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As irrigation water decreases, crop transpiration also decreases, resulting in an increase in leaf temperature and an increase of the crop water stress index (CWSI). Therefore, in the study, the response of Capsicum to different irrigation regimes was evaluated with periodic measurements of leaf temperature, stomatal conductance and estimation of the CWSI. The treatments consisted of a complete drip irrigation (RO) and deficit irrigation (RD-78 and RD-58) that received 78% and 58% of the complete irrigation, applying a total volume of water of 3363, 2618 and 1956 m3 ha-1 for RO, RD-78 and RD-58, respectively; and obtaining maximum yields of 30.2, 13.9 and 12.9 t ha-1 with CWSI of 0.50, 0.62 and 0.54 in C. bacatum, C. annumm and C. chinense, respectively. The highest stomatal conductance values ​​ranged from 724 to 887 mmol s-1 m-2, with CWSI from 0.1 to 0.3. The CWSI value of 0.3 (soil moisture from 25 to 33%) results in a good indicator of the time of irrigation, and it might be a criterion to be incorporated to save water and improve the management of Capsicum irrigation programs. A medida que disminuye el agua de riego, la transpiración del cultivo disminuye, resultando en un incremento de la temperatura foliar y un aumento del índice de estrés hídrico del cultivo (IEHC). Por ello, en el estudio, se evaluó la respuesta del Capsicum a diferentes regímenes de riego, con mediciones periódicas de la temperatura de la hoja, la conductancia estomática y la estimación del IEHC. Los tratamientos consistieron en un riego por goteo completo (RO) y riego con déficit (RD-78 y RD-58) que recibieron el 78% y 58% del riego completo, aplicándose un volumen total de agua de 3363, 2618 y 1956 m3 ha-1 para RO, RD-78 y RD-58, respectivamente; and obteniéndose rendimientos máximos de 30,2, 13,9 y 12,9 t ha-1 con IEHC de 0,50, 0,62 y 0,54 en C. bacatum, C. annumm y C. chinense, respectivamente. Los mayores valores de conductancia estomática variaron de 724 a 887 mmol s-1 m-2, con IEHC de 0,1 a 0,3. El valor IEHC de 0,3 (humedad del suelo del 25% al 33%), resulta en un buen indicador del momento del riego, criterio a incorporar con la finalidad de ahorrar agua y mejorar la gestión de programas de riego del Capsicum.

The temperature-based crop water stress index (CWSI) can accurately reflect the extent of crop water deficit. As an ideal carrier of onboard thermometers to monitor canopy temperature (Tc), center pivot irrigation systems (CPIS) have been widely used in precision irrigation. However, the determination of reliable CWSI thresholds for initiating the CPIS is still a challenge for a winter wheat–summer maize cropping system in the North China Plain (NCP). To address this problem, field experiments were carried out to investigate the effects of CWSI thresholds on grain yield (GY) and water use efficiency (WUE) of winter wheat and summer maize in the NCP. The results show that positive linear functions were fitted to the relationships between CWSI and canopy minus air temperature (Tc − Ta) (r2 &gt, 0.695), and between crop evapotranspiration (ETc) and Tc (r2 &gt, 0.548) for both crops. To make analysis comparable, GY and WUE data were normalized to a range of 0.0 to 1.0, corresponding the range of CWSI. With the increase in CWSI, a positive linear relationship was observed for WUE (r2 = 0.873), while a significant inverse relationship was found for the GY (r2 = 0.915) of winter wheat. Quadratic functions were fitted for both the GY (r2 = 0.856) and WUE (r2 = 0.629) of summer maize. By solving the cross values of the two GY and WUE functions for each crop, CWSI thresholds were proposed as being 0.252 for winter wheat, and 0.229 for summer maize, corresponding to a Tc − Ta threshold value of 0.925 and 0.498 °C, respectively. We conclude that farmers can achieve the dual goals of high GY and high WUE using the optimal thresholds proposed for a winter wheat–summer maize cropping system in the NCP.

Under the current water crisis in agriculture, irrigation methods for saving and conserving water are necessary. However, these methods must guarantee an appropriate yield with a concomitant economic benefit and a reduced environmental impact. In this study, two irrigation thresholds for irrigation timing (IT) based on thermal imagery were analyzed with the UNICA potato variety in three trials under drip (DI) and furrow (FI) irrigation during 2017–2018 in Lima, Peru. The control (T1) remained at >70% of soil field capacity. For other treatments, thresholds were defined based on stomatal conductance at light saturation (T2: 0.15 and T3: 0.05 mol H2O m−2s−1) and crop water stress index (T2: 0.4 and T3: 0.6) based on canopy temperature. An integrated index (IIN) was established for the valuation of treatments using the criteria of high fresh tuber yield (FTY) and a low total amount of irrigated water, production cost (PC), and total C emissions (TE) and using criteria of a score. FI-T2 (0.69–0.72) and DI-T3 (0.19–0.29) showed the highest and lowest IIN value, respectively. FTY in T2 was not significantly reduced under FI, resulting in a lower PC regarding DI–T2 and emphasizing the usefulness of thermal imagery in determining watering schedules in potatoes under furrow irrigation systems.

Relationship between canopy temperature and soil moisture is important for using the potential of canopy temperature as an indicator of crop water stress. A two-year field experiment was carried ou...

