High Evapotranspiration Demand Research Articles

Three-dimensional Budyko framework incorporating terrestrial water storage: Unraveling water-energy dynamics, vegetation, and ocean-atmosphere interactions

The two-dimensional steady-state Budyko framework, widely used to study water-energy dynamics in landscapes, primarily focused on the partitioning of precipitation into evapotranspiration (ET) and water yield. Though this framework has been extended by incorporating water storage changes into precipitation input for non-steady state conditions, the interactions among water-energy dynamics, vegetation covers, and ocean-atmosphere oscillations within the Budyko framework at finer spatial and temporal scales have been unexplored. This study aims to investigate the interactions of regional hydroclimatic conditions, vegetation, and climate teleconnections over the Indo-China Peninsula (ICP), a region highly vulnerable to climate change. To achieve the objective, we propose a three-dimensional Budyko framework that incorporates the ratio of Gravity Recovery and Climate Experiment (GRACE)-based terrestrial water storage (TWS) or its changes (TWSC) to precipitation (SI/SCI) as the third dimension alongside the traditional two-dimensional Budyko framework. Our findings reveal that TWS has a significant impact on the Budyko framework, particularly during the dry season. The dryness index (DI)/evaporative index (EI) and SI/SCI exhibit positive (strongly negative) linear relationships in the wet (dry) season, respectively. Vegetation covers strongly influence the three-dimensional Budyko framework, with poor performance observed in highly vegetated regions due to high ET demand. Through relative importance analysis, we identify the Silk Road Pattern (SRP) as the most influential climate teleconnection among nine different teleconnections, affecting hydroclimatic conditions over the ICP. Positive (negative) phases of SRP encourage water-limited (energy-limited) ET conditions. This demonstrates that the Budyko parameter is influenced not only by landscapes but also by climate teleconnections, offering potential benefits for Budyko parameter estimation. Furthermore, the linear relationships between DI/EI and SI/SCI in three-dimensional Budyko framework can provide a promising alternative method for evapotranspiration and groundwater estimation.

Effect of Drought on Photosynthesis of Trees and Shrubs in Habitat Corridors

Drought and high evapotranspiration demands can jeopardise trees and shrubs in windbreaks and habitat corridors, where they are more exposed to the effects of extreme weather than in the forest. This study utilised chlorophyll fluorescence to assess how the leaf-level physiological processes of 13 woody species typically planted in Czech habitat corridors responded to the effects of naturally occurring drought and their ability to recover after rain. Linear electron flow (LEF) responded only weakly to the drought, indicating high levels of photorespiration. Trees and shrubs increased the proportion of energy which was dissipated in a harmless way (ΦNPQ) during drought and decreased the proportion of energy dissipated through non-regulated processes (ΦNO). In this way, they reduced processes potentially leading to the production of reactive oxygen species. All species except Tilia cordata Mill. maintained high ΦNPQ even after its release from drought. Tilia cordata was potentially the most susceptible tree to drought due to its low LEF and high ΦNO. The most drought-resistant tree species appeared to be Acer campestre L. and shrubs such as Prunus spinosa L., Viburnum lantana L, and Crataegus monogyna L. These shrubs may be planted at the sunny edges of habitat corridors. The woody species identified as resistant to drought in habitat corridors may also be considered resistant in a warming climate or suitable for planting in the urban environment which is generally warmer and drier than in a forest.

