Energy efficiency of potato production practices for bioethanol feedstock in northern Japan

Europ. J. Agronomy 44 (2013) 1–8

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Energy efficiency of potato production practices for bioethanol feedstock in northern Japan Nobuhisa Koga a,∗ , Tsutomu Kajiyama b , Keiichi Senda c,1 , Satoru Iketani c , Seiji Tamiya a , Shogo Tsuda a a Upland Farming Research Division, Hokkaido Agricultural Research Center, National Agriculture and Food Research Organization (NARO), Shinsei, Memuro, Kasai, 082-0081 Hokkaido, Japan b Hokkaido Research Organization, Tokachi Agricultural Experiment Station, Shinsei, Memuro, Kasai, Hokkaido 082-0081, Japan c Hokkaido Research Organization, Kitami Agricultural Experiment Station, 52, Aza Yayoi, Kun-neppu, Tokoro, Hokkaido 099-1496, Japan

a r t i c l e

i n f o

Article history: Received 31 January 2012 Received in revised form 1 July 2012 Accepted 2 July 2012 Keywords: Bioethanol Energy input Planting density Potato Ridging Starch yield

a b s t r a c t In 2007–2009, field experiments were conducted to identify agronomic practices affording the lowest energy inputs (i.e. total energy inputs from fuels and other agricultural material inputs required to produce 1 L of ethanol) under potato-based bioethanol feedstock production in northern Japan. On a hectare basis, for a standard 4.4 m−2 planting density, conventional practices [two inter-row cultivations (weeding and preparation for ridging) and final ridging] yielded an estimate of 4.85 kL ha−1 , representing an energy input of 5.86 MJ L−1 . The energy input savings arising from the lesser fuel consumption associated with fewer tractor operations under no- and low-ridge cropping practices were outweighed by a reduction in ethanol yields, resulting in slightly greater energy inputs (6.09 ± 0.65 and 5.89 ± 0.30 MJ L−1 , respectively). Similarly, poorer ethanol yields outweighed the reduction in energy inputs arising from lessened seed potato production-associated energy inputs under lowered planting densities of 3.8 and 3.3 m−2 , resulting in ethanol yield-based energy inputs of 5.98 ± 0.33 and 6.01 ± 0.41 MJ L−1 , respectively. Omitting fungicide applications significantly lowered biocide-related energy inputs, but yielded 20 and 63% lower ethanol yields for Phytophthora-resistant and -susceptible genotypes, respectively, substantially worsening energy efficiencies (6.24 ± 0.42 and 12.2 ± 6.3 MJ L−1 ). In northern Japan, use of high starch-yielding genotypes served as the only way to increase ethanol yields and improve energy efficiency for potatoes used in bioethanol feedstock production. A 29% greater ethanol yield (6.26 ± 0.46 kL ha−1 ) and 21% better energy efficiency (4.63 ± 0.23 MJ L−1 ) were achieved by replacing the standard potato cultivar with a high starch-yielding variety. The yield-based energy inputs with a high starch-yielding potato variety were significantly lower than those with conventional sugar beet in northern Japan (5.82 MJ L−1 ). © 2012 Elsevier B.V. All rights reserved.

1. Introduction For a wide range of crop-based bioethanol production systems, the major feasibility and sustainability issues include ethanol yields, along with energy use and greenhouse gas emissions during feedstock cultivation, transportation and transformation processes. In seeking to develop more energy-efficient bioethanol production systems, energy balances accounting for the full range of processes involved have been applied to a variety of feedstock crops: sugarcane (Saccharum officinarum L.) (Macedo, 1998; Renouf et al., 2008), maize (Zea Mays L.) (Kim and Dale, 2005; Renouf et al., 2008), sugar beet (Beta vulgaris L. subsp. vulgaris) (Malc¸a and Freire, 2006;

∗ Corresponding author. Tel.: +81 155 62 9274; fax: +81 155 61 2127. E-mail address: [email protected] (N. Koga). 1 Present address: Hokkaido Research Organization, Kamikawa Agricultural Experiment Station, Pippu, Kamikawa, Hokkaido 078-0397, Japan. 1161-0301/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.eja.2012.07.001

Renouf et al., 2008), cereal crops (Rosenberger et al., 2001) and cassava (Manihot esculenta Crantz) (Nguyen et al., 2007; Papong and Malakul, 2010). Feedstock production in the field is a key process in bioethanol production, where energy is generated by means of photosynthesis, but also intensively consumed through fuelconsuming machine operations and other agricultural material inputs (seeds, fertilizers, biocides and agricultural machinery). The importance of optimizing feedstock cultivation practices resides in the potential improvement of the energetic efficiency of bioethanol production. In Japan, domestic bioethanol production from sugarcane, sugar beet, rice (Oryza sativa L.) and wheat (Triticum aestivum L.) recently reached the pilot plant scale. Currently targeted toward human consumption, the production of these crops follows highly fueldependent and material-intensive agronomic practices. In view of this, ethanol yields and energy efficiencies were assessed for sugar beet feedstock crop production practices in northern Japan. A combination of reduced tillage, high-yielding genotypes and

