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This study was conducted to investigate the effects of two irrigation regimes (55 and 85% of soil available water depletion) and two nitrogen levels (0 and 112.5 kg ha−1) on yield as well a...

Research on water stress strategies (WSS) and crop response to water stress is important to improve irrigation water productivity (WPI) and crop production especially for regions where water is a limited resource. This study was conducted to assess (i) the response of silage maize to water stress at different growth stages for contrasting water stress strategies in the semi-arid environment under pot and field experiments irrigated by a drip-tape system, (ii) to determine the relationship between applied water and total biomass (TB) in different WSS in both experiments. The hybrid 704-single-cross of maize was assessed at pot experiment during 2009 and 2010 and field experiment was conducted in 2017 under two WSS including WS1 (same irrigation event with different applied water depth) and WS2 (same applied water depth in different irrigation event) at three growth stages. Each WSS consisted of four different irrigation levels, including severe, moderate, and mild drought stress and a full irrigation. In both pot and field experiments, severe drought stress under WS1 and WS2 strategies led to a depression in LA and TB at tassel (S2) and silage harvest (S3) stages. At each growth stage, WPI values decreased with increasing water-deficit levels in both WSS’s and experiments. We found a linear relationship between TB and applied water for WS1 and WS2 in both experiments. However, the yield performance per unit of water used was higher for WS1 than for WS2. The yield response factor to stress (Ky) values for LA and TB were higher under WS2 than WS1 in both experiments, indicating that WS1 can be employed as an effective deficit irrigation management under the drip-tape irrigation system for maize in an arid area with shortage of water.

Knowledge about biomass partitioning of maize grown in arid and semi-arid climates is scarce and yet essential to select a robust and effective deficit irrigation management (DIM) strategy for these regions. The objectives of this study were to: i) investigate the effects of different levels of water application under two DIM strategies on the root and aboveground characteristics, the response factor to water stress (Ky) and irrigation water use efficiency (IWUE) of silage maize at different growth stages, and ii) determine the best DIM strategy that would maximize biomass productivity. Field pot experiments were conducted in Isfahan, Iran, during 2009 and 2010. The two DIM strategies were fixed irrigation interval-variable irrigation depth (M1), and variable irrigation interval-fixed irrigation depth (M2). Each DIM strategy was tested at four water-deficit levels, including: severe, moderate, mild, and a full-irrigation. In M1, irrigation intervals were consistent for all irrigation treatments but were varied over the growing season. Treatment effects were measured at the 10-leaf, 16-leaf, tasseling, milk, and silage harvest crop growth stages. There was significant effect of irrigation and growth stage on total aboveground biomass (TB), leaf area (LA), root biomass (RB), and root:shoot ratio (RSR) for both DIM strategies during the two years. For M2, there was significant difference in TB, LA, RB, and RSR between all irrigation levels at all growth stages. TB production was on the average around 25% higher for M1 compared to M2, even though total applied irrigation water was only 6% higher for M1. Comparing the two DIMs showed that RSR and Ky were both higher for M2, indicating that the crop was more sensitive to this strategy. In conclusion, M1 was selected as the best management practice since it had more favorable effects on improving the IWUE and also on the development of maize roots during the growing season.

Alfalfa (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.

Water scarcity encourages municipalities to use more precise irrigation systems in arid urban landscapes. However, major concerns are associated with the adaptation of mature trees to new irrigation systems after they have matured under traditional management. We investigated the adaptation of mature olive trees to a change in irrigation system from a traditional surface to an automatic drip irrigation system in a coarse-textured urban forest park. The growth indices of eight-year-old olive trees were monitored for the period of 2012–2014 under three irrigation systems: (1) automated drip irrigation (ADI) for trees that matured under traditional basin-surface irrigation (TSI), (2) TSI since plantation, and (3) traditional drip irrigation (TDI) irrigating the trees depending on water availability since the time of planting. We additionally determined the spatial pattern of root development by collecting 156 soil samples from each irrigation system with a 20 × 20-cm grid system (120 cm width × 80 cm depth) in the soil profile. Results showed no significant differences in terms of fruit productivity between TSI and recently established ADI systems. Automated drip irrigation resulted in the maximum root density with a uniform root distribution pattern, where roots expanded all over the soil profile. In TSI, however, the roots were distributed irregularly, with the highest density close to the irrigation basin. The wide spacing between drippers in the TDI system created large gaps between the wetted zones in the soil with a low water-holding capacity, leading to a discrete small root system. The present study highlights the positive response of mature olive trees to the replacement of the irrigation system in an urban forest park with limited available water and low soil quality. Our findings will help municipalities to properly preserve mature urban trees and the ecosystem services for their inhabitants. Non

