Doumkou et al. (2026) Effects of complementary irrigation on carob tree (Ceratonia siliqua) physiology and productivity in a Mediterranean semi-arid orchard

Identification

• Journal: Scientia Horticulturae
• Year: 2026
• Date: 2026-01-01
• Authors: Olga Doumkou, Beatriz Lorente, Carlota Ma Martí-Martinez, Jesús Mª Domínguez-Niño, Teresa Munuera-Pérez, Francisco Pedrero Salcedo
• DOI: 10.1016/j.scienta.2025.114590

Research Groups

• Water And Plant Production Department, Centro de Edafología y Biología Aplicada del Segura (CEBAS-CSIC), Murcia, Spain
• SISTEMA AZUD S.A., Alcantarilla, Spain

Short Summary

This study evaluated the effects of complementary irrigation (CI) and deficit complementary irrigation (DCI) on carob tree physiology and productivity in a Mediterranean semi-arid orchard over two years. Results showed that DCI increased production in the second year with higher water use efficiency, while CI improved fruit quality, and physiological measurements proved effective for monitoring tree water status.

Objective

• To increase the physiological understanding and water requirements of the carob tree, a traditional rainfed crop.
• To hypothesize that accurate identification of critical phenological stages combined with rational irrigation adapted to plant water requirements will strengthen physiological condition and significantly improve productivity.
• To propose that appropriate precision agriculture indicators and sensors can effectively support irrigation decision-making, reducing water stress and ensuring more efficient and sustainable carob cultivation.

Study Configuration

• Spatial Scale: 8-hectare commercial carob tree orchard (Ceratonia siliqua, L., cv. Ramillete) in Fuente Álamo de Murcia, Murcia region (South-East of Spain; 37°45’57.1”N, 1°14’39.6”W; 218 m a.s.l.). Tree spacing was 12 m × 12 m.
• Temporal Scale: Two-year experiment (2023–2024).

Methodology and Data

• Models used: SUDIPRO (irrigation system design software from AZUD).
• Data sources:
  • Climatic parameters: Rainfall, reference evapotranspiration (ET0), vapor pressure deficit (VPD), and air temperature (Ta) from Murcia's agricultural information system SIAM.
  • Soil measurements: Soil moisture, temperature, and electrical conductivity (EC) using Teros-12 sensors at 30 cm and 60 cm depths.
  • Plant measurements:
    • Trunk Diameter Variation (TDV) using DDL dendrometers.
    • Stomatal conductance (gs) using a LI-600 porometer.
    • Stem water potential (Ψstem) using a pressure chamber.
    • Leaf temperature using a FLIR thermal camera.
  • Yield and productivity parameters: Total production (kilograms per hectare), irrigation water applied (cubic meters per hectare), total water supplied (irrigation + precipitation, cubic meters per hectare), and productivity (kilograms per cubic meter).
  • Fruit quality: Pod weight, seed weight, pod length, and number of seeds per pod.
  • Soil analysis: Texture, bulk density, pH, and electrical conductivity at 30 cm and 90 cm depths.

Main Results

• The Deficit Complementary Irrigation (DCI) treatment showed increased production in the second year (2024), reaching 1792.62 kg/ha, while Complementary Irrigation (CI) yield decreased to 1057.77 kg/ha.
• CI treatment consistently improved fruit quality, specifically leading to higher seed weight in both years. DCI resulted in longer and heavier pods with more seeds in 2024.
• DCI demonstrated significantly higher water use efficiency (productivity) in both years (3.83 kg/m³ in 2023 and 5.09 kg/m³ in 2024, considering irrigation only) compared to CI (2.05 kg/m³ in 2023 and 2.49 kg/m³ in 2024).
• A negative correlation was observed between stem water potential (Ψstem) and both air temperature (Ta) (R² CI=0.5156, DCI=0.4358) and vapor pressure deficit (VPD) (R² CI=0.5737, DCI=0.4868), with VPD being a more significant indicator.
• Physiological measurements (stomatal conductance, stem water potential, trunk diameter variation) effectively monitored the tree's response to environmental conditions and water stress, showing clear differences between treatments and years.
• Dendrometers were identified as effective continuous sensors for monitoring water status, while stomatal conductance proved useful for spot measurements in the field.
• Soil Water Content (SWC) in the CI treatment was consistently higher and more stable (ranging from approximately 13% to 20%) compared to the DCI treatment (ranging from approximately 11% to 17%).

Contributions

• Provided an important contribution to the ecophysiological understanding of carob trees under different irrigation conditions, highlighting their adaptive responses to water interventions.
• Demonstrated that complementary irrigation, particularly regulated deficit irrigation, can be an effective strategy for enhancing water use efficiency and productivity in carob trees in semi-arid Mediterranean climates.
• Offered insights into the trade-off between yield quantity (favored by DCI in the second year) and fruit quality (higher seed weight in CI).
• Validated the precision of plant-based sensing methods (dendrometers, porometer, pressure chamber, thermal camera) for monitoring carob tree water status and informing irrigation scheduling.
• Laid the groundwork for future studies focused on long-term effects of complementary irrigation and the development of adapted irrigation protocols for carob trees, contributing to sustainable crop intensification in water-limited environments.

Funding

• CICLICA part of the PRIMA project (1727) – Smart agriculture optimization to climate change adaptation
• European Union
• Center for Technological and Industrial Development (CDTI)

Citation

@article{Doumkou2026Effects,
  author = {Doumkou, Olga and Lorente, Beatriz and Martí-Martinez, Carlota Ma and Domínguez-Niño, Jesús Mª and Munuera-Pérez, Teresa and Salcedo, Francisco Pedrero},
  title = {Effects of complementary irrigation on carob tree (Ceratonia siliqua) physiology and productivity in a Mediterranean semi-arid orchard},
  journal = {Scientia Horticulturae},
  year = {2026},
  doi = {10.1016/j.scienta.2025.114590},
  url = {https://doi.org/10.1016/j.scienta.2025.114590}
}