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N. Koga et al. / Europ. J. Agronomy 44 (2013) 1–8

root + crown harvesting proved to be the most energy-efficient combination of cultural practices for sugar beet-based ethanol production (Koga et al., 2009). The below-ground biomass of cassava and sweet potatoes (Ipomoea batatas (L.) Lam.) represents their main yield component. The significant ethanol yields obtained from them and the modest fuel and material inputs required under their relatively simple crop management operations recommend them as a bioethanol feedstock crop (Ziska et al., 2009). However, northern Japan’s cool climate renders their cultivation impractical; however, 80% of Japan’s domestic potatoes are produced there (Tokachi Subprefectural Office, Hokkaido Government, 2009), where they are well adopted to the cool climate. Potato is a high biomassproducing and energy-efficient crop (Koga, 2008), whose high concentration of tuber-housed starch results in starch yields as high as 8.5 Mg ha−1 (Ministry of Agriculture, Forestry and Fisheries, Japanese Government, 2008). Moreover, tubers can be harvested using a conventional potato harvester without any new investment. Although bioethanol production from potatoes is currently uncommon in the world, and thus poorly studied, potato is being considered as a potential bioethanol feedstock crop for northern Japan. Current potato production in northern Japan is funneled toward three main uses: (i) table use (grocery store stock), (ii) materials for fried potato foods (chips and French fries), and (iii) material for starch production (Department of Agriculture, Hokkaido Government, 2005; Tokachi Subprefectural Office, Hokkaido Government, 2009). Taking into account their particularly high starch content, potato cultivars used for starch production meet the requirement for bioethanol feedstock production. However, given their highly energy-dependent and material-intensive nature, current potato cultivation practices in northern Japan are not targeted to bioethanol feedstock production. The energy dependence under the current potato production system is largely a result of the number of tractor-based field operations (e.g. soil preparation, planting and fertilization, inter-row cultivation, ridge construction, biocide spraying and harvesting) and large inputs of agricultural materials. Therefore, alternative potato cultivation practices suitable for bioethanol feedstock production are required. As tuber yields, starch yields and energy inputs from fuels and agricultural materials can vary considerably as a result of changes in cultivation practices, careful assessment of cultivation and transportation steps is necessary. This study sought to optimize potato cultivation practices for bioethanol feedstock production.

2.2. Conventional potato production Under conventional starch potato production, tractor-based field operations include soil preparation, sowing and fertilization, herbicide spraying, inter-row cultivation, ridge construction, pesticide (fungicides and insecticides) application as well as harvesting and plowing (Department of Agriculture, Hokkaido Government, 2005). Compound fertilizers containing N, P, K and Mg were banded concurrently with the planting of seed potatoes (100, 180, 130 and 40 kg ha−1 for N, P2 O5 , K2 O and MgO, respectively, based on the local government fertilizer recommendations). Two inter-row cultivations were implemented: the first mainly targeted to weeding, and the second a soil loosening preparatory to subsequent full ridge construction. This latter process built on the low (15 cm) ridge generated by the second cultivation, using a potato ridger to further mound the ridge up to a 20 cm height, thus preventing greening of exposed tubers. Pesticides were applied 7 times over the growing season, using a boom sprayer, 3 times of which were practiced for insecticide spraying. After harvest, soils were plowed to a depth of roughly 25 cm. 2.3. Alternative cultural practices studied 2.3.1. Simplified ridge construction Under low- and no-ridge practices, full ridging or full ridging and the second inter-row cultivation were eliminated, respectively, thereby reducing diesel fuel consumption. Under both practices, fuel consumption associated with the use of a potato ridger was eliminated, while under the no-ridge practice an additional energy saving was obtained by eliminating the second inter-row cultivation. Besides the fuel savings, not using a potato ridger also contributed to reduced material consumption-derived energy inputs from agricultural machinery. The 5-year mean expenditure (2003–2007) of the cultivator and potato ridger was 1600 yen ha−1 yr−1 (Ministry of Agriculture, Forestry and Fisheries, Japanese Government, 2009). Assuming the expenditures for the cultivator and potato ridger to be equal, 800 yen ha−1 yr−1 would be deducted from the costs for agricultural machinery under noand low-ridge practices. This cost saving would be equivalent to a reduction in energy inputs by 0.04 GJ ha−1 . Potato variety ‘Konafubuki’, commonly used in starch production in northern Japan, was used in the ridge treatment field experiments carried out in 2007–2009 at two different field sites at Memuro. Another such variety, ‘Musamaru’ was similarly tested in 2009. Besides ridging, cultural conditions (planting densities and fungicide application) followed conventional potato production practices.

2. Materials and methods 2.1. Effects of agronomic practices on starch production Field experiments carried out in 2007–2009 at Memuro (42◦ 55 N) and Kitami (43◦ 48 N), Hokkaido prefecture, northern Japan, served to assess potato tuber yields, starch contents and final starch yields, as well as their comparison amongst a range of alternative or conventional cropping practices. According to Hijmans (2001), one of the potato-producing zones in the world was between 45◦ N and 57◦ N, and the other was between 23◦ N and 34◦ N. In the former zone, potato was a summer crop. As the study sites in northern Japan are close to the former zone, potatoes are grown as a summer crop. The meteorological data for the Memuro and Kitami sites were shown in Fig. S1 and Table S1 in Supplementary Data. The soil type at both sites was an Andosol (volcanic ash-derived soil), a well-drained soil typical of Hokkaido’s arable lands. Paired t-tests, computed using R (version 2.9.2), assessed the significance of alternative practices’ effects on tuber yields, starch contents and starch yields (R Development Core Team, 2009).

