(2022) 3:20
Lailati et al. CABI Agriculture and Bioscience
https://doi.org/10.1186/s43170-022-00087-6

CABI Agricultureand Bioscience
Open Access

RESEARCH

Effects of ground bamboo application
on weed suppression and rice production:a 3‑year paddy field experiment
Masfiro Lailati1,2†, Yichen Shang1†, Thien Quang Huynh1,3†, Koji Ito4, Naoya Katsumi5, Yumiko Mizuuchi6,
Masaya Ino6, Tadao Takashima7 and Nisikawa Usio1,8*

Abstract
Background: In light of the dramatic expansion of Japan’s bamboo forests, it is necessary to develop a strategy forthe effective use of bamboo biomass resources. In this study, we tested the effects of ground bamboo as an organic
mulching material or soil conditioner during a 3-year, agrochemical-free rice cultivation period.
Methods: We performed field experiments in 16 experimental paddy fields and established five treatments withthree or four replicates each: control, manual weeding, low-volume ground bamboo application (0.5 kg ­m−2),
medium-volume ground bamboo application (1.0 kg ­m−2), and high-volume ground bamboo application(2.0 kg ­m−2).
Results: We observed no suppression of aquatic weeds with the ground bamboo treatments. Nevertheless, in thefirst year, rice yields were 1.7–1.8 times greater in the medium- and high-volume ground bamboo treatments thanin the controls. In the second and third years, rice yields did not differ among treatments. During the 3-year period,
mean rice yields dropped dramatically to around 20%. Simple linear regression analyses indicated that rice yields werepositively associated with available phosphate, and negatively associated with the silicic acid content of post-experiment paddy soils after the second and third years of cultivation. Multiple linear regression analyses indicated thatavailable phosphate and silicic acid were important variables explaining rice yields. Application of ground bamboo
did not appear to reduce external rice grain quality.
Conclusions: Application of ground bamboo may enhance the production of high-quality rice, particularly when soil
phosphorus is not deficient.
Keywords: Environmentally friendly farming, Moso bamboo, Organic farming, Satoyama, Silicon
Introduction
In recent decades, there have been more bamboo forests
in human-modified landscapes, particularly in southern, western, and central Japan, due to farmers’ aging,*Correspondence: usio@se.kanazawa-u.ac.jp†
Masfiro Lailati, Yichen Shang, and Thien Quang Huynh contributed
equally to this study
1
Graduate School of Natural Science and Technology, Kanazawa
University, Kanazawa 920‑1192, Japan
Full list of author information is available at the end of the article

heavy management burdens, and a decline in bamboo exploitation (Okutomi et al. 1996). From 1986 to
2012, the total area of bamboo forest in Japan increased
by around 10%, from 147,000 to 161,000 ha (Forestry
Agency 2018). Consequently, native deciduous forestsand uncultivated agricultural land in particular havebeen progressively invaded by introduced moso bamboos(Phyllostachys edulis (Carrière) J. Houz.) (Okutomi et al.
1996; Suzuki and Nakagoshi 2011). Bamboo invasion offorests and agricultural land has reportedly caused the© The Author(s) 2022. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which
permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to theoriginal author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images orother third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line
to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory
regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of thislicence, visit http://​creat​iveco​mmons.​org/​licen​ses/​by/4.​0/. The Creative Commons Public Domain Dedication waiver (http://​creat​iveco​
mmons.​org/​publi​cdoma​in/​zero/1.​0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data.

Lailati et al. CABI Agriculture and Bioscience(2022) 3:20

death of coniferous trees, promoted sediment erosion,and reduced plant diversity (Hiura et al. 2004; Yamamoto
et al. 2004; Suzuki 2010).
In recent years, various strategies have been implemented in Japan with the aim of effectively utilizing
bamboo biomass resources. Bamboo has generally been
considered unsuitable as fertilizer because its essential
nutrient contents (e.g., nitrogen, phosphorus and potassium) are low. However, recent studies have reported
that microbial fermentation progresses remarkably bygrinding the xylem, because the internal organs of bamboo contain abundant sugars (Rural Culture Association2012). Therefore, ground bamboo’s (or ‘bamboo chips’)
potential applications as a soil conditioner or mulch haveattracted considerable attention in dryland farming. For
example, several studies have reported that surface application of ground or chipped bamboo increased yields ofsoybeans (Nakagawa et al. 2009), tomatoes (Yagi et al.
2016a), and spinach (Asagi and Noda 2006). Research has
also demonstrated that application of ground or chippedbamboo suppresses weed growth in horticultural fields(Yagi et al. 2016b). However, with the exception of bamboo charcoal (Toma et al. 2019), the effectiveness ofground bamboo application for rice farming has rarely
been tested.
Rice yields in agrochemical-free farms are only 32–88%
of those in conventional farms (Oomori 2015). Suppression of aquatic weeds (and consequent enhancement ofrice yields) presents major challenges in agrochemicalfree rice farming. Major weed control techniques include
physical controls that use weeding machines or herbivorous animals (Anas platyrhynchos var. domesticus L.,
Oreochromis niloticus (L.), Cyprinus carpio L., and Triopsspp.), organic or paper mulch, or summer deep flooding practices (Katayama et al. 1974; Harada et al. 2001;
Frei et al. 2007; Nakai and Toritsuka 2009). Rice bran is
typically used in organic rice farming owing to its wideavailability and low cost. Several studies have tested theeffectiveness of rice bran application for aquatic weed
control and rice production (Chiba et al. 2001; Nakai
and Toritsuka 2009; Nakayama 2010). However, rice bran
application has been shown to be unstable in the presence of major aquatic weeds, such as Monochoria vaginalis (Burm. f.) C. Presl ex Kunth and Schoenoplectiellajuncoides (Roxb.) Lye (Nakai and Toritsuka 2009). The
protein content of rice grains may be elevated (an indicator of bad taste) under rice bran application due to thehigh nitrogen content of rice bran (Kujira et al. 2004).
In a microcosm experiment, Usio et al. (2021) foundthat application of ground bamboo suppressed aquatic
weeds and increased rice yields, without causing any
deterioration of external grain quality or enhancementof protein content. In a preliminary experiment, weed

Page 2 of 16

suppression, and fertilizer or soil conditioning effects(via nutrient supply from ground bamboo), were considered major mechanisms of rice yield enhancement(Usio et al. 2021). Silicon is among the major ingredientsof bamboo (see Table 1). Although silicon is not considered an essential nutrient, its addition can enhance plant
growth by mitigating various abiotic stresses, such as
salinity, metal toxicity, and ultraviolet irradiation, as wellas biotic stress caused by pests and plant diseases (Ma2004; Epstein 2009). In rice plants, silicon contributes toincreased photosynthetic rates by reducing lodging andimproving leaf and stalk erectness (Savant et al. 1999;
Mihara et al. 2017). Silicon also affects phosphorus availability for plants via phosphorus mobilization (reviewed
in Hu et al. 2021).
In this study, we scaled up the experiment, both spatially and temporally. In experimental paddy fields, we
conducted a field experiment to evaluate whether groundbamboo application would yield stable or reproducible
results with respect to consecutive agrochemical-freerice cultivation. We hypothesized that ground bamboo
application would suppress aquatic weeds and thereby
enhance rice yields. An alternative hypothesis was thatground bamboo application would have fertilizing or soil
conditioning effects. We also expected ground bamboo
application to not enhance rice grain protein content
owing to its low nitrogen content.

