Synergistic effects of biochar and poultry manure improve soil water availability and drought tolerance in Ananas comosus

Enhancing soil water availability is critical for improving the drought resilience of crops in coarse-textured tropical soils. This study aimed to evaluate the effects of charcoal fines and poultry litter on pineapple ( Ananas comosus ) water status, comparing a process-based, flux-based model (FBM) with the traditional FAO-56 method for a mechanistic assessment. The experiment was conducted in a greenhouse using a completely randomized factorial design with nine treatments and four replications. Treatments included various combinations of biochar and/or poultry litter added at 5% and 10% on a volume-per-volume (v/v) basis. Soil hydraulic properties, root distribution, and potential transpiration were measured and estimated to determine plant water availability and drought stress. The combined application of charcoal fines and poultry litter was essential for significantly increasing both total (TAW) and readily available water (RAW). In contrast, the sole application of charcoal fines was detrimental, reducing RAW by up to 16.5%. Modeling revealed that the direct enhancement of soil hydraulic properties, rather than increased root growth, was the dominant mechanism driving these improvements. Furthermore, RAW calculated via the FBM proved to be a more sensitive indicator of plant performance, showing significant correlations with biomass and water use efficiency, which traditional metrics failed to capture. We conclude that for industrial byproducts like charcoal fines, co-application with an organic source is a necessary strategy to improve soil water retention and mitigate crop water stress.