Plant Water Demand Research Articles

Enhanced Fertigation Control System towards Higher Water Saving Irrigation

<span>Water saving in agriculture is increasingly important due to critical issues of water and climatic crisis. The focus of agricultural researches nowadays is to minimize the water consumption and at the same time increasing the agricultural yield. This paper presents the three-types of automatic fertigation controller for irrigation system with different application tools. A weather station, soil moisture and timer based system were used to determine the volume of water supply needed by plants to calculate an accurate irrigation operation timing. The experiment was conducted by supplying water for capsicum annum test crop located in a greenhouse. The plant water demand parameter was calculated and compared for each application tools and the best application tool was chosen to be implemented in controlling the irrigation system.</span>

Physiological and Biochemical Responses of Lavandula angustifolia to Salinity Under Mineral Foliar Application.

Saline water has been proposed as a solution to partially cover plant water demands due to scarcity of irrigation water in hot arid areas. Lavender (Lavandula angustifolia Mill.) plants were grown hydroponically under salinity (0–25–50–100 mM NaCl). The overcome of salinity stress was examined by K, Zn, and Si foliar application for the plant physiological and biochemical characteristics. The present study indicated that high (100 mM NaCl) salinity decreased plant growth, content of phenolics and antioxidant status and essential oil (EO) yield, while low-moderate salinity levels maintained the volatile oil profile in lavender. The integrated foliar application of K and Zn lighten the presumable detrimental effects of salinity in terms of fresh biomass, antioxidant capacity, and EO yield. Moderate salinity stress along with balanced concentration of K though foliar application changed the primary metabolites pathways in favor of major volatile oil constituents biosynthesis and therefore lavender plant has the potential for cultivation under prevalent semi-saline conditions. Zn and Si application, had lesser effects on the content of EO constituents, even though altered salinity induced changings. Our results have demonstrated that lavender growth/development and EO production may be affected by saline levels, whereas mechanisms for alteration of induced stress are of great significance considering the importance of the oil composition, as well.

Temperature correction of substrate moisture measurements made in coir in polytunnel-grown strawberries

The aim of this work is to assess the use of temperature corrected soil moisture data to improve the relationship between environmental drivers and the measurement of substrate moisture content in high porosity soil-free growing environments such as coir. Substrate moisture sensor data collected from strawberry plants grown in coir bags installed in a table-top system under a polytunnel illustrates the impact of temperature on capacitancebased moisture measurements. Substrate moisture measurements made in our coir arrangement possess the negative temperature coefficient of the permittivity of water where diurnal changes in moisture content oppose those of substrate temperature. The diurnal substrate temperature variation was seen to range from 7C to 25C resulting in a clearly observable temperature effect in substrate moisture content measurements during the 23 day test period. A temperature correction algorithm is presented in this work that has been derived from the Complex Refractive Index Model (CRIM) equation which was easily calibrated for coir and applied to the substrate moisture and temperature data. The diurnal variations seen with the temperature compensated substrate moisture data now align very well with the expected diurnal water demands of the strawberry plants. To further evaluate the relationship between environmental drivers of solar radiation and vapour pressure deficit with substrate moisture the temperature correction algorithm was programmed within a GP2 data logger. The GP2 was also collecting solar radiation, air temperature and relative humidity data. The resulting comparison of substrate moisture responses to environmental drivers illustrates a significantly improved correlation with temperature corrected substrate moisture measurements. We conclude that this new temperature correction algorithm addresses the effect of temperature on the relative permittivity of water which will affect all capacitance based sensor measurements in high porosity soil-free growing substrates such as coir.

ON THE IRRIGATION REGIME OF AGRICULTURAL CROPS

The article presents a comparative analysis of the results of long-term fundamental and applied researches to establish the total water consumption and irrigation regime of cotton crops in the irrigated zone of Zakavkazye (Azerbaijan) and Central Asian countries. It is marked their adequacy in determining the water demand of plants and suggested the necessity of transition to methods widely used in the world.