Methods
Ground bamboo preparation

In mid-May 2017, 2018, and 2019, we harvested approximately 50 bamboos from the Satoyama Zone of Kanazawa University Kakuma Campus, Ishikawa Prefecture,

Table 1 Chemical properties of the ground bamboo used in the
paddy field experiments conducted in 2017–2019
Parameter

2017

2018

2019

Water ­contenta (%)

35.70

28.45

31.50

pHa

–

5.07

4.92

Electrical ­conductivitya (mS ­cm−1)

–

0.70

0.59

Total ­nitrogenb (%)

0.19

0.20

0.34

Total ­carbonb (%)

49.50

52.90

50.20

Phosphorus ­pentoxideb (%)

0.21

0.12

0.08

Potassium ­oxideb (%)

0.54

0.41

0.27

Calcium ­oxideb (%)

–

0.03

0.05

Magnesium ­oxideb (%)

–

0.05

0.07

Silicic ­acidb (%)

–

0.28

0.20

Data from 2018 were based on the chemical properties of bamboo culm
provided in Usio et al. (2021)a

Based on wet samplesb

Based on dry samples

Lailati et al. CABI Agriculture and Bioscience(2022) 3:20

Japan. After removing the leaves and branches, weground the bamboo culms using a fuel-operated woodcrusher (DraCom KDC-1301B; Karui Corporation,
Yamagata, Japan). We packed the ground bamboo inplastic bags (60 L) secured at the mouth. The groundbamboo culms were placed inside a glasshouse to ferment for 15–20 days. The mean ± SD temperature in
the glasshouse was 22.3 ± 4.9 °C (range: 13.3–34.1 °C)
in 2017, 22.3 ± 6.0 °C (range: 12.1–41.1 °C) in 2018, and29.2 ± 9.4 °C (range: 15.2–53.6 °C) in 2019, according tohourly measurements made using a temperature logger(HOBO Water Temp Pro v2; Onset Computer Corporation, Bourne, MA, USA).
The fertilizer properties of two 250 g subsamples of fermented culm samples were determined by the Physicochemical Analysis Center (Vegetech Co., Ltd., Kanagawa,Japan) in 2017, and by the Bio Innovation Center (Yanmar Holdings Co., Ltd., Kurashiki, Japan) in 2018 and2019 (Table 1). Ground bamboo contains few essential
nutrients such as total nitrogen (mean, 0.24%; range:
0.19–0.34%), phosphorus pentoxide (mean, 0.14%; range:
0.08–0.21%), and potassium oxide (mean, 0.41%; range:
0.27–0.54%). All fertilizer analyses were performed inaccordance with official procedures (National Institutefor Agroenvironmental Sciences 1992).
Paddy field experiment

We performed a 3-year field experiment in 16 experimental paddy fields (each 30 ­m2; 7.5 m long × 4 m wide)at the Botanical Garden, Institute of Nature and Environmental Technology, Kanazawa University (Fig. 1). Theseexperimental paddy fields were newly developed fromcrop fields in winter 2016. Eight experimental paddy
fields were aligned in two rows, and groundwater was
supplied to each field using a bulb.
We established five treatments, with three or four replicates each, using a completely randomized design as follows: control (three replicates in 2017, four replicates in
2018–2019); manual weeding (three replicates); low-volume ground bamboo application (three replicates) (15 kg
paddy ­field−1 or 0.5 kg ­m−2); medium-volume groundbamboo application (three replicates) (30 kg paddy­field−1 or 1 kg ­m−2); and high-volume ground bamboo
application (three replicates) (60 kg paddy fi­eld−1 or−2
2 kg ­m ). Although we initially transplanted the rice into
16 experimental paddy fields, we omitted the 2017 resultsfor one field due to shading effects from a riparian tree.
From 2018, we included this paddy field as a control after
cutting down the riparian tree. We retained the original treatments in all paddy fields over the 3-year study
period.
We ploughed twice each year (on 24 and 29 May
in 2017, 13 and 22 May in 2018, and 19 and 29 May inPage 3 of 16

Control
Inlet

ManualWater flow

L-bam

M-bam

H-bam

OutletFig. 1 Plan of the 16 experimental paddy fields (30 ­m2; 7.5 mlong × 4 m wide) used in this study (not to scale). Manual, manual
weeding treatment; L-bam, low-volume ground bamboo application
treatment (15 kg paddy ­field−1; 0.5 kg ­m−2); M-bam, medium-volume
ground bamboo application treatment (30 kg paddy ­field−1;
1.0 kg ­m−2); L-bam, high-volume ground bamboo application
treatment (60 kg paddy ­field−1; 2.0 kg ­m−2)2019) using fuel-operated ploughing machines (TA400 or
TRS60; Kubota, Tokyo, Japan). We obtained Koshihikari
seedlings (Oryza sativa L. cv. Koshihikari) from JA Hakui;these were grown without the use of agrochemicals. In
both years, we transplanted the agrochemical-free Koshihikari seedlings in early June (on 3 June in 2017, 3 June in2018 and 1 June in 2019). To facilitate rice transplantation, a wooden device called a “waku” was used to markgrids on the bottom surfaces of the experimental paddy
fields. We manually transplanted 322 (14 × 23 rows; 3
seedlings per locale) (2017) or 345 rice plants (15 × 23
rows; 3 seedlings per locale) (2018–2019) in each paddy
field. Soon after rice transplantation, we manually applied
fermented ground bamboo culms to the paddy surfaceof the three ground bamboo treatments. In each paddy
field, we installed a temperature logger (HOBO Water
Temp Pro v2) near the outlet. Water temperatures wererecorded hourly during the experiments; the mean ± SD
water temperature was 25.0 ± 4.3 °C (range: 9.2–39.4 °C)
in 2017, 26.4 ± 4.9 °C (range: 10.0–42.7 °C) in 2018, and26.5 ± 4.3 °C (range: 14.7–41.9 °C) in 2019.
Experimental paddy fields were continuously inundated (5‒17 cm of water depth) from early June to early
September without mid-season drainage. During ricecultivation, no agrochemical or fertilizer (other thanground bamboo culms) was applied in the experimental
paddy fields. In conventional rice farming in Ishikawa
Prefecture, mid-season drainage is typically performed
from early June for approximately 1 month to prevent theoverdiversification of rice plants. However, we did not
perform mid-season drainage because dramatic waterlevel fluctuations may lead to the overgrowth of aquatic
weeds. In addition, agrochemical-free rice seedlings do

Lailati et al. CABI Agriculture and Bioscience(2022) 3:20

not diversify as much as those grown using fertilizers.
Thus, overdiversification is uncommon in agrochemicaland fertilizer-free farming.
In the manual weeding treatment, one to three people
manually removed aquatic weeds once between mid-Julyand early August, prior to panicle initiation (14 July 2017,
6–8 August 2018, and 18–21 July 2019).
We measured the paddy sediment’s oxidation–reduction potential (ORP) approximately 1.5 cm below the soil
surface using a portable ORP meter (RM-30P; Toa-DKK
Corporation, Tokyo, Japan). We took ORP measurements
three times in 2017 (4, 7, and 11 days after rice transplantation), 2018 (after 5, 8, and 12 days), and 2019 (after 3,8, and 13 days). On each day, we arbitrarily selected two
locales each from the long sides and one locale from theoutlet side. For each paddy field, we calculated the average ORP value based on five measurements. The ORP
values were measured using a silver–silver chloride electrode containing 3.33 mol ­L−1 potassium chloride. To
estimate standard hydrogen electrode ORP ­(ORPSHE)values, we used the following formula (Matsushita et al.
1974):

ORPSHE = E + 206−0.7 × (t−25),
where E (mV) is the ORP value measured using a silver–
silver chloride electrode containing 3.33 mol ­L−1 potassium chloride and t (°C) is the water temperature.
Between July and August, we measured rice plantheight, tiller numbers, and leaf color [soil plant analysis development (SPAD) values] as indices of rice plant
growth. In each paddy field, we selected three healthy rice
plants from each of the two long sides and the outlet side,
for a total of nine plants. We measured plant height fromthe base of the rice plant’s aboveground part to the tip ofthe longest leaf using a folding scale. The tiller numbers
reflected the total number of diversified stems. Owing toan erroneous measurement, the tiller numbers in 2018
were not used in the analyses. Using a SPAD chlorophyll
meter (SPAD-502; Konica Minolta Inc., Tokyo, Japan), we
measured the SPAD value by averaging three measurements from three leaves in each rice plant. The average
rice plant height, tiller numbers, and SPAD values were
calculated based on nine rice plants from each paddy
field.
In late July (24–25 July in 2017, 22–23 July in 2018and 29–30 July in 2019) and late August (21–22 August
in 2017, 30–31 August in 2018 and 26–27 August in2019), we surveyed aquatic plants using a wire quadrat(50 cm × 50 cm). On each date, we arbitrarily selected
one locale each from the two long sides and the outlet
side, for a total of three locales. We selected different
locales for the first and second samplings. After placing the quadrat on the paddy sediment, we manually

