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.     

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.     

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.     

Review of measured crop water productivity values for irrigated wheat,rice, cotton and maize

The great challenge of the agricultural sector is to produce more food from less water, which can be achieved by increasing Crop Water Productivity (CWP). Based on a review of 84 literature sources with results of experiments not older than 25 years, it was found that the ranges of CWP of wheat, rice, cotton and maize exceed in all cases those reported by FAO earlier. Globally measured average CWP values per unit water depletion are 1.09, 1.09, 0.65, 0.23 and 1.80 kg m⁻³ for wheat, rice, cotton_seed, cotton_lint and maize, respectively. The range of CWP is very large (wheat, 0.6–1.7 kg m⁻³; rice, 0.6–1.6 kg m⁻³; cotton_seed, 0.41–0.95 kg m⁻³; cotton_lint, 0.14–0.33 kg m⁻³ and maize, 1.1–2.7 kg m⁻³) and thus offers tremendous opportunities for maintaining or increasing agricultural production with 20–40% less water resources. The variability of CWP can be ascribed to: (i) climate; (ii) irrigation water management and (iii) soil (nutrient) management, among others. The vapour pressure deficit is inversely related to CWP. Vapour pressure deficit decreases with latitude, and thus favourable areas for water wise irrigated agriculture are located at the higher latitudes. The most outstanding conclusion is that CWP can be increased significantly if irrigation is reduced and crop water deficit is intendently induced.     

Latent heat flux over a furrow-irrigated tomato crop using Penman–Monteith equation with a variable surface canopy resistance

The Penman–Monteith (P–M) model with a variable surface canopy resistance (r_c) was evaluated to estimate latent heat flux (LE) or crop evapotranspiration (ET) over a furrow-irrigated tomato crop under different soil water status and atmospheric conditions. The hourly values of r_c were computed as a function of environmental variables (air temperature, vapor pressure deficit, net radiation, and soil heat flux) and a normalized soil water factor (F), which varies between 0 (wilting point, θ_WP) and 1 (field capacity, θ_FC). The Food and Agricultural Organization (FAO-56) method was also evaluated to calculate daily ET based on the reference evapotranspiration, crop coefficient and water stress coefficient. The performance of the P–M model and FAO-56 method were evaluated using LE values obtained from the Bowen ratio system. On a 20 min time interval, the P–M model estimated daytime variation of LE with a standard error of the estimate (SEE) of 46 Wm⁻² and an absolute relative error (ARE) of 3.6%. Thus, daily performance of the P–M model was good under soil water content ranging from 118 to 83 mm (θ_FC and θ_WP being 125 and 69 mm, respectively) and LAI ranging from 1.3 to 3.0. For this validation period, the calculated values of r_c and F ranged between 20 and 114 s m⁻¹ and between 0.87 and 0.25, respectively. In this case, the P–M model was able to predict daily ET with a SEE of 0.44 mm h⁻¹ (1.1 MJ m⁻² d⁻¹) and an ARE of 3.9%. Furthermore, the FAO-PM model computed daily ET with SEE and ARE values of 1.1 mm h⁻¹ (2.8 MJ m⁻² d⁻¹) and 5.2%, respectively.     

The influence of crop canopy on evapotranspiration and crop coefficient of beans (Phaseolus vulgaris L.)

Experiments were conducted to investigate the effect of crop development on evapotranspiration and yield of beans (Phaseolus vulgaris L.) at the Instituto Agronômico (IAC), Campinas, State of São Paulo, Brazil, during the dry season of 1994. A completely randomized design was carried out with three population density treatments and four replications. The treatments were: (a) crop sown in evapotranspirometers at a density of 50 plants m⁻², and thereafter thinned to 25 plants m⁻², when the canopy achieved full ground cover; (b) crop sown with population densities of 14 and 28 plants m⁻² in an irrigated field. Crop growth was evaluated considering dry matter (DM), vegetative ground cover (GC%) and leaf area index (LAI). These parameters were successfully related to basal crop coefficient (k_cb) and crop coefficient (k_c), demonstrating the strong dependence of both coefficients on canopy development. A simulation study was carried out and showed that k_cb based on LAI would allow good estimates of water use for different plant density populations in the field.     

Water use and lint yield response of drip irrigated cotton to the length of irrigation season

A 2-year experiment was conducted at Tal Amara Research Station in the Bekaa Valley of Lebanon to determine water use and lint yield response to the length of irrigation season of drip irrigated cotton (Gossypium hirsutum L.). Crop evapotranspiration (ET_crop) and reference evapotranspiration (ET_rye-grass) were directly measured at weekly basis during the 2001 growing period using crop and rye-grass drainage lysimeters. Crop coefficients (K_c) in the different growth stages were calculated as ET_crop/ET_rye-grass. Then, the calculated K_c values were used in the 2002 growing period to estimate evapotranspiration of cotton using the FAO method by multiplying the calculated K_c values by ET_rye-grass measured in 2002. The length of irrigation season was determined by terminating irrigation permanently at first open boll (S1), at early boll loading (S2), and at mid boll loading (S3). The three treatments were compared to a well-watered control (C) throughout the growing period. Lint yield was defined as a function of components including plant height at harvest, number of bolls per plant, and percentage of opened bolls per plant.Lysimeter-measured crop evapotranspiration (ET_crop) totaled 642 mm in 2001 for a total growing period of 134 days, while when estimated with the FAO method in 2002 it averaged 669 mm for a total growing period of 141 days from sowing to mature bolls. Average K_c values varied from 0.58 at initial growth stages (sowing to squaring), to 1.10 at mid growth stages (first bloom to first open boll), and 0.83 at late growth stages (early boll loading to mature bolls).Results showed that cotton lint yields were reduced as irrigation amounts increased. Average across years, the S1 treatment produced the highest yield of 639 kg ha⁻¹ from total irrigations of 549 mm, compared to the S2 and S3 treatments, which yielded 577 and 547 kg ha⁻¹ from total irrigations of 633 and 692 mm, respectively, while the control resulted in 457 kg ha⁻¹ of lint yield from 738 mm of irrigation water. Water use efficiency (WUE) was found to be higher in S1 treatment and averaged 1.3 kg ha⁻¹ mm⁻¹, followed by S2 (1.1 kg ha⁻¹ mm⁻¹), and S3 (1.0 kg ha⁻¹ mm⁻¹), while in the control WUE was 0.80 kg ha⁻¹ mm⁻¹. Lint yield was negatively correlated with plant height and the number of bolls per plant and positively correlated with the percentage of opened bolls. This study suggests that terminating irrigation at first open boll stage has been found to provide the highest cotton yield with maximum WUE under the semi-arid conditions of the Bekaa Valley of Lebanon.     

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.     

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.     

Trickle and sprinkler irrigation of potato (Solanum tuberosum L.) in the Middle Anatolian Region in Turkey

