Research Paper
Effect of Nitrogen Topdressing on Seed Yield and 
Flour Protein Content in Semidwarf Common 
Buckwheat
Shinya KASAJIMA1*, Mirai YOSHIDA1, Koji ISHIGURO2, Takashi HARA2,  
Shiori OTSUKA2
1 Faculty of Bioindustry, Tokyo University of Agriculture, Yasaka 196, Abashiri, Hokkaido 099-2493, Japan
2 Hokkaido Agricultural Research Center, NARO, Shinsei, Memuro-cho, Kasai-gun, Hokkaido 082-0081, Japan
* Corresponding author: Shinya Kasajima, Faculty of Bioindustry, Tokyo University of Agriculture, Yasaka 196, Abashiri, 
Hokkaido 099-2493, Japan, E-mail: s3kasaji@nodai.ac.jp 
E-mail addresses of authors: s3kasaji@nodai.ac.jp (SK); 49520093@nodai.ac.jp (MY); kuro@affrc.go.jp (KI);  
harat302@affrc.go.jp (TH); otsukas517@affrc.go.jp (SO)
DOI https://doi.org/10.3986/fag0040
Received: April 25, 2024; accepted May 2, 2024
Key words: buckwheat, flour protein content, nitrogen fertilization, nutritional quality, seed yield, semidwarf line
ABSTRACT
This study evaluated the effects of nitrogen topdressing on the semidwarf common buckwheat (line ‘18-601’), fo-
cusing on growth, seed yield, and flour protein content. We conducted a field experiment and applied four nitrogen 
topdressing treatments at different growth stages: basal fertilization alone (2-0-0), basal fertilization plus nitrogen 
at flower bud appearance (2-2-0), basal fertilization plus nitrogen at full flowering (2-0-2), and basal fertilization plus 
nitrogen at both stages (2-2-2), using a randomized complete block design, with each plot measuring 1.2 × 2.5 m. Basal 
dressing was applied at 2, 8, and 4.7 g m-2 N, P2O5, and K2O, respectively. Nitrogen topdressing significantly increased 
chlorophyll content. The branch number, seed yield, number of seeds per square meter, and flour protein content tended 
to increase with nitrogen topdressing. The highest seed yield and protein content were observed in the 2-0-2 treat-
ment, suggesting that nitrogen application at full flowering optimizes the yield and nutritional quality of semidwarf 
buckwheat. These findings highlight the importance of timing in nitrogen topdressing to enhance the agronomic and 
nutritional value of semidwarf common buckwheat.
Fagopyrum 41 (2): 41-47 (2024)
41
INTRODUCTION
Common buckwheat (Fagopyrum esculentum Moench) 
is valued for its significant nutritional contributions, 
offering a rich source of protein, minerals, and the fla-
vonoid rutin. Despite its benefits, this crop suffers from 
low and unstable seed yields, especially in Japan, where 
yields stagnate between 50 and 100 kg/10a (Tanaka, 
2016). A major challenge in common buckwheat cultiva-
tion is lodging—a condition where stems bend, causing 
plants to lie horizontally, leading to pre-harvest sprouting 
and seed shattering, significantly impacting seed yield 
(Morishita et al., 2020). The development of semidwarf 
cultivars has emerged as a potential strategy to enhance 
lodging resistance and yield stability.
Although the identification of dwarf and semidwarf 
genetic variants within the species has been reported 
(Ohnishi and Nagakubo, 1982; Minami et al., 1999), the 
availability of practical semidwarf cultivars for common 
buckwheat remains limited. Recent progress in breeding 
programs has led to the development of new semidwarf 
variants (Morishita et al., 2015). These variants have 
seed yields that are either similar to or slightly lower 
than those of standard-height cultivars. It also shows 
enhanced seed production when influenced by nitro-
gen fertilizer (Kasajima et al., 2017). Additionally, the 
National Agriculture and Food Research Organization 
(NARO) of Japan has developed a semidwarf line resist-
ant to seed shattering and pre-harvest sprouting (Suzuki 
et al., 2023). These developments highlight the need for 
optimized cultivation techniques for semidwarf common 
buckwheat lines.
In wheat cultivation, nitrogen fertilization, especially 
topdressing after the booting stage, significantly increas-
es grain protein content, influencing yield and nutrition-
al quality (Farrer et al., 2006; Shimazaki and Watanabe, 
2010). Similarly, previous research on buckwheat has 
explored the effects of nitrogen fertilization on seed 
yield and protein properties (Fang et al., 2018; Wan et 
al., 2023). Nevertheless, the specific effects of nitrogen 
topdressing on the seed yield and flour protein content of 
semidwarf common buckwheat lines have yet to be fully 
explored. This study aims to examine the effects of nitro-
gen topdressing on the growth, yield, and flour protein 
content of a semidwarf breeding line of common buck-
wheat, and optimize the cultivation practices for this nu-
tritionally valuable crop.