This paper evaluates the usefulness of the Crop Water Stress Index (CWSI) for monitoring transpiration and water status in almond trees, and proposes a methodology for assessing crop yield derived from the relation between canopy temperature and transpiration. For this purpose, a Non-Water Stress Baseline (NWSB) was developed from canopy temperature measurements taken with Infrared Thermometers (IRT) installed permanently over well-watered trees for three years. Tree transpiration was measured continuously with sap flow probes installed in the same trees than the IRT sensors. The calculated CWSI was closely related to water potential and stomatal conductance measured during kernel filling, as well as with transpiration and the ratio kT/GC (the transpiration coefficient over the ground cover). Taking into consideration this relation and the water production function recently published, the seasonal CWSI was compared to final yield and the regression yielded good results (R2 = 0.80). An empirical relationship between the CWSI acquired remotely from two flights performed during the kernel filling stage and crop yield was determined for this orchard. The estimated yield from the proposed methodology was compared to ground-truth measurements of crop yield measured in 80 trees during 2014 and 2015. The result obtained a RMSE that yielded 1.54 kg/tree. This study thus demonstrates that CWSI is closely related to the transpiration and the ratio kT/GC. This relation settles the basis for the development of methodologies for estimating water-limited crop yield from thermal derived information., Financial support for this work was provided by Junta de Andalucia (P12-AGR-2521), by the Spanish Ministry of Science and Innovation (AGL2015-66141-R)), by IRIDA project financed under the ERA-NET Cofund WaterWorks 2014 and by project INNOVA-NUTS (AVA.AVA201601.18) funded by the European Regional Development Fund (FEDER).

Smartphones have several advantages over specialist monitoring systems including ubiquity, price, and ease of implementing updates. Thermal imaging can be used to assess plant water status and allow more informed irrigation decisions; unfortunately, this technique has not been widely adopted due to the high cost of equipment and the lack of a system to provide analysis and results in real-time. Several inexpensive thermal cameras that connect to smartphones have recently been released and one of these (FLIR One) was evaluated as part of a system to assess grapevine water status. Irrigation treatments were established on Cabernet Sauvignon and Chardonnay vines in an arid region. Thermal images were taken from the shaded side of the grapevine canopy and software was developed to automatically determine the temperature of the canopy and artificial reference leaves. The temperature readings and metrological inputs were used to calculate five indices of water status including the Crop Water Stress Index (CWSI) and the stomatal conductance index. The best performing was the CWSI, which does not require input from a weather station. Over 30 days of assessment, and a range of irrigation levels, measurements collected with the thermal camera were correlated with stem water potential (R2 = 0.61) and stomatal conductance (R2 = 0.74). Windy conditions appeared to be the major cause of variation between CWSI and stomatal conductance. Inexpensive thermal cameras have the potential to be an easy and accessible tool for the assessment of plant water status and to make better irrigation decisions.

An efficient management of water relies on the correct estimation of tree water requirements and the accurate monitoring of tree water status and canopy growth. This study aims to test the suitability of visible and thermal images acquired by an unmanned aerial vehicle (UAV) for monitoring tree water status and canopy growth in an irrigation experiment. We used mature olive trees of two cultivars subjected to full irrigation, deficit irrigation (41–44% of full irrigation), or rainfed conditions. Deficit irrigation had limited or no effect on fruit and oil yield. There was a significant relationship between the remotely sensed crop water stress index derived from thermal images and the stem water potential (R2 = 0.83). The RGB images by UAV allowed to estimate tree canopy volume and were able to detect differences in canopy growth across irrigation regimes. A significant relationship between canopy volume and LAI was found for both cultivars (R2 of 0.84 and 0.88 for Frantoio and Leccino, respectively). Our results confirm the positive effects of deficit irrigation strategies to save relevant volumes of water and show that aerial images from UAV can be used to monitor both tree water stress and its effects on canopy growth and yield.

Water deficit stress is a major factor that inhibits the overall growth and development in cassava (Manihot esculenta), leading to decreased storage root yield. We conducted a study to investigate whether thermal sensing could be used to indicate water deficit stress and the health and yield of cassava crops in field. The objective of the study was to use thermal imaging to determine relationship between crop water stress index (CWSI) and physiological changes, and to identify the critical CWSI point in fields of cassava cv. Rayong 9 under well-irrigated and water-deficit conditions. At the time of storage root initiation (85 DAP [day after planting]), thermal imagery was collected and the physiological changes and growth characters were measured prior to storage root harvesting (162 DAP). Thermal infrared imager was used to measure the canopy temperature and CWSI of cassava plants. Net photosynthetic rate (Pn), stomatal conductance (gs) and transpiration rates (Tr) of cassava plants under water deficit conditions for 29 d (114 DAP) were significantly decreased, leading to delayed plant growth as compared to those under well-irrigated conditions. In contrast, air vapor pressure deficit (VPDair) and CWSI in drought-stressed plants were higher than well irrigated plants. High correlations between Tr/gs/Pn and CWSI were observed. The study concludes that CWSI is a sensitive indicator of water deficit stress caused due to stomatal function. Abbreviations: CWSI: crop water stress index; DAP: day after planting; Pn: net photosynthetic rate; gs: stomatal conductance; Tr: transpiration rate; VPDair: air vapor pressure; RMSE: root mean square error

The present research was carried out to determine water-stress tolerance of linoleic sunflower genotypes (P64LE119, PR63F73, P64LL62) grown under different water stress conditions [no water-stress (I100); mild water-stress (I70); strong water-stress (I35)] in the years 2015 and 2016. Variance analyses revealed significant differences between the genotypes (P

The determination of crop water status has positive effects on the Chinese Brassica industry and irrigation decisions. Drought can decrease the production of Chinese Brassica, whereas over-irrigation can waste water. It is desirable to schedule irrigation when the crop suffers from water stress. In this study, a random forest model was developed using sample data derived from meteorological measurements including air temperature (Ta), relative humidity (RH), wind speed (WS), and photosynthetic active radiation (Par) to predict the lower baseline (Twet) and upper baseline (Tdry) canopy temperatures for Chinese Brassica from 27 November to 31 December 2020 (E1) and from 25 May to 20 June 2021 (E2). Crop water stress index (CWSI) values were determined based on the predicted canopy temperature and used to assess the crop water status. The study demonstrated the viability of using a random forest model to forecast Twet and Tdry. The coefficients of determination (R2) in E1 were 0.90 and 0.88 for development and 0.80 and 0.77 for validation, respectively. The R2 values in E2 were 0.91 and 0.89 for development and 0.83 and 0.80 for validation, respectively. Our results reveal that the measured and predicted CWSI values had similar R2 values related to stomatal conductance (~0.5 in E1, ~0.6 in E2), whereas the CWSI showed a poor correlation with transpiration rate (~0.25 in E1, ~0.2 in E2). Finally, the methodology used to calculate the daily CWSI for Chinese Brassica in this study showed that both Twet and Tdry, which require frequent measuring and design experiment due to the trial site and condition changes, have the potential to simulate environmental parameters and can therefore be applied to conveniently calculate the CWSI.