2.3.2. Lowered planting density To reduce seed tuber usage along with its attendant material consumption-linked energy inputs, planting densities of 3.8 and 3.3 plant m−2 were implemented, representing 14 and 25% reductions over the conventional planting density of 4.4 plant m−2 , respectively. The effects of planting densities on tuber yields, starch content and starch yields were tested with ‘Konafubuki’ from 2007 to 2009 and additionally with ‘Musamaru’ in 2008. Besides planting densities, these experiments were carried out under normal cultural conditions (full ridging and fungicide application). 2.3.3. No fungicide application Late blight [Phytophthora infestans (Mont.) de Bary], one of the severest potato diseases in Hokkaido, is normally controlled by fungicide application. The effects of omitting fungicide applications on tuber yields, starch content and final starch yields were tested in field trials at Kitami, using late blight-resistant and -susceptible potato genotypes. Omitting fungicide applications reduced material consumption-linked energy inputs from biocides

N. Koga et al. / Europ. J. Agronomy 44 (2013) 1–8

by 3.08 GJ ha−1 . The susceptible genotypes, ‘Konafubuki’ and ‘Koniku No. 38’ were grown in 2007–2009, whereas the resistant ‘Kitakei No. 32’ was grown in 2007, ‘Saya-akane’ in 2007 and 2008, ‘Hokuiku No. 16’ and ‘K04113-1’ in 2008 and 2009 and ‘K000512-2’ in 2008. These field trials were performed without any additional pathogen inoculation of the soil since P. infestans is endemic to arable fields in Hokkaido (Kato et al., 1998). Besides fungicide application, cultural conditions followed conventional practices (full ridging and standard planting density). 2.3.4. Use of high-yielding genotypes ‘Kachikei No. 24’ and ‘Kon-iku No. 38’ are promising high starchyielding potato genotypes under development at the Hokkaido Agricultural Research Center, NARO and the Hokkaido Research Organization, Kitami Agricultural Experiment Station, respectively. The effect on starch production of replacing the conventional cultivar ‘Konafubuki’ with either of these genotypes was assessed in field trials. The field trials were carried out in Memuro (2007–2009) and Kitami (2008–2009) for ‘Kachikei No. 24’ and in Kitami (2007–2009) for ‘Kon-iku No. 38’. These field trials were conducted under normal cultural conditions in terms of ridging, planting densities and disease control. 2.4. Energy consumption through fossil fuels and materials To assess the energy consumed in cultivation and transportation of potatoes, diesel fuel consumption in tractor operations and truck transportation and the consumption of materials such as seed potatoes, fertilizers, biocides (herbicides, fungicides and insecticides) and agricultural machinery were taken into account. The diesel fuel consumption rate in each tractor operation was obtained from the Department of Agriculture, Hokkaido Government (2005). Diesel consumption for harvest and transportation was assumed to be proportional to tuber yields. The rate of energy consumption from diesel fuel used in harvest operations, Eh (MJ ha−1 ) was calculated as: Eh = 111 × Fy × 37.8

(1)

111 L ha−1

where was the diesel fuel consumption rate under conventional potato harvesting conditions (Department of Agriculture, Hokkaido Government, 2005), Fy was a unitless tuber yield factor representing the ratio of tuber yields under alternative vs. conventional practices (Table 1), and 37.8 MJ L−1 was the mean energy equivalent of diesel fuel (MJ L−1 ) between 2004 and 2006 (Greenhouse Gas Inventory Office of Japan, 2008). Calculating Et (MJ ha−1 ), the rate of diesel fuel energy consumption resulting from the transport of potato tubers, assumed the bioethanol plant to be 10 km from the field and a round trip being completed: Et = 39.2 ×

Fy 20 × 37.8 × 6 4

(2)

where 39.2 Mg ha−1 was the mean tuber yield of starch potatoes (2003–2007) in Hokkaido (Ministry of Agriculture, Forestry and Fisheries, Japanese Government, 2008), 4 Mg was the truck’s loading capacity, 20 km was the total transport distance, 6 km L−1 was the truck’s fuel efficiency (Center for Environmental Information Service, 1998) and 37.8 MJ L−1 was the energy equivalent of diesel fuel. Energy consumption derived from consuming materials was calculated using the document ‘Embodied Energy and Emission Intensity Data for Japan Using Input–Output Tables for 2000’ (Center for Global Environmental Research, 2007), which provided retail price-based energy equivalents for particular commodities. The energy equivalents for seeds (i.e. seed potatoes in this study), fertilizers, biocides and agricultural machinery were