MATERIAL AND METHODS
The common buckwheat variant used in this study 
was the semidwarf line ‘18-601’, developed by the NARO 
Hokkaido Agricultural Research Center. It is character-
ized by a shorter plant height than conventional varieties, 
attributed to a single recessive gene conferring lodging 
resistance. A field experiment was conducted in an un-
used field on a local farm in the Yobito district, Abashiri, 
Hokkaido, from June to August 2023. Soil samples were 
collected prior to the application of basal fertilizer and 
analyzed by a specialized agency, Miraizou Co., Ltd., lo-
cated in Oita, Japan. The chemical parameters of the field 
soil are presented in Table 1. Seeding was conducted on 
June 8, 2023, using seeder tapes (Nippon Plant Seeder 
Co., Ltd.) with row spacing of 30 cm and a hill distance of 
2 cm (one plant per hill) at a seeding rate of 167 seeds/
m2. Basal dressing by chemical fertilizer was applied at 
rates of 2, 8, and 4.7 g m-2 N, P2O5, and K2O, respectively. 
Nitrogen topdressing treatments in the form of ammo-
nium sulfate were established according to application 
timing in four treatment plots: 2-0-0 (basal fertilization 
of 2 g m-2 N only), 2-2-0 (basal fertilization plus an ad-
ditional 2 g m-2 N at flower bud appearance stage), 2-0-
2 (basal fertilization plus an additional 2 g m-2 N at full 
flowering stage), and 2-2-2 (basal fertilization plus 2 g 
m-2 N at both the flower bud appearance and full flow-
ering stages). Fertilizer applications for basal dressing 
and during the flower bud appearance and full flowering 
stages were conducted on June 6, June 30, and July 14, 
respectively. The time of flower bud appearance was de-
fined as the day on which flower buds were observed on 
50% of all plants, and the time of full flowering was the 
pH
(H2O)
EC
(mS/cm)
CEC
(meq/100 g)
Nitrate 
nitrogen
(mg/100 g)
Ammonium 
nitrogen
(mg/100 g)
Available  
P2O5
(mg/100 g)
Exchangeable cation
(mg/100 g)
K Ca Mg
6.3 0.04 16.0 0.5 0.7 32.8 24.2 251.2 26.0
Table 1. Chemical parameters of soil sampled in the field.
Kasajima et al. (2024): Nitrogen topdressing in semidwarf buckwheat
42
day the apical inflorescence of the main stem bloomed 
on all plants. Each plot measured 1.2 × 2.5 m and was 
arranged in a randomized complete block design with 
three replications. To determine the chlorophyll content, 
we measured the SPAD value of five individual plants per 
plot, using one leaf from either the second or third leaf 
from the top. The measurements were taken on July 25 
using a SPAD meter (SPAD-502, Konica Minolta). Before 
harvesting the plants, the main stem length and number 
of primary branches were recorded for ten individuals of 
average growth per plot. Then, we harvested plants on 
August 25 when 80% of the seeds changed color from 
green to black. Twenty individuals per plot were sam-
pled, threshed by hand on site, and dried over two weeks. 
The seeds were then winnowed, and their dry weight 
was measured (seed yield). The number of seeds per 20 
plants was counted using a multi-auto counter (Fujiwara 
Scientific Co., Ltd). The 1000-seed weight was calculat-
ed from this value, and the number of seeds per square 
meter was calculated from the seed yield and 1000-seed 
weight, corrected to a 15% moisture basis. These samples 
were used to determine the flour protein content. After 
removing the husks, the seeds were finely ground, and 
the total nitrogen content was measured using an NC 
analyzer (SUMIGRAPH NC-22F; Sumika Chemical Anal-
ysis Service Ltd., Tokyo, Japan). The protein content in 
flour was calculated by multiplying the nitrogen value by 
a nitrogen-to-protein conversion factor of 6.25. Statis-
tical analysis (Dunnett’s multiple comparison test) was 
performed using BellCurve for Excel provided by Social 
Survey Research Information Co., Ltd.
RESULTS AND DISCUSSION
In this study, lodging was not observed in any of the 
treatment plots. Remarkably, even after Typhoon No. 7 
hit Hokkaido in 2023, lodging was absent across all plots, 
including those where only basal nitrogen was applied (2-
0-0) and those with nitrogen topdressing (2-2-0, 2-0-2, 
and 2-2-2). This resistance to lodging in common buck-
wheat is believed to be related to stem strength, which is 
associated with lignin content (Wang et al., 2015). Thus, 
the significance of lignin synthesis in enhancing the lodg-
ing resistance of semidwarf lines warrants further explo-
ration.