Page 4 of 16

collected all aquatic plants (other than rice plants) within
the quadrat. We identified aquatic plant species using
a guidebook (Asai 2015). In the laboratory, all aquaticplants were washed with tap water to remove sediment,
placed in envelopes according to species, and dried inan oven (DKN812; Yamato, Co., Ltd., Tokyo, Japan) at
50 °C for 4‒7 days. We determined the dry weights of theaquatic plants using an electronic balance, and recorded
the most dominant species.
In each year, we harvested rice plants in late September(21 September 2017, 23 September 2018, and 24 September 2019). In each paddy field, we arbitrarily selected fiverice plants from the second or third row, along the twolong sides and the outlet side, for a total of 15 rice plants.
We air-dried harvested rice plants for several weeks
until the rice grains’ water content dropped to around
15%. After air drying, we performed threshing using anelectric threshing machine (MR-400MD; Ogihara, Ota,Japan) and hulling using a rice huller (FC2K; Otake Seisakusho, Aichi, Japan). We determined the rice yields
based on the air weights of brown rice.
We measured external rice grain quality parameters
and the protein and amylose contents of brown rice as
described previously (Usio et al. 2021). A grain discriminator (RN-310; Kett, Tokyo, Japan) was used to calculate
the percentages of sound, immature, cracked, damaged,
discolored, and dead grains. A multi-auto counter (KC10; Fujiwara Seisakusho, Co., Ltd, Tokyo, Japan) was used
to determine thousand-grain weights. A near-infraredtransmittance rice composition analyzer (AN-820; Kett)was used to measure the protein and amylose contentsof rice grains. Within the damaged grain category, we
retained only data for malformed grains, omitting allother data (i.e., data on grains that were germinated,fermented, damaged by insects, damaged by fungus ormold, brown-colored or broken) together with those ofcracked, discolored, and dead grains, because these grain
quality measurements comprised < 5% of all measurements on average among all treatments. In summary, wemeasured thousand-grain weight; percentages of normal,
immature, and malformed grains; and protein and amylose content (%) as indicators of rice grain quality. For
each measurement, we obtained two subsamples and calculated the mean value.
In 2018 and 2019, we determined the air-dry mass ofrice straw and the nutrient contents of the powderedrice straw samples. After threshing, we determined theair-dry mass of the rice straw in each paddy field. Usinga plant sample crusher (Wonder Blender WB-1; As One
Corp., Osaka, Japan), we ground the straw subsamples
into powder. Then, we obtained a 200-g straw subsample from each paddy and dried it in an oven at 50 °C for
5 days.

Lailati et al. CABI Agriculture and Bioscience(2022) 3:20

We measured the carbon, nitrogen, phosphate, andpotassium contents of the powdered rice straw samples. We measured the nitrogen and carbon contentsof the straws using the combustion method. For eachpaddy field, approximately 50-μg samples of powderedstraw were placed in tin capsules. The capsules wereanalyzed using an automatic elemental analyzer (vario
ISOTOPE cube; Elementar, Japan, Yokohama, Japan)
under the following operating conditions: oxidation furnace, 1150 °C; reduction furnace, 850 °C; and He flow
rate, 230 mL ­min−1. We measured the potassium andphosphate contents of the straws by the wet incineration method using an inductively coupled plasma optical emission spectrometer (ICP-OES; 5800 ICP-OES;
Agilent Technologies Japan, Tokyo, Japan). Duplicate
0.2 g samples of powdered straw from each paddy field
were transferred into centrifuge tubes. Following aciddecomposition with concentrated nitric acid and hydrogen peroxide followed by dilution, the phosphate andpotassium contents of the samples were obtained using
the 5800 ICP-OES. The silicic acid contents of the straws
were determined using the perchloric acid method by the
Bio Innovation Center in accordance with official procedures (National Institute for Agroenvironmental Sciences
1992).
In 2018 and 2019, we collected soil samples before
transplantation (late May) and after harvest (late September), representing the pre- and post-experimental
samples. In each paddy field, we arbitrarily selectedfour locales near the corners, and one near the center,
for a total of five locales. Using a bulb planter (Arkland
Sakamoto, Sanjo, Japan), we collected soil to a depth of
7 cm. Subsamples were thoroughly mixed in a bucket
and air-dried in a glass house for 2 weeks. A 200-g subsample was placed in a sealed plastic bag and stored in arefrigerator. Soil samples were sent to the Bio Innovation
Center for analyses of pH, electrical conductivity (EC),humus, cation exchange capacity (CEC), the phosphateabsorption coefficient, ammonium nitrogen, nitrate
nitrogen, available phosphate, exchangeable potassium,
exchangeable calcium, exchangeable magnesium, freeiron oxide, and available silicic acid. In line with the present study’s purposes, we present the pH, total inorganic
nitrogen (sum of ammonium and nitrate nitrogen), available phosphate, exchangeable potassium, and available
silicic acid data. Analytical procedures for soil chemistry are described in the supplementary material of Usioet al. (2021). In brief, pH in the paddy soils was measured
using an APS-40 pH/EC autoanalyzer (HRD Technology
Co. Ltd., Toyokawa, Japan); ammonium and nitrate nitrogen, available phosphate, and silicic acid contents were
measured using a high-speed soil nutrient automatic analyzer (SNA24i; Fujihira Industry Co. Ltd., Tokyo, Japan);Page 5 of 16

and the exchangeable potassium contents were measured
using ICP-OES (iCAP-7200 Duo; Thermo Fisher Scientific K. K., Tokyo, Japan).
Statistical analyses

We used generalized linear models (GLMs) to explore
differences among treatments in surface soil O­ RPSHEvalues, aquatic plant dry biomass, and rice plant growth(height, tiller numbers, and SPAD values). Treatment and
day were fixed factors and day was the repeated measures factor, with compound symmetry designated as acovariate. For variables without repeated measurements(rice yield, rice grain quality, straw chemical properties, and soil chemical properties), we used a GLM withtreatment as a fixed factor. For all response variables, weused normal models with identity links. When the normality assumption was not satisfied by the raw data, weused a square root or log transformation. When a significant treatment effect or treatment × day interaction
was obtained, we performed the Bonferroni correction
to control for type I error. GLM analyses were performed
using SPSS software (version 24.0; IBM Corporation,
Armonk, NY, USA).
We performed simple and multiple linear regression
analyses to explore the relationships between brownrice yields and post-experimental paddy soil nutrients.
Because post-experiment soil phosphorus and potassium contents showed high collinearity in 2018 and 2019
(r = 0.76 and r = 0.75, respectively), we omitted potassium as a predictor. We selected models based on Akaike’s information criterion correction for small samples(AICc) and considered the model with the smallest AICc
to be the best model. The models were considered equivalent when the difference in AICc (∆AICc) was less than
2. Simple and multiple linear regression analyses were
performed using R software (version 4.1.0; R Core Team2021). In multiple linear regression analyses, AICc calculations and model selection were performed using the R
package MuMIn (Barton and Barton 2015).

Results
Oxidation–reduction potential

Significant treatment and treatment × day interaction
effects for ORP on the soil surface were observed for all
years (Fig. 2, Table 2). Although the magnitude of treatment differences varied among dates, the ­ORPSHE values
for the three ground bamboo treatments were lower relative to the control, implying that paddy soils treated withground bamboo provided anti-oxidizing conditions.
Aquatic plants

The dry biomass of all aquatic plants, and of themost dominant species, M. Vaginalis, differed among

Lailati et al. CABI Agriculture and Bioscience(2022) 3:20

Page 6 of 16

2017

ORPSHE (mV)

500

2018

Treatment***
Controla, Manuala > L-bamb, M-bamb, H-bamb

500

400

400

300

300

200

200

100

100

0

6/6

-100

6/11

500
400
200

Treatment***
Controla, Manuala> L-bamb, M-bamb, H-bamb

100
0
6/8

-100

-200

ControlManual
L-bam
M-bam
H-bam

300

0

6/15

2019

Treatment***
Controla, Manuala > L-bamb, M-bamb, H-bamb

6/11

6/15

6/4

-100

6/9

6/14

-200

-200

Month/dateMonth/dateMonth/date

Fig. 2 Oxidation–reduction potential (ORP) of paddy surface soil in paddy field experiments conducted in 2017–2019. ORP is expressed as standardhydrogen electrode ORP ­(ORPSHE). Data are mean ± SE. Different superscript letters indicate significant differences (α = 0.05) according to Bonferroni
post-hoc tests. Treatments are described in Fig. 1. ***P < 0.001

Table 2 Selected statistics from generalized linear models of the standard hydrogen electrode oxidation–reduction potential ­(ORPSHE)
of paddy surface soil in paddy field experiments conducted in 2017–2019
Parameter

