報告書番号

V08035

タイトル（和文）

中山間地における草本性バイオマス生産に関するＬＣＡ的手法による評価

タイトル（英文）

A life cycle assessment for a crop field type biomass production at Akagi semi-mountain area, Japan

概要 （図表や脚注は「報告書全文」に掲載しております）

中山間地における耕作放棄地等の利用を模擬した栽培試験を行い、収穫量、燃料特性を把握すると共に、ＬＣＡ手法を用いた二酸化炭素収支の算出などからバイオマス生産拠点としての有効性を検証した。また、慣行農法と粗放農法の比較により二酸化炭素収支改善に有効な方策を探った。その結果、平地での生産に比べて慣行区では収量あたり2～5倍程度の二酸化炭素を排出しており、その大半が農薬や肥料に使用によるものと考えられた。また、これらをもとに正味二酸化炭素固定量を算出したところ、ナタネを除く全ての作物種において慣行区が粗放区を下回った。このことから、エネルギー消費を抑制した粗放的農法の導入などによりある程度の改善が見込めるが、中山間地は一般的な草本性バイオマス生産拠点としての有効性が低いことが示された。

概要 （英文）

A practical field experiment for life cycle assessment (LCA) of a crop field type biomass production was performed at Akagi testing center, CRIEPI, which was located in halfway up of Mt. Akagi, Gunma pref. A paired field in size of 1 are (100 sq. meters) each was newly developed from a grass land. One of the pair was fully managed with conventional agricultural activities, such as fertilizing, spraying and irrigation (conventional block, CB), and the other was not managed other than tillaring (semi-farming block, SFB). Totally, 10 cropping test was carried out between April 2006 and October 2008 with 8 crops, buckwheat, rice, sunflower, sorghum, oilseed rape, rye grass, dent corn, and carthamus. Of note, the rice cultivar was a specialized for crop land cultivation. Oilseed rape and rye grass was cultivated during winter season, and the others were cultivated during summer season. Dent corn was used for three croppings, which was aimed to compare the productivity of a long single cropping and a short double cropping. Basically, whole upper parts of plants in the fields were harvested at the end of cultivation and measured for fresh weight. A part of the harvests was dried and used to calculate the dry yield ratio and further analyses for the chemical properties as a fuel (e.g. calorie, carbon content, and ash content). On the other hand, direct/indirect energy consumptions related to the cropping was measured for each agricultural machine or was estimated for fertilizers and agrichemicals. Total CO2 emission from each energy consumption was basically calculated following IPCC 2006 Guidelines. GHG emission (N2O and CH4) from soil generated with the biomass production was also estimated as CO2 equivalent volume. Results showed that the dry yield ratios of each cropping in SFB and CB (DY-SFB/CB) were between 0 (oilseed rape) and 83 % (dent corn). Thus, each cropping in CB always showed higher dry yield than the control cropping in SFB. Total yield of the double cropping of dent corn demonstrated only 30% and 0% increase than that of the single cropping in CB and SFB, respectively. Thus, no effect of double cropping could be seen on the increase of yield in this experiment. Productivities of each cropping were about 18% to 51% of those of flatland croppings. The chemical properties of these biomasses (e.g. lower heating value and higher volatile combustible matter, and lower sulfur and ash content, when compared to those of average coal) were almost the same as those of flatland croppings. Also, these properties were not significantly different between the biomass in SFB and CB. The total CO2 emissions per dry-yield were two to five times higher in this experiment than a case of flatland cropping (Pelletier et al., 2008). It may be caused from the reduced yield by lower sunshine and temperature of the semi-mountain area with higher energy inputs for cultivation. Interestingly, balances of CO2 emission were always higher in SFB than in CB except the case of oilseed rape, meaning that the increase in CO2 fixation by management (e.g. fertilization and spraying) did not exceed the increase in CO2 emission. It is indicated that biomass production at such semi-mountain area was not reasonable, although a level of improvement could be expected by an exploitation of semi-farming-styled agriculture.

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