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Soil and Plant Nutrition
Nitrogen doses and sources applied as top-dressing in onion crops
grown under no-tillage and conventional tillage systems
Leandro Hahn1*
Andressa Mariani Bee1
, Claudinei Kurtz2
, Analice Ferlin Grazziotin1
, Anderson Luiz Feltrim1
,
, Rafael Goulart Machado3
10.1590/0034-737X202370060010
ABSTRACT
Nitrogen (N) fertilization effectiveness in onion depends on N source, as well as on soil type and management system.
The aim of the study is to investigate the effect of N sources and doses applied as top-dressing on bulb yield, leaf N
contents and on the postharvest conservation of onion bulbs grown under no-tillage (NTS) and conventional tillage
(CTS) systems. Three experiments were carried out: two in Lebon Régis County-SC, under NTS; and one in Caçador
County-SC, under CTS. The herein tested N sources comprised urea, ammonium nitrate, calcium nitrate and ammonium
sulfate, in combination to N doses applied as top-dressing (70, 140, 210, 280 and 350 kg N ha-1) in addition to the control,
without N. The N sources did not affect yield parameters, leaf N content and post-harvest onion losses. The maximum
technical efficiency in bulb yield was observed at N doses of 195.8 and 258.4 kg ha-1 in the no-tillage system (NTS) and
at 270.7 kg N ha-1 in the CTS. The NTS enabled maximum yield at N dose 47% lower than the officially recommended
one. Maximum relative commercial yield was associated with 31.1 g kg-1 of leaf N.
Keywords: Allium cepa; urea; calcium nitrate; ammonium nitrate ammonium sulfate.
INTRODUCTION
Nitrogen (N) is the nutrient mostly absorbed by onion
plants (Kurtz et al., 2016); however, it is the element mostly
influencing crop yield, bulb quality (Kurtz et al., 2013) and
disease incidence (Pfeufer & Gugino, 2018). Crops producing 37.34 t ha-1 of bulbs extract 101.4 kg ha-1 of N from the
soil; 58.3 kg ha-1 (57%) of this total is exported through bulb
harvesting (Kurtz et al., 2016). This value represents a significant amount of exported N, which must be replenished
to help maintaining soil fertility (Moraes et al., 2016).
Nitrogen fertilization can significantly increase bulb
yield. According to Kurtz et al. (2012), maximum economic returns observed in three cycles under CTS were
recorded at N doses ranging from 116 kg ha-1 to 142 kg ha-1
in medium-texture soil presenting medium organic matter
(OM) content, as well as at 249 kg ha-1 of N in sandy soil
presenting low OM content. Maximum economic return in
NTS was observed at N doses ranging from 102 kg ha-1 to
131 kg ha-1 (Kurtz et al., 2013). Resende & Costa (2014)
observed the highest commercial yield at N dose of 161.4
kg ha-1. On the other hand, excess N induces exuberant
vegetative plant growth due to increased protein synthesis
and water content, a fact that reduces plant resistance to
diseases and bulb quality (Robles & García, 2013). According to Kurtz et al. (2016), maximum nutrient absorption
rates were concentrated at bulbing stage, at 73 days after
transplantation.
_______________________________________________
Submmited on May 12th, 2022 and accepted on July 05th, 2023.
Empresa de Pesquisa Agropecuária e Extensão Rural de Santa Catarina (Epagri), Estação Experimental de Caçador, Caçador, SC, Brazil. leandrohahn@epagri.sc.gov.br; analiceferlin@epagri.sc.gov.br;
andressabee@epagri.sc.gov.br; andersonfeltrim@epagri.sc.gov.br
2
Empresa de Pesquisa Agropecuária e Extensão Rural de Santa Catarina (Epagri), Estação Experimental de Ituporanga, Ituporanga, SC, Brazil. kurtz@epagri.sc.gov.br
3
Instituto de Assistência Técnica e Extensão Rural (EMATER), Lagoa Nova, RS, Brazil. rgoulartmachado@gmail.com
*Corresponding author: leandrohahn@epagri.sc.gov.br
1
Rev. Ceres, Viçosa, v. 70, n. 6, e70610 oct/nov, 2023
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Leandro Hahn et al.
