1,721,056 research outputs found
A semi-empirical approach for surface soil water content estimation from radar data without a-priori information on surface roughness
No full textIn this study, the spatial distribution of soil water content in an agricultural area of 30 km2 in Southern Italy has been estimated by using high-resolution space-borne Synthetic Aperture Radar data. Multi-polarised SAR images acquired during the SIR-C mission in April 1994 have been analysed by using the semi-empirical surface backscattering model derived by Oh et al. (1992). A site-specific calibration procedure of the cited model has been proposed to derive soil dielectric constant values without a-priori information on the surface roughness by using ground measurements on a regular grid in two bare-soil fields. The calibrated model applied to L-band data reproduced quite satisfactorily the spatial variability of the soil dielectric constant in the two fields. Diversely, C-band data gave poor results. Successively, the calibrated Oh’s model was applied to estimate the soil dielectric constant in bare soil and low vegetation fields of the entire irrigation district, where the output of a distributed simulation model of soil water balance were available. From the comparison between the Oh’s backscattering model and the soil water balance model, it was confirmed that, under bare soil conditions, the values of soil water content near the soil surface estimated from SIR-C L-band data differ by ± 20% from the simulated ones. Furthermore, as expected, the presence of a fractional vegetation cover, even if small, reduced the sensitivity of radar backscattering to soil moisture. The results of this study confirmed that L-band SAR data represent a minimum requirement for possible assimilation schemes in regional hydrological modelling
Sulle tecniche di stima dell�indice di Area Fogliare da dati MIVIS: applicazione e confronto dei modelli SAIL e CLAIR
No full textASSESSING FAO-56 MODEL TO ESTIMATE TABLE OLIVE WATER CONSUME UNDER SOIL WATER DEFICIT CONDITIONS
No full textAgro-hydrological models can be considered an economic and simple tool to quantify crop water requirements. In the last two decades, agro-hydrological physically based models have been developed to simulate mass and energy exchange processes in the soil-plant-atmosphere system. Although very reliable, due to the high number of required variables, simplified models have been proposed as simple tools to quantify crop water consumes. The main aim of the paper is to assess, for a Sicilian orchard of table olive, the suitability of FAO-56 agro-hydrological model to estimate the crop transpiration under soil water deficit conditions. The model validation is carried out by means of measurements of sap-flow and soil water contents, acquired during three years of field observations. An amendment of the model is suggested in order to take into account the water stress function and the soil water uptake ability as experimentally evaluated. The results show that the modified model improves the estimation of crop transpiration and soil water content, considered that the associated RMSEs resulted higher than the corresponding values obtained with the original version of the mode
Rethinking vineyard ground management to counter soil tillage erosion
No full textTillage erosion is a relevant process of soil redistribution in sloping arable land, but little research has analysed the effect of shallow tillage on soil erosion in vineyards. The goal of this study was to quantify the soil tillage effect on soil translocation and erosion at the territorial level in a large vineyard area in Sicily. The soil loss and soil erosion tolerance limits were compared to identify the vineyards with a high risk of soil degradation. An alternative management scenario to traditional tillage was proposed to evaluate the effectiveness of the best management practices on soil conservation. The experimental trials were conducted in 14 vineyards with different slopes and soil characteristics. Soil translocation after shallow tillage was determined using coloured sand as the tracer. Regression results between the slope and mean translocation distance (T) were used to estimate tillage erosion (Qplot) in 2840 vineyard plots within a Protected Designation of Origin (PDO) area, considering the number of inter-rows and the length of each plot. After a single tillage operation in the downslope direction, the mean translocation distance ranged