Introduction
Tobacco
(Nicotiana tabacum L.) is an important industrial crop for many countries (Bilalis et al.
2015; Guang et al. 2019). Especially, China’s flue-cured tobacco planting area is about one-third of the worldwide and the tobacco industry nets accounts for about 10% of the national tax income (Zou et al.
2018). Tobacco also plays an important social and economic role, being main source
of income for many families, due to the high quality and good characteristics
of tobacco leaves in Anhui province (Dong et al. 2015). Flue-cured tobacco region in Anhui is typically multiple
cropping of tobacco-rice, which is one of the representatives producing areas of
characteristic and high quality tobacco leaves (Dong et al. 2015; Zhang et al.
2016). However,
tobacco leaf quality
and farmers' income have potentially declined with the increase of continuous
cropping years of tobacco-rice (Jin et al.
2014; Zhang et al. 2016).
Tobacco-rice cropping system is special agricultural
system that only occurs in some southern provinces of China such as Anhui,
Hunan, Jiangxi, Fujian, Guangdong, Guangxi, Guizhou and Yunnan, with a planting
area of 300, 000 ha−1 which accounts for nearly 30% of the tobacco planting
area in China (Zhang et al.
2015; Jiang et al. 2016). The soils of tobacco-rice cropping system are a typical paddy soil in Anhui province, most of which
is acid with a pH lower than 5.5 (Jiang et al. 2015). Moreover, soil acidification can be accelerated by
intensive farming and overuse of chemical fertilizers in intensive farmland,
including tobacco-rice field (Karaivazoglou et
al. 2007; Jiang et al. 2015;
Kunhikrishnan et al. 2016). Dolomite is a common practice
to ameliorate acid soils and widely applied
to tobacco-rice field in southern China (Jiang et al.
2015; Zou et al. 2018). The application
of dolomite is a
conventional technique for alleviating soil acidification in tobacco-rice
cropping system (Jiang et al.
2015). Our previous
study found that soil pH was increased by 0.11 units by the application of dolomite in flue-cured
tobacco field (Jiang et al.
2015). However,
research on the effects of dolomite on tobacco growth, leaf yield and
quality in tobacco-rice cropping system is still limited.
Tobacco straw
is an important organic resource, and the total annual yields averaged 8–10 Mt
in China (Liu et
al. 2017). Previous studies found that the potassium (K) of tobacco straw could
reach 20 g K2O kg–1, and the nitrogen (N) and phosphorus (P) was about 14
g
N kg–1, and 16.9 g P2O5 kg–1, respectively (Xiao et al. 2008; Jiang et al. 2016; Liu et al. 2017). Several studies have found that
straw return could increase crop yield due to nutrient replenishment and
improved soil fertility (Huang et al. 2013; Murphy et al.
2016; Liao et al. 2018). Therefore, as
one of the renewable resources, the reasonable and effective use of tobacco
straw is getting more and more attention. After the harvest of tobacco leaves,
the tobacco straws were incorporated by a rotary cultivator cut into 10–15 cm
pieces before rice transplanting (Jiang et al. 2016; Liu et al. 2017). The
decomposition and nutrient release of tobacco straw under the condition of
returning to the field have been demonstrated, and it was also
found that the dolomite could accelerate the
decomposition of tobacco straw (Jiang et al. 2016; Liu et al. 2017). However, few studies have been conducted on how tobacco straw return and dolomite affect soil pH, tobacco leaf
yield and quality. Therefore, in this study, a field
experiment of tobacco straw return and dolomite application in tobacco-rice cropping system were carried
out during 2015–2018. The objective was to determine
the effect of both tobacco straw return, dolomite application and their interaction on soil pH, yield, quality
and chemical characteristics of flue-cured tobacco leaf.
