Black Soil, Green Rice

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					Black soil, green rice
                                                                                                                                                                                                            of terra preta contains more than         by heat in the absence of oxygen—of
                                                                                                                                                                                                            three times as much carbon from           biomass for energy production
                                                                                                                                                                                                            biochar—an average 25 tons per            where biochar is a by-product.
                                                                                                                                                                                                            hectare. Assuming a biomass carbon              These examples also show that
                                                                                                                                                                                                            concentration of 36% (typical for         biochar from rice residues is already
                                                                                                                                                                                                            rice straw) and carbon loss during        used in many Asian countries. In
by Stephan M. Haefele                                  Wim Sombroek, a renowned                  benefit greatly                                                                                             charring of 50%, to obtain even the       Japan, biochar from rice husks (called
                                                       Dutch soil scientist, sparked             from the                                                                                                   8-ton level, 44 tons of dry biomass       kuntan) has been used in agriculture




I
                                                       international interest by including       incorporation of                                                                                           (plant matter) per hectare would          for a long time (mainly for seedbeds
      n the 1870s, scientists exploring                several pages on the “terra preta”        organic matter                                                                                             need to be converted into biochar.        and as a soil amendment for upland
      Amazonia in South America                        (black soil) and “terra mulata”           but its rapid                                                                                              To reach the 25-ton terra preta level,    crops and orchards). Use of biochar
      made an unusual discovery.                       (brown soil) in his influential            decomposition in                                                                                           138 tons of dry biomass is required.      from rice husks as an additive to the
      Working independently, James                     1966 book on Amazon soils.                the humid tropics                                                                                               In most Asian rice lands,            culture medium of ornamental plants
Orton, Charles Hartt, and Herbert                           Several studies have since           makes this a very                                                                                          the only feasible source for such         and in vegetable gardens is common
Smith described patches of black                       confirmed that the dark color of terra     labor-intensive                                                                                            large quantities of biomass is rice       and several nongovernmental
or dark brown soils, varying in size                   preta and terra mulata is caused by       and short-lived                                                                                            residue left over after harvest and       organizations promote the use
from 5 to more than 300 hectares,                      the incorporation, by humans, of          solution.                                                                                                  milling. The total amount of rice         of it in organic farming.
within a landscape otherwise                           black carbon (also called biochar)—            Addition                                                                                              residue produced each year in Asia              It appears that biochar can
typified by highly weathered                            incompletely burned organic matter        of biochar to                                                                                              is estimated at 549 million tons of       increase the “greenness” of rice-based
reddish or bleached soils.                             such as charcoal. The soils were          soils has similar      An extraordinary                                                                    rice straw and 110 million tons of        systems and that it can be integrated
      A detailed report from Smith, a                  created by Amerindian populations         positive effects—it                                                                                        rice husks. Rice residue is used for      into existing rice production.
                                                                                                                        type of soil from
geologist, characterized these “dark                   500–2,500 years ago and some              increases nutrient                                                                                         several purposes (such as organic         Especially on bad soils, it offers
earths in Amazonia” as having a                        of the carbon in terra preta soils        availability,          South America                                                                       fertilizer, fuel, fodder, and building    new opportunities to sustainably
top-layer of a fine, dark loam, up                      dates back to 450 B.C. Their high         boosts nutrient-                                                                                           material), but its use is dwindling.      improve system productivity and
to 60 centimeters thick. He also                       fertility compared to surrounding         and moisture-          has implications                                                                    Today, it is often perceived as more of   farmer livelihoods. Applied on a
described them as the best soils                       soils is attributed to the high           holding capacity,                                                                                          a problem than a valuable resource.       larger scale and beyond unfavorable
of the Amazon, producing much                          levels of soil organic matter (which      and contributes        for both rice                                                                       Worse, the most convenient way to         environments, it could also reduce
higher crop yields than surrounding                    includes biochar), higher nutrient        plant-available                                                                                            eliminate rice residue, field burning,     the negative effect of rice-based
soils, and speculated that they                        concentrations, high nutrient- and        nutrients—and is       production and                                                                      is a waste of resources and causes        systems on the global climate. And, if
owed their fertility “to the refuse                    moisture-holding capacity, and lower      reported to last                                                                                           severe air pollution in some regions.     the use of rice residues for energy and
of a thousand kitchens for maybe                       acidity. Amazingly, the soils have        for centuries.         the environment                                                                          This leads to another question.      biochar production is combined, rice
a thousand years.” That they were                      generally sustained this fertility        If researchers                                                                                             Usually, biochar is the product           producers, rice consumers, and the
                                                                                                                        in Asia
human-made was indicated by the                        to the present despite the tropical       can confirm this                                                                                            of burning at low temperatures            environment could all profit. Much re
abundance of fragments of Indian                       climate (in which soil organic            much-delayed                                                                                               (280–500 °C) and restricted               search remains to be done, but the
pottery that “cover the ground ...                     matter tends to rapidly degrade) and      decomposition                                                                                              oxygen supply. Consequently, local        possible prize seems worth the effort.
like shells on a surf-washed beach.”                   frequent or periodic cultivation.         in modern                                                                                                  biochar production by farmers in
      Despite the unusual nature                            But what has all this to do with     agricultural                                                                                               simple earthen mounds or pits             Dr. Haefele is a senior agronomist




