Depletion Of Available Soil Water Research Articles

Partial Relief of Drought-Stressed Fennel (Foeniculum vulgare Mill.) in Response to Foliar-Applied Zinc

Few attempts have been made to explore the effect of Zn fertilization on the performance of medicinal plants in general and fennel in particular, under adverse conditions. This study was conducted to examine the efficacy of zinc (Zn) in correcting physiological responses of fennel to water deficit. Twelve field-grown fennel genotypes were subjected to two levels of irrigation (irrigation after 25%–35% and 75%–85% depletion of available soil water) and two levels of foliar-applied Zn (0 and 4 g kg−1). Water deprivation had significant effects on all characteristics; i.e., in contrast to seed essential oil concentration, harvest index, and superoxide dismutase (SOD) and catalase activities, it led to decreases in the rest of the attributes. Varietal differences in response to drought were meaningful for most of the traits. Genotypic variations for dry mass and seed yield were consistent with differences among the genotypes in leaf water potential, relative water content, proline concentration, and chlorophyll concentrations. Zinc led to significant increases in all physiological attributes, including activation of antioxidant defense responses manifested in ascorbate peroxidase and SOD activities and carotenoid concentration. The Zn-effect tended to be more notable in drought-stricken fennel plants in a majority of the traits. Based on our findings, Zn could be considered an effective micronutrient for ameliorating, at least in part, the stressful effects of water deficit on fennel.

Application of biochemical markers for the assessment of drought tolerance in alfalfa (Medicago sativa L.) cultivars

AbstractAlfalfa (Medicago sativa L.) cultivars respond differently to drought stress levels and oxidative injury. This may provide us with an important tool to identify the chemical mechanisms operative in drought tolerant genotypes. The present experiment was conducted to determine catalase (CAT), ascorbate peroxidase (APX) and peroxidase (POX) activities; malondialdehyde (MDA) content; herbage yield; stress susceptibility index (SSI); and drought tolerance index (DTI) of 10 alfalfa cultivars under four irrigation regimes (55, 65, 75 and 85% depletion of available soil water). Drought stress was observed to reduce herbage yield but increase CAT, APX and POX activities as well as MDA content; however, such alterations were cultivar‐drought level‐specific. With a few exceptions, Baghdadi had the highest CAT, POX and APX activities and lowest MDA content, lowest reduction in herbage yield and the lowest SSI and the highest DTI under all irrigation regimes suggesting that it was the most adapted and drought‐tolerant cultivar. Herbage yield had a significant and positive correlation with POX and a significant and negative correlation with MDA under all irrigation regimes indicating that they could be used as markers for selecting more drought‐tolerant cultivars in alfalfa. Catalase and APX also had a significant and positive correlation with herbage yield, thus they could be used as markers for selection of more drought‐tolerant cultivars. The results suggested that a wide variation in drought tolerance exists within alfalfa cultivars, thus selection for more drought tolerance is possible. In addition, chemical markers such as POX, CAT and APX activities and MDA content may be used to assist in selection for more drought tolerance cultivar in this species.

Iron supplement ameliorates drought-induced alterations in physiological attributes of fennel (Foeniculum vulgare)

This study was conducted to examine the response of fennel to foliar applied Fe under contrasting moisture conditions. Twelve fennel genotypes were subjected to two levels of irrigation (irrigation after 35 and 85 % depletion of available soil water) and two levels of Fe solution (0 and 4 g kg−1). Plants subjected to drought showed notable reductions in leaf chlorophyll a (Chl a), Chl b, relative water content (RWC), water potential (ψw), carotenoids, ascorbate peroxidase (APX), seed yield and plant dry mass (DM). Though, drought-treated plants indicated notable increases in proline concentration, super oxide dismutase (SOD) and catalase activities and seed essential oil concentration. Genotypic variations for DM and grain yield were consistent with differences among the genotypes in ψw, RWC, proline, Chl a and Chl b concentrations. Fe led to significant increases in APX and SOD activities and carotenoids, Chl a and Chl b concentrations. The mitigative effect of Fe tended to be more notable on the drought-stricken plants for a majority of the traits. From our findings, Fe could be appreciated as a micronutrient effective in ameliorating at least in part the stressful effects of drought on plants.