Temperature vegetation dryness index (TVDI) and crop water stress index (CWSI) are two commonly used remote sensing-based agricultural drought indicators. This study explored the applicability of monthly moderate resolution imaging spectroradiometer (MODIS) normalized difference vegetation index (NDVI) and land surface temperature (LST) data for agricultural drought monitoring in the Guanzhong Plain, China in 2003. The data were processed using TVDI, calculated by parameterizing the relationship between the MODIS NDVI and LST data. We compared the effectiveness of TVDI against CWSI, derived from the MOD16 products, for drought monitoring. In addition, the surface soil moisture and monthly precipitation were collected and used for verification of the results. Results from the study showed that: (1) drought conditions measured by TVDI and CWSI had a number of similarities, which indicated that both CWSI and TVDI can be used for drought monitoring, although they had some discrepancies in the spatiotemporal characteristics of drought intensity of this region; and (2) both standardized precipitation index (SPI) and SM contents at the depth of 10 and 20 cm had better correlations to CWSI than to TVDI, indicating that there were more statistically significant relationships between CWSI and SPI/SM, and that CWSI is a more reliable indicator for assessing and monitoring droughts in this region.

Climate change is projected to be a key influence on crop yields across the globe. Regarding viticulture, primary climate vectors with a significant impact include temperature, moisture stress, and radiation. Within this context, it is of foremost importance to monitor soils&rsquo, moisture levels, as well as to detect pests, diseases, and possible problems with irrigation equipment. Regular monitoring activities will enable timely measures that may trigger field interventions that are used to preserve grapevines&rsquo, phytosanitary state, saving both time and money, while assuring a more sustainable activity. This study employs unmanned aerial vehicles (UAVs) to acquire aerial imagery, using RGB, multispectral and thermal infrared sensors in a vineyard located in the Portuguese Douro wine region. Data acquired enabled the multi-temporal characterization of the vineyard development throughout a season through the computation of the normalized difference vegetation index, crop surface models, and the crop water stress index. Moreover, vigour maps were computed in three classes (high, medium, and low) with different approaches: (1) considering the whole vineyard, including inter-row vegetation and bare soil, (2) considering only automatically detected grapevine vegetation, and (3) also considering grapevine vegetation by only applying a normalization process before creating the vigour maps. Results showed that vigour maps considering only grapevine vegetation provided an accurate representation of the vineyard variability. Furthermore, significant spatial associations can be gathered through (i) a multi-temporal analysis of vigour maps, and (ii) by comparing vigour maps with both height and water stress estimation. This type of analysis can assist, in a significant way, the decision-making processes in viticulture.

Water stress can positively or negatively impact grape yield and yield quality, and there is a need for wine growers to accurately regulate water use. In a four-year study (2010&ndash, 2013), energy balance fluxes were measured with an eddy-covariance (EC) system in a North Carolina vineyard (Vitis vinifera cv. Chardonnay), and evapotranspiration (ET) and the Crop Water Stress Index (CWSI) calculated. A multiple linear regression model was developed to upscale ET using air temperature (Ta), vapor pressure deficit (VPD), and Landsat-derived Land Surface Temperature (LST) and Enhanced Vegetation Index (EVI). Daily ET reached values of up to 7.7 mm day&minus, 1, and the annual ET was 752 &plusmn, 59 mm, as measured with the EC system. The grapevine CWSI was between 0.53&ndash, 0.85, which indicated moderate water stress levels. Median vineyard EVI was between 0.22 and 0.72, and the EVI range (max&ndash, min) within the vineyard was 0.18. The empirical models explained 75%&ndash, 84% of the variation in ET, and all parameters had a positive linear relationship to ET. The Root Mean Square Error (RMSE) was 0.52&ndash, 0.62 mm. This study presents easily applicable approaches to analyzing water dynamics and ET. This may help wine growers to cost-effectively quantify water use in vineyards.

The definition of irrigation schedules depends on the understanding of the response of key plant traits to different water restriction characteristics with the aim to avoid physiological impairment. In this study, different timings (at tuber initiation and bulking) and intensities (four soil moisture levels) of water restriction were tested in the potato crop. The temporal patterns of mid-morning or maximum, light saturated stomatal conductance ( g s_max ), recovery of net photosynthesis ( A recovery ), stem water potential (Ψ stem ), carbon isotope discrimination in tubers (Δ tuber ), plant water concentration ( PWC ), photochemical reflectance index ( PRI ) and crop water stress index ( CWSI ) were analyzed. Early-severe water restriction caused a drastic yield reduction, with low recovery of physiological responses ( g s_max , Δ tuber , Ψ stem , CWSI , A recovery ) after 15 days of post-restriction irrigation and even a continued reduction of some of them ( PWC , PRI ). It also caused a prolonged g s_max reduction below 0.05 mol H 2 O m −2 s −1 (≈ 5 μmol CO 2 m −2 s −1 of net photosynthesis) suggesting that this value defines a physiological severity threshold in potato, under which a metabolic impairment occurs. CWSI and PRI showed a close linear (R 2 = 0.76) and no linear (natural logarithm function, R 2 = 0.67) relationship with g s_max respectively. In cloudless dry environments, irrigation schedules in potato should aim to avoiding CWSI values higher than 0.4, especially until before of maximum canopy cover establishment. A close relationship between A recovery at maximum stress moment and yield reduction was found. The strong relationship between the measured traits (except PWC and Ψ stem ) and final yield at maximum stress moment found in the present study warrants further research on drought phenotyping immediately before post-restriction irrigation or when the defined severity threshold in potato is reached.

