Agriculture Reference
In-Depth Information
Biochars are made by heating organic materials ranging from wood waste
to crop residues to animal manures, usually at temperatures of 350 o to 500 o C,
in the absence of O 2 . Volatile elements and organic compounds are driven of,
leaving approximately 50% of the original C in a recalcitrant form, together with
a variable amount of mineral ash. Biochar in agriculture is often promoted as a
“win-win” material because, in addition to long-term C storage, biochars can
increase cation exchange capacity ( CEC ) (thereby retaining nutrients such as Ca 2+ ,
Mg 2+ , and K + ), increase water holding capacity (in sandy soils), and improve bio-
logical function. However, according to Lehmann et al. (2011), the wide range
of products with diverse physical and chemical properties, and their unknown
interaction with various groups of soil organisms, raise questions about the ben-
eficial effects of biochars. Moreover, the expectation that a biochar will remain as
a C store for a very long period because of its recalcitrant nature is contrary to the
expectation that it will improve soil fertility through its decomposition and release
of mineral nutrients.
Experiments with biochar in vineyards are few, starting in a Swiss vineyard in
2007-2008 with trials using a charcoal-compost mixture (Niggli and Schmidt,
2010). Subsequently, trials with commercially available biochar have been estab-
lished in vineyards in several European countries by the Delinat Institute (see
www.ithaka-journal.net ). Applied at 10t/ha, the biochar required “activation”
or “charging,” usually by prior mixing with a compost or manure. This reduced
its C-to-N ratio, loaded the CEC sites with essential nutrients, and inoculated it
with a range of microorganisms. Despite early positive trends, the Swiss propo-
nents have not yet made recommendations for biochar use in viticulture, primar-
ily because of the variation in products and their complex interaction with soil
type, climate, grape variety, cover crop, and microbial colonization. In Australia,
a recent biochar trial on a N-deficient soil in the King Valley, Victoria, showed
no significant effect on yeast assimilable N in the harvested fruit (Winter et al.,
2013), which was not surprising given that biochar was applied at only 0.7 and
1.4 t/ha.
A material similar to nonactivated biochar has been used for centuries to
counteract the decline in soil C and fertility in the pale, thin soils on Chalk in the
Champagne region, France. Lignite (called cendres noires ) has been mined from
local clay and silt deposits and spread in the vineyards, which are predominantly
clean-cultivated.
Conclusions on How to Build Up Soil Organic Matter
Generalizing, one concludes that SOM accumulates more readily and to higher
levels in cool, humid climates than in hot, dry climates. Soil type has a signifi-
cant effect, with SOM accumulation being increasingly favored as clay content
increases and sand content decreases. The contribution of SOM to increasing a
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