Temperature anomalies affect violent conflicts in African and Middle Eastern warm regions
, 102118. Publisher's VersionAbstract
Several studies have linked high temperatures to increases in violent conflicts. The findings are controversial, however, as there has been no systematic cross-sectional analysis performed to demonstrate the generality of the proposed relationship. Moreover, the timescale of temperature/violence relationships have not been fully investigated; it is unclear how short versus long-term, or seasonal and inter-annual temperature variability contribute to the likelihood or frequency of violent events. We here perform systematic regional and grid-based longitudinal analyses in Africa and the Middle East for the period 1990–2017, using geolocated information on armed conflicts and a recently released satellite-based gridded temperature data set. We find seasonal synchrony between temperature and number of armed conflicts at the regional scale (climatic region), as well as a positive relationship in temperature and conflict anomalies on inter-annual timescales at the grid cell level (for the entire African and ME region). After controlling for ‘location effects’, we do not find that long-term warming has affected armed conflicts for the last three decades. However, the effects of temperature anomalies are stronger in warmer places (~5% increase per 10 °C, P < 0.05), suggesting that populations living in warmer places are more sensitive to temperature deviations. Taken together, these findings imply that projected warming and increasing temperature variability may enhance violence in these regions, though the mechanisms of the relationships still need to be exposed.
Using Landsat satellites to assess the impact of check dams built across erosive gullies on vegetation rehabilitation
, 138873. Publisher's VersionAbstract
Gully erosion, a process of soil removal due to water accumulation and runoff, is a worldwide problem affecting agricultural lands. Building check dams perpendicular to the flow direction is one of the suggested control practices to stabilize this process. Though there are many studies on the effect of erosive controls on land stabilization, few examine its effect on the rehabilitation of vegetation. Here we use information from the satellites Landsat-7 (1999–2018) and Landsat-8 (2013–2018) to assess the effect of soil check dams built during 2012 across three gullies with distinct structures in a dryland area on vegetative cover and water status. We use a time series analysis technique to decompose Landsat-derived soil adjusted vegetation index (SAVI) into woody (SAVIW) and herbaceous (iSAVIH) contributions. The integral over the seasonal signal of the normalized difference water index (iNDWI) was used to assess changes in water status in the gully. We used herbaceous biomass collected in the field in 2014–2017 to validate iSAVIH as a proxy of herbaceous biomass. Our results show that following the construction of the check dams, the change in woody vegetation cover is best described by a sigmoid model with an increase of ~57% (95% CI: 39%–76%; p < 0.0001), while the herbaceous vegetation increases linearly at a rate of ~71% per year (95% CI: 48%–93% y−1; p < 0.0001). The correlation between iSAVIH and herbaceous biomass (R2 = 0.56; n = 16; p < 0.001) corroborates this increase. We found higher herbaceous productivity in the deeper gully compared to the shallower gullies but not statistically different increase rates. An increase in iNDWI of ~68% (95% CI: 43%–95%; p < 0.0001) likely implies an improved water infiltration rate that favored the vegetation expansion. Our satellite-based approach can be used to assess the impact of erosive control practices on vegetation rehabilitation in heterogeneous gullies.
The indigenous Bedouin farmers as land rehabilitators—Setup of an action research programme in the Negev
. Land Degradation & DevelopmentLand Degradation & DevelopmentLand Degrad Dev 2020
. Publisher's VersionAbstract
Abstract The Negev suffers from enhanced land degradation, mostly due to lack of awareness about its state, and hostility between the region's indigenous Bedouin farmers and the authorities. In order to examine a potential solution to this 'Lose?Lose' situation, a unique project is underway, with the collaboration of the Yeroham Municipality and the adjacent Rahma Bedouin farmers' village. The concept of this ongoing Programme is based on bidirectional knowledge transfer of farming data between the farmers and land scientists, aimed to adapt Bedouin traditional cultivation methods and transform them into methods that restore the environment and are also profitable. In order to reach this goal, a highly knowledgeable Bedouin liaison person was appointed to carry out the project together with the Coordinating Team. A comprehensive study and tour were carried out in order to analyze the different landforms and Bedouin cultivation preferences. An initial survey was carried out and data from literature collected in order to determine the ecological and archaeological characteristics of the ecosystem. The area was then prepared for agricultural utilization by removing widespread garbage and dealing with wadis that have been filled with construction waste. This project, which integrates soil enhancement, agriculture utilization, and traditional Bedouin farming, aims for rehabilitation of the northern Negev gullied areas. However, the implementation of the study concept in the field is accompanied by many challenges related to Bedouin interclan communication and the diverse types of degraded lands.