Optimizing Tillage and Irrigation Requirements of Sorghum in Sorghum-Pigeonpea Intercrop in Hamelmalo Region of Eritrea

Sorghum (Sorghum bicolor L. Moench) is cultivated as monocrop in Eritrea. Efforts were made to grow sorghum-pigeonpea (Cajanus cajan L. Millspp.) intercrop on the tillage, fertilizers and supplementary irrigations necessary for sorghum. Experiments were conducted in terraced fields at Hamelmalo during 2013-15 to evaluate growth and yield of sorghum-pigeonpea intercrop in split plot design with conventional tillage (CT), reduced tillage (RT) and zero tillage (ZT) in main plots and rainfed (I0), 50% of full irrigation (I1), 75% of full irrigation (I2) and 100% of full irrigation (I3) in subplots. All irrigations were stopped 15 days before sorghum maturity. Full irrigation was 60 mm applied at 50% depletion of available soil water in 1 m profile. Sorghum growth was faster than pigeonpea until 85 days from planting and pigeonpea growth accelerated only after sorghum harvesting. About 80% of sorghum roots were within 0.6 m profile but more than 75% of pigeonpea roots were below 0.60 m depth. This showed a weaker competition between the two crops for nutrients, water and light. Both grain and stover yields of sorghum were optimum in RT + I2 during the 2 years. Highest grain yield was 6900 kg·ha-1 in RT + I3 in 2013, which was at par with that in RT + I2. Mean residual soil moisture at sorghum harvesting was 74 mm·m-1, which decreased to 8 mm·m-1 by pigeonpea harvesting. Residual moisture was more in the irrigated than non-irrigated plots. Pigeonpea yields were optimum (1363 kg·ha-1) in RT + I3 and lowest (297 kg·ha-1) in ZT + I0. Average water use by sorghum-pigeonpea was 374 mm by sorghum harvesting and 438 mm by pigeonpea harvesting, producing total sorghum equivalent yield of 7475 kg·ha-1. This raised average water use efficiency from 12.6 kg·ha-1·mm-1 at sorghum harvesting to 17.1 kg·ha-1·mm-1 at pigeonpea harvesting. Benefit was doubled at 50% of full irrigation and >4 times at 75% of full irrigation.

Effectiveness of exogenous salicylic acid on root and shoot growth attributes, productivity, and water use efficiency of water-deprived fennel genotypes

This study was carried out to investigate the response of fennel (Foeniculum vulgare Mill.) to water deficit and exogenous application of salicylic acid (SA). Six fennel genotypes, from Iran (namely ‘Urmia’, ‘Hamadan’, ‘Kerman’, ‘Shiraz’, ‘Birjand’ and ‘Yazd’) were subjected to two levels of irrigation consisting of either irrigation after 35% (control) or 75% depletion of available soil water (water deficit) and 3 levels of treatment with SA (0.0, 0.5 and 1.0 mM). Root growth attributes, yield and yield components as well as irrigation water use efficiencies for seed, oil and dry masses of the shoot and whole plant were studied. Shoot dry mass, grain yield and essential oil yield were decreased due to water deficit. Furthermore, root growth attributes were decreased under water deficit, except for root diameter and dry mass, and root/shoot ratio. With the exception of irrigation water use efficiency for seed yield, all irrigation water use efficiency aspects were increased when fennel was subjected to water deprivation. Fennel genotypes were grouped according to their stress susceptibility indices (SSI) into drought-tolerant, moderately drought-tolerant and drought-sensitive groups. The largest drought-induced decreases in root length, root dry mass, root length density, number of fruits per umbel, seed yield, 1000-seed weight, seed essential oil yield, and irrigation water use efficiency for seed and oil yield were observed in genotype ‘Hamadan’ from the drought-sensitive group. Salicylic acid led to increases in root growth and yield attributes, seed essential oil content and yield, and irrigation water use efficiency aspects under both moisture conditions. Overall, foliar application of SA appeared to attenuate the negative effects of drought stress on fennel through increases in most of the root growth and yield attributes and the attenuation was more substantial in the drought-tolerant set of fennel genotypes.