Sunflower has become an important crop for oil production in many arid regions across the globe. However, with water as a scarce resource, efficient water and nutrient management systems need to be identified. The goal of this project was to determine the interaction between water and nitrogen (N) for sunflower grown in an arid environment. Experiments were conducted during 2010 and 2011 in an arid region in Iran that included two sunflower hybrids, four levels of surface drip irrigation, ranging from severe deficit irrigation to over irrigation, and three levels of N fertilizer, i.e. 0, 47, and 93 kg N ha−1. The treatments were arranged in a strip-plot design with complete randomized blocks with three replications. Irrigations were based on daily monitoring of soil moisture in the experimental plots. For both hybrids, irrigation and the interaction of water and N had a significant effect (P

Identification and selection of plant genotypes with survival, recovery and sustainable performance during drought periods is one of the main objectives of plant improvement for arid and semi-arid regions. This study aimed to evaluate root traits and recovery of tall fescue genotypes after a period of drought stress. A total of twenty four tall fescue genotypes were selected from a wide polycross population and assessed for field drought tolerance based on stress tolerance index (STI) and recovery during 2010–2013. The genotypes were classified as tolerant, moderately tolerant and susceptible based on STI. Then, in 2014, genotypes were assessed in a pot experiment for root characteristics under two levels of moisture environments (control and intense drought stress). In both moisture environments, root length (RL), root area (RA), root volume (RV) and root weight (RW) were negatively correlated with days to recovery (DR). Genotypes that recovered from drought had greater RL, RA, RV and RW than the genotypes unable to recover. Principle component analysis (PCA) was performed to identify genotypes with superior root characteristics, stress tolerance and recovery potential that can be used for future breeding programmes. Results indicated that selection based on combining STI, recovery and extensive root system might improve drought tolerance of tall fescue.

Water shortage has encouraged the quest for alternative sources of water for food production and agricultural development. Recycled water (RW) is one of the most available water resources with great potential for use in farm irrigation. This experiment was carried out to investigate the use of RW as the irrigation source and its application method, subsurface leaky irrigation (SLI) system or surface irrigation, in an orchard with young olive trees in central Iran. The results revealed that the SLI system was able to enhance tree growth, leaf area, maximum fluorescence (Fv/Fm) and photosynthesis rate by 68%, 26%, 4%, and 42%, respectively. In addition, trees irrigated with the SLI system using RW exhibited increased N and Mg uptakes by 138% and 8%, respectively. Plants irrigated with RW showed a growth improvement (42%), leaf area (26%), and photosynthesis rate (23.4%) compared with those irrigated with clean water. Furthermore, Mg, Na, K, P, and N content increased by 12%, 59%, 30%, 7%, and 92%, respectively, in leaf tissue when RW was applied. The results indicated that RW could be employed as a reliable irrigation source especially when it was delivered with the SLI system.

Silicon (Si) is considered as a beneficial element to higher plants especially under stress conditions. A factorial experiment, in a completely randomized design with four replications, was used to investigate the effects of two application methods (spraying and soil drenching) and eight levels of Si compounds including 0, 5, 10 and 15 mM of potassium silicate (K2SiO3) and 0, 5, 10 and 15 mM of nanosilica (SiO2). The results indicated that Si application (all or some treatments) decreased transpiration, specific leaf area, petiole length, and promoted the flowering, fruit firmness, leaf/crown number, fresh and dry weight of shoot and root, water use efficiency. They also showed it did not affect the fruit set percentage, yield, chlorophyll index, total soluble solid, leaf area, fresh and dry weight of crown, photosynthesis, stomatal conductance, internal carbon dioxide (CO2) concentration and mesophyll efficiency of strawberry. The results suggest the beneficial effects of Si on growth and develop...

Because of limiting water resources and increasing demand for food, it is necessary to investigate the effect of irrigation systems on water productivity. This research was conducted to evaluate yield and yield characteristics of two potato varieties under sprinkler and trickle irrigation systems. The treatments were two irrigation systems (sprinkler and trickle irrigation) and two potato varieties (Burren and Satina) in a randomized complete block design with three replications. Full irrigation was done based on moisture depletion from depth of root development in both irrigation methods.. Potato yield and water productivity (WP) in drip and sprinkler irrigation systems showed significant differences (P

