Victoria Gonzalez-dugo | CSIC (Consejo Superior de Investigaciones Científicas-Spanish National Research Council) (original) (raw)

Papers by Victoria Gonzalez-dugo

Remote Sensing of Environment, 2019

Plant photosynthetic traits may be indicative of stress tolerance and performance in the field, m... more Plant photosynthetic traits may be indicative of stress tolerance and performance in the field, making their accurate assessment critical in phenotyping trials. The maximum rate of carboxylation (Vcmax) is a key parameter for estimating CO 2 assimilation (A), as it controls the CO 2 fixation rate. This study demonstrates the utility of combining airborne-based solar-induced chlorophyll fluorescence (SIF) and hyperspectral imagery through the inversion of the Soil-Canopy Observation of Photosynthesis and Energy (SCOPE) model to estimate Vcmax, using sensor resolutions available in precision agriculture technologies. Vcmax was quantified in three wheat phenotyping experimental fields during the 2015-2018 growing seasons, comprising both rainfed and irrigated conditions. Airborne campaigns were carried out with two hyperspectral sensors, covering the 400-850 nm (20 cm resolution) and 950-1750 nm (70 cm resolution) spectral regions, and with a thermal camera (25 cm resolution) in the 8-14 μm region. Validation between model-estimated and field-measured Vcmax was statistically significant (r 2 = 0.77; p-value ≤2.2e−16), and Vcmax was reliably associated with net assimilation both in irrigated and rainfed conditions (r 2 = 0.65 and 0.5, respectively). By contrast, simulated chlorophyll content (Cab) and airborne-derived structural and chlorophyll indicators (NDVI and PSSRb) lacked significant correlations with assimilation rate in irrigated plots, while the relationship between assimilation rate and the crop water stress index (CWSI) was not significant in rainfed plots. The superior sensitivity of remotely-sensed Vcmax under irrigated conditions was likely related to its robustness to distortions from high canopy densities observed in other indices. The remote sensing retrieval of Vcmax, and the methodology demonstrated in this study is directly relevant for high-throughput plant phenotyping and for precision agriculture applications.

Remote Sensing for Agriculture, Ecosystems, and Hydrology XXIII

Agronomy for Sustainable Development, 2010

Among the environmental factors that can be modified by farmers, water and nitrogen are the main ... more Among the environmental factors that can be modified by farmers, water and nitrogen are the main ones controlling plant growth. Irrigation and fertilizer application overcome this effect, if adequately used. Agriculture thus consumes about 85% of the total fresh water used worldwide. While only 18% of the world’s cultivated areas are devoted to irrigated agriculture, this total surface represents more

Sustainable Agriculture Volume 2, 2011

Nutrient Cycling in Agroecosystems, 2010

Water deficits alter the nitrogen nutrition of crops. In grasslands, this has a major impact on b... more Water deficits alter the nitrogen nutrition of crops. In grasslands, this has a major impact on both forage yield and nitrogen fluxes in the soil. It is important to assess the N balance in order to adjust fertilization to the expected needs of the crop and thus minimize any environmentally negative impacts of crops. Grassland species, including grasses, display a

Australian Journal of Agricultural Research, 2005

Grasslands are rarely irrigated, thus water deficits often induce a reduction of the nitrogen nut... more Grasslands are rarely irrigated, thus water deficits often induce a reduction of the nitrogen nutrition index (NNI) during summer. This is measured using the ratio between the actual N concentration and the minimum N concentration required to achieve the maximum growth rate. NNI is derived from the standing biomass by a simple relationship.

Una aplicación reciente del Photochemical Reflectance Index (PRI) es la detección de estrés hídri... more Una aplicación reciente del Photochemical Reflectance Index (PRI) es la detección de estrés hídrico en cultivos. Sin embargo, un uso correcto del PRI requiere modelizar a nivel de hoja y cubierta aquellos parámetros que tienen gran influencia en la reflectancia. El presente trabajo propone una metodología basada en modelos de transferencia radiativa (TR) que simulan el "PRI teórico" para determinar su valor en ausencia de estrés. Los experimentos se realizaron en frutales con distintos tratamientos de riego. Las imágenes multiespectrales (6 bandas, 10 nm FWHM y 15 cm de resolución) se obtuvieron en 2007 y 2008 usando un vehículo aéreo no tripulado (UAV). Los resultados muestran relaciones entre PRI y temperatura de cubierta de r 2 =0.8 y 0.65. Los tratamientos deficitarios mostraron valores de PRI superiores al teórico, mientras que los árboles bien regados mantuvieron siempre valores de PRI alrededor del nivel teórico. Estos resultados indican que usando modelos TR para considerar los efectos de la estructura de la cubierta, el índice PRI es un buen indicador de estrés hídrico.