Effect of Mulching and Permanent Planting Basin Dimensions on Maize (Zea mays L.) Production in a Sub-Humid Climate

In sub-humid regions, declining maize (Zea mays L.) yield is majorly attributed to unreliable rainfall and high evapotranspiration demand during critical growth stages. However, there are limited farm technologies for conserving soil water and increasing water use efficiency (WUE) in rainfed production systems amidst a changing climate. This study aimed at assessing the performance of different climate smart agriculture (CSA) practices, such as mulching and permanent planting basins (PPB), on maize growth, yield, water use efficiency and soil moisture storage. Field experiments involving mulches of 2 cm (M_2 cm), 4 cm (M_4 cm) and 6 cm (M_6 cm) thickness, permanent planting basins of 20 cm (PPB_20 cm) and 30 cm (PPB_30 cm) depths and the control/or conventional treatments were conducted for three maize growing seasons in the sub-humid climate of Western Uganda. Results indicate that maize biomass significantly increased under the tested CSA practices in the study area. Use of permanent planting basins relatively increased maize grain yield (11–66%) and water use efficiency (33–94%) compared to the conventional practice. Additionally, plots treated with mulch achieved an increase in grain yield (18–65%) and WUE (28–85%) relative to the control. Soil amendment with M_4 cm and M_6 cm significantly increased soil moisture storage compared to permanent planting basins and the conventional practice. Overall, the results highlight the positive impact of CSA practices on improving maize yield and water use efficiency in rainfed agriculture production systems which dominate the sub-humid regions.

Yields, Fruit Quality, and Water Use in a Jalapeno Pepper and Tomatoes under Open Field and High-tunnel Production Systems in the Texas High Plains

The Texas High Plains has a semi-arid, hot, windy climate that features high evapotranspiration (ET) demands for crop production. Irrigation is essential for vegetable production in the region, but it is constrained by depleting groundwater from the Ogallala Aquifer. High-tunnel (HT) production systems may reduce irrigation water demand and protect crops from severe weather events (e.g., hail, high wind, freezing) common to the region. The objective of this study was to compare yields, fruit quality, crop water use, and crop water use efficiency (WUE) of jalapeno pepper (Capsicum annuum L.) and tomatoes (Solanum lycopersicum L.) in HT and open field (OF) production systems. We hypothesized that the protection from dry and high winds by HT would improve yields and quality of fruits and reduce water use of peppers and tomatoes. During the 2018 and 2019 growing seasons, peppers and tomatoes were transplanted on two HT plots and two identical OF plots. Plastic mulch was used in combination with a surface drip irrigation system. Micrometeorological variables (incoming solar irradiance, air temperature, relative humidity, and wind speed) and soil physical variables (soil temperature and volumetric soil water) were measured. Air temperatures were significantly higher during the daytime, and wind speed and light intensity were significantly lower in HT compared with OF. Despite the lower light intensity, yields were greater in HT compared with OF. The fruits grown in HT did not show significant differences in chemical quality attributes, such as ascorbic acid and lycopene contents, compared with those grown in OF. Because of protection from dry, high winds, plants in HT required less total water over the growing seasons compared with OF, resulting in increased WUE. The 2018 and 2019 data showed that HT production is advantageous as compared to conventional OF production in terms of increased WUE and severe weather risk mitigation for high-value vegetable production in the Texas High Plains.

Stalk dry mass and industrial yield of 16 varieties of sugar cane cultivated under water restriction

The great extension of the cultivated area, associated with the low water availability to supply the sugarcane demand in the periods of drought and the high evapotranspiration demand, requires varieties adapted to these specific conditions. The aim of this study was to assess 16 sugarcane varieties regarding the efficiency in water use (EWU) and in photosynthetically active radiation (PAR), cultivated under a water restriction, in the production of stalks dry matter, sugar and alcohol. The experiment was carried out in the Brazilian savannah biome, Goiás State, during the 2011/2012 crop year, in a randomized blocks design, with four repetitions. The treatments consisted of 16 varieties of sugarcane cultivated on a supply of only 50% of the water demand demanded by the crop. The EWU and EUPAR of the varieties were evaluated for the production of stalk dry mass (SDM), sugar and alcohol. During the crop cycle there was sufficient precipitation to supply the water demand of sugarcane; however, the irregular distribution of rainfall resulted in a water deficit of -697 mm during its cycle. The varieties IAC 91-1099, CTC-15, CTC-11, SP 86-0042 and IAC 87-3396 showed higher EWU and better photosynthetically active radiation for the production of stalks dry matter, sugar and alcohol. IACSP 94-2094 and CTC 09 varieties presented the same efficiency in industrial yield and lower dry matter yield than the five following varieties IAC 91-1099, CTC-15, CTC-11, SP 86-0042 and IAC 87-3396. Therefore, these last varieties are the most efficient in water use and photosynthetically active radiation aiming the stalks dry matter, sugar and alcohol production under water restriction.