SummaryTwo sources of water (clean water or recycled water) and two types of irrigation system [sub-surface leaky irrigation (SLI) or surface irrigation (SI)] were applied in a split-plot experimental design, with four replicates, to study the effects of water quality and irrigation system on the physiological behaviour and growth of olive trees (Olea europea L.) in a semi-arid region.The results showed that SLI affected not only the number of open stomata, stomatal length, rate of net photosynthesis (by 32%), leaf areas (by 21%), and stomatal conductance, but also leaf nitrogen and proline concentrations. Plants irrigated with recycled water had higher rates of photosynthesis (by 22%) and leaf areas (by 14%) compared to those given clean water. Recycled water increased the uptake of nitrogen (N) and magnesium (Mg2+) ions by 67.5% and 6.0%, respectively, which could result in higher chlorophyll concentrations, rates of photosynthesis and, eventually, enhanced plant growth. The results suggest that the use...

Genetic analysis of root and physiological traits and selection of genotypes with higher drought tolerance through these traits is generally limited in tall fescue. In this study, some parental genotypes of tall fescue first were assessed for field drought tolerance in 2014–2015 and then the polycross seeds were harvested to provide half-sib families. Sixteen half-sib families along with their corresponding parental genotypes were assessed in a pot experiment for root and physiological characteristics under three irrigation levels (control, mild and intense) in 2016. The results showed that drought stress decreased dry forage yield (DFY), relative water content and total chlorophyll and increased carotenoid and proline in both parental genotypes and half-sib families. Intense drought stress decreased most of the root traits at 0-30 cm soil depth while at 30–60 cm depth length, area, volume and dry weight of roots were increased. A broad range of general combining ability (GCA) was observed for DFY (21M and 9E), root (21M, 12L and 20L) and physiological characteristics (12L and 9E) at three irrigation levels. Moderate to high estimates of narrow sense heritability (0.40–0.72) as well as genetic variation for root and physiological traits, indicated that phenotypic selection can be successful to attain genetic progress. Indirect selection to improve DFY was more effective through selection for root and some physiological traits. Significant associations of root and some physiological traits with drought tolerance demonstrated that these traits could be used as appropriate selection criteria to elevate forage yield and identify superior genotypes for arid and semi-arid regions.

International audience; Climate change models predict more frequent and severe droughts in the world. For the future adaptation of perennial forage grasses, identification and selection of genotypes with enhanced recovery and persistence under repeated drought is crucial. The aim of the present study was to investigate traits related to persistence, recovery, and root adaptation in three sets of tall fescue genotypes with different flowering date, after successive drought stress. A total of 72 genotypes of tall fescue (24 medium, 24 late, 24 early flowering) were assessed for agro-morphological traits and persistence during 2010-2014 under two levels of soil moisture. In 2015, irrigation was withheld and all genotypes were evaluated for drought recovery in the field. Then 18 genotypes were chosen based on field results to evaluate their root traits at two irrigation levels (control and intense drought stress) in pots. In the field, plant persistence decreased from year 2 to 5 under both control and intense drought stress conditions in all three sets of genotypes, although persistence of late flowering genotypes was higher. The results also indicated that most of the genotypes with greatest persistence had higher recovery after the final severe drought. Persistence and recovery were positively correlated with root length (RL), root area (RA), root volume (RV), root weight (RW) and root to shoot ratio (R/S) under both soil moisture. Moreover, genotypes with higher recovery after drought had more RL, RA, RV and R/S than others. Application of principle component analysis to identify genotypes of interest for future breeding programs is discussed.

Research on crop response to deficit irrigation is important to reduce agricultural water use in areas where water is a limited resource. The objective of this study was to evaluate changes in physiological and root traits under mild and intense drought stress in tall fescue. It also sought to find associations between these changes and field drought tolerance. A total of 24 tall fescue genotypes were selected from a wide polycross population and assessed for field drought tolerance during 2011–2012 in the field. The genotypes were classified as tolerant, moderately tolerant, and susceptible based on drought stress tolerance index (STI), tolerance index (TOL), and yield reduction (YR). In 2013, 24 genotypes were clonally propagated and planted in polyvinylchloride (PVC) tubes under, three levels of moisture regimes. Root characteristics were investigated at 0–30 and 30–60 cm depths of soil. Also 11 physiological traits, dry forage yield, STI, TOL, and YR were recorded. At the 30–60 cm depths of soil, the root length increased by 5.95 and 7.30 % under mild and intense stress, respectively. Under mild stress, root area and root volume were positively correlated with STI. Consequences of drought stress, manifested as declined relative water content and chlorophyll, could be associated with a decrease in the activity of antioxidant enzymes. Some tall fescue genotypes had extensive root systems, high photosynthetic capacity, and less YR in the field. These genotypes may adapt to drought through drought avoidance and drought tolerance mechanisms. The application of principle component analysis for screening suitable genotypes was also discussed.