Pharmaceuticals in treated wastewater induce a stress response in tomato plants
. Sci Rep 2020
Pharmaceuticals remain in treated wastewater used to irrigate agricultural crops. Their effect on terrestrial plants is practically unknown. Here we tested whether these compounds can be considered as plant stress inducers. Several features characterize the general stress response in plants: production of reactive oxygen species acting as stress-response signals, MAPKs signaling cascade inducing expression of defense genes, heat shock proteins preventing protein denaturation and degradation, and amino acids playing signaling roles and involved in osmoregulation. Tomato seedlings bathing in a cocktail of pharmaceuticals (Carbamazepine, Valporic acid, Phenytoin, Diazepam, Lamotrigine) or in Carbamazepine alone, at different concentrations and during different time-periods, were used to study the patterns of stress-related markers. The accumulation of the stress-related biomarkers in leaf and root tissues pointed to a cumulative stress response, mobilizing the cell protection machinery to avoid metabolic modifications and to restore homeostasis. The described approach is suitable for the investigation of stress response of different crop plants to various contaminants present in treated wastewater.
Eco-hydrology and geomorphology of the largest floods along the hyperarid Kuiseb River, Namibia
. Journal of Hydrology 2020
, 124450. Publisher's VersionAbstract
Flood-fed aquifers along the sandy lower reach of the Kuiseb River sustain a 130-km-long green belt of lush oases across the hyperarid Namib desert. This oasis is a year-round source for water creating dense-tall woodland along the narrow corridor of the ephemeral river valley, which, in turn, supports human activity and fauna including during the long dry austral winters and multi-year droughts. Occasional floods, originating at the river’s wetter headwaters, travel ∼280 km downstream, before recharging these aquifers. We analyzed the flood-aquifer-vegetation dynamics at-a-site and along the river, determining the relative impact of floods with diverse magnitude and frequency on downstream reaches. We find that flood discharge that feeds the alluvial aquifers also affects vegetation dynamics along the river. The downstream aquifers are fed only by the largest floods that allow the infrequent germination of plants; mean annual recharge volume is too low to support the aquifers level. These short-term vegetation cycles of green-up and then fast senescence in-between floods are easily detected by satellite-derived vegetation index. This index identifies historical floods and their magnitudes in arid and hyperarid regions; specifically, it determines occurrences of large floods in headwater-fed, ephemeral Namib streams as well as in other hyperarid regions. Our study reveals the importance of flood properties on the oasis life cycle, emphasizing the impact of drought and wet years on the Namib’s riparian vegetation.
The influence of surfactant-application method on the effectiveness of water-repellent soil remediation
. Geoderma 2020
. Publisher's VersionAbstract
Soil water repellency (SWR) has a substantial effect on soil–water hydrology: it hinders infiltration, leading to enhanced surface runoff and soil erosion, and causes preferential flow in the soil profile beyond that from the soil's natural heterogeneity. SWR is associated with soil organic matter content, the latter added to the soil by vegetation exudates, litter and residues, forest fires, and replacement of fresh water by treated wastewater for irrigation. Surfactants are surface-active substances composed of organic molecules with hydrophobic tails and hydrophilic heads that can reduce the surface tension (γ) of the aqueous solution, thereby reducing SWR, via adsorption to soil particles. Surfactants are commonly used to remediate water-repellent soils. We investigated the role of two surfactant-application methods on the efficacy of SWR remediation. Aqueous solutions of two commercial surfactants had a substantial effect on parameters used to characterize the persistence and severity of SWR. However, the efficacy of these surfactants in remediating sandy soils rendered water-repellent by irrigation with treated effluent was substantially affected by their application method. Whereas application of aqueous surfactant solution to the surface of water-repellent soil, the commonly used remediation method, formed finger-like plumes similar to those obtained for water application, bulbous-like plumes were formed when the soil was premixed with the aqueous surfactant solution prior to water application. These differences were attributed to the significant role of the rate-limited surfactant adsorption to the soil particles. © 2019 Elsevier B.V.
Chemical Versus Mechanical Denudation in Meta-Clastic and Carbonate Bedrock Catchments on Crete, Greece, and Mechanisms for Steep and High Carbonate Topography
. Journal of Geophysical Research: Earth Surface 2019
, 124. Publisher's VersionAbstract
Abstract On Crete—as is common elsewhere in the Mediterranean—carbonate massifs form high mountain ranges whereas topography is lower in areas with meta-clastic rocks. This observation suggests that differences in denudational processes between carbonate-rich rocks and quartzofeldspathic units impart a fundamental control on landscape evolution. Here we present new cosmogenic basin-average denudation rate measurements from both 10Be and 36Cl in meta-clastic and carbonate bedrock catchments, respectively, to assess relationships between denudation rates, processes, and topographic form. We compare total denudation rates to dissolution rates calculated from 49 new and previously published water samples. Basin-average denudation rates of meta-clastic and carbonate catchments are similar, with mean values of 0.10 mm/a and 0.13 mm/a, respectively. The contribution of dissolution to total denudation rate was <10% in the one measured meta-clastic catchment, and 40% for carbonate catchments ( 0.05 mm/a), suggesting the dominance of physical over chemical weathering at the catchment scale in both rock types. Water mass-balance calculations for three carbonate catchments suggests 40–90% of surface runoff is lost to groundwater. To explore the impact of dissolution and infiltration to groundwater on relief, we develop a numerical model for carbonate denudation. We find that dissolution modifies the river profile channel steepness, and infiltration changes the fluvial response time to external forcing. Furthermore, we show that infiltration of surface runoff to groundwater in karst regions is an efficient way to steepen topography and generate the dramatic relief in carbonates observed throughout Crete and the Mediterranean.
Combining micelle-clay sorption to solar photo-Fenton processes for domestic wastewater treatment
. Environmental Science and Pollution Research 2019
, 18971-18978. Publisher's VersionAbstract
A tertiary treatment of effluent from a biological domestic wastewater treatment plant was tested by combining filtration and solar photocatalysis. Adsorption was carried out by a sequence of two column filters, the first one filled with granular activated carbon (GAC) and the second one with granulated nano-composite of micelle-montmorillonite mixed with sand (20:100, w/w). The applied solar advanced oxidation process was homogeneous photo-Fenton photocatalysis using peroxymonosulfate (PMS) as oxidant agent. This combination of simple, robust, and low-cost technologies aimed to ensure water disinfection and emerging contaminants (ECs, mainly pharmaceuticals) removal. The filtration step showed good performances in removing dissolved organic matter and practically removing all bacteria such as Escherichia coli and Enterococcus faecalis from the secondary treated water. Solar advanced oxidation processes were efficient in elimination of trace levels of ECs. The final effluent presented an improved sanitary level with acceptable chemical and biological characteristics for irrigation. © 2018, Springer-Verlag GmbH Germany, part of Springer Nature.
