Wenqing Zhang, Yuanchuang Lu, Sven Sommer, Yang Wang, Ying Liu, Gang Wang, Kun Zhu
ABSTRACT
The incorporation of crop straw creates decomposition hotspots, and the microscale variability of pH in soil-straw hotspots is a critical driver of microbial activity and nutrient cycling. However, little is known about the pH dynamics at the soil–straw interface, particularly under conditions of fluctuating moisture. In this study, we applied high-resolution planar optode imaging to monitor in situ microscale pH dynamics at the straw–soil interface in a typical fluvo-aquic soil during three consecutive drying–rewetting cycles. Two straw incorporation patterns—heterogeneous (patch) and homogeneous (uniform)—were compared to assess their effects on localized pH variations. The heterogeneous straw treatment induced pronounced acidification hotspots (pH < 6.6) concentrated around straw patches. During wetting, the acidic zones expanded radially outwards, accompanied by a progressive steepening of the pH gradient (up to 0.10 units mm−1). Upon drying, water limitation caused these zones to contract inwards as the pH gradient flattened. In contrast, the homogeneous treatment exhibited dispersed, less intense acidification (pH 6.7–6.9) with smaller spatial and temporal fluctuations. Repeated drying–rewetting cycles promoted cyclic accumulation and depletion of formic and acetic acids at the straw–soil interface. The magnitude of both acidification and cation release (Ca2+, Mg2+, and K+) diminished across successive cycles, indicating the progressive depletion of labile straw components. These findings highlight the importance of straw spatial arrangement in shaping microscale soil acidification under moisture fluctuations, offering valuable insights for optimizing crop residue management and predicting soil biogeochemical responses.
European J Soil Science - 2025 - Zhang - Mapping Microscale pH Dynamics at Soil Straw Interfaces Under Fluctuating Moisture.pdf