Automated sensor-based quantification of soil water retention and microbial respiration across drying conditions

Abstract

Understanding soil responses to climate-induced precipitation variability is important for improving global carbon models and the development of climate-resilient agriculture. However, our knowledge remains limited regarding factors that influence soil water dynamics and microbial respiration across drying conditions, partially hindered by the lack of easily accessible methodologies. We developed a low-cost, automated, and integrated system to simultaneously quantify microbial respiration and soil water retention in response to drought conditions. This system integrates a CO2 sensor and a digital scale, enabling continuous measurement of CO2 concentration and soil water loss by evaporation when soils are incubated with desiccants inside air-tight chambers. Here we show that the sensor platform provides accurate and repeatable CO2 measurements when compared to a spectroscopy gas analyzer and the alkali trap method. Using the sensor platform, we further demonstrated that averaged microbial respiration of rewetted soil over 4-day incubation declined as management intensity increased following the order of Till ≤ NoTill ≤ Till_fallow ≤ NoTill_fallow = Hay field < Forest. These soils were air-dried for two years before use in incubation experiments, and microbial respiration upon rewetting showed a unimodal response, which rapidly increased and peaked within 12 h except for in forest soils that exhibited a delayed response with respiration peaking at 30 h. Under drying conditions, rewetted soil from the Hay field showed lower water loss than other soils. Volumetric water content at the end of the drying period increased in the order of Till ≤ NoTill < Till_fallow ≤ NoTill_fallow = Hay field < Forest. We posit that this sensor platform provides a powerful tool for functional soil health assessments and fundamental understanding of soil water dynamics and microbial activities in responses to climate-induced water stress.