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Journal of Resources and Ecology >

2021 , Vol. 12 >Issue 2: 254 - 259

DOI: https://doi.org/10.5814/j.issn.1674-764x.2021.02.011

Land Use Change and Land Multifunction Tradeoffs

Effect of Japanese knotweed (Fallopia japonica) Mulching on Continuous Potato Cropping: Modern Evaluation of Traditional Japanese Knotweed-mulch Farming in Nishi-Awa Steep Slope Land Agriculture System, Japan

  • INAGAKI Hidehiro , * ,
  • UNNO Nahoko ,
  • SAKAKIBARA Takumi ,
  • KUBOTA Sakiko ,
  • HASEGAWA Kana
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  • Shizuoka University, Kariyado, Fujieda, Shizuoka 426-0001, Japan
*: INAGAKI Hidehiro, E-mail:

Received date: 2020-03-19

  Accepted date: 2020-10-20

  Online published: 2021-05-30

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Abstract

Poaceae species such as silver grass or reed are commonly used in traditional mulch farming in Japan, where the Nishi-Awa area is a Globally Important Agricultural Heritage Systems (GIAHS) site. Farmers here have traditionally used silver grass for mulch farming; furthermore, local farmers have learned from long-standing experience that Japanese knotweed (Fallopia japonica, Polygonaceae) is better for cultivation of solanaceous crops in this area. However, it is unclear why Japanese knotweed mulching is beneficial for cultivation of solanaceous crops. Thus, in this study, we hypothesized that Japanese knotweed mulching may be effective in avoiding hazards associated with continuous potato cropping, as native potato used to be cultivated twice a year in the past. Therefore, we investigated the effects of Japanese knotweed mulching on continuous potato cropping and after tomato cropping, which is another solanaceous crop species. Field experiments were conducted in 2018. First, we compared Japanese knotweed mulching, silver grass mulching and no grass mulching (control) in a soil under continuous potato cultivation and in an uncultivated soil. As a result, the extent of the potato yield decrease was reduced by Japanese knotweed mulching. Secondly, we compared Japanese knotweed-mulching and no grass mulching in a soil after a tomato crop and in an uncultivated soil. The extent of decrease in potato growth and yield was also reduced by Japanese knotweed mulching. These findings indicate that mulching with Japanese knotweed helped to avoid the risks associated with continuous potato cropping.

Key words： continuous cropping; Globally Important Agricultural Heritage Systems (GIAHS); Japanese knotweed; mulch farming; potato; traditional farming

Cite this article

INAGAKI Hidehiro , UNNO Nahoko , SAKAKIBARA Takumi , KUBOTA Sakiko , HASEGAWA Kana . Effect of Japanese knotweed (Fallopia japonica) Mulching on Continuous Potato Cropping: Modern Evaluation of Traditional Japanese Knotweed-mulch Farming in Nishi-Awa Steep Slope Land Agriculture System, Japan[J]. Journal of Resources and Ecology, 2021 , 12(2) : 254 -259 . DOI: 10.5814/j.issn.1674-764x.2021.02.011

