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The objectives of the current study were to implement affordable and non-invasive measurements of infrared thermometry, leaf relative water content (RWC), crop water stress index (CWSI), leaf area index (LAI) from computer vision analysis and seed yield of sunflowers. The experiment was designed as split-plot based on randomized complete blocks with three replications. Treatments were four different levels of deficit irrigation as the main plots and three fertilization treatments were applied as sub-plots. Results showed a significant effect (P ≤ 0.01) of water stress and fertilizer on CWSI during different stages of sunflower growth. Changes in fertilizer amount and type resulted in a change in lower (dTLL) and upper (dTUL) limits of canopy-air temperature difference. A combination of chemical fertilizer with biofertilizer could help to decrease CWSI. From computer vision analysis, the normalized difference red blue index (NDRBI) had a strong linear relationship with RWC and CWSI for sunflowers (R2 of 0.87 and 0.93, respectively) and the normalized difference green blue index (NDGBI) had a linear relationship with seed yield (R2 = 0.79). Therefore, analysis of digital RGB images and CWSI were efficient, non-destructive and low-cost methods to assess crop water status for sunflowers under different irrigation and fertilizer treatments. HIGHLIGHTS The CWSI values were sensitive not only to different irrigation regimes but also to amount and type of fertilizer.; The CWSI can be derived from the plant index (NDRBI) and used for appropriate irrigation scheduling.; A positive correlation was observed between image indices with CWSI and LAI.; Combination of chemical fertilizer with biofertilizer could help to decrease CWSI.

The aim of this study was to find out the effects of crop water stress index (CWSI) and soil water content (SWC) under subsurface drip irrigation system on yield and water use efficiency. The CWSI was estimated and SWC was measured under seven irrigation strategies: sustainable deficit irrigation (DI), regulated deficit irrigation (RDI), partial root zone drying (PRD) at two levels i.e. 80% and 60% and full irrigation water (FI) (control). The results showed that, the highest SWC and CWSI during the growth season compared with FI were regulated deficit irrigation (RDI) at 80% followed by PRD at 80% whereas the lowest ones were DI at 60% and PRD at 60%. Also, the highest values of yield and water use efficiency were achieved under RDI at 80% (19.54 t ha-1 in summer and 21.55 t ha-1 in winter) followed by PRD at 80 % whereas the lowest values were achieved under DI and PRD at 60%. The winter season gave values of yield higher than the corresponding ones in obtained summer season by 17.02%.

Plant-based measurements such as leaf water potential (LWP) are widely used for irrigation scheduling because they are accurate at indicating when irrigation is needed. Despite being a good indicator, scheduling irrigation with LWP is time consuming and scale-limited. The work reported in this study explored the potential of using thermal remote sensing to estimate cotton crop water status in the humid southeastern U.S.A. The study was conducted over two growing seasons (2018 and 2020) in southwestern Georgia, U.S.A using a complete randomized block design plot scheme with three irrigation treatments (0% ETc (crop evapotranspiration; rainfed), 100% ETc (well-irrigated), and 125% ETc (over-irrigated). To monitor the irrigation treatment effects on cotton physiological responses, predawn LWP (LWPPD), stomatal conductance (gs) and leaf area index (LAI) data were collected in both growing seasons. UAV-based images collected in the thermal infrared waveband were used to calculate crop water stress index (CWSI) based on three different methodologies and evaluated as predictors of LWPPD. Results in this study suggest that LWPPD values above -0.45 MPa indicate a non-stressed crop. No negative effects in leaf stomatal conductance and crop growth were observed in 2018. In 2020, the less and more irregular precipitation led to significant differences in LAI and gs, as well as in LWPPD. A moderate to strong relationship was observed for all dates in 2020, with the CWSI based on the Monteith approach (CWSIMonteith) showing the two highest R2 values among the 3 dates (0.65 and 0.58) with low RMSE values of 0.02 and 0.04 MPa, respectively. Overall, the results showed that there is potential of using an affordable UAV-based thermal system to produce predicted LWP maps that are representative of the current field water status.

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...

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.

