Non-limiting Water Conditions Research Articles

Identifying plant traits to increase wheat yield under irrigated conditions

Crop models have frequently been used to identify desired plant traits for rainfed wheat (Triticum aestivum L.). However, efforts to apply these models to irrigated wheat grown under non-limiting water and nitrogen conditions have been rare. Using simulation models to identify plant traits that impact yield can facilitate more targeted cultivar improvement and reduce time and cost. In this study, the SSM-iCrop model was employed to identify effective plant traits for increasing the yield of irrigated wheat in four distinct environments in Iran. A comprehensive range of traits related to phenology, leaf area development, dry matter production, and yield formation, which exhibited reported genetic variation, were tested. The impact of these traits on yield showed slight variation across different environmental zones due to genetic × environment interaction. However, across all environments, modifying current cultivars to increase radiation use efficiency (RUE) resulted in a 19% increase in yield, accelerating leaf area development led to a 10% to 15% increase, lengthening the grain filling period resulted in a 14% increase, and extending the vegetative period led to a 6% increase. These improvements were all statistically significant. Considering that longer duration cultivars may disrupt cropping systems and the need to develop simple methods for targeting and phenotyping RUE, faster leaf area development was found as the most promising option to increase irrigated wheat yield under optimal water and nitrogen management within a short time frame. It should be noted that cultivars with modified traits needed higher water and nitrogen inputs to support increased yields. These findings can be applied to select desirable key traits for targeted breeding and expedite the production of high-yielding cultivars of irrigated wheat in various environmental zones. The potential for further improvement through combined traits requires further investigation.

Use of an automatic fruit-zone cooling system to cope with multiple summer stresses in Sangiovese and Montepulciano grapes.

Grapevines are frequently subjected to heatwaves and limited water availability during ripening. These conditions can have consequences for the physiological health of the vines. Moreover, the situation is often exacerbated by intense solar radiation, resulting in reduced yield due to sunburn and a decline in quality. In light of these challenges, our study aimed to develop a fruit-zone cooling system designed to mitigate grape sunburn damage and improve the microclimate conditions within the vineyard. The system comprises a network of proximal sensors that collect microclimate data from the vineyard and an actuator that activates nebulizers when the temperature exceeds the threshold of 35°C. The research was conducted over two years (2022 and 2023) in Bologna (Italy) using potted Sangiovese and Montepulciano vines. These two vintages were characterized by high temperatures, with varying amounts of rainfall during the test period, significantly impacting the evaporative demand, which was notably higher in 2023. Starting from the veraison stage we compared three treatments: Irrigated control vines (WW); Control vines subjected to 50% water restriction during the month of August (WS); WS vines treated with nebulized water in the bunch area during the stress period (WS+FOG). The application of nebulized water effectively reduced the temperature of both the air around the clusters and the clusters themselves. As we expected, Montepulciano showed better single leaf assimilation rate and stomatal conductance under non-limiting water conditions than Sangiovese while their behavior was unaffected under water-scarce conditions. Importantly, for the first time, we demonstrated that nebulized water positively affected gas exchange in both grape varieties. In addition to this, the vines treated with the misting system exhibited higher productivity compared to WS vines without affecting technological maturity. In the 2023 vintage, the activation of the system prevented the ripening blockage that occurred in Montepulciano under water stress. Regarding the concentration of total anthocyanins, a significant increase in color was observed in WS+FOG treatment, suggesting a predominant role of microclimate on anthocyanin biosynthesis and reduction of oxidative phenomena. In conclusion, the fruit-zone cooling system proved to be an invaluable tool for mitigating the adverse effects of multiple summer stresses.

A multi-level approach reveals key physiological and molecular traits in the response of two rice genotypes subjected to water deficit at the reproductive stage.