Effect of drip irrigation scheduling and mulching on plant growth, physiology, yield, water use efficiency and weed growth in spring-summer okra (Abelmoschus esculents Muench)

Spring summer okra requires high and frequent applicationof water due to high evapo-transpiration demand. Deficitirrigation (supply less water than required) coupled withmulching is good agricultural practice to enhance water useefficiency in vegetable crops. In this study, three dripirrigation scheduling and two types mulches were evaluatedwith surface irrigation and without mulch. Maximum soilmoisture content of 12.2% and 13.5% was reported underorganic mulch, respectively at 20 and 30 cm depth. Plantsgrown under organic and black-silver mulch have registered52.5% and 35% higher chlorophyll content than control.Maximum stomatal conductance was reported with 100%PE + black-silver mulching (956.05 mmole/m2/sec).Significantly higher fruit yield (555.42 g/plant and 112.05 q/ha) was observed with drip irrigation at 100% PE, whereasin mulches, it was maximum under organic mulch (585.13 g/plant and 112.30 q/ha). As far as interaction of irrigation xmulch was concerned, the maximum yield of 684 g/plant and125.32 q/ha was reported with drip irrigation 100% PE +organic mulch, which was 64.8% higher in yield with 15.2%water saving than the control.

Investigating young water fractions in a small Mediterranean mountain catchment: Both precipitation forcing and sampling frequency matter

AbstractThe proportion of water younger than 2–3 months (young water fraction, Fyw) has become increasingly investigated in catchment hydrology. Fyw is typically estimated by comparing seasonal tracer cycles in precipitation and streamflow, through water sampling. However, some open research questions remain, such as: (i) whether part of the summer precipitation should be discarded because the high evapotranspiration demand, (ii) how well Fyw serves as a metric to compare catchments, and (iii) how sampling frequency affects Fyw estimates. To address these questions, we investigated Fyw in soil‐, ground‐ and stream waters for the small Mediterranean Can Vila catchment. Rainfall was sampled at 5‐mm intervals. Mobile soil water and groundwater were sampled fortnightly. Stream water was sampled depending on flow at variable time intervals (30 min to 1 week). Over 58 months, this sampling provided 1,529 δ18O determinations. Isotopic analyses results led us to include summer precipitation in the input signal. We found the highest Fyw in mobile soil waters (34%), while this was almost zero for groundwater except during wet periods. For stream waters, Fyw depended on the discharge variations, so that the flow‐weighted young water fraction () was 22.6%, whereas the time‐weighted Fyw was just 6.2%. Both and its discharge sensitivity (Sd) varied when different 12‐month sampling periods were investigated. The young water fraction that would be obtained from a virtual thorough sampling () was estimated from the Sd and the observed stream flow. This showed an underestimation of by 25% for the frequent dynamic sampling and 66% for weekly sampling, due to missing high flows. Our results confirm that Fyw and its discharge sensitivity are metrics very sensitive to meteorological forcing during the analysed period. Thus, comparisons between catchments need long‐term mean annual values and their variability. Our findings also support the dependence of Fyw estimates on the sampling rate and show the advantages of flow‐weighted analysis. Finally, catchment water turnover investigations should be accompanied by the analysis of flow duration curves.

Opportunities and Limitations of Crop Phenotyping in Southern European Countries.