The knowledge on the relationships of protein and micronutrient concentration in wheat grain with edaphic characteristics could provide valuable information for site-specific fertilization of crops for producing grains denser in micronutrients such as iron (Fe) and zinc (Zn) in rain-fed agriculture. In this study, we used soil properties and topographic parameters in the artificial neural network (ANN) methodology as a power tool for improving models for predicting wheat grain micronutrient and protein contents in the hilly regions of western Iran. Soil and grain samples were collected from 1 m2 plots using the stratified random method, whereas the slope positions were considered as the basis of soil sampling, at 100 selected points. The mean grain Zn, Fe, Cu (copper) and Mn (manganese) concentrations were 37.02, 65.86, 14.79 and 44.93 mg–1 kg–1, respectively, and mean grain protein was 13.76%. Application of the ANN models for predicting Zn, Fe, Cu, Mn and protein contents in grains improved prediction b...

Quantification of the interactive effects of nitrogen (N) and water on nitrate (NO3) loss provides an important insight for more effective N and water management. The goal of this study was to evaluate the effect of different irrigation and nitrogen fertilizer levels on nitrate-nitrogen (NO3-N) leaching in a silage maize field. The experiment included four irrigation levels (0.7, 0.85, 1.0, and 1.13 of soil moisture depletion, SMD) and three N fertilization levels (0, 142, and 189 kg N ha−1), with three replications. Ceramic suction cups were used to extract soil solution at 30 and 60 cm soil depths for all 36 experimental plots. Soil NO3-N content of 0–30 and 30–60-cm layers were evaluated at planting and harvest maturity. Total N uptake (NU) by the crop was also determined. Maximum NO3-N leaching out of the 60-cm soil layer was 8.43 kg N ha−1, for the 142 kg N ha−1 and over irrigation (1.13 SMD) treatment. The minimum and maximum seasonal average NO3 concentration at the 60 cm depth was 46 and 138 mg l−1, respectively. Based on our findings, it is possible to control NO3 leaching out of the root zone during the growing season with a proper combination of irrigation and fertilizer management.

Water scarcity and environmental pollution due to excessive nitrogen (N) applications are important environmental concerns. The Varamin region, which is located in the central part of Iran, is one of the locations where farmers apply 250–350 kg N ha−1 for silage maize without any concerns with respect to the available water for irrigation. The objective of this study was to quantify the response of the silage maize (Zea mays L.) to variable irrigation and N fertilizer applications under arid and semi-arid conditions and to determine the optimum amount of N fertilizer as a function of irrigation. The maize Hybrid 704 single-cross was planted on 3 August 2003 and on 25 June 2004. The experimental treatments consisted of three N rates (0, 150, and 200 kg N ha−1) and four levels of irrigation, including two deficit irrigation levels 0.70 SWD (soil water depletion) and 0.85 SWD, a full-irrigation level (1.0 SWD) and an over-irrigation level (1.13 SWD). Twelve treatments were arranged in a strip-plot design in a randomized complete block with three replicates. Gravimetric soil samples were collected in 2003 and a neutron probe was used in 2004 to measure soil water content. Leaf area index, total aboveground biomass (TB), plant height, stem diameter, and leaf, stem, and ear dry weight were measured during the growing seasons and at final harvest. Total aboveground biomass was affected by irrigation (P 0.5). Total aboveground biomass and biomass of the crop components increased as a function of the amount of water and N applied. For each of the irrigation levels, there was an associated optimum amount of N, which increased as the amount of irrigation water that was applied increased. Among the four irrigation levels that were studied, 0.85 SWD was the optimum level of irrigation for the conditions at the experimental site. The results also indicated that an increase in N applications is not a good strategy to compensate for a decrease of TB under drought stress conditions. We concluded that the effect of N fertilizer on TB depends on the availability of water in the soil, and that the amount of N fertilizer applied should be decreased under drought stress conditions. Further research will combine these results with a crop simulation model to help optimize nitrogen and water management for silage maize.