A new consistent sap flow baseline-correction approach for the stem heat balance method using nocturnal water vapour pressure deficits and its application in the measurements of urban climbing plant transpiration

The stem heat balance (SHB) method is a widely used sap flow technique to determine the transpiration and the water demands of herbaceous and woody plants, especially those with small diameters (e.g. climbers). The accuracy of the sap flow derived by this method (QS) depends on correction of the total measured heat input (Qt) by subtracting unintended heat losses; these heat losses are referred to as “fictitious flow” (Qfic) (QS=Qt−Qfic).We developed a physically consistent baseline-correction approach using minimum nocturnal water vapour pressure deficits (VPD). This VPD approach was compared to the so-called “night value subtraction” (NVS) approach and direct gravimetric determination for potted climbing plants and an outdoor climbing plant stand. In addition, performance tests were also conducted on artificial model stems and cut plant stems.In the tests with the outdoor climbing plant stand, sap flow corrected by the NVS approach underestimated daily transpiration by up to 33% compared to direct gravimetric determination. In contrast, the newly developed VPD approach underestimated or overestimated transpiration by only 5%–10%. The VPD approach makes use of the direct dependence of sap flow on VPD during zero-radiation conditions (night). This means, Qfic is the constant of the linear regression of the VPD and the lowest recorded Qt at night. Therefore, the correction is based on all recorded sap flow data from the measurement period itself, which in turn accounts for all factors influencing Qfic, including RH and Tair; these latter parameters are often recorded in any case. This also means that this method can be subsequently applied to currently available data sets in order to improve their quality.Our results suggest that when the raw data are corrected appropriately, the SHB method is viable when attempting to determine transpiration rates of climbing plants. This is especially true for urban areas, with their illumination, typically high VPDs and increased Tair at night.

A model exploring whether the coupled effects of plant water supply and demand affect the interpretation of water potentials and irrigation management

Water potential is a useful predictive tool in irrigation scheduling as it, or a component, is associated with physiological responses to water deficit. Increasing atmospheric demand for water increases transpiration and decreases water potential for the same stomatal conductance. However, based on supply by the soil-plant-atmosphere-continuum, decreasing soil water potential should decrease stomatal conductance and thus transpiration but also decrease water potential. Such contradictory behavior of supply and demand responses, may limit the value of water potential as an indicator of plant water status. This work studied the relationship between plant water potential and transpiration affected by supply (soil moisture) and atmospheric evaporative demand, and has implications for interpretation of water potentials and irrigation management. Results were that plant water potential has a narrow range of sensitivity to variation in supply and demand in hydrated soils, but greatly varying sensitivity in dry soils, limiting interpretation under dry conditions. Loss of soil conductance in dry, coarse soil types affects the trajectory of plant water potential response to supply and demand. Sapflow measurements on almonds indicated that variation in reference evapotranspiration and/or soil moisture deficit led to similar variation in stem water potentials to that predicted by the model. The model indicates hypotheses that with further testing may have important repercussions on the measurement of plant water use and irrigation scheduling.

CLIMATE CHANGE IMPACTS ON WATER DEMAND OF MELON PLANTS IN JAGUARIBE-APODI REGION, BRAZIL

ABSTRACT The aim of this study was to evaluate the impacts of climate change on irrigation water demand of melon plants grown in Jaguaribe-Apodi Irrigation District (DIJA), which is located between the states of Ceara and Rio Grande do Norte, in Northeastern Brazil. Future scenarios were developed using the Eta-CPTEC/HadCM3 climate change projections, after being submitted to downscaling method. We used a set of climate data from the same model for the period of 1961 through 1990, and further projections after bias correction. Local geographic coordinates were interpolated using GIS techniques. Reference evapotranspiration (ETo) was estimated from the monthly minimum and maximum mean temperatures, using a limited data method. The rainfall, temperature, ETo, and water demand future projections were mapped for the area of investigation to analyze spatial variability. ETA model simulations for climatic change showed growth in irrigation water demands due to evapotranspiration increase (from 28.4% to 33.4%), even though rainfall increases (between 61.9% and 89.9%). The increase in the average gross water demand is varied from 37.5% to 78.2% within the period of 2031 to 2060, respective to the common planting season.