Rice is more vulnerable to drought than maize, wheat, and sorghum because its water requirements remain high throughout the rice life cycle. The effects of drought vary depending on the timing, intensity, and duration of the events, as well as on the rice genotype and developmental stage. It can affect all levels of organization, from genes to the cells, tissues, and/or organs. In this study, a moderate water deficit was applied to two contrasting rice genotypes, IAC 25 and CIRAD 409, during their reproductive stage. Multi-level transcriptomic, metabolomic, physiological, and morphological analyses were performed to investigate the complex traits involved in their response to drought. Weighted gene network correlation analysis was used to identify the specific molecular mechanisms regulated by each genotype, and the correlations between gene networks and phenotypic traits. A holistic analysis of all the data provided a deeper understanding of the specific mechanisms regulated by each genotype, and enabled the identification of gene markers. Under non-limiting water conditions, CIRAD 409 had a denser shoot, but shoot growth was slower despite better photosynthetic performance. Under water deficit, CIRAD 409 was weakly affected regardless of the plant level analyzed. In contrast, IAC 25 had reduced growth and reproductive development. It regulated transcriptomic and metabolic activities at a high level, and activated a complex gene regulatory network involved in growth-limiting processes. By comparing two contrasting genotypes, the present study identified the regulation of some fundamental processes and gene markers, that drive rice development, and influence its response to water deficit, in particular, the importance of the biosynthetic and regulatory pathways for cell wall metabolism. These key processes determine the biological and mechanical properties of the cell wall and thus influence plant development, organ expansion, and turgor maintenance under water deficit. Our results also question the genericity of the antagonism between morphogenesis and organogenesis observed in the two genotypes.

A new technique for monitoring plant transpiration under field conditions using leaf optical dendrometry

Monitoring plant transpiration (Ec) is important for quantifying irrigation amounts and maintaining optimum soil moisture conditions for maximum growth potential. However, real-time quantification of Ec dynamics under field conditions is still challenging due to technical limitations. Here, we present a new approach for monitoring plant water use using continuous measurement of stem water potential dynamics (Ψstem) under non-limiting water conditions. According to Darcy's law, if daytime root to stem hydraulic conductance (Kr-s) remains constant and the contribution of plant capacitance to Ec is minimal or accounted for, then daytime Ec could potentially be continuously inferred from Ψstem dynamics. We investigated the viability of this approach by first quantifying the dynamics of daytime Kr-s and the transient buffering effects of plant capacitance in irrigated plants of two crop species with contrasting physiology and life history: the perennial herbaceous Tanacetum cinerariifolium and the annual monocot Triticum aestivum. Daytime Kr-s dynamics and the effects of plant capacitance were determined by continuously and simultaneously measuring Ψstem with optical dendrometers and Ec with gravimetric method under naturally variable conditions of light, temperature and humidity. Kr-s remained relatively stable throughout the day and the effects of plant capacitance were negligible in both species under field conditions implying that the dynamics of Ec can be inferred from Ψstem. This was clearly supported by the close agreement between measured Ec and that predicted from the optically derived Ψstem. We conclude that optical dendrometry has the potential to continuously monitor both Ec and plant hydration status at high accuracy and temporal resolution under naturally variable atmospheric conditions and optimum water supply. Combining these two aspects of the optically derived Ψstem should create new opportunities to monitor crop water use and maintain plant hydration at optimum levels for maximum productivity in various crops under field conditions.

Evaluation and management of soil microbial potentialities for improving the carob tree tolerance to water constraints

