Irrigation with saline water in the reclaimed marsh soils of south-west Spain: impact on soil properties and cotton and sugar beet crops

The drained and irrigated marshes in south-west Spain are formed on soils of alluvial origin from the ancient Guadalquivir river estuary. The most important characteristics of these soils are the high clay content (about 70%), high salinity, and a shallow, extremely saline, water table. The reclaimed area near Lebrija, called Sector B-XII (about 15,000 ha), has been under cultivation since 1978. Some years, however, water supply for irrigation is limited due to drought periods. The objective of this work was to evaluate the effects of irrigation with high and moderately saline waters on soil properties and growth and yield of cotton and sugar beet crops. The experiments were carried out during 1997 and 1998 in a farm plot of 12.5 ha (250 m×500 m) in which a drainage system had been installed, consisting of cylindrical ceramic sections (0.3 m long) forming pipes 250 m long, buried at a depth of 1 m and spaced at intervals of 10 m. These drains discharge into a collecting channel perpendicular to the drains. Two subplots of 0.5 ha (20 m×250 m) each were selected. In 1997 cotton was growing in both subplots, and irrigation was applied by furrows. One subplot (A) was irrigated with fresh water (0.9 dS m⁻¹) during the whole season, while in the other subplot (B) one of the irrigations (at flowering stage) was with water of high salinity (22.7 dS m⁻¹). During 1998 both subplots were cropped with sugar beet. Subplot A was irrigated with fresh water (1.7 dS m⁻¹) during the whole season, while in subplot B two of the irrigations were with moderately saline water (5.9–7.0 dS m⁻¹). Several measurement sites were established in each subplot. Water content profile, tensiometric profile, water table level, drainage water flow, soil salinity, and crop development and yield were monitored. The results showed that after the irrigation with high saline water (subplot B) in 1997 (cotton), the soil salinity increased. This increase was more noticeable in the top layer (0–0.3 m depth). In contrast, for the same dates, the soil of subplot A showed no changes. After five irrigations with fresh water, the salinity of the soil in the subplot B reached values similar to those before the application of saline water. In 1998 (sugar beet) the application of moderately saline water in subplot B also increased soil salinity, but this increase was lower than in 1997. The irrigation with high saline water affected crop development. Cotton growth was reduced in comparison with that in the subplot irrigated only with fresh water. Despite this negative effect on crop development, the crop yield was the same as in the subplot A. Sugar beet development did not show differences between subplots, but yield was higher in subplot B than in subplot A.     

Effects of timing and duration of brackish irrigation water on fruit yield and quality of late summer melons

Brackish water (7 dS m⁻¹) is frequently utilized to drip-irrigate crops in the Negev desert of Israel, the practice being to use deep sandy soils (96% sand) to avoid soil salinization. When muskmelon (Cucumis melo L.), a moderately salt-sensitive crop species, was grown using brackish irrigation under these conditions, yields declined due to a significant reduction in fruit size, but fruit quality parameters improved markedly. In the present study, we tested the hypothesis that the use of fresh irrigation water during the early vegetative phase would increase canopy size and leaf area index (LAI) and hence the potential productivity of the melon plant. The application of brackish water during the reproductive phase, on the other hand, would improve fruit quality. Using multiple irrigations within a 24-h period, applied with drip irrigation, we examined the timing, the duration, and the concentration of brackish irrigation water as tools to optimize fruit yield and quality in late-summer melons. Indeed, the combination of fresh (1.2 dS m⁻¹) and brackish (7 dS m⁻¹) irrigation water increased the yield level to that of fresh water plants whereas it brought about the improvement of fruit quality typical to brackish water plants, thus providing an attractive approach to optimize late-summer melon production. Our results demonstrate the trade-off between fruit size and fruit quality as related to the timing and the duration of brackish irrigation water. The use of a milder (<4.5 dS m⁻¹) salinity level of irrigation water from plant emergence until harvest may be considered as well.     

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.     