The Mediterranean climate is characterized by hot dry summers and frequent droughts. Mediterranean crops are frequently subjected to high evapotranspiration demands, soil water deficits, high temperatures, and photo-oxidative stress. These conditions will become more severe due to global warming which poses major challenges to the sustainability of the agricultural sector in Mediterranean countries. Selection of crop varieties adapted to future climatic conditions and more tolerant to extreme climatic events is urgently required. Plant phenotyping is a crucial approach to address these challenges. High-throughput plant phenotyping (HTPP) helps to monitor the performance of improved genotypes and is one of the most effective strategies to improve the sustainability of agricultural production. In spite of the remarkable progress in basic knowledge and technology of plant phenotyping, there are still several practical, financial, and political constraints to implement HTPP approaches in field and controlled conditions across the Mediterranean. The European panorama of phenotyping is heterogeneous and integration of phenotyping data across different scales and translation of “phytotron research” to the field, and from model species to crops, remain major challenges. Moreover, solutions specifically tailored to Mediterranean agriculture (e.g., crops and environmental stresses) are in high demand, as the region is vulnerable to climate change and to desertification processes. The specific phenotyping requirements of Mediterranean crops have not yet been fully identified. The high cost of HTPP infrastructures is a major limiting factor, though the limited availability of skilled personnel may also impair its implementation in Mediterranean countries. We propose that the lack of suitable phenotyping infrastructures is hindering the development of new Mediterranean agricultural varieties and will negatively affect future competitiveness of the agricultural sector. We provide an overview of the heterogeneous panorama of phenotyping within Mediterranean countries, describing the state of the art of agricultural production, breeding initiatives, and phenotyping capabilities in five countries: Italy, Greece, Portugal, Spain, and Turkey. We characterize some of the main impediments for development of plant phenotyping in those countries and identify strategies to overcome barriers and maximize the benefits of phenotyping and modeling approaches to Mediterranean agriculture and related sustainability.

Spring maize (Zea maysL.) response to different crop establishment and moisture management practices in north-west plains of India

Maize cultivation for green cobs during the spring season is a remunerative proposition for the farmers in the north Indian plains. However, high evapo-transpiration demand of spring maize exerts considerable pressure on already depleting water resources. Thus, a two-year field experiment was conducted at GBPUA & T, Pantnagar, Uttarakhand, India to determine the effect of rice residue mulch, earthing-up, alternate furrow irrigation and crop establishment methods on productivity, profitability and irrigation water use efficiency (IWUE) of spring maize. Results revealed that application of rice straw mulch (6 t/ha) enhanced plant height, number of green leaves, dry matter accumulation, leaf area index and yield attributes. Reproductive stage set in advance in mulch treated plots compared to plots under other treatments. Green cob yield from mulched plot was the highest that was 37% higher over the flat planting alone. Broad bed planting and flat planting followed by earthing-up treatments produced the second and third highest cob yield, respectively. Planting on broad bed registered the highest IWUE (352.5 kg/ha-cm). Mulch treatment also earned higher net returns and B: C ratio than remaining treatments.

Climate variability and water resource scarcity in drylands of Rajasthan, India

The world is experiencing a high climatic variability and has its impact on all ecosystems, regions and sectors, but the nature and extent of vulnerability to climate change differs with adaptive capacity of individual, society and region. The regions which are scarce on resources are among the very vulnerable systems of the earth and most of such regions have existing extreme climatic conditions like deserts and snow covered areas. The vulnerability of arid regions is further accentuated by low levels of socio-economic development, and this is the case with arid regions of India, which leads to fast depletion of water resources. The study analyses the climate variability over last 35 years (1973–2008) in the Western drylands of Rajasthan and the results show that the temperature has shown a great variability with an average rise of about 0.5°C for the month of June. The maximum rise is visible during 1995–2000. The scarcity of water resource accompanied by variability creates water stress conditions in the region and is responsible for droughts. During last 35 years (1973–2008) the average annual rainfall has shown a decrease of 50 mm. With an overall rise in temperature over the region and changing precipitation trends the humidity provinces as defined by Thornthwaite have shifted eastward. The climate variability has direct impact on the water resources of the region. The low to medium rainfall in most parts, high evapo-transpiration demands for water, high frequency of occurrence of droughts resulting from the departure of rainfall from mean values, and the high per capita arable land increases the demand for irrigation water. The free power in agriculture continued for many years, and the existing pump horse power based pricing of electricity encourage over-pumping and inefficient and often wasteful use of groundwater. The advent of Indira Gandhi Canal in the fragile desert ecosystems helps the region to cope with high variability in rainfall. The study suggests that water security in the region can be attained through expansion of canal network.