Irrigation uses more than 70% of all water diverted to various uses worldwide. In the Mediterrane... more Irrigation uses more than 70% of all water diverted to various uses worldwide. In the Mediterranean region, due to the limited rainfall and the erratic distribution within the year, irrigation of crops is essential to ensure high yields. The increase in water demand from other users coupled with wáter scarcity is leading to the reduction in the amount of water diverted for agriculture. One of the strategies that are actually being implemented in order to reduce water inputs in agriculture is déficit irrigation, which consists on the application of water below crop water requirements (English, 1990). In order to test the applicability of this technique in this region, an experiment was set up during 2007 and 2008 in a clementine orange commercial orchard, where a sustained deficit irrigation (SDI) was compared against the irrigation program used by the farmer in the orchard. (…) In conclusion, the reduction of water application to 62% of that applied in the farm practice (an applicat...

ABSTRACT Remotely sensed crop water stress index (CWSI) can be used to depict fruit tree water st... more ABSTRACT Remotely sensed crop water stress index (CWSI) can be used to depict fruit tree water status. The aim of this study was: i) to develop an empirical approach for assessing the CWSI of peach trees throughout a growing season and validate it with ground-based leaf water potential (Ψleaf) measurements, and ii) to detect the spatial variability of fruit tree water status in a 2-ha peach orchard and throughout a complete growing season based on remotely estimates of leaf water potential (Ψrem) from airborne thermal imagery. Ψrem was estimated from the seasonal relationships with CWSI. This study was carried out during 2012 and 2013 growing seasons. CWSI and Ψleaf were significantly correlated both years indicating a similar tendency between years, but differences between phenological stages. Differences in the spatial variability of peach tree water status were successfully remotely detected, demonstrating that remote estimates of leaf water potential can be used for precise irrigation purposes.

ABSTRACT Crop water stress index (CWSI) has been used as a tool for mapping spatial variability i... more ABSTRACT Crop water stress index (CWSI) has been used as a tool for mapping spatial variability in water requirements of vineyards. During 2009-2011, CWSI seasonal equations were obtainedfor varieties ‘Pinot-noir’, ‘Chardonnay’, ‘Tempranillo’ and ‘Syrah’by using infrared temperature sensors and high resolution airborne thermal imagery. Leaf water potential (ΨL) measurements were used to validate the proposed methodology. Coefficients of determination (R2) ranged from 0.54 to 0.93 indicating a contrasted CWSI sensitivity to water stress between phenological stages. In 2012, irrigation scheduling of a 16-ha ‘Chardonnay’ plot was carried outsolely on the basis of remotely sensed ΨL obtained throughout the season.

Remote Sensing of Environment, 2013

ABSTRACT This work advances the evaluation and interpretation of the Photochemical Reflectance In... more ABSTRACT This work advances the evaluation and interpretation of the Photochemical Reflectance Index (PRI) as an indicator of water stress, over a range of canopy structures and pigment content levels. Very high resolution (VHR) narrow-band multispectral (10 cm) and thermal (20 cm) imagery was acquired diurnally, in four airborne campaigns conducted over an experimental vineyard site undergoing three different irrigation treatments. Field measurements of leaf stomatal conductance (G(s)) and leaf water potential (Psi(leaf)) were acquired concurrently with the airborne campaigns and compared against the Crop Water Stress Index (CWSI), a widely accepted, thermal-based indicator of water stress, and against narrow-band multispectral indices calculated from pure-vegetation pixels. The study proposes a new formulation, a normalized PRI (PRInorm), in which the standard PRI index is normalized by an index that is sensitive to canopy structure (Renormalized Difference Vegetation Index, RDVI) and by a red edge index that is sensitive to chlorophyll content (R-700/R-670). The hypothesis investigated is that the new index, calculated as PRInorm = PRI/[RDVI center dot R-700/R-670], not only detects xanthophyll pigment changes as a function of water stress, but also normalizes for the chlorophyll content level and canopy leaf area reduction induced by stress. Results demonstrated that when comparing PRInorm against stomatal conductance (r(2) = 0.79; p <0.001) and leaf water potential (r(2) = 0.77; p < 0.001) measured at midday, the new index performed better than the standard PRI (r(2) = 0.52 and 0.49, respectively). Further, when using the four flights conducted during the diurnal experiment, the relationships with stomatal conductance also showed the superior performance of PRInorm (r(2) = 0.68) as opposed to PRI (r(2) = 0.4). The proposed normalized PRI was highly related (r(2) = 0.75; p <0.001) to the thermal indicator of water stress, CWSI, which was used here as a benchmark. In comparison, the standard PRI index was found to be significantly related to CWSI (p < 0.001), although the relationship was weaker (r(2) = 0.58) than that obtained for PRInorm. In summary, this study demonstrates that PRInorm isolated better than PRI the physiological changes against a changing background of altered pigments and structure, tracking more precisely the diurnal dynamics of the stomatal aperture. Simulations conducted, using leaf and canopy radiative transfer models to elucidate these results, showed that PRInorm is more linearly related to canopy pigment content than the standard PRI, and was more capable of differentiating between stress levels, providing better insight into the results of this diurnal study.

