Biochar Effects On Carbon and Nitrogen Mineralization in a Loamy Sand Soil.

Biochars from different feedstocks and different pyrolysis methods vary in carbon:nitrogen (C:N) ratios and nutrient content which may affect carbon and nitrogen mineralization rates. We investigated C and N mineralization in a loamy sand soil (C:N = 23) amended with two different low-temperature (400^oC) biochars at 22 and 44 Mg ha^-1.  Peanut hull (PN) biochar had high nutrient concentrations with a C:N ratio of 38 and pine chip (PC) biochar contained low nutrients with a C:N ratio of 487. Carbon mineralization rate (k), predicted maximum respired C (rmax) and N mineralization rate were calculated  from data collected periodically over a 136-day incubation study. Mass loss curves of the fresh and incubated biochar were compared using thermogravimetric analysis (TGA) to evaluate the aliphatic content of the biochar.  Mass spectrophometry was used to determine whether N was present in aliphatic or aromatic fractions. The k and rmax for the PN biochar was greater than for the PC biochar with the greatest k and rmax seen at the 44 Mg ha^-1 rate. Although the PN biochar had a greater N concentration, N mineralization was low for both biochars.  Ammonium-N concentrations were lowest at the highest application rate (44Mg ha^-1) for both PN and PC biochar. The TGA analysis indicated mass loss was different between the fresh and incubated biochars, which may be related to aliphatic compounds present in the fresh biochar. Nitrogen appears to be dominantly in the aromatic fraction even in the PN biochar: consequently, it is not readily mineralizable.