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.     

Comparison of sprinkler,trickle and furrow irrigation efficiencies for onion production

In the Mesilla Valley of southern New Mexico, furrow irrigation is the primary source of water for growing onions. As the demand for water increases, there will be increasing competition for this limited resource. Water management will become an essential practice used by farmers. Irrigation efficiency (IE) is an important factor into improving water management but so is economic return. Therefore, our objectives were to determine the irrigation efficiency, irrigation water use efficiency (IWUE) and water use efficiency (WUE), under sprinkler, furrow, and drip irrigated onions for different yield potential levels and to determine the IE associated with the amount of water application for a sprinkler and drip irrigation systems that had the highest economic return.Maximum IE (100%) and economic return were obtained with a sprinkler system at New Mexico State University’s Agriculture Science Center at Farmington, NM. This IE compared with the 54–80% obtained with the sprinkler irrigation used by the farmers. The IEs obtained for onion fields irrigated with subsurface drip irrigation methods ranged from 45 to 77%. The 45% represents the nonstressed treatments, in which an extra amount of irrigation above the evapotranspiration (Et) requirement was applied to keep the base of the onion plates wet. The irrigation water that was not used for Et went to deep drainage water. The return on the investment cost to install a drip system operated at a IE of 45 was 29%. Operating the drip system at a IE of 79% resulted in a yield similar to surface irrigated onions and consequently, it was not economical to install a drip system. The IEs at the furrow-irrigated onion fields ranged from 79 to 82%. However, the IEs at the furrow-irrigated onion fields were high because farmers have limited water resources. Consequently, they used the concept of deficit irrigation to irrigate their onion crops, resulting in lower yields. The maximum IWUE (0.084 t ha⁻¹ mm⁻¹ of water applied) was obtained using the sprinkler system, in which water applied to the field was limited to the amount needed to replace the onions’ Et requirements. The maximum IWUE values for onions using the subsurface drip was 0.059 and 0.046 t ha⁻¹ mm⁻¹ of water applied for furrow-irrigated onions. The lower IWUE values obtained under subsurface drip and furrow irrigation systems compared with sprinkler irrigation was due to excessive irrigation under subsurface drip and higher evaporation rates from fields using furrow irrigation. The maximum WUE for onions was 0.009 t ha⁻¹ mm⁻¹ of Et. In addition, WUE values are reduced by allowing the onions to suffer from water stress.     

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.     

Different irrigation methods and water stress effects on potato yield and yield components

This research was conducted during the spring seasons of 2000 and 2002 in Hatay province located in the East Mediterranean Region of Turkey. The research investigated the effects of two drip irrigation methods and four different water stress levels on potato yield and yield components. The surface drip (SD) and subsurface drip (SSD) irrigation methods were used. The levels were full irrigation (I₁₀₀), 66% of full irrigation (I₆₆), 33% of full irrigation (I₃₃) and un-irrigated (I₀) treatments. Five and three irrigation were applied in 2000 and 2002 early potato growing seasons, respectively. Total irrigation amount changed from 102 to 302 mm and from 88 to 268 mm in 2000 and 2002, respectively. Seasonal evapotranspiration changed between 226 and 473 mm and 166 and 391 mm in 2000 and 2002, respectively. SD and SSD irrigation methods did not result in a significant difference on yield. However, SD method has more advantages than SSD method, which has difficulties in replacement and higher system cost. Irrigation levels resulted in significant difference in both years on yield and its components. Water stress significantly affected the yield and yield parameters of early potato production. Water deficiency more than 33% of the irrigation requirement could not be suggested.Water use efficiency (WUE) of SD irrigation methods had generally higher values than SSD irrigation methods. Treatment I₃₃ gave maximum irrigation water use efficiency (IWUE) for both years. SSD irrigation method did not provide significant advantage on yield and WUE, compared to SD irrigation in early potato production under experimental conditions. Therefore, the SD irrigation method would be recommended in early potato production under Mediterranean conditions.     

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.     