The crop water stress index (CWSI) is usually used to normalize crop temperature for efficient irrigation management. For CWSI computation, the temperature of a non-transpiring crop (Tdry) and that of a crop transpiring at its potential rate (Twet) are required. Alternatively, the use of artificial reference surfaces (ARS) that mimic Tdry and Twet has been proposed. However, to date, little effort has been made on the development of such surfaces, and there is still much uncertainty concerning what is measured. The aim of this research was to design, develop and evaluate the feasibility of new artificial reference surfaces for real time CWSI computation in maize. Hemispherical cellulose paper-based surfaces were constructed using three shades of green. The paper-based hemispheric surfaces were placed in a 3D-printed plastic structure that allows water storage and the placement of an upward-looking infrared thermometer at the bottom of the ARS. An experimental array comprising 18 randomly located ARS was designed, of which 9 were wet ARS (3 replicates per colour) and 9 were dry ARS (3 replicates per colour). The prototypic ARS were able to accurately determine Tdry and Twet in maize canopies. The CWSI values determined using the ARS developed in this research were validated in a commercial maize breeding trial against leaf gas exchange variables. The shade of green that provided the best results in both cases was the RGB colour R32, G66, B34. While Tdry could be obtained directly from a dry ARS temperature, a solar radiation-based transformation is required to determine Twet from the wet ARS temperature.

Thermal imaging can become a readily usable tool for crop agricultural water management, since it allows a quick determination of canopy surface temperature that, as linked to transpiration, can give an idea of crop water status. In the last years, the resolution of thermal imaging systems has increased and its weight decreased, fostering their implementation on Unmanned Aerial Vehicles (UAV) for civil and agricultural engineering purposes. This approach would overcome most of the limitations of on site thermal imaging, allowing mapping plant water status at either field or farm scale, taking thus into account the naturally existing or artificially induced variability at those scales. The aim of this work was to evaluate to which extent high-resolution thermal imaging allows evaluating the instantaneous and seasonal variability of water status within a vineyard. The novelty and significance of our approach is that the specifically designed and build unmanned aerial vehicle (UAV) provided very high-resolution imaging (pixel

A study was conducted in a large pistachio farm in Madera County, California, to assess the spatial variability in water status and irrigation needs by using high-resolution thermal imagery acquired by an unmanned aerial system. We determined the Crop Water Stress Index (CWSI) of two fields, 130 ha each, based on canopy temperature measurements of individual tree crowns, thus assessing the spatial variations in tree water status within each field. The CWSI of each potential management unit (sectors encompassing about 175 trees) was then calculated and related to the days since last irrigation (DSLI) in F1 and F2. The relationship between CWSI and DSLI was established to calculate the average CWSI corresponding to the whole area that was irrigated on the same day. This value was afterward compared with the actual CWSI value of each management unit as a proxy of the spatial variability in CWSI. This information was used to calculate the deviation of each irrigation unit from the fixed irrigation schedule for the whole fields. Our results show that it is feasible to use high-resolution thermal imagery for integrating the crop response in irrigation performance assessment and for providing recommendations at the farm scale., Chris Wylie and Richard Paslay, from Agri-World Cooperative, are also acknowledged. This work was funded by the Spanish Ministry of Science and Innovation (CONSOLIDER CSD2006-0067 and AGL2009-13105).

Plant water stress is linked to both above- and below-surface parameters; with above-surface parameters being generally easier to measure. Models utilizing above-surface parameters, such as canopy temperature to identify plant water stress, frequently employ the crop water stress index (CWSI). Alternatively, the regular usage of the transpiration reduction function (FRF), as proposed by Feddes in the 1970s, requires more difficult to measure below-surface parameters such as soil water pressure head. In order to assess the agreement between these models, we experimentally compared plant water stress predicted by the CWSI and FRF using Common Bean grown in Brazil under full and deficit irrigation; the sensitivity of the models to the key parameters, water stressed baseline and limiting soil water pressure head, was also evaluated. The simple equation 1 − CWSI = Tr provided a good fit when relating CWSI to the relative transpiration Tr as predicted by the Feddes model. We show that above ground measurements that are combined within the CWSI are just as effective at predicting plant water stress as soil-based factors like soil water pressure head. The models show high sensitivity to variations in key parameters, implying significant differences will result in the identification of the onset of plant water stress; with sensitivity highest for the CWSI under dry conditions.

Field experiments were conducted for 2 years to evaluate the use of the crop water stress index (CWSI) for irrigation scheduling of soybeans under a sub-humid climate of Bursa, Turkey. Additionally, statistical relationships between CWSI and seed yield, quality parameters, crop evapotranspiration (ET c ) and water use efficiency (WUE) were investigated. Irrigations were scheduled based on the replenishment of 100 ( T 100 ), 75 ( T 75 ), 50 ( T 50 ), 25 ( T 25 ), and 0% ( T 0 ) of soil water depletion from a soil depth of 90 cm using a 7-day irrigation interval. To compute CWSI, lower (nonstressed) and upper (stressed) baselines were developed based on the canopy temperature ( T c ) measurements of fully irrigated and rain-fed treatments, respectively. According to results, CWSI could be used to determine the irrigation time of soybean for sub-humid climate and 0.22 could be offered as a threshold value. Statistically significant relationships were determined between CWSI and seed yield, protein yield, oil yield, ET c and WUE. The polynomial relationship between WUE and CWSI demonstrated that highest WUE could be obtained under CWSI close to 0.6. Consequently, an irrigation schedule that considers water stress could be employed when the cost of water is high and/or water is scarce. However, because of the yield reduction, all economic aspects of water limited irrigation scheduling should be considered before making this decision. We conclude that the CWSI could be used to evaluate crop water stress and improve irrigation scheduling for soybeans under sub-humid climatic conditions.