Nowadays, there is large supply of N sources available
in the market; these sources vary in concentration, chemical
N form and association with other nutrients. Overall, many
of these fertilizers present high cost per nutrient unit, a
fact that increases production costs. In addition, there are
losses associated with each of these sources; they result
from leaching (Wang et al., 2019), volatilization (Huang
et al., 2016) and denitrification (Alsina et al., 2013) processes, as well as influence N availability in the soil and N-use
efficiency by plants.
Systems based on seedling production in flower beds
and on subsequent seedling transplantation prevail in
Southern Brazil (Kurtz et al., 2013). However, there has
been fast expansion of no-tillage seeding in recent years;
this system has been adopted in approximately 20% of
production fields. It mainly happens due to scarcity of, and
high cost with, manpower to perform seedling transplanting
operations (Epagri, 2013).
Conventional tillage system (CTS) is the traditional soil
preparation method adopted for onion crops; however, it
leads to intense soil physical (Vizioli et al., 2021), chemical
(Thomaz & Antoneli, 2020) and biological (Bhaduri et al.,
2017) degradation. Thus, the onion no-tillage system (NTS)
- which performs seeding without turning over the soil, crop
rotation and cover crops - is a soil management alternative
that should be implemented by technicians, researchers and
producers due to broad benefits provided by this system
to different ecosystems. Cover crops used in onion NTS
in Santa Catarina State, Southern Brazil, were efficient in
recovering and increasing total organic carbon contents, as
well as in improving soil physical quality (Loss et al., 2015).
Nitrogen management in CTS, mainly in onion no-till-
age sowing in NTS, is an important research demand to
help defining the N doses and sources to be applied, mainly
due to increase in the adoption of these techniques in Santa
Catarina State, which is the largest onion producer among
Brazilian states (IBGE, 2023). The aim of the current study
was to assess the effect of N sources and doses, applied as
top-dressing, on onions planted based on no-tillage seeding,
under conventional tillage and no-tillage management
systems.
MATERIALS AND METHODS
Two experiments - called experiments 1 and 2 - were
carried out in the 2016/2017 planting season; one experiment - called experiment 3 - was carried out in the
2017/2018 planting season. Experiments 1 and 2 (at coordinates: -26.911225 S and -50.766628 W; and -26. 846680
S and -51.077776 W, respectively) were implemented in
Lebon Régis County/SC. Experiment 3 (at coordinates:
-26.904108 S and -50.751973 W) was implemented in
Caçador County/SC. All experiments were carried out in
typical Dystrophic Bruno Nitosol (Embrapa, 2013). Based
on Köeppen’s classification, the climate in the experimental
region is of the Cfb type – i.e., temperate, humid mesothermal, with mild summer (Alvares et al., 2013). Climatic
data were collected in meteorological stations located 100
m away from the experiments (Figure 1).
Soil samples were collected from the 0-20 cm soil layer
at experiments’ implementation time (Table 1). Soil acidity was corrected based on limestone application (PRNT
80%); fertilizations with phosphorus and potassium were
performed based on the CQFS-RS/SC (2016) to achieve
crop yield of 70 t ha-1.
Figure 1: Daily rainfall rate, minimum and mean temperatures recorded throughout the months in two years of experiments.
