Yield and quality of two tomato (Solanum lycopersicum L.) cultivars as influenced by drip and furrow irrigation using waters having high residual sodium carbonate

Performance of tomato when irrigated with sodic waters particularly under drip irrigation is not well known. A field experiment was conducted for 3 years to study the response of tomato crop to sodic water irrigation on a sandy loam soil. Irrigation waters having 0, 5 and 10 mmol_c L⁻¹ residual sodium carbonate (RSC) were applied through drip and furrow irrigation to two tomato cultivars, Edkawi (a salt tolerant cultivar) and Punjab Chhuhara (PC). High RSC of irrigation water significantly increased soil pH, ECe and exchangeable sodium percentage progressively; the increases were higher in furrow compared to drip irrigation. Effect of high RSC on increasing bulk density and decreasing infiltration rate of soil was also pronounced in furrow-irrigated plots. Higher soil moisture and lower salinity near the plant was maintained under drip irrigation than under furrow irrigation. Performance of the two cultivars was significantly different; pooled over 2002–03 and 2003–04 seasons, PC yielded 38.8 and 30.0 Mg ha⁻¹ and Edkawi yielded 31.8 and 22.9 Mg ha⁻¹ under drip and furrow irrigation, respectively. At RSC10, cultivar PC produced 38 and 46% higher fruit yield than cultivar Edkawi under drip and furrow irrigation, respectively. Reduction in fruit yield at higher RSC was due to lower fruit weight under drip irrigation and due to reduced fruit number as well as fruit weight under furrow irrigation. Decrease in fruit weight was more pronounced in cultivar Edkawi than in cultivar PC. Increase in RSC lowered quality of the fruits except the ascorbic acid content. High RSC under drip irrigation, in general, had lesser deteriorating effect on the fruit quality particularly for cultivar PC than under furrow irrigation. For obtaining high tomato yield and better-quality fruits using high RSC sodic waters, drip irrigation should be preferred over furrow irrigation. Better performance of local cultivar PC compared to Edkawi at medium and high RSC suggests that cultivars categorized as tolerant to salinity should be evaluated in the sodic environment particularly when irrigated with high RSC sodic waters.     

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.     

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.     

Forage production of cool season pasture grasses as related to irrigation

A significant portion of the irrigated acreage in the intermountain western U.S. is comprised of cool season grass pastures. Droughts, coupled with increasing demands for limited water supplies in the region, have decreased the water volumes available for irrigating these pastures and other crops. Consequently, relationship between crop yield and irrigation (water production functions) should be defined for various species and cultivars to help growers and water managers make appropriate selections based on water availability.During a 3-year study on the Colorado Plateau, a line-source irrigation system was used to evaluate the relationship between applied water and dry forage production of orchardgrass (Dactylis glomerata L.), tall fescue (Festuca arundinacea Schreb.), meadow brome (Bromus riparius Rehmann), smooth brome (Bromus inermis Leyss.), two cultivars of intermediate wheatgrass (Elytrigia intermedium [Host] Nevski), crested wheatgrass (Agropyron cristatum L. Gaertn. X desertorum [Fisch. ex Link] J.A. Schultes) and perennial ryegrass (Lolium perenne L.). Irrigation treatments, including precipitation, ranged from 457 to 970 mm in 1996, 427 to 754 mm in 1997 and 490 to 998 mm in 1998. There was a positive linear relationship between yield and irrigation for all cultivars when averaged over all years but the relationships varied between cultivars and years. Orchardgrass, meadow brome and tall fescue produced more dry forage than the other grasses at the highest irrigation levels in all years. These grasses also produced the greatest rates of yield increase per unit of irrigation (average of 0.0129 Mg ha⁻¹ mm⁻¹) and exhibited greater yield stability from year to year than the other grasses at irrigation levels above 700 mm. The intermediate wheatgrasses produced more forage than the other grasses under limited irrigation (less than 600 mm) but the average production rate with irrigation (0.0066 Mg ha⁻¹ mm⁻¹) was only about half that of the aforementioned grasses. The average rate of forage produced per mm of irrigation was intermediate in the smooth brome (0.0096 Mg ha⁻¹) and lowest in the crested wheatgrass and perennial ryegrass (0.0048 and 0.0034 Mg ha⁻¹, respectively). These results suggest that orchardgrass and meadow brome be included in irrigated pastures receiving more than 700 mm of water annually while the intermediate wheatgrasses be selected for pastures receiving an annual water application of less than 700 mm.     