Does predawn water potential discern between irrigation treatments in Galician white grapevine cultivars?

<p style="text-align: justify;"><strong>Aims</strong>: To evaluate the usefulness of predawn water potential (<strong>Ψ</strong><sub>pd</sub>) to assess the water status of Galician grapevine cultivars for irrigation purposes.</p><p style="text-align: justify;"><strong>Methods and results</strong>: Three Galician white grapevine cultivars (Albariño, Godello and Treixadura) were subjected to rain-fed and irrigation conditions during the 2013 growing season. Diurnal changes in leaf water potential (<strong>Ψ</strong><sub>l</sub>) were measured using a pressure chamber on days with high evapotranspiration demand. Stem water potential (<strong>Ψ</strong><sub>s</sub>) was measured at midday. <strong>Ψ</strong><sub>pd</sub> was not able to discriminate between treatments, whereas <strong>Ψ</strong><sub>l</sub> and <strong>Ψ</strong><sub>s</sub> at midday were able to detect significant differences in water status among plants.</p><p style="text-align: justify;"><strong>Conclusion</strong>: <strong>Ψ</strong><sub>pd</sub> was not useful to evaluate vine water status under the Galician climatic conditions. In contrast, both <strong>Ψ</strong><sub>l</sub> and <strong>Ψ</strong><sub>s</sub> were effective for detecting differences between treatments and can thus be used for irrigation management purposes.</p><p style="text-align: justify;"><strong>Significance and impact of the study</strong>: This is the first study evaluating water status of Galician grapevine cultivars. It also provides useful information about the strategy for its control through measurements of midday <strong>Ψ</strong>l or <strong>Ψ</strong>s.</p>

Ecological significance of wood anatomy in two lianas from arid southwestern Saudi Arabia

The hot and arid lowlands of southwestern Saudi Arabia are home to two common lianas, Cocculus pendulus and Leptadenia arborea. This paper attempts to relate the adaptation of these two climbing woody perennials to such a harsh environment to the anatomy and hydraulic characteristics of their wood. The stems of these lianas have wood with wide xylem vessels and high hydraulic conductivity which should enhance water flow to the upper canopy despite their severe twisting. Hydraulic conductivity is further helped by the simple perforation plates of xylem vessels. The circular thickening of xylem walls gives them strength and reduces the risk of their collapse and the ensuing embolism in the advent of high tension created by severe water deficit and high evapo-transpiration demand. Wide vessels, on the other hand, are more susceptible to embolism. This problem may be overcome by reducing the solute potential of xylem sap by hydrolysis of starch grains which were found to be abundant in the vicinity of the vessels. This should help absorb water by the deep roots from the capillary fringes of the typically shallow water table in this particular habitat. Furthermore, the abundance of ray parenchyma cells between xylem groups of both lianas provides great flexibility with minimum damage to water conduits in the stem during climbing and twisted growth. It was concluded that these wood features in both lianas are crucial for survival under the harsh conditions of arid Tihama plains of southwestern Saudi Arabia.