Soil salinity reduction and prediction of salt dynamics in the coastal ricelands of Bangladesh

Field experiments were conducted in moderately saline and saline soils during the 1996 dry and wet seasons and the 1997 dry season to document salt dynamics and establish their relationship with local hydrology. Topsoil (0–15 cm) salinity in the dry season varied from 4.0 to 9.0 dS m⁻¹ in moderately saline soils at Mirzapur and from 5.0 to 12.0 dS m⁻¹ in saline soils at Barodanga. In wet season, the corresponding figures were from 1.5 to 2.5 dS m⁻¹ and from 2.0 to 3.0 dS m⁻¹, respectively. Dry season cropping significantly reduced topsoil salinity at both the research sites. Overall peak salinity in non-plowed cropped lands was 25–38% lower than that of fallow lands, and in plowed cropped lands it was about 30–40% less than the non-plowed cropped lands.Multiple linear and non-linear regression models were developed to predict topsoil salinity of the fallow land for both moderately saline and saline soils by using daily rainfall and evaporation as independent variables. The prediction level was not significantly improved when a non-linear model was employed in place of linear model. Therefore, a linear model may be used to predict topsoil salinity of the coastal ricelands of Bangladesh.     

Effect of water supply and salinity on pima cotton

A field study was conducted in northwestern Negev to determine the effect of the amount of water and its salinity level on the yield of Pima cotton (cv. S5). Irrigations were applied by means of a double line-source sprinkler system using two parallel lines, each supplied with water of a different salinity. The water salinity ranged from 2 to 7.5 dS m⁻¹ and the seasonal water application ranged from 30.0 to 68.0 cm. With water amounts of up to 50.0 cm (42% of Class A evaporation), an increase in water salinity caused a reduction in the seed cotton yield and the salinity threshold increased with an increasing amount of water. The maximum yield of seed cotton (about 5000 kg ha⁻¹) was obtained with a water application of 50 cm and a water salinity between 4 to 5 dS m⁻¹. With seasonal water applications exceeding 50 cm, an increase in salinity increased the yield. This is attributed to a depression of excessive vegetative growth in the presence of large amounts of water.     

Growth response of four turfgrass species to salinity

The need for salinity tolerant turfgrasses is increasing because of the increased use of effluent or other low quality waters for turfgrass irrigation. Greenhouse container and hydroponic experiments were conducted to determine the relative salinity tolerance and growth responses of ‘Challenger’ Kentucky bluegrass (Poa pratensis L.) (KBG), ‘Arid’ tall fescue (Festuca arundinacea Schreb) (TF), ‘Fults’ alkaligrass (Puccinellia distans (L.) Parl.) (AG), and a saltgrass (Distichlis spicata (Torr.) Beetle) collection (SG). In the container experiments, irrigation waters of different salinity levels were applied to experimental plants grown in plastic pots filled with a mix of sand and Isolite. The results indicated that KBG, TF, AG, and SG experienced a 50% shoot growth reduction at 4.9, 10.0, 20.0, and 34.9 dS m⁻¹, respectively, and a 50% root growth reduction at 5.8, 19.6, 24.9 and 41.0 dS m⁻¹, respectively. In the hydroponic experiment, grasses were grown in saline solution at 2.0, 4.7, 9.4, 14.1, 18.8, and 23.5 dS m⁻¹. Kentucky bluegrass, TF, AG, and SG experienced a 50% shoot growth reduction at 5.5, 14.2, 23.0, and 34.5 dS m⁻¹, respectively, and a 50% root growth reduction at 7.9, 21.5, 30.4 and 40.8 dS m⁻¹, respectively. Root to shoot ratio of KBG remained constant, whereas those of TF, AG, and SG increased at all salinity levels. Salinity caused root cortex cells to collapse, in KBG at 14.1 dS m⁻¹ and in TF at 23.5 dS m⁻¹. Alkaligrass and SG only had a few cell collapses even at 23.5 dS m⁻¹. Bi-cellular salt glands were observed only on leaves of SG. The ranking for salinity tolerance of selected grasses was: SG>AG>TF>KBG. Salt glands present in SG, root growth stimulation of SG and AG, and maintenance of relatively high root to shoot ratio in TF are apparent adaptive mechanisms exhibited by these grasses for salinity tolerance.     

Analysis of several discharge rate–spacing–duration combinations in drip irrigation system

In order to study the use of water irrigation in a rational way, several combinations of discharge rate, irrigation duration and inter-emitter distances were tested. For instance, three dripper spacings of 30, 50 and 70 cm which delivered water volumes of 4, 8 and 16 l per dripper, respectively, and three discharge rates of 2, 4 and 8 l/h for each spacing, were applied.An overlapping of the wetted bulbs was observed at the end of the different irrigation experiments. The inter-dripper root-zone had an average water content of 45% and a coefficient of uniformity of 90%.The discharge rate of 2 l/h applied to a 70 cm dripper spacing was characterised by water losses of 15% due to the significant irrigation duration (8 h).From this study, we reach the following conclusions, specific to the soil type and practical culture.