Osmoregulation-mediated differential responses of field-grown fennel genotypes to drought

This study was aimed at examination of physiological and agronomic responses of fennel (Foeniculum vulgare Mill.) to water deficit. Twelve fennel genotypes namely ‘Kashan’, ‘Urmia’, ‘Hamadan’, ‘Kerman’, ‘Shiraz’, ‘Birjand’, ‘Mashhad’, ‘Ardabil’, ‘Bushehr’, ‘Avicenna’, ‘Isfahan’, and ‘Yazd’ were subjected to four levels of irrigation (irrigation after 35%, 55%, 75%, and 85% depletion of available soil water) in a field study in two years. Leaf water potential, relative water content (RWC), proline, total soluble sugars, chlorophyll a (Chl a), b (Chl b), total (Chl a+b), a/b (Chl a/b) along with dry mass (DM), seed yield and its attributes and seed essential oil content were measured. Water deprivation left significant effects on all characteristics, i.e. in contrast to seed essential oil content and harvest index, the rest of the attributes were decreased significantly with drought intensification. Varietal differences in response to drought were meaningful for most of the traits; i.e. genotypic variations for DM, grain yield and stress susceptibility index (SSI) were consistent with differences among the genotypes in physiological traits such as leaf water potential, RWC, proline, soluble sugars and chl content. Genotypes were discriminated according to their response to drought and SSI. Drought tolerant genotypes (‘Yazd’, ‘Kerman, ‘Mashhad’ and ‘Shiraz’) exhibited a greater capacity for accumulation of osmotic solutes associated with higher leaf water potential and RWC, compared to drought sensitive genotypes (‘Ardabil’, ‘Avicenna’, ‘Hamadan’ and ‘Birjand’). From our findings, fennel could be appreciated as a promising species in potentiating alternative industrial-medicinal crops in the face of the eminent challenge of water scarcity in arid and semi-arid climatic regions.

Drought stress mitigation by foliar application of salicylic acid and their interactive effects on physiological characteristics of fennel (Foeniculum vulgare Mill.) genotypes

This study was aimed at characterization of physiological responses of fennel to water deficit and exogenous application of salicylic acid (SA). Six fennel genotypes namely ‘Urmia’, ‘Hamadan’, ‘Kerman’, ‘Shiraz’, ‘Birjand’, and ‘Yazd’ were subjected to two levels of irrigation (irrigation after 35 and 75 % depletion of available soil water) and three levels of SA (0.0, 0.5, and 1.0 mM). Leaf water potential, relative water content (RWC), proline, total soluble carbohydrates, chlorophyll a (Chl a), b (Chl b), total (Chl a + b), a/b (Chl a/b) and carotenoids contents, catalase (CAT), ascorbate peroxidase (APX), and superoxide dismutase (SOD) specific activities along with seed yield per plant and seed essential oil content were measured. Water deprivation left significant effects on all characteristics, i.e., in contrast to the antioxidative enzymes activities and seed essential oil content, the rest of the attributes were decreased significantly with water deficit. Drought-tolerant genotypes (‘Yazd’ and ‘Shiraz’) exhibited higher accumulation of osmotic solutes and carotenoids along with higher leaf water potential, RWC, and antioxidant enzymes activities (CAT, APX, and SOD) than drought sensitive genotypes (‘Hamadan’ and ‘Birjand’). SA affected the activities of antioxidant enzymes and increased water potential, RWC, leaf osmolytes, chlorophyll and carotenoids, and seed essential oil content; the extent of the increases appeared greater when fennel was grown under drought. All the above effects helped the seed yield of fennel genotypes to increase with increase in SA level and led to the conclusion that drought-induced harmful effects on fennel could be alleviated by exogenously applied SA.

Identify Physiological Markers for Drought Tolerance in Alfalfa

Physiological markers may provide a shortcut for identifying drought tolerance in alfalfa (Medicago sativa L.). Thus, the objective of this study was to understand physiological properties of alfalfa to assess drought tolerance of its cultivars. Ten alfalfa cultivars (Qomi, Isfahani, Hamedani, Bami, Ordobadi, Gharayonje, Nikshahri, Yazdi, Baghdadi, and Cody) and four irrigation regimes (55, 65, 75, and 85% depletion of available soil water) were arranged as split plot in a completely randomized block design with three replications to determine the chlorophyll, carotenoid, soluble sugars, proline, relative water contents, and herbage yield response of alfalfa cultivars to drought stress. Physiological and herbage yield traits were drought level‐cultivar‐specific and discriminated the cultivars based on their drought tolerance. Based on the correlation between drought tolerance and measured traits at the highest drought level, carotenoid content (r = 0.94), was the most important marker followed by relative water content (r = 0.92) and soluble sugars content (r = 0.89), respectively, and Baghdadi was the most drought tolerant cultivar. The results showed that the physiological markers may be used to identify alfalfa germplasms for drought tolerance.