Materials and Methods
Site description, soil properties and weather conditions
The field
experiments were conducted from 2015 to 2018 at a famous tobacco planting area
in the south of Anhui Province, China. The cropping system consists of tobacco
(March to July) and rice (July to November). The soil is paddy field had an
initial pH 5.5, organic matter 22.9 g kg−1, total N 1.71 g kg−1,
available N 171.7 mg kg−1, Olsen-P 36.5 mg kg−1,
and available K 209.3 mg kg−1 in the 0–20 cm soil layer prior
to the experiment. The region is considered to have a subtropical, humid
monsoon climate with an average annual air temperature of 16.9°C and mean
annual precipitation of 1554 mm.
Experimental design and farm management
Four treatments were designed as
follows: control (tobacco straw removed, CK), tobacco straw return (St), tobacco straw
return with dolomite (St + D), and
tobacco straw return with lime (St + L). Each treatment was replicated for three times,
resulting in 12 plots each with an individual area of 36 m2 (3.6 m ×
10 m). In order to prevent the flow of water and fertilizer, four stringent
ridges (30 cm in height, and 30 cm in width) were built around each plot, and
each plot was equipped with a separate water inlet and outlet. For all straw
return treatments, the tobacco straws were incorporated by a rotary cultivator
cut into 10–15 cm pieces after the harvested of tobacco leaves in early July in
2014, 2015, 2016 and 2017. The lime and dolomite were broadcasted uniformly
before the straws returned at a rate of 1.5 t ha−1. For the
CK, the tobacco straws were removed from the plot. The lime was used in the
form of calcitic lime (Ca 396 g kg−1
and Mg 2.5 g kg−1). The dolomite
was applied as a fine powder < 0.3 mm, with Ca 220 g kg−1 and Mg 124 g kg−1.
Fertilizers were consisted of 115 kg N ha−1, 180 kg P2O5
ha−1 and 375 kg K2O
ha−1 for flue-cured
tobacco. The commercial fertilizers used were compound fertilizer for tobacco
(N: P: K 9–13.5–22.5), superphosphate (0–15–0), potassium sulfate (0–0–50),
and potassium nitrate (13.5–0–46). All the fertilizers were applied one day
before transplanting of tobacco seedlings.
The tobacco
variety used was flue-cured tobacco (Nicotiana
tabacum L.) “Yunyan 87”, the most popular in the region. The inter-rows
were 120 cm wide and plants were spaced 50 cm apart in the rows (16,667 plants
ha−1). Seedlings
were transplanted during the sec half of March in each experimental year.
Irrigation, pesticide and herbicide applications were the same for all treatments
and recommended for flue-cured tobacco in the area by Chizhou Tobacco Company
of Anhui Province. The plant was topped (by removing the tobacco flowers) at
during the period 60–70 days after transplanting, and the unproductive leaves
(suckering) was removed manually.
Crop and soil analysis
Trade yield
and market value: All plants were
harvested five times by hand at 7- or 8-day intervals, by removing three to
five leaves each time, starting 70–80 days after transplanting. The leaves were
cured immediately after harvest in a flue-curing barn for flue-cured tobacco.
The gross yield was measured at a 17% moisture content of the cured leaves, and
the leaves were divided into commercial (trade yield) and noncommercial
fractions, then the trade yield and market value were calculated.
Appearance
Quality and Smoking Quality: Appearance quality of the commercial
leaves was graded using a scale from 1 to 10 (quality index) by estimating and
grading visual and physical characteristics including cured leaf color,
maturity, body, leaf structure, oil, color intensity (Karaivazoglou et al. 2007). Smoking quality
was graded using a scale from 1 to 10 (quality index) by evaluating and grading
the smoking characteristics such as aroma quality and quantity, offensive odor,
physiological strength, irritancy, comfortable aftertaste, sweet, dry sense,
and moisturizing mellow (Jin et al. 2014).
Leaf sample
analysis: Twenty leaves
were randomly selected from the commercial leaves for chemical measurements. Samples were dried at 70°C
for 48 h, to constant dry weight, and milled into powder for analysis. The
samples were digested using the H2SO4-H2O2
method, and N, K, Ca and Mg were determined
according to the method of Shao et al. (2012) and Tang et al. (2013). Nicotine and reducing
sugars were measured by Continuous Flow Analysis (Karaivazoglou et al. 2007; Guo et al. 2013).