from 0.22 m to 0.45 m in the slope of 4% and 32%, respectively. At the plot level (Mg yr−1 per plot), the size and shape of the field must be considered, and the number of inter-rows was the predominant factor in tillage erosion estimation in vineyards. When comparing tillage erosion of each inter-row and soil erosion tolerance, the findings showed that 94% of the analysed plots had a high tillage erosion risk. Therefore, more attention should be paid to tillage operations in terms of type and intensity. The plots with high erosion risk decreased to 74% when best management practices with a cover crop in the entire PDO area were adopted. This study highlights the contribution of high tillage erosion to overall soil erosion losses, suggesting specific attention should be paid to more sustainable practices in soil management
Gestione dell'irrigazione del vigneto attraverso l'uso di modelli di simulazione e misure di campo
No full textViene valutata l’applicabilità di un modello numerico, SWAP (Soil Water Atmosphere Plant, van Dam et al., 1997) e di uno funzionale, FAO 56 (Allen et al., 1998), nella programmazione degli interventi irrigui a scala aziendale. Dopo la validazione, i due modelli sono stati utilizzati al fine di verificare la possibilità di simulare la gestione dell’irrigazione tipica dell’area di indagine, attraverso la determinazione del numero e della distribuzione degli adacquamenti, nonché stima dei consumi idrici totali nel corso del ciclo vegeto-produttivo della coltura. Entrambi i modelli simulano in modo soddisfacente l’andamento dei contenuti idrici medi del suolo, evidenziando errori di stima non superiori al 2,0%. Il modello SWAP ha consentito di simulare con buona approssimazione la gestione irrigua tipica della zona, permettendo di valutare sia l’inizio della stagione irrigua che i consumi idrici totali da parte della coltura. Nella sua formulazione originale, il modello FAO 56, invece, non si è dimostrato altrettanto affidabile. In vista di un successivo uso ai fini della gestione irrigua vengono suggerite delle modifiche utili a migliorare la performance del modello FAO. L’analisi delle performance ha evidenziato che, in annate caratterizzate da carenza di piogge, il numero di adacquamenti suggeriti da entrambi i modelli risulta comparabile
Detecting crop water status in mature olive groves using vegetation spectral measurements
Full text linkFull spectral measurements (350-2500nm) at tree canopy and leaf levels and the corresponding leaf water potentials (LWP) were acquired in an olive grove of Sicily, at different hours of the day, during summer season 2011. The main objective of the work was to assess, on the basis of the experimental data-set, two different approaches to detect crop water status in terms of LWP. Specifically, using existing families of Vegetation Indices (VIs) and applying Partial Least Squares Regression (PLSR) were optimised and tested. The results indicated that a satisfactory estimation of LWP at tree canopy and leaf levels can be obtained using vegetation indices based on the near infrared-shortwave infrared (NIR-SWIR) domain requiring, however, a specific optimisation of the corresponding "centre-bands". At tree canopy level, a good prediction of LWP was obtained by using optimised indices working in the visible domain, like the Normalized Difference Greenness Vegetation Index (NDGI, RMSE=0.37 and R2=0.57), the Green Index (GI, RMSE=0.53 and R2=0.39) and the Moisture Spectral Index (MSI, RMSE=0.41 and R2=0.48). On the other hand, a satisfactory estimation of LWP at leaf level was obtained using indices combining SWIR and NIR wavelengths. The best prediction was specifically found by optimising the MSI (RMSE of 0.72 and R2=0.45) and the Normalized Difference Water Index (NDWI, RMSE=0.75 and R2=0.45). Even using the PLSR technique, a remarkable prediction of LWP at both tree canopy and leaf levels was obtained. However, this technique requires the availability of full spectra with high resolution, which can only be obtained with handheld spectroradiometers or hyper-spectral remote sensors
Analisi delle relazioni tra indici di stato idrico e firme spettrali in piante adulte di olivo (Olea europea L.)
No full textLa conoscenza dello stato idrico della vegetazione riveste un ruolo rilevante in svariate
applicazioni biofisiche riguardanti gli ecosistemi, naturali ed agrari, dove lo stress
idrico costituisce una delle più importanti limitazioni per la produzione primaria ed
agricola.
