heating biomass, resulting in a dominantly aromatic chemical structure that is resistant to biological degradation (Baldock and. Smernik, 2002). This process can ...
Journal of Environmental Quality
TECHNICAL REPORTS ATMOSPHERIC POLLUTANTS AND TRACE GASES
Biochar and Nitrogen Fertilizer Alters Soil Nitrogen Dynamics and Greenhouse Gas Fluxes from Two Temperate Soils Jiyong Zheng, Catherine E. Stewart,* and M. Francesca Cotrufo
P
otential environmental benefits of biochar
Biochar (BC) application to agricultural soils could potentially sequester recalcitrant C, increase N retention, increase water holding capacity, and decrease greenhouse gas (GHG) emissions. Biochar addition to soils can alter soil N cycling and in some cases decrease extractable mineral N (NO3− and NH4+) and N2O emissions. These benefits are not uniformly observed across varying soil types, N fertilization, and BC properties. To determine the effects of BC addition on N retention and GHG flux, we added two sizes (>250 and 250 μm) and BC2 (250 250 μm; BC2: 250 μm; BC2: 250 μm; BC2 250 μm; BC2 60% WFPS), and low pH (Burford and Bremner, 1975; Blackmer and Bremner, 1978; Blackmer and Bremner, 1979). www.agronomy.org • www.crops.org • www.soils.org
Because the enzyme responsible for the reduction of N2O to N2 (N2O reductase) is highly pH dependent in activity and in catalytic reactions (Fujita and Dooley, 2007), this has been hypothesized as one mechanism for the observed reduction in N2O efflux after BC addition (Van Zwieten et al., 2009). To assess the effect of pH, we plotted the first 4 d of N2O production against treatment pH and found that in both soils N2O flux was significantly negatively related to pH (Fig. 6). The strongest and logarithmic decrease is in the acidic soil (MN) (R2 = 0.89) (Fig. 6), strongly suggesting a pH control over N2O flux in MN. In the more basic soil (CO), N2O flux was linearly related to soil pH (R2 = 0.384; p = 0.0079) (Fig. 6). The relatively small decrease in N2O after BC addition in CO compared with the large reduction after BC addition in the MN soil suggests that the potential for N2O reduction after BC addition is pH dependent, although there are likely other factors. The liming effect of BC on soils is expected to be transitory, and thus the beneficial effects of BC addition to soil on N2O reduction may diminish over time. Another primary control on N2O production is soil N content. To assess the effect of treatment N content (i.e., soil N + BC N + fertilizer N) on N2O production, we plotted the cumulative N2O flux (to 123 d) from both soils as a function of added N (Fig. 6b). Cumulative N2O flux was remarkably well explained by an increasing exponential relationship with total N content across both soils. Biochar addition significantly decreased the slope of this relationship (BC1 and BC2 combined; R2 = 0.967) (Fig. 1367
Fig. 5. Greenhouse gas balance expressed as CO2 equivalents (mg g soil−1) for Colorado soil (CO) and Minnesota soil (MN) with N and 0N treatments with biochar additions (0BC: no biochar; BC1: >250 μm); BC2: 250 μm; BC2, 250 μm; BC2:
