Agriculture Reference
In-Depth Information
the nitrate leaching losses. Soil amendment with cereal straw has often found to be effective in
reducing
NO
3
−
concentration under grain legume crops, resulting in reduced acidification through
reduced
NO
3
−
leaching.
2.9.6 u
se
of
B
IoChar
One option that has received increasing attention in recent years is the application of charred bio-
mass (biochar) to agricultural soils to protect N loss and leaching from top soil layer (Lehmann
et al., 2006; Atkinson et al., 2010; Bruun et al., 2012).
Biochar
is currently the accepted term for
pyrolysis-derived charcoal when designated for use as a soil amendment (Sohi et al., 2010). However,
char, charcoal
, and
black carbon
, and other names for this product have also been used (Streubel
et al., 2011). Biochar is produced through thermal decomposition (400-600°C) of biomass in the
absence of oxygen (pyrolysis) and is defined as “charred organic matter produced and applied to soil
in a deliberate manner, with the intent to sequester C and improve soil properties” (Lehmann and
Joseph, 2009). The ability of biochar to retain N and other nutrients has been documented in several
studies (Ding et al., 2010; Laird et al., 2010). The ammonium that was readily adsorbed to biochar
has been reported by Ding et al. (2010) and Dunisch et al. (2007).
The beneficial effect of biochar on N retention has been reported in the field trials (Steiner
et al., 2008). Biochar has large surface area and also increases cation-exchange capacity of soil that
may be responsible for nutrient retention (Liang et al., 2006; Van Zwieten et al., 2009; Novotny
et al. 2009; Lehmann and Joseph, 2009; Roberts et al., 2010). Biochar application in soils has been
reported to reduce the nitrification process in the soil by reducing the oxygen and/or substrate avail-
ability—for example, by N adsorption to biochar surfaces (Laird et al., 2010) and by microbial N
immobilization (Kolb et al., 2009; Novak et al., 2010; Bruun et al., 2011). In addition, the nitrifica-
tion process inhibited by microbial toxic biochar substances could also explain the lower production
of
NO
3
−
(DeLuca et al., 2006).
Biochars nutrient retention potential is also physically influenced by the biochar particle size.
Smaller particles have greater surface area/volume ratios than larger particles and thus, in general, a
larger capacity to hold nutrients (Bruun et al., 2012). However, fine biochar particles or components
may also be transported downward in soil with the water movement or horizontally by surface water
runoff (Leifeld et al., 2007; Major et al., 2010).
Much of the recent interest in biochar as a soil amendment was prompted by studies of Amazonian
soils (Terra Preta), where the presence of charcoal was associated with significant improvements in
soil quality such as organic matter and nutrient concentrations and increase in crop yields (Glaser
et al., 2002; Lehmann, 2007; Lehmann and Joseph, 2009; Novotny et al., 2009). The application
of charcoal reportedly increased soil pH, and in acid soils, charcoal decreases the concentration of
Al, which often limits crop growth in the tropics (Piccolo et al., 1997). In many tropical and sub-
tropical soils, charcoal increases base saturation, cation-exchange capacity and nutrient availability,
decreases soil bulk density, and improves water-holding capacity (Liang et al., 2006; Busscher et al.,
2010; Novak et al., 2010). The addition of biochar to soil also increases soil C concentrations that
further improve nutrient storage and soil physical properties (Streubel et al., 2011).
An outstanding attribute of biochar is its high sorption affinity and capacity for organic com-
pounds, generally far exceeding those of humic substances and soil organic matter (Zhang et al.,
2006; Yang et al., 2009; Chen and Chen, 2009; Graber et al., 2011). At the same time, chars fre-
quently demonstrate sorption hysteresis or hindered desorption kinetics (Braida et al., 2003). The
sorption capacity of char may be important to prevent N from the soil-plant system.
2.9.7 u
se
of
G
Ypsum
The use of gypsum can reduce
NH
4
+
loss in the runoff (Favaretto et al., 2012). The beneficial effect
of gypsum on decreasing
NH
4
+
losses in runoff was also observed by Favaretto et al. (2008), due to