Treatment

Treatment × day

Post-hoc comparison by day
Day 1

Day 2

Day 3

df

F

P

df

F

P

df

F

P

df

F

P

df

F

P

4, 10

21.73

< 0.001

8, 20

2.50

< 0.001

4, 23

23.75

< 0.001

4, 23

10.10

< 0.001

4, 23

7.21

0.001

4, 11

16.36

< 0.001

8, 22

3.06

0.018

4, 26

21.47

< 0.001

4, 26

7.04

0.001

4, 26

4.06

0.011

4, 11

73.63

< 0.001

8, 22

18.12

< 0.001

4, 24

11.31

< 0.001

4, 24

85.49

< 0.001

4, 24

62.21

< 0.0012017
 ­ORPSHE2018
 ­ORPSHE2019
 ­ORPSHE

Significant differences (P < 0.05) are indicated by bold font. See Fig. 2 for the exact sampling dates for days 1–3 in each year

treatments in 2018 and 2019, but not in 2017 (Fig. 3,
Table 3). In 2018 and 2019, the total biomass was significantly reduced only in the manual treatment relative toother treatments. The differences in M. vaginalis biomassamong treatments generally followed those of the total
aquatic plants. The dry biomass of M. vaginalis in 2018and 2019 was less abundant only in the manual treatmentcompared to the control.
Rice plant growth

GLM analyses revealed a significant treatment × day
interaction effect on tiller numbers in 2017 (P < 0.05;
Fig. 4, Table 4). Post-hoc comparisons indicated thattreatment effects were significant for Days 2 (7/28) and3 (8/11). However, on Day 2, post-hoc within-day treatment comparisons did not reveal statistical differences
between any treatment pairs. On Day 3, post-hoc withinday treatment comparisons indicated that tiller numbers
were 1.6 times greater in the high-volume ground bamboo treatments than the control.
In 2019, a significant treatment × date interaction effecton plant height was found (P < 0.05). However, post-hoc

within-day treatment comparisons revealed no statisticaldifferences among treatments on any day.
The effect of treatment was not significant for any rice
plant growth variables across the 3 years.
Chemical properties of rice straw

In both 2018 and 2019, the air-dry mass of rice straw,
and contents of total carbon, total nitrogen, phosphorus
pentoxide, potassium oxide, and silicic acid, did not differ
among the treatments (Table 5).
Rice yield and grain quality

The mean brown rice yield was 734.84 g 15 rice ­plants−1(ca. 5258 kg ­ha−1) in 2017, 240.94 g 15 rice ­plants−1 (ca.
1847 kg ­ha−1) in 2018, and 144.34 g 15 rice p­ lants−1 (ca.
−11107 kg ­ha ) in 2019. Over the 3 years from 2017 to
2019, the mean rice yield has dramatically dropped to20%. In all years, rice yields did not differ among treatments (Fig. 5, Table 6). However, when the results of the
low-volume ground bamboo treatments in 2017 wereomitted, a significant difference in brown rice yields
was evident among treatments, with medium- andLailati et al. CABI Agriculture and Bioscience(2022) 3:20

Page 7 of 16

2017

2018

Dry weight (g) 15 rice plants-1

Dry weight (g) 15 rice plants-1(a) Total aquatic plants
200

200

150

150

100

100

50

50

0

0

180

Treatment**
Manuala ≤ L-bamab, Controlb, M-bamb, H-bamb(a) Total aquatic plants
140

Treatment**
Manuala < Controlb, L-bamb, M-bamb, H-bamb

120
100
80
60
40
20

7/24

8/21

(b) Monochoria vaginalis
200

150

7/22

0

8/30

90

(b) Monochoria vaginalis
Treatment*
Manuala ≤ Controlab, L-bamab, H-bamab, M-bamb

120

100
80
60
40

50

30
7/24

ControlManual
L-bam
M-bam
H-bam

20

0

8/21

8/26

Treatment*
140
Manuala ≤ Controlab, L-bamab, H-bamab, M-bamb

100

60

7/29

(b) Monochoria vaginalis

150

120

0

2019

(a) Total aquatic plants

7/22

Month/date

0

8/30

7/29

Month/date

8/26

Month/date

Fig. 3 Dry biomass of total aquatic plants and the most dominant species (Monochoria vaginalis) in paddy field experiments conducted in 2017–2019. Data are means ± standard error (SE). Different superscript letters indicate significant differences (α = 0.05) according to Bonferroni post-hoc
tests. Treatments are described in Fig. 1. *P < 0.05, **P < 0.01

Table 3 Selected summary statistics from generalized linear models of the effects of treatment on the dry biomass of total aquaticplants and the most dominant species (Monochoria vaginalis) in the paddy field experiments conducted in 2017–2019
Parameter

Treatment
dfF

Treatment × day
P

df

F

Post-hoc comparison by day
P

Day 1
df

Day 2
F

P

df

F

P

2017
Total aquatic plants

4, 10

2.44

0.115

4, 10

1.36

0.944

–

–

–

–

–

–

Monochoria vaginalis

4, 10

1.36

0.314

4, 10

2.09

0.156

–

–

–

–

–

–

2018
Total aquatic plants

4, 11

7.87

0.003

4, 11

52.11

< 0.001

4, 13

1.54

0.247

4, 13

23.31

< 0.001

Monochoria vaginalis

4, 11

4.03

0.030

4, 11

29.18

< 0.001

4, 15

1.22

0.343

4, 15

14.95

< 0.0012019
Total aquatic plants

4, 11

6.66

0.006

4, 11

3.00

0.067

–

–

–

–

–

–

Monochoria vaginalis

4, 11

3.95

0.032

4, 11

5.94

0.009

4, 14

1.51

0.253

4, 14

6.85

0.003

Significant differences (P < 0.05) are indicated by bold font. See Fig. 3 for exact sampling dates for days 1–2 in each year

high-volume ground bamboo treatments having 1.7–
1.8 times greater rice yields than the control (GLM: F3,
7 = 10.94, P = 0.005).
The six rice grain quality indices did not differ significantly among treatments across the 3 years (Table 6).
Overall, application of ground bamboo as mulch was

not associated with any deterioration in rice grain
external quality or protein content. In particular, themean protein content of brown rice in the mediumand high-volume ground bamboo treatments (5.42–
6.55%) was generally within or close to the adequate
range of 5.50–6.50% (Oida et al. 2016).

Lailati et al. CABI Agriculture and Bioscience(2022) 3:20

Page 8 of 16

Fig. 4 Rice plant height, tiller number and leaf color according to soil plant analysis development (SPAD) values in paddy field experiments
conducted in 2017–2019. SPAD values indicate leaf chlorophyll contents. Different superscript letters indicate significant differences (α = 0.05)
according to Bonferroni post-hoc tests. Data are means ± SE. Treatments are described in Fig. 1. *P < 0.05, NA = data not available

Chemical properties of paddy soils and nutrient absorptionof rice plants

Prior to the commencement of rice transplantation (preexperiment) in 2018, the five soil chemical variables did
not differ significantly among treatments (Additional
file 1: Table S1). Following the rice harvest (post-experiment) in 2018, the total inorganic nitrogen content
of paddy soils differed significantly among treatments(Table 7). The total inorganic nitrogen content of postexperimental paddy soils was 1.5–1.6 times greater inthe high-volume ground bamboo treatments than in thecontrol.
In 2019, the five soil chemical variables did not differ
significantly among treatments either before or after theexperiment (Additional file 1: Table S1, Table 7).
When simple linear regression analyses were performed between brown rice yields and each of the fourpost-experiment paddy soil nutrients, a positive relationship was evident between brown rice yield andsoil-available phosphate in 2018 (R2 = 0.52, P = 0.002)
and 2019 (R2 = 0.28, P = 0.034). By contrast, a negative
relationship was found between brown rice yield andsoil-available silicic acid in 2018 (R2 = 0.38, P = 0.011) and2019 (R2 = 0.51, P = 0.002). No significant relationshipwas found between brown rice yield and soil total inorganic nitrogen content (2018: R2 = 0.002, P = 0.87; 2019:
R2 = 0.04, P = 0.46) or soil exchangeable potassium content (2018: R2 = 0.23, P = 0.06; 2019: R2 = 0.04, P = 0.46)
in either year.
When multiple linear regression analyses were performed between brown rice yields and post-experiment
paddy soil nutrients (without exchangeable potassium),the model incorporating available phosphate, available
silicic acid, and their interaction was most supported in2018 (Table 8, Additional file 1: Table S2). In particular,
there was a strong negative relationship between brownrice yield and the available silicic acid content of postexperiment paddy soils. Such a negative relationship was