The carob tree (Ceratonia siliqua L.), an ecological, cultural and industrial component of the Mediterranean basin, has been experiencing a decline of its abundance in recent decades. Three contributing factors have been identified, an agricultural policy in favour of other plant species, an increasing urbanisation of the Mediterranean coastline, which leads to habitat fragmentation, and negative climatic conditions, notably longer periods of drought. The dependency of the carob tree on water resources is an underestimated trait, and yet a crucial one for its survival. The optimisation of the symbiotic association between carob and mycorrhizal fungi has been proposed as a promising strategy to improve its resistance to water stress. However, a more holistic view of plant-microorganism interactions within the environment seems essential to sustainably address the challenges of plant adaptation to environmental stresses. The central hypothesis of the thesis is that the management of interactions between the carob tree and the microbiota of some pioneer plants in its habitat could be the key for a better adaptation of the carob tree to drought. The objectives were (i) to assess the specificity of microbiota associated with plants living with the carob, and (ii) to quantify their impact on carob growth and resistance to water deficit. The results showed a predominance of actinobacteria, proteobacteria and ascomycetes in the studied habitats, with significant functional divergences between North and South of Morocco. Common garden experiments revealed that the type of microbiota was a major driver of the effect on carob growth and resistance, with strong variations depending on the water status. Indeed, the native microbiota of the carob tree is one of the most efficient under non-limiting water conditions but confers little resistance to drought. On the other hand, the microbiota associated with the lentisk provides the best growth-resistance trade-off. This benefit seems to be attributable to a higher abundance of DSE (dark septate endophytes) fungi and an increase in mycorrhizal colonisation in response to water stress. The integration of lentisk in technical practices as a lever for the management of a beneficial microbiota could therefore represent a future strategy for the adaptation of carob to increasing drought in the Mediterranean basin.

Harnessing phenological traits of wild ancestor Chenopodium hircinum to improve climate adaptation of quinoa

Context Cultivation of quinoa (Chenopodium quinoa Willd.) is rapidly expanding worldwide. Characterisation of populations of Chenopodium hircinum Schard., its wild ancestor, which thrives in some of the hottest environments in South America, may provide adaptations to new environments. Aims This study evaluated the developmental patterns of populations of C. hircinum collected from a range of agroecological environments in Argentina, in order to quantify variability among sites of origin and to explore the association between climatic data from environments of provenance and variation in development. Methods Thirty-three populations of C. hircinum from contrasting sites of origin in Argentina were multiplied in a common-garden experiment under non-limiting conditions of water and nutrient availability. Plants were sampled once or twice weekly (according to parameter) for estimation of the duration of developmental phases, leaf number, and dates of initiation of branching on the main stem. Key results Significant variation was detected for all phenological traits, and populations were categorised into six groups based on similarity of patterns of variation. We found positive association of the duration of development phases and the number of leaves on the main-stem with maximum temperature during the growing season, and negative association with altitude of origin, consistent with variation in growing-season duration. Conclusions The finding that late-flowering populations are associated with warmest climates reveals that longer vegetative growth is an adaptive strategy to cope with heat stress in Chenopodium spp. Implications Time to flowering should be considered in attempts to improve quinoa performance under heat-stress conditions. Further work is needed to understand the genetic basis controlling this response in wild populations of C. hircinum.

Sensitivity analysis of soil parameters in the Agricultural Production Systems sIMulator (APSIM)

Context The performance of process-based agroecosystem simulation models is highly sensitive to the numerous input parameters, many associated with high variability and uncertainty. Aims Our aims were to: (1) test the accuracy of the Agricultural Production Systems sIMulator (APSIM) model regarding the prediction of soil water storage and movement in a pasture system with a free draining pumice soil based on site-specific soil hydraulic properties; (2) identify sensitive soil hydraulic properties on model outputs; and (3) identify the influence of uncertainty in the description of soil properties on various model outputs. Methods We carried out a sensitivity analysis (SA) to identify sensitive soil hydraulic parameters. We set up APSIM to simulate a pasture system on a free-draining pumice soil in New Zealand. The model was first established with site-specific soil hydraulic properties and outputs were compared with measured soil moisture status and drainage. Next, the model’s sensitivity to the soil hydraulic parameters was assessed for various outputs linked to production and environmental outcomes. Key results Varying the various hydraulic parameters affected soil moisture status, but it had generally little effect on drainage, N leaching, and pasture production in this system. Conclusions The results suggest that for well-drained soils in a high precipitation zone with no water limitation, the model has low sensitivity to soil hydraulic parameters. Further analysis is required for different soils and for drier conditions. Implications For well-drained soils and under non-limiting water conditions the use of general data from databases, rather than site specific measurement of hydraulic properties is justified.

