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Projeto de investigação
Sustainable use of soil and water for improving crops productivity in irrigated areas
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Water use, soil water balance and soil salinization risks of Mediterranean tree orchards in southern Portugal under current climate variability: Issues for salinity control and irrigation management
Publication . Ramos, Tiago B.; Darouich, Hanaa; Oliveira, Ana R.; Mohammad, Farzamian; Monteiro, Tomás; Castanheira, Nádia; Paz, Ana; Alexandre, Carlos; Gonçalves, Maria C.; Pereira, L.S.
Secondary salinization has long been reported in the Roxo irrigation district (RID), southern Portugal, due to the
use of saline-prone irrigation water and the existence of poorly structured soils. This study assessed the soil water
and salt budgets in nine commercial orchards located in the RID using the multiple ion chemistry module
available in the HYDRUS-1D model during the 2019 and 2020 growing seasons. The studied crops were almond,
olive, citrus (orange, mandarin, and clementine), and pomegranate. The model successfully simulated soil water
contents measured in the different fields but there was a clear underestimation of the electrical conductivity of
the soil saturation paste extract (ECe) in some locations, while simulations of the sodium adsorption ratio (SAR)
were generally acceptable. Modeling errors were mostly associated with missing information on fertigation
events rather than related to the effects of irrigation water quality. The water and salt balances were also
computed for the 1979–2020 period. Considering the probability of non-exceedance of salt accumulation during
this period, the risk of salinity build-up was high to very high for the very dry years in most fields, except in the
citrus sites. The factors influencing the salt accumulation were the irrigation strategy, the seasonal irrigation and
rainfall depths, the duration of the crop growth period, the rainfall distribution in the late and non-growing
stages, the soil drainage conditions, and the irrigation water quality. For the current climate conditions and
irrigation water quality, the risk of soil salinity levels affecting crop development and yields was found to be
minor. This means that, despite salts tended to accumulate in the rootzone over a season, under current conditions the salinity stress did not reach harmful levels for plants. Only in two of the study sites, there was a need
to promote salt leaching. Hence, this study shows that soil salinization risks in the study area are low but, for
given locations during drier seasons, there is a need for tailored irrigation solutions aimed at the conservation of
soil and water resources.
Water use and soil water balance of Mediterranean tree crops assessed with the SIMDualKc model in orchards of southern Portugal
Publication . Ramos, Tiago B.; Darouich, Hanaa; Oliveira, Ana R.; Farzamian, Mohammad; Monteiro, Tomás; Castanheira, Nádia; Paz, Ana; Gonçalves, Maria C.; Pereira, Luís S.
Orchards consist of complex agricultural systems, with a variety of characteristics (planting density, tree height,
training system, canopy cover, irrigation method, interrow management) influencing crop evapotranspiration
(ETc). Thus, irrigation water management requires finding crop coefficients (Kc) that represent the characteristics
of local orchards, evidencing the need for site specific data. The main objective of this study was to derive the Kc
of almond, olive, citrus, and pomegranate orchards in Alentejo, southern Portugal, wherein they became
dominant over the last decade. Monitoring was carried out in nine orchards, which management decisions were
performed by the farmers. The ETc was estimated from the soil water balance computed for each orchard using
the FAO56 dual-Kc approach with the SIMDualKc model. The model successfully simulated the soil water contents measured in the various fields along two growing seasons, with root mean square error values lower than
0.005 m3 m− 3 and modeling efficiencies from 0.363 to 0.782. The estimated basal crop coefficients (Kcb) for the
initial, mid- and end-seasons were respectively 0.22, 0.58, and 0.50 for almond; 0.32–0.33, 0.35–0.36, and
0.33–0.34 for olive; 0.40, 0.40–41, and 0.40–0.41 for citrus; and 0.24, 0.60, and 0.52 for pomegranate. Small
variations in olive and citrus Kcb values were found to be related to differences in the fraction of the ground
covered by trees’ canopies and tree height. The single Kc values, which included the component relative to soil
evaporation, were also estimated. Furthermore, evaluation of the soil water balance in the nine case studies
showed salinity effects in one almond orchard, mild irrigation water deficits in olive systems, and large nonconsumptive water use in citrus and pomegranate orchards. These results evidence the need for better management of orchards irrigation water in the region, and the current study provides for reliable information on the
Kc of tree crops to support improving the management of local orchard systems and the preservation of soil and
water resources. Aimed at these resources and the sustainability of their use, simulated alternative irrigation
schedules were performed, which identified possible water savings of 20 mm in case of olives, up to 855 mm for
citrus.
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Entidade financiadora
Fundação para a Ciência e a Tecnologia
Programa de financiamento
3599-PPCDT
Número da atribuição
PTDC/ASP-SOL/28796/2017