Environmental and agricultural relevance of humic fractions extracted by alkali from soils and natural waters
. Journal of Environmental Quality 2019
, 217-232. Publisher's VersionAbstract
To study the structure and function of soil organic matter, soil scientists have performed alkali extractions for soil humic acid (HA) and fulvic acid (FA) fractions for more than 200 years. Over the last few decades aquatic scientists have used similar fractions of dissolved organic matter, extracted by resin adsorption followed by alkali desorption. Critics have claimed that alkali-extractable fractions are laboratory artifacts, hence unsuitable for studying natural organic matter structure and function in field conditions. In response, this review first addresses specific conceptual concerns about humic fractions. Then we discuss several case studies in which HA and FA were extracted from soils, waters, and organic materials to address meaningful problems across diverse research settings. Specifically, one case study demonstrated the importance of humic substances for understanding transport and bioavailability of persistent organic pollutants. An understanding of metal binding sites in FA and HA proved essential to accurately model metal ion behavior in soil and water. In landscape-based studies, pesticides were preferentially bound to HA, reducing their mobility. Compost maturity and acceptability of other organic waste for land application were well evaluated by properties of HA extracted from these materials. A young humic fraction helped understand N cycling in paddy rice (Oryza sativa L.) soils, leading to improved rice management. The HA and FA fractions accurately represent natural organic matter across multiple environments, source materials, and research objectives. Studying them can help resolve important scientific and practical issues. Copyright © American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.
Olive tree survival and adaptation to the harsh growing conditions in the arid desert environment of the Negev Highlands, Southern Israel
. Israel Journal of Plant Sciences 2019
, 147-152. Publisher's VersionAbstract
Twenty-three olive trees were found to grow in traditional orchard sites in the Negev Highlands desert, southern Israel. Their location was marked on maps, and their growth, morphology, biology, preservation and survival was monitored. Some of them are presently maintained by the Bedouin population of the Negev, whereas others seemed to have survived from earlier periods. The average annual rainfall in this region is 90-130 mm. Most of the orchards were deliberately planted in preexisting agricultural plots, built during the Byzantine and Early Muslim era (3rd-8th centuries CE). They were irrigated by harvesting runoff water. The Byzantine era was the most populated period in the Negev Highlands, when wine and olive oil were the main horticultural products. A variety of domesticated fruit trees are found in the present abandoned orchards: olive, fig, grapevine, pomegranate, almond, date palm, carob, pistachio and bitter orange. The trees have not been artificially irrigated for at least seven decades. Nevertheless, most of them continue to flourish and bear fruit. We focused on understanding the abandoned olive trees' survival and adaptation mechanisms. Olive trees growing was a favorite crop to Byzantine farmers due to the significant economic value of olive oil and good adaptation to the environmental conditions in the Negev Highlands. © Koninklijke Brill NV, Leiden, 2018.
Using humic fractions to understand natural organic matter processes in soil and water: Selected studies and applications
. Journal of Environmental Quality 2019
, 1633-1643. Publisher's VersionAbstract
Natural organic matter (NOM) plays key environmental roles in both aquatic and soil systems. A long-standing approach for evaluating NOM composition and activity is to extract soils with alkali solutions to obtain humic substances, namely humic acids (HA), and fulvic acids (FA), or to briefly expose isolated fractions of dissolved organic matter to alkali. Critics have claimed these methods create laboratory artifacts and are thus unsuitable for studying NOM behavior in field conditions. In response, we describe case studies in which humic fractions were analyzed to identify significant processes in environmental or agricultural issues. Specifically, humic fractions played a key role in maintaining toxic levels of arsenic (As) in drinking water supplies in South and Southeast Asia. Elsewhere, binding reactions of FA and HA with prions were shown to provide a plausible mechanism for variable persistence of prion infectivity across soil types. Humic substances were also shown to enhance iron (Fe) uptake by plants in solution culture and field conditions. Their specific binding sites for mercury (Hg) as determined in laboratory conditions enabled accurate modeling of soil Hg binding under varying conditions. A young HA fraction reproduced in controlled conditions the capacity of animal manure to maintain potassium (K) availability in strongly K-fixing field soils, leading to development of a commercially successful humic-K fertilizer. Humic fractions accurately represented NOM across multiple settings and research objectives while providing novel opportunities for advanced analyses. The study of humic fractions has helped resolve scientific and practical issues in aquatic and soil systems. © 2019 The Author(s).