Optimizing the establishment of bean and maize varieties in tropical environments

The successful establishment of any crop is the initial indication of its productivity. Optimizing the establishment of a crop implies ensuring generalized, fast and concentrated emergence. This work studies optimal temperature ranges, under non-limiting water conditions, for both germination and emergence of two bean (Phaseolus vulgaris L.) varieties (catarina and ervilha) and two maize (Zea mays L.) varieties (matuba and sam3).Experiments used a thermogradient plate. Petri dishes were used for germination experiments. Emergence experiments were performed in aluminium containers filled with packed portions of a sandy loam clay textured soil. Size, speed and spread of both germination and emergence were measured at different temperatures by Cu-CuNi thermocouples.Thermal ranges with optimal counts of both germination and emergence [To1 sz, To2 sz] were identified using a flattened bell curve function. Speed was maximized for either germination or emergence over thermal ranges [To1 sp, To2 sp] defined using the plateau model to relate either germination or emergence rates with temperature. Ranges along which the spread of both germination and emergence are nearly minimized [To1 sd, To2 sd] were identified with the aid of even-degree polynomials. The intersection of all three thermal ranges gave rise to optimal temperature ranges [To1, To2] for germination (OTRG) of the four varieties in study and for emergence (OTRE) of three of them. In general, the lower thermal limit of OTRg was determined by speed (To1 = To1 sp) and the upper thermal limit by size (To2 = To2 sz). OTRe begins at To1 sp for ervilha and sam3 and at To1 sd for catarina and ends at To2 sz for catarina and at To2 sd for the others. The endpoints and length of both the OTRG and OTRE were also found to be crop-dependent. Thus, farmers can choose between crops and optimize their establishment. The identification of these parameters may also be useful in assessing weather forecasts and for warning systems and agro-climatic zoning. The influence of the substrate used in each experiment was also discussed.

Effects of induced water deficit and biofertilization on growth dynamics and bulb yield of onion (Allium cepaL.) in a neotropical semi-arid environment

In a scenario of world population increase and climate change, an efficient use of water is key for agricultural production. Onion is one of the most profitable crops and can adapt to particular conditions of water stress. The objective of this research was to determine growing degree-days and accumulated radiation under non-stress conditions and yield of an F1 2000 hybrid of onion (Allium cepa L.) under water deficit (WD) and biofertilization in a semi-arid environment. An established nutrient requirement of 247 kg N, 240 kg P2O5(105 kg P), 240 kg K2O (199 kg K), and two irrigation factors were applied: normal irrigation with a daily and WD with a 3 d interval irrigation frequencies. The effect of biofertilization was evaluated through the inoculation of a microbial consortium (MC) in combination with four NPK fertilizer treatments. The crop accumulated 1334 degree-days and 1188 MJ m−2·d−1at the time of harvest at 71 d after transplanting. The yield was 36 t·ha−1, similar under both irrigation conditions; and the WD treatment resulted in a 35% water savings, a 47% and 65% increase in water use efficiency and modulus of elasticity, respectively. The MC resulted in a 50% NPK savings under non-limiting water conditions and produced a similar yield compared with the 100% NPK non-inoculated control. The lower irrigation frequency together with the 100% NPK fertilization dose without the MC and the use of the microorganisms and the 50% NPK treatment without water stress are recommended as agrosustainable practices for onion production.

Phenotyping Root Systems in a Set of Japonica Rice Accessions: Can Structural Traits Predict the Response to Drought?