Nitrogen topdressing significantly influenced SPAD 
values (Fig. 1), indicating its impact on chlorophyll con-
tent. The SPAD values were highest in the 2-2-2 treat-
ment, followed by the 2-0-2, 2-2-0, and 2-0-0 treatments. 
Despite increased nitrogen fertilization, the main stem 
length remained consistent across treatment plots (Fig. 2), 
suggesting that the semidwarf common buckwheat line is 
Fig. 1. Chlorophyll content (SPAD value) in each treatment. 
Vertical bars represent standard errors based on three replicates. 
*Asterisks indicate significant differences from the 2-0-0 
treatment by Dunnett’s multiple comparison test (p < 0.05). 
Nitrogen topdressing treatments at different growth stages: basal 
fertilization alone (2-0-0), basal fertilization + nitrogen at flower 
bud appearance (2-2-0), basal fertilization + nitrogen at full 
flowering (2-0-2), and basal fertilization + nitrogen at both stages 
(2-2-2).
Fig. 2. Main stem length in each treatment. Vertical bars represent 
standard errors based on three replicates.
50
40
30
20
10
0
SP
A
D
 v
al
ue
 2-0-0 2-2-0 2-0-2 2-2-2
90
80
70
60
50
40
30
20
10
0
M
ai
n 
st
em
 le
ng
ht
 (c
m
)
 2-0-0 2-2-0 2-0-2 2-2-2
Fagopyrum 41 (2): 41-47 (2024)
43
less susceptible to lodging and benefits from nitrogen top-
dressing in terms of yield enhancement. Furthermore, the 
number of branches was generally higher in plots receiving 
nitrogen topdressing (2-2-0, 2-0-2, and 2-2-2) compared 
to the plot without the topdressing (2-0-0) (Fig. 3). Given 
buckwheat’s significant plasticity in branching in response 
to planting density and its reported increase in the num-
ber of flower clusters on branches (Kasajima et al., 2023), 
the nitrogen topdressing-induced increase in branch num-
ber may contribute to higher yields, highlighting the need 
for further research on the underlying mechanism of this 
process.
Seed yield was positively influenced by nitrogen top-
dressing, as shown in Fig. 4. The 2-0-2 treatment result-
ed in the highest seed yield, followed by the 2-2-0 treat-
ment, with yields of 97.9 g and 89.5 g m-2, respectively, 
representing increases of 1.34 and 1.23 times compared 
to 2-0-0. Similar studies in buckwheat have shown that 
yields are higher when nitrogen is primarily applied as 
basal fertilization rather than during the flowering stage 
as topdressing, even when the total amount of nitrogen 
used is the same. This suggests that nitrogen application 
timing critically impacts both yield and nitrogen-use ef-
ficiency (Sugimoto et al., 2004). This finding supports 
the notion that the semidwarf trait may enhance ni-
trogen-use efficiency, which warrants further investi-
gation. Interestingly, no significant yield difference was 
observed between the 2-2-2 and 2-0-0 treatments. It has 
been reported that applying nitrogen up to 4 g m-2 can 
increase yields but applying between 4 and 10 g m-2 may 
reduce yields (Sugimoto et al., 2004; Fang et al., 2018). 
These studies also highlight that excessive nitrogen con-
ditions can increase the vegetative growth of stems and 
leaves. This indicates that the triple nitrogen dosage in 
the 2-2-2 treatment might cause nitrogen metabolism 
imbalance within the plant, highlighting the importance 
of determining the optimal nitrogen application rate. 
Thousand-seed weight showed minimal variation across 
treatments (Fig. 5), and the number of seeds per square 
Fig. 4. Seed yield in each treatment. Vertical bars represent 
standard errors based on three replicates.
Fig. 5. 1000 seed weight in each treatment. Vertical bars represent 
standard errors based on three replicates.
Fig. 3. Number of primary branches in each treatment. Vertical 
bars represent standard errors based on three replicates.
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
N
um
be
r o
f p
rim
ar
y 
br
an
ch
es
 2-0-0 2-2-0 2-0-2 2-2-2
140
120
100
80
60
40
20
0
Se
ed
 y
ie
ld
 (g
 m
-2
)
 2-0-0 2-2-0 2-0-2 2-2-2
25
20
15
10
5
0
10
00
 s
ee
d 
w
ei
gh
t (
g)
 2-0-0 2-2-0 2-0-2 2-2-2
Kasajima et al. (2024): Nitrogen topdressing in semidwarf buckwheat
44
meter mirrored seed yield trends (Fig. 6). This finding 
suggests that the observed yield increase with nitrogen 
topdressing at the flowering and flower bud appearance 
stages is mainly due to an increase in the number of 
seeds per unit area. However, this study did not inves-
tigate yield-forming processes such as fertilization and 
seed set; thus, further physiological investigations are 
required.
