Crude glycerol, a biodiesel byproduct, used as a soil amendment to temporarily immobilise and then release nitrogen

Loss of nitrate-nitrogen (NO3−–N) from Midwestern U.S. agricultural fields can impair water quality and be an economic loss to farmers. Winter cover crops have shown promise as a remedy, but low adoption illustrates the need for alternatives. Here, we tested whether adding carbon (C)-rich soil amendment (i.e., crude glycerol, biodiesel byproduct) increase microbial biomass (MB) promote N immobilisation under various conditions then determined when immobilised would released. We conducted laboratory incubation with full factorial combination four glycerol rates (0, +117, +468 +1872 mg C kg−1 soil), three supplemental NO3−–N +10 +40 kg−1) two soils (Clarion clay loam Sparta loamy sand). Soil inorganic (NH4+–N NO3−–N) MB were measured at seven time points, respectively, across 98 days period. Across all treatments, increased MBN in both short term (7 days; 4%–1137% compared no addition) long (98 10%–169%) decreased increasing rate glycerol. Adding caused net 21%–61% (+117 ~100% (+468 control. Some that was likely released through turnover, timing release depended on added rate. 40 showed nearly twice mineralisation than or applied – providing evidence priming. Overall, has potential use temporarily immobilise make some crop available turnover. Highlights Crude by-product, evaluated reduce nitrate. Glycerol strongly nitrate conditions. temporary, mineralised lower rates, type affected immobilisation-mineralisation dynamics.