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19.98, 117.24. 73.41 and 50.41 kJ yen−1 , respectively. The 5-year mean expenditure (2003–2007) for each commodity was obtained from the Ministry of Agriculture, Forestry and Fisheries, Japanese Government (2009). 2.5. Estimation of ethanol yields Ethanol yields were estimated from starch yields. The starch yield under conventional production conditions prevailing in Hokkaido was obtained by multiplying the mean (2003–2007) potato tuber yield (Ministry of Agriculture, Forestry and Fisheries, Japanese Government, 2008) by the mean (2003–2007) starch content (Ministry of Agriculture, Forestry and Fisheries, Japanese Government, 2008) (i.e. 39.2 Mg ha−1 × 21.7% = 8.51 Mg ha−1 ). Starch yields under alternative agronomic practices were calculated by multiplying the mean starch yield (8.51 Mg ha−1 ) with starch yield factors expressed as ratios of starch yield under alternative vs. conventional practices (Table 1). Estimated ethanol yields were calculated by multiplying starch yields by 0.51, the theoretical starch-to-ethanol conversion efficiency, then by 0.90, the practical conversion efficiency of potato starch to ethanol (unpublished results). A value of 0.806 kg L−1 (0 ◦ C) was used for the density of ethanol. 3. Results 3.1. Tuber yields, starch contents and starch yields under different cultural conditions Tuber yields were decreased slightly under no- and lowridge field operations, compared to the conventional production (Table 1). Similarly, lowered planting densities (14 and 25% reductions) led to a marginal decrease in tuber yields. Neither the absence or reduction of ridges nor lower planting densities had much effect on starch contents. These alternative production systems resulted in a slight decrease in final starch yields though the effects of these practices on starch yields were not significant. While the omission of fungicide applications had a significant negative impact on tuber yields, starch contents and final starch yields, the resistance/susceptibility of individual genotypes was most closely linked to the magnitude of these impacts. For the resistant potato genotypes, tuber yields, starch contents and starch yields were 14, 6.6 and 20% lower, respectively, when no fungicide was applied than when it was. On the other hand, these yield parameters of susceptible potato genotypes showed a serious decline (56, 21 and 63% reductions, respectively). Use of high-yielding genotypes enhanced tuber yields: 13 and 21% increases in tuber yields were noted for ‘Kon-iku No. 38’ and ‘Kachikei No. 24’, respectively, in comparison with the conventional starch potato variety, ‘Konafubuki’. However, these genotypes differed significantly in their starch content: compared to the conventional variety, ‘Kon-iku No. 38’ showed greater starch content, whereas ‘Kachikei No. 24’ showed significantly lower levels. As a result of increases in tuber yield and starch content, the final starch yield of ‘Kon-iku No. 38’ was 29% greater than that of the conventional variety. For ‘Kachikei No. 24’, this improvement was only 10%, as a result of its relatively lower starch content. 3.2. Energy consumption in diesel and material use Under conventional potato production, diesel fuels consumed in tractor operations (excluding harvesting) amounted to 117 L ha−1 , or the energy equivalent of 4.42 GJ ha−1 (Table 2). Tillage-related operations such as soil preparation and plowing represented 55% of total diesel consumption. This diesel consumption rate under

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N. Koga et al. / Europ. J. Agronomy 44 (2013) 1–8

Table 1 Effects of agronomic practices on tuber yields, starch contents and starch yields of potatoes in northern Japan. Tuber yield (Mg ha−1 )

Alternative agronomic practice

No ridge construction (n = 7) Low ridge construction (n = 7) Planting density lowered (−14%) (n = 5) Planting density lowered (−25%) (n = 5) Fungicide applications omitted (registant genotypes) (n = 8) Fungicide applications omitted (susceptible genotypes) (n = 6) High-yielding genotype (cv. ‘Kachikei No. 24’) (n = 5) High-yielding genotype (cv. ‘Kon-iku No. 38’) (n = 3)

Starch content (%)

Starch yield (Mg ha−1 )

C

A

A/C

Effect

C

A

Effect

C

A

A/C

Effect

48.0 48.0 49.8 49.8 46.2 49.8 45.4 46.8

44.7 45.4 47.4 46.9 39.6 21.8 54.9 52.7

0.93 (0.11) 0.95 (0.06) 0.95 (0.08) 0.94 (0.08) 0.86 (0.05) 0.44 (0.18) 1.21 (0.12) 1.13 (0.11)

ns ns ns ns

19.4 19.4 19.1 19.1 19.7 20.8 21.5 20.7

19.3 19.8 19.3 19.1 18.4 16.4 19.5 23.8

ns ns ns ns

9.31 9.31 9.50 9.50 9.16 10.2 9.72 9.67

8.62 9.00 9.10 8.97 7.34 3.72 10.7 12.5

0.93 (0.11) 0.97 (0.06) 0.96 (0.07) 0.94 (0.09) 0.80 (0.06) 0.37 (0.17) 1.10 (0.13) 1.29 (0.09)

ns ns ns ns

*** ** **

ns

*** * *** *

*** ***

ns *

C: conventional practice, A: alternative practice. The numbers in brackets represent standard deviation. *** Significance level of 0.001. ** Significance level of 0.01. * Significance level of 0.05. ns – no significance.

conventional practices (excluding harvesting) was unaltered by either decreasing the planting density or using high-yielding genotypes. Harvesting consumed a further 111 L ha−1 of diesel fuel, or the equivalent of 4.20 GJ ha−1 (Table S2 in Supplementary Data). The transportation of feedstock potato by trucks was equivalent to 1.24 GJ ha−1 (Table S3 in Supplementary Data). Therefore, energy consumption from diesel fuel-consuming operations totaled 9.86 GJ ha−1 for conventional cultural conditions. As a result of fuel consumption savings from eliminating one or both of inter-row cultivation and ridge construction field operations, diesel energy consumed in tractor operations under no- and low-ridge production systems was reduced to 3.89 and 4.08 GJ ha−1 , respectively (Table 2). As marginal reductions in tuber yields occurred under no- and low-ridge production, diesel consumption in harvest and transport was also reduced (Tables S2 and S3 in Supplementary Data). Therefore, total energy inputs from diesel fuel consumption for no- and low-ridge production systems were equivalent to 8.93 and 9.22 GJ ha−1 , representing 9 and 6% reductions in comparison with conventional ridge production systems, respectively (Table 4). Likewise, as slight reductions in tuber yields occurred with lowered planting densities, total energy inputs from harvest and transport were also reduced. When no fungicide was applied, diesel fuel consumption from tractor operations was reduced as a result of the reduced frequency of fungicide spraying (only insecticides applied), and the significant decrease