Agricultural and Forest Meteorology, 2014

ABSTRACT Accurate measurements of the crop water status are becoming essential in irrigated agric... more ABSTRACT Accurate measurements of the crop water status are becoming essential in irrigated agriculture, as water resources are limited and its use must be optimized, especially in semi-arid conditions. Indicators derived from thermal information have shown to be closely related to water status in several fruit tree species, and have shown promise for assessing the spatial variations among and within whole orchards. Here, a methodology is proposed for assessing the Crop Water Stress Index (CWSI) of mandarin (Citrus reticulata Blanco cv. Clemenvilla) and navel orange (Citrus sinensis L cv. Powell) located in Southern Spain, taking into account the short-term fluctuations in canopy temperature observed in both species. Infrared thermal sensors were installed above trees to record canopy temperature (Tc) continuously for three seasons from 2009 to 2011. The Non Water Stress Baseline (NWSB) was calculated using Tc of well irrigated trees on cloudless days during summertime. The NWSB was affected by flushes of growth that occurred periodically, depending on the crop load of a given year. Nevertheless, the close relationship observed between CWSI and stem water potential (R2 ranging between 0.59 and 0.66; p < 0.001) demonstrated that it is a suitable indicator of water status in citrus. The results showed that care must be taken when using CWSI in citrus to account for the presence of new growth at the top of the canopy, and for the short-term fluctuations in canopy temperature. The canopy temperature information acquired from point sensors was used in conjunction with high resolution airborne thermal imagery to derive CWSI maps. The approach presented here demonstrates that CWSI is a valuable method to assess the water status, and to quantify the spatial variability in water stress among and within citrus orchards using high-resolution airborne thermal imagery.

Sustainable Irrigation and Drainage V, 2014

ABSTRACT Knowledge on crop water status at the orchard scale is necessary for the efficient manag... more ABSTRACT Knowledge on crop water status at the orchard scale is necessary for the efficient management of irrigation water. Canopy temperature has long been recognized as a plant water status indicator, and crop water stress index (CWSI), which is obtained from canopy temperature could be used as a tool for remotely detecting plant water status from airborne high-resolution thermal imagery. In 2012, CWSI baselines for olive and peach trees were derived from infrared thermometer data. An aircraft equipped with a thermal sensor flew over two orchards acquiring high-resolution thermal images. At the same time, leaf water potential (ΨL) was measured in eighteen trees per specie. Relationship between the difference of canopy and air temperature (Tc -Ta) and ΨL had a R2 of 0.74 and 0.82, for peach and olive, respectively. CWSI ranged from zero to one and showed a significant correlation with ΨL. Maps of estimated ΨL (derived from CWSI -ΨL relationships) were able to detect the spatial variability of plant water status within the orchards, and may be a feasible tool for irrigation purposes.

Irrigation Science, 2014

ABSTRACT A study was conducted in a large pistachio farm in Madera County, California, to assess ... more ABSTRACT 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.

