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Multi-season effects of biochar and N on N2O-N fluxes in a Ferralsol
Introduction
Márcia Thaís de Melo CARVALHO1, Beáta Emöke MADARI1, Aline de Holanda Nunes MAIA2
1 Embrapa Rice and Beans, 2 Embrapa Environment
E-mail address of presenting author*: [email protected]
Materials and Methods
Gases accumulated in the static chamber in a period of 30 minutes were
collected using manual vacuum pump. Following, gas samples were analyzed
via gas chromatography with an Electron Capture Detector (ECD) calibrated
with certified N2O standards of 350 and 1000 ppb. The air temperature was
measured simultaneously with N2O-N flux sampling. Fluxes of N2O-N
(µg m-2 per hour) were calculated according to Rochette et al. (2004).
Soil moisture, ammonium (N-NH4+) and nitrate (N-NO3
-) concentrations were
determined from 100 g soil samples (formed by 3 subsamples) collected
within 0-10 cm soil depth simultaneously with N2O-N sampling. Around 10 g of
soil was weighed before and after drying in an oven for 24 hours in a
temperature of 105 ºC. The water filled pore space (WFPS) was calculated by
considering the soil moisture (g g-1) at the moment of N2O-N sampling, the
soil bulk density (g cm-3) and the mineral particle density (g cm-3).
Biochar is the charred by-product of biomass pyrolysis (Sohi et al. 2010). A wood
biochar is generally alkaline and rich in micro pores, characteristics that in theory
would contribute to increase absorption of ammonium and soil water in soil and
then availability to plants, lowering potential nitrous oxide (N2O) emission in
cropping systems (Clough and Condron 2010). Yet, detailed and consistent
information about soil born N2O-N fluxes with biochar amendment under real
farming conditions are lacking. Very often, the amount of biochar applied in
laboratory studies is much higher than what is feasible under field conditions. For
example, in an incubation experiment, Spokas et al. (2009) only found a significant
decrease in N2O emission with biochar amendment rate higher than 20% (w/w).
Such an application rate is improbable under field conditions. The over-presence of
laboratory studies and the lack of long term field studies of biochar effects on N2O
emission with realistic biochar rates is therefore a problem.
Our objective was to investigate the impact of a single application of wood biochar,
32 Mg ha-1 or 1.6% (w/w), combined with annual N fertilization (90 kg N ha-1), on
N2O-N fluxes from immediately up to 2.5 years after biochar application. In this
study we tested a by-product of charcoal production from plantation timber as a soil
amendment in a cropping system. This type of biochar is potentially available in
large quantities in the Brazilian Savannah, but the value for agriculture is yet
unclear.
Results
Wood biochar amendment (1.6% w/w) does not interact with N fertilization and
does not affect N2O-N fluxes up to 2.5 years after its application in a clay
Ferralsol of the Brazilian Savannah under aerobic conditions.
The mineral N application enhances N2O-N fluxes, soil N-NH4+ and N-NO3
-
availability, especially along seasons characterized by lower WFPS.
Our findings highlight the importance of long-term, longitudinal field studies
that quantify (i) the impact of biochar on N2O-N fluxes and (ii) the dependency
of the dynamics of N2O-N fluxes on soil related variables, such as WFPS.
Bibliography
We used manual, static chambers to quantify N2O-N fluxes and soil related
variables on a kaolinitic clay Rhodic Ferralsol throughout four cropping seasons
after a single application of wood biochar (32 Mg ha-1, incorporated to a depth of 0-
15 cm) followed by annual N applications (90 kg N ha-1).
Here we report on the effects of the treatments (N, biochar and N*biochar) at the
first (16/June/2009 to 21/September/2009), second (03/November/2009 to
22/February/2010), third (08/November/2010 to 21/February/2011) and fourth
(28/November/2011 to 19/March/2012) cropping seasons (S) after biochar
application. These seasons are equivalent to immediately (S0.0), 0.5 (S0.5), 1.5
(S1.5) and 2.5 (S2.5) years after biochar application to the clay soil, respectively.
Measurements of N2O-N fluxes were taken in 16 plots using manual static
chambers. Fluxes were measured weekly and 3 to 6 consecutive days after
sowing and synthetic N fertilization events. Gas samples were taken between 9:00
and 11:00 a.m..
Objective
CLOUGH, T.J. and CONDRON, L.M. Biochar and the nitrogen cycle: introduction. Journal of
Environmental Quality, 2010. p. 1218-1223.
ROCHETTE, P.; ANGERS, D.A.; BÉLANGER, G.; CHANTIGNY, M.H.; PRÉVOST, D.; LÉVESQUE, G.
Emissions of N2O from alfalfa and soybean crops in Eastern Canada. Soil Science Society of America
Journal, 2004. p.493-506.
SOHI, S.P.; KRULL, E.; LOPEZ-CAPEL, E.; Bol, R. A review of biochar and its use and function in soil.
Advances in Agronomy, 2010. p. 47-82.
SPOKAS, K.A.; KOSKINEN, W.C.; BAKER, J.M.; REICOSKY, D.C. Impacts of woodchip biochar
additions on greenhouse gas production and sorption/degradation of two herbicides in a Minnesota
soil. Chemosphere, 2009. p.574–581.
This area can be used for
graphics, tables and
illustrations.
AcknowledgementsFunds provided by Embrapa, CNPq and CCAFS/CLIFF Network.
Effects N2O-N N-NH+4 N-NO-
3 WFPS N2O-N N-NH+4 N-NO-
3 WFPS
---------------------------S0.0------------------------- ---------------------------S0.5-------------------------
N 0.4605 0.2075 0.0081(↑) 0.9362 0.0408(↑) <.0001(↑) 0.0001(↑) 0.2685
CHAR 0.7876 0.8772 0.4548 0.5487 0.4012 0.7191 0.8314 0.4633
N*CHAR 0.1159 0.6985 0.5054 0.3153 0.3256 0.8515 0.5461 0.9359
----------------------------S1.5------------------------ --------------------------S2.5--------------------------
N 0.0791 <.0001(↑) <.0001(↑) <.0001(↓) 0.0024(↑) <.0001(↑) <.0001(↑) <.0001(↓)
CHAR 0.0804 0.1898 0.6637 <.0001(↓) 0.9767 0.1898 0.6637 <.0001(↓)
N*CHAR 0.5707 0.5212 0.6818 0.5093 0.3098 0.5212 0.6818 0.5093
N2O-N: nitrous oxide fluxes (µg m-2 per hour); N-NO3-: available soil nitrate (mg kg-1); N-NH4
+: available
soil ammonium (mg kg-1); and WFPS: soil water filled pore space (%). Seasons: immediately (S0.0) and at
0.5 (S0.5), 1.5 (S1.5) and 2.5 (S2.5) years after biochar application. (↑): increases; (↓) decreases.
Table 1. Nominal significance level (p values) arising from F tests for the effects of mineral N fertilization (N)
and biochar (CHAR), and their interaction (N*CHAR), on N2O-N fluxes and soil related variables along four
cropping seasons on a clay Ferralsol.