Optimization of olive oil quantity and quality requires finely tuned water management, as increased irrigation, up to a certain level, results in increasing yield, but a certain degree of stress improves oil quality. Monitoring tools that provide accurate information regarding orchard water status would therefore be beneficial. Amongst the various existing methods, those having high resolution, either temporally (i.e., continuous) or spatially, have the maximum adoption potential. One of the commonly used spatial methods is the Crop Water Stress Index (CWSI). The objective of this research was to test the ability of the CWSI to characterize water status dynamics of olive trees as they enter into and recover from stress, and on a diurnal scale. CWSI was tested in an empirical form and in two analytical configurations. In an experiment conducted in a lysimeter facility in the northwestern Negev, Israel, irrigation was withheld for 6 days for 5 of 15 trees, while daily irrigation continued for the rest of the trees. After resuming irrigation, the trees were monitored for 5 additional days. Water status measurements and thermal imaging were conducted daily between 12:00 and 14:00. Diurnal monitoring (predawn to after dusk) of the same indicators was conducted on the day of maximum stress. Continuous meteorological data were acquired throughout the experimental period. Empirical and analytical CWSI were calculated based on canopy temperature extracted from thermal images. The empirical CWSI differentiated between well watered and stressed trees, and depicted the water status dynamics during the drought and recovery periods as well as on a diurnal scale. Analytical approaches did not perform as well at either time scale. In conclusion, the empirical CWSI seems to be promising even given its limitations, while analytical forms of CWSI still require improvement before they can be used as a water status monitoring tool for olive orchards. Practically, it is proposed to compute the wet temperature analytically and set the dry temperature to 5 °C higher than air temperature.

Infrared thermography is a useful technology for examining water status in terres- trial vegetation. This research was focused on assessing the water status of soybean plants (Glycinemax (L.) Merrill) using high resolution thermal infrared images. The plants were subjected to a range of moisture stress treatments in order to evaluate the water content in sampled leaves. The plants were irrigated with 8 different treat- ment levels (control (i.e., fully irrigated) and 1 to 7 days of water being withheld). One specific trifoliate was segmented from each of the thermal images for every plant sample, and both mean temperature and Crop Water Stress Index (CWSI) were computed for each plant. Leaf discs were taken from the same trifoliate to gravi- metrically measure relative water content (RWC). RWC had statistically significant correlation coefficients with both CWSI (r = -0.92, n = 56; p�< 0.001) and raw mean temperature (r = -0.84, n = 56; p�< 0.001). Two separate regression models were developed to predict RWC using mean raw trifoliate temperature and CWSI. Our results document that a CWSI-based regression model was better in predicting RWC than a model based on mean raw trifoliate temperature.

In this study the suitability of thermal imaging for phenotyping was investigated as part of a breeding experiment carried out by the International Maize and Wheat Improvement Centre (CIMMYT) at Tlaltizapan experimental station in Mexico. Different subtropical maize genotypes with two replications were screened with respect to their tolerance to water stress. Thermal images of the canopy of 92 different maize genotypes were acquired on two different days in the time interval between anthesis and blister stages (grain filling 1), whereby each picture contained five plots of different genotypes and canopy temperatures calculated for each plot. Significantly, lower canopy temperatures were found in well-watered genotypes compared with water-stressed genotypes. Furthermore significant differences (p

This study is a contribution to an ongoing research to develop a thermal-reflectance imaging system (TRIS) for detecting water stress in Sunagoke moss (Rhacomitrium canescens). The correlation between visual and thermal water stress symptoms in a sample of Sunagoke moss as a function of time and water content was evaluated. Visible light imaging was used to report changes in the surface structure and reflectance. Infrared (IR) thermal imaging was used to monitor transpiration patterns and the crop water stress index (CWSI) was used to quantify those changes. Grey-level concurrence matrix (GLCM) texture features were used to quantify changes in the sample surface structure while the RGB colour ratios were used to detect changes in its reflectance. The sample exhibited water-related stress at water contents below 1.5 g g−1 and above 3.0 g g−1 (grams of water per gram of dry sample). The maximum possible total uncertainty of IR temperatures for the sample was ±0.50 °C at 17 °C, ambient temperature. The maximum uncertainty of its visible light data was ±7.65 grey level attributed to the red bandwidth. The results showed a clear correlation between the water status of the sample and its CWSI, GLCM texture and RGB colour ratios. These results demonstrate the possibility of detecting both drought and flood water stress in Sunagoke moss by combining thermal and visible light imaging. Although Sunagoke moss was used in this study, this method is novel and could be extended to both biotic and abiotic stress detection in other plants.

The main objective of this study was to determine canopy-air temperature differential, which can be used to quantify crop water stress index (CWSI) for potato. The crop was cultivated under furrow ...

Irrigation scheduling requires an operational means to quantify plant water stress. Remote sensing may offer quick measurements with regional coverage that cannot be achieved by current ground-based sampling techniques. This study explored the relation between variability in fine-resolution measurements of canopy temperature and crop water stress in cotton fields in Central Arizona, USA. By using both measurements and simulation models, this analysis compared the standard deviation of the canopy temperature $$ {\left( {\sigma _{{T_{{\text{c}}} }} } \right)} $$ to the more complex and data intensive crop water stress index (CWSI). For low water stress, field $$ \sigma _{{T_{{\text{c}}} }} $$ was used to quantify water deficit with some confidence. For moderately stressed crops, the $$ \sigma _{{T_{{\text{c}}} }} $$ was very sensitive to variations in plant water stress and had a linear relation with field-scale CWSI. For highly stressed crops, the estimation of water stress from $$ \sigma _{{T_{{\text{c}}} }} $$ is not recommended. For all applications of $$ \sigma _{{T_{{\text{c}}} }} , $$ one must account for variations in irrigation uniformity, field root zone water holding capacity, meteorological conditions and spatial resolution of T c data. These sensitivities limit the operational application of $$ \sigma _{{T_{{\text{c}}} }} $$ for irrigation scheduling. On the other hand, $$ \sigma _{{T_{{\text{c}}} }} $$ was most sensitive to water stress in the range in which most irrigation decisions are made, thus, with some consideration of daily meteorological conditions, $$ \sigma _{{T_{{\text{c}}} }} $$ could provide a relative measure of temporal variations in root zone water availability. For large irrigation districts, this may be an economical option for minimizing water use and maximizing crop yield.