The potato (Solanum tuberosum L.) is widely planted in the Middle Anatolian Region, especially in the Nigde-Nevsehir district where 25% of the total potato growing area is located and produces 44% of the total yield. In recent years, the farmers in the Nigde-Nevsehir district have been applying high amounts of nitrogen (N) fertilizers (sometimes more than 900 kg N ha⁻¹) and frequent irrigation at high rates in order to get a much higher yield. This situation results in increased irrigation and fertilization costs as well as polluted ground water resources and soil. Thus, it is critical to know the water and nitrogen requirements of the crop, as well as how to improve irrigation efficiency. Field experiments were conducted in the Nigde-Nevsehir (arid) region on a Fluvents (Entisols) soil to determine water and nitrogen requirements of potato crops under sprinkler and trickle irrigation methods. Irrigation treatments were based on Class A pan evaporation and nitrogen levels were formed with different nitrogen concentrations.The highest yield, averaging 47,505 kg ha⁻¹, was measured in sprinkler-irrigated plots at the 60 g m⁻³ nitrogen concentration level in the irrigation treatment with limited irrigation (480 mm). Statistically higher tuber yields were obtained at the 45 and 60 g m⁻³ nitrogen concentration levels in irrigation treatments with full and limited irrigation. Maximum yields were obtained with about 17% less water in the sprinkler method as compared to the trickle method (not statistically significant). On the loam and sandy loam soils, tuber yields were reduced by deficit irrigation corresponding to 70% and 74% of evapotranspiration in sprinkler and trickle irrigations, respectively. Water use of the potato crop ranged from 490 to 760 mm for sprinkler-irrigated plots and 565–830 mm for trickle-irrigated treatments. The highest water use efficiency (WUE) levels of 7.37 and 4.79 kg m⁻³ were obtained in sprinkle and trickle irrigated plots, respectively. There were inverse effects of irrigation and nitrogen levels on the WUE of the potato crops. Significant linear relationships were found between tuber yield and water use for both irrigation methods. Yield response factors were calculated at 1.05 for sprinkler methods and 0.68 for trickle methods. There were statistically significant linear and polynomial relationships between tuber yield and nitrogen amounts used in trickle and sprinkler-irrigated treatments, respectively. In sprinkler-irrigated treatments, the maximum tuber yield was obtained with 199 kg N ha⁻¹. The tuber cumulative nitrogen use efficiency (NUE_cu) and incremental nitrogen use efficiency (NUE_in) were affected quite differently by water, nitrogen levels and years. NUE_cu varied from 16 to 472 g kg⁻¹ and NUE_in varied from 75 to 1035 g kg⁻¹ depending on the irrigation method. In both years, the NH₄-N concentrations were lower than NO₃-N, and thus the removed nitrogen and nitrogen losses were found to be 19–87 kg ha⁻¹ for sprinkler methods and 25–89 kg ha⁻¹ for trickle methods. Nitrogen losses in sprinkler methods reached 76%, which were higher than losses in trickle methods.     

The effects of different irrigation regimes on cucumber (Cucumbis sativus L.) yield and yield characteristics under open field conditions

A study was conducted to determine the effects of different drip irrigation regimes on yield and yield components of cucumber (Cucumbis sativus L.) and to determine a threshold value for crop water stress index (CWSI) based on irrigation programming. Four different irrigation treatments as 50 (T-50), 75 (T-75), 100 (T-100) and 125% (T-125) of irrigation water applied/cumulative pan evaporation (IW/CPE) ratio with 3-day-period were studied.Seasonal crop evapotranspiration (ET_c) values were 633, 740, 815 and 903 mm in the 1st year and were 679, 777, 875 and 990 mm in the 2nd year for T-50, T-75, T-100 and T-125, respectively. Seasonal irrigation water amounts were 542, 677, 813 and 949 mm in 2002 and 576, 725, 875 and 1025 mm in 2003, respectively. Maximum marketable fruit yield was from T-100 treatment with 76.65 t ha⁻¹ in 2002 and 68.13 t ha⁻¹ in 2003. Fruit yield was reduced significantly, as irrigation rate was decreased. The water use efficiency (WUE) ranged from 7.37 to 9.40 kg m⁻³ and 6.32 to 7.79 kg m⁻³ in 2002 and 2003, respectively, while irrigation water use efficiencies (IWUE) were between 7.02 and 9.93 kg m⁻³ in 2002 and between 6.11 and 8.82 kg m⁻³ in 2003.When the irrigation rate was decreased, crop transpiration rate decreased as well resulting in increased crop canopy temperatures and CWSI values and resulted in reduced yield. The results indicated that a seasonal mean CWSI value of 0.20 would result in decreased yield. Therefore, a CWSI = 0.20 could be taken as a threshold value to start irrigation for cucumber grown in open field under semi-arid conditions.Results of this study demonstrate that 1.00 IW/CPE water applications by a drip system in a 3-day irrigation frequency would be optimal for growth in semiarid regions.     

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.     