The vitality of fruit trees in ancient Bedouin orchards in the Arid Negev Highlands (Israel): Implications of climatic change and environmental stability
. Quaternary International 2019
. Publisher's VersionAbstract
Thirty-seven sites with fruit tree orchards were found in the arid Negev Highlands of southern Israel. A variety of domesticated fruit trees were planted in these orchards, including date palm, fig, olive, pomegranate, almond, carob, pistachio, grapevine and bitter orange. The orchards were irrigated only by runoff water accumulating in runoff-harvesting systems built during the Byzantine and Early Muslim eras, some 1000–1500 years ago, which, despite their antiquity, are still vivid and occasionally fruit bearing today. The oldest olive trees seem to be direct descendants of trees planted during Byzantine times, whereas the youngest trees were planted by the Bedouin population of the Negev Highlands in the last few decades. The fact that the Bedouin population, with very little experience in agriculture, has succeeded to cultivate a large variety of fruit trees in the present harsh arid climate utilizing the historical agricultural installations has important environmental implications. It indicates that the original builders of the desert agriculture systems were highly sophisticated in transforming desert soil into arable land. However, this was achieved through hard labor, involving the construction of a vast number of stone dams and agricultural terraces to divert channels, and the clearing of rocky surfaces. This huge effort indicates that the climate and environment prevailing during the Byzantine–Early Muslim eras was equally harsh and arid; otherwise, the invested labor would not have been justified. We conclude that the Byzantine farmers, with their greater agricultural experience and long heritage in dry land agriculture, have achieved greater success than today Bedouin population, at cultivating of fruit trees under the harsh conditions of the Negev Highlands. Therefore we deduce that the ancient desert agriculture was not the outcome of better climate; rather, the climate prevailing during the relevant historical times was probably dry and harsh, much like today. The fact that the Bedouin population in that geograghical area is cultivating orchards utilizing the same constructions, and technologies indicates that the present environmental and climatic conditions were are suitable for practicing desert agriculture and have hardly changed since the Byzantine era. © 2019 Elsevier Ltd and INQUA
Dynamic physiological phenotyping of drought-stressed pepper plants treated with “productivity-enhancing” and “survivability-enhancing” biostimulants
. Frontiers in Plant Science 2019
. Publisher's VersionAbstract
The improvement of crop productivity under abiotic stress is one of the biggest challenges faced by the agricultural scientific community. Despite extensive research, the research-to-commercial transfer rate of abiotic stress-resistant crops remains very low. This is mainly due to the complexity of genotype × environment interactions and in particular, the ability to quantify the dynamic plant physiological response profile to a dynamic environment. Most existing phenotyping facilities collect information using robotics and automated image acquisition and analysis. However, their ability to directly measure the physiological properties of the whole plant is limited. We demonstrate a high-throughput functional phenotyping system (HFPS) that enables comparing plants’ dynamic responses to different ambient conditions in dynamic environments due to its direct and simultaneous measurement of yield-related physiological traits of plants under several treatments. The system is designed as one-to-one (1:1) plant–[sensors+controller] units, i.e., each individual plant has its own personalized sensor, controller and irrigation valves that enable (i) monitoring water-relation kinetics of each plant–environment response throughout the plant’s life cycle with high spatiotemporal resolution, (ii) a truly randomized experimental design due to multiple independent treatment scenarios for every plant, and (iii) reduction of artificial ambient perturbations due to the immobility of the plants or other objects. In addition, we propose two new resilience-quantifying-related traits that can also be phenotyped using the HFPS: transpiration recovery rate and night water reabsorption. We use the HFPS to screen the effects of two commercial biostimulants (a seaweed extract –ICL-SW, and a metabolite formula – ICL-NewFo1) on Capsicum annuum under different irrigation regimes. Biostimulants are considered an alternative approach to improving crop productivity. However, their complex mode of action necessitates cost-effective pre-field phenotyping. The combination of two types of treatment (biostimulants and drought) enabled us to evaluate the precision and resolution of the system in investigating the effect of biostimulants on drought tolerance. We analyze and discuss plant behavior at different stages, and assess the penalty and trade-off between productivity and resilience. In this test case, we suggest a protocol for the screening of biostimulants’ physiological mechanisms of action. © 2019 Dalal, Bourstein, Haish, Shenhar, Wallach and Moshelion.
