Nitrogen (N) is an essential macronutrient for plant growth; however, excessive use of N fertilizers causes negative environmental impacts. The complexity of the N cycle imposes several challenges in controlling the timing of N availability to plants and preventing N losses from the soil. The objective of this study was to develop a biochar-based slow-release fertilizer (SRF) to reduce N loss and increase N use efficiency in crop production. We performed a laboratory-based assessment of several H3PO4 (5% and 15%) activated biochar-based SRFs, produced from different combinations of biochar to urea (1:2, 1:3, 1:4, and 1:6), calcium lignosulfonate (5%), and paraffin wax (10%). Characterization analyses (SEM-EDS, XRD, FTIR, and XPS) of developed SRFs suggest successful urea grafting onto biochar through the urea amine N mode, without urea crystal structure disruption. The SRFs were more efficient than uncoated urea (control); (1) urea released in aqueous medium was 61-90% in 4320 min for the SRFs vs. 99.6% in 12 min for the control; (2) cumulative N leached from soil columns was 68-71% after 41 leaching events for SRF vs. 99.9% after 4 leaching events for the control; and (3) NH3-N volatilization from soil was 0.2-0.9% for the SRFs vs. 2% for the control. Our results suggest that the developed SRFs are effective for reducing N loss from soil and provide larger quantities of NH4-N to plants for a longer time relative to untreated urea. Future field tests will determine whether the developed SRFs are optimal for synchronizing N release with plant N uptake and thereby improving N use efficiency in crop production systems.

Biochar supported slow-release nitrogen fertilizer for sustainable agriculture

ACS Fall 2021

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