Apparent steady state conditions in high resolution weighing-drainage lysimeters containing date palms grown under different salinities

This study presents a novel investigation of long-term apparent steady state conditions under a prescribed leaching fraction criterion. The research was carried out during a 7-year investigation of date palm (Phoenix dactylifera L., cv. Medjool) trees exposed to elevated levels of irrigation water salinity. High resolution weighing lysimeters were designed and constructed to generate an accuracy of ±0.0075mm. The lysimeters were equipped with precision flux data acquisition that measured the oscillations of their daily water storage difference (ΔW) and evapotranspiration. The leaching fraction was kept constant throughout the study.The results generally confirmed that the assumption of apparent steady state conditions under the preprogrammed irrigation procedure was correct, even though inter- and intra-seasonal climate variations were observed. Measured ΔW oscillated slightly around zero even under high evapotranspiration demands. Drainage water electrical conductivity and leaching fraction were also found to stay fairly constant. The evapotranspiration of the date trees was found to be a function of the potential evapotranspiration, and rather insensitive to changes in the soil water storage (ΔW). Our analysis also indicates that for most practical purposes of monitoring and sustaining apparent steady state conditions, simple low-cost lysimeters, without weighing capability, can serve to monitor and sustain apparent steady state conditions, as long as there is water outflow from the lysimeters.However, the high resolution (high cost) weighing lysimeters proved to be an efficient system for accurate data acquisition, which is necessary for accurate modeling. An annual numerical crop yield model, modified for a date palm field study, was successfully calibrated using data from a 2 month period, and subsequently validated against measured data from the following 8 months. The modified model closely predicted the daily oscillations of drainage water salinity and actual leaching fraction throughout the eight-month period.

Environmental controls and patterns of cumulative radial increment of evergreen tree species in montane, temperate rainforests of Chiloé Island, southern Chile

AbstractWe investigated the local environmental controls on daily fluctuations of cumulative radial increment and cambial hydration of three dominant, evergreen tree species from montane, Coastal rainforests of Chiloé Island, Chile (42° 22′ S). During 2 years (1997–1998 and 1998–1999) we recorded hourly cumulative radial increments using electronic band dendrometers in the long‐lived conifer Fitzroya cupressoides (Cupressaceae), the evergreen broad‐leaved Nothofagus nitida (Nothofagaceae), and the narrow‐leaved conifer Podocarpus nubigena (Podocarpaceae). We also measured soil and cambial tissue hydration using capacitance sensors, together with air and soil temperature and rainfall during the period of the study. In addition, we collected cores of these tree species to evaluate how dendrometer measurements reflect annual tree ring width. One‐year long daily time series of cumulative radial increments suggests that radial growth of Fitzroya cupressoides was initiated slowly in early spring, with a maximum in early summer. Multiple regressions showed positive relations between daily precipitation and radial index (i.e. the difference in cumulative radial increment of two consecutive days) in the three species. According to path analysis there was a significant direct effect of changes in tree hydration on radial index of the three focal species. In emergent, pioneer species such as Nothofagus and Fitzroya, radial index was negatively affected by changes in maximum air temperature and photosynthetically active radiation, probably because of high evapotranspiration demand on warm sunny days. The shade‐tolerant species Podocarpus nubigena was positively affected by photosynthetically active radiation. Our diel scale findings support the use of tree ring widths for reconstructing past climate in these southern temperate forests and provide evidence that rainforest trees may be highly sensitive to future declines in rainfall and temperature increases during summer.

