Anthropogenic Factors Affecting Soil Water Repellency: Comparative Analysis of Fire Events, Microplastic Pollution, and Soil Amendment

Soil water repellency (SWR) is a parameter that can significantly impact agricultural productivity by altering water infiltration, retention, and distribution in soils. This study compares three anthropogenic factors that increase SWR in sandy soils: fire (simulated by burning of soil in a muffle furnace), high-density polyethylene (HDPE) microplastic pollution (5% w/w), and hydrophobic biochar amendment (1% w/w). The severity of water repellency was quantified by measuring the soil-water contact angle (CA). Results demonstrate that all three treatments increased the CA of sandy soils, with HDPE microplastic addition causing the highest relative increase (10.06-fold), followed by hydrophobic biochar addition (3.89-fold), and fire event with 300 °C (4.35-fold). The mechanisms underlying these increases vary: microplastic and biochar introduce new hydrophobic surfaces to the soil matrix, while burning transforms existing organic matter into more hydrophobic compounds. These findings highlight the potential risks of these anthropogenic factors for soil hydrological properties and provide insights for future soil management strategies in agricultural systems.