Effects of Salt and Water Stress on Leaf Production, Sodium and Potassium Ion Accumulation in Soybean

Leaf traits of three soybean genotypes viz., Galarsum, BD 2331 and BARI Soybean 6 were evaluated for their salt and water stress tolerance under the salinity levels of 0, 50 and 75 mM NaCl and water stress with 70% depletion of available soil water at the Bangabandhu Sheikh Mujibur Rahman Agricultural University (BSMRAU), Salna, Gazipur, Bangladesh. The treatment were imposed in plants on 21 days after emergence and continued up to 56 days of age. The results of this study indicated that leaf traits like leaf number, leaf area and its dry weight of the soybean genotypes were sharply decreased when the plants were exposed to water stress, salt stress and, combined salt and water stress conditions. Least reduction in leaf traits was observed in Galarsum in all stress conditions. All leaf traits decreased more in 75 mM NaCl salinity combined with water stress treatment. The leaf dry weight was decreased to 39.72, 38.58 and 39.43% of the control in Galarsum, BD 2331 and BARI Soybean 6, respectively. The genotype Galarsum also accumulated lower amount of Na+ and higher amount of K+ in leaf tissues under salt stress and, combined salt and water stress environments as compared to others.

Impact of soil water stress on Nigellone oil content of black cumin seeds grown in calcareous-gypsifereous soils

► Crop water stress index (CWSI) reflect the water requirement at different crop growth stages of black cumin crop. ► Soil water stress as well as soil gypsum content influence the yield of black cumin crop seed and its constituents, i.e., the pharmacologically active volatile oil dithymoquinone. ► The semi-empirical equations developed for CWSI can be used to determine the crop water stress using observed canopy-air temperature difference and vapor pressure deficits for pre-heading and post-heading stages of the black cumin crop grown in soils with different gypsum contents. Nigellone (dithymoquinone) is the main active constituent of volatile oil of black cumin ( Nigella sativa ) seeds. It is presently used in traditional medicines, for culinary as ornamentals, and is also considered for its abundant nectar secretion. While black cumin, investigated recently (for the oil, essential oil, and other biologically active constituents of their seeds) the effects of deficit irrigation on seeds Nigellone content produced on gypsifereous soils are not known. Randomized complete block design experiments were conducted with three replications and four irrigation treatments on soils with five different gypsum contents over two growing seasons (2008–2009 and 2009–2010). These experiments aim to monitor and quantify water stress and Nigellone volatile oil content of black cumin as a function of crop water stress index and soil gypsum content. The soil gypsum content treatments were 60.0 (G 1 ), 137.6 (G 2 ), 275.2 (G 3 ), 314.2 (G 4 ) and 486.0 (G 5 ) g kg −1 . Three irrigation treatments were based on replenishing the 0.60 m deep root zone to field capacity when the maximum allowable depletion (MAD) of the available soil water holding capacity of 25% (I 1 ), 50% (I 2 ) and 75% (I 3 ) were maintained in the crop experiments. A dryland treatment (fully stressed, I 4 ) was also included. The lower (non-stressed) and upper (stressed) baselines were measured to calculate crop water stress index. The crop water stress index behaved as expected, dropping to near zero following an irrigation and increasing gradually as black cumin plants depleted soil water reserves. The seasonal mean values of crop water stress index for the irrigation treatments; I 1 , I 2 , and I 3 were increased from 0.189, 0.287, 0.380 to 0.239, 0.366, 0.467, respectively when the soil gypsum content increased from 60.0 to 486.0 g kg −1 . The highest Nigellone volatile oil content of black cumin seeds was obtained for G 1 I 1 treatment (5.1 g kg −1 ) while the lowest content (3.5 g kg −1 ) was obtained for G 5 I 1 treatment. Equations that can be used to predict the Nigellone volatile oil content of black cumin seeds were developed for the three irrigation schedules of different maximum allowable depletion of available soil water holding capacity using the relationships between the Nigellone volatile oil content and the seasonal mean crop water stress index for different soil gypsum contents. The relationships between black cumin seed yield, Nigellone volatile oil content and seasonal mean crop water stress index values were primarily linear. These relations can be used to predict the yield of black cumin seeds, seeds Nigellone volatile oil content, and irrigation timing in soils with different soil gypsum contents. Thus, the obtained data will be beneficial for further research.