Structure and hydraulic properties in soils under long-term irrigation with treated wastewater
. Geoderma 2019
, 90-98. Publisher's VersionAbstract
Secondary treated wastewater, a commonly used water resource in agriculture in (semi-)arid areas, often contains salts, sodium, and organic matter which may affect soil structure and hydraulic properties. The main objective of this study was to jointly analyse the effects of long-term irrigation with treated wastewater on physicochemical soil characteristics, soil structure, and soil water dynamics in undisturbed soils. X-ray microtomography was used to determine changes in macro-porosity (> 19 μm), pore size distribution, and pore connectivity of a sandy clay loam and a loamy sand. Differences in the pore network among soils irrigated with treated wastewater, fresh water that replaced treated wastewater, and non-irrigated control plots could be explained by changes in textural composition, soil physicochemical parameters, and hydraulic properties. In this study we showed that irrigation led to the development of a connected macro-pore network, independent of the studied water quality. The leaching of silt and clay particles in the sandy soil due to treated wastewater irrigation resulted in an increase of pores < 130 μm. While this change in texture reduced water retention, the unsaturated hydraulic conductivity was diminished by physicochemical alteration, i.e. induced water repellency and clay mineral swelling. Overall, the fine textured sandy clay loam was much more resistant to soil alteration by treated wastewater irrigation than the loamy sand. © 2018 Elsevier B.V.
Induced polarization applied to biogeophysics: recent advances and future prospects
. Near Surface Geophysics 2019
, 595-621. Publisher's VersionAbstract
This paper provides an update on the fast-evolving field of the induced polarization method applied to biogeophysics. It emphasizes recent advances in the understanding of the induced polarization signals stemming from biological materials and their activity, points out new developments and applications, and identifies existing knowledge gaps. The focus of this review is on the application of induced polarization to study living organisms: soil microorganisms and plants (both roots and stems). We first discuss observed links between the induced polarization signal and microbial cell structure, activity and biofilm formation. We provide an up-to-date conceptual model of the electrical behaviour of the microbial cells and biofilms under the influence of an external electrical field. We also review the latest biogeophysical studies, including work on hydrocarbon biodegradation, contaminant sequestration, soil strengthening and peatland characterization. We then elaborate on the induced polarization signature of the plant-root zone, relying on a conceptual model for the generation of biogeophysical signals from a plant-root cell. First laboratory experiments show that single roots and root system are highly polarizable. They also present encouraging results for imaging root systems embedded in a medium, and gaining information on the mass density distribution, the structure or the physiological characteristics of root systems. In addition, we highlight the application of induced polarization to characterize wood and tree structures through tomography of the stem. Finally, we discuss up- and down-scaling between laboratory and field studies, as well as joint interpretation of induced polarization and other environmental data. We emphasize the need for intermediate-scale studies and the benefits of using induced polarization as a time-lapse monitoring method. We conclude with the promising integration of induced polarization in interdisciplinary mechanistic models to better understand and quantify subsurface biogeochemical processes. © 2019 European Association of Geoscientists & Engineers
Spectral induced polarization of roots in hydroponic solution and soil
. In 2018 SEG International Exposition and Annual Meeting, SEG 2018
; 2018 SEG International Exposition and Annual Meeting, SEG 2018; 2019; pp. 2566-2570. Publisher's VersionAbstract
Monitoring plant root within the subsurface is important but challenging, due to the opacity of the soil. Recently, it was demonstrated that the spectral induced polarization (SIP) method has the potential to image roots, but the mechanisms governing the SIP signal of roots remain poorly understood. Here, we present a numerical model and experimental setup that was designed to establish relationships between root properties and the SIP response and to enhance our understanding of the polarization mechanisms of roots. Our preliminary results show a positive correlation between root mass and quadrature conductivity in nutrient solution. Surprisingly, a negative relation was found in soil. Overall, the results from this study further demonstrate the potential of the SIP method to monitor roots. © 2018 SEG.