                                                                                                                                                                                   JOSE RAYMOND PANALIGAN
of these findings, they initially                       rice in Asia? Terra preta and terra       systems, biochar                                                                                           could also cause considerable air         in IRRI’s Crop and Environmental
failed to excite many scientists.                      mulata are limited to Amazonia,           could contribute                           STEPHAN HAEFELE holds a pile of                                 pollution. However, relatively clean      Sciences Division.
Almost a century later, however,                       they are not used to grow rice,           to sustainable                             biochar—essentially charcoal—that                               biochar production from rice husks
                                                                    and they represent a         production                                 has been produced from rice husks.                              can already be achieved with, for
FIELD WORKERS incorporate biochar into an experimental              technology predating         increases in                                                                                               example, an improved rice husk
plot at the IRRI farm in Los Baños, Philippines.                    modern agriculture.          some of the                                                                                                furnace like the one pictured (right).
                                                                                                                                            through decomposition, the buildup
                                                                    The answer is that           most disadvantaged agricultural                                                                                 Developed at the International
                                                                                                                                            of carbon in the atmosphere could
                                                                    people started to wonder     environments, which are frequently                                                                         Rice Research Institute (IRRI), this
                                                                                                                                            be slowed. And, in flooded rice
                                                                    whether this ancient         characterized by very low yields                                                                           type of furnace produces carbonized
                                                                                                                                            soils, where the decomposition
                                                                    indigenous technology        and widespread extreme poverty.                                                                            rice husks as a by-product of the
                                                                                                                                            of organic matter produces
                                                                    could offer solutions to          The delayed decomposition of                                                                          paddy drying process. Some large
                                                                                                                                            methane—30 times more potent as
                                                                    some of the problems of      biochar could also help with another,                                                                      rice mills in Thailand have already
                                                                                                                                            a greenhouse gas than CO2—this
                                                                    modern agriculture.          more recent problem. It is widely                                                                          perfected this approach. Using
                                                                                                                                            effect would be even greater.
                                                                         Poor soils comparable   agreed that global climate change is                                                                       rice husks to produce energy and
                                                                                                                                                 This sounds very exciting—but
                                                                    with soils in Amazonia       related to an increase in atmospheric                                                                      biochar simultaneously, these
                                                                                                                                            can it be done? To start with, the
                                                                    can be found in tropical     carbon dioxide (CO2) concentration.                                                                        mills reduce their fossil fuel bill
                                                                                                                                            amounts of biochar needed are
                                                                    regions around the globe,    If some of the atmospheric carbon                                                                          and carbon emissions, and sell the
                                                                                                                                            enormous. Agronomic trials have                                                                            THIS MODIFIED rice husk
                                                                    including Asia, where        fixed by plants could be locked                                                                             biochar by-product to producers of         furnace, developed at




                                                                                                                                                                                                                                                                                            MARTIN GUMMERT
                                                                                                                                            achieved good results with biochar
                                                          JOEL SIOPONGCO




                                                                    they are—unfortunately       up in soils (a process known as                                                                            bio-fertilizers. A similar solution        IRRI, produces biochar
                                                                                                                                            applications equivalent to 8 tons of                                                                       as a by-product of the
                                                                    for farmers—depressingly     carbon sequestration) instead of                                                                           under development is the use of
                                                                                                                                            carbon per hectare. The top 30 cm                                                                          paddy drying process.
                                                                    abundant. Such soils         being returned to the atmosphere                                                                           pyrolysis—decomposition caused

26                                                               Rice Today April-June 2007                                                                                                                         Rice Today April-June 2007                                             27

				
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