The flour protein content exhibited an upward trend 
with nitrogen topdressing (Fig. 7), with the highest pro-
tein content observed in the 2-0-2 treatment, followed 
by the 2-2-2 treatment. Both treatments had a protein 
content of 15.0 g/100 g, representing a relative increase 
of 108% compared to the 2-0-0 treatment. Shimazaki 
and Watanabe (2010) indicated that applying nitrogen 
fertilizer after the booting stage of wheat, when the 
sink capacity is almost determined, is the main factor 
in increasing the grain protein concentration. A similar 
mechanism may be involved in buckwheat, necessitating 
further research into nitrogen allocation between vegeta-
tive and reproductive growth, given buckwheat’s indeter-
minate growth habit (Funatsuki et al., 2000). Moreover, 
the protein content of buckwheat flour is crucial for its 
noodle-making quality (Matsuura et al., 2010), advocat-
ing for additional cultivation trials focused on processing 
suitability.
CONCLUSION
This study confirms that nitrogen topdressing can 
boost seed yield and protein content in semidwarf com-
mon buckwheat without increasing lodging risk. The 
observed lack of statistical significance in most param-
eters, except chlorophyll content (SPAD value), suggests 
variability in plant responses, highlighting the need for 
further research to optimize nitrogen application rates 
and avoid metabolic imbalances. Despite these complex-
ities, our findings highlight a viable path to enhance the 
nutritional and agricultural value of buckwheat, a crucial 
crop for diversifying global food sources. Future efforts 
should focus on understanding the physiological mech-
anisms behind these benefits and assessing their impact 
on buckwheat’s processing quality, ensuring the full po-
tential of nitrogen topdressing is realized.
ACKNOWLEDGEMENTS
This study was financially supported by the 2023 To-
kyo University of Agriculture and National Agriculture 
and Food Research Organization Matching Fund Joint 
Research Project.
Fig. 6. Number of seeds per square meter in each treatment. Verti-
cal bars represent standard errors based on three replicates.
Fig. 7. Flour protein content in each treatment. Vertical bars 
represent standard errors based on three replicates.
7000
6000
5000
4000
3000
2000
1000
0
N
um
be
r o
f s
ee
ds
 (m
-2
)
 2-0-0 2-2-0 2-0-2 2-2-2
16.0
15.6
15.2
14.8
14.4
14.0
13.6
13.2
12.8
Pr
ot
ei
n 
co
nt
en
t (
g 
10
0 
g-
1 )
 2-0-0 2-2-0 2-0-2 2-2-2
Fagopyrum 41 (2): 41-47 (2024)
45
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46
IZVLEČEK
Vpliv dognojevanja z dušikom na pridelek semen in vsebnost beljakovin v moki polpritlikave navadne ajde
V raziskavi so ocenjeni učinki dognojevanja z dušikom na polpritlikavo navadno ajdo (linija ‚18-601‘), pri čemer je 
raziskava osredotočena na rast, donos semen in vsebnost beljakovin v moki. Izvedli smo poljski poskus in uporabili štiri 
dognojevanja z dušikom v različnih fazah rasti: samo osnovno gnojenje (2-0-0), osnovno gnojenje z dušikom ob pojavu 
cvetnih popkov (2-2-0), osnovno gnojenje z dušikom ob polnem cvetenju (2-0-2) in osnovno gnojenje z dušikom na 
obeh stopnjah (2-2-2) z uporabo naključne zasnove blokov, pri čemer vsaka parcela meri 1,2 × 2,5 m. Osnovno gnoje-
nje je bilo uporabljeno pri 2, 8 in 4,7 g m-2 N, P₂O5 oziroma K2O. Dodatek dušika je znatno povečal vsebnost klorofila. 
Število vej, pridelek semen, število semen na kvadratni meter in vsebnost beljakovin v moki so se povečali z dodatkom 
dušika. Najvišji pridelek semen in vsebnost beljakovin sta bili ugotovljeni pri obdelavi 2-0-2, kar kaže, da uporaba du-
šika pri polnem cvetenju optimizira pridelek in hranilno kakovost polpritlikave ajde. Te ugotovitve poudarjajo pomen 
časovnega usklajevanja pri dodajanju dušika za povečanje agronomske in hranilne vrednosti polpritlikve navadne ajde.
Fagopyrum 41 (2): 41-47 (2024)
47