Rev. Ceres, Viçosa, v. 70, n. 6, e70610 oct/nov, 2023
Nitrogen doses and sources applied as top-dressing in onion crops
grown under no-tillage and conventional tillage systems
3
Table 1: Chemical attributes of, and clay content in, soils used in all three experiments conducted in the 2016 and 2017 crop seasons
Soil
management
system
Experiments
2016
NTS
1
50
2017
NTS
2
2017
CTS
3
Crop seasons
Clay
OM
P
5,4
4,2
3,9
160
20,2
1,5
0,8
15,8
67
5,7
5,4
7,8
412
29,8
6,1
3,2
17,1
55
5,8
5,7
8,2
321
24,5
7,2
3,6
16,9
%
K
S
Ca
mg dm-3
Mg
CEC
pH 7,0
pH
(H2O)
cmolc dm-3
NTS: no-tillage soil management system; CTS: conventional tillage system; Clay: pipette method; OM: organic matter determined according to the
Walkley-Black method; pH(H2O) at a soil:solution ratio of 1:1; P and K were extracted with Mehlich-1; Ca2+ and Mg2+ were extracted by KCl 1 mol L-1;
S was extracted with calcium phosphate; CEC: cation exchange capacity at pH 7.0.
Experiments were carried out based on a randomized
block design, with 4 repetitions. Experiment 1 has followed
factorial arrangement 3x4+1; it combined 3 N sources
(urea, ammonium nitrate and calcium nitrate) and 4 N
doses applied as top-dressing (70, 140, 210 and 280 kg
ha-1), in addition to the control treatment (without N application) – this experiment comprised 13 treatments, in total.
Experiments 2 and 3 have followed factorial arrangement
4x5+1; it comprised 4 N sources (ammonium sulfate was
added to the N sources of experiment 1) and 5 N doses
applied as top-dressing (N dose of 350 kg ha-1 was added to
N doses adopted in experiment 1), in addition to the control
treatment (without N application as top-dressing) – these
experiments comprised 21 treatments, in total. Nitrogen
sources presented the following compositions: urea (UR,
45% of N), calcium nitrate (CN, 15.5% of N and 19% of
Ca), ammonium nitrate (AN, 32% of N) and ammonium
sulfate (AS, 21% of N and 22% of S). All experiments
were 3.0-m wide and 5.0-m long, spacing between rows
was 0.30 m and usable area was 1.2 m2.
Experiments 1 and 2 were conducted in no-tillage
(NTS) soil management system; they comprised previous
soybean crop in Summer, which was followed by black
oat crop used as cover crop in Fall. Black oat was sown in
April in both crop seasons and managed through desiccation before stem elongation (phenological stage V6), at 30
days before onion sowing. Experiment 3 was implemented
in area subjected to conventional tillage system (CTS),
after subsoiling and double harrowing procedures. Onion
sowing density was set at 26 seeds / meter; thinning was
carried out at 60 days after sowing (DAS) and left a final
population comprising 550 thousand plants ha-1. In total,
20 kg N ha-1, 370 kg ha-1 of P2O5 and 60 kg ha-1 of K2O
were applied in the sowing furrow via formulated fertilizer,
at sowing time. Top-dressing comprised the application
Rev. Ceres, Viçosa, v. 70, n. 6, e70610, oct/nov, 2023
of 120 kg ha-1 of K2O divided into two equal doses at 45
and 80 DAS. Top-dressing N doses were split into 5 doses
applied at 45 (25% of N), 80 (25% of N), 110 (30% of N)
and 140 (20% of N) DAS (CQFS-RS/SC, 2016).
Experiments 1 and 2 have used onion cv. Mulata,
whereas experiment 3 used onion cv. Salto Grande. Onion
seeds were treated with fungicides pyraclostrobin and
thiophanate methyl, as well as with insecticide fipronil.
Invasive plants, pests and diseases were controlled based
on spraying with chemical products registered for onion
crops in the Ministry of Agriculture.
The last fully expanded leaf was collected from 10
plants at bulbing stage (at approximately 90 DAS) for leaf
N content determination purposes. Leaves were dried in
forced air circulation oven, at 65 ± 5 °C, until they reached
constant mass; then, they were ground in Wiley mill. Samples were digested with sulfuric acid, and the N content
in them was determined in micro-kjeldahl still (Tecnal,
TE-0363, Brazil), based on Tedesco et al. (1995).