in tuber yields led to reduced diesel consumption in harvest and transport. Omitting fungicide applications contributed to 11 and 34% reductions in diesel energy consumption for resistant and non-resistant potato genotypes, respectively. Use of high-yielding genotypes increased tuber yields as well as fuel consumption for harvest and transport (12 and 6% increases for ‘Kachikei No. 24’ and ‘Kon-iku No. 38’, respectively compared to the conventional variety). Under conventional starch potato production in Hokkaido, energy inputs from seed potatoes, fertilizers, biocides and agricultural machinery were equivalent to 2.40, 9.04, 5.09 and 1.96 GJ ha−1 , respectively, resulting in 18.5 GJ ha−1 of total energy inputs from materials (Table 3). The energy inputs from materials under use of high-yielding genotypes were identical to those under the conventional practice because there was no difference in material use between these practices. While energy inputs from agricultural machinery did not differ according to the potato variety grown, it was lowered by the lack of potato ridger use under no- and low-ridge production systems. However, this impact was minimal as the mean expenditure for the potato ridger was negligible. Energy inputs from seed potatoes were reduced when planting occurred at lower densities than standard densities. The largest reduction in material consumption-linked energy inputs was attained by not applying fungicides. This practice allowed a reduction of energy inputs of 3.08 GJ ha−1 .

Table 2 Total energy inputs in tractor operations (excluding harvesting). Tractor operation

Soil preparation Planting and fertilization Herbicide spraying Inter-row cultivation Ridge construction Pesticide spraying Plowing Total diesel fuel consumption (L ha−1 ) Energy input (GJ ha−1 )c a

Tractor implement

Rorary harrow Potato planter Boom sprayer Cultivator Potato ridger Boom sprayer Moldboard plow

Diesel fuel consumption rateb (L ha−1 )

20.7 17.3 1.92 5.74 8.28 1.92 22.8

Conventional practicea

No ridge construction

Low ridge construction

No fungicide application

Frequency

Total (L ha−1 )

Frequency

Total (L ha−1 )

Frequency

Total (L ha−1 )

Frequency

Total (L ha−1 )

2 1 1 2 1 7 1

41.4 17.3 1.92 11.5 8.28 13.4 22.8 117

2 1 1 1 0 7 1

41.4 17.3 1.92 5.74 0 13.4 22.8 103

2 1 1 2 0 7 1

41.4 17.3 1.92 11.5 0 13.4 22.8 108

2 1 1 2 1 3 1

41.4 17.3 1.92 11.5 8.28 5.76 22.8 109

4.42

3.89

4.08

4.12

Total diesel fuel consumption in tractor operations excluding harvesting for lowered planting density and use of high-yielding genotypes were the same as that for the conventional practice. b Tractor operations and diesel fuel consumption rates were derived from the Department of Agriculture, Hokkaido Government (2005). c The energy equivalent was 37.8 MJ L−1 for diesel fuel (Greenhouse Gas Inventory Office of Japan, 2008).

N. Koga et al. / Europ. J. Agronomy 44 (2013) 1–8

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Table 3 Total energy inputs from material use. Alternative agronomic practice

Conventional practice No ridge construction Low ridge construction Planting density lowered (−14%) Planting density lowered (−25%) Fungicide applications omitted (registant genotypes) Fungicide applications omitted (susceptible genotypes) High-yielding genotype (cv. ‘Kachikei No. 24’) High-yielding genotype (cv. ‘Kon-iku No. 38’)

Mean expenditure (103 yen ha−1 )a

Energy consumption (GJ ha−1 )b

Total energy input (GJ ha−1 )

Seed potatoes

Fertilizers

Biocides

Agricultural machinery

Seed potatoes

Fertilizers

Biocides

Agricultural machinery

120 (1200)c 120 (1200) 120 (1200) 103 (1030) 90.0 (900) 120 (1200)

77.1 (771) 77.1 (771) 77.1 (771) 77.1 (771) 77.1 (771) 77.1 (771)

69.3 (693) 69.3 (693) 69.3 (693) 69.3 (693) 69.3 (693) 27.4 (274)

38.9 (389) 38.1 (381) 38.1 (381) 38.9 (389) 38.9 (389) 38.9 (389)

2.40 2.40 2.40 2.06 1.80 2.40

9.04 9.04 9.04 9.04 9.04 9.04

5.09 5.09 5.09 5.09 5.09 2.01

1.96 1.92 1.92 1.96 1.96 1.96

18.5 18.5 18.5 18.2 17.9 15.4

120 (1200)

77.1 (771)

27.4 (274)

38.9 (389)

2.40

9.04

2.01

1.96

15.4

120 (1200) 120 (1200)

77.1 (771) 77.1 (771)

69.3 (693) 69.3 (693)

38.9 (389) 38.9 (389)

2.40 2.40

9.04 9.04

5.09 5.09

1.96 1.96

18.5 18.5

a Mean expenditures (2003–2007) for seed potatoes, fertilizers, biocides and agricultural machinery were drawn from the Ministry of Agriculture, Forestry and Fisheries (2009). b Energy equivalents for seed potatoes, fertilizers, biocides and agricultural machinery were 19.98, 117.24, 73.41 and 50.41 kJ yen−1 , respectively (Center for Global Environmental Research, 2007). c D ha−1 for parenthesis with the exchange rate of 100 yen per euro (June 2012).