Effect of frequency of sodic and saline-sodic irrigations and gypsum on the buildup of sodium in soil and crop yields

The effect of three frequencies of irrigation with sodic (high residual alkalinity) and saline-sodic (high residual alkalinity and high NaCl concentration) waters in presence and absence of gypsum application on soil properties and crop yields were investigated under millet (fodder) — wheat — maize (fodder) rotation in a field experiment carried out for 6 years (1986–1992) on a well drained sandy loam Typic Ustochrept soil. Irrespective of the irrigation intervals, sustained use of sodic and salinesodic waters increased pH, electrical conductivity and ESP of the soil and hence significantly decreased crop yields. Application of gypsum decreased ESP and significantly improved crop yields. The beneficial effect of gypsum was lower under saline-sodic irrigation. There were no significant beneficial effects of increasing the frequency of sodic and saline-sodic irrigation, both in presence and absence of applied gypsum, on the yields of wheat and millet (f) crops grown during winter and monsoon seasons, respectively. But decrease in irrigation interval significantly improved yields of maize (f) grown during the hot dry summer period. Frequency of irrigation did not appreciably alter the effectiveness of applied gypsum in wheat and millet (f) but in maize (f), the gypsum treatment was more effective under more frequent irrigation.     

Effect of initial soil salinity and subirrigation water salinity on potato tuber yield and size

A field lysimeter study was conducted to investigate the effect of initial soil salinity and salinity level of brackish subirrigation water on tuber weight and tuber size of three potato (Solanum tuberosum L.) cultivars (Kennebec, Norland and Russet Burbank) under simulated arid conditions. Both saline and non-saline initial soil conditions were simulated in a total of 36 lysimeters. Eighteen lysimeters were flushed with fresh water (0.2 dS/m), while the remaining 18 lysimeters were flushed with brackish water (2 dS/m). For each soil condition, two subirrigation water concentrations, 1 and 9 dS/m, were used in nine lysimeters each. For each subirrigation water treatment, three potato cultivars were grown. In all lysimeters, water table was maintained at 0.4 m from the soil surface. Arid conditions were simulated by covering the lysimeter top with plastic mulch, allowing the potato shoots to grow through a cut in the mulch. The average root zone salinities (EC_w) were found to be 1.2 and 1.5 dS/m in non-saline lysimeters subirrigated with 1 and 9 dS/m waters, respectively. The corresponding salinities were 3.2 and 3.7 dS/m in the saline lysimeters. Across cultivars, there was no significant effect of either initial soil salinity or subirrigation water salinity on total tuber weight. However, the weight of Grade A tubers was higher in non-saline soil than in saline soil. Kennebec and Russet Burbank Grade A tuber weights were not affected by the initial soil salinity. On the contrary, a significant reduction in Grade A and total tuber weight under initially saline soil was evident for the Norland cultivar.     

Performance of sugarcane genotypes grown under sodic soil and water conditions

An experiment was conducted to evaluate the effect of residual sodium carbonates (RSC) of irrigation water on the growth and yield of sugarcane grown on sierozem light textured alkaline soil with sodic ground water and to study the performance of some promising sugarcane genotypes under these conditions. Treatments consisted of five levels of irrigations water viz RSC 2.8, 6.5, 12 me l⁻¹ and RSC 6.5 and 12.0 me l⁻¹ fully amended with gypsum. Plant and ratoon crops of eight genotypes of sugarcane were harvested. Cane yield and yield attributing characters like cane height, number of internodes per cane and number of millable canes were recorded. Juice quality viz percent juice extraction, percent sucrose, and commercial cane sugar (CCS%) in juice were determined at the harvest of crop. For both plant and ratoon crops, the average cane yield of all the genotypes of sugarcane and cane yield attributing characters decreased significantly with the increase in RSC of irrigation water to 6.5 and 12.0 me l⁻¹ (35% and 51% decline in the average cane yield for plant crop). For ratoon crop, the corresponding decrease in the average cane yield was less than the plant crop (only 14% and 21%). Amending RSC with gypsum increased the yield in all genotypes. The cane yield of various genotypes obtained under amended RSC with gypsum treatments were almost equal to the yield obtained under RSC 2.8 me l⁻¹ treatment (89% to 92% average cane yield for plant crop and 93% to 96% for ratoon crop). The effect of RSC of irrigation was variable for different genotypes (for example, for the plant crop of CoH 97, 65% and 76% and for CoH 108, 9% and 20% decline in the cane yield was observed with the application of high RSC irrigation water). As compared to plant crop, the ratoon crop of all genotypes recorded higher average cane yield and lesser decline in the cane yield with the application of high RSC irrigation water. Average juice extraction % decreased from 40.5% to 35.8%, and sugar yield decreased significantly (5.61 to 2.91 t ha⁻¹ for plant crop and 6.18 to 5.38 t ha⁻¹ for ratoon crop) with the increase in RSC of irrigation water, and amending RSC with gypsum increased the juice extraction % and sugar yield per unit area.     