BackgroundThe root system plays a major role in plant growth and development and root system architecture is reported to be the main trait related to plant adaptation to drought. However, phenotyping root systems in situ is not suited to high-throughput methods, leading to the development of non-destructive methods for evaluations in more or less controlled root environments. This study used a root phenotyping platform with a panel of 20 japonica rice accessions in order to: (i) assess their genetic diversity for a set of structural and morphological root traits and classify the different types; (ii) analyze the plastic response of their root system to a water deficit at reproductive phase and (iii) explore the ability of the platform for high-throughput phenotyping of root structure and morphology.ResultsHigh variability for the studied root traits was found in the reduced set of accessions. Using eight selected traits under irrigated conditions, five root clusters were found that differed in root thickness, branching index and the pattern of fine and thick root distribution along the profile. When water deficit occurred at reproductive phase, some accessions significantly reduced root growth compared to the irrigated treatment, while others stimulated it. It was found that root cluster, as defined under irrigated conditions, could not predict the plastic response of roots under drought.ConclusionsThis study revealed the possibility of reconstructing the structure of root systems from scanned images. It was thus possible to significantly class root systems according to simple structural traits, opening up the way for using such a platform for medium to high-throughput phenotyping. The study also highlighted the uncoupling between root structures under non-limiting water conditions and their response to drought.

Optimizing germination of seven Mediterranean crops

ABSTRACTCrop establishment is a major factor determining crop productivity. Successful crop establishment requires generalized, fast and concentrated germination. Final germination counts (size), speed and spread depend on soil temperature and moisture. This work seeks to determine, under non-limiting water conditions, optimal temperature ranges for the germination of seven common Mediterranean crops, viz., pea (Pisum sativum L.), lupine (Lupinus luteus L.), chickpea (Cicer arietinum L.), broad bean (Vicia faba L.), sunflower (Helianthus annuus L.), corn (Zea mays L.) and sorghum (Sorghum bicolor (L.) Moench). Experiments used a thermogradient plate, with temperatures monitored by Cu-CuNi thermocouples. Thermal ranges [To1sz, To2sz] along which germination counts are nearly maximized were identified by the successful use of a flattened bell curve function. Thermal ranges [To1sp, To2sp], where germination speed is maximized, were defined using the plateau-shaped model for rate of germination vs. temperature relationship. Ranges [To1sd, To2sd], along which dispersion is nearly minimized, were successfully identified using even-degree polynomials. The intersection of these three thermal ranges provided an optimal temperature range (OTRG) for the germination of each crop. In most cases, OTRG begins at the lowest temperature that guarantees a maximum germination rate (To1sp) and ends at the maximum temperature that ensures minimal dispersion (To2sd). The endpoints and length of the OTRG were found to be crop-dependent. For each crop, OTRG also depended on the fraction of germinated seeds and on the level of dispersion that is considered acceptable. The results allow farmers to choose between different crops and to optimize their germinations.

Modeling the spread of germination of four Mediterranean crops at different temperatures

ABSTRACTMinimizing the dispersion of germination across time allows greater uniformity during crop development. The aim of this paper was to model the spread of germination, under non-limiting water conditions and as a function of temperature, of four Mediterranean crops: pea (Pisum sativum L.), broad bean (Vicia faba L.), corn (Zea mays L.) and sorghum (Sorghum vulgare L.). Experiments were performed using a thermogradient plate. Four temperature ranges suitable for the thermal responses of each crop were used. Dispersion was expressed as standard deviation (σ) of the frequency distribution of thermal times in the population, modeled by a probit regression and by differences between both accumulated temperatures above the base temperature (θ0.8–θ0.2) or chronological times (t0.8-t0.2) required to reach 0.2 and 0.8 of final germination. Estimates of σ were obtained both within thermal ranges defined by applying the plateau-shaped model to the rate vs. temperature relationship and at single temperatures. The differences (θ0.8–θ0.2) and (t0.8-t0.2) were evaluated for each temperature. Reference values were successfully assigned to the germination dispersion of each crop, either to the different thermal ranges used or to single temperatures. Furthermore, a thermal range ensuring minimum values of dispersion was obtained for each crop using a polynomial equation to model the variation of t0.8-t0.2 on the set of temperatures used. The dimension of this thermal range was larger for winter than for summer crops. Crop competitiveness depends on the indicators used to assess dispersion. The results allow farmers to choose between different crops and thus optimize germination.