基于树木年轮技术的塔里木河下游河岸胡杨林生态需水量研究

PDF HTML阅读 XML下载 导出引用 引用提醒 基于树木年轮技术的塔里木河下游河岸胡杨林生态需水量研究 DOI: 10.5846/stxb201609211901 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 新疆青年科技创新人才培养工程（201472035）；国家自然科学基金（41271006）；国家支撑计划项目（2014BAC15B02） Estimation of ecological water demand of a desert riparian forest using tree rings of Populus euphratica in the Lower Tarim River Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:生态需水量计算是干旱脆弱生态区恢复重建的一个关键问题。分析了塔里木河下游荒漠河岸林关键种-胡杨树木年轮近90年来的变化特征及对气候水文过程的响应，并基于树木年轮技术提出了维系荒漠河岸林不同恢复状态的生态需水量。研究结果表明，塔里木河下游胡杨树木年轮主要承载的是区域水文历史变化信息，可以作为定量评估生态输水工程的生态恢复效应和定量计算植被生态需水量的新指标；胡杨标准年轮宽度指数与生长年生态输水量呈显著正相关（P < 0.05），近15年生态输水对胡杨年轮宽度指数增加的平均贡献率为42.96%；若要维持塔里木河下游英苏段垂直河道300 m范围内的胡杨达到近90年来的平均生长水平，则需在生长年下泄生态需水量0.84×108 m3，若要达到断流前（1933-1974年）的平均径向生长，则每个生长年内生态需水量应达到0.91×108 m3。 Abstract:Estimation of the ecological water demand of natural plants is a key issue for the restoration and reconstruction of a fragile ecological region in arid areas. Tree rings of Populus euphratica in the Yingsu section of the lower reaches of the Tarim River and their responses to climate change and hydrological conditions were analyzed using the nonparametric Mann-Kendall trend test, Mann-Kendall-Sneyers test, moving t-test, one-way ANOVA, and Pearson correlation. The ecological water demand of a desert riparian forest in the Yingsu section was then estimated based on the tree ring characteristics using regression and stepwise regression models. The results showed that the abrupt temporal changes of temperature and precipitation were different from that of the standard chronology of P. euphratica in the lower reaches of the Tarim River. Moreover, there was no significant relationship between temperature and standard chronology of P. euphratica or between precipitation and standard chronology of P. euphratica in the lower reaches of the Tarim River. The Pearson correlation analysis also revealed no significant relationship between temperature and groundwater depth or between precipitation and groundwater depth in the lower reaches of the Tarim River. However, the width indexes of tree rings of P. euphratica were significantly and negatively related to the groundwater depth, and they were significantly and positively related to the amount of ecologically conveyed water from August to July in the Yingsu section of the lower reaches of the Tarim River. These results proved that historical information regarding water conditions could be accurately reproduced by the tree rings of P. euphratica in the lower reaches of the Tarim River. Therefore, the tree rings of P. euphratica could be used for quantitatively assessing the restoration effects of ecological water conveyance to desert riparian forests and calculating the ecological water demand for natural vegetation in the lower reaches of the Tarim River. The average contribution of ecological water conveyance to the increased tree ring width index was 42.96% in the Yingsu section of the lower reaches of the Tarim River. Estimated from the equation of the tree rings of P. euphratica and the amount of ecologically conveyed water, an annual ecological water conveyance of 0.84×108 m3 was expected to maintain the average growth (i.e., average tree ring index of 0.997 during 1933-2015) of P. euphratica in the Yingsu section within a distance of 300 m to the river channel in the lower reaches of the Tarim River. Furthermore, an annual water conveyance of 0.91×108 m3 was estimated to keep P. euphratica at an average radial growth rate of 0.972 during the period of 1933-1974 (i.e., before the main channel of the Tarim river near Yingsu section dried up). 参考文献 相似文献 引证文献

Stomatal resistance of New Guinea Impatiens pot plants. Part 1: Model development for well watered plants based on design of experiments