1 Introduction

An increasingly widespread awareness of the food security challenges posed by an ever growing global population, and exacerbated by the environmental problems resulting from intensive industrialization of the global food system and climate change, has forced researchers and policymakers to search for hope in local traditional knowledge by looking to ingenious agricultural systems that reflect a profound relationship with nature, and which have played a determinant role in the evolution of humankind (United Station University, 2011). The Food and Agriculture Organization of the United Stations (FAO) started the program named Globally Important Agricultural Heritage Systems (GIAHS) in 2002 with the aim to transmit the value and knowledge of traditional agriculture to the next generations (FAO, 2020a), and thus, allow us to learn important cues for achieving sustainable agriculture in the future, from the traditional agricultural systems preserved in the GIAHS site.
The mountainous area of Nishi-Awa in Tokushima, Japan, was registered a GIAHS site in 2018 (FAO, 2020b). The area is located in the steep Shikoku Mountains on the south side of the Median tectonic line, one of the largest faults in the world. Farmers in Nishi-Awa farm on steep terrain angled at over 40 degrees (Tokushima Tsurugisan Globally Important Agricultural Heritage Promotion Council, 2019). The farmlands of Nishi-Awa are too steep for terracing and they are characterized by crop cultivation on steep slopes (Tokushima Tsurugisan Globally Important Agricultural Heritage Promotion Council, 2019). Traditional agriculture at the site relies on mulching with cut wild plants (Hayashi, 2015). This type of mulching using plants effectively prevents soil erosion and actually contributes to soil formation, as it replenishes organic matter (Hayashi, 2015).
Generally, Poaceae species, such as silver grass (Miscanthus sinensis) and reed (Phragmites australis) are used for mulching-cultivation in Japan (Hadama et al., 1996; Inagaki and Kusumoto, 2015). Thus, in the Nishi-Awa area, silver grass has been the main species used for this purpose (Hayashi, 2015), whereas the Japanese knotweed (Fallopia japonica, Polygonaceae) has been considered by local farmers as better for cultivation of solanaceous crops (Hasegawa et al., 2018). Japanese knotweed is a perennial weed species that grows around crop fields and along forest edges. Indeed, mulching of cut Japanese knotweed is currently practiced for cultivation of eggplant, which is another solanaceous crop (Hayashi, 2015). However, this traditional farming method is simply based on tradition, while it remains unclear why knotweed is used only for eggplant cultivation.
To date, we have examined the positive effects of knotweed mulching on eggplant cultivation and we have shown that it increases brix and softens the peel of eggplants fruits (Hasegawa et al., 2018; Inagaki et al., 2019). Furthermore, we demonstrated that knotweed-mulching increased brix in tomato fruits, another solanaceous species (Unno and Inagaki, 2019; Unno et al., 2020). However, it is unlikely that a traditional farming practice that has been used for centuries, might have aimed only at improving modern quality and present commercial value of agricultural products. On the other hand, the local potato variety called ‘Goshuimo’ has been cultivated as an important food in this area where rice paddy fields are impossible to develop (Tokushima Tsurugisan Globally Important Agricultural Heritage Promotion Council, 2019). Potato is a typical solanaceous plant and a more important crop than eggplant or tomato in this area. In the mountainous regions of Japan, potatoes are locally called “Nidoimo”, Japanese for “a crop that can be harvested twice a year”. However, continuous cropping of a solanaceous species such as potato poses important damage to crops (Davis et al., 1994; Cambouris et al., 2008; Qin et al., 2014; Wang et al. 2014), whereby it is believed that it certainly has not been easy to cultivate potatoes while rotating crops on limited arable land in mountainous areas. Although potato is currently cultivated once a year without knotweed mulching, we assumed that Japanese knotweed mulching has been used for potato cultivation; further, we hypothesized that Japanese knotweed mulching may be effective in avoiding the hazards associated with continuous potato cropping. Therefore, in this study, we examined the effect of Japanese knotweed mulching on preventing the hazards related with continuous potato cultivation.

2 Materials and methods

2.1 Design of experiment 1: Effects on hazards related to continuous potato cropping

Potato autumn variety ‘Degima’ was tested. Seed potatoes were cut in half and planted in 30 cm diameter plastic pots on September 23, 2018. These pots were set in a greenhouse in the Fujieda field at Shizuoka University (63 Kariyado, Fujieda, Japan). Six experimental pots were prepared with two treatments of the potted soil: 1) uncultivated soil, 2) continuous cropping soil, which is used potato cultivation of spring cultivation variety ‘Dansyku’, and three mulching treatments: 1) Japanese knotweed mulching, 2) Silver grass mulching, and 3) no mulching (control). The pot experiment was laid in a randomized block design with five replications. Plant height and stem length were recorded during cultivation period. The chlorophyll content values (SPAD values) were obtained using SPAD-502Plus (KONICA MINOLTA, INC., Japan) and photosynthesis efficiency was measured using miniPPM (EARS, The Netherlands) on November 30. All potatoes were harvested and fresh and dry weights of stems and leaves, and the weight of each potato were measured on December 7.