Soil analysis: Before the experiment, a 0–20 cm soil
layer sample was collected to determine the basic fertility. After the harvest of tobacco
leaf for each year, soil samples (0-20 cm) were collected from 12 plots for
chemical properties analysis. Soil pH, alkali-hydrolyzed N, available K,
exchangeable Ca and Mg were determined according to the method of Shao et al. (2012) and Tang et al. (2013).
Statistical
analysis
Statistical analyses were performed
using one-way ANOVA with S.P.S.S. 19.0 (S.P.S.S. Inc., Chicago, IL, U.S.A.).
The treatments were compared by the method of least significance difference
(LSD) test at P < 5%.
Results
Cured leaf trade yield and market
value
Straw return and
liming had a significant effect on the trade yield and market value of cured tobacco leaves during the experimental
years (Fig. 1). Trade yield was not
affected by lime and straw retention in 2015 and
2017, but significantly affected by lime in both 2016 and 2018. Similarly, market value was not affected by lime and straw retention in 2015, but significantly
increased by lime since 2016, and also increased by straw retention in 2018.
Compared with the CK, St + L increased trade yield by 8.0, 7.8 and 21.4% in 2016,
2017 and 2018, respectively, while St + D
and St treatments increased trade yield by
16.1 and 11.7% in 2018, respectively. Compared with the CK, St + L and St + D
increased market value of cured leaves by 33.7 and 24.7% in 2018. Moreover, the
market value of cured leaves in St + L was 8.7% higher than in St treatments in
2018. In general, trade yield and market value of cured leaves were both in the
following order: St + L > St + D > St
> CK.
Appearance quality and
smoking quality
Straw retention and liming had significant
positive effect on the appearance quality and smoking quality index of cured
leaves (Fig. 2). However, the appearance quality of cured leaves did not show a significant difference among the St,
St + D and St + L treatments except in 2017. The St + L and St + D significantly increased the smoking quality of cured
leaves compared to the CK and St in 2017 and 2018. However, for all treatments, the smoking quality of
cured leaves was decreased with the increase of planting time.
Chemical characteristics of
cured leaves
The N and
nicotine contents of the cured leaves in the first (2015) and sec (2016) year
showed no significant difference among all treatments (Table 1). However, compared with the CK, the St, St + D and St +
L treatments increased the N content by 21.5, 21.5 and 19.8% in 2017, and by
14.8, 17.2 and 18.9% in 2018, respectively. Similarly, the St, St + D and St + L
treatments increased the nicotine content by 10.9, 13.0 and 13.8% in 2017, and
by 10.4, 7.6 and 9.0%, in 2018, respectively. Liming had a statistically
significant increasing effect on the reducing sugars of the cured leaf. The
reducing sugars in the first (2015) year showed no significant difference among
all treatments. However, after two years, the reducing sugars in St + D (26.7–27.0%) were significantly higher than other
treatments (23.4–24.5%).
The K concentration of cured leaves ranged from 1.69 to 2.22%,
and decreased by increasing the year of cultivation (Table 2). However, the K concentration was significantly
increased by liming and straw retention after two years treatments. Compared
with the CK, the K concentration of cured leaves for the St, St + D and St +
L treatments were significantly increased by 16.5, 14.3 and 14.8% in 2016,
respectively. However, there was no significant difference of K concentration
of cured leaves among St, St + D and St + L.
Lime application had significant positive effect on Ca concentration of cured leaves (Table 2). In 2016, 2017 and 2018, the treatments St + L and St + D achieved significantly higher
Ca concentration in leaves compared to CK. In both 2017 and
2018, the highest Ca concentration in leaves was observed in treatment St + L
(23.68 and 24.79%), which was significantly higher compared to all other
treatments. The Ca concentration of cured leaves was significantly higher
in treatment St + L compared to St + D in both 2017 and 2018, but not in both 2015 and 2016.
