Climate variability governs mulch performance and stability in date palm (Phoenix dactylifera L.) in arid oases

Résumé

Introduction Plastic mulch recommendations for date palm cropping systems in arid oases rest on demonstration trials conducted in favorable seasons. Yet the yield value of mulch-induced phenological advancement may depend on whether the season’s thermal regime places reproductive development within the effective pollination window, a contingency single-season trials cannot expose. Methods We tested this hypothesis across three seasons (2023 baseline, 2024, 2025) using four mulching treatments: no mulch (NM), shredded date palm fronds (SDPF), polyethylene film over SDPF (PP+SDPF), and polypropylene woven ground cover over SDPF (PWGC+SDPF), on 64 mature Phoenix dactylifera L. cv. Najda trees at Errachidia, Morocco. Canopy development, spathe production, and marketable yield were recorded on individually tagged trees, and inter-seasonal stability was assessed using the Alternate Bearing Index and a Risk Index. Results PP+SDPF maintained the largest canopy in both 2024 and 2025, whereas treatment effects on spathe production and yield differed between seasons. In 2024, PP+SDPF recorded a marketable yield of 29.92 ± 3.56 kg tree −1 , 4.2× the unmulched control; in 2025, it fell to the lowest marketable yield recorded (11.84 ± 2.22 kg tree −1 ), 7.93 kg tree −1 below the unmulched control (treatment × season interaction: p < 0.001). The association between frond number and spathe count was significant in 2024 (r s = +0.455, p < 0.001) but not in 2025 (r s = +0.206, p = 0.122), indicating that relationships among canopy development, spathe production, and yield differed between seasons. Across three seasons, PWGC+SDPF achieved the lowest Alternate Bearing Index (0.419 ± 0.065) and Risk Index (8.3%). Discussion These results are consistent with the phenological-window hypothesis and indicate that mulch permeability was associated with lower inter-seasonal yield volatility under the conditions of this trial. They suggest a possible trade-off between productivity and stability: PWGC+SDPF was associated with lower observed inter-seasonal variability, whereas PP+SDPF achieved a higher three-season mean yield but greater variability. As the trial was conducted at a single site with a single cultivar over three seasons, these relationships require verification across other locations, cultivars, and climates before broader recommendation.

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