This study was conducted to determine the crop water stress index (CWSI) for potato (Solanum tuberosum L.) grown under furrow and drip irrigation methods and subjected to three different irrigation levels (100, 50 and 0% replenishment of soil water depleted). The lower (non-stressed) and upper (stressed) baselines were determined empirically from measurements of canopy temperatures, ambient air temperatures and vapor pressure deficit values. Tuber yield decreased when mean CWSI prior to irrigation exceeded 0.68 in furrow and 0.81 in drip irrigation. The tuber yield was directly correlated with the seasonal CWSI values and the linear equations for furrow and drip irrigation methods, Y = −45.82 CWSI + 50.69 and Y = −52.65 CWSI + 58.44, respectively, can be used for yield prediction.

Canopy temperature measured with infrared thermometers or other remote infrared sensors is an important tool for detecting crop water stress. The crop water stress index (CWSI) is the most often used index which is based on canopy temperature to detect crop water stress. This study evaluates the application of three different forms of CWSI for winter wheat water stress monitoring in the North China Plain (NCP): the Idso empirical model, the Jackson theoretical model, and the new Alves model, which replaces the radiometric surface temperature with a surface “wet bulb” temperature, thereby avoiding the evaluation of the surface resistance of the crop. The results show that the CWSI based on Jackson’s definition and Alves’ definition are better than the empirical CWSI for monitoring winter wheat water stress in NCP. Both definitions are useful tools to evaluate winter wheat water stress in NCP, but the CWSI based on Alves’ definition is more practical for monitoring winter wheat water stress in NCP, mainly due to not having to estimate the crop surface resistance, while the CWSI based on Jackson’s definition is more reasonable for quantifying winter wheat water stress in NCP. © 2003 Elsevier B.V. All rights reserved.

Shallow water-tables strongly influence agro-ecosystems and pose difficult management challenges to farmers trying to minimize their negative effects on crops and maximize their benefits. In this paper, we evaluated how the water-table depth interacts with rainfall and sowing date to shape maize performance in the Western Pampas of Argentina. For this purpose, we analyzed the influence of water-table depth on the yields of 44 maize plots sown in early and late dates along eight growing seasons (2004-2012)that we rated as dry or wet. In addition, we characterized the influence of the water-table depth on intercepted radiation and crop water status by analyzing MODIS and Landsat images, respectively. The four conditions we evaluated (early sown-dry growing season, early-wet, late-dry, late-wet) showed similar yield response curves to water-table depth, with an optimum depth range (1.5-2.5 m) where yields were highest and stable (∼11.6 Mg ha−1on average). With water-table above this range, yields declined in all conditions at similar rates (p > 0.1), as well as the crop water status, as suggested by the Crop Water Stress Index, evidencing the negative effects of waterlogging. Water-tables deeper than the optimum range also caused declines of yield, intercepted radiation and crop water status, being these declines remarkably higher in early maize during dry seasons, evidencing a greater reliance of this condition on groundwater supply. Yield in areas with deep water-tables (>4 m) was significantly reduced to between a quarter and a half of yields observed in areas with optimum water-tables. Rainfall occurred around flowering had a strong impact on maize yield in areas with deep water-tables, but not in areas with optimum depth, where yields showed high temporal stability and independence from rainfall in that period. Our study confirmed the strong influence of water-table on rainfed maize and provides several guidelines to help farmers to take better decisions oriented to minimize hydrological risks and maximize the benefits of shallow water-tables. Fil: Florio, Eva Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi". Universidad Nacional de San Luis. Facultad de Ciencias Físico, Matemáticas y Naturales. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi"; Argentina Fil: Mercau, Jorge Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi". Universidad Nacional de San Luis. Facultad de Ciencias Físico, Matemáticas y Naturales. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi"; Argentina Fil: Jobbagy Gampel, Esteban Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi". Universidad Nacional de San Luis. Facultad de Ciencias Físico, Matemáticas y Naturales. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi"; Argentina Fil: Nosetto, Marcelo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi". Universidad Nacional de San Luis. Facultad de Ciencias Físico, Matemáticas y Naturales. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi"; Argentina. Universidad Nacional de Entre Ríos; Argentina

The crop water stress index (CWSI) is a valuable tool for monitoring and quantifying water stress as well as for irrigation scheduling. This study was conducted during the 1990 and 1991 growing seasons at the Colorado State University Horticulture Farm near Fort Collins, CO, USA (40835 0 N latitude, 105805 0 W longitude and 1524 m elevation). The main objective was to develop a baseline equation, which can be used to calculate CWSI for monitoring water status and irrigation

Surface temperature measured with infrared thermometers is an important tool for irrigation scheduling which has been in practice for some decades. Several indices have been developed to time irrigation events. The most useful is the Crop Water Stress Index (CWSI). Its use, however, relies on a non-water-stressed baseline that, although having a theoretical basis, is to be determined experimentally given the uncertainties related to the surface resistance of the crop. The drawbacks of this procedure, besides the non-transferability of the lines from place to place, are that the surface temperature measurements have always to be made under similar weather conditions. A new definition of a non-water-stressed baseline theoretically based and driven by weather variables that can easily be measured and/or estimated is proposed that allows measurements at any time of the day and whatever the weather conditions, thus simplifying the task of the irrigator.

