Introduction
Biochar amendment into soils has been suggested as an effective means to
abate global warming by storing the carbon rich but decomposition
resistant biomass materials in soils, while simultaneously bettering
soil properties and increasing plant biomass yields (Christian, 2001;
Farji-Brener and Ghermandi, 2000). Biochar technology could potentially
reduce about 1.8 Pg CO2-C yearly, equal to 12% of
current anthropogenic CO2-C emissions (Christian, 2001).
It was estimated that biochar application would reduce 3–4 folds of
current carbon loss from the soil pool (Zhao et al., 2015).
Biochar-amended soil could sequester C over a long time by physical
stabilization (Novak et al., 2009; Yin et al., 2014). The mean residence
time of biochar is estimated to about 2000 years, and the half-life is
about 1400 years. Biochar application also has positive effects up to
30% on biomass production with the large-volume application of BC
(30~60t/ha), and this would yield more plant-derived
biomass input into soils (Yin et al., 2014). However, carbon
mineralization usually was stimulated or suppressed by biochar through
positive or negative priming effects and varied significantly and
separately (Prommer et al., 2014; Sui et al., 2016). This might offset
the benefit of increasing SOC by biochar addition in short-term time. It
was believed that credible data are needed from varied field experiments
and soil types while using biochar as a soil amendment may be a
potentially useful option to mitigate climate change.
Saline-sodic soils cover 3.1% of the global land area, and world soils
that are currently saline have lost an average of 3.47 t SOC/ha since
they become saline (Yang et al., 2018). Improvement of saline-sodic soil
is increasingly undertaken as a means of reclaiming otherwise
unproductive agricultural land, and biochar application is a potential
choice for fertilizing saline-sodic soils for replantation (Munda et
al., 2018). Saline-sodic soils are flocculated with high soluble salts
and exchangeable Na+ and would become disperse when pH
is higher than 8.5. Organic matter contents in saline-sodic soils are
usually low due to poor plant growth, which is restricted by poor
aeration, compaction, and lower nutrient bioavailability (Sun et al.,
2016). Since biochar materials are charcoal-like, high porous,
fine-grained, and have a large surface area, its incorporation
application to soils has attracted considerable attentions as an
effective and economic soil amendment for improving soil physicochemical
properties, enhancing plant biomass and increasing soil organic carbon
pool. Biochar has been successfully used to reduce the nutrient
deficiency and salt stress (Sun et al., 2016), reclaim degraded soils
(Sun et al., 2016), facilitate plant growth (Brodowski et al., 2005),
and suppress SOC mineralization (Lin et al., 2015). However, the effects
of biochar addition on SOC pool were usually with inconsistent results
depending on the nature of soil and biochar, soil types, and incubation
time. Besides as a direct carbon source that can increase SOC pool,
biochar addition would act as nutrient sources such as nitrogen and
phosphorus, which facilitate plant growth and increase the SOC pool
indirectly. The large adsorption capacity of biochar could also preserve
organic carbon in the pores that prevent them from decomposition by
microorganisms. However, most studies about biochar amendment were
carried out on nonsalt-affected soils, and knowledge about the effects
of biochar application on carbon dynamics in saline-sodic soils is still
scant and not well understood, which need further evaluation (Sollins et
al., 1996).
As one of the largest saline-sodic soil areas in the world, the
salt-affected areas were estimated to 3.84×106 ha in
the Songnen Plain of northeast China. Saline-sodic soils here have high
montmorillonite clay and sodium bicarbonate and very low SOC content,
and carbon sequestration rates were <60
gC/m2/yr in the Momoge wetland site (Sollins et al.,
1996). How to improve soil physicochemical properties, fertilizer
saline-sodic soil for more biomass yield, and to increase soil carbon
pool for mitigating rising atmospheric CO2 is one the
most important environmental spot here. The objectives of the present
work are: (1) to compare impacts of biochar addition on soil organic
carbon pools based on incubation experiments in the field, and (2) to
reveal potential factors that govern SOC contents before and after
biochar addition. Based on these two aims, it is hoped to manageably
provide carbon farming solutions to the global climate and satisfying
food demand using biochar technology.