Lailati et al. CABI Agriculture and Bioscience(2022) 3:20

Page 9 of 16

Table 4 Selected statistics from generalized linear models of shoot height, tiller numbers and leaf color (SPAD values) in the paddy
field experiments conducted in 2017–2019
Parameter

Treatment

Treatment × day

Post-hoc comparison by day
Day 1

df

F

P

df

F

P

df

Day 2
F

P

df

Day 3
F

P

df

F

P

2017
Plant height

4, 10

0.70

0.612

8, 20

0.87

0.559

–

–

–

–

–

–

–

–

–

Tiller number

4, 10

3.07

0.068

8, 20

3.33

0.014

4, 13

0.93

0.478

4, 13

3.65

0.034

4, 13

4.73

0.015

Leaf color (SPAD)

4, 10

2.14

0.150

8, 20

0.59

0.777

–

–

–

–

–

–

–

–

–

2018
Plant height

4, 11

0.99

0.451

8, 22

0.75

0.647

–

–

–

–

–

–

–

–

–

Tiller number

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

Leaf color (SPAD)

4, 11

2.54

0.100

8, 22

1.19

0.351

–

–

–

–

–

–

–

–

–

2019
Plant height

4, 11

0.24

0.911

8, 22

2.78

0.028

4, 17

1.34

0.298

4, 17

0.55

0.699

4, 17

0.32

0.861

Tiller number

4, 11

1.02

0.437

8, 22

1.28

0.306

–

–

–

–

–

–

–

–

–

Leaf color (SPAD)

4, 11

0.57

0.689

8, 22

2.11

0.079

–

–

–

–

–

–

–

–

–

Significant differences (P < 0.05) are indicated by bold font. See Fig. 4 for the exact sampling dates for days 1–3 in each year

Table 5 Effects of treatment on the physicochemical properties of rice straw in the paddy field experiments conducted in 2018–2019
Parameter

ControlManual

L-bam

M-bam

H-bam

df

F

P

241.54 ± 41.98

283.04 ± 24.39

218.42 ± 66.12

292.64 ± 28.97

320.72 ± 35.19

0.64 ± 0.04

0.69 ± 0.10

0.65 ± 0.04

0.64 ± 0.04

2018
Air-dry weight (g 15 ­plants−1)
Total carbon (%)
Total nitrogen (%)
Phosphorus pentoxide (%)
Potassium oxide (%)
Silicic acid (%)
2019
Air-dry weight (g 15 ­plants−1)
Total carbon (%)
Total nitrogen (%)
Phosphorus pentoxide (%)
Potassium oxide (%)
Silicic acid (%)

37.12 ± 1.30

0.26 ± 0.02

2.13 ± 0.20

36.77 ± 0.40

36.42 ± 0.27

0.32 ± 0.03

0.28 ± 0.01

2.08 ± 0.12

2.13 ± 0.14

35.92 ± 0.11

0.27 ± 0.02

2.34 ± 0.11

4, 11

0.730

0.590

35.57 ± 0.30

4, 11

0.648

0.640

0.62 ± 0.05

4, 11

0.182

0.943

0.24 ± 0.01

4, 11

2.206

0.135

2.57 ± 0.13

4, 11

1.585

0.246

15.43 ± 0.40

14.27 ± 0.35

15.23 ± 0.41

15.20 ± 0.32

14.93 ± 0.35

4, 11

1.439

0.285

147.42 ± 24.45

138.66 ± 23.38

104.04 ± 22.17

150.89 ± 20.27

180.71 ± 38.33

0.64 ± 0.05

0.61 ± 0.06

0.61 ± 0.03

0.56 ± 0.03

35.70 ± 0.08

0.27 ± 0.01

1.83 ± 0.18

15.50 ± 0.14

36.23 ± 0.30

0.30 ± 0.01

1.85 ± 0.07

14.50 ± 0.47

35.94 ± 0.19

0.30 ± 0.02

1.77 ± 0.06

15.03 ± 0.52

35.85 ± 0.21

0.31 ± 0.01

1.95 ± 0.08

15.03 ± 0.48

4, 11

0.643

0.643

35.92 ± 0.22

4, 11

0.982

0.456

0.58 ± 0.05

4, 11

0.543

0.708

0.29 ± 0.01

4, 11

1.761

0.207

2.03 ± 0.07

4, 11

0.727

0.591

14.73 ± 0.55

4, 11

0.846

0.525

Values are means ± standard error. Summary statistics of the generalized linear models are provided in the last three columns. Manual, manual weeding treatment;
L-bam, low-volume ground bamboo treatment; M-bam, medium-volume ground bamboo treatment; H-bam, high-volume ground bamboo treatment

evident in experimental paddy fields with < 0.15 g ­kg−1 ofavailable phosphate but not in those with ≥ 0.15 g ­kg−1 ofavailable phosphate in post-experiment soils (Fig. 6).
In 2019, multiple linear regression models incorporating available silicic acid in post-experiment soils alone,
and available phosphate and silicic acid in post-experiment soils, were supported (ΔAICc < 2) (Fig. 6, Table 8).
As in 2018, the negative relationship between brown rice

yield and soil-available silicic acid in post-experimentsoils was particularly strong.
When silicic acid absorption of rice plants was calculated (silicic acid content of rice straw × rice plant
air-dry mass), a strong positive relationship was evident between brown rice yield and silicic acid absorption in both 2018 and 2019 (Fig. 7). In 2018, the brownrice yield and silicic acid absorption were greater inthe experimental paddy fields with ≥ 0.15 g ­kg−1 ofLailati et al. CABI Agriculture and Bioscience(2022) 3:20

Page 10 of 16

Air-dry weight (g) 15 rice plants-1

2017
1200
1000

2018

Treatment (without L-bam)**Controla, Manuala < M-bamb, H-bamb

800
600
400
200
0

Control Manual L-bam M-bam H-bam

2019

400

400

300

300

200

200

100

100

0

Control Manual L-bam M-bam H-bam

0

ControlManual
L-bam
M-bam
H-bam

Control Manual L-bam M-bam H-bam

Fig. 5 Brown rice yield in paddy field experiments conducted in 2017–2019. Data are means ± SE. Treatments are described in Fig. 1. **P < 0.01

Table 6 Effects of treatment on the yield and grain quality of brown rice in the paddy field experiments conducted in 2017–2019
Parameter

ControlManual

L-bam

M-bam

H-bam

df

F

P

509.45 ± 123.88

691.04 ± 76.24

721.63 ± 308.64

857.57 ± 58.06

894.51 ± 49.49

75.48 ± 3.28

76.33 ± 1.13

75.20 ± 2.18

77.13 ± 1.95

2017
Brown rice yield (g 15 ­plants−1)
Thousand-grain weight (g)Sound grains (%)
Immature grains (%)
Malformed grains (%)
Protein content (%)
Amylose content (%)
2018
Brown rice yield (g 15 ­plants−1)
Thousand-grain weight (g)Sound grains (%)
Immature grains (%)
Malformed grains (%)
Protein content (%)
Amylose content (%)
2019
Brown rice yield (g 15 ­plants−1)
Thousand-grain weight (g)Sound grains (%)
Immature grains (%)
Malformed grains (%)
Protein content (%)
Amylose content (%)