This study was designed to evaluate the crop water stress index (CWSI) for low-energy precision application (LEPA) irrigated corn (Zea mays L.) grown on slowly-permeable Pullman clay loam soil (fine, mixed, Torrertic Paleustoll) during the 1992 growing season at Bushland, Tex. The effects of six different irrigation levels (100%, 80%, 60%, 40%, 20%, and 0% replenishment of soil water depleted from the 1.5-m soil profile depth) on corn yields and the resulting CWSI were investigated. Irrigations were applied in 25 mm increments to maintain the soil water in the 100% treatment within 60-80% of the "plant extractable soil water" using LEPA technology, which wets alternate furrows only. The 1992 growing season was slightly wetter than normal. Thus, irrigation water use was less than normal, but the corn dry matter and grain yield were still significantly increased by irrigation. The yield, water use, and water use efficiency of fully irrigated corn were 1.246 kg/m2, 786 mm, and 1.34 kg/m3, respectively. CWSI was calculated from measurements of infrared canopy temperatures, ambient air temperatures, and vapor pressure deficit values for the six irrigation levels. A "non-water-stressed baseline" equation for corn was developed using the diurnal infrared canopy temperature measurements as Tc-Ta = 1.06-2.56 VPD, where Tc was the canopy temperature (°C), Ta was the air temperature (°C) and VPD was the vapor pressure deficit (kPa). Trends in CWSI values were consistent with the soil water contents induced by the deficit irrigations. Both the dry matter and grain yields decreased with increased soil water deficit. Minimal yield reductions were observed at a threshold CWSI value of 0.33 or less for corn. The CWSI was useful for evaluating crop water stress in corn and should be a valuable tool to assist irrigation decision making together with soil water measurements and/or evapotranspiration models.

Ce travail etait destine a etablir les liens entre l'indice de contrainte hydrique d'une culture (CWSI) et l'evapotranspiration, la transpiration et le rendement chez Vigna sinensis L afin d'appliquer cette relation a des modeles de gestion de l'irrigation et de prevision du rendement. On a par ailleurs etudie l'influence de parametres du sol et de l'air sur l'application du differentiel de temperature entre l'air et le couvert vegetal (Tc - Ta) sur la gestion de l'irrigation. La limite inferieure a ete: (Tc - Ta) = 1.62 - 0.113 (VPD), en °C et mb pendant la saison de vegetation. Ses coefficients etaient plus petits que ceux de la plupart des cultures rapportees par d'autres auteurs. La limite superieure pendant cette meme saison a ete 5 °C ce qui est comparable a celle de la betterave a sucre dans la meme region. La valeur de k dans l'equation Yt/T = k/e* - e) a ete 0,041 mb, ce qui est analogue a celle pour le soja. On a conclu que l'indice de recolte du (grain / matiere seche aerienne), HI, dependait de la transpiration (T, kg/ha) par: HI = 2,37/10 -4 *T-0.5. Les fonctions de production (rendement et eau d'irrigation, et/ou ET) pour le grain et la matiere seche aerienne ont ete obtenues. Le facteur de sensibilite a l'eau pour le grain et la matiere seche aerienne ont ete 1,01 et 0,53, respectivement, ce qui est inferieur a ceux du soja. Le CWSI a ete 1,31 *(1 - ET/ETm), parce qu'il a ete mesure et moyenne sur une partie de la saison vegetative. De ce fait, on a conclu que, si on corrige le CWSI pour la saison entiere, il doit etre proche de (1 - ET/ETm). Le calendrier d'irrigation du niebe peut etre determine par un CWSI de 0,106. De plus on a trouve que (Tc - Ta) = 0,26 * RH - 3, 71 peut etre utilisable pour fixer le calendrier d'irrigation en fonction de mesures de la temperature du couvert vegetal et de l'air entre 13 et 14 h 00. Enfin, les equations adequates ont ete donnees pour l'estimation de ET en utilisant la temperature du couvert et de l'air a cette meme heure.

Evaluation of the Penman-Monteith-based crop water stress index (CWSI), as a potential indicator of turf irrigation timing, requires reliable estimates of potential (minimum) canopy resistance, r cp , and aerodynamic resistance, r a . This paper compare various methods of estimating r cp and r a for evaluation of water stress of bermudagrass turfgrass (Cynodon dactylon cv. Midiron) in the desert Southwest of the USA. First, two empirical CWSI models were developed using field data collected from well-watered and severely water-stressed turf plots during the 1986 growing season in Tucson, AZ [...]

A field study assessed the accuracy and consistency of crop water stress index (CWSI) estimates determined by two empirical models and one theoretical model for evaluation of bermudagrass [Cynodon dactylon (L.) Pers. cv. Midiron] water status. The simplest empirical model, describing canopy temperature minus air temperature (T c − T a ) of well-watered turf as a linear function of air vapor pressure deficit, was inadequate for estimating CWSI, since seasonal averages of CWSI for well-watered, moderately stressed, and stressed turf had corresponding coefficients of variation of 1170, 160, and 86, respectively [...]

Crop growth/irrigation scheduling simulation models are becoming an integral part of crop management schemes designed to maximize input use. The selection of a particular model over others must be based on the model's performance under local conditions. Three crop simulation models, COTTAM, GOSSYM and IRRSCH, were evaluated for their accuracy in approximating field-observed crop water stress index (CWSI) of cotton grown under different irrigation regimes in a semiarid environment. The purpose is to use CWSI measured in the field to evaluate and to select an appropriate simulation model to schedule irrigation for cotton production. Generally, CWSI predicted by the models was lower than the measured values. Comparatively, IRRSCH was the best of all the models in predicting CWSI regardless of the irrigation treatments. Statistical analysis showed no significant difference (at 95% significance level) between the measured and the predicted CWSI by IRRSCH when cotton was irrigated at −0.40 MPa in 1983. Analysis of variance of paired data showed that COTTAM and IRRSCH predicted similar CWSI (P = 0.05) in cotton irrigated at −1.50 MPa in 1983. This study showed IRRSCH, a simple water balance model, is superior to COTTAM and GOSSYM in approximating CWSI at water stress levels most encountered in irrigated fields (−0.15 and −0.40 MPa) and best approximates field water balance.

