The growing water scarcity is a real concern in Mediterranean countries characterized by semi-arid or arid climate and particularly in Tunisia, where it is crucial to improve water use efficiency without affecting agricultural productivity. The importance of identifying methods and technologies to optimize water use in agriculture has been recognized worldwide in response to the limited water availability. The main objective of the paper was to verify the potential of infrared thermography and simulation models to assess the response of potato crop parameters and yield to water and salt stress, under the environmental conditions of central Tunisia. Field activities were carried out in 2015 at the High Agronomic Institute of Chott Mariem, Sousse (Tunisia), in order to investigate the crop response to two water qualities (electrical conductivity of 1.6 and 4.2 dS m-1) and two different seasonal irrigation depths (full and deficit irrigation) supplied with a subsurface drip irrigation system. A weather station installed in the field allowed measuring all the climate variables affecting crop transpiration, whilst soil water contents were monitored by using the Time Domain Reflectometry (TDR) technique and soil salinity with direct measurements of saturated extract electrical conductivity acquired on disturbed soil samples. Root length, leaf area and leaf temperatures were also measured at different stages of vegetative growth. Soil physical and hydraulic properties, as well as hydraulic characteristics of the installed emitters were also evaluated at University of Palermo. The experimental database also allowed the application of Hydrus-2D model to simulate water and salt stress. The achieved results evidenced that in Tunisia considerable water savings are possible if irrigation is scheduled on the basis of the monitored climate variables, soil and/or plant water status. Field experiments showed that the rooting depth, leaf area and crop yield are strongly affected by the seasonal amount and quality of applied water. In particular, crop yield decline resulted in 17.0 t/ha per each 100 mm decrease of applied water, when water is characterized by the better quality and in 12.0 t/ha in the other case. An increase of 1.0 dS m-1 of water electrical conductivity, determined a yield decline rate of about 10%. The high variability on crop yield observed within the treatments was associated to the variability of emitters’ flow rate mainly due to possible clogging phenomena, rather than emitters’ quality or deficiency in field distribution uniformity. When considering the thermal image analysis, it was demonstrated that crop water stress index (CWSI) is strongly correlated to soil matric potential, so that handled infrared thermography can be considered a powerful tool for irrigation scheduling of potato crop. Moreover, it was observed that the rate of maximum evapotranspiration reduction, estimated by model simulations, resulted fairly well correlated with the corresponding CWSI obtained by thermal images, thus evidencing the suitability of Hydrus-2D model to assess the effects of water and saline stress on crop transpiration and to identify irrigation scheduling parameters aimed to optimize water use efficiency.

Potential of thermal images and simulation models to assess water and salt stress: Application to potato (Solanum Tuberosum L.) in central Tunisia

RALLO, GIOVANNI;
2017-01-01

Abstract

The growing water scarcity is a real concern in Mediterranean countries characterized by semi-arid or arid climate and particularly in Tunisia, where it is crucial to improve water use efficiency without affecting agricultural productivity. The importance of identifying methods and technologies to optimize water use in agriculture has been recognized worldwide in response to the limited water availability. The main objective of the paper was to verify the potential of infrared thermography and simulation models to assess the response of potato crop parameters and yield to water and salt stress, under the environmental conditions of central Tunisia. Field activities were carried out in 2015 at the High Agronomic Institute of Chott Mariem, Sousse (Tunisia), in order to investigate the crop response to two water qualities (electrical conductivity of 1.6 and 4.2 dS m-1) and two different seasonal irrigation depths (full and deficit irrigation) supplied with a subsurface drip irrigation system. A weather station installed in the field allowed measuring all the climate variables affecting crop transpiration, whilst soil water contents were monitored by using the Time Domain Reflectometry (TDR) technique and soil salinity with direct measurements of saturated extract electrical conductivity acquired on disturbed soil samples. Root length, leaf area and leaf temperatures were also measured at different stages of vegetative growth. Soil physical and hydraulic properties, as well as hydraulic characteristics of the installed emitters were also evaluated at University of Palermo. The experimental database also allowed the application of Hydrus-2D model to simulate water and salt stress. The achieved results evidenced that in Tunisia considerable water savings are possible if irrigation is scheduled on the basis of the monitored climate variables, soil and/or plant water status. Field experiments showed that the rooting depth, leaf area and crop yield are strongly affected by the seasonal amount and quality of applied water. In particular, crop yield decline resulted in 17.0 t/ha per each 100 mm decrease of applied water, when water is characterized by the better quality and in 12.0 t/ha in the other case. An increase of 1.0 dS m-1 of water electrical conductivity, determined a yield decline rate of about 10%. The high variability on crop yield observed within the treatments was associated to the variability of emitters’ flow rate mainly due to possible clogging phenomena, rather than emitters’ quality or deficiency in field distribution uniformity. When considering the thermal image analysis, it was demonstrated that crop water stress index (CWSI) is strongly correlated to soil matric potential, so that handled infrared thermography can be considered a powerful tool for irrigation scheduling of potato crop. Moreover, it was observed that the rate of maximum evapotranspiration reduction, estimated by model simulations, resulted fairly well correlated with the corresponding CWSI obtained by thermal images, thus evidencing the suitability of Hydrus-2D model to assess the effects of water and saline stress on crop transpiration and to identify irrigation scheduling parameters aimed to optimize water use efficiency.
2017
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11568/833418
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