22.44 ± 0.41

15.68 ± 2.60

2.95 ± 0.90

5.66 ± 0.23

22.28 ± 0.27

14.07 ± 0.61

3.70 ± 0.47

5.43 ± 0.04

22.41 ± 0.17

14.93 ± 0.92

3.43 ± 1.16

5.43 ± 0.16

22.59 ± 0.13

13.97 ± 0.41

3.13 ± 0.64

5.42 ± 0.07

4, 10

0.96

0.472

22.64 ± 0.21

4, 10

0.23

0.915

78.70 ± 2.57

4, 10

0.30

0.870

14.87 ± 2.51

4, 10

0.15

0.961

2.77 ± 0.86

4, 10

0.18

0.942

5.78 ± 0.23

4, 10

0.82

0.540

19.80 ± 0.12

19.77 ± 0.02

19.83 ± 0.09

19.88 ± 0.14

19.58 ± 0.27

4, 10

0.56

0.686

238.91 ± 64.91

226.22 ± 26.06

180.75 ± 62.22

259.63 ± 34.09

299.17 ± 23.01

64.76 ± 3.16

67.52 ± 2.61

66.25 ± 1.98

70.88 ± 1.87

20.82 ± 0.70

12.99 ± 2.50

16.96 ± 3.71

6.65 ± 0.04

20.74 ± 0.50

10.98 ± 0.75

17.67 ± 2.89

6.47 ± 0.12

21.00 ± 0.28

11.50 ± 1.39

17.85 ± 2.08

6.42 ± 0.06

21.29 ± 0.21

13.27 ± 1.26

12.38 ± 1.50

6.38 ± 0.04

4, 11

1.00

0.448

21.39 ± 0.55

4, 11

0.28

0.885

67.92 ± 2.97

4, 11

0.73

0.588

16.38 ± 2.61

4, 11

1.05

0.427

12.47 ± 4.48

4, 11

0.70

0.606

6.55 ± 0.10

4, 11

2.18

0.139

18.81 ± 0.09

18.87 ± 0.12

18.88 ± 0.10

18.90 ± 0.05

18.78 ± 0.04

4, 11

0.30

0.874

147.42 ± 24.45

138.66 ± 23.38

104.04 ± 22.17

150.89 ± 20.27

180.71 ± 38.33

61.03 ± 2.84

56.90 ± 4.49

50.27 ± 5.70

60.33 ± 2.82

20.83 ± 0.65

17.43 ± 0.94

18.65 ± 3.13

6.46 ± 0.20

18.95 ± 0.05

20.57 ± 0.39

20.83 ± 2.69

19.35 ± 2.73

6.77 ± 0.28

19.02 ± 0.02

19.33 ± 0.84

15.63 ± 0.87

30.53 ± 5.70

6.73 ± 0.25

18.93 ± 0.13

20.48 ± 0.48

15.98 ± 1.86

21.38 ± 2.48

6.48 ± 0.07

18.93 ± 0.07

4, 11

1.01

0.442

21.01 ± 0.52

4, 11

1.11

0.399

65.47 ± 0.38

4, 11

2.32

0.121

14.45 ± 1.72

4, 11

2.06

0.154

18.42 ± 1.84

4, 11

2.12

0.146

6.32 ± 0.06

4, 11

0.90

0.499

19.13 ± 0.11

4, 11

1.06

0.420

Values are means ± standard error. Summary statistics of generalized linear models are provided in the last three columns. Manual, manual weeding treatment; L-bam,low-volume ground bamboo treatment; M-bam, medium-volume ground bamboo treatment; H-bam, high-volume ground bamboo treatment

available phosphate in post-experimental soils than inthose with < 0.15 g ­kg−1 of soil-available phosphate.

Discussion
Effects of ground bamboo application on aquatic plants

In all years, the O­ RPSHE values of surface paddy soils
decreased in the ground bamboo treatments, implyingthat the paddy soils provided anti-oxidizing conditions
under these treatments (Fig. 2). Nakai and Toritsuka(2009) reported that, when rice brans were applied toorganic rice paddy fields (0.15 kg ­m−2), ORP in the surface paddy soils had strong negative values, which inturn suppressed the growth of several weed species. This
was likely because application of rice brans increases

Lailati et al. CABI Agriculture and Bioscience(2022) 3:20

Page 11 of 16

Table 7 Post-experiment soil chemical properties in the paddy field experiments conducted in 2018–2019
ControlManual

L-bam

M-bam

H-bam

df

F

P

6.13 ± 0.27

4, 11

1.26

0.344

4, 11

4.80

0.017

126.67 ± 67.41

4, 11

0.58

0.682

306.67 ± 42.56

4, 11

1.01

0.443

314.67 ± 23.88

4, 11

3.16

0.059

5.90 ± 0.15

4, 11

1.43

0.289

4, 11

0.48

0.749

183.33 ± 63.33

4, 11

0.70

0.608

4, 11

1.79

0.201

4, 11

2.37

0.116

2018
pH
Total inorganic nitrogen (mg ­kg−1)
Available phosphate (mg ­kg−1)
Exchangeable potassium (mg k­ g−1)
Available silicic acid (mg ­kg−1)
2019pH
Total inorganic nitrogen (mg ­kg−1)
Available phosphate (mg ­kg−1)
Exchangeable potassium (mg k­ g−1)
Available silicic acid (mg ­kg−1)

6.48 ± 0.06

11.75 ± 0.63a

85.00 ± 41.13

257.50 ± 31.19

436.25 ± 29.28
6.15 ± 0.06

25.25 ± 6.46

135.00 ± 22.17

120.00 ± 9.13

387.50 ± 37.06

6.13 ± 0.03

6.30 ± 0.10

14.33 ± 0.67ab

16.67 ± 12.02

226.67 ± 20.28

12.33 ± 2.33ab

86.67 ± 66.92

260.00 ± 47.26

398.67 ± 23.10

494.00 ± 65.90

6.17 ± 0.09

6.07 ± 0.03

19.67 ± 1.76

19.67 ± 4.70

96.67 ± 21.86

126.67 ± 31.80

96.67 ± 3.33

120.00 ± 11.55

343.33 ± 17.64

376.67 ± 3.33

6.13 ± 0.17

18.00 ± 1.53ab

110.00 ± 68.07

320.00 ± 41.63

370.67 ± 30.75
6.07 ± 0.07

35.33 ± 17.33

153.33 ± 40.55

130.00 ± 10.00
356.67 ± 6.67

19.00 ± 2.08b

26.33 ± 1.86

123.33 ± 8.82

286.67 ± 27.28

Values are means ± standard error. Summary statistics of generalized linear models are provided in the last three columns. Manual, manual weeding treatment;
L-bam, low-volume ground bamboo application treatment; M-bam, medium-volume ground bamboo application treatment; H-bam, high-volume ground bamboo
application treatment. Significant effects (P < 0.05) detected by generalized linear models are indicated by bold font. Different superscript letters indicate significant
pairwise differences (α = 0.05) according to Bonferroni post-hoc tests

Table 8 Parameter estimates of the best linear regression models of the relationship between brown rice yield and post-experiment
paddy soil nutrients in 2018–2019
Model

Estimate

SE

t

P

AICc

∆AICc

Akaike weights

170.630

0.678

164.3300.415

164.60

0.28

0.362

2018
Yield ~ available phosphate + available silicic
acid + available phosphate × available silicic acid
Intercept

512.30

74.15

6.91

Available phosphate− 5.394.41− 1.22Available silicic acid− 7.78

1.76

0.27

0.11

Intercept

390.08Available silicic acid

< 0.001
0.246− 4.41< 0.001

2.45

0.030

64.31

6.07

< 0.001− 6.51

1.69− 3.850.002

318.76

72.69

4.39

< 0.001

Available phosphate

2.40

1.38

1.74

0.105

Available silicic acid− 5.501.68− 3.27

0.006

Available phosphate × available silicic acid

2019

Yield ~ silicic acid

Yield ~ available phosphate + available silicic acid
Intercept

microbial respiration and thereby reduces oxygen concentrations in surface paddy soils (Nakayama 2010). Nevertheless, several weed species, including M. vaginalis
and S. juncoides, were not suppressed by rice bran application (Nakai and Toritsuka 2009).
In our paddy field experiments, the biomass of total
aquatic plants and M. vaginalis did not differ markedly
among treatments, except for the manual treatments
applied in 2018 and 2019 (Fig. 3, Table 3). By contrast,
in a small-scale microcosm experiment, Usio et al (2021)
reported that the total aquatic plants and M. vaginalis
were significantly less abundant when ground bamboo

was applied. Differences in weed suppression between
the study of Usio et al. (2021) and the present paddy
experiment are likely attributable to the difference inspatial scale between the experiments. Ground bamboo
may have been more uniformly distributed in the smallscale experiment than in the paddy fields. Furthermore,
little water exchange took place in the microcosms;
water was supplied occasionally when the water level
dropped owing to evapotranspiration and lack of rain.
By contrast, water exchange was presumably more frequent in the experimental paddy fields owing to the highrates of underground exudation and evapotranspiration.