A technique using an infrared thermometer to measure plant water stress in cotton from stand establishment to final irrigation is defined. This study used the crop water stress index (CWSI) to measure plant water stress and relates these measurements to leaf water potential values. Two non water stress baselines are generated and used for calculating CWSI values for SJ-2 Acala cotton during two segments of the growing season. Two regression lines were generated of CWSI values with leaf water potential values for these segments of the growing season. Applications of the growth regulator mepiquat chloride (PIX) were found to have no effect on the ability of the CWSI method to measure plant water stress. The technique presented makes use of the CWSI method through the entire growing season in a manner that is preferred to the leaf water potential method when measured with the pressure chamber.

A field study was conducted to determine the utility of the crop water stress index ( cwsi ) for assessing plant water status of seed alfalfa ( Medicago sativa L.). Six irrigation treatments consisting of combinations of three rates of irrigation and two irrigation frequencies were used in assessing the influence of vegetative, flowering, and pod-filling periods on non-stressed canopy-air temperature differences versus vapour pressure deficit baselines and calculated cwsi values. Three distinct non-stressed baselines were determined and found to be related to the following crop morphological stages: (1) fully vegetative (few or no flowers); (2) flowering (few drying pods); and (3) pod development and maturation. Crop water stress index values across all treatments were highly and linearly correlated with stem water potentials. A less distinct curvilinear relationship existed between cwsi and leaf conductance. Use of the vegetative period non-stressed baseline to calculate cwsi values during flowering and pod-filling resulted in cwsi values 0.1 to 0.2 higher than those determined using growth-stage-dependent baselines. For irrigation scheduling, use of two baselines is suggested, one for the vegetative period and another baseline determined using pooled data from the flowering and pod-filling periods.

SUMMARYThe ability to detect and measure water stress accurately is critical for optimizing crop production. The Crop Water Stress Index (CWSI), the linear relationship of the difference between foliage and air temperatures as a function of the air vapour pressure deficit, is one widely used method. Under well-watered conditions, a ‘baseline’ is derived that is crop specific and presumed fairly constant, despite differences in development and physiology. This study reports changes in the baseline of the CWSI for lucerne crops not subjected to water shortage over 3 years. Studies of lucerne in California from April 1986 to October 1988 used the CWSI to plan irrigations. It was necessary to re-establish the baseline periodically throughout the experiment. In the first year it was similar to that reported in the literature, but in the second year it had a statistically significant steeper slope and higher intercept. In the third year, the regression equation was similar to that in the first year. The changes in the baseline are thought to be a result of crop age rather than year-to-year weather fluctuations. The baseline needs to be determined periodically as the crop matures, to ensure accurate interpretation of plant water stress.

Hand-held infrared radiometers, developed during the past decade, have extended the measurement of plant canopy temperatures from individual leaves to entire plant canopies. Canopy temperatures are determined by the water status of the plants and by ambient meteorological conditions. The crop water stress index (CWSI) combines these factors and yields a measure of plant water stress. Two forms of the index have been proposed, an empirical approach as reported by Idso et al. (1981), and a theoretical approach reported by Jackson et al. (1981). Because it is simple and requires only three variables to be measured, the empirical approach has received much attention in the literature. It has, however received some criticism concerning its inability to account for temperature changes due to radiation and windspeed. The theoretical method is more complicated in that it requires these two additional variables to be measured, and the evaluation of an aerodynamic resistance, but it will account for differences in radiation and windspeed. This report reexamines the theoretical approach and proposes a method for estimating an aerodynamic resistance applicable to a plant canopy. A brief history of plant temperature measurements is given and the theoretical basis for the CWSI reviewed.

Guayule (Parthenium argentatum Gray, cv. N565 II) was grown at Phoenix, Arizona, in well-watered and water-stressed conditions. The relationships between the crop water stress index (CWSI) and other physiological indicators of plant water status were examined. The drought treatment lasted for 70 days (29 May through 5 August 1986) during which time the available soil moisture content declined from 100 to 0%, while the well-watered plants were maintained at greater than 70% available soil moisture. The CWSI results were normalized to reduce environmental effects by subtracting the values obtained for the well-watered plants from those of the water-stressed plants. Significant (P

A crop water stress index (CWSI) was derived from air temperatures, air vapor pressure deficits and the midday radiant leaf temperatures of cotton plants that were exposed to different early-season irrigation treatments at Phoenix, AZ, U.S.A. To calculate the CWSI, an infrared thermometer was used to measure leaf temperatures which were then scaled relative to minimum and maximum temperatures expected for no-stress (CWSI=0) and extreme drought-stress conditions (CWSI=1). Results showed the CWSI behaved as expected, dropping to low levels following an irrigation and increasing gradually as the cotton plants depleted soil moisture reserves. The final yield of seed cotton was significantly inversely correlated with the average CWSI observed over the interval from the appearance of the first square until two weeks following the final irrigation.

Degagement des limites superieures de Tf-Ta (temperature du feuillage, temperature de l'air ambiant) derivees selon Idso etal. et mesurees au champ. Effets de divers facteurs de milieu, principalement la vitesse du vent sur les limites inferieures et superieures de Tf-Ta et de l'indice de contrainte hydrique de la culture (CSWI). Comparaison du potentiel hydrique foliaire, de Tf-Ta et du CSWI dans des cultures (sorgho, mais, haricots, cotonniers)