There was no significant difference in Ca concentration in leaves between
the treatment CK and St.
The treatment St + D achieved
the highest Mg concentration in leaves during the experiment, with
significantly higher Mg concentration than all other treatments in 2016, 2017
and 2018 (Table 2). There was no significant difference in Mg
concentration between the CK and St during the experiment. The Mg concentration
of leaves in St + D
increased with the increase of treatment time, while decreased in St + L during the experimentation
period. Moreover, since 2016, St + D significantly
increased the Mg content of leaves compared with all other treatments. The lowest Mg content
of leaves was observed for St + L, that were significantly lower compared to treatments St + D and St in both 2017 and 2018.
Soil pH
Lime
application had significant
positive effect on soil pH (Fig.
3). The soil pH of St + L and St + D was
5.61 and 5.57 in 2015, which increased to 6.53 and 6.39 in 2018, respectively.
Since 2017, St + L and St + D treatment resulted in significant higher soil pH
compared with the treatments CK and St. However, straw return alone (St) did not significant affect the soil pH for
two years application. In general, the soil pH was in the following order: St + L ≥ St + D > St ≥ CK.
Table 1: Effect of liming and straw returning on total nitrogen, nicotine and reducing sugars content of tobacco
leaves
|
Treatments |
Total
nitrogen content (%) |
Nicotine
content (%) |
Reducing sugars (%) |
|||||||||
|
2015 |
2016 |
2017 |
2018 |
2015 |
2016 |
2017 |
2018 |
2015 |
2016 |
2017 |
2018 |
|
|
CK |
1.71 a |
1.40 a |
1.21 b |
1.22 b |
1.69 a |
1.54 a |
1.38 b |
1.44 b |
27.9 a |
28.2 b |
23.4 b |
24.3 bc |
|
St |
1.69 a |
1.46 a |
1.47 a |
1.40 a |
1.79 a |
1.56 a |
1.53 a |
1.59 a |
28.0 a |
28.6 ab |
23.9 b |
23.5 c |
|
St + D |
1.72 a |
1.56 a |
1.47 a |
1.43 a |
1.83 a |
1.62 a |
1.56 a |
1.55 a |
29.1 a |
29.6 a |
26.7 a |
27.0 a |
|
St + L |
1.76 a |
1.49 a |
1.45 a |
1.45 a |
1.83 a |
1.71 a |
1.57 a |
1.57 a |
27.7 a |
27.7 b |
24.4 b |
24.5 b |
Means sharing different
letters, within a column, differ significantly from each other at P < 0.05
Here CK, St, St + D
and St + L are respectively tobacco
straw removed, tobacco straw return, tobacco straw return with dolomite,
tobacco straw return with lime
%20291-297_files/image002.png)
Fig. 1: Effect of straw return and liming on trade yield and
output value of tobacco leaves (mean ± SD)
Here CK, St, St + D
and St + L are respectively tobacco
straw removed, tobacco straw return, tobacco straw return with dolomite,
tobacco straw return with lime
Columns with different lowercase letters indicate a significant
difference for different year (P <
0.05)
%20291-297_files/image004.png)
Fig. 2: Effect of straw return and liming on
appearance quality and smoking quality of tobacco leaves (mean ± SD)
Here CK, St, St + D
and St + L are respectively tobacco
straw removed, tobacco straw return, tobacco straw return with dolomite, tobacco
straw return with lime
Columns with different lowercase letters indicate a significant
difference for different year (P <
0.05)
Soil nitrogen, potassium,
calcium and magnesium content
Straw return significantly increased the soil
alkaline hydrolyzable-N in 2018 (Table 3).