Yield response of greenhouse grown tomato to partial root drying and conventional deficit irrigation

Greenhouse grown tomato was used to test partial root drying (PRD), a newly developing irrigation technique to save irrigation water, in Spring- and Fall-planted fresh-market tomato (Lycopersicon esculentum L., cv. Fantastic) cultivar. The PRD practice simply requires wetting of one half of the rooting zone and leaving the other half dry, thereby utilizing reduced amount of irrigation water applied. The wetted and dry sides are interchanged in the subsequent irrigations. Six irrigation treatments were tested during the two-year work in 2000 and 2001: (1) FULL, control treatment where the full amount of irrigation water, which was measured using Class-A pan evaporation data, was applied to the roots on all sides of the plant; (2) 1PRD30, 30% deficit irrigation with PRD in which wetted and dry sides of the root zone were interchanged with every irrigation; (3) 1PRD50; (4) 2PRD50, 50% deficit irrigation with PRD in which wetted and dry sides of the root zone were interchanged every and every other irrigation, respectively; (5) DI30 and (6) DI50, 30 and 50% deficit irrigations, respectively. The defined deficit levels were all in comparison to FULL irrigation. During the first year study in 2000, only three treatments (FULL, 1PRD30 and 2PRD50) were tested. Five treatments with exception of 2PRD50 were included in 2001. The FULL irrigation treatment, in Spring-planted tomato having a 153 day growth period, yielded 110.9 t ha⁻¹. The resulting irrigation-water-use efficiency (IWUE) was 321.8 kg (ha mm)⁻¹. The 1PRD50 treatment gave 86.6 t ha⁻¹, which was not statistically different (P ≤ 0.05) from the FULL irrigation (the control) and had 56% higher IWUE. Although yield differences were not statistically significant in Fall-planted tomato, the highest fruit yield was again obtained under FULL irrigation treatment (205.2 t ha⁻¹) over a growth period of 259 days after transplanting. The PRD treatments had 7–10% additional yield over the deficit irrigation receiving the same amount of water. The PRD treatments gave 10–27% higher marketable tomato yield (>60 g per fruit), compared with the DI treatments. Abscisic acid (ABA) concentrations measured in fresh leaf tissue was the highest under PRD practice relative to FULL and DI treatments. The high ABA content of fresh-leaf tissue observed in the work supports the root signalling mechanism reported earlier in plants having undergone partial root drying cycles.     

Wheat water productivity and yield in a cool highland environment: Effect of early sowing with supplemental irrigation

The Central Anatolian Plateau of Turkey is a typical cool highland rainfed wheat area with an annual rainfall of 300–500 mm. Due to suboptimal seasonal rainfall amounts and distribution, wheat yields in the region are low and fluctuate substantially over seasons. Delayed sowing due to late rainfall affects early crop establishment before winter frost and causes substantial reduction in yield. A 4-year field study (1998/1999 to 2001/2002) was carried out at Ankara Research Institute of Rural Services to assess the impact of early sowing with supplemental irrigation (SI) and management options during other dry spells on the productivity of a bread wheat cultivar, “Bezostia”. Treatments included early sowing with 50 mm irrigation and normal sowing with no irrigation as main plots. Four spring (SI) levels occupied the sub-plots. These are rainfed (no-irrigation), full irrigation to sature crop water requirements and two deficit irrigation levels of 1/3 and 2/3 at the full irrigation treatments.Results showed that early establishment of the crop, using 50 mm of irrigation water at sowing, increased grain yield by over 65% and adding about 2.0 t/ha to the average rainfed yield of 3.2 t/ha. Early sowing with SI allowed early crop emergence and development of good stand before being subjected to the winter frost. As a result, the crop used rainwater more efficiently. Additional supplemental irrigation in the spring also increased yield significantly. Grain yields of 5120, 5170 and 5350 kg/ha were obtained by applying 1/3, 2/3 and full SI, respectively. The mean productivity of irrigation water given at sowing was 3.70 kg/m³ with maximum value of 4.5 kg/m³. Water productivity of 1/3, 2/3 and full SI were 2.39, 1.46 and 1.27 kg/m³, respectively, compared to rainwater productivity of 0.96 kg/m³.     

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.     

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.     

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.     