Integrated management of irrigation water and fertilizers for wheat crop using field experiments and simulation modeling

The reported study aimed at developing an integrated management strategy for irrigation water and fertilizers in case of wheat crop in a sub-tropical sub-humid region. Field experiments were conducted on wheat crop (cultivar Sonalika) during the years 2002–2003, 2003–2004 and 2004–2005. Each experiment included four fertilizer treatments and three irrigation treatments during the wheat growth period. During the experiment, the irrigation treatments considered were I 1 = 10% maximum allowable depletion (MAD) of available soil water (ASW); I 2 = 40% MAD of ASW; I 3 = 60% MAD of ASW. The fertilizer treatments considered in the experiments were F 1 = control treatment with N:P 2O 5:K 2O as 0:0:0 kg ha −1, F 2 = fertilizer application of N:P 2O 5:K 2O as 80:40:40 kg ha −1; F 3 = fertilizer application of N:P 2O 5:K 2O as 120:60:60 kg ha −1 and F 4 = fertilizer application of N:P 2O 5:K 2O as 160:80:80 kg ha −1. In this study CERES-wheat crop growth model of the DSSAT v4.0 was used to simulate the growth, development and yield of wheat crop using soil, daily weather and management inputs, to aid farmers and decision makers in developing strategies for effective management of inputs. The results of the investigation revealed that magnitudes of grain yield, straw yield and maximum LAI of wheat crop were higher in low volume high frequency irrigation (I 1) than the high volume low frequency irrigation (I 3). The grain yield, straw yield and maximum LAI increased with increase in fertilization rate for the wheat crop. The results also revealed that increase in level of fertilization increased water use efficiency (WUE) considerably. However, WUE of the I 2 irrigation schedule was comparatively higher than the I 1 and I 3 irrigation schedules due to higher grain yield per unit use of water. Therefore, irrigation schedule with 40% maximum allowable depletion of available soil water (I 2) could safely be maintained during the non-critical stages to save water without sacrificing the crop yield. Increase in level of fertilization increases the WUE but it will cause environmental problem beyond certain limit. The calibrated CERES-wheat model could predict the grain yield, straw yield and maximum LAI of wheat crop with considerable accuracy and therefore can be recommended for decision-making in similar regions.

Effect of fertilization and irrigation schedule on water and fertilizer solute transport for wheat crop in a sub-humid sub-tropical region

In order to increase the water and fertilizer use efficiency and decrease the losses of water and fertilizer solutes (N and P), it is necessary to assess the influence of level of fertilization and irrigation schedule on movement and balance of water and fertilizers in the root zone. With this goal, the reported study was undertaken to determine the effect of fertilization and irrigation schedule on water movement and fertilizer solute transport in wheat crop field in a sub-tropical sub-humid region. Field experiments were conducted on wheat crop of cultivar Sonalika ( Triticum aestivum L.) during the years 2002–2003, 2003–2004 and 2004–2005. Each experiment consisted of four fertilizer treatments and three irrigation treatments during the wheat growth period. During the experiment, the irrigation treatments were: I 1 = 10% maximum allowable depletion (MAD) of available soil water (ASW); I 2 = 40% MAD of ASW; I 3 = 60% MAD of ASW. The fertilizer treatments during the experiment were: F 1 = control treatment with N:P 2O 5:K 2O as 0:0:0 kg ha −1; F 2 = fertilizer application of N:P 2O 5:K 2O as 80:40:40 kg ha −1; F 3 = fertilizer application of N:P 2O 5:K 2O as 120:60:60 kg ha −1 and F 4 = fertilizer application of N:P 2O 5:K 2O as 160:80:80 kg ha −1. The results of the investigation revealed that low volume high frequency irrigation results in higher deep percolation losses than the low frequency high volume irrigation with different levels of fertilization for wheat crop in coarse lateritic soil, whereas different levels of fertilization did not significantly affect soil water balance of the wheat crop root zone during all the irrigation schedules. Level of fertilization and irrigation schedule had significant effect on nitrogen leaching loss whereas irrigation schedules had no significant effect on nitrogen uptake under different levels of fertilization. On the other hand, the leaching loss of phosphorus was not significantly influenced by the irrigation schedule and level of fertilization of wheat crop. This indicated that PO 4–P leaching loss was very low in the soil solution as compared to nitrogen due to fixation of phosphorus in soils. From the observed data of nitrogen and phosphorus use efficiency, it was revealed that irrigation schedule with 40% maximum allowable depletion of available soil water with F 2 fertilizer treatment (N:P 2O 5:K 2O as 80:40:40 kg ha −1) was the threshold limit for wheat crop with respect to nitrogen and phosphorus use, crop yield and environmental pollution.