2.2 Design of experiment 2: Effects on potato cultivation after tomato cultivation

The potato autumn variety ‘Degima’ was tested. Seed potatoes were cut in half and planted in 30 cm diameter plastic pots on October 8, 2018. These pots were also set in a greenhouse in the Fujieda field at Shizuoka University. Four experimental pots were prepared with two treatments in potted soil: 1) uncultivated soil, 2) continuous cropping soil after tomato ‘Aiko’ cultivation and two mulching treatments: 1) Japanese knotweed mulching, 2) no mulching (control). The experiment was laid in a randomized block design with five replications. Plant height and stem length are recorded during the cultivation period. The chlorophyll content values (SPAD values) were measured using SPAD-502Plus (KONICA MINOLTA, INC., Japan) and photosynthesis efficiency was measured using miniPPM (EARS, The Netherlands) on November 30. Potatoes were harvested and fresh and dry weight of stems and leaves, and weight of each potato were measured on December 5.

3 Results

3.1 Hazards related to continuous potato cropping

There were no obvious negative effects of continuous cropping on plant growth measured in terms of plant height, stem length, plant fresh weight, or plant dry weight either in uncultivated soil or continuous cropping soil (Table 1). We observed that plants tended to lie down because of succulent growth in the pots with continuous cropping soil. Because there were no differences in plant height, stem length, plant fresh weight, plant dry weight, photosynthesis efficiency or SPAD value, no effects of mulching on growth of potato were observed (Table 1).
Table 1 The effect of grass mulching on potato growth under conditions of continuous cropping
Soil Mulching Plant height (cm) Stem length (cm) Plant fresh weight
(g)		 Plant dry weight
(g)		 Photosynthesis
efficiency (%)		 Chlorophyll content
values (SPAD)
Continuous
cropping soil		 Japanese knotweed 34.1±11.2 43.1±9.1 135.4±14.1 11.7±1.0 68.4±0.8 30.5±2.0
silver grass 32.9±6.7 42.6±4.9 121.3±12.1 10.6±0.8 64.0±7.9 32.1±5.0
Non-treated (control) 32.3±11.2 42.4±6.1 128.0±20.8 11.7±1.9 67.6±2.7 31.3±2.3
Uncultivated soil Japanese knotweed 38.0±6.8 37.3±5.9 122.5±20.4 10.7±1.6 64.6±2.6 28.1±2.0
silver grass 38.3±7.9 38.3±5.1 123.6±10.6 10.5±0.5 65.6±1.9 29.4±2.2
Non-treated (control) 35.1±3.5 34.0±4.4 114.4±18.9 10.0±1.4 67.6±1.6 32.4±2.8
Sig. of ANOVA ns ns ns ns ns ns

Note: “ns” means not significant.

Neither were there any obvious differences in the mean number of potatoes among pots (Fig. 1). In comparison with uncultivated soil and continuous cropping soil, in the untreated plot, the mean number of harvested potatoes in uncultivated soil was 3.9, whereas in the continuous cropping plot the mean number was 2.8. In addition, in the silver grass mulching plot, the number of harvested potatoes in uncultivated soil was 4.9, whereas in the continuous cropping plot the number was 2.2. In contrast, in the Japanese knotweed mulching plot, there was little difference in number of harvested potatoes: 4.0 in uncultivated soil and 4.4 in the continuous cropping plot. No potatoes weighing 100 g or more were harvested in the continuous cropping soil in Japanese knotweed-mulching plot, whereas potatoes weighing 100 g or more were harvested in the uncultivated soil in Japanese knotweed mulching plot. However, no difference was observed between uncultivated soil and continuous cropping soil with regard to the number of potatoes of 50 g or more, compared to the Japanese knotweed-mulching plot.
Fig. 1 The effect of grass mulching on potato yield under conditions of continuous cropping

3.2 Potato cultivation after tomato cultivation

There was no difference in plant height or stem length of potato plants among pots (Table 2). Compared to uncultivated soil pots, there was no difference in plant fresh weight between Japanese knotweed-mulching and untreated soil (Table 2). On the other hand, potato plant fresh-weight in the two continuous-cropping soil pots decreased compared with the two uncultivated soil pots. However, the extent of decrease in fresh weight in the continuous cropping soil treatment was significantly smaller in the Japanese knotweed-mulching pots than in untreated pots. Mean potato plant dry-weight in untreated pots of continuous cropping soil was significantly lower than in any other pots. In comparison with untreated pots, photosynthesis efficiency in continuous cropping soil was significantly lower than in uncultivated soil pots (Table 2). In contrast, in comparison with Japanese knotweed mulching, there was no significant difference in photosynthesis efficiency between uncultivated soil and continuous cropping soil. SPAD values in continuous cropping soil were significantly lower than those in uncultivated soil, compared to untreated pots (Table 2). There was no significant difference in SPAD values between continuous cropping soil and uncultivated soil, compared with Japanese knotweed mulching pots (Table 2). The number of harvested potatoes in the two continuous-cropping soil pots was drastically reduced, compared with the two uncultivated soil pots (Fig. 2). In comparison with the two continuous-cropping soil pots, there was no difference in the number of harvested potatoes between Japanese knotweed-mulching and untreated soils. However, all the harvested potatoes weighed more than 10 g in the Japanese knotweed-mulching pots. On the other hand, there were many small potatoes (10 g or less) in untreated pots (Fig. 2).
Table 2 Effects of Japanese knotweed mulching on potato growth following tomato cultivation
Soil Mulching Plant height
(cm)		 Stem length
(cm)		 Plant fresh weight
(g)		 Plant dry weight
(g)		 Photosynthesis efficiency (%) Chlorophyll content
values (SPAD)
Continuous
cropping soil		 Japanese knotweed 33.5±1.5 38.0±2.0 179.8±28.3 b 35.3±1.7 a 58.3±0.6 ab 31.5±1.6 b
Non-treated (control) 28.0±2.0 29.0±2.0 137.5±22.5 c 24.3±2.2 b 48.0±8.2 b 29.2±3.0 b
Uncultivated soil Japanese knotweed 22.5±2.5 28.5±3.5 211.3±19.8 a 33.1±3.0 a 65.7±2.5 a 34.5±2.3 ab
Non-treated (control) 29.5±15.5 42.3±3.1 229.0±29.0 a 37.5±5.1 a 69.3±2.3 a 42.0±1.6 a
Sig. of ANOVA ns ns ** ** ** *

Note: “ns” means not significant; * and ** mean significant at P<0.05 and P<0.01, respectively. Different letters indicate significant differences among treatments based on Tukey’s multiple range test at 5% level.

Fig. 2 The effect of Japanese knotweed mulching on potato yield in the condition after tomato cultivation

