Biochar Effects On Nitrogen Fertilizer in a Loamy Sand of the Southeastern United States.

Depending on feedstock and pyrolysis conditions, biochar may have a high carbon concentration,  sorptive properties, and variable pHs that can affect the utilization and transformation of nitrogen fertilizer. We investigated the effect of eight different biochars on sorption and volatilization of ammonium nitrate in a Norfolk soil (Fine-loamy, kaolinitic, thermic Typic Kandiudults ).  Soil was amended  with low temperature (250-400 ^oC) and high temperature (500 – 700 ^oC) biochars made from pecan shells, peanut hulls, poultry litter, and switchgrass at a rate of  44 Mg ha^-1 .  The treatments with and without ammonium nitrate fertilizer addition were incubated for 120 days and leached four times with deionized water during the incubation. Cold and hot potassium chloride (KCl) extractions as well as phosphate-borate (PB) and sodium hydroxide (NaOH) distillations were used to measure N fractions before and after incubation. The pH of the biochars ranged from 5.4 in the low temperature switchgrass biochar (LTSW produced at 250° C) to 10.3 in the high temperature poultry litter biochar (HTPL produced at 700° C).  The biochars altered the poorly buffered soil pH before incubation with a 3.8 unit increase seen in the HTPL treatment before incubation. Large reductions in the cold and hot KCL extractable NH₄-N occurred in the pre-incubation treatments where the soil pH was above 7.5. Additional work confirmed the decrease in NH₄-N concentrations in this fraction was due to volatilization rather than sorption to the biochar.  Potentially mineralizable nitrogen (PMN) increased after incubation in the control and most of the biochar amended soils where no N was added.  When N fertilizer was added, a similar increase was not seen though the effect depended on the biochar amendment.