3.3. Total energy inputs and ethanol yields For conventional starch potato production, the total energy input from fuel and material consumption was 28.4 GJ ha−1 , of which 65% was contributed by material consumption (Table 4). As a result of slightly reduced tuber yields and material use, total energy inputs were slightly reduced under no- and low-ridge construction as well as under lowered planting densities. Compared to conventional pest management, the greatest reduction in total energy inputs was obtained when no fungicide applications were made; 15 and 23% reductions occurred for resistant and susceptible genotypes, respectively. Total energy inputs were increased by using high-yielding genotypes as greater tuber yields increased fuel consumption at harvest and during transport. The ethanol yield under conventional potato production conditions was estimated at 4.85 kL ha−1 (Table 4). Marginal reductions in final starch yields led ethanol yields to a decline by 3–7% under no- and low-ridge production, and when planting densities were lowered. The reduction in ethanol yields was most pronounced when no fungicides were applied, as this omission led to significantly lower starch contents in tubers as well as lower tuber yields (Table 1). The estimated ethanol yields for late blight-resistant and -susceptible varieties were 3.88 ± 0.28 and 1.79 ± 0.82 kL ha−1 , respectively, representing 20 and 63% reductions compared to those achieved under the conventional disease management. Use of the high-yielding genotypes ‘Kachikei No. 24’ and ‘Kon-iku No. 38’, both had a positive impact on ethanol yields (10 and 29% increases, respectively). The total energy inputs required to produce 1 L of ethanol under conventional potato production was 5.86 MJ L−1 (Fig. 1). When total energy inputs were reduced and ethanol yields also dropped, noor low-ridge practices along with decreased planting densities led to a marginally greater energy input (5.89–6.09 MJ L−1 ). The greater energy inputs were much more apparent for susceptible genotypes (12.2 ± 6.3 MJ L−1 ) than resistant ones (6.24 ± 0.42 MJ L−1 ). Of the agronomic practices studied, use of high-yielding genotypes was the only practice that lowered the energy input per liter of ethanol produced. In this case, rises in ethanol yields exceeded the increases in total energy inputs for both high-yielding genotypes. The variety, ‘Kon-iku No. 38’ presented an energy input of 4.63 ± 0.23 MJ L−1 , representing a 21% improvement over the conventional practice and variety.

In calculating total energy inputs, the one-way distance for transport of feedstock potatoes was assumed to be 10 km (20 km for a round trip) because bioethanol production from potatoes was not practiced at present in northern Japan. In this assumption, energy inputs for transport and total energy inputs were 1.24 and 28.4 GJ ha−1 , respectively (Table 4), accounting for 4.4% of total energy inputs for transporting. If the one-way distance was 20 km, transport of feedstock potatoes represents 8.4% of total energy inputs (2.48 GJ ha−1 over 29.64 GJ ha−1 of total energy inputs). This illustrates the significance of transportation distances between potato fields and bioethanol plants in assessing total energy inputs for bioethanol feedstock production. 4. Discussion 4.1. Agronomic options for bioethanol feedstock potatoes No- or low-ridge construction, lowered planting densities and omitting fungicide applications were chiefly aimed at reducing energy inputs from fuels and materials, while the use of high-yielding genotypes sought to increase potato starch-derived ethanol yields, thus lowering energy inputs to produce 1 L of ethanol. No- or low-ridge construction and lowered planting densities reduced energy inputs slightly, but also reduced ethanol yields, resulting in greater energy inputs per liter of ethanol produced (Table 4 and Fig. 1). This indicates no- or low-ridge construction and lowered planting densities would not likely contribute to energy-efficient bioethanol generation from potatoes. Even with potato genotypes tolerant to late blight, a significant decrease in ethanol yield and slightly greater energy inputs per liter of ethanol produced occurred when no fungicides were applied. As large reductions in ethanol yields are unacceptable from a viewpoint of stable feedstock supply, this practice is not appropriate for feedstock potato production. Similarly, Koga et al. (2009) have reported that omitting fungicide applications caused a large decrease in ethanol yields (a 31% decrease over conventional disease management), adversely affecting the overall energy balance of bioethanol-oriented sugar beet production in northern Japan. These results imply that proper disease management through pesticide applications is essential to any bioethanol feedstock crop production. The present study demonstrated that only the use of high-yielding genotypes providing consistently higher ethanol

The numbers in brackets represent standard deviation. a Starch yield = 8.51 (mean starch yield in Hokkaido) (Ministry of Agriculture, Forestry and Fisheries, Japanese Government, 2008) × starch yield factor (Table 1).

4.85 8.51

7.91 8.25 8.17 8.00 6.81 3.15 9.36 11.0 27.4 27.7 27.8 27.4 24.2 21.9 29.5 29.0

28.4 18.5

18.5 18.5 18.2 17.9 15.4 15.4 18.5 18.5 8.93 9.22 9.56 9.51 8.79 6.51 11.0 10.5

9.86

3.89 4.08 4.42 4.42 4.12 4.12 4.42 4.42

3.89 3.97 3.97 3.93 3.61 1.85 5.07 4.73

4.20 4.42 Conventional practice

No ridge construction Low ridge construction Planting density lowered (−14%) Planting density lowered (−25%) Fungicide applications omitted (registant genotypes) Fungicide applications omitted (susceptible genotypes) High-yielding genotype (cv. ‘Kachikei No. 24’) High-yielding genotype (cv. ‘Kon-iku No. 38’)

1.24

Total (GJ ha−1 ) Transportation (GJ ha−1 ) Harvesting (GJ ha−1 ) Tractor operations (GJ ha−1 )

1.15 1.17 1.17 1.16 1.06 0.544 1.49 1.39

Starch yielda (Mg ha−1 ) Total energy input (GJ ha−1 ) Materials (GJ ha−1 ) Diesel fuel Alternative agronomic practice

Table 4 Total energy inputs and estimated ethanol yields under different potato cultivation practices.