Daily heliotropic movements assist gas exchange and productive responses in DREB1A soybean plants under drought stress in the greenhouse

Drought stress is one of the most severe environmental constraints on plant production. Under environmental pressures, complex daily heliotropic adjustments of leaflet angles in soybean can help to reduce transpiration losses by diminishing light interception (paraheliotropism), increase diurnal carbon gain in sparse canopies and reduce carbon gain in dense canopies by solar tracking (diaheliotropism). The plant materials studied were cultivar BR 16 and its genetically engineered isoline P58, ectopically overexpressing AtDREB1A, which is involved in abiotic stress responses. We aimed to follow the movements of central and lateral leaflets in vegetative stages V7-V10 and reproductive stages R4-R5, integrating the reversible morphogenetic changes into an estimate of daily plant photosynthesis using three-dimensional modeling, and to analyze the production parameters of BR 16 and P58. The patterns of daily movements of central leaflets of BR 16 in V7-V10 and R4-R5 were similar, expressing fewer diaheliotropic movements under drought stress than under non-limiting water conditions. Daily heliotropic patterns of lateral leaflets in V7-V10 and R4-R5 showed more diaheliotropic movements in drought-stressed P58 plants than in those grown under non-limiting water conditions. Leaf area in R4-R5 was generally higher in P58 than in BR 16. Drought significantly affected gas exchange and vegetative and reproductive architectural features. DREB1A could be involved in various responses to drought stress. Compared with the parental BR 16, P58 copes with drought through better compensation between diaheliotropic and paraheliotropic movements, finer tuning of water-use efficiency, a lower transpiration rate, higher leaf area and higher pod abortion to accomplish the maximum possible grain production under continued drought conditions.

Effect of planting density and pattern on maize yield and rainwater use efficiency in the Loess Plateau in China

We conducted a two-year field research to evaluate the effect of three planting densities (L: 52,500, M: 75,000 and H: 97,500 plants ha−1) and three different planting patterns (RF: ridge with plastic film mulching; FM: flat planting with plastic film mulching; and CP: conventional planting without mulching) on maize yield. Results showed that, at each planting density, average topsoil temperature (5–25 cm) was improved under FM and RF, relative to CP, before silking. This resulted in earlier emergence and accelerated plant development. Compared to CP, RF significantly increased soil water storage (SWS) at the end of the fallow season and provided non-limiting water conditions for early seedling growth. During the growing season, when rainfall was more abundant, RF prevented evapotranspiration (ET); thereby, favouring SWS. Furthermore, when rainfall was scarce, RF provided the crop with additional soil moisture, which resulted in increased ET. Under RF and FM, the two-year average grain yield increased by 33.4% and 30%, respectively; while, water use efficiency (WUE) increased by 34.2% and 27.5%, respectively; similarly, rainwater use efficiency (RUE) increased by 35.6% and 32.1%, respectively. In a normal year (2015), grain yield, WUE and RUE, significantly increased as planting density increased from low to moderate; but not in a dry year (2016). Under such conditions, no significant differences were observed in grain yield, WUE or RUE among planting density treatments within the same planting pattern. Under moderate planting density, the two-year average final aboveground dry matter, grain yield, WUE and RUE in RF increased by 14.7%, 31.8%, 31.9% and 34.1%, respectively, compared to CP. Therefore, we conclude that RF is the most suitable planting pattern under moderate planting density for increasing maize yield in the Loess Plateau in China.

