have changed their practices to accommodate the changes in the flow. Currently these claims for water do not clash as upstream water users use the base flow (which does not reach downstream anymore) and downstream water users utilise the flood flows. The water sharing arrangements at sub-catchment scale are negotiated through the social networks of the smallholder farmers and are therefore build on the social ties between the communities. However, at catchment scale, the social ties appear relatively weak in addition to the hydrological disconnect; these links are possibly too weak to build new water sharing arrangements on. It may therefore be necessary to involve more formal levels of government, such as Pangani Basin Water Office, to facilitate the negotiation process and create awareness on the inter-linkages of various water uses at catchment scale.     

Salinity dynamics of wetland ditches receiving drainage from irrigated agricultural land in arid and semi-arid regions

Agricultural drainage ditches are considered as wetland ecosystems when they possess the characteristic hydrology, soil and vegetation of wetlands. In arid and semi-arid regions, wetlands receiving agricultural drainage have to cope with the conservative nature of salts leached from soils. Excessive accumulation of salts in wetlands may threaten the ecological functions of the system, thus endanger the sustainability of the drainage disposal system and the productivity of the farmlands. Based on the salt and water balance in a farmland drainage and wetland disposal system in arid regions, this paper presents a thorough investigation on salinity dynamics of wetland ditches receiving agricultural drainage. Theoretical equations were derived to describe salinity changes in water and soils of wetlands under both equilibrium and pre-equilibrium conditions; a case example was then used to display model predictions of salinity variations over time under different salinity management goals. The example wetlands are de facto drainage ditches that possess wetland characteristics, and the ditch to farmland area ratio is 9.1%. The results showed that salt as a conservative substance will eventually concentrate in the ditches to a very high level if there is little outflow discharge; but the salt accumulation process may develop over a relatively long time, which opens a time window for management practice, such as flushing the salts when fresh water is available. By assuming different threshold salinity levels in the ditches, the proposed analytical models were used to predict time intervals when fresh water recharge is needed to bring down the salinity level in the ditches. For the study area under current drainage practice, the predicted outflow to inflow ratio for salinity was 58.2% and reached an equilibrium level of 9.60 g L⁻¹ in the ditches; salinity levels in the ditches reached threshold values of 5, 7 and 9 g L⁻¹, in about 1, 4 and 12 years, respectively. Salinity analysis showed that the salt retention capacity of the ditch soil is limited, the soil salinity varied according to the ditch water; salt removal through plant uptake and harvest was insignificant. This study indicates that although salt concentration in wetlands receiving agricultural drainage may eventually build up to a critical level, timely recharge with fresh water may bring down salt content in the wetlands and sustain adequate environmental and ecological functions of such a drainage disposal system in arid and semi-arid regions.     

Effect of sodium and nitrogen on yield function of irrigated maize in southern Portugal

Salinization and nitrate leaching are two of the leading threats to the environment of the European Mediterranean regions. Inefficient use of water and fertilizers has led to a nitrate increase in the aquifers and reduction in crop yields caused by salts. In this study, a triple emitter source irrigation system delivers water, salt (Na⁺), and fertilizer (N) applications to maize (Zea mays L.). The objective of the study was to evaluate the combined effect of saline water and nitrogen application on crop yields in two different textured soils of Alentejo (Portugal) and to assess if increasing salinity levels of the irrigation water can be compensated by application of nitrogen while still obtaining acceptable crop yield. Maximum yield was obtained from both soils with an application of 13 g m⁻² of nitrogen. Yield response to Na⁺ application was different in the two studied soils and depended on the total amount of Na⁺ or irrigation water applied. No significant interaction was found between nitrogen and sodium, but a positive effect on maize yield was observed in the medium textured soil for amounts of Na⁺ less than 905 g m⁻² when applied in the irrigation water.     

Effects of irrigation water salinity and electrostatic water treatment for sugarcane production

Excess salinity in irrigation water reduces sugarcane yield and juice quality. This study was conducted to compare the effect of irrigation with water of 1.3 dS m⁻¹ vs. 3.4 dS m⁻¹ on sugarcane yield and quality, and to evaluate whether an electrostatic conditioning treatment of the water influenced the salt effects. The study was conducted in a commercial field divided into large plots ranging from 1.0 to 1.2 ha in size. Cane and sugar yields were reduced approximately 17% by the 3.4 dS m⁻¹ water compared to the 1.3 dS m⁻¹ water, but juice quality parameters were not affected. Conditioning of the irrigation water using a device called an ‘electrostatic precipitator’ which claimed to affect various water properties had no effect on cane yield, juice quality or soil salinity levels. The detrimental effect of the high salt irrigation water was somewhat less than might be expected, probably due to good late summer rainfall which may have flushed the root zone from the excessive salts.