4.50 (0.53) 4.70 (0.28) 4.65 (0.34) 4.56 (0.42) 3.88 (0.28) 1.79 (0.82) 5.33 (0.62) 6.26 (0.46)

N. Koga et al. / Europ. J. Agronomy 44 (2013) 1–8 Estimated ethanol yield (kL ha−1 )

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yields could lower the energy inputs required to produce 1 L of ethanol. An increase in ethanol yields and a reduction in energy inputs achieved by employing high-yielding genotypes has been reported for sugar beet (Koga et al., 2009) and paddy rice (Koga and Tajima, 2011) in northern Japan, even though increased yield biomass increased energy requirements for harvest and transport of feedstock. Taking into account the uncertainty in energy inputs to produce 1 L of ethanol for simplified ridging and lowered planting densities (Fig. 1), there were no significant difference between these practices and conventional practice. The energy inputs per liter of ethanol produced of no fungicide application (susceptible genotypes) were highly uncertain in response to highly variable starch yields. Even with the uncertainty, no fungicide application for susceptible genotypes is an unfavorable practice. In feedstock crop production fully dedicated to bioethanol production, use of a high-yielding genotype is a proven way of improving overall energy balances. As shown in Tables 3 and 4, fertilizers used in potato cultivation were the major contributor to total energy consumption under the conventional practice (32% of the total energy input). This illustrates that fertilizer reductions allow us to reduce energy use although such reductions may have negative impacts on final starch yields. However, the relationship between soil nutrient status, and tuber yields and starch contents is highly uncertain because the impact of fertilizer reductions on tuber yields and starch contents depends largely on soil fertility. Unpublished data from a field experiment in 2008 (Table S4 in Supplementary Data) showed that final starch yields remained unchanged after fertilizer reductions at soils with a high inorganic N content (70 kg N ha−1 ) while fertilizer reductions lowered starch yields by 24% at soils with a low inorganic N content (20 kg N ha−1 ). Consequently, fertilizer reductions based on soil diagnosis contribute to reduced energy consumption and improved energy balances in feedstock production without sacrificing bioethanol yields. For energy balance of bioethanol feedstock production from root and tuber crops such as cassava has been intensively studied. Keeping in mind that the boundary conditions and energy equivalents used were different, energy input estimates for the production of ethanol from cassava feedstock in Thailand were 3.91 MJ L−1 (Nguyen et al., 2007) or 3.19 MJ L−1 (Papong and Malakul, 2010). Normalizing boundary conditions and energy equivalents for bioethanol feedstock production and transportation of sugar beet (Koga et al., 2009), paddy rice (Koga and Tajima, 2011) and potato in northern Japan, allowed the comparison of energy inputs to produce 1 L of ethanol (Fig. 2). Sugar beet under the improved practice of a combination of reduced tillage, use of high yielding genotypes and root + crown harvesting gave the best performance with respect to ethanol yield and energy inputs. Although the ethanol yield from potatoes under improved practice was slightly lower than that from sugar beets grown under conventional practices, the energy inputs were lower in potato under improved practice than in sugar beet under conventional practice. Potato was much superior to paddy rice as a feedstock crop in terms of ethanol yield and energy efficiency. Potato is thus as viable and available a bioethanol feedstock crop as sugar beet in northern Japan when high starchyielding varieties are grown. 4.2. Atmospheric greenhouse gas concentrations While crop-based bioethanol production contributes to fossil energy conservation, the contribution to atmospheric greenhouse gas concentrations of modern cropping systems, involved in producing bioethanol feedstock crops, remains a major concern. The cultivation of such crops involves both greenhouse gas emissions – nitrous oxide (N2 O) emissions from soils and CO2 emissions from fossil energy consumption – and soil C sequestration arising

N. Koga et al. / Europ. J. Agronomy 44 (2013) 1–8

Conventional practice

7

5.86

No-ridge construction

6.09

Low-ridge construction

5.89

Lowered planting density (-14%)

5.98

Lowered planting density (-25%)

6.01

Fungicide applications omitted (registant genotypes)

6.24 12.2

Fungicide applications omitted (susceptible genotypes) High-yielding genotype (cv. Kachikei No.24)

5.53

High-yielding genotype (cv. Kon-iku No.38)

4.63

0

2

4

6

8

10

12

14

16

18

20

Total energy input to produce 1 L of ethanol (MJ L-1) Fig. 1. Total energy inputs to produce 1 L of ethanol under different potato cultivation practices in northern Japan. Error bars indicate the range of standard deviation.