Precipitation thresholds for CO2 uptake in grass and shrub plant communities on Walnut Gulch Experimental Watershed

In semiarid ecosystems, precipitation is the major driving force for carbon uptake and subsequent plant growth. The hypothesis for this study was that the timing, frequency, and precipitation amount would produce different precipitation thresholds for uptake of carbon dioxide in grass and shrub plant communities. Eight years of precipitation data were used to determine the amount needed for carbon dioxide uptake thresholds in spring and summer seasons. Bowen ratio energy balance systems were used to measure carbon dioxide and moisture fluxes. In spring at the shrub site, close to or above long‐term average spring precipitation of 59 mm was required to produce an uptake response. At the grass site a minimum of 23 mm was needed to produce an uptake response, which was much less than the long‐term precipitation average of 68 mm. At both sites, spring or multiple summer responses reduced the threshold values for a summer response. Summer threshold ranges for the shrub site were 57–94 mm with a spring response and 123–140 mm without. Grass site summer thresholds were 51–95 mm with a spring response and 80–148 mm without. Summer precipitation threshold values were higher than spring values relating to the high summer evapotranspiration demand. The influence and variability of precipitation timing and frequency on carbon dioxide uptake threshold values resulted in no definitive conclusions as to differences between the grass and shrub plant communities, except that the grass site had slightly lower thresholds. Precipitation timing and frequency influence on total carbon uptake in some situations were more important than total precipitation. The lower grass site threshold values, along with a shift in climate toward more frequent and smaller precipitation events, may give grass ecosystems a competitive growth advantage.

Operator-splitting errors in coupled reactive transport codes for transient variably saturated flow and contaminant transport in layered soil profiles

One possible way of integrating subsurface flow and transport processes with (bio)geochemical reactions is to couple by means of an operator-splitting approach two completely separate codes, one for variably-saturated flow and solute transport and one for equilibrium and kinetic biogeochemical reactions. This paper evaluates the accuracy of the operator-splitting approach for multicomponent systems for typical soil environmental problems involving transient atmospheric boundary conditions (precipitation, evapotranspiration) and layered soil profiles. The recently developed HP1 code was used to solve the coupled transport and chemical equations. For steady-state flow conditions, the accuracy was found to be mainly a function of the adopted spatial discretization and to a lesser extent of the temporal discretization. For transient flow situations, the accuracy depended in a complex manner on grid discretization, time stepping and the main flow conditions (infiltration versus evaporation). Whereas a finer grid size reduced the numerical errors during steady-state flow or the main infiltration periods, the errors sometimes slightly increased (generally less than 50%) when a finer grid size was used during periods with a high evapotranspiration demand (leading to high pressure head gradients near the soil surface). This indicates that operator-splitting errors are most significant during periods with high evaporative boundary conditions. The operator-splitting errors could be decreased by constraining the time step using the performance index (the product of the grid Peclet and Courant numbers) during infiltration, or the maximum time step during evapotranspiration. Several test problems were used to provide guidance for optimal spatial and temporal discretization.

Physiological Changes in Plant Hydraulics Induced by Partial Root Removal of Irrigated Grapevine (Vitis viniferacv. Syrah)

The influence of partial root removal on hydraulic conductivity of the root system, vine water status, stomatal conductance to water vapor (g_s), net photosynthetic carbon assimilation (A), and recharging of hydraulic capacitance overnight for 5-year-old Syrah grapevines growing on 101-14 Mgt rootstock was examined. The study was conducted in a drip-irrigated vineyard on deep sandy clay loam soils under the conditions of high evapotranspiration demand. Severing approximately 25 to 35% of the total cross-sectional area of framework roots emerging from the trunk resulted in an immediate (one week) decline in predawn leaf water potential (Ψ_PD), xylem water potential (Ψ_stem), and leaf water potential (Ψ_leaf) and was paralleled by reductions in g_s and A. In addition, there was an immediate decline in leaf-specific hydraulic conductance (k_l), indicating that the root system was well balanced with shoot water demands before root severance. These responses were sustained throughout the growing season, although some convergence in g_s, A, and k_l was observed toward the end of the season. Severing roots from the drip-irrigation zone had a slightly greater influence on Ψ_PD, Ψ_stem, Ψ_leaf, g_s, and A, suggesting there was greater hydraulic resistance to water transport and diminished ability to refill xylem or to recharge hydraulic capacitance from nonirrigated soils. Root severance resulted in adjustments to leaf area per vine in 2004, but no such adjustment to leaf area was observed in 2005, and vine water status among the three treatments was similar throughout the 2005 season. Our results indicated that root severance could change water relations under field conditions even for well-watered vines in deep soils with a high water-holding capacity but that grapevines probably have limited quantitative stem and root hydraulic capacitance.

