ARTICLE pubs.acs.org/est
Interactive Priming of Biochar and Labile Organic Matter Mineralization in a Smectite-Rich Soil Alexandra Keith,† Balwant Singh,*,† and Bhupinder Pal Singh‡ † ‡
Faculty of Agriculture, Food, and Natural Resources, The University of Sydney, NSW, 2006, Australia NSW Department of Primary Industries, P.O. Box 100, Beecroft, NSW 2119, Australia
bS Supporting Information ABSTRACT: Biochar is considered as an attractive tool for long-term carbon (C) storage in soil. However, there is limited knowledge about the effect of labile organic matter (LOM) on biochar-C mineralization in soil or the vice versa. An incubation experiment (20 °C) was conducted for 120 days to quantify the interactive priming effects of biochar-C and LOM-C mineralization in a smectitic clayey soil. Sugar cane residue (source of LOM) at a rate of 0, 1, 2, and 4% (w/w) in combination with two wood biochars (450 and 550 °C) at a rate of 2% (w/w) were applied to the soil. The use of biochars (∼ 36%) and LOM (12.7%) or soil (14.3%) with isotopically distinct δ13C values allowed the quantification of C mineralized from biochar and LOM/soil. A small fraction (0.41.1%) of the applied biochar-C was mineralized, and the mineralization of biochar-C increased significantly with increasing application rates of LOM, especially during the early stages of incubation. Concurrently, biochar application reduced the mineralization of LOM-C, and the magnitude of this effect increased with increasing rate of LOM addition. Over time, the interactive priming of biochar-C and LOM-C mineralization was stabilized. Biochar application possesses a considerable merit for long-term soil C-sequestration, and it has a stabilizing effect on LOM in soil.
’ INTRODUCTION Biochar production, the centuries old tradition of heating organic residues under oxygen limited conditions for application to soil, is now the focus of a rapidly expanding area of research. The interest in biochar is manifold and stems from the observations on old agricultural soils, called Terra Preta, in the Amazon Basin. These soils were treated with charcoal (or biochar) creating much higher soil fertility and carbon (C) content than the neighboring natural soils.1 Based on these observations, biochars produced by pyrolyzing organic waste materials in thermal reactors have been promoted as soil amendments. Biochar application to the soil can reduce greenhouse gas emissions,2 decrease the availability of heavy metals,3 and benefit soil fertility and plant productivity.1,4,5 Furthermore, the demonstrated large mean residence time (MRT) of natural char or biochar in soils and sediments68 has generated interest in the use of biochar for increasing C-sequestration in soil. Consequently, the production and application of biochar to soil is considered to possess considerable greenhouse gas emissions mitigation benefits compared to conventional management of biomass feedstocks.9,10 Despite the recalcitrant nature of biochars, research shows that biochar oxidizes both by abiotic and biotic mechanisms.8,11,12 The stability of biochar-C in soils is dependent on several factors, including the properties of biochar and soil, and environmental conditions.7,13 Furthermore, biochar application may affect the r 2011 American Chemical Society
mineralization rate of native soil organic matter (SOM), and similarly the addition labile organic matter (LOM), that is, organic material that mineralizes more rapidly than biochar or native SOM, may also impact biochar-C mineralization in soil.13,16 There are conflicting reports on the interactive priming effects on mineralization of biochar-C and LOM-C in the soil.1316 Here, we define the interactive, positive or negative, priming effect as the stimulation or suppression, respectively, of biochar-C or LOM-C mineralization above or below the respective control.17 Liang et al.13 studied the effects of black C, a form of biochar-type C, in Anthrosols (Terra Preta soils) on the C mineralization and cycling of relatively labile plant residues, that is, sugar cane leaves. They reported that the presence of black C in the soil caused rapid incorporation of added LOM into aggregates and organo-mineral fractions and thus stabilizing LOM in soil. Contrary to the study of Liang et al.,13 Wardle et al.14 reported that charcoal presence promoted the loss of humus-C from the forest floor in a 10-year old study at three contrasting boreal forest sites in northern Sweden. However, neither of these studies13,14 observed the effect of added or native organic matter on the mineralization of biochar-C. Black C in the Received: June 27, 2011 Accepted: September 28, 2011 Revised: September 13, 2011 Published: September 28, 2011 9611
dx.doi.org/10.1021/es202186j | Environ. Sci. Technol. 2011, 45, 9611–9618
Environmental Science & Technology
ARTICLE
Table 1. Important Properties of the Soil, Biochars, and Sugar Cane Residue Used in the Incubation Experiment property
soil
450 °C biochar
550 °C biochar
sugar cane residue
total C (%)
0.45
67.8
74.9
total N (%)
0.04
0.5
0.6
39.6 0.4
δ13C
14.3
36.3
36.4
12.7
pH (1:5 H2O)
8.10
8.60
9.90
Electrical conductivity (1:5, dS m1)
0.11
0.90
1.10
CECa (mmolc kg1)
347
11.4
54.0
clay (%)
53
silt (%) sand (%)
14 33
specific surface areab (m2 g1)
191.0
228.3
pore volume (%)
57.2
67.5
clay minerals
S****, K*, I*
a Cation-exchange capacity measured by the silver thiorurea method. b CO2 adsorption method: S**** = smectite (>80%); K* = kaolinite (
