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1 Pocas, I.; Calera, A.; Campos, I.; Cunha, M. 2020. Remote sensing for estimating and mapping single and basal crop coefficientes: a review on spectral vegetation indices approaches. Agricultural Water Management, 233:106081. [doi: https://doi.org/10.1016/j.agwat.2020.106081]
Remote sensing ; Crops ; Water requirements ; Evapotranspiration ; Vegetation index ; Irrigation management ; Soil water balance ; Soil moisture ; Earth observation satellites ; Landsat ; Geographical information systems ; Monitoring ; Water stress ; Mapping ; Models
(Location: IWMI HQ Call no: e-copy only Record No: H049654)
(0.77 MB)
The advances achieved during the last 30 years demonstrate the aptitude of the remote sensing-based vegetation indices (VI) for the assessment of crop evapotranspiration (ETc) and irrigation requirements in a simple, robust and operative manner. The foundation of these methodologies is the well-established relationship between the VIs and the basal crop coefficient (Kcb), resulting from the ability of VIs to measure the radiation absorbed by the vegetation, as the main driver of the evapotranspiration process. In addition, VIs have been related with single crop coefficient (Kc), assuming constant rates of soil evaporation. The direct relationship between VIs and ET is conceptually incorrect due to the effect of the atmospheric demand on this relationship. The rising number of Earth Observation Satellites potentiates a data increase to feed the VI-based methodologies for estimating and mapping either the Kc or Kcb, with improved temporal coverage and spatial resolution. The development of operative platforms, including satellite constellations like Sentinels and drones, usable for the assessment of Kcb through VIs, opens new possibilities and challenges. This work analyzes some of the questions that remain inconclusive at scientific and operational level, including: (i) the diversity of the Kcb-VI relationships defined for different crops, (ii) the integration of Kcb-VI relationships in more complex models such as soil water balance, and (iii) the operational application of Kcb-VI relationships using virtual constellations of space and aerial platforms that allow combining data from two or more sensors.
2 Jovanovic, N.; Pereira, L. S.; Paredes, P.; Pocas, I.; Cantore, V.; Todorovic, M. 2020. A review of strategies, methods and technologies to reduce non-beneficial consumptive water use on farms considering the FAO56 methods. Agricultural Water Management, 239:106267. (Online first) [doi: https://doi.org/10.1016/j.agwat.2020.106267]
Water use efficiency ; Irrigation management ; Irrigation methods ; Remote sensing ; Soil management ; Water scarcity ; Water stress ; Water conservation ; Crop water use ; Water requirements ; Evapotranspiration ; Water productivity ; Deficit irrigation ; Irrigation systems ; Sprinkler irrigation ; Drip irrigation ; Irrigation scheduling ; Mulching ; Models
(Location: IWMI HQ Call no: e-copy only Record No: H049833)
(0.97 MB)
In the past few decades, research has developed a multitude of strategies, methods and technologies to reduce consumptive water use on farms for adaptation to the increasing incidence of water scarcity, agricultural droughts and multi-sectoral competition for water. The adoption of these water-saving practices implies accurate quantification of crop water requirements with the FAO56 crop coefficient approach, under diverse water availability and management practices. This paper critically reviews notions and means for maintaining high levels of water consumed through transpiration, land and water productivity, and for minimizing non-beneficial water consumption at farm level. Literature published on sound and quantified experimentation was used to evaluate water-saving practices related to irrigation methods, irrigation management and scheduling, crop management, remote sensing, plant conditioners, mulching, soil management and micro-climate regulation. Summary tables were developed on the benefits of these practices, their effects on non-beneficial water consumption, crop yields and crop water productivity, and the directions for adjustment of FAO56 crop coefficients when they are adopted. The main message is that on-farm application of these practices can result in water savings to a limited extent (usually <20%) compared to sound conventional practices, however this may translate into large volumes of water at catchment scale. The need to streamline data collection internationally was identified due to the insufficient number of sound field experiments and modelling work on the FAO56 crop water requirements that would allow an improved use of crop coefficients for different field conditions and practices. Optimization is required for the application of some practices that involve a large number of possible combinations (e.g. wetted area in micro-irrigation, row spacing and orientation, plant density, different types of mulching, in-field water harvesting) and for strategies such as deficit irrigation that aim at balancing water productivity, the economics of production, infrastructural and irrigation system requirements. Further research is required on promising technologies such as plant and soil conditioners, and remote sensing applications.
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