Soil–plant water status and yield of sweet corn (Zea mays L. cv. Saccharata) as influenced by drip irrigation and planting methods

A field experiment was conducted during summer season of 1998 at the Main Research Station, University of Agricultural Sciences, Hebbal, Bangalore. Experiment consisted of four irrigation levels and two methods of planting. Drip irrigation at 0.8 Epan with normal planting recorded significantly higher green cob (20.07 t ha⁻¹) and fodder yield (24.87 t ha⁻¹) compared to either drip at 0.6 Epan or weekly surface irrigation at 0.8 Epan, while drip at 0.4 Epan under paired planting (10.53 and 15.23 t ha⁻¹, respectively registered the lowest. Drip at 0.4 Epan with normal planting recorded higher WUE of green cob and fodder (48.21 and 61.22 kg ha mm⁻¹) with total water requirement of 330.46 mm. With increase in water use (drip at 0.6 Epan, drip/surface irrigation at 0.8 Epan) the water use efficiency decreased. Drip irrigation at 0.8 Epan resulted in higher leaf water potential (−4, −7, −8 bars) at 20, 40 and 60 DAS before irrigation. Consequently, the RWC in the leaf was 81.10% and the available soil moisture ranged from 55.62 to 61.91%.     

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.     

Irrigation frequency and amount affect yield components of summer squash (Cucurbita pepo L.)

The aim of this study carried out in Van, Turkey was to determine the most suitable irrigation frequencies and quantities in summer squash (Cucurbita pepo L. cv. Sakız) grown under field conditions. Irrigation quantities were based on pan evaporation (E_pan) from a screened class-A pan. Irrigation treatments consisted of two irrigation intervals (I1: 5 days; I2: 10 days), and three pan coefficients (K_cp1: 0.45; K_cp2: 0.65 and K_cp3: 0.85). Plants were adequately watered from seed sowing to first fruit emergence, then, scheduled irrigations were initiated at 5- and 10-day intervals.Irrigation quantities applied to the treatments varied from 279 to 475 mm; seasonal plant water consumption or evapotranspiration (E_t) of irrigation treatments varied from 336 to 539 mm; and the summer squash yield varied from 22.4 to 44.7 t ha⁻¹. The highest total yield was obtained from I1K_cp3 treatment. However, K_cp2 treatments had the earliest yield. Treatments irrigated with higher amount of water generally gave lower irrigation water use efficiency (IWUE) values than others. E_t/E_pan ratios of treatments ranged from 0.12 to 1.16. Moreover, irrigation treatments had significant effects (P<0.01) on yield and there were significant positive linear relations among irrigation water, plant water consumption, fruit traits and yield.In conclusion, K_cp3 treatment with 5-day irrigation interval is recommended for summer squash grown under field conditions in order to get higher summer squash yield. However, if the irrigation water is scarce, it will be suitable to irrigate summer squash frequently using K_cp1 values.     

Cotton yield and water use efficiency at various levels of water and N through drip irrigation under two methods of planting

The present investigation was undertaken to evaluate the effect of various levels of water and N application through drip irrigation on seed cotton yield and water use efficiency (WUE). In this experiment three levels of water (Epan 0.4, 0.3, and 0.2) and three levels of N (100, 75, and 50% of recommended N, 75 kg/ha) through drip were compared with check-basin method of irrigation under two methods of planting (normal sowing, NS; paired sowing, PS). The results revealed that when the same quantity of irrigation water and N was applied through drip irrigation system, it increased the seed cotton yield to 2144 from 1624 kg/ha (an increase of 32%) under check-basin method of irrigation. When the quantity of water through drip was reduced to 75%, the increase in seed cotton yield was 12%; however, when water was reduced to 50%, it resulted 2% lower yield than check-basin. The decrease in N through fertigation resulted in reduction in seed cotton yield at all the levels of water supply, but the magnitude of reduction was the highest at highest level of water supply. In paired sowing (PS), 20% higher seed cotton yield was obtained as compared with check-basin method under NS along with 50% saving of water. In paired sowing the sacrifice of 9% seed cotton yield as compared with NS resulted in saving of 50% water as well as the cost of laterals because there was one lateral for two paired rows. The WUE increased by 26% (22.1 from 17.6 kg/ha cm) in drip irrigation system when same quantity of water and N fertilizer was applied as compared with check-basin. WUE was not affected with quantity of water but decrease in rate of N caused a decrease in WUE at all the quantities of water applied. In general, WUE was higher in PS as compared with NS. The agronomic efficiency of nitrogen increased from 21.65 to 28.59 kg of seed cotton per kg of N applied when same quantity of water and N was applied through drip irrigation as compared with check-basin. However, decrease in quantity of water applied resulted in a decrease in agronomic efficiency of N but reverse was true for rates of N applied. When the same quantity of water and N was applied under both the methods of planting, PS produced 22% higher seed cotton yield and along with reduced cost owing to half the number of laterals required.     