Implications of plant functional traits and drought survival strategies for ecological restoration

Abstract Restoration of degraded grasslands through active revegetation often involves re‐establishing populations of native grasses, which must withstand increasing drought stress to persist beyond initial establishment. In perennial species, superior dehydration tolerance is expected to result in more conservative growth, but this trade‐off has seldom been studied among populations of herbaceous species. We measured seasonal growth and foliar and root functional traits under non‐limiting water conditions, followed by recovery after severe drought in four populations of Elymus glaucus, a perennial grass from California's Mediterranean‐climate region. We hypothesized that populations from harsher sites would be more dehydration tolerant, summer dormant and resource‐conservative. Dehydration tolerance and summer dormancy were associated with a more conservative strategy (lower productivity, lower specific leaf area and specific root length), as well as earlier reproductive phenology. Multivariate trait variation was associated with water availability in both the growing season and summer, while greater dehydration tolerance and summer dormancy were associated with increasing summer climatic water deficit. Synthesis and applications. Our study provides evidence of an intraspecific trade‐off between dehydration tolerance and rapid resource acquisition. We discuss the implication that restored populations with superior drought survival may therefore be less competitive, and recommend further investigation to inform plant materials selection protocols and management practices.

Impacts of Kaolin and Pinoline foliar application on growth, yield and water use efficiency of tomato (Solanum lycopersicum L.) grown under water deficit: A comparative study

Abstract The impacts of Kaolin particle film (KPF) and Pinoline (P) Antitranspirants (ATs) on growth, yield components (marketable and unmarketable), fruit quality and on-farm irrigation water use efficiency (WUE) of tomato plants ( Solanum lycopersicum L. ) grown under water deficit of 40%, 60%, and 80% depletion of available water (DAW) were studied, to determine if ATs application would mitigate water deficit stress and increase WUE. The field experiments were elaborated in the open field for two seasons under the drip irrigation system. The results revealed that deficit irrigation (DI) significantly reduced the relative water content of the leaves (RWC), CO 2 assimilation rate (P-net), marketable yield, while canopy temperature (CT) and WUE were increased. Results indicated that KPF under DI effectively enhanced the physiological activities and marketable yield production, while reduced sunscald fruits and those with blossom-end rot symptoms (unmarketable yield), particularly under 60%DWA, but it did not compensate the negative effects under 80%DWA. Also, the effect was null under non-limiting water conditions. Generally, P had no significant effects under different water stress severities. Under 60%DWA, application of KPF increased the marketable yield to 93% of the unstressed-unsprayed plants, while conserving 25% of irrigation water, leading to an increase in WUE by 26.24% with respect to unstressed-unsprayed plants.

Satellite-Based Method for Estimating the Spatial Distribution of Crop Evapotranspiration: Sensitivity to the Priestley-Taylor Coefficient

This work discusses an operational method for actual evapotranspiration (ET) retrieval from remote sensing, considering a minimum quantity of ancillary data. The method consists in a graphical approach based on the Priestley-Taylor (PT) equation, where the dry soil and non-limiting water conditions are defined by land surface temperature (LST) and vegetation index (VI) space, both retrieved from remote sensing. Using ET tower flux measurements and Landsat 5 TM images of an irrigation scheme in southeast Spain, a sensitivity analysis of ET spatial distribution was performed for the period 2009–2011 with respect to: (i) the shape (trapezoidal or rectangular) of the LST-VI space; and (ii) the value of the PT coefficient, α. The results from ground truth validation were satisfactory, both shapes providing similar performances in estimating ET, with root mean square error ~30 W/m2 and relative difference ~10% with respect to tower-based measurements. Importantly, the best fit with ground data was found for α close to 1, a somewhat different value from the commonly used value of 1.27, indicating that substantial error might arise when using the latter value. Overall, our study underlines the importance of a more precise knowledge of the actual value of α coefficient when using ET retrieval methods based on the LST-VI space.