Bulbs were harvested at 170 DAS, when approximately
80% of plants showed shoot popping. Plants’ shoot was
cut; bulbs were placed in plastic boxes and stored in
shed at room temperature for approximately 10 days, for
pre-curing purposes. Subsequently, bulbs were separated
into commercial and non-commercial classes, based on
Maara (1995). All commercial bulbs were placed in plastic
boxes, stored in shed at room temperature and evaluated
again after 150 days in order to determine post-harvest
losses (%).
Data were subjected to analysis of variance and to
regression analysis for quantitative data; bifactorial comparisons between N doses and sources were performed. All
analyses were carried out in R software (R Development
Core Team, 2020). Regressions were applied to adjust
the polynomial degree in order to establish the maximum
Leandro Hahn et al.
4
technical efficiency (MTE) and economic efficiency (MEE)
of the variables of interest, based on equation 1:
y = a ± b1x ± b2x2
(1)
Equation 2 was used to estimate the MTE:
MTE = -b1 : 2b2
(2)
Equation 3 was used for the estimation of the MEE:
t
w b1
MEE
2b2
(3)
Where: t is the value of the input (nitrogen source) and
w is the marketable value of the product (onion).
The average price of UR, CN, AN and AS in the
year 2016 was US$0.77, 6.18, 1.34 and 1.91 kg-1 of N,
respectively, and US$0.86, 6.76, 1.47 and 2.09 kg-1 of N,
in the year 2017 (Conab, 2021a). The average price of a
kilogram of marketable onion in the years 2016 and 2017
was US$0.19 kg-1 (Conab, 2021b).
Critical leaf N level was estimated through the regression equation obtained by associating MTE with leaf N
contents.
RESULTS AND DISCUSSION
Climate differed between the two crop seasons
(Figure 1), since there were considerably higher and better
distributed rainfall events in 2016 (780 mm) than in 2017
(564 mm).
Nitrogen sources tested in experiment 1 – i.e., urea,
ammonium nitrate and calcium nitrate, which were added
with ammonium sulfate in experiments 2 and 3 - did not
show difference in commercial bulb yield (Figure 2),
post-harvest losses (Figure 3), distribution in commercial
classes (Figure 4) and leaf N levels (Figure 5). Lack of N
sources’ effect on onions was also reported in other studies
(Sullivan et al., 2001; Boyhan et al., 2007). According to
the aforementioned authors, splitting top-dressing N applications into smaller doses, based on the N demand curve, is
more important than the used N source.
The tested N sources provide different N concentrations
in their amide (e.g., urea), ammoniacal (e.g., ammonium
sulfate) and nitric (e.g., calcium nitrate) forms. Some studies
have evidenced positive effect of N source combinations on
species belonging to genus Allium. Gamiely et al. (1991)
have shown that nitrate and ammonium supply at ratio 1:3
has favored the production of onion leaves, roots and bulbs.
NH4-NO3- applications to Allium tuberosum, at ratios 50:50
Figure 2: Doses of maximum technical efficiency (MTE) and maximum economic efficiency (MEE) for commercial onion yield in the
three experiments, at different N doses (70, 140, 210, 280 and 350 kg ha-1) applied as top-dressing and treatment without N application.
*: Significant at 5% probability level.
Rev. Ceres, Viçosa, v. 70, n. 6, e70610 oct/nov, 2023
Nitrogen doses and sources applied as top-dressing in onion crops
grown under no-tillage and conventional tillage systems
and 75:25, were the most suitable for the species quality
and growth (Sun et al., 2014). The application of calcium
nitrate and ammonium nitrate in two crops investigated in
the state of Georgia (USA) has increased the total weight
of onions when N concentrations increased from 84 kg
ha-1 to 168 kg ha-1, in comparison to results recorded for
sodium nitrate, potassium sodium nitrate and potassium
nitrate (Batal et al., 1994). In addition, the aforementioned
authors have shown that ammonium nitrate was capable
of increasing the production of onions belonging to larger
diameter classes.