We examined the main and interactive effects of nitrogen (N) and deficit irrigation (DI) on the yield response factor ( K y ), water use efficiency (WUE), and irrigation water use efficiency (IWUE) of silage maize from a semiarid region of Iran. Experiments were conducted in 2003 and 2004 that included three N fertigation rates (0, 150, and 200 kg N ha −1 N0, N150, and N200, respectively) and four irrigation levels (0.7, 0.85, 1.0, and 1.13 of soil water depletion, W1, W2, W3, and W4, respectively). The soil water content measurements showed that most of the water was extracted from the top 60 cm of the soil profile. DI increased WUE for all N fertilizer treatments with the maximum value being observed at the W2 level. The average of the IWUE for the two years of the study showed that the lowest IWUE was 1.38 kg m −3 for the N0W1 treatment, while the highest IWUE was 1.8 kg m −3 for the N200W3 treatment. A linear relationship was observed between evapotranspiration and the total biomass for all N fertilizer levels in 2003 and 2004. The minimum K y to water was obtained from the N0 level as 0.64 in 2003 whereas the maximum K y was recorded from the N200 level as 0.95 in 2004. This reveals that higher N rates application would enhance corn yield sensitivity to water stress. Overall, the sensitivity of the silage maize to water stress was affected by different planting date and nitrogen fertilizer levels. We also discuss emergent trends in water and nutrient management in light of the increased need for food security in the face of changing climate and growing populations.

Development of drought-tolerant cultivars is hampered by a lack of effective selection criteria. In this research, drought tolerance of 75 genotypes of tall fescue in three sets (25 parental, 25 early, 25 late-flowering progenies) was evaluated under no soil moisture stress and soil moisture stress in the field during 2009 and 2010. Five drought-tolerance indices were calculated: stress tolerance (TOL), mean productivity (MP), geometric mean productivity (GMP), stress susceptibility index (SSI), and stress tolerance index (STI). These calculations were based on forage yield (dry matter basis) under drought (Ys) and non-drought (Yp) conditions. Soil moisture stress caused significant reduction in forage yield. Considerable genetic variation for drought tolerance was found among genotypes. A moderately high relationship was found between Yp and Ys using regression analysis, with a clear relationship in the second year. Indices GMP and STI were found to be valuable aids in the selection of drought-tolerant, high-yielding genotypes. Plots of the first and second principal components identified drought-tolerant genotypes in each set. Results indicated that selection for drought-tolerant genotypes should be planned separately for first year (establishment stage) and second year (productive stage) in tall fescue.

The reduction of NO3--N contamination and increase in crop production depend upon proper management of irrigation and nitrogen fertilizer. To optimize crop management, it is necessary to evaluate all parameters that are involved in the soil nitrogen cycle, including the date, amount and type of nitrogen fertilizer and irrigation applications. The objective of this study was to evaluate the effect of different levels of irrigation and nitrogen management on nitrate leaching of corn grown for silage. The experiment included four levels of irrigation, e.g., 1.13 ETC, 1.0 ETC, 0.85 ETC, and 0.7 ETC, and three levels of nitrogen, e.g., 200 kg N ha--1, 150 kg N ha--1, and 0 kg N ha--1. The soil solution was sampled at a depth of 60 cm 24 hours after each irrigation and rainfall event. The nitrate concentration of each sample was determined to quantify the amount of NO3--N that was leached below the root zone. The NO3--N content of the soil up to the depth of 60 cm at planting and harvesting and the total nitrogen uptake by the crop were also determined. The amount of NO3--N leached below the depth of 60 cm in the 1.13 ETC and 1.0 ETC treatments with 200 kg nitrogen were 7.0 and 6.5 kg ha--1 and with 150 kg nitrogen applied were 8.4 and 3.1 kg ha--1, respectively. No nitrate leaching occurred from the 0.85 ETC and 0.7 ETC treatments. The major portion of the fertilizer that was applied for 0.85 ETC and 0.7 ETC treatments remained unused in the soil, while a small amount was taken up by the corn crop and the remainder was volatilized. Increasing the amount of fertilizer resulted in an increase in nitrogen uptake but reduced the ratio of plant uptake to total nitrogen applied. The amount of nitrate leaching significantly increased in response to an increase in the amount of fertilizer applied in the 1.13 ETC treatments. N leaching was controlled by irrigation and fertilizer management for the 150 and 200 kg nitrogen levels at full and over irrigation treatments, but a portion of N was lost as volatilization or remained in the soil at deficit irrigation levels. Irrigation should be based on crop demand, such as ETc, rather than a fixed application rate. Fertilizer should be applied through the irrigation system and should also be based on crop demand. In this experiment, N uptake decreased and nitrogen volatilization and final soil nitrogen increased for the deficit irrigation treatments as compared to the full irrigation treatments. Therefore, in order to avoid nitrogen loss, the amount of nitrogen fertilizer application should be reduced in proportion to the severity of the existing water stress condition.