Functional Plant Biology, 2014

ABSTRACT The links between water and crop yield are well known. In agricultural systems, maximum ... more ABSTRACT The links between water and crop yield are well known. In agricultural systems, maximum yield and maximum water productivity (WP; yield divided by water use) are not always compatible goals. In water-limited situations, optimal solutions must be reached by finding a compromise between the levels of crop production and WP. The tradeoffs between production and WP are reviewed here and the dominant effects of the environment on WP are examined. Genetic improvement for WP generally has yield tradeoffs, whereas management measures devised to improve WP also enhance yield. It is shown that partial closure of the stomata in response to environmental stimuli has a variable impact on canopy transpiration, depending on the degree of coupling between the canopy and the atmosphere. In contrast to the behaviour of the major herbaceous crops, WP increases in some woody crops in response to water stress, suggesting that biomass and transpiration are not linearly related, and that deficit irrigation should be successful in these species. Avoiding high evaporative demand periods (e.g. through tolerance to low temperatures) is an important option that aims to increase production and WP. A case study is presented for improving sunflower (Helianthus annuus L.) yield and WP in temperate environments.

Scientia Horticulturae, 2007

... Processing industries demand a fully coloured fruit with a reduced fruit water content to dim... more ... Processing industries demand a fully coloured fruit with a reduced fruit water content to diminish transport and storage costs (Dorji et al., 2005). ... used in the region because of its high colour production, were transplanted 15 April, 2001, at a density of 66.000 plants/ha in 0.75 m ...

Remote Sensing of Environment, 2012

The remote detection of water stress in a citrus orchard was investigated using leaf-level measur... more The remote detection of water stress in a citrus orchard was investigated using leaf-level measurements of chlorophyll fluorescence and Photochemical Reflectance Index (PRI) data, seasonal time-series of crown temperature and PRI, and high-resolution airborne imagery. The work was conducted in an orchard where a regulated deficit irrigation (RDI) experiment generated a gradient in water stress levels. Stomatal conductance (Gs) and water potential (Ψ) were measured over the season on each treatment block. The airborne data consisted on thermal and hyperspectral imagery acquired at the time of maximum stress differences among treatments, prior to the re-watering phase, using a miniaturized thermal camera and a micro-hyperspectral imager on board an unmanned aerial vehicle (UAV). The hyperspectral imagery was acquired at 40 cm resolution and 260 spectral bands in the 400-885 nm spectral range at 6.4 nm full width at half maximum (FWHM) spectral resolution and 1.85 nm sampling interval, enabling the identification of pure crowns for extracting radiance and reflectance hyperspectral spectra from each tree. The FluorMOD model was used to investigate the retrieval of chlorophyll fluorescence by applying the Fraunhofer Line Depth (FLD) principle using three spectral bands (FLD3), which demonstrated that fluorescence retrieval was feasible with the configuration of the UAV micro-hyperspectral instrument flown over the orchard. Results demonstrated the link between seasonal PRI and crown temperature acquired from instrumented trees and field measurements of stomatal conductance and water potential. The sensitivity of PRI and Tc-Ta time-series to water stress levels demonstrated a time delay of PRI vs Tc-Ta during the recovery phase after re-watering started. At the time of the maximum stress difference among treatment blocks, the airborne imagery acquired from the UAV platform demonstrated that the crown temperature yielded the best coefficient of determination for Gs (r 2 = 0.78; p b 0.05) and Ψ (r 2 = 0.34; p b 0.001). Among the narrow-band indices calculated, the PRI 515 index (reference band=515 nm) obtained better results than PRI 570 , with r 2 =0.59 (pb 0.01) for Gs, and r 2 =0.38 (pb 0.001) for Ψ. The BGI1 index calculated from the blue (R 400 ) and green (R 550 ) bands resulted on the highest significance levels (p b 0.001) for both Gs (r 2 = 0.62) and Ψ (r 2 = 0.49). Out of the structural indices assessed, RDVI, MTVI1 and TVI showed greater sensitivity for Gs (r 2 = 0.6; p b 0.01) and Ψ (p b 0.001) than NDVI. Chlorophyll fluorescence calculated from the microhyperspectral imagery with the FLD3 method tracked stress levels, obtaining r 2 = 0.67 (p b 0.05) with stomatal conductance, and r 2 =0.66 (pb 0.001) with water potential. The work presented in this manuscript demonstrates the feasibility of thermal, narrow-band indices and fluorescence retrievals obtained from a micro-hyperspectral imager and a light-weight thermal camera on board small UAV platforms for stress detection in a heterogeneous tree canopy where very high resolution is required.