Effect of Almond\nResidue Soil Amendments and Irrigation\nRegiment on Organic Acid Development and Transport in Soil

Preplant soil disinfestation often relies on harmful\nsoil fumigants;\nhowever, the efficacy of sustainable alternatives using biomass amendment\nfermentation is limited to tillage depths (0–15 cm). This soil\ncolumn study evaluated whether increasing the irrigation frequency\ncould promote anaerobic pest-suppressive conditions in deeper soils\nby leaching biocidal fermentation products (organic acids) from surface-applied\namendments. Columns received either singular (standard) or weekly\nirrigation. Almond hulls, an agricultural byproduct, were either incorporated\n0–15 cm into soil or applied as a surface mulch. Oxygen and\norganic acids were measured at 4–50 cm over 21 days, and the\nexperiment was conducted in triplicate. Anaerobic conditions (3% O<sub>2</sub>) were achieved after 5 days, corresponding to acetic acid\naccumulation below amended layers: maximum concentrations ranged from\n42 to 93 mM at 19–50 cm depths. Additional irrigation further\nincreased concentrations in the deepest layer (50 cm) by almost 50%,\ndemonstrating that water management can enable strategies for depth-dependent\nsoil pest control. This may be particularly valuable for soil disinfestation\nahead of the establishment of deep-rooted crops.