Simulating yield potential by irrigation and yield gap of rainfed soybean using APEX model in a humid region

Soybean is generally grown under rainfed conditions in a humid region, Mississippi, USA. In order to determine how much maximum yield could be increased by irrigation, it is crucial to investigate the yield potential (Yp) without any drought stress and yield gap (Yg, between Yp and rainfed yield (Yw)). Further, it is also important to determine the amount of irrigation water needed to alleviate any drought stress during the entire growing season, and conduct cost-return analysis for irrigated soybean. Therefore, the objectives of this study were to: (1) simulate Yp, analyze Yg and determine the irrigation timing and amount needed to achieve Yp for soybean using the Agricultural Policy/Environmental eXtender (APEX) model; and (2) compute water use efficiency (WUE), irrigation water use efficiency (IWUE) and conduct the cost-return analysis on irrigation events. Simulated Yp of soybean without water stress for nine soil types from 2002 to 2014 ranged from 4.47 to 6.51Mgha−1, and was strongly correlated with accumulative solar radiation during the growing season (R2=0.71, P≤0.01). The Yg in dry years was much higher than that in normal and wet years, with average Yg of 1.58, 0.60 and 0.71Mgha−1 for dry, normal and wet years, respectively. Griffith, Sumter and Demopolis soils had the highest average Yg over 13 years, ranging from 1.37 to 1.60Mgha−1. The average irrigation amount was 308, 192 and 157mm in dry, normal and wet years, respectively. The average irrigation amount was 75mm from R1 to R8 stages. The WUE of nine soil types from 2002 to 2014, under non-limiting water conditions, ranged from 9.5 to 13.8kgha−1mm−1. The magnitude of Yg was the principle factor affecting IWUE among nine soil types. The average IWUE over 13 years ranged from 1.8 to 7.8kgha−1mm−1 for nine soil types. Compared with a rainfed condition, average net return of irrigated soybean increased by 93 $ ha−1 (dollar per hectare) among nine soil types from 2002 to 2014. The average net return increased by 195, 58 and 70 $ ha−1 for dry, normal and wet years, respectively.

Summer dormancy, drought survival and functional resource acquisition strategies in California perennial grasses

Evidence suggests drought severity is increasing due to climate change, but strategies promoting severe drought survival in perennial grasses have been seldom explored. This is particularly true of summer dormancy, an adaptation common in summer-dry Mediterranean-type climates. In addition, though theory predicts superior drought survival results in lower potential productivity, studies rarely measure both drought survival and growth under optimal conditions. Physiological and functional ecological approaches were integrated to quantify interspecific variation in foliar and root traits in a suite of eight California perennial grass species. In a glasshouse experiment, summer dormancy, foliar functional trait variation, and seasonal growth and phenology under non-limiting water conditions and dehydration tolerance under progressive drought were quantified. In a second glasshouse study, root functional traits were quantified under non-limiting water conditions in rhizotrons. Summer dormancy was associated with higher dehydration tolerance, and negatively associated with traits conferring dehydration avoidance. Species with greater summer dormancy were characterized by greater springtime productivity, earlier reproduction, and a shallow and fine root system, which are indicative of dehydration escape. Summer dormancy was associated with an acquisitive, competitive functional strategy in spring, and a conservative strategy in summer. Both the escape and acquisitive springtime strategies observed in summer dormant perennial taxa are typically associated with annual grasses. California grasslands were once dominated by perennial species, but have been overtaken by non-native Mediterranean annual grasses, which are expected to be further favoured by climate change. Owing to functional similarity with these exotic annuals, it is suggested that native summer dormant taxa may play an important ecological role in the future of both natural and restored California grasslands.

Effect of pine bark volume and ventilation for bell pepper production in high tunnels

Bell peppers cultivated in Florida represent one third of the U.S. fresh-market production. Protected cultivation offers an advantage in a subtropical, humid climate to obtain high-quality colored bell peppers. However, multiple factors such as ventilation, high temperatures, and potting media volume can affect the success of bell pepper production under protected cultivation. The objective of this study was to evaluate the combination of two ventilation types and four pine bark volumes on bell pepper yield, plant growth and fruit quality. No significant effects of ventilation or pine bark volume on plant growth or commercial yield were found. This study suggested bell pepper can be cultivated in small pots as long as the plants are in non-limiting water and nutrient conditions. Moreover, a ventilation system with only a central roof vent in the ridge of the tunnel with a metallic gutter has no additional beneficial effect on colored bell pepper yields.