Fig. 2. Estimated ethanol yields and total energy inputs to produce 1 L of ethanol under conventional and improved feedstock cultivation practices for potato, sugar beet and paddy rice in northern Japan. The values for potato, sugar beet and rice were drawn from the present study, Koga et al. (2009) and Koga and Tajima (2011), respectively. The improved practices were use of high-yielding genotypes for potato; a combination of reduced tillage, use of high-yielding genotypes and root + crown harvesting for sugar beet; use of high-yielding genotypes for paddy rice. For rice, the energy efficiency was recalculated for a 10 km one-way transport distance.

from the enhanced incorporation of crop residues and organic amendments (Haas et al., 2000; Greenhouse Gas Inventory Office of Japan, 2008). Emissions of N2 O form soils are primarily dependent on N application rates and methods: those which increase crop N recovery are known to decrease N2 O emissions from soils (Cole et al., 1997). Not applying fungicide notably reduced tuber yields of susceptible potato genotypes. This and other yield-lowering cultural practices likely reduce crop N uptake, leaving more residual N in soil, and thus creating the potential for increased N2 O emissions from soils. On the other hand, the use of high-yielding genotypes would tend to reduce residual N in soils, and in turn decreased N2 O emissions from soils. In terms of soil C sequestration, it is important to assess the balance between C inputs to the soil from crop residues and organic amendments and C losses resulting from decomposition of organic materials in soils. At present, few studies have investigated the impacts of ridging (no, low or full ridging) on decomposition of organic matter in soils. However, if full ridging accelerates decomposition of organic matter in the soil as a result of improved soil drainage, soil C sequestration may take place under no or low ridging management. If use of high-yielding potato genotypes increases the amount of haulm to be incorporated into the soil, this may enhance soil C sequestration. Meanwhile, field management practices that decrease the amount of haulm as well as crop yields may have adverse effects on soil C sequestration. While the omission of fungicide application reduced material consumption-derived CO2 emissions, this practice can have negative impacts on atmospheric greenhouse gas concentrations as a result of increased soil N2 O emissions and C losses from soils. In contrast, use of high-yielding genotypes which increased

CO2 emissions from fossil energy use, potentially reduced N2 O emissions from soils and increased soil C sequestration. Planting densities had little impact on potato tuber yields (Table 1). This implies that planting densities have little impact on N2 O emissions from soil and soil C sequestration. 4.3. Further improvement in conversion of potato starch to ethanol Further improvement in ethanol yields and energy efficiencies might be possible for potato-based bioethanol production. It has been reported that starches from potatoes have a higher phosphorus content, greater granule size and higher peak viscosity than starches from other root crops such as sweet potato, cassava and Japanese yam (Dioscorea japonica Thunb.) (Noda et al., 2008; Absar et al., 2009). In addition, potato starches with a high content of phosphorus tend to have low hydrolysis rates while the starches undergo amylase digestion (Absar et al., 2009). This illustrates that in addition to improving starch yields, improvement of qualities of the potato starches through breeding programs or post-harvest technologies (e.g. dephosphorylation) might contribute to a further improvement of energy efficiencies in a full potato-based bioethanol production system. 5. Conclusion As potato is a promising bioethanol feedstock crop for northern Japan, this study sought to identify less energy-dependent and more ethanol-yielding potato cultivation practices to contribute

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N. Koga et al. / Europ. J. Agronomy 44 (2013) 1–8

to energetically viable bioethanol production systems. Results from 3 years’ field experiments indicated that no- or low-ridge construction, lowered planting densities and omission of fungicide applications worsened bioethanol energy efficiencies, mainly as a result of reductions in ethanol yield. Meanwhile, use of high-yielding genotypes contributed to improved energy efficiency (4.63 MJ L−1 for the high-yielding ‘Kon-iku No. 38’ compared to 5.86 MJ L−1 for the conventional practice). By the use of superior high-yielding potato genotypes, an ethanol yield of 6.26 kL ha−1 was achieved, only slightly lower than that obtained with conventionally produced sugar beet. Acknowledgements This study was funded by the Ministry of Agriculture, Forestry and Fisheries of Japan (Rural Biomass Research Project, BUMCm1320, BCD-A1111, BCD-A1113 and BCD-A1121). The author (N. Koga) wishes to thank Takahiro Noda and Hiroyuki Takahashi for their assistance in the research project. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.eja.2012.07.001. References Absar, N., Zaidul, I.S.M., Takigawa, S., Hashimoto, N., Matsuura-Endo, C., Yamauchi, H., Noda, T., 2009. Enzymatic hydrolysis of potato starches containing different amounts of phosphorus. Food Chemistry 112, 57–62. Center for Environmental Information Service, 1998. Guidebook for Life Cycle Inventory Analysis. The Chemical Daily Co. Ltd., Tokyo (in Japanese). Center for Global Environmental Research, 2007. Embodied Energy and Emission Intensity Data for Japan using Input–Output Tables. Center for Global Environmental Research, Tsukuba, Japan. Cole, C.V., Duxbury, J., Freney, J., Heinemeyer, O., Minami, K., Mosier, A., Paustian, K., Rosenberg, N., Sampson, N., Sauerbeck, D., Zhao, Q., 1997. Global estimates of potential mitigation of greenhouse gas emissions by agriculture. Nutrient Cycling in Agroecosystems 49, 221–228. Department of Agriculture, Hokkaido Government, 2005. Technological Protocols for Agricultural Production in Hokkaido, 3rd ed. Hokkaido Nogyo Kairyo Fukyu Kyokai, Sapporo, Japan (in Japanese). Greenhouse Gas Inventory Office of Japan, 2008. National Greenhouse Gas Inventory Report of Japan (2008). National Institute for Environmental Studies, Tsukuba, Japan.

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