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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.
Searching for Sustainable-Irrigation Issues of Clementine Orchards in the Syrian Akkar Plain: Effects of Irrigation Method and Canopy Size on Crop Coefficients, Transpiration, and Water Use with SIMDualKc Model
Publication . Darouich, Hanaa; Karfoul, Razan; Ramos, Tiago B.; Moustafa, Ali; Pereira, Luís Santos
Citrus is one of the most valuable crops in Syria, with the largest production areas in the
Tartus and Latakia provinces. Water-saving policies have been adopted to modernize the irrigation
systems and increase water productivity. Following dedicated research, this study aimed to evaluate
the water balance in clementine trees irrigated with diverse methods and schedules using the
SIMDualKc software model. Two experiments are reported: one with 10–14 years old trees irrigated
with different methods (20072011) and the other with the same trees but now 1820 years old,
irrigated with different schedules (20152019). The SIMDualKc model successfully simulated the
soil water contents measured in the various field plots, with root mean square error values lower
than 0.004 m3 m3 and modeling efficiencies up to 0.83. The model-calibrated standard basal crop
coefficients (Kcb) were approximately constant throughout all growing stages, assuming values of
0.540.55 for the mature trees having smaller height (h) and fraction of ground cover (fc), and 0.64 for
older trees with larger canopies, i.e., larger h and fc. With drip irrigation, single Kc had a higher value
(1.14) at the end, non-growing, and initial stages, and a lower value (0.75–0.76) during mid-season
(Kc mid), because precipitation was lesser then, contributing less to soil evaporation. On the other
hand, Kc values were nearly constant with micro-sprinkler and surface irrigation techniques because
the ground was fully wetted. The Kcb values derived from the fraction of ground cover and height
(A&P approach) were similar to those obtained from the model, thus showing that the A&P approach
represents a practical alternative to estimate Kcb in the practice of irrigation management. The soil
water balance further revealed a large weight of the terms corresponding to the non-beneficial water
consumption and non-consumptive water use when the fraction wetted was large and the application
efficiencies were low. These terms were reduced, namely, evaporation losses when drip irrigation
was used. This study, thus, provides a valuable tool for improving the irrigation management, water
saving, and water productivity of Syrian citrus production systems
Salts dynamics in maize irrigation in the Hetao plateau using static water table lysimeters and HYDRUS-1D with focus on the autumn leaching irrigation
Publication . Ramos, Tiago B.; Liu, Meihan; Paredes, Paula; Shi, Haibin; Feng, Zhuangzhuang; Lei, Huimin; Pereira, L.S.
Soil salinization problems are widespread in the Hetao plain, Inner Mongolia, resulting from arid climate con-
ditions, a shallow saline water table, poor irrigation water management, and insufficient drainage. This study
follows previous research aimed at evaluating crop water use and controlling the salinity build-up in the region,
namely using weighing and static water table lysimeters to parameterize a water balance model aimed at the
development of appropriate irrigation scheduling. Two sets of five static water table lysimeters, which fixed
depths ranged from 1.25 to 2.25 m, were used over two maize crop seasons. The mechanistic HYDRUS-1D model
was further used to daily predict measured data on soil water contents, boundary fluxes in the interface between
the saturated and unsaturated zones, the electrical conductivity of the soil saturation paste extract (ECe), and the
actual crop evapotranspiration (ETc act). The soil water balance helped quantify the combined effect of water and
salinity stresses on root water uptake as well as groundwater fluxes into the rootzone. The salt balance showed
that the salinity build-up was much related to irrigation and capillary fluxes, and that the autumn irrigation
carried out during the non-growing season was essential for controlling soil salinity. The efficiency of the autumn
irrigation much depended on groundwater depth and the amount of water applied for salt leaching, with the best
results found for the lysimeters with water table depths at 2.0 and 2.25 m (85–100%) for irrigation depths ≥ 220
mm. The lysimeters with shallower water tables never showed a leaching efficiency higher than 88%. This
research shows that the sustainability of irrigation in Hetao depends on finding adequate solutions for controlling
the depth of the saline groundwater, minimizing capillary fluxes to the rootzone, and developing consequent
approaches for autumn irrigation leaching.
Setting irrigation thresholds for building a platform aimed at the improved management of Citrus orchards in coastal Syria
Publication . Darouich, Hanaa; Karfoul, Razan; Ramos, Tiago B.; Pereira, Luís S.
Citrus is one of the most valuable crops in Syria, with the largest production areas being in
the coastal provinces of Tartus and Latakia, where this study was performed. A companion paper
reported on the basal crop coefficients derived from the field water balance and on the performance
assessment of various irrigation methods used in a citrus orchard located in the same region. That
study evidenced the need for the improved management of irrigation water, mainly reducing water
applications and increasing productivity, thus leading to the current research. The main objectives
consisted of (i) providing a set of reliable basal (Kcb) and average (Kc) crop coefficients to be used
in practice in the citrus orchards of the Syrian coastal area, while accounting for the diversity of
characteristics observed; (ii) to estimate the seasonal consumptive use of typical orchards under
different climate-demand and deficit-irrigation scenarios; and (iii) to assess possible water savings
and related yield reductions. The previously calibrated water balance model SIMDualKc was used
for these purposes. The computed Kcb values for the mid-season and average demand for water
ranged from 0.52, when the plant density was low, to 0.84, when plant density was very high. The
corresponding Kc values, which further reflected the impact of drip irrigation on controlling soil
evaporation, were 0.72 and 0.97, respectively. Overall, the consumptive use of water was estimated to
range from 867 to 1573 mm. The assessed water-saving scenarios consisted of adopting increased
management-allowed depletion (MAD) thresholds relative to the p depletion fraction for no stress:
MAD = 1.05, 1.10, 1.20, and 1.30 p. For trees under a very high climatic demand, water savings ranged
from 12 to 34%, but the yield losses induced by the water deficits ranged from 8 to 48%. Although
the selection of optimal strategies should be based upon economic terms, these may only be used
when the Syrian economy recovers from civil war and the current crisis. The present results show the
feasibility of adopting such MAD thresholds for building an irrigation management platform. The
data provided by the current study are valuable because they can be efficiently used to support of the
irrigation management of Syrian citrus production systems.
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.
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Entidade financiadora
Fundação para a Ciência e a Tecnologia
Programa de financiamento
CEEC IND 2017
Número da atribuição
CEECIND/01152/2017/CP1461/CT0019