In greenhouses, reducing water consumption by increasing water efficiency in order to fulfil the requirements of sustainability is a challenge. To reach this goal, we need to better understand the water demand of plants. Transpiration is the main mechanism involved in water transfer, which is controlled by stomatal resistance Rs. Predictive models can be used to assess this parameter. However, few models currently exist for greenhouse plants grown in pots. The aim of this work is to develop a model of Rs based on full factorial design (FFD), and to validate it for greenhouse plants at various growth stages. FFD is based on an optimisation process to establish a polynomial relationship between Rs and radiation, humidity, and temperature. To establish the parameters of the model, a set of experiments was conducted inside a 10-m2 growth chamber with New Guinea Impatiens grown in pots. Rs was measured with a porometer under nine climatic scenarios. Once the parameters were determined, the FFD model was validated against experimental data recorded from a greenhouse Impatiens crop, and compared with the Jarvis model. The slopes of the linear regression between measured Rs values and Rs values predicted from the FFD and Jarvis models varied within the range 0.89–1.12 for FFD and 0.45–0.54 for Jarvis. FFD was therefore able to correctly simulate Rs. Its main advantage was to only require few data for its calibration, contrary to the Jarvis model. In a next step, it will be used to predict transpiration rates.

Using SWAT for Strategic Planning of Basin Scale Irrigation Control Policies: a Case Study from a Humid Region in Northern Germany

The eco-hydrological model SWAT is used worldwide for simulating hydrology and water quality of agricultural catchments. One of the main water uses is irrigation, predominantly in arid and semi-arid regions. Climate impact simulations show that a future increase of irrigation demand can be expected for humid regions. Options for adaptation include the improvement of irrigation techniques and the modification of crop patterns. In our study we investigate the application of SWAT for the development of water saving irrigation control strategies in a humid river catchment in Northern Germany. We developed different scenarios using both soil moisture deficit control and plant water demand control. The results show plausible changes of irrigation amounts when changing the trigger points of both control methods. By deficit control strategies, the water consumption could be reduced with only a moderate decrease of crop yield. Differences between soil characteristics were well shown in the SWAT simulations, but the model consistently overestimated irrigation values. Furthermore we found a high variability of the model errors between the different years, even if the long term average values are considered acceptable. Future research is needed to improve the model accuracy in automatic irrigation control.

永定河北京段生态需水量研究

永定河北京段是人工重建河道，人工重建河道的生态需水量估算是河道修复研究中的重要课题。永定河北京段生态需水主要包括生态基流，人工重建河道的河湖蒸散发和渗漏量以及河滨带植被的生态补水量等。根据研究河段的不同要求，本文概化了天然河道，设计了人工河道断面形状和河床特征，较为清晰地划分了消耗性生态需水和非消耗性生态需水的范畴。在确定各种生态需水目标前提下，计算不同河段的消耗性生态需水和非消耗性生态需水量。结果显示, 北京市最低到最优生态的目标下，永定河山峡段和平原河段的生态基流需水量为0.79 - 4.75 × 108 m 3；平原城市段和平原郊野段的河湖和河滨带植被用水0.28 - 0.92 × 108 m3，其中河湖蒸发渗漏用水0.34 - 0.59 × 108 m 3，河滨带植被用水0.33 × 108 m 3。研究显示，人工河道的生态基流与河道断面、河道粗糙度、纵坡比及河道防渗关系密切。为满足生态修复目标，在水量受到限制的情况下，可以通过调整人工河道的断面、粗糙度、水力坡度和河道渗透性来达到相应的生态需水量。 The Beijing section of Yongding River is an artificial rebuilt river. The environment flow study is of great significance on ecology and environment rebuilt in a polluted watershed and river course. The principle of environment flow in an artificial river is studied in this paper. First of all, the ecological goal theory and specific ecological objectives are studied for different purposes. This paper indicates that environmental flow in an artificial rebuilt river includes ecological base flow, water evaporation and infiltration in the artificial river and lakes, and water demand of the riverside plants. In this research, the natural river course is abstracted and generalized based on specific requirements of different sections of natural river course and artificial river bed; the artificial river cross-section is designed subsequently. Furthermore, this paper has divided the content of consumptive and non-consumptive environmental flow. Based on the ecological targets decided, research result of the consumptive and non-consumptive environmental flow is calculated in the case study as follows: 1) the ecological base flow of the gorges section and the plain section is 0.79 - 4.75 × 108 m3 under the basis of the lowest to best target; normally the main course flow is included only in the low objective and some tributary environment flow could be also included in the higher objective; 2) the consumptive water demand of the urban plain section and rural plain section is 2.81 - 9.17 × 107 m3 under different ecological targets, among which the water demand for evaporation and infiltration of the artificial river and lake is 3.40 - 5.87 × 107 m3; the water demand for riverside plant is 3.30 × 107 m3 for different ecological targets. The research indicates that the environmental flow of the artificial rebuilt river is related to the transect of the river, the roughness of the river course, the ratio of longitudinal slope, and the seepage prevention works in the course. In the case of water limitation, the above factors could be adjusted to regulate environmental flow for proper ecological targets.