Spatial variability of solutes in a pecan orchard surface-irrigated with untreated effluents in the upper Rio Grande River basin

Untreated effluents are blended with water from the Rio Grande River and used for irrigation in the Juarez Valley of northern Mexico. Effluents are a source of nutrients, but may also be a source of heavy metal contamination. This study was conducted to characterize deposition patterns of selected metals, salts, and total nitrogen in a 6 ha pecan (Carya illinoenisis K.) orchard which had healthy-to-stunted trees with dieback. Orchard soil was collected along multiple transects to depths of 1.2 m, with spacing every 20 m. All solutes showed a magnitude variability in particular ions. Chromium, Ni, Pb, and Cd concentrations averaged <14 mg kg⁻¹. Soil Na, Ca, K, Mg, SO₄, Cl and NO₃–N averaged <100 mg kg⁻¹. Total N was <0.21%. Most solutes accumulated at the soil surface with the exception of Na and SO₄. Linear semi-variograms best described spatial metal deposition and surface clay content with a range of influence >189 m. Spherical semi-variograms best described spatial distribution of salts and total N, but accounted <50% of the variability. The solubility of solutes in moderately alkaline irrigation water and their specific behavior in calcareous soils likely affected deposition patterns. Estimated metal loads from irrigation over a 15-year period were <3 kg ha⁻¹, but about 187 Mg ha⁻¹ for total dissolved solids (salts). Pecan leaf tissue showed no signs of heavy metal accumulation. Suboptimum pecan growth was associated with salt accumulation in a clayey area with low permeability. Salts, in particular Na, rather than metals may be the most important inorganic contaminants for irrigated agriculture in this region. Salt loads in irrigation waters are expected to increase as agriculture increasingly relies on urban effluents too expensive to convert to potable water.     

Role of straw mulching in non-continuously flooded rice cultivation

Rice (Oryza sativa L.) cultivation under non-flooded (NF) condition is a new alternative to the conventional flooded (CF) rice cultivation system in the regions where rainfall and fresh water resources are limited. Non-flooded rice cultivation may mediate rice growth performance and mulching may be good practice to reduce evapotranspiration and increase water use efficiency (WUE). The research objectives of this study were to investigate the effects of non-flooded cultivation with straw mulching on the rice agronomic traits and water use efficiency of the second rice cropping season (late rice). The treatments were conventional flooded rice cultivation, non-flooded rice cultivations without (NF-ZM) and with rice straw mulching (NF-SM). Irrigation water was 19950 m³ ha⁻¹ in 2003 and 15,850 m³ ha⁻¹ in 2004 in the CF treatments and 7200 m³ ha⁻¹ in 2003 and 5045 m³ ha⁻¹ in 2004 in the non-flooded rice fields (NF-ZM and NF-SM treatments).The field measurements showed that water seepage was 13,442 m³ ha⁻¹ in the CF treatment, 5510 m³ ha⁻¹ in the NF-ZM treatment and 5424 m³ ha⁻¹ in the NF-SM treatment. Rice straw mulching decreased evapotranspiration by 33% and 63% (in 2003), 36.5% and 57.1% (in 2004) to the NF-ZM treatment and CF treatment, respectively. Compared with the NF-ZM treatment, mulch application significantly increased the leaf area per plant, main root length, tap root length and root dry weight per plant of crop. The yield of the NF-SM treatment (2003: 6489 kg/hm²; 2004: 8574.8 kg/hm²) was similar with the value of the CF treatment (2003: 6811.5; 2004: 8630.5 kg/hm²), and much higher than the NF-ZM treatment (2003: 4716; 2004: 6394.8 kg/hm²). The order of irrigation water use efficiency (IWUE) and water use efficiency were as follows: NF-SM > NF-ZM > CF.     

Water quality assessment of different reservoir types in relation to nutrient solution use in hydroponics