Nitrate is the main N form absorbed by onions (Geisseler et al., 2022). Moreover, soil and climate features in
sub-tropical regions favor amide and ammoniacal N transformation into NO3- (Silvia & Bohannan, 2016). Therefore,
the tested N sources may have supplied different NH4-NO3rates to onion plants, and they did not affect onion plants’
growth and yield.
Urea N losses due to NH3 volatilization may have been
minimized by irrigation after fertilizer application (Viero et
al., 2015). Soil acidification promoted by ammonia sources
(Bindraban et al., 2015) has also shown insignificant negative effects on results in the present study. The addition
of Ca and S deriving from calcium nitrate and ammonium
5
sulfate sources, respectively, did not have impact on the
current results. Soil Ca and S contents (Table 1) were
higher than the critical values recommended by CQFSRS/SC (2016) for onion - 4.0 cmolc cm-3 and 15 mg dm-3,
respectively.
Maximum technical efficiency (MTE) in experiment 1
was achieved at N dose of 195.8 kg ha-1; it recorded commercial onion production of 79,410.7 kg ha-1 (Figure 1). On
the other hand, MTE in experiments 2 and 3 was achieved
at higher N doses - 258.4 kg ha-1 and 270.7 kg ha-1 –; these
experiments recorded commercial onion yield of 65,491.2
kg ha-1 and 56,391.2 kg ha-1, respectively. On the other
hand, maximum economic efficiency (MEE) in experiment
1, 2 and 3 was achieved at N dose of 183.1, 230.1 and 235.0
kg ha-1, respectively. The difference between the doses of
MTE and MEE, were 12.7, 28.3, and 35.7 kg N ha-1. This
reduction in fertilizer application causes the decrease of
only 1,885.0, 200.7 and 235.7 kg ha-1 of marketable onion,
respectively in experiment 1, 2 and 3.
CQFS-RS/SC (2016) recommends using 288 kg ha-1 of
N for expected onion yield of 70.000 kg ha-1. MTE doses
obtained in experiments 2 and 3 in the present study were
close to the official recommendation, mainly if one takes
into consideration that CQFS-RS/SC (2016) has suggested
Figure 3: Post-harvest losses based on N doses (70, 140, 210, 280 and 350 kg ha-1) and sources (calcium nitrate (Ca(NO3-)2), ammonium nitrate (NO3NH4), ammonium sulfate ((NH4NO3)) and urea applied as top-dressing, and on treatment without N application in
onion crop grown under NTS in experiment 2.
*: Significant at 5% probability level.
Rev. Ceres, Viçosa, v. 70, n. 6, e70610, oct/nov, 2023
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Leandro Hahn et al.
Figure 4: Onion production rate in five commercial classes based on nitrogen rates (70, 140, 210, 280 and 350 kg ha-1) applied as
top-dressing and treatment without N application, in all three experiments. Different letters indicate differences between treatments
(Tukey, 0.05).
reducing the N dose by up to 25% in consolidated no-till
system, as observed in experiment 2. However, MTE in
experiment 1 was achieved at N dose 47% lower than the
recommended one. Experiment 1 was conducted under
CTS, whose management is well-known for increasing the
efficiency of N applied in these production systems (Silva
et al., 2020; Yang et al., 2020), mainly by increasing OM
and N availability and by improving soil quality (Tiritan et
al., 2016; Daigh et al., 2018).
Assumingly, the higher performance of plants subjected
to lower N doses in NTS is explained by N produced by
soybean and black oat straw decomposition – these crops
were precursors to onion sowing. This N likely replaced
most of the applied mineral N. According to Kurtz et al.