Integrating water resources and power generation: The energy–water nexus in Illinois

Thermoelectric power plants contribute 90% of the electricity generated in the United States. Steam condensation in the power generation cycle creates a need for cooling, often accomplished using large amounts of water. These large water requirements can lead to negative consequences of power plants dialing down or shutting down during times of low water availability. Consequently, water constraints can translate into energy constraints. Projected future population growth and changing climate conditions might also increase the competition for water in many areas, motivating a resource accounting analysis to both establish a baseline of current water requirements and simulate possible impacts from future water and energy management decisions. Our analysis of the current water demands for power generation, focused on the state of Illinois, combined existing digital spatial datasets with engineering basic principles to synthesize a geographic information systems (GIS) model of current and projected water demand for thermoelectric power plants. We evaluated two potential future cases based on water use implications: (1) a shift in fuel from coal to natural gas, and (2) a shift in cooling technology from open-loop to closed-loop cooling. Our results show that a shift from coal-generated to natural gas-generated electricity could decrease statewide water consumption by 0.10billionm3/yr (32% decrease) and withdrawal by 7.9billionm3/yr (37% decrease), on average. A shift from open-loop to closed-loop cooling technologies could decrease withdrawals by an average of 21billionm3/yr (96% decrease), with the tradeoff of increasing statewide water consumption for power generation by 0.18billionm3/yr (58% increase). Furthermore, we performed an economic analysis of retrofitting open-loop cooling systems to closed-loop cooling, revealing an annual cost between $0.58 and $1.3billion to retrofit the 22 open-loop cooling plants considered, translating to an effective water price between $0.03 and $0.06/m3. The synergies and tradeoffs between water resources and power generation yield interesting implications for integrated decision making and policy in Illinois and elsewhere.

Growth, Photosynthesis and Pollen Performance in Saline Water Treated Olive Plants under High Temperature

Olive cultivation in hot arid areas is hindered by the scarcity of irrigation water. The exploitation of saline water has been proposed as a solution to partially cover plant water demands. This paper presents the effects of salinity [0, 60 and 120 mM sodium chloride (NaCl)] on physiological and reproductive functions of cultivars Koroneiki and Amphissis in a closed hydroponic system. Shoot growth was markedly reduced in high salinity dose in Amphissis (−81%) and Koroneiki (−75%). The photosynthetic rate was significantly reduced at 120 mM NaCl for both cultivars, as well as chlorophyll and carotenoids content (43% and 44%, respectively). The Na+ content in all plant parts increased in both salinity doses especially in Amphissis while K concentration decreased for both cultivars. Inflorescences in Amphissis were severely damaged due to salinity. Consequently, pollen sampling and in vitro germination study was only feasible for Koroneiki. Indeed, Koroneiki pollen germination was reduced at 60 mM NaCl (−42%) and at 120 mM NaCl (−88%). Pollen tube length was also reduced by 15% and 28% for the middle and high salinity dose, respectively. The results of the present study indicate that Amphissis is more sensitive in high salinity doses compared to Koroneiki and that reproductive functions are severely affected by salinity.

Acclimations to light quality on plant and leaf level affect the vulnerability of pepper (Capsicum annuum L.) to water deficit.