This paper deals with the possibility of using infrared thermography to determine the irrigation requirement for a given field depending on the water stress level of the plants. The experiments were performed on vines at the site in the village of Jadrtovac near Šibenik, Croatia. The water stress level of plants was determined through leaf temperature measurements and measurements of leaf water potential (LWP). Leaf temperature measurements were performed using infrared thermography. Based on these measurements the relationship between the LWP and a derived factor, Crop Water Stress Index (CWSI) was investigated. The results obtained show that infrared thermography could be successfully used to measure the leaf temperature, which is the input parameter for calculating the CWSI.

Precise irrigation management of grapevines in greenhouses requires a reliable method to easily quantify and monitor the grapevine water status to enable effective manipulation of the water stress of the plants. This study evaluated the applicability of crop water stress index (CWSI) based on the leaf temperature for diagnosing the grapevine water status. The experiment was conducted at Yuhe Farm (northwest China), with drip-irrigated grapevines under three irrigation treatments. Meteorological factors, soil moisture contents, leaf temperature, growth indicators including canopy coverage and fruit diameter, and physiological indicators including SPAD (relative chlorophyll content), stem water potential (&phi, s), stomatal conductance (gs), and transpiration rate (E) were studied during the growing season. The results show that the relationship between the leaf-air temperature difference (Tc-Ta) and the plant water status indicators (&phi, s, gs, E) were significant (P &lt, 0.05), and the relationship between gs, E and Tc-Ta was the closest, with R2 values ranging from 0.530&ndash, 0.604 and from 0.545&ndash, 0.623, respectively. CWSI values are more easily observed on sunny days, and it was determined that 14:00 BJS is the best observation time for the CWSI value under different non-water-stressed baselines. There is a reliable linear correlation between the CWSI value and the soil moisture at 0&ndash, 40 cm (P &lt, 0.05), which could provide a reference when using the CWSI to diagnose the water status of plants. Compared with the Tc-Ta value, the CWSI could more accurately monitor the plant water status, and above the considered indictors, gs has the greatest correlation with the CWSI.

The midday stem water potential (&Psi, s) and stomatal conductance (gs) have been traditionally used to monitor the water status of cherry trees (Prunus avium L.). Due to the complexity of direct measurement, the use of infrared thermography has been proposed as an alternative. This study compares &Psi, s and gs against crop water stress indexes (CWSI) calculated from thermal infrared (TIR) data from high-resolution (HR) and low-resolution (LR) cameras for two cherry tree cultivars: &lsquo, Regina&rsquo, and &lsquo, Sweetheart&rsquo, For this purpose, a water stress&ndash, recovery cycle experiment was carried out at the post-harvest period in a commercial drip-irrigated cherry tree orchard under three irrigation treatments based on &Psi, s levels. The water status of trees was measured weekly using &Psi, s, gs, and compared to CWSIs, computed from both thermal cameras. Results showed that the accuracy in the estimation of CWSIs was not statistically significant when comparing both cameras for the representation of &Psi, s and gs in both cultivars. The performance of all evaluated physiological indicators presented similar trends for both cultivars, and the averaged differences between CWSI&rsquo, s from both cameras were 11 &plusmn, 0.27%. However, these CWSI&rsquo, s were not able to detect differences among irrigation treatments as compared to &Psi, s and gs.

Canopy temperature has been proposed as a relevant variable for crop water stress monitoring. Since crop temperature is highly influenced by the prevailing climatic conditions, it is usually normalized with indices such as the crop water stress index (CWSI). The index requires the use of two baselines that relate canopy temperature under maximum stress and non-water stress conditions with vapor pressure deficit (VPD). These reference baselines are specific to each crop and climatic region. In maize, they have been extensively studied for certain climatic regions but very little is known on their suitability to be used under Mediterranean-type conditions nor their temporal stability, both diurnally and between seasons. Thus, the objective of this work was to determine the reference baselines for maize grown under Mediterranean conditions, as well as its diurnal and long-term stability. An experiment was conducted for 3 years in a maize breeding field, under well-watered and water-stressed irrigation treatments. The determined reference baselines for computing CWSI in maize have shown to be stable in the long term but markedly influenced by the meteorological variations between 10–17 h UTC (Coordinated Universal Time). These results indicate that several reference baselines should be used for CWSI computing throughout the abovementioned time interval. The CWSI values calculated for well-watered and water-stressed maize breeding plots using the reference baselines derived in this study were successfully correlated with other physiological indicators of plant water stress.

