Abstract
Biochar can potentially increase soil fertility and sequester carbon by incorporating nutrients and stable black carbon into the soil; however its effect on soil nitrogen (N) and carbon (C) processes is not well understood. A defined methodology to characterize biochar is necessary to predict how specific biochars will affect C and N mineralization. We amended a Tifton soil (Fine-loamy, siliceous, thermic Plinthic Kandiudults) with peanut hull (Arachis hypogaea; PH; 2.1% N) and pine chip (Pinus taeda; PC: 0.4% N) biochar at application rates of 1% and 2% (w/w) and performed a 136-day mineralization study. A companion 24-day mineralization study amended Tifton soil with PH and PC biochar at 2% and their respective feedstocks at equal C rates. Soil C mineralization rates were monitored periodically throughout each study and total N mineralization rates were also measured. In addition, we characterized each biochar using thermogravimetric analysis with mass spectrometer (TGA-MS), proximate analysis, Fourier transform infrared spectroscopy (FTIR), and total mineral analysis to identify biochar characteristics that might correlate with mineralization properties. Limited C (<2%) mineralized from both biochars, but mineralization rates of soil amended with PH biochar were higher than PC biochar. Carbon mineralization correlated well with estimated aliphatic content determined by TGA-MS but not with volatile content indicated by proximate analysis. Nitrogen was not mineralized from either biochar, indicating that plant-based biochar should not be considered a source of N for plant growth. The N in biochar may be contained in the stable aromatic structure of the biochar, as indicated by TGA-MS, and not available to soil microbes.
Highlights
Pyrolysis, an alternative energy process, converts biomass feedstock into syngas, bio-oil, and biochar through rapid heating in the absence of oxygen [1]
Carbon mineralization correlated well with estimated aliphatic content determined by thermogravimetric analysis with mass spectrometer (TGA-MS) but not with volatile content indicated by proximate analysis
Aliphatic content of biochar as measured by TGA may be a better indicator of mineralizable C than volatile matter content as measured by ASTM D5142 method
Summary
An alternative energy process, converts biomass feedstock into syngas, bio-oil, and biochar through rapid heating in the absence of oxygen [1]. It potentially provides carbon-negative, renewable energy if biochar is land applied [2]. Many researchers have proposed that land application of biochar from industrial pyrolysis may create a carbon sink as well as providing productivity benefits [8]. At a similar pyrolysis temperature, a manure-based poultry litter biochar contains greater amounts of nutrients and a higher CEC than a pine chip biochar. Higher pyrolysis temperature (500 °C) compared to lower temperature (400 °C) decreases the CEC and increases most macronutrient concentrations in the biochar. Varying production temperature [10] and feedstock [11]
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