We investigated the influence of light quality on the vulnerability of pepper plants to water deficit. For this purpose plants were cultivated either under compact fluorescence lamps (CFL) or light-emitting diodes (LED) providing similar photon fluence rates (95 µmol m(-2) s(-1)) but distinct light quality. CFL emit a wide-band spectrum with dominant peaks in the green and red spectral region, whereas LEDs offer narrow band spectra with dominant peaks at blue (445 nm) and red (665 nm) regions. After one-week acclimation to light conditions plants were exposed to water deficit by withholding irrigation; this period was followed by a one-week regeneration period and a second water deficit cycle. In general, plants grown under CFL suffered more from water deficit than plants grown under LED modules, as indicated by the impairment of the photosynthetic efficiency of PSII, resulting in less biomass accumulation compared to respective control plants. As affected by water shortage, plants grown under CFL had a stronger decrease in the electron transport rate (ETR) and more pronounced increase in heat dissipation (NPQ). The higher amount of blue light suppressed plant growth and biomass formation, and consequently reduced the water demand of plants grown under LEDs. Moreover, pepper plants exposed to high blue light underwent adjustments at chloroplast level (e.g., higher Chl a/Chl b ratio), increasing the photosynthetic performance under the LED spectrum. Differently than expected, stomatal conductance was comparable for water-deficit and control plants in both light conditions during the stress and recovery phases, indicating only minor adjustments at the stomatal level. Our results highlight the potential of the target-use of light quality to induce structural and functional acclimations improving plant performance under stress situations.

Agroecological Approaches to Mitigate Increasing Limitation of Corn Yields by Water Availability

A key strategy for climate change adaptation in the rain-fed northern Corn Belt is to decrease cropping system vulnerability to changes in precipitation patterns by building resilience. Using 50- year of county level yield and environmental data from Iowa and Ontario, we first demonstrate that sensitivity of corn yield to precipitation, particularly in July and August, has increased over the past five decades despite no changes in precipitation patterns. This can be attributed to steady improvement in corn yield potential and so plant water demand since the mid-20th century and removal of non-water constraints to crop production. Such vulnerability of corn-based cropping systems to water limitations is of increasing concern as climate change models predict higher summer temperatures and year-to-year variations in precipitations in this region. As suggested in the ecology literature, increasing agroecosystem temporal and spacial diversity is one of the key management strategies to deal with impending weather variability. Using yield and environmental data from a 30-year long-term rotation and tillage trial in Ontario, we show that diversification of short corn-based rotations using small grains and forage crops increases corn yield stability and resilience to both limiting and excess soil moisture1. We also demonstrate the importance of conservation tillage and measured the impact of rotation and tillage history on plants ability to access water resources, plant available soil water and their combined effects on timing of physiological water stress and grain yield when drought occurs at reproductive stages. Our results emphasize the growing importance of developing strategies for managing soil moisture in rain-fed regions and the significance of agroecological approaches to develop hardy agricultural systems and protect food and feed production against the upcoming extreme weather events.

Reductions in a Commercial Potato Irrigation Schedule during Tuber Bulking in Florida: Physiological, Yield, and Quality Effects

Proper irrigation scheduling in potato (Solanum tuberosum L.) can lead to higher returns and more sustainable production practices when compared to systems that do not take plant water demand into account. In an attempt to reduce irrigation applications while minimizing yield reduction, we evaluated a novel deficit irrigation treatment utilizing a mild irrigation reduction during tuber bulking by comparing a typical commercial irrigation schedule to a partial irrigation schedule. Physiological, yield, and quality effects were quantified. Reducing the number of irrigation applications by 14 in 2011 and by 9 in 2012 minimally affected most parameters measured. However, a significant yield reduction of 11,713 kg/ha in the partial irrigation treatment occurred in 2011, likely because of the irrigation treatment commencing at the latter portion of tuber initiation. In 2012, the initiation of the partial irrigation was delayed and resulted in no significant difference in yield between the partial and full irrigation treatments. This study shows the potential for a reduced irrigation schedule for use by Florida potato growers as a sustainable option for potato production in this region.

Influence of site-specific parameters on environmental impacts of desalination

Many metropolitan areas have a high dependency on Seawater Reverse Osmosis (SWRO) desalination plants for bulk water supply. Location and scale decisions are important for SWRO desalination plants owing to the significant environmental costs associated with long distance water pumping. The aim of this study is to introduce a Geographical Information System (GIS)-based method to assist such site-specific decisions. The method has 3 stages. Stage 1 uses GIS to identify feasible plant locations and water demand areas. Stage 2 develops a range of scenarios that balance plant size and number with water demand. In stage 3, the preferred scenario is selected based on environmental life cycle assessment. The method’s applicability was tested using data for the northern corridor of Perth, Western Australia (WA). Spatial water demand and suitable vacant land for accommodating SWRO plants in the case study are obtained in Stage 1. Based on these spatial data, two water planning options are designed in order to supply desalinated water to the demand area. The first option consists of a large SWRO desalination plant and its connected trunk main which supplies water into the demand centrally (centralized scenario). Second option consists of five medium-sized SWRO desalination plants integrated within the demand area (distributed scenario). The best scenario for environmental performance was found to be the distributed scenario which has 18% less GHG emission compared to centralized scenario. This method is adaptable to other case studies for identifying optimal SWRO plant sizes and locations based on environmental criteria.