Lailati et al. CABI Agriculture and Bioscience(2022) 3:20

Page 12 of 16

2019

400

300
200
100
0

0

0.05

0.1

0.15

0.2

0.25

Brown rice yield (g) 15 plants-1

Brown rice yield (g) 15 plants-1

2018
300
250
200
150
100
50
0

0

Available phosphate (g kg-1)

0
-50
-100
0.3

0.4

0.5

0.6

Brown rice yield (g) 15 plants-1

Residuals

50

0.2

0.2

0.3

Available phosphate (g kg-1)

100

-150

0.1

300
250
200
150
100
50

0

0.2

Available silicic acid (g kg-1)

0.3

0.4

0.5

Available silicic acid (g kg-1)

Fig. 6 Relationships between brown rice yield and available phosphate and silicic acid in post-experiment paddy soils, in paddy field experiments
conducted in 2018–2019 according to multiple linear regression analyses. Available silicic acid in post-experiment paddy soils was used as thepredictor, and the residual of brown rice yield regressed onto available phosphate in post-experiment paddy soils was used as the response
variable. Regression lines are shown for low (< 0.15 g ­kg−1, solid line with closed diamonds, y =  − 717.33x + 501.99, R2 = 0.67, P = 0.002) and highsoil-available phosphate (≥ 0.15 g ­kg−1, dashed line with open diamonds, y =  − 174.88x + 385.20, R2 = 0.47, P = 0.204). For available silicic acid in
2019, brown rice yield was regressed onto available silicic acid in post-experiment paddy soils (y =  − 650.45x + 390.08, R2 = 0.51, P = 0.002)

2019

400
300

200
100
0

0

20

40

60

Silicic acid absorption (g 15 plants-1)

80

Brown rice yield (g) 15 plants-1

Brown rice yield (g) 15 plants-1

2018
300

200

100

0

20

30

40

50

Silicic acid absorbtion (g 15 plants-1)

Fig. 7 Relationship between brown rice yield and silicic acid absorption by rice plants in the paddy field experiments conducted in 2018(y = 6.97x − 51.50, R2 = 0.94, P < 0.001) and 2019 (y = 6.58x − 64.58, R2 = 0.87, P < 0.001). Closed diamonds indicate experimental paddies withlow available phosphate in post-experiment paddy soils (< 0.15 g ­kg−1) and open diamonds indicate those with high soil-available phosphate(≥ 0.15 g ­kg−1)

Lailati et al. CABI Agriculture and Bioscience(2022) 3:20

Furthermore, in the field conditions, as the ground bamboo may not have been uniformly distributed acrossthe paddy surface soils, the shading effect was probably
insufficient to inhibit weed germination. Studies havealso reported that volatile fatty acids, aromatic carboxylic
acids, and allelochemicals were produced during organic
matter decomposition, which in turn suppressed thegermination or growth of weeds (Tanaka and Ono 2000;
Ueno and Suzuki 2005). However, although such chemicals were produced during ground bamboo decomposition, they may have been diluted by the frequent waterexchange in paddy fields.
Effects of ground bamboo application on soil chemical
properties

Ueno and Suzuki (2005) reported that application of
distilled spirits and rice brans markedly increased theammonia, potassium, calcium, and magnesium contentsof paddy soils. However, in our experiments, no consistent increase in essential nutrients was observed. Based onmean nutrient input values (Table 1), averages of 0.15 kg
total nitrogen (equivalent to 4.87 g ­m−2), 0.08 kg phosphorus pentoxide (equivalent to 2.73 g ­m−2) and 0.24 kg
potassium (equivalent to 8.13 g ­m−2) were added to eachexperimental paddy field (30 ­m2) in each year. Because
ground bamboo contains few nutrients, it may have little
effect as a nutrient enhancer in paddy soils.
At the end of our paddy field experiment in 2018 (postexperiment), the total inorganic nitrogen content of the
paddy soils was significantly higher in the medium- andhigh-volume ground bamboo treatments than in thecontrol. This may be because of the nitrogen-fixation
activities of cyanobacteria and photosynthetic bacteria
associated with organic matter addition, as also reportedwith surface application of rice straw to paddy soils (Yooet al. 1987). Recently, Masuda et al (2021) reported thatiron-reducing bacteria (Anaeromyxobacter and Geobacter), belonging to Deltaproteobacteria, also play important roles in nitrogen fixation in paddy soils. However, nosuch nitrogen enhancement effect was seen consistently
over the years in our study (see “Chemical properties of
paddy soils and nutrient absorption of rice plants” section). Similarly, the effects of ground bamboo applicationon the available phosphate, silicic acid, and exchangeable potassium content of paddy soils were inconsistentacross years. Future studies should consider the roles of
microbes in mediating nutrient availability for rice plants.
Effects of ground bamboo application on rice plant growthand yield

The effects of ground bamboo application on rice
plant growth and yield differed by year. In the first year(2017), tiller numbers of rice plants were higher with

Page 13 of 16

high-volume ground bamboo application than in thecontrol on 8/11 (Fig. 4, Table 4). Rice yields were 1.7–1.8
times greater in the medium- and high-volume groundbamboo treatments than in the control (Fig. 5). However,after the second and third years of consecutive rice cultivation in the paddy fields, rice growth and yields differedlittle between treatments with and without ground bamboo application (Figs. 4, 5, Tables 4 and 6).
Over the 3-year study period, mean rice yield decreased
dramatically (Fig. 5). Although the available phosphatein post-experiment paddy soils did not differ statistically between any of the ground bamboo treatments andthe control, simple regression analysis revealed that rice
yields were positively associated with available phosphatein post-experiment paddy soils in 2018 and 2019 (see“Chemical properties of paddy soils and nutrient absorption of rice plants” section). In an 89-year consecutive
rice cultivation study, phosphorus was among the mostlimiting nutrients (Ohashi et al. 2015). The results imply
that phosphorous was also a major limiting nutrient inour paddy fields.
Another key nutrient that may have affected rice
yields is silicon. An earlier microcosm experiment demonstrated that, when ground bamboo was applied torice cultivated in fertilizer-free soil, silicic acid content
approximately halved in post-experiment soils relative
to pre-experiment soils (Usio et al. 2021). Furthermore,
the silicic acid content of rice straw was 10–12% lower inthe ground bamboo treatments compared to the control,
which in turn led to 1.8–2.1-fold greater rice yields forthe ground bamboo treatments (Usio et al. 2021). These
results imply that silicic acid in haulms was actively
used by rice plants for grain and husk production whenground bamboo was applied. A negative relationshipwas evident between brown rice yields and the silicic
acid contents of post-experiment paddy soils in 2018 and2019, in both simple and multiple regression analyses(Fig. 6, Table 8) (see “Chemical properties of paddy soils
and nutrient absorption of rice plants” section). However,the silicic acid content of rice straw did not differ among
treatments in those years (Table 5). In 2018, rice plants inthe experimental paddies with high silicic acid absorption
and rice yields had relatively high available phosphate(≥ 0.15 g ­kg−1) in post-experiment paddy soils (Fig. 7). In
2019, although rice plants in experimental paddies withhigh silicic acid absorption had relatively high rice yields,
the GLM that included the interaction term between
available phosphate and silicic acid was not supported.
The literature suggests that the effects of silicon addition
on plants differ depending on the plant-available phosphorus, among other physicochemical properties of soils.
Kostic et al. (2017) reported that the addition of silicon
to wheat (Triticum aestivum L.) in low-phosphorus soil