Enhanced gemfibrozil removal from treated wastewater by designed “loopy” clay-polycation sorbents: Effect of diclofenac and effluent organic matter
. Applied Clay Science 2019
. Publisher's VersionAbstract
Novel clay-polymer nano composites (CPN) were designed for the removal of gemfibrozil (GFZ) from treated wastewater (TWW). The pyridine groups of poly-4-vinylpyridine (PVP) were 100% or 50% (randomly) substituted with bromo-ethanol to synthesize OH100PVP and OH50PVP, respectively. The effect of polymer charge density and loading on the structures of the CPNs, were investigated. At high polymer loadings OH100PVP adsorbed mainly in a flat configuration, as trains, while OH50PVP adsorbed in a more extended configuration, as loops and tails. The affinity and capacity of GFZ towards the OH50PVP CPN was significantly higher than to the OH100PVP, despite the latter's higher charge density, this high affinity of GFZ was explained in terms of more accessible adsorption sites due to the extended configuration of OH50PVP. The kinetics of GFZ removal from TWW by the CPN and by granulated activated carbon (GAC) was measured and modeled by the time dependent Langmuir equation. The effect of effluent organic matter (EfOM) and of a competing anionic pharmaceutical, diclofenac (DCF), on the kinetics of GFZ removal was thoroughly explored. Finally, the overall removal of the studied anionic pharmaceuticals was four-fold higher than by GAC at realistic contact times. © 2019 Elsevier B.V.
Early prediction of wheat grain yield production from root-zone soil water content at heading using Crop RS-Met
. Field Crops Research 2019
, 11 - 23. Publisher's VersionAbstract
Wheat production in drylands is determined greatly by the available water at the critical growth stages. In dry years, farmers usually face the dilemma of whether to harvest at an early stage for hay or silage, with reduced profit, or leave the crop for grain production with the risk of a major economic loss. Thus, an early prediction of potential wheat grain yield production is essential for agricultural decision making, particularly in water-limited areas. Here, we test whether using a proximal-based biophysical model of actual evapotranspiration (water use) and root-zone soil water content (SWC) – Crop RS-Met – may assist in providing early grain yield predictions in dryland wheat fields. Crop RS-Met was examined in eight experimental fields comprising a variety of spring wheat (Triticum aestivum L.) cultivars exposed to different treatments and amounts of water supply (185 mm - 450 mm). Crop RS-Met was first validated against SWC measurements at the root-zone profile. Then, modeled SWC at heading (SWCHeading) was regressed against end-of-season grain yields (GYEOS), which ranged from 1.30 tons ha−1 to 7.12 tons ha−1, for a total of 56 treatment blocks in 4 seasonal years (2014–2017). Results show that Crop RS-Met accurately reproduce seasonal changes in SWC with an average R2 of 0.89 ± 0.05 and RMSE and bias of 0.014 ± 0.004 m3 m−3 and -0.002 ± 0.004 m3 m−3, respectively. Modeled SWCHeading showed high and significant positive linear relationship with GYEOS (GYEOS[tons ha-1] = 0.080×SWCHeading[mm] - 5.387; R2 = 0.90; P < 0.001; N=56). Moreover, Crop RS-Met showed to be capable of accurately predicting GYEOS even in cases where water supply and grain yield had adverse relationships. Aggregating results to the field-scale level and classifying fields per water supply conditions resulted in an even stronger linear relationship (R2 = 0.94; P < 0.001; N=9). We conclude that Crop RS-Met may be used to predict GYEOS at heading in dryland fields for possible use by farmers in decision making at critical wheat growth stages.