Effects of drip irrigation frequency on soil wetting pattern and potato growth in North China Plain

The effect of irrigation frequency on soil water distribution, potato root distribution, potato tuber yield and water use efficiency was studied in 2001 and 2002 field experiments. Treatments consisted of six different drip irrigation frequencies: N1 (once every day), N2 (once every 2 days), N3 (once every 3 days), N4 (once every 4 days), N6 (once every 6 days) and N8 (once every 8 days), with total drip irrigation water equal for the different frequencies. The results indicated that drip irrigation frequency did affect soil water distribution, depending on potato growing stage, soil depth and distance from the emitter. Under treatment N1, soil matric potential (ψ_m) Variations at depths of 70 and 90 cm showed a larger wetted soil range than was initially expected. Potato root growth was also affected by drip irrigation frequency to some extent: the higher the frequency, the higher was the root length density (RLD) in 0–60 cm soil layer and the lower was the root length density (RWD) in 0–10 cm soil layer. On the other hand, potato roots were not limited in wetted soil volume even when the crop was irrigated at the highest frequency. High frequency irrigation enhanced potato tuber growth and water use efficiency (WUE). Reducing irrigation frequency from N1 to N8 resulted in significant yield reductions by 33.4 and 29.1% in 2001 and 2002, respectively. For total ET, little difference was found among the different irrigation frequency treatments.     

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.     

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.     

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.     

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.     

The role of supplemental irrigation and nitrogen in producing bread wheat in the highlands of Iran

The West Asia and North Africa (WANA) region, with a Mediterranean climate type, has an increasing deficit in cereal production, especially bread wheat. Rainfed cropping in the highlands of this region coincides with the severely cold winter with mostly, snow from November to April. Cereal yields, are low and variable mainly as a result of inadequate and erratic seasonal rainfall and associated management factors, such as late sowing (or late crop emergence). In an area where water is limited, small amounts of supplemental irrigation (SI) water can make up for the deficits in seasonal rain and produce satisfactory and sustainable yields. This field study (1999–2002) on a deep clay silty soil in north west of Iran was conducted with four SI levels (rainfed, 1/3, 2/3 and full irrigation requirements) combined with different N rates (0, 30, 60, 90 and 120 kg ha⁻¹) with one wheat variety (Sabalan). Yields of rainfed wheat varied with seasonal rainfall and its distribution. A delay in the crop emergence from October (SI treatment) to November (rainfed) consistently reduced yields. With irrigation, crop responses to nitrogen were generally significant up to 60 kg N ha⁻¹. An addition of only limited irrigation (1/3 of full irrigation) significantly increased yields and maximized water use efficiency (WUE). Use efficiency for water and N was greatly increased by SI. Under deficit irrigation, maximum WUE would be achieved when 60 kg N ha⁻¹ is combined with 1/3 of full SI. Early crop germination is essential to ensure adequate crop stand before the winter frost and to achieve high yield. Early emergence can be achieved by applying a small amount (40–50 mm) of SI after sowing. Thus, when limited SI is combined with appropriate management, wheat production can be substantially and consistently increased in this highland semi-arid zone.     

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.     

