Microplastic Contamination Alters Soil Hydraulic Properties and Inhibits Maize Growth: A Factorial Assessment Across Contrasting Soil Textures.

Microplastic pollution in agricultural soils constitutes an emerging threat to food security, yet the interactive influence of soil texture and contamination intensity on crop productivity remains inadequately characterized. A 3 × 4 factorial pot experiment was conducted under controlled conditions at Bendeghe Ekiem, Cross River State, Nigeria, to evaluate the combined effects of high-density polyethylene (HDPE) microplastic contamination at four levels (0, 1, 5 and 10 g/kg) across three contrasting soil textures (Sandy Loam, Loamy Sand and Sandy Clay Loam) on selected soil hydraulic properties and the early growth of maize (Zea mays L.). Soil samples were collected from 0–15 cm depth, air-dried, sieved (2 mm) and characterized using standard laboratory procedures, while water retention parameters were derived using SPAW Hydrology software (version 6.02.74). Maize growth indices (plant height, stem girth, fresh biomass and leaf number) were recorded at four weeks after planting, and data were subjected to two-way analysis of variance (ANOVA) with treatment means separated using the Least Significant Difference (LSD) test at p < 0.05. Significant soil type × contamination level interactions were observed for permanent wilting point (LSD = 1.77), field capacity (LSD = 4.41), available water (LSD = 0.027), saturated hydraulic conductivity (LSD = 22.6) and hydraulic conductivity (LSD = 3.16 × 10⁻⁶). Sandy Loam recorded a 2.8-fold higher hydraulic conductivity (3.27 × 10⁻⁶ mm/hr) than Loamy Sand (1.17 × 10⁻⁶ mm/hr). Maize growth was significantly suppressed in Sandy Clay Loam (plant height = 27.55 cm; stem girth = 4.56 mm; biomass = 0.61 g) relative to Sandy Loam and Loamy Sand (p < 0.05). Interestingly, the highest contamination level (10 g/kg) produced increased stem girth (6.26 mm) and leaf number (7.61), suggesting possible adaptive responses or modifications in soil–plant water relations. The findings indicate that microplastic contamination disrupts soil hydraulic functioning in a texture-dependent manner, with finer-textured soils being more vulnerable to growth suppression. The non-linear dose–response pattern observed implies complex underlying mechanisms warranting further molecular-scale investigation. The study underscores the necessity for texture-specific soil quality thresholds in regulatory frameworks aimed at managing agricultural microplastic pollution in Nigeria and similar tropical agroecosystems.