Crop RS-Met: A biophysical evapotranspiration and root-zone soil water content model for crops based on proximal sensing and meteorological data
. Agricultural Water Management 2019
, 210 - 219. Publisher's VersionAbstract
Assessing crops water use is essential for agricultural water management and planning, particularly in water-limited regions. Here, we present a biophysical model to estimate crop actual evapotranspiration and root-zone soil water content using proximal sensing and meteorological data (Crop RS-Met). The model, which is based on the dual FAO56 formulation, uses a water deficit factor calculated from rainfall and atmospheric demand information to constrain actual evapotranspiration and soil water content in crops growing under dry conditions. We tested the Crop RS-Met model in a dryland experimental field comprising a variety of wheat (Triticum aestivum L. and T. durum) cultivars with diverse phenology. Crop RS-Met was shown to accurately capture seasonal changes in wheat water use during the growing season. The average R2 of modeled vs. observed soil water content for all cultivars (N = 11) was 0.92 ± 0.02 with average relative RMSE and bias of 9.29 ± 1.30% and 0.13 ± 0.03%, respectively. We found that changing the integration time period of the water deficit factor in Crop RS-Met affects the accuracy of the model implying that this factor has a vital role in modeling crop water use under dry conditions. Currently, Crop RS-Met has a simple representation of surface runoff and does not take into consideration heterogeneity in the soil profile. Thus, efforts to combine numerical models that simulate soil water dynamics with a Crop RS-Met model driven by high-resolution remote sensing data may be needed for a spatially continuous assessment of crop water use in fields with more complex edaphic characteristics.
Explicit wheat production model adjusted for semi-arid environments
. Field Crops Research 2019
, 93 - 104. Publisher's VersionAbstract
Current literature suggests that wheat production models are limited either to wide-scale or plot-based predictions ignoring pattern of habitat conditions and surficial hydrological processes. We present here a high-spatial resolution (50 m) non-calibrated GIS-based wheat production model for predictions of aboveground wheat biomass (AGB) and grain yield (GY). The model is an integration of three sub-models, each simulating elemental processes relevant for wheat growth dynamics in water-limited environments: (1) HYDRUS-1D, a finite element model that simulates one-dimensional movement of water in the soil profile; (2) a two-dimensional GIS-based surface runoff model; and (3) a one-dimensional process-driven mechanistic wheat growth model. By integrating the three sub-models, we aimed to achieve a more accurate spatially continuous water balance simulation with a better representation of root zone soil water content (SWC) impacts on plant development. High-resolution grid-based rainfall data from a meteorological radar system were used as input to HYDRUS-1D. Twenty-two commercial wheat fields in Israel were used to validate the model in two seasons (2010/11 and 2011/12). Results show that root zone SWC was accurately simulated by HYDRUS-1D in both seasons, particularly at the top 10-cm soil layer. Observed vs simulated AGB and GY were highly correlated with R2 = 0.93 and 0.72 (RMSE = 171 g m−2 and 70 g m−2) having low biases of -41 g m−2 (8%) and 52 g m−2 (10%), respectively. Model sensitivity test showed that HYDRUS-1D was mainly driven by spatial variability in the input soil characteristics while the integrated wheat production model was mostly affected by rainfall spatial variability indicating the importance of using accurate high-resolution rainfall data as model input. Using the integrated model, we predict decreases in AGB and GY of c. 10.5% and c. 12%, respectively, for 1 °C of warming and c. 7.7% and c. 7.3% for 5% reduction in rainfall amount in our study sites. The suggested model could be used by scientists to better understand the causes of spatial and temporal variability in wheat production and the consequences of future scenarios such as climate change.