(2016), the estimated N uptake by onions reached 409 mg
plant-1, which corresponded to N extraction of 101.4 kg
ha-1. The aforementioned authors have pointed out that the
amount of absorbed N was 35.2% higher than that added by
mineral fertilization; this finding highlights the important
contribution of soil organic matter in N supply.
Figure 5: Leaf nitrogen contents based on N doses (70, 140, 210, 280 and 350 kg ha-1) applied as top-dressing and treatment without
N application, in onion crop grown in all three experiments - experiment 1 does not present treatment with N dose of 350 kg (Statistical significance level at 5%).
Rev. Ceres, Viçosa, v. 70, n. 6, e70610 oct/nov, 2023
Nitrogen doses and sources applied as top-dressing in onion crops
grown under no-tillage and conventional tillage systems
7
Figure 6: Association between leaf N contents and relative commercial yield in 3 experiments conducted with different N sources
and doses.
Experiments 1 and 3 did not show difference in onion
losses after storage for approximately 150 days. However,
storage losses presented quadratic increase associated
with calcium nitrate source and linear increase associated
with urea in experiment 02 (Figure 3). Post-harvest losses
reached approximately 20% at the highest N doses.
Class-2 bulbs, which have low commercial value,
recorded increased participation in commercial yield due to
lack of N in experiments 2 and 3 (Figure 4). Class-4 bulbs,
which have high commercial value, recorded increased
participation in commercial yield due to N application in
experiments 1 and 2. However, N application in experiment
1 reduced the participation of class-3 onions in commercial
yield. According to Rodrigues et al. (2015), class-3 and -4
onions are commercially desirable, since these classes are
preferred by the consumer market and enable producers
to get higher marketing price. These very same authors
recorded yield by 86% in these two onion classes, and considered 168 kg ha-1 of N as the efficient dose to be applied
to this crop type.
Leaf N levels recorded quadratic increase due to the
application of increasing N doses as top-dressing, in all
three experiments (Figure 5). Maximum estimated values
reached 37.9 g kg-1, after the application of 185.9 kg N
ha-1 in experiment 1; 28.9 g kg-1, after the application of
288.6 kg N ha-1 in experiment 2; and 28.9 g kg-1, after the
application of 329.5 kg N ha-1 in experiment 3. Differences
between cultivars and different climates between crop seasons can explain these variations. Nitrogen application has
also increased N content in onions in studies carried out by
Rev. Ceres, Viçosa, v. 70, n. 6, e70610, oct/nov, 2023
Kurtz et al. (2012), who observed maximum N levels of 40,
35 and 32 g kg-1 after the application of 237, 136 and 150
kg N ha-1, respectively, in three consecutive onion crops.
Rodrigues et al. (2018) recorded maximum estimated value
for leaf N content equal to 32.7 g kg-1 at N dose of 168 kg
ha-1, and 41.2 g kg-1 at N dose of 67 kg ha-1, in two different
experiments. Relative commercial yield recorded quadratic
increase due to leaf N content (Figure 6) - maximum commercial yield was obtained at leaf N content of 31.1 g kg-1.
CONCLUSIONS
Nitrogen, ammonium nitrate and sulfate, calcium nitrate
and urea sources did not affect onion yield parameters, leaf
N content and postharvest losses;
The maximum technical efficiency recorded for bulb
yield was observed at N doses of 195.8 kg ha-1 and 258.4 kg
ha-1 in the no-tillage system (NTS) and at N dose of 270.7
kg ha-1 in the conventional tillage system (CTS).
Onion postharvest losses took place as N doses deriving
from calcium nitrate and urea sources increased in NTS.
Maximum relative commercial yield was associated
with 31.1 g kg-1 of leaf N.
ACKNOWLEDGMENTS, FINANCIAL
SUPPORT AND FULL DISCLOSURE
We thank the anonymous reviewers for their contribution to manuscript. This article was supported financially
by Santa Catarina State Agricultural Research and Rural
Extension Agency (Epagri). No potential conflict of interest was reported by the authors.
8
Leandro Hahn et al.
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