Assessment of effects of two runoff control engineering practices on soil water and plant growth for afforestation in a semi-arid area after 10 years

Water is the primary constraint for vegetation development in the semi-arid area in the loess plateau of China. Afforestation aimed at runoff control in association with engineering practices have been considered an effective approach to improving the utilization of limited rainfall in the ecological restoration of wild lands and abandoned farmland in semi-arid areas in China. This research investigated the long-term effects of two adopted engineering measures on soil water content, total water consumption, and plant growth after having been applied in afforestation areas for 10 years. These engineering measures included: slope-separate flat terraces (SSFT) and cone-shape focused fluid pit (CFFP). The results indicated that the mean annual soil water deficit with SSFT on the forested site that originated from wild land was 6.7mm with evapotranspiration of 419.66mm while the mean annual soil water deficit from abandoned farmland with CFFP was 9.26mm with evapotranspiration of 422.26mm. The mean annual soil water deficit in the abandoned farmland site with SSFT was 15.60mm with evapotranspiration of 428.60mm. This research strongly suggested that the engineering runoff control practices in the study effectively reduced soil erosion, increased water storage, and eased the water demand of forest-grass vegetation at the beginning of afforestation, but over-consumption of soil water that may not have been replenished by the limited rainfall, could potentially cause the soil to dry-out. Consideration of soil water storage capability and plant water demand, with possibly a lower initial tree density, should be considered when designing engineering practices for regulating runoff water in afforestation.

Statistical patterns in tropical tree cover explained by the different water demand of individual trees and grasses

Tree cover varies enormously across tropical ecosystems-from arid savannas to closed rain forests-and yet a general predictive theory of tropical tree cover remains elusive. Here we use the maximum-entropy method to predict the most likely sample frequency distribution of ecosystems with different tree and grass fractional cover if balance between water supply and demand were the dominant constraint on community assembly. Assuming a hierarchy of individual plant water demand in which trees require more water than grasses, we reproduce observed trends in the means and the upper and lower limits of tropical tree and grass cover across the entire spectrum of tropical ecosystem water supply. Finer details not captured by our predictions indicate the influence of additional factors, such as disturbance. Our results challenge the view that tropical tree-grass coexistence is largely sustained by disturbances in moist environments ("unstable" coexistence) with water supply playing a dominant role only in arid conditions ("stable" coexistence). More generally, they suggest that macroecological patterns can be understood and predicted as the most likely outcome of a large number of stochastic processes being played out within a relatively small number of ecological constraints.

Model Predictive Control for Real-Time Irrigation Scheduling

Irrigation underpins agricultural productivity. The purpose of irrigation is to match water supply to crop water demand. The effectiveness of irrigation depends on the quality of the timing and duration of watering events, also called irrigation scheduling. Most farmers use heuristic rules to determine irrigation events. This often leads to over-watering which results in lower crop yields and wasted water. By acquiring good estimates of a plant's water demand and local weather, it is possible to use optimization theory to compute an irrigation schedule that matches supply and demand thereby improving crop yields. Previous work has focused on scheduling irrigation over long time frames such as seasonal water allocations. Real-time irrigation scheduling, e.g. hourly or daily, has received little attention. Farmers rely on heuristic approaches implemented using simple spreadsheet tools to help them in this task. This approach cannot deal effectively with operational constraints and thereby results in poor performance. In this paper we develop a Model Predictive Control framework for real-time irrigation scheduling. The proposed formulation can take into account common operational constraints, including limitations on water availability as well as practical limits on the maximum or minimum amount of water that should be applied. We use measured climate data coupled with a simulation model to evaluate the proposed algorithm.