نوع مقاله : مقاله پژوهشی
نویسندگان
1 گروه علوم و مهندسی خاک، دانشکده کشاورزی و منابع طبیعی، دانشگاه تهران، کرج، ایران
2 مؤسسه تحقیقات خاک و آب (SWRI)، سازمان تحقیقات، آموزش و ترویج کشاورزی (AREEO)، کرج، ایران
چکیده
کلیدواژهها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
Background and Objectives: Direct evaporation from bare soil is a major pathway of “green water” loss in arid and semi‑arid regions, and reducing it can improve agricultural water use efficiency. In this study, the effect of inoculating the γ‑PGA‑producing plant growth‑promoting rhizobacterium Bacillus velezensis on evaporation intensity and key hydraulic indicators was evaluated in two contrasting soil textures: sand and sandy clay loam. A complementary objective was to use HYDRUS‑1D inverse modelling as an analytical tool to estimate effective hydraulic parameters and interpret shifts in evaporation regime after inoculation.
Materials and Methods: A column experiment was conducted using PVC cylinders (15 cm height, 4.5 cm internal diameter) packed with a sandy soil (S) and a sandy clay loam (SCL). Treatments consisted of a distilled‑water control (C) and two inoculum levels, with volumetric suspension‑to‑water ratios of 1:5 and 1:10, corresponding to approximately 8×10^8 and 4×10^8 CFU mL⁻¹, respectively. Columns were saturated from the bottom with the assigned solution and then exposed to laboratory evaporation for 10–11 days, while daily mass loss was recorded and converted to cumulative evaporation. The cumulative evaporation time series for each column were used in HYDRUS‑1D (Richards equation with van Genuchten–Mualem functions) to inversely estimate θr, θs, α, n, and Ks. From the fitted parameters, dynamic soil–water indicators such as characteristic evaporation length (Lc), matric potential at field capacity (ΨFC), characteristic time to reach field capacity (tFC) and an effective mean unsaturated hydraulic conductivity (km) were derived to diagnose the mechanisms underlying evaporation changes.
Results: Bacterial inoculation suppressed cumulative evaporation in both textures, with markedly larger effects in the sand: after 11 days, S-B1:5 and S‑B1:10 reduced evaporation by 40.5% and 54.4% versus S-C (3.12 cm → 1.85 cm and 1.42 cm), while SCL‑B1:5 and SCL-B1:10 achieved 6.9% and 12.1% reductions versus SCL-C (3.62 cm → 3.38 and 3.19 cm). HYDRUS-1D reproduced dynamics with high fidelity (R² = 0.996–0.999; low bias/error), enabling robust parameter inference. In the sand, inoculation transformed evaporation from step-like capillarity control into smoother diffusion -dominated trends via near-surface γ-PGA biofilm, disrupting capillary continuity. Metrics confirmed this: Lc decreased (26.5 → 17.6 → 15.4 cm), tFC increased (0.32 → 0.40 → 0.52 days), and ΨFC declined (36.2 → 21.4 → 19.7 cm). SCL showed modest but evident effects, with higher inoculum reducing Lc (~18 cm) and extending tFC (~4.5 days). The 1:10 inoculum often outperformed 1:5, indicating self-limitation at higher densities constraining γ-PGA efficacy. γ-PGA biofilms reshape hydraulic networks, shifting coarse sands from capillary-to diffusion-limited evaporation, wich was captured by VGM parameters and dynamic indicators (Lc↓, tFC↑). Coarser textures yielded greater gains, aligning with capillary theory.
Conclusion: In conclusion, the results support the potential of Bacillus velezensis inoculation as a “bioengineering” strategy to suppress bare‑soil evaporation, particularly in coarse‑textured soils where green‑water conservation is most critical. The observed non‑monotonic response to inoculum level highlights the need to optimise dosage with respect to soil texture and target process. Given the laboratory column scale of this proof‑of‑concept, field‑scale validation and explicit quantification of γ‑PGA/EPS production are recommended to refine the mechanistic interpretation and to develop practical guidelines for the use of B. velezensis in water‑limited cropping systems.
کلیدواژهها [English]
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