Development of crop water stress index of wheat crop for scheduling irrigation using infrared thermometry

This study was conducted to develop the relationship between canopy–air temperature difference and vapour pressure deficit for no stress condition of wheat crop (baseline equations), which was used to quantify crop water stress index (CWSI) to schedule irrigation in winter wheat crop ( Triticum aestivum L.). The randomized block design (RBD) was used to design the experimental layout with five levels of irrigation treatments based on the percentage depletion of available soil water (ASW) in the root zone. The maximum allowable depletion (MAD) of the available soil water (ASW) of 10, 40 and 60 per cent, fully wetted (no stress) and no irrigation (fully stressed) were maintained in the crop experiments. The lower (non-stressed) and upper (fully stressed) baselines were determined empirically from the canopy and ambient air temperature data obtained using infrared thermometry and vapour pressure deficit (VPD) under fully watered and maximum water stress crop, respectively. The canopy–air temperature difference and VPD resulted linear relationships and the slope ( m) and intercept ( c) for lower baseline of pre-heading and post-heading stages of wheat crop were found m = −1.7466, c = −1.2646 and m = −1.1141, c = −2.0827, respectively. The CWSI was determined by using the developed empirical equations for three irrigation schedules of different MAD of ASW. The established CWSI values can be used for monitoring plant water status and planning irrigation scheduling for wheat crop.

Effective management of irrigation water for maize under stressed conditions

Fresh water is becoming scarce not only in arid and drought prone areas but also in regions where rainfall is abundant. Effective management of water for agricultural production in water scarcity regions therefore requires the use of innovative and sustainable approaches. The reported study was undertaken to determine an efficient strategy for management of irrigated maize under water stressed conditions, in a sub-tropical region. Field experiments were conducted on the crop over a period of 3 years with five different irrigation treatments. Layer-wise soil moisture status was continuously monitored to determine the crop water extraction pattern and hence the optimum irrigation management depth. Five irrigation treatments were maintained based on predefined levels of maximum allowable depletion (MAD) of available soil water. The treatments were 10% ( T 1), 30% ( T 2), 45% ( T 3), 60% ( T 4) and 75% ( T 5) maximum allowable depletion of available soil water. CERES-Maize growth simulation model was calibrated and validated for further use. The depth and time variation of soil moisture were assessed by measuring the soil moisture periodically in 15–30 cm, 30–45 cm, 45–60 cm, 60–90 cm and 90–120 cm soil profiles with a neutron probe; while the soil moisture in 0–15 cm soil profile was determined by gravimetric method. It was observed that the plants extracted most of the soil moisture from 0–45 cm soil layer. Therefore, it is recommended that only 0–45 cm soil profile be considered for scheduling of irrigation in case of maize, grown in sandy loam soil in the sub-tropical regions. Measured and simulated results revealed that under water scarcity condition, plant extractable soil water depletion of more than 45% of ASW must be avoided even during non-critical growth stages to obtain high water use efficiency and net return. The calibrated CERES-Maize Model was found to be quite efficient in simulation of yield parameters and layer-wise soil moisture extraction pattern.

Effects of Water Stress at Different Growth Stages on Greenhouse Tomato Yield and Quality

Tomatoes (Lycopersicon esculentum Mill. cv. Sunstart) were grown in a greenhouse during Summer 1999 and again in Winter 2000. Two available soil water (ASW) deficit thresholds, 65% and 80%, at which plants were irrigated to field capacity were factorially combined with five irrigation timing patterns: 1) no water stress; 2) stress throughout the entire growing season; 3) stress during first cluster flowering and fruit set 4) stress during first cluster fruit growth; and 5) stress during first cluster fruit ripening. Crop yields, water use efficiency, as well as maximum and minimum equatorial fruit diameters and fruit height were measured. Quality parameters of soluble solids, pH, and fruit color were also measured. Water stress throughout the growing season significantly reduced yield and fruit size, but plants stressed only during flowering showed fewer but bigger fruit than completely non-stressed plants. Consequently, on a weight basis the stressed at flowering and nonstressed plants had similar yields. Nonstressed and flowering-stressed fruit showed lower soluble solids and a lighter color of red ripe fruit than the other stress treatments. No significant differences in yield or quality were found between the two stress levels (65% vs. 80% ASW depletion before irrigation). Water stress only during flowering resulted in better yields and quality than stress at other specific developmental stages or at all times, but equal or poorer yields and water use efficiency than nonstressed plants.