Managing subsurface drip irrigation in the presence of shallow ground water

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

Phenology based irrigation scheduling and determination of crop coefficient of winter maize in rice fallow of eastern India

Vast rainfed rice area (12 million ha) of eastern India remains fallow after rainy season rice due to lack of appropriate water and crop management strategies inspite of having favourable natural resources, human labourers and good market prospects. In this study, a short duration crop, maize, was tried as test crop with different levels of irrigation during winter season after rainy season rice to increase productivity and cropping intensity of rainfed rice area of the region. Maize hybrid of 120 days duration was grown with phenology based irrigation scheduling viz., one irrigation at early vegetative stage, one irrigation at tassel initiation, two irrigation at tassel initiation + grain filling, three irrigation at early vegetative + tassel initiation + grain filling and four irrigation at early vegetative + tassel initiation + silking + grain-filling stages. Study revealed that one irrigation at tassel initiation stage was more beneficial than that of at early vegetative stage. Upto three irrigation, water use efficiency (WUE) was increased linearly with increased number of irrigation. With four irrigations, the yield was higher, but WUE was lower than that of three irrigations, which might be due to increased water application resulted in increase crop water use without a corresponding increase of yield for the crop with four irrigations. The crop coefficients (K_c) at different stages of the crop were derived after computing actual water use using field water balance approach. The crop coefficients of 0.42–0.47, 0.90–0.97, 1.25–1.33, and 0.58–0.61 were derived at initial, development, mid and late season, respectively with three to four irrigation. Study showed that leaf area index (LAI) was significantly correlated with K_c values with the R² values of 0.93. When LAI exceeded 3.0, the K_c value was 1. Study revealed that the K_c values for the development and mid season stage were slightly higher to that obtained by the procedure proposed by FAO, which might be due to local advection.     

Dry-period irrigation and fertilizer application affect water use and yield of spring wheat in semi-arid regions

Based on a field study on the semi-arid Loess Plateau of China, the strategies of limited irrigation in farmland in dry-period of normal-precipitation years are studied, and the effects on water use and grain yield of spring wheat of dry-period irrigation and fertilizer application when sowing are examined. The study includes four treatments: (1) with 90 mm dry-period irrigation but without fertilizer application (W); (2) with fertilizer application but without dry-period irrigation (F); (3) with 90 mm dry-period irrigation plus fertilizer application (WF); (4) without dry-period irrigation and fertilizer application (CK). The results indicate that dry-period irrigation resulted in larger and deeper root systems and larger leaf area index (LAI) compared with the non-irrigated treatments. The root/shoot ratio (R/S) in the irrigated treatments was significantly higher than in the non-irrigated treatments. The grain yields in F, W and WF are 1509, 2712 and 3291 kg ha⁻¹, respectively, which are 13.7, 104.3 and 147.9% higher than that (1328 kg ha⁻¹) of CK, and at the same time the grain yields in W and WF are also significantly higher than in F. Water use efficiencies (WUE) in terms of grain yield are 5.70 and 6.91 kg ha⁻¹ mm⁻¹ in W and WF, respectively, being 65.7 and 101.1% higher than that (3.44 kg ha⁻¹ mm⁻¹) of CK. The highest WUE and grain yield consistently occurred in WF, suggesting that the combination of dry-period irrigation and fertilizer application has a beneficial effect on improving WUE and grain yield of spring wheat.     

LEPA and trickle irrigation of cotton in the Southeast Anatolia Project (GAP) area in Turkey

This study was designed to evaluate the yield response of low-energy precision application (LEPA) and trickle-irrigated cotton grown on a clay-textured soil under the arid Southeast Anatolia Project (GAP) area conditions during the 1999 growing season at Koruklu in Turkey. The effects of four different irrigation levels (100, 75, 50, and 25% of cumulative Class-A pan evaporation on a 6-day basis) for LEPA, and two irrigation intervals (3-day and 6-day) and three different levels (100, 67, and 33% of cumulative Class-A pan evaporation on a 3-day and 6-day basis) for the trickle system on yield were investigated. Water was applied to alternate furrows through the double-ended Fangmeier drag-socks in the LEPA system. Trickle irrigation laterals were laid out on the soil surface at a spacing of 1.40 m. A total of 814 mm of water was applied to the full-irrigation treatments (100%) for both irrigation systems. Seasonal water use ranged from 383 to 854 mm in LEPA treatments; and 456 to 868 mm in trickle treatments. Highest average cotton yield of 5850 kg/ha was obtained from the full-irrigation treatment (100%) in trickle-irrigated plots with 6-day intervals. The highest yield in LEPA plots was obtained in LEPA-100% treatment with an average value of 4750 kg/ha. Seed cotton yields varied from 2660 to 5040 kg/ha and 2310 to 5850 kg/ha in trickle irrigation plots with 3-day and 6-day intervals, respectively, and from 2590 to 4750 kg/ha in LEPA plots. Irrigation levels both in LEPA and trickle-irrigated plots significantly increased yield. However, there was no significant yield difference between 100 and 67% irrigation levels in trickle-irrigated plots. Maximum irrigation water use efficiency (IWUE) and water use efficiency (WUE) were found as 0.813 and 0.741 kg/m³ in trickle-irrigated treatment of 67% with 6-day interval. Both IWUE and WUE values varied with irrigation quantity and frequency. The research results revealed that both the trickle and LEPA irrigation systems could be used successfully for irrigating cotton crop under the arid climatic conditions of the GAP area in Turkey.     