• 1.The maximum irrigation duration does not exceed 4 h.
• 2.Two hours durations can be used for the different spacings, each of which was characterised by its own discharge rate.

     

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.     

Estimating spatial mean soil water contents of sloping jujube orchards using temporal stability

Estimating spatial mean soil water contents from point-scale measurements is important to improve soil water management in sloping land of semiarid areas. Temporal stability analysis, as a statistical technique to estimate soil water content, is an effective tool in terms of facilitating the upscaling estimation of mean values. The objective of this study was to examine temporal stability of soil water profiles (0–20, 20–40, 40–60 and 0–60 cm) in sloping jujube (Zizyphus jujuba) orchards and to estimate field mean root-zone soil water based on temporal stability analysis in the Yuanzegou catchment of the Chinese Loess Plateau, using soil water observations under both dry and wet soil conditions. The results showed that different time-stable locations were identified for different depths and the temporal stability of soil water content in 20–40 cm was significantly (P < 0.05) weaker than that in other depths. Moreover, these time-stable locations had relatively high clay contents, relatively mild slopes and relatively planar surfaces compared to the corresponding field means. Statistical analysis revealed that the temporal stability of root zone soil water (0–60 cm) was higher in either dry or wet season than that including both, and soil water exhibited very low temporal stability during the transition period from dry to wet. Based on the temporal stability analysis, field mean soil water contents were estimated reasonably (R² from 0.9560 to 0.9873) from the point measurements of these time-stable locations. Since the terrains in this study are typical in the hilly regions of the Loess Plateau, the results presented here should improve soil water management in sloping orchards in the Loess Plateau.     

The effect of degradation of phalaris + white clover pasture on soil water regimes of a Brown Chromosol on the Northern Tablelands of NSW,Australia

The soil water regimes of a Brown Chromosol in response to drying and wetting are reported under three pastures types that were grazed all year long. The study was conducted at the Big Ridge 2 site near Armidale, on the Northern Tablelands of New South Wales (NSW) between 1994 and 1998. The three pasture types were degraded pasture (dominated by annual species), a phalaris dominant pasture, and an improved pasture containing phalaris + white clover. This study was conducted to assess the hydrological implications of losing perennial pasture species from the high rainfall (summer dominant) zone of south-eastern Australia. Pasture active rooting depth, water use and extraction during drying periods, and the ability of the soil profile to store water during wet periods were evaluated for each pasture type.Pasture active rooting depth, which affects water use, varied with season and water availability. During a typical autumn drying period between 1 and 22 March 1996, the phalaris + white clover pasture with an active rooting depth down to 100 cm used 46 ± 3.9 mm of water, with 16% of this extracted from the 55–130 cm zone. In the same period, the degraded and the phalaris pasture with active rooting depths of ≤60 cm used 30.7 ± 5.2 and 23.6 ± 7.9 mm of water, respectively, all from the surface 0–55 cm zone. However, under extreme drought conditions such as those in spring and early summer 1997 and autumn 1998, no differences in water use were detected between pastures.Pasture water use during dry periods affects the amount of water that can be stored in the soil profile and the potential amount of water loss during subsequent wet periods. In any wet period, the increase in soil water storage was greater in the 0–55 cm depth than in the 55–130 cm zone. For example, between 24 January and 14 February 1997 with total rainfall of 203 mm, water storage in the 0–55 cm zone was increased by 104.4 ± 6.7 mm under the phalaris + white clover pasture compared with 86.4 ± 4.3 and 84.4 ± 3.3 mm for the degraded and the phalaris pastures, respectively. The water storage increase in the 55–130 cm zone was not different between pastures (<12 mm).It was concluded that without appropriate grazing management and the presence of the legume component, the phalaris based pasture became unstable and failed to persist. The decline in the phalaris pasture caused invasion of annual species and weeds resulting in low water use, similar to that of the degraded pasture. In contrast, the combination of white clover and phalaris pasture showed a greater potential to maintain the phalaris component and a greater total biomass, and so was able to extract more water and from deeper parts of the soil profile. The vigorous phalaris + white clover pasture has greater potential to store more water than the degraded pasture and the phalaris pasture without legumes in the summer dominant rainfall area of temperate Australia. Therefore, maintaining pasture in good condition should be the main objective for sustainability of a grazing system in this region.     

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.