Effects of Biochar and Arbuscular Mycorrhizal Fungal Inoculation on Soil Phosphorus Availability and Growth of Pisum sativum (Dwarf Snap Pea)

Abstract

Limited plant-available phosphorus (P) in agricultural soils and the depletion of finite phosphate rock reserves present major challenges to sustainable food production. Biochar and arbuscular mycorrhizal fungi (AMF) are independently recognised as strategies to enhance soil P availability and plant productivity, yet their combined effects in organic soils and on legume crops remain poorly understood. This study investigated the effects of wood-derived biochar applied at 2% and 10% (w/w) and commercial AMF inoculation, individually and in combination, on soil physicochemical properties, plant productivity, and AMF root colonisation in dwarf snap pea (Pisum sativum L.) grown under pot conditions in organic soil at Drew University, Madison, New Jersey, USA. Six treatments were arranged in a randomised complete block design with five replications: control (T0), AMF only (T1), 2% biochar (T2), 2% biochar + AMF (T3), 10% biochar (T4), and 10% biochar + AMF (T5). Soil moisture content, pH, available P, and AMF root colonisation differed significantly among treatments (p ≤ 0.01), while plant biomass, shoot height, root length, and tissue phosphorus did not. The co-application of 10% biochar and AMF (T5) produced the highest available soil P (43.27 ± 2.14 ppm), significantly exceeding all other treatments including the control and single-amendment treatments. This synergistic effect was absent at the 2% biochar rate, indicating a dose-dependent threshold for the biochar-AMF interaction. AMF root colonisation increased progressively with biochar rate, peaking at 70 ± 3.8% in T5. Soil moisture was greatest under 10% biochar alone (T4; 37 ± 1.94%), while AMF-only treatment (T1) recorded the lowest pH (6.61 ± 0.05), consistent with organic acid exudation during phosphate solubilisation. The absence of significant plant growth responses is attributed to the abbreviated experimental duration relative to the cultivar's recommended maturation period. These findings demonstrate that co-application of wood-derived biochar at 10% with AMF inoculation synergistically enhances soil phosphorus availability and root colonisation in organic soil, supporting its potential as a low-input strategy for reducing synthetic P fertiliser dependency in small-scale and organic agricultural systems.