Optimizing irrigation scheduling for winter wheat in the North China Plain

In the North China Plain (NCP), more than 70% of irrigation water resources are used for winter wheat (Triticum aestivum L.). A crucial target of groundwater conservation and sustainable crop production is to develop water-saving agriculture, particularly for winter wheat. The purpose of this study was to optimize irrigation scheduling for high wheat yield and water use efficiency (WUE). Field experiments were conducted for three growing seasons at the Wuqiao Experiment Station of China Agriculture University. Eleven, four and six irrigation treatments, consisting of frequency of irrigation (zero to four times) and timing (at raising, jointing, booting, flowering and milking stage), were employed for 1994/95, 1995/96 and 1996/97 seasons, respectively. Available water content (AWC), rain events, soil water use (SWU), evapotranspiration (ET) and grain yield were recorded, and water use efficiency (WUE) and irrigation water use efficiency (IWUE) were calculated.The results showed that after a 75-mm pre-sowing irrigation, soil water content and AWC in the root zone of a 2-m soil profile during sowing were 31.1% (or 90.7% of field capacity) and 16.1%, respectively. Rainfall events were variable and showed a limited impact on AWC. The AWC decreased significantly with the growth of wheat. At the jointing stage no water deficits occurred for all treatments, at the flowering stage water deficits were found only in the rain-fed treatment, and at harvest all treatments had moderate to severe soil water deficits. The SWU in the 2-m soil profile was negatively related to the irrigation water volume, i.e. applying 75 mm irrigation reduced SWU by 28.2 mm. Regression analyses showed that relationships between ET and grain yield or WUE could be described by quadratic functions. Grain yield and WUE reached their maximum values of 7423 kg/ha and 1.645 kg/m³ at the ET rate of 509 and 382 mm, respectively. IWUE was negatively correlated with irrigated water volume. From the above results, three irrigation schedules: (1) pre-sowing irrigation only, (2) pre-sowing irrigation + irrigation at jointing or booting stage, and (3) pre-sowing irrigation + irrigations at jointing and flowering stages were identified and recommended for practical winter wheat production in the NCP.     

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

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

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.     

Response of green bean (P. vulgaris L.) to subsurface drip irrigation and partial rootzone-drying irrigation

Effects on water use, green bean yield, irrigation water-use efficiency (IWUE), water-use efficiency (WUE), plant dry weight and crop water relationship were investigated for two-drip irrigation techniques and four irrigation water levels in the Mediterranean region of Turkey. The treatments were conventional (SDI) and alternating subsurface drip irrigation (SPRD). At each irrigation event, half of the volume of water applied to the SDI was applied to one side of the crop, representing the partial rootzone-drying treatment. All treatments received 295 mm of irrigation during crop establishment, prior to beginning the different irrigation regimes. Differing irrigation amounts corresponded to four crop-pan coefficients (Kcp₁ = 0.6, Kcp₂ = 0.8, Kcp₃ = 1.0 and Kcp₄ = 1.2), appropriate to pan data. Total water applied to the SDI and SPRD treatments ranged from 366 to 437 mm and from 331 to 366 mm, respectively, depending on Kcp values, with water uptake varying from 396 to 470 mm and 364 to 409 mm, respectively. While differences of green bean yield and dry plant weights were not significantly affected by the SDI and SPRD irrigation techniques, the overall irrigation water saving was found to be 16% for the SPRD irrigation treatment compared with the SDI treatment. SPRD irrigation techniques increased IWUE, WUE, and slopes of yield water relationships. Increase in slopes of the yield–irrigation water and yield–water-use function of SPRD according to the equivalent slopes of the SDI were 215.8 and 151.4%, respectively. SPRD increased the green bean yield response factor (ky) with value of 128.4% according to the equivalent slopes of the SDI. In conclusion, irrigation scheduling based on a 0.8 crop-pan coefficient is recommended for conventional SDI, with 1.0 being more appropriate for partial rootzone-drying practice.