4 Discussion

Continuous cultivation of crops in the same soil causes reduced growth and quality of crops because of hazards related to continuous cropping. In particular, solanaceous plants exhibit severe problems due to continuous cropping and it is difficult to cultivate solanaceous crops uninterruptedly for a long time. Potato is one of the solanaceous crop species that shows a wide range of hazards associated to continuous cropping (Davis et al., 1994; Cambouris et al., 2008).
In this study, we found that the extent of decrease in potato yield was reduced by Japanese knotweed-mulching; further, we propose that Japanese knotweed-mulching effectively prevented problems resulting from continuous potato cultivation. Although the Japanese knotweed is not currently used for potato cultivation in the Nishi-Awa area, we believe that Japanese knotweed might have been traditionally used there in the past.
The mechanisms underlying Japanese knotweed mulching-mediated avoidance of continuous-cropping hazards are not clearly understood. The causes of continuous cropping disorders are broadly classified into 1) deterioration of the soil nutritional balance due to depletion of specific soil nutrients, 2) increase of specific soil pests and pathogens, and 3) autotoxicity due to allelochemicals. One of the ways to avoid continuous-cropping hazards is to supply nutrients by incorporation of organic matter into the soil (Reeves, 1997; Tabuchi et al., 2017). Therefore, the effect of Japanese knotweed mulching may be due to the replenishment of soil minerals by decomposition of Japanese knotweed residues. However, if Japanese knotweed plants used for mulching are not sufficiently decomposed prior to the cultivation period, then there will be no change in soil mineral nutrient content during the course of a short period①(① Kubota and Inagaki, Some data not published.). Although nutrients would be supplied to the soil as Japanese knotweed was continuously used for many years, it is unlikely that nutrients were supplied from Japanese knotweed plants in this test, which was conducted over a very short period of time.
One the other hand, there is a possibility that allelochemicals of Japanese knotweed had a positive effect. Sometimes allelochemicals from plant litter have positive effects, not only negative effects. For example, one way to avoid continuous-cropping hazards is intercropping of companion plants (Yamada, 2001; Jankowska et al., 2009; Xiao et al., 2012; Xiao et al., 2013). The reason of this is that allelochemicals from companion plants control soil pests and pathogens, thereby having a positive effect on crop growth. Similar to companion plants, other allelochemical exudates from Japanese knotweed litter might reduce soil disease or reduce allelochemical autotoxicity. Therefore, the mechanism underlying the effects of Japanese knotweed-mulching certainly warrants further study.
In traditional agriculture, rotation and fallow have been practiced in order to avoid continuous-cropping hazards. On the other hand, modern agriculture has enabled continuous cropping by supplying nutrients through the application of chemical fertilizers and by chemically controlling soil pests and pathogens in order to increase crop production. However, chemical control of plant pest and disease incidence negatively affect the environment, causing pollution and ecosystem degradation. Therefore, continuous cropping has become a serious problem in modern world agriculture. The data reported herein suggested that the components of Japanese knotweed avoided potato continuous-cropping hazards. Traditional use of Japanese knotweed-mulching is an effective method for small farms. However, it would be very difficult and impractical to harvest and mulch large quantities of Japanese knotweeds for large scale agriculture. Future research and development efforts must focus on the extraction and identification of active bioingredients contained in Japanese knotweed for developing useful materials derived from Japanese knotweed.

5 Conclusions

Poaceae species such as silver grass or reed are commonly used in traditional mulch farming in Japan. However, local farmers have learned from long-standing experience that Japanese knotweed (Fallopia japonica, Polygonaceae) is better for cultivation of solanaceous crops in the Nishi-Awa area, where is a Globally Important Agricultural Heritage Systems (GIAHS) site. It is unclear why Japanese knotweed mulching is beneficial for cultivation of solanaceous crops. We hypothesized that Japanese knotweed mulching may be effective in avoiding hazards associated with continuous potato cropping, as native potato used to be cultivated twice a year in the past. In this study, we investigated the effects of Japanese knotweed mulching on continuous potato cropping and after tomato cropping, which is another solanaceous crop species. As a result, the extent of the potato yield decrease was reduced by Japanese knotweed mulching. In addition, we compared Japanese knotweed-mulching and no grass mulching in a soil after a tomato crop and in a uncultivated soil. The extent of decrease in potato growth and yield was also reduced by Japanese knotweed mulching in a soil after a tomato crop cultivation. These findings indicate that mulching with Japanese knotweed helped to avoid the risks associated with continuous potato cropping.
Traditional farming communities in rural areas have developed various traditional ecological knowledge (TEK) systems as products of long years of interaction and co-evolution between natural environments and human society. Recently, such TEK systems are being reevaluated for potential application in future sustainable agriculture activities. The traditional agricultural systems in GIAHS should offer insights on how to achieve sustainable agricultural production in the future. From present study, we concluded that Japanese knotweed mulching (which is traditional farming in Japanese GIAHS site) had a positive effect on avoiding the problems associated with continuous potato cropping, and we recognize this farming as one of the most valuable TEKs.

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