Ouaadi et al. (2026) Combined effect of different irrigation and fertilization scenarios on wheat and barley development and their C-band radar response in a semi-arid region

Identification

• Journal: Agricultural Water Management
• Year: 2026
• Date: 2026-09-11
• Authors: Nadia Ouaadi, Ayoub Medkour, Jamal El Farkh, Bouchra Ait Hssaine, Emna Ayari, Lahcen Ousayd, Zoubair Rafi, Abdelghani Chehbouni
• DOI: 10.1016/j.agwat.2026.110770

Research Groups

• CRSA, Mohammed VI Polytechnic University, Ben Guerir, Morocco
• VPE, Swedish University of Agricultural Sciences, Umeå, Sweden
• IWRI, Mohammed VI Polytechnic University, Ben Guerir, Morocco

Short Summary

This study investigates the combined effects of various irrigation and fertilization scenarios on wheat and barley development and their C-band radar response in a semi-arid region of Morocco. It reveals that irrigation is the primary factor determining crop development and yield, while C-band radar data shows promising potential for monitoring crop growth and water stress.

Objective

• To assess the combined impact of different irrigation and fertilization scenarios on wheat and barley biomass evolution (straw and heads) and yield.
• To evaluate the potential of C-band radar data (Sentinel-1) to monitor the effects of these scenarios, including specific events like water stress.
• To investigate whether fertilizer application can enable high biomass production and yield if water input is reduced in a semi-arid environment.

Study Configuration

• Spatial Scale: 15 wheat and barley fields (ranging from 0.179 hectares to 0.329 hectares) in the Haouz plain, Morocco.
• Temporal Scale: One agricultural season (167 days) from December 17, 2024, to June 2, 2025. In situ measurements were collected at near-weekly to daily intervals, Sentinel-1 data every 6-12 days, and Sentinel-2 data every 5 days (cloud-free).

Methodology and Data

• Models used:
  • FAO-56 single approach (Penman-Monteith equation) for estimating daily crop evapotranspiration (ETc).
  • Multiple linear regression model for statistical analysis of yield responses.
• Data sources:
  • In-situ measurements:
    • Vegetation variables: Above-ground biomass (AGB), vegetation water content (VWC), stem and head density, canopy height, and crop yield.
    • Soil variables: Surface soil moisture (SSM) using thetaprob ML3 and Time Domain Reflectometry (TDR) stations at 5 cm, 15 cm, 30 cm, and 60 cm depths.
    • Land surface temperature (Ts) using infrared thermometers (Apogee sensors).
    • Irrigation amounts (measured by flowmeters and field notebooks).
    • Fertilization amounts (base dressing NPK, and fertigation with Ammonium nitrate 33.5% and Sulphate Of Potassium 0-0-50).
    • Weather data: Air temperature (Ta), wind speed, air humidity, solar radiation, and rainfall from a meteorological station.
  • Remote sensing data:
    • Sentinel-1 (C-band Synthetic Aperture Radar): Backscattering coefficient (σ0 VV, σ0 VH), interferometric coherence (ρVV, ρVH), backscattering ratio (σ0 VH/σ0 VV), radar vegetation index (RVI), and interferometric coherence ratio (ρVH/ρVV).
    • Sentinel-2 (Multispectral): Normalized Difference Vegetation Index (NDVI) from red and near-infrared bands.

Main Results

• Irrigation was identified as the main factor determining vegetation development and yield in the semi-arid region, showing a strong correlation of 0.86 (p < 0.001) between seasonal irrigation amount and final yield.
• Fertilization increased the percentage of straw biomass by 13–22% across all irrigation scenarios.
• Applying only 25% of the recommended fertilizer amount resulted in a 26% decrease in yield. Conversely, high fertilization (100%) combined with severe deficit irrigation (30%) led to significant reductions in total above-ground biomass (up to 47%), head biomass (up to 66%), and yield (up to 76%).
• The C-band backscattering coefficient (σ0 VV and σ0 VH) demonstrated greater sensitivity to vegetation growth differences between fields compared to interferometric coherence and NDVI.
• A period of water stress, characterized by a decrease of 1.12 kg/m² in VWC and 0.13 m³/m³ in SSM, caused a notable decrease of 1.81 dB in σ0 VV and 2.82 dB in σ0 VH.
• Fertilization influenced the soil moisture profile, with well-fertilized fields exhibiting faster water uptake in the root zone (e.g., a significantly steeper drawdown rate at 60 cm depth for W4 compared to W3, t = 24.67, df = 28, p < 0.001).

Contributions

• Provides a comprehensive analytical study on the synergistic effects of irrigation and fertilization on wheat and barley development and their C-band radar response in a semi-arid region, addressing a gap in literature that often focuses on individual drivers.
• Quantitatively demonstrates the predominant role of water availability over fertilization in determining crop yield in semi-arid environments.
• Highlights the promising potential of C-band Sentinel-1 radar data for monitoring crop growth and detecting water stress, including specific quantitative changes in backscatter during stress events.
• Offers a foundational analysis for future modeling studies aimed at optimizing water and fertilizer use efficiency and advancing precision agriculture strategies.

Funding

• Center of Remote Sensing Applications (CRSA) at Mohammed VI Polytechnic University (UM6P)
• OCP S.A. (Office Chérifien des Phosphates)
• Projects: EOAFRICA THESM, PRIMA AQUEDUCT, AFOEP CRSA-UM6P and MIT (grant N◦89), FIRMA (Grant n◦AS140).

Citation

@article{Ouaadi2026Combined,
  author = {Ouaadi, Nadia and Medkour, Ayoub and Farkh, Jamal El and Hssaine, Bouchra Ait and Ayari, Emna and Ousayd, Lahcen and Rafi, Zoubair and Chehbouni, Abdelghani},
  title = {Combined effect of different irrigation and fertilization scenarios on wheat and barley development and their C-band radar response in a semi-arid region},
  journal = {Agricultural Water Management},
  year = {2026},
  doi = {10.1016/j.agwat.2026.110770},
  url = {https://doi.org/10.1016/j.agwat.2026.110770}
}