L’obiettivo della ricerca ha riguardato la valutazione dello stato idrico di piante di
olivo, a partire da misure di riflettanza nelle bande del visibile (VIS) e del vicino
infrarosso (NIR), eseguite sia a scala fogliare che di canopy. Si sono, pertanto,
analizzate le firme spettrali in riflettanza fogliare e di canopy di piante di olivo il cui
stato idrico è stato monitorato attraverso l’ausilio di indicatori ecofisiologici quali il
potenziale idrico xilematico. Le misure spettrali sono state condotte utilizzando uno
spettroradiometro da campo operante nell’intervallo spettrale 350-1050 nm. Per
l’analisi spettrale si è fatto riferimento sia a indici legati direttamente lo stato idrico
della foglia/canopy, quali il “Water Index” (WI) e l’Absorption Index (AI), che ad
indici indiretti come il “Normalized Difference Vegetation Index” (NDVI) e il “Red
Edge Position” (REP), che tengono conto della variazione di altri parametri
biochimici, quali la quantità e l’attività della clorofilla, nonché la variazione delle
caratteristiche morfo-anatomici della vegetazione
Uso di modelli agroidrologici per la gestione dell’irrigazione di colture arboree mediterranee
Full text linkNel presente lavoro viene presentato un confronto tra due modelli di bilancio idrologico: il modello proposto dalla
FAO e il modello SWAP, basato sulla soluzione dell’equazione di Richards. Il confronto ha riguardato i valori delle
componenti del bilancio idrologico ed i contenuti idrici del suolo relativamente alle due stagioni irrigue 2005 e 2006
su colture di Vite ed Olivo. È stata inoltre valutata la performance dei due modelli sulla programmazione
dell’irrigazione impostando i parametri di scheduling ordinari della zona
Evapotranspiration from an Olive Orchard using Remote Sensing-Based Dual Crop Coefficient Approach
No full textA remote sensing-based approach to estimate actual evapotranspiration (ET) was tested in an area covered by olive trees and characterized by Mediterranean climate. The methodology is a modified version of the standard FAO-56 dual crop coefficient procedure, in which the crop potential transpiration, Tp, is obtained by directly applying the Penman-Monteith (PM) equation with actual canopy characteristics (i.e., leaf area index, albedo and canopy height) derived from optical remote sensing data. Due to the minimum requirement of in-situ ancillary inputs, the methodology is suitable also for applications on large areas where the use of tabled crop coefficient values become problematic, due to the need of corrections for specific crop parameters, i.e., percentage of ground cover, crop height, phenological cycles, etc. The methodology was applied using seven airborne remote sensing images acquired during spring-autumn 2008. The estimates based on PM approach always outperforms the ones obtained using simple crop coefficient constant values. Additionally, the comparison of simulated daily evapotranspiration and transpiration with the values observed by eddy correlation and sap flow techniques, respectively, shows a substantial agreement during both dry and wet days with an accuracy in the order of 0.5 and 0.3 mm d-1, respectively. The obtained results suggest the capability of the proposed approach to correctly partition evaporation and transpiration components during both the irrigation season and rainy period also under conditions of significant reduction of actual ET from the potential one. © 2013 Springer Science+Business Media Dordrecht
A distributed agro-hydrological model for irrigation water demand assessment.
No full textThe actual irrigation water demand in a district in Sicily (Italy) was assessed by the spatially distributed agro-hydrological model SIMODIS (SImulation and Management of On-Demand Irrigation Systems). For each element with homogeneous crop and soil conditions, in which the considered area can be divided, the model numerically solves the one-dimensional water flow equation with vegetation parameters derived from Earth Observation data. In SIMODIS, the irrigation scheduling is set by means of two parameters: the threshold value of soil water pressure head in the root zone, hm, and the fraction of soil water deficit to be re-filled, Δ. This study investigated the possibility of identifying a couple of irrigation parameters (hm, Δ) which allowed to reproduce the actual irrigation water demand, given that the study area was adequately characterized with regard to the spatial distribution of the soil hydraulic properties and the vegetation conditions throughout the irrigation season. The spatial distribution of the soil and vegetation properties of the study area, covering an irrigation district of approximately 800 ha, was accurately characterized during the summer of 2002. The soil hydraulic properties were identified by an intensive undisturbed soil sampling, while the vegetation cover was characterized in terms of leaf area index, surface albedo and fractional soil cover by analysing multispectral LandSat TM imageries. Irrigation volumes were monitored at parcel scale.
A reference scenario with hm = −700 cm and Δ = 50% (corresponding to a mean actual to potential transpiration ratio of 0.95) allowed to reproduce the spatial and temporal distribution of the actual irrigation demand at the district scale. The spatial variability of the crop conditions in the considered area had much more influence to assess the irrigation water demand than the soil hydraulic spatial variability. The proposed approach showed that, under the agro-climatic conditions typical for the Mediterranean region, SIMODIS may be a valuable tool in managing irrigation to increase water productivity
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