Effective management of irrigation water for wheat under stressed conditions

Scarcity and growing competition for fresh water resource will reduce its availability for irrigation. At the same time, the need to meet the growing demand for food will require increased crop production using less water. Regulated deficit irrigation provides a means of reducing water consumption while minimizing adverse effects on yield. The reported study was undertaken to determine an efficient strategy for management of irrigated wheat under water stressed conditions, in a sub-tropical sub-humid region. Field experiments were conducted on the crop over a period of 3 years with five different irrigation treatments. Layer-wise soil moisture status was continuously monitored to determine the crop water extraction pattern and hence the optimum irrigation management depth. Irrigation treatments consisted of different levels of depletion of available soil water. The five levels of depletion considered in the study were 10, 30, 45, 60 and 75%. CERES-wheat growth simulation model was calibrated and validated for further use. In order to asses the depth and time variation of soil moisture under different scheduling of irrigation, soil moisture was measured periodically in 15–30, 30–45, 45–60, 60–90 and 90–120 cm soil layers using a neutron probe, while the soil moisture in 0–15 cm soil layer was determined by gravimetric method. It was observed that the plants extracted most of the soil moisture from 0 to 45 cm soil layer. Therefore, it is recommended that only 0–45 cm of soil layer be considered for scheduling of irrigation for wheat grown in sandy loam soil in a sub-tropical regions under water scarcity conditions. The field water use efficiency of wheat was found to be the highest when irrigation was scheduled at 45% depletion of available soil water (ASW). It is therefore recommended that under the condition of water scarcity, plant extractable soil water depletion of more than 45% of ASW must be avoided during non-critical stages. The calibrated CERES-wheat model was found to be quite efficient in the simulation of yield parameters and layer-wise soil moisture extraction pattern. It can therefore be successfully used for decision making in the region.

The Impact of Drought Stress and/or Nitrogen Fertilization in Some Medicinal Plants

SUMMARY Several pot experiments were set up to follow the impact of drought stress and/or nitrogen fertilization on the yield and secondary metabolites content of medicinal and aromatic plants (MAP) accessions held within Genebank for MAP in Slovenia. The results of pot trials with fenugreek and with deadly nightshade are presented. In fenugreek (Trigonella foenumgraecum L., Fabaceae) the maximal yield of dios-genin was achieved in plants grown under an optimal irrigation regime (35% depletion of available soil water). Drought stressed seeds of cv. Margaret contained less diosgenin (p = 0.0021) than irrigated plants (0.123%, dw). In deadly nightshade (Atropa belladonna L., Solanaceae), the content of tropane alkaloids was determined. The results of the plant treatment responses showed that the maximal yield of tropane alkaloids (hyoscyamine: 54 mg/plant; scopolamine: 7 mg/plant) was achieved in plants grown under an optimal irrigation regime (35% depletion of available soil water) accompanied with a total nitrogen supply of 0.37 g/pot. By contrast, the maximal content of alkaloids was achieved with 95% depletion of available soil water and a nitrogen supply of 1.60 g/pot.

Sequential Cropping as a Function of Water in a Seasonal Tropical Region

In the seasonal (wet–dry) tropics, yields of rainfed staple crops are usually low and variable. However, our simulations have indicated that rainfall could be used more efficiently, increasing the length of the rainfed cropping season, the number of crops grown, and their yields, while decreasing yield variability and risk. To evaluate these predictions, cropping schemes with two or three annual rainfed crops grown in sequence were field‐tested. Irrigated plantings were subsequently added to evaluate year‐round cropping. Work was conducted in Costa Rica during 4 yr at one site and 1 yr at a second site. Both sites have a half‐year‐long, bimodal rainy season, and have deep soils with high water‐holding capacity. The first crop of each year was planted early using preseason rains, and the last was planted to mature after the rainy season to maximize depletion of available soil water. Rainfed cropping sequences averaged 255 d long, which is from 50 to 100 d longer than local practices. Adding an irrigated planting during the dry season brought the mean length of the cropping season up to 346 d. Of 115 plantings, only 7 had low yields; all others had medium or high yields. Adding an irrigated crop increased yield potential of a year‐round cropping season composed of two or more plantings. All low yields were attributed here to extended water excess conditions. However, water excess effects do not remain after the rainy season, nor into the next rainy season.