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.

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 supplies have been decreasing in several semi-arid regions, and it is therefore necessary to adopt irrigation strategies aimed at maximizing water use efficiency. In this paper, the effects of saline and deficit irrigation on water use efficiency and on potato crop response, based on observations of soil and plant water status, were investigated. Experiments were carried out in Central Tunisia, by monitoring potato crop growth during two seasons in four distinct treatments (T1&ndash, T4), represented by two different irrigation doses and two water qualities. For irrigation scheduling purposes, thresholds of soil matric potential, soil water content and Crop Water Stress Index (CWSI) were identified with the aim to quantify the effects of water and/or salinity stress on the achievable yield. Experiments allowed verifying that crop yield is strongly affected by the seasonal amount and quality of applied water. Despite differences of crop yield between treatments T2, T3 and T4 not being statistically significant (P &lt, 0.05), crop yield varied between 26.3 t/ha (T3 in 2015) to 16.3 t/ha (T4 in 2015). However, crop yield decline of 17.0 t/ha and 12.0 t/ha per each 100 mm decrease of applied water were observed under the application of water electrical conductivity of 1.6 dS/m and 4.1 dS/m respectively. On the other hand, an increase of 1.0 dS/m in water electrical conductivity caused a yield decline rate of about 10%. The results achieved showed that under the semi-arid climate of Tunisia, potato crop irrigation should be scheduled to avoid water deficit, however, the possibility to reduce water supply can be envisaged when water availability is limited, but with the awareness to accept the shortage of production. Finally, when saline water is the only source available to the farm, it is necessary to avoid the reduction of irrigation doses, to prevent excessive salt accumulation in the root zone with unavoidable effects on crop yield.

A study was conducted to analyse the physiological response of red pepper (Capsicum annuum L.) to different irrigation regimes by means of periodical measurements of leaf water potential (LWP) and stomatal resistance (rs) and crop water stress index (CWSI) at midday during 2010 and 2011 seasons in the Mediterranean region of Turkey. The treatments consisted of full irrigation (FI), deficit irrigation (DI-75, DI-50), partial root zone drying (PRD-A, PRD-F, A: alternative, F: fixed). The greatest yield was obtained from the FI treatment followed by DI-75, PRD-A, DI-50 and PRD-F treatments resulted in the smallest yield. The FI irrigation treatment had less stomatal resistance (17.4 s cm-1 in 2010 and 16.4 s cm-1 in 2011) and CWSI (0.25 in 2010 and 0.27 in 2011) in comparison with deficit irrigation treatments. Red pepper performed best at FI with a corresponding leaf water potential of -0.65 to -0.53 MPa for experimental years. There were large differences among treatments in LWP, CWSI and rs, indicating that crop responded differently to different soil water levels. Significant relationship between stomatal resistance, water use and yield were obtained. The results also revealed significant dependency among CWSI, rs and LWP were found. © 2018 Elsevier B.V. TOVAG-109O693 The authors would like to thank the Turkish Scientific and Technical Research Council (TUBITAK) for its financial support to the project of TOVAG-109O693. We thank Dr. Terry Howell, retired Researcher Leader at USDA-ARS, Bushland, Texas, for valuable comments on the manuscript.

Automated irrigation is effective in optimizing water use in irrigation. The study presents the application of environmental canopy sensing based Crop Water Stress Index (CWSI) to develop a highly effective sprinkler based irrigation system. Field experiments were utilized for observing plant canopy temperature and soil moisture status. CWSI of 0.35 resulted in maximum water use efficiency and optimum yield of wheat crop. CWSI approach resulted in 10-15% water savings in comparison to soil moisture based irrigation. Based on results of field experiments, an automated approach is proposed, in which the CWSI will be used to trigger the sprinkler irrigation system at critical levels of stresses.