Hydroponics requires good quality water. For this purpose, water quality is based on concentrations of specific ions and phytotoxic substances as well as the presence of organisms and substances that can clog irrigation systems. Here, four irrigation reservoirs, i.e. two rainwater ponds, a peat ditch, and a natural lake, were analyzed to determine whether or not they conform to water quality guidelines. Based on our data, the four reservoirs could be divided into two categories in respect to their water quality. The two rainwater ponds belong to the category characterized by low input of ionic strength (480 μmol m⁻¹), low concentration of unwanted ions, such as SO₄²⁻ (63 μmol l⁻¹) and Zn²⁺ (3.9 μmol l⁻¹), a moderate bacterial population (lg 4.9 CFU m⁻¹), and moderate algae density (lg 6.0 cells ml⁻¹). The rainwater ponds were found to contain a good diversity in bacteria (45 species from 25 genera), and a poor diversity of algae (15 species from 4 groups). The other category, to which the peat ditch and natural lake belong, is characterized by a high ionic strength (12,200 μmol l⁻¹), high concentrations of alkali ions (Mg²⁺: 890 μmol l⁻¹; Ca²⁺: 3.260 μmol l⁻¹; K⁺: 470 μmol l⁻¹), a moderate bacterial (lg 4.7 CFU ml⁻¹), but low algae density (lg 5.0 cells ml⁻¹). In comparison to the first category, the diversity of the bacteria was poor (seven species from three genera). However, in sharp contrast was the rich algal community detected in the peat ditch, for which 32 species from six groups were found, whereas in the natural lake, only one group with seven species was identified. In all reservoirs, species of the genera Paenibacillus and Bacillus were detected, and small green algae, e.g. Scenedesmus spp., also dominated in each case. Overall, the bacterial and algal densities showed wide fluctuations between water sources, and neither caused filter clogging as observed in investigations of others. The quality of the rainwater investigated was assessed to be well suited for use in hydroponics due to appropriate nutrient concentration (except Zn²⁺ in one pond), and lack of potential bacterial and algal development. However, we recommend water from the natural lake and the peat ditch to be used with care because of the high nutrient concentration.     

Nitrogen loss through subsurface drainage effluent in coastal rice field from India

Experiments were conducted to estimate nitrogen loss through drainage effluent in subsurface drained farmers’ field at a coastal site near Machilipatnam, Andhra Pradesh, India. The concentration of three forms of nitrogen, namely, NH₄–N, NO₂–N and NO₃–N in the subsurface drainage effluent from 15, 35 and 55 m drain spacing areas were measured in 1999 and 2000. The area with 15 m spacing was already reclaimed during 1986–1998 by the subsurface drainage system. The soil salinity of the root zone was brought down from an initial high of 35 to 4 dS m⁻¹. The subsurface drainage system with 35 and 55 m drain spacing was laid in the adjoining area and commissioned in 1998. Earlier raising of any crop in the area with 35 and 55 m spacings was not possible due to very high salinity, sodicity and poor drainage conditions. The nitrate-nitrogen loss dominated in reclaimed land with 15 m spacing whereas ammonium-nitrogen loss dominated in the land that was highly saline and in the initial stage of reclamation by the subsurface drainage technology with 35 and 55 m drain spacing. The total nitrogen loss of 3.75 kg per ha per year in 15 m drain spacing area was minimum and 23.53 kg per ha per year in 35 m drain spacing area was maximum. The nitrate-nitrogen loss contributed the maximum of 82% and ammonium- and nitrite-nitrogen contributed 11 and 7%, respectively, in 15 m drain spacing area whereas the ammonium losses contributed 93 and 82% in 35 and 55 m drain spacing areas, respectively. The losses in the form of nitrite and nitrate remained negligible in 35 m drain spacing area, but the losses to the tune of 8 and 15% in the form of nitrite and nitrate, respectively, occurred in 55 m drain spacing area.     

Cotton yield and applied water relationships under drip irrigation

Different irrigation scheduling methods and amounts of water ranging from deficit to excessive amounts were used in cotton (Gossypium hirsutum L.) irrigation studies from 1988 to 1999, at Lubbock, TX. Irrigation scheduling treatments based on canopy temperature (T_c) were emphasized in each year. Surface drip irrigation and recommended production practices for the area were used. The objective was to use the 12-year database to estimate the effect of irrigation and growing season temperature on cotton yield. Yields in the irrigation studies were then compared with those for the northwest Texas production region. An irrigation input of 58 cm or total water application of 74 cm was estimated to produce maximum lint yield. Sources of the total water supply for the maximum yielding treatments for each year averaged 74% from irrigation and 26% from rain. Lint yield response to irrigation up to the point of maximum yield was approximated as 11.4 kg ha⁻¹ cm⁻¹ of irrigation between the limits of 5 and 54 cm with lint yields ranging from 855 to 1630 kg ha⁻¹. The intra-year maximum lint yield treatments were not limited by water input, and their inter-year range of 300 kg ha⁻¹ was not correlated with the quantity of irrigation. The maximum lint yields were linearly related to monthly and seasonal heat units (HU) with significant regressions for July (P=0.15), August (P=0.07), and from May to September (P=0.01). The fluctuation of maximum yearly lint yields and the response to HU in the irrigation studies were similar to the average yields in the surrounding production region. The rate of lint yield increase with HU was slightly higher in the irrigation studies than in the surrounding production area and was attributed to minimal water stress. Managing irrigation based on real-time measurements of T_c produced maximum cotton yields without applying excessive irrigation.     