Effect of water stress and nitrogen fertilization on the content of hyoscyamine and scopolamine in the roots of deadly nightshade ( Atropa belladonna)

The study intended to elaborate the optimal environmental conditions of water supply and nitrogen fertilization for maximum content of hyoscyamine (% dw) and scopolamine (% dw). Plants grown from seeds of Slovene autochthonous population of deadly nightshade ( Atropa belladonna), were treated with different water regimes (35–95% depletion of available soil water) together with enhanced nitrogen supply (0.37–1.60 g/pot N) in a greenhouse experiment. Dry plant extracts from 32-week old roots were analysed with capillary electrophoresis (CE) for the presence of tropane alkaloids (hyosciamyne, scopolamine). The results of the plant treatment responses showed that the maximal yield of tropane alkaloids (hyoscyamine: 54 mg/plant; scopolamine: 7 mg/plant) was achieved in plants grown under an optimal irrigation regime (35% depletion of available soil water) accompanied with total nitrogen supply of 0.37 g/pot. By contrast, the maximal content of alkaloids was achieved with 95% depletion of available soil water and a nitrogen supply of 1.60 g/pot.

Irrigation management methods for reducing water use of cowpea (Vigna unguiculata [L.] Walp.) and lima bean (Phaseolus lunatus L.) while maintaining seed yield at maximum levels

In a previous study conducted at the University of California at Riverside, it was shown that water use of cowpea could be reduced while maintaining seed yields by withholding irrigation during the vegetative stage in a rain-free environment, and then irrigating when estimates based on potential evapotranspiration, indicated 40% depletion of available moisture in 90-cm depth of soil. The general applicability of this efficient irrigation management method was tested by experiments conducted at the West Side Field Station in the San Joaquin Valley of California with six irrigation treatments, three different row spacings (single rows on 76- and 102-cm beds, and double rows on a 102-cm bed), a semi-erect cultivar of cowpea (Vigna unguiculata [L.] Walp.), and a prostrate cultivar of lima bean (Phaseolus lunatus L.). Withholding irrigation during the vegetative stage following pre-irrigation substantially reduced dry matter at anthesis (−17% to −38%) and water use (−101 mm) of cowpea, but did not influence seed yield or shoot dry matter at harvest for either cowpea or lima bean. Increasing the irrigation interval until 75% nominal depletion of available water in 90-cm depth of soil reduced water use (−139 cm), but did not affect seed yield of cowpea. Lima bean, however, showed a significant decrease in shoot dry matter production (−17%) and in seed production (−18%) at the longest irrigation interval involving 75% nominal depletion. The different row spacings used in this experiment did not affect shoot dry matter or seed production of the semi-erect cowpea. However, shoot dry matter and seed yield were significantly greater for the prostrate lima bean grown with double rows on a 102-cm bed. Seed yield was 46% and 18% greater than with single rows on 76-cm and 102-cm beds, respectively. Generally, variations in seed yields of lima bean were positively correlated with variations in shoot dry matter production. Nominal depletion of available soil water provided a practical method for scheduling irrigations, but the results with cowpea indicated that the critical level, which resulted in the greatest reductions in water use while maintaining maximum seed yield varied from 40% (at Riverside) to 75% (at West Side Field Station). Additional methods are needed to fine-tune irrigation which is based mainly on nominal depletion of available water. Generally, pressure chamber estimates of leaf water potential exhibited too little variation among plants subjected to different irrigation treatments for it to be useful for fine-tuning irrigation schedules for either cowpea or lima bean. However, differences in temperature between canopy and air, when expressed as a function of either vapor pressure deficit or canopy temperature, and related to percent reduction in yield, appeared to have sufficient resolution to provide a practical method for fine-tuning irrigation schedules for cowpea during flowering and pod-filling, but not lima bean. Normalizing temperature differences with vapor pressure deficit was more effective, but normalizing with canopy temperatures is more convenient because it does not require a measurement of air humidity.