Water requirement of drip irrigated tomatoes grown in greenhouse in tropical environment

Four different levels of drip fertigated irrigation equivalent to 100, 75, 50 and 25% of crop evapotranspiration (ET_c), based on Penman–Monteith (PM) method, were tested for their effect on crop growth, crop yield, and water productivity. Tomato (Lycopersicon esculentum, Troy 489 variety) plants were grown in a poly-net greenhouse. Results were compared with the open cultivation system as a control. Two modes of irrigation application namely continuous and intermittent were used. The distribution uniformity, emitter flow rate and pressure head were used to evaluate the performance of drip irrigation system with emitters of 2, 4, 6, and 8 l/h discharge. The results revealed that the optimum water requirement for the Troy 489 variety of tomato is around 75% of the ET_c. Based on this, the actual irrigation water for tomato crop in tropical greenhouse could be recommended between 4.1 and 5.6 mm day⁻¹ or equivalent to 0.3–0.4 l plant⁻¹ day⁻¹. Statistically, the effect of depth of water application on the crop growth, yield and irrigation water productivity was significant, while the irrigation mode did not show any effect on the crop performance. Drip irrigation at 75% of ET_c provided the maximum crop yields and irrigation water productivity. Based on the observed climatic data inside the greenhouse, the calculated ET_c matched the 75–80% of the ET_c computed with the climatic parameters observed in the open environment. The distribution uniformity dropped from 93.4 to 90.6%. The emitter flow rate was also dropped by about 5–10% over the experimental period. This is due to clogging caused by minerals of fertilizer and algae in the emitters. It was recommended that the cleaning of irrigation equipments (pipe and emitter) should be done at least once during the entire cultivation period.     

Water-use efficiency of dwarf-green coconut (Cocos nucifera L.) orchards in northeast Brazil

Field experiments were conducted in a tropical region to determine the water-use efficiency (WUE), yield (Y) and evapotranspiration (ET) of a 6-year-old dwarf-green coconut (Cocos nucifera L.) orchard. Three water levels were applied in plots with nine palms. The irrigation treatments denoted as T:50, T:100 and T:150 received 50, 100 and 150 L/plant/day, respectively. The actual evapotranspiration was obtained by the soil water balance (SWB) method. Yield and water-use efficiency were assessed in terms of bunches per plant, fruits per plant and water volume per fruit. The application of the SWB resulted in mean daily ET values of 2.5; 2.9 and 3.2 mm/day for irrigation treatment of T:50, T:100 and T:150, respectively, while the cumulative ET varied from 900 to 1100 mm as irrigation treatment increased from T:50 to T:150. Results also showed that ET values were higher in the beginning and end of the year and lower in the middle of the experimental period. The application of a high irrigation water volume does not necessarily resulted in high coconut fruits yield. Evapotranspiration, fruits yield and water-use efficiency were strongly affected by irrigation water volume in coconut palms. WUE values decreased with increasing irrigation water level for all productivity parameters.     

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.     

Regional cotton lint yield,ETc and water value in Arizona and California

Water value as agriculture production may be overlooked, though it is an important factor to rational water allocations within a region. An analysis of cotton (Upland and Pima) lint yield, lint yield-consumptive use ratio (LY:ET_c), water-use efficiency (WUE) and lint price for Arizona (AZ) and California (CA) during 1988–1999 is considered as part of an attempt to determine lint water value, or benefit. It included determination of means and variability of cotton lint production, LY:ET_c ratios and associated irrigation water values (IWVs) and compared these numbers with published estimates of WUE, forage hay water values and municipal water costs. Available rainfall, reference evapotranspiration (ET_o), lint yields and price data for counties in both states were used. Consumptive use was estimated using a four-stage crop coefficient function verified by literature values or County Advisor experience. As with dry matter production, cotton lint yields in interior valley regions of CA were weakly correlated with ET_c and averaged 1.33 Mg/ha (Upland) and 1.08 Mg/ha (Pima). Cotton lint yields in desert regions of AZ and CA were not correlated with ET_c. The greatest LY:ET_c ratios (1.9–2.1 kg/ha-mm) were in the San Joaquin valley of CA, were similar to that from WUE type studies and resulted in gross IWVs (∼3400–3800 US$/ha-m), with relatively moderate variability at a net irrigation water requirement (IWR) of approximately 720 mm. While this IWV is 2.5 times greater than water delivery prices below the California Delta, it is less than average municipal water costs of ∼4200 US$/ha-m for Los Angeles, San Francisco and Pheonix while the overall AZ/CA average cotton lint IWV is considerably less. However, cotton lint IWV is two to three times greater than that obtained for alfalfa and sudangrass hay crops in all regions.