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.     

Water productivity analysis of irrigated crops in Sirsa district,India

Water productivity (WP) expresses the value or benefit derived from the use of water, and includes essential aspects of water management such as production for arid and semi-arid regions. A profound WP analysis was carried out at five selected farmer fields (two for wheat–rice and three for wheat–cotton) in Sirsa district, India during the agricultural year 2001–02. The ecohydrological soil–water–atmosphere–plant (SWAP) model, including detailed crop simulations in combination with field observations, was used to determine the required hydrological variables such as transpiration, evapotranspiration and percolation, and biophysical variables such as dry matter or grain yields. The use of observed soil moisture and salinity profiles was found successful to determine indirectly the soil hydraulic parameters through inverse modelling.Considerable spatial variation in WP values was observed not only for different crops but also for the same crop. For instance, the WP_ET, expressed in terms of crop grain (or seed) yield per unit amount of evapotranspiration, varied from 1.22 to 1.56 kg m⁻³ for wheat among different farmer fields. The corresponding value for cotton varied from 0.09 to 0.31 kg m⁻³. This indicates a considerable variation and scope for improvements in water productivity. The average WP_ET (kg m⁻³) was 1.39 for wheat, 0.94 for rice and 0.23 for cotton, and corresponds to average values for the climatic and growing conditions in Northwest India. Including percolation in the analysis, i.e. crop grain (or seed) yield per unit amount of evapotranspiration plus percolation, resulted in average WP_ETQ (kg m⁻³) values of 1.04 for wheat, 0.84 for rice and 0.21 for cotton. Factors responsible for low WP include the relative high amount of evaporation into evapotranspiration especially for rice, and percolation from field irrigations. Improving agronomic practices such as aerobic rice cultivation and soil mulching will reduce this non-beneficial loss of water through evaporation, and subsequently will improve the WP_ET at field scale. For wheat, the simulated water and salt limited yields were 20–60% higher than measured yields, and suggest substantial nutrition, pest, disease and/or weed stresses. Improved crop management in terms of timely sowing, optimum nutrient supply, and better pest, disease and weed control for wheat will multiply its WP_ET by a factor of 1.5! Moreover, severe water stress was observed on cotton (relative transpiration < 0.65) during the kharif (summer) season, which resulted in 1.4–3.3 times lower water and salt limited yields compared with simulated potential yields. Benefits in terms of increased cotton yields and improved water productivity will be gained by ensuring irrigation supply at cotton fields, especially during the dry years.     

Responses of five almond cultivars to irrigation: Photosynthesis and leaf water potential

In the Trás-os-Montes region, almond orchards are usually planted in the dry soils on the upper valley of the Douro river and are typically cultivated under non-irrigated conditions, leading to low yields. This study aimed to compare the physiological responses of five almond varieties (Francoli, Ferragnès, Glorieta, Lauranne and Masbovera) growing under non-irrigated and irrigated conditions. In irrigated conditions, all cultivars had higher photosynthetic rates, with maximum rates in a range of 10–12 μmol CO₂ m⁻² s⁻¹. Study of daily photosynthesis (June–August) indicates that, irrigated plants showed maximal values at 11 h (32 °C), while in water stressed ones highest values were found at 9 h (28 °C). The irrigation induced an increase in photosynthesis of around 173% in Lauranne, 187% in Francoli, 204% in Glorieta, 266% in Masbovera and 331% in Ferragnès. In relation to values of water potential that allow half-rate of photosynthesis (ψ_w50), they were calculated as −2.95, −2.50, −3.10, −3.20 and −3.30 MPa for Ferragnès, Glorieta, Masbovera, Francoli and Lauranne, respectively.