Lailati et al. CABI Agriculture and Bioscience(2022) 3:20

increased phosphorus uptake via the roots by upregulating the expression of inorganic phosphorus transporter
genes (TaPHT1.1 and TaPHT1.2). Schaller et al. (2019)
reported that the addition of silicon to 143 undisturbed
Arctic soils increased phosphorus mobilization in ironphosphate phases on mineral surfaces. Such phosphorus
mobilization under high-silicon conditions occurs as aresult of silicon’s competition with phosphorus for binding at the surface of soil minerals (reviewed in Hu et al.
2021). Other studies have observed a beneficial effect ofsilicon addition on the growth of rice plants under low
and high phosphorus conditions (Ma and Takahashi
1990; Che et al. 2016). Under low phosphorus conditions,silicon addition reduced the uptake of iron and manganese by rice plants, which in turn increased phosphorus availability for the plants (Ma and Takahashi 1990).
Under high phosphorus conditions, by contrast, silicon
addition reduced phosphorus uptake by rice plants tocontrol inorganic phosphorus concentrations in shoots
within an optimal concentration range, which is otherwise detrimental to plants (Ma and Takahashi 1990).
The present study’s findings are somewhat divergent
from those of earlier studies, in that brown rice yields
were higher when the available phosphate contents ofthe post-experiment soils were above a certain threshold(≥ 0.15 g ­kg−1). However, available phosphate is not necessarily equivalent to plant-available phosphorus, as most
phosphorus in soil is usually stored in plant-unavailable
forms, such as organic phosphorus, or is bound with minerals including iron, calcium and aluminum (Beauchemin
et al. 2003). The conditions under which ground bamboo addition enhances rice yields requires further study,
especially in terms of the interaction between silicon andplant-available phosphorus under different soil chemical
conditions.
In general, nitrogen is among the most limiting nutrients with respect to rice yields in irrigated rice paddy
fields (Myint et al. 2010). In the second year of ourexperiment (2018), the total inorganic nitrogen content of post-experiment paddy surface soils was 1.5-foldgreater in the medium- and high-volume ground bamboo treatments compared to the control (Table 7). The
multiple linear regression models incorporating soil
inorganic nitrogen content were not the best models in2018 or 2019 (Table 8, Additional file 1: Table S2). These
results imply that nitrogen was not a limiting nutrient in
the present experiment. This is likely attributable to thenitrogen-fixation activities of cyanobacteria and photosynthetic bacteria (Yoo et al. 1987) and iron-reducing
bacteria (Masuda et al. 2021).
Likewise, exchangeable potassium was unlikely to
be a limiting nutrient in the present experiment. The
exchangeable potassium content of the paddy soil surface

Page 14 of 16

did not differ significantly between any of the groundbamboo treatments and control, in either 2018 or 2019.
Potassium is supplied by surface water, groundwater, andrainwater (Momii and Izawa 2007). Moreover, plants utilize sodium in lieu of potassium when potassium supply
is limited (Hasegawa et al. 1990; Takahashi and Maejima
1998). Therefore, in the field cultivation of rice, potassium is rarely a limiting nutrient.
Rice straw contains essential nutrients, including nitrogen (0.5–0.8%), phosphorus pentoxide (0.16–0.27%),
potassium oxide (1.4–2.0%), and silicic acid (4.0–7.0%)(Dobermann and Fairhurst 2002). In agrochemical-freeand organic rice farming, shredded rice straw is typically incorporated into paddy fields after rice harvest.
These straw incorporation practices directly enhance soil
nitrogen, phosphate, potassium, and soil organic carbon
content, as well as CEC (Zhao et al. 2019), and indirectly
enhance nitrogen availability for rice plants throughnitrogen fixation by cyanobacteria and photosynthetic
bacteria (Yoo et al. 1987). Future experiments should use
shredded rice plants as soil conditioners, particularly inconsecutive rice cultivation years with ground bamboo
application. However, the effects of rice straw incorporation on nitrogen fixation by iron-reducing bacteria have
yet to be investigated.
Usio et al. (2021) showed that bamboo leaves have asilicic acid content 21 times higher than that of bamboo
culms. To augment silicic acid in paddy soils efficiently,
bamboo leaves may be ground and applied together withculms.
Effects of ground bamboo application on rice grain quality

Across the 3-year-study period, application of groundbamboo was not associated with deterioration of ricegrain quality. In the Koshihikari cultivar, the protein content required for good taste is suggested to be in the rangeof 5.50–6.50% in brown rice (Oida et al. 2016). The mean
protein contents under the medium and high-volume
ground bamboo treatments in this study were close to thesuggested range, at 5.42–6.55% (Table 6). This is consistent with the result of Usio et al. (2021), who reported thatground bamboo applications in microcosm experimentswith different pre-treatments (refrigeration or fermentation) and organs (culms or leaves) did not lead to marked
differences in the external quality or protein content of ricegrains compared to the control (without ground bamboo
application). In the previous experiment, thousand-grain
weights were 3% higher in the fermented ground bamboo
leaf application treatment than in the control (Usio et al.
2021). In the present study, we found no evidence thatapplication of ground bamboo affects these external grain
quality parameters. In conventional farming, applicationof additional silicon fertilizer during the panicle formation

Lailati et al. CABI Agriculture and Bioscience(2022) 3:20

stage accelerates rice grain ripening, thereby increasing
rice yield and thousand-grain weight, with pronounced
fertilizer effects seen in years with short solar radiation periods (Fujii et al. 2008; Mizuno and Inatsu 2016).
Increased rice yield following application of additional
silicon is thought to result from improved photosynthetic
activity of rice plants, especially under low light conditions(Mizuno and Inatsu 2016). Future studies should evaluate
whether additional ground bamboo application during thepanicle formation stage can enhance rice yield, thousandgrain weight, and other external grain quality parameters.
Although controlled experiments would be difficult, such
effects may also be evaluated through long-term cultivation under different solar radiation conditions.

Conclusions
Application of ground bamboo may enhance rice production when soil nutrients—particularly phosphate—are
not deficient. Despite dramatic declines in rice yields
over consecutive years of rice cultivation, application ofground bamboo did not appear to reduce external ricegrain quality. In a working paddy field, 1.0–2.0 kg ­m−2
of ground bamboo is suggested to be the appropriate
application amount. To obtain a more comprehensive
understanding of its underlying mechanisms, the interaction between silicon and plant-available phosphorus
under different soil chemical conditions and the roles of
microbes in enhancing nutrient availability for rice plants
should be further studied. To maximize the efficiencyof ground bamboo application on rice growth and production, the combined effects of rice straw and groundbamboo application, as well as additional application ofground bamboo during the panicle formation stage, may
need to be tested.
Supplementary Information
The online version contains supplementary material available at https://​doi.​
org/​10.​1186/​s43170-​022-​00087-6.
Additional file 1: Table S1. Soil chemical properties in the paddy prior tofield experiments conducted in 2018–2019. Table S2. Summary statistics
of models of the relationship between brown rice yield and post-experiment paddy soil nutrients in 2018–2019.
Acknowledgements
We are grateful to Shuhei Kudo and Teruyuki Kameda for assisting with field
work, and to Karui Co. Ltd. (Yamagata, Japan) and Kyowa Co. Ltd. (Toyama,
Japan) for providing a wood crusher. We also thank anonymous reviewers fortheir constructive comments, which substantially improved this manuscript.
During the study, ML received a RISET-Pro scholarship from the Ministry of
Research and Technology/National Research and Innovation Agency of the
Republic of Indonesia (RISTEK-BRIN), and TQH received a Ministry of Education,
Culture, Sports, Science and Technology of Japan (MEXT) scholarship.
Authors’ contributions
ML, YS, TQH, and NU performed the field experiments; KI, ML, YS, and TQH
performed the aquatic plant survey; KN, ML and TQH performed plant chemical analyses; ML, YS, TQH, YM, and MI performed rice grain quality analyses; TT

Page 15 of 16

provided technical advice and resources; ML and NU led the writing; NU, KI,
and KN obtained the funding; and NU conceived and supervised the study. All
authors read and approved the final manuscript.
Funding
This study was funded by a JSPS KAKENHI (No. 21K19860) and a Grant for Environmental Research Project from the Sumitomo Foundation (No. 183353).
Availability of data and materials
The data used in this study are available from the corresponding author upon
reasonable request.

Declarations
Ethics approval and consent to participate
Not applicable.
Consent for publication
Not applicable.
Competing interests
The authors declare that they have no competing interests.
Author details
1
Graduate School of Natural Science and Technology, Kanazawa University,
Kanazawa 920‑1192, Japan. 2 Research Center for Plant Conservation, Botanic
Gardens and Forestry, National Research and Innovation Agency, Bogor 16122,
West Java, Indonesia. 3 Southern Institute of Ecology, Institute of Applied
Materials Science, Vietnam Academy of Science and Technology, Ho Chi Minh
City 700000, Vietnam. 4 Noto Satoyama Satoumi SDGs Research Program,
Kanazawa University, Suzu 927‑1462, Japan. 5 Department of Environmental
Science, Ishikawa Prefectural University, Nonoichi 921‑8836, Japan. 6 Agricultural Experiment Station, Ishikawa Agriculture and Forestry Research Center,
Kanazawa 920‑3198, Japan. 7 JA Hakui Main Branch, Hakui 925‑8588, Japan.
8Institute of Nature and Environmental Technology, Kanazawa University,
Kanazawa 920‑1192, Japan.
Received: 27 November 2021 Accepted: 22 March 2022

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