Soil Water Dynamics Using Multisensor Capacitance Probes in Nontraffic Interrows of Corn

AbstractWater is often the primary factor limiting plant growth, and it is the primary agent for moving plant nutrients and pesticides to streams and groundwater. This study was conducted to assess the capabilities of recently developed multisensor capacitance probes and monitoring systems to measure the dynamics of soil water content under long‐term field‐scale conditions, and to quantify in real time the spatial variation of soil water content under plow‐tillage (PT) and no‐tillage (NT) corn (Zea mays L). Probes were placed at eight nontraffic interrow locations, with cable lengths ranging from 25 to 125 m, on a 0.5‐ha field site. The capacitance sensors were centered at four soil depths and readings were taken every 10 min by the data‐logging system. Real‐time dynamics of soil water change following 82 mm of rainfall in the spring were used to identify the apparent water‐holding capacity within the sensor depths (5–55 cm) under NT as 171 mm and 155 mm under PT. Rates of soil water loss with a full canopy of corn were 90% of high evapotranspiration (ET) demand. Breaking points were observed and calculated between high and low rates of soil water loss, under full canopy and high ET demand. Changes from high to low rates of soil water loss were more evident in PT plots (62% reduction) than in NT plots (46% reduction). At the end of three drying cycles during the growing season, there was an average of 37 mm more water (5–55‐cm soil depth) under NT than PT. The multisensor capacitance probes proved to be highly sensitive and robust for field‐scale, real‐time, soil water research.

Saline-water irrigation for the establishment of furrow-planted trees in northwestern India

Appropriate tree species and planting methods can help rehabilitation of arid areas — that are characterized by low rainfall, high evapotranspiration demands, highly saline ground waters and calcareous subsoils. The growth of Acacia nilotica and Dalbergia sissoo saplings planted in irrigation furrows in such an arid zone of northwest India was not affected adversely by irrigation with saline water of EC W 10.5 dS m−1. The growth of A. nilotica, measured in terms of sapling survival, plant height and biomass yields, was better than that of D. sissoo. Increasing the period of irrigation from the recommended practice of irrigating only in the first year dry season (October–June) to second and third dry seasons (years) improved the sapling survival, growth and biomass (two-to-three-fold) and water use efficiency (two-to-four fold). Most of the salts added with saline irrigation were accumulated below the irrigation channels and were pushed laterally during the monsoon season. The results indicate that the furrow planting technique could be adopted as an afforestation practice in view of the creation of favourable water and salt regimes and their impact on the establishment of trees saplings. Irrigation water supplies for a minimum of intitially two years after transplanting seemed necessary.

Evapotranspiration measurements over a soybean field

Evapotranspiration data over a soybean field were obtained from a weighing lysimeter during 1988, when the month of July was marked by intense heatwave in Greece. Soil water contents were determined by neutron probe at regular intervals before and after irrigation. Meteorological measurements, including mean daily values of air temperature, relative humidity, wind speed, solar radiation and precipitation allowed the study of reference evapotranspiration and its comparison with class-A pan evaporimeter data during this period of extreme exposure conditions. Values of the Priestley-Taylor parameter, α, were derived and a mean value of 1.58 was found. A generalized basal crop coefficient curve was determined from the lysimetric data and the time evolution of soil moisture profiles according to Wright's procedure. A rather high peak value, 1.4, for the soybean crop coefficient was obtained. This is mainly attributed to the very high crop evapotranspiration demands during the 1988 heatwave in Greece and the differences in the method of deriving the crop coefficient and computing the reference evapotranspiration.