However, no significant effect of liming was observed for soil alkaline
hydrolyzable-N during the experiment. The available K content
in soil was the lowest in treatment CK among all the
treatments in all four years. In 2015 and 2016, there was no significant
difference in available
K content among all the treatments. In
both 2017 and 2018, the highest available K content
was determined in treatment St (239.6 and 319.4 mg kg−1), which was significantly higher compared to treatment
CK, but not to the treatments St + D and St + L. Straw retention significantly increased the soil available K content after the three year experiment.
The highest exchangeable Ca content of soil was observed in the St + L treatment, which was 1540.1 mg kg−1 in 2017
and 1813.4 mg kg−1 in 2018
(Table 4). The exchangeable Ca content of soil in the St + L was 30.6, 57.1 and 65.0% higher than in the St + D, St and CK treatments in 2018. Similar, the Ca content of soil in
the St + D was 20.3 and 26.3% higher than in the St and CK
treatments in 2018. The exchangeable Ca content of soil in both St + L
and St + D
increased with the increase of treatment time during the experimentation period. Treatment St + D achieved a significantly higher
exchangeable Mg content of soil compared to all other treatments in
2016, 2017 and 2018, and exchangeable Mg content of soil in St + D was increased with the increase
of treatment time. However, there was no significant difference in exchangeable
Mg content of soil among the treatments CK, St and St + L
for all years.
Discussion
Table 2: Effect of liming and straw return on
K, Ca and Mg concentration of tobacco leaves
|
Treatments |
K
concentration (g kg–1) |
Ca concentration (g kg–1) |
Mg concentration (g kg–1) |
|||||||||
|
2015 |
2016 |
2017 |
2018 |
2015 |
2016 |
2017 |
2018 |
2015 |
2016 |
2017 |
2018 |
|
|
CK |
20.1 a |
18.2 b |
17.7 b |
16.9 b |
18.40 b |
18.14b |
18.19c |
18.23c |
2.41 a |
2.28 b |
2.11bc |
1.97bc |
|
St |
21.8 a |
21.2 a |
21.0 a |
20.4 a |
19.09ab |
19.38ab |
19.30c |
19.82c |
2.45 a |
2.39 b |
2.36 b |
2.21 b |
|
St + D |
22.0 a |
20.8 a |
20.7 a |
19.5 a |
19.13ab |
20.86 a |
21.46b |
22.48b |
2.48 a |
2.83 a |
2.98 a |
3.06 a |
|
St + L |
22.2 a |
20.9 a |
20.5 a |
19.2 a |
19.71 a |
21.80 a |
23.68a |
24.79a |
2.39 a |
2.24 b |
2.02 c |
1.76 c |
Means sharing different
letters, within a column, differ significantly from each other at P < 0.05
Here CK, St, St + D
and St + L are respectively tobacco
straw removed, tobacco straw return, tobacco straw return with dolomite,
tobacco straw return with lime
Table 3: Effect of liming and straw return on alkaline hydrolyzable-N, and available
K content of soil
|
Treatments |
Alkaline
hydrolyzable-N content (mg kg–1) |
Available
K content (mg kg–1) |
||||||
|
2015 |
2016 |
2017 |
2018 |
2015 |
2016 |
2017 |
2018 |
|
|
CK |
133.0 a |
131.0 a |
119.4 a |
110.5 b |
181.7 a |
184.2 a |
168.3 b |
216.8 b |
|
St |
139.9 a |
143.9 a |
137.1 a |
136.2 a |
194.6 a |
211.2 a |
239.6 a |
319.4 a |
|
St + D |
142.2 a |
137.2 a |
132.9 a |
129.8 a |
191.9 a |
205.0 a |
206.2 ab |
288.7 a |
|
St + L |
137.9 a |
139.7 a |
133.2 a |
134.5 a |
195.5 a |
190.9 a |
207.4 ab |
281.3 a |
Means sharing different
letters, within a column, differ significantly from each other at P < 0.05
Here CK, St, St + D
and St + L are respectively tobacco
straw removed, tobacco straw return, tobacco straw return with dolomite, tobacco
straw return with lime
Table 4: Effect of
liming and straw return on exchangeable Ca and