This study was conducted in 2015 and 2016 to investigate potential use of crop water stress index (CWSI) in irrigation scheduling for drip-irrigated pumpkin seed plants. Six different irrigation levels (I0, I20, I40, I60, I80 and I100) were used. Amount of irrigation water applied to plants varied between 24.0–258.4 mm in 2015 and between 13.0–470.2 mm in 2016. Plant water consumptions (ET) varied between 256–479 mm in 2015 and between 227–628 mm in 2016. The greatest seed yields (1417 kg/ha in 2015 and 1306 kg/ha in 2016) were obtained from I100 treatments and the lowest seed yields (470 kg/ha in 2015 and 427 kg/ha in 2016) were obtained from I0 treatments. In 2015, water use efficiency (WUE) values varied between 0.18 - 0.30 kg/m3 and irrigation water use efficiency (IWUE) values varied between 0.55 – 0.89 kg/m3. In 2016, WUE values varied between 0.19 - 0.24 kg/m3 and IWUE values varied between 0.28 – 0.71 kg/m3. The average lower limit baseline equation for CWSI calculations was identified as Tc-Ta = - 2.3728 × VPD + 4.4254. CWSI values varied between 0.24–1.0 in 2015 and between 0.08 - 0.93 in 2016. CWSI significantly correlated with seed yield, leaf area index (LAI), leaf water potential (LWP), oil and protein content. It was concluded based on present findings that CWSI could reliably be used in irrigation scheduling and yield estimation of pumpkin seed plants.

Aerial thermal remote sensing can provide a means for collecting spatial plant water status data. Many studies have shown their potential in irrigation management but the adaptation of this technology is not straight forward. In this paper, knowledge accumulated in recent years on thermal imagery analysis methodology for water status mapping is summarized aiming at indicating alternatives to calculate the Crop Water Stress Index (CWSI) for commercial scale water status mapping. Based on literature overview, four forms of wet-baselines to calculate CWSI were selected, namely: artificial wet reference surface, two theoretical calculations and a statistical bio-indicator. These baselines were used to calculate CWSI based on multi-temporal aerial thermal images of cotton fields. CWSI based on a statistical bio-indicator and one of the theoretical wet-baselines provided the best correlations. It is argued though that the statistical one is preferable since it includes the plant characteristics and it is farmer-friendly. Based on bio-indicators, leaf water potential maps of three commercial fields were produced on several dates through the season. Water status spatial patterns were not static and the effect of static factors like sandy soil patches also changed through the season. The maps show the importance of in-season variability mapping for rational irrigation management. To improve current variable-rate irrigation, the concept of in-season irrigation management zones (IMZ) based on thermal-images should be considered and integrated with the delineation of static irrigation IMZ.

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.

Deficit irrigation is a common practice to cope with limited water availability. A two-year field experiment was conducted in order to determine the water status of cotton crop (Gossypium hirsutum L.) under full and deficit irrigation conditions. The experiment was set up as a split plot design with four replicates, two main plots (irrigation treatments) and two sub plots (cotton cultivars). The lower (non-stressed) and upper (fully stressed) base lines for the determination of Crop Water Stress Index (CWSI) of cotton crop were estimated. Plant water status, expressed in terms of the water potential index (WPI) and CWSI, was measured throughout the growing seasons. The adopted irrigation schemes produced a clear differentiation among cultivars concerning their plant water status. Water shortage resulted in more negative leaf water potential and WPI and greater CWSI values. Leaf water potential, WPI and CWSI values, variation throughout both growing seasons, indicated greater adaptability for “Julia” in water stress conditions, while “Zoi” showed a significant water stress behavior during the phases of yield formation and ripening, even for the full irrigated treatment. In general, use of limited drip irrigation regime with 50% of water requirement had significant benefits in terms of saved irrigation water.

Due to climate change, the application of water saving strategies is of particular interest. The aim of this study was to evaluate the effects of deficit irrigation (DI) and partial root-zone drying (PRD) techniques on the crop water stress index (CWSI), water use efficiency (WUE), and quality parameters in processing tomatoes grown in open field conditions in a Mediterranean climate. Two cultivars were grown for two growing seasons under four irrigation regimes as follows: (i) IR100: full irrigation by restoring 100% of the maximum tomato evapotranspiration (ETc); (ii) IR70DI: 70% of the amount of water given to the IR100; (iii) IR70PRD: 70% of the amount of water given to the IR100 by applying partial root-zone drying and (iv) IR0: irrigation only at transplanting and during fertigation. During the flowering period, the first growing season was characterized by an absence of rainfall and by higher temperatures also showing a higher CWSI. Despite, under IR70PRD, the CWSI was significantly higher than under IR70DI, the marketable yield obtained was significantly higher. Both IR70DI and IR70PRD regimes received approximately 24% less water than IR100, but the yield reduction with relation to the optimum regime was equal to 16.2% under IR70DI, and only 7.6% under IR70PRD. The WUE increment of IR70PRD with respect to IR100 was equal to 27% in the first growing season and to 17% in the second one, showing that the positive effect of PRD on the WUE is more evident in the more stressed year. Finally, the results from the principal component analysis (PCA) showed that the two cultivars had different qualitative responses in the two extreme regimes (IR100 and IR0) but not under PRD and DI regimes.

Remotely sensing plant canopy water status remains a long term goal of remote sensing research. Established approaches to estimating canopy water status — the Crop Water Stress Index, the Water Deficit Index and the Equivalent Water Thickness — involve measurements in the thermal or reflective infrared. Here we report plant water status estimates based upon analysis of polarized visible imagery of a cotton canopy measured by ground Multi-Spectral Polarization Imager (MSPI). Such estimators potentially provide access to the plant hydrological photochemistry that manifests scattering and absorption effects in the visible spectral region.

U ovome radu provedeno je istraživanje na uzorcima presadnica industrijske rajčice (Lycopersicon ecvulentum Mill.) i paprike (Capiscum annuum L.). Mjerenja temperature su provedena termoparovima i infracrvenom termografskom kamerom. Na uzorku rajčice su provedena i mjerenja bioloških svojstava biljke poput vodnog potencijala lista (LWP). Analizirana je promjena temperature i indeksa vodnog stresa usjeva (CWSI) tijekom dana. Na osnovu vrijednosti CWSIa dobivenih pomoću više modela analize i mjerenih vrijednosti LWPa napravljeno je više modela koji opisuju vezu tih dviju vrijednosti. Dobiveni modeli su pokazali statistički značajan stupanj korelacije između tih vrijednosti. Vrijednosti CWSIa dobivene ručnom obradom termograma su se dale najveći stupanj korelacije, no i neke automatske metode obrade su pokazale usporedive rezultate s ručnima. Zaključeno je da je uz korištenje metode automatskog termografskog snimanja koja proizvodi termograme dovoljno visoke kvalitete automatska obrada termograma za izračun CWSI pouzdano primjenjiva. Research was conducted on samples of tomato (Lycopersicon ecvulentum Mill.) and bell pepper (Capiscum annuum L.) plants. Temperature measurements were carried out using thermocouples and an infrared thermal imaging camera. Biological properties of the plant, such as the leaf water potential (LWP), were measured only on the sample of tomatoes. For both samples, an analysis of the change of temperature and crop water stress index (CWSI) during the day was conducted. For the tomato sample the obtained CWSI values and the measured LWP values were used to create multiple models describing their relationship. The obtained relationships showed a statistically significant degree of correlation. Values of CWSI obtained by manual analysis of thermal images produced the highest degree of correlation, but some of the automatic analysis methods produced results comparable to those obtained using the manual methods of analysis. It was concluded that if an automatic thermal imaging method which produced thermal images of sufficiently high quality is used, then the automatic method for the calculation of CWSI developed here is confidently applicable.

This research was conducted during 2009, 2010 and 2012 growing seasons in the experimental vineyard of the Department of Horticulture at Cukurova University in Adana located in the Eastern Mediterranean Region of Turkey on 12 years old Royal table grape variety to evaluate the crop water stress index under various deficit and partial rootzone drying irrigation strategies applied with drip system. In the study, six different treatments were considered; namely full irrigation (FI), deficit irrigations (DI-75 and DI-50), partial rootzone drying (PRD-75 and PRD-50) and rainfed (RF). In FI soil water deficit in the 80 cm within the seven-day intervals was replenished to the field capacity. DI-75, DI-50, and PRD-75, PRD-50 treatments received 75 and 50% of water applied to FI. In PRD plots, drip laterals on both sides of the vine rows operated alternately. Experimental design was randomized blocks with three replications. Canopy temperatures were measured throughout the growing season with an infrared thermometer, and vapor pressure deficit of air was used for calculating the crop water stress index (CWSI). Lower and upper limits of basic graphic, which is necessary to CWSI calculation, were developed for grapevine. The effect of irrigation treatments on yield, vine growth and juice quality differred significantly among the treatments. Highest yield was obtained from the full irrigation (FI) as 30.2 t ha-1, and the lowest yield was obtained from the RF treatment as 14.2 t ha-1. PRD vines exhibited a stronger control over vegetative growth as compared with DI and FI plants. This was expressed by lower values of total leaf area at harvest. Higher water use efficiency (WUE) was observed in RF and PRD-75 treatments while the lowest WUE was obtained from DI-50 treatment. Results showed significant differences in grape quality components among treatments and seasons studied. The highest brix value was obtained in RF while the lowest brix value was from the FI treatment. Three years seasonal average CWSI values ranged from 0.20 in FI to 0.77 in RF. Significant linear relations were found between yield and CWSI in three experimental years. The results revealed that Royal variety should be irrigated when average CWSI value is approximately 0.20 for high yield. According to the experimental findings, PRD-75 application with water savings as compared to full irrigation might be a suitable strategy for irrigation under water scarcity. © 2017 Elsevier B.V.

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).

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.

5th IFAC Conference on Sensing, Control and Automation Technologies for Agriculture (AGRICONTROL) -- AUG 14-17, 2016 -- Seattle, WA WOS: 000401238100039 Measurement of plant water status (PWS) provides the key information necessary to implement efficient irrigation management schemes in almond orchards and vineyards. A continuous leaf monitoring system based on leaf temperature and relevant microclimatic variables is currently available to obtain PWS. These systems can be installed after careful analysis of how soil and plant characteristics are distributed throughout the field to implement site-specific irrigation. Crop water stress index (CWSI) or modified water stress index (MCWSI) values are usually computed with leaf monitor data, which requires a knowledge of well-watered and fully stressed conditions. Although these values can be estimated by assuming that trees reach saturation after each irrigation event, this is not the case when deficit irrigation is implemented. We proposed a new methodology to compute CWSI and MCWSI using the continuous leaf monitor data, where the well-watered and dry conditions were measured using a well-watered tree and a simulated dry leaf. The objectives of this work were: (1) to implement a plant water stress based site-specific irrigation management scheme in an almond orchard and (2) to assess PWS of grapes and almond trees by comparing MCWSI and CWSI with deficit stem water potential (DSWP). A wireless network was used in each study site to interface the leaf monitors, soil and pressure sensors, as well as latching solenoid valves. Two management zones were created using unsupervised fuzzy classification based on soil and plant characteristics in the almond orchard. In each management zone two treatments were implemented: grower and stress based. Leaf monitors were tested in grapes by measuring PWS in eight vines, where four of them corresponded to vines that were not being watered following full irrigation to experience increasing amount of stress and four other vines corresponded to vines that were watered daily after a long period of stress to recover from stress. In grapes, MCWSI and DSWP were found to be linearly related with a coefficient of determination value of 0.70. In almonds, CWSI and DSWP were found to be strongly correlated with a second order relationship and a coefficient of determination value of 0.78. Additionally, preliminary results indicated that the management zones #1 and #2 of the almond orchard required approximately 70% and 90%, respectively, of the water used in grower based irrigation. (C) 2016, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved. Int Federat Automat Control, Tech Comm 8 1 Control Agr, Int Federat Automat Control, Tech Comm 4 2 Mechatron Syst, Int Federat Automat Control, Tech Comm 7 5 Intelligent Autonomous Vehicles, Int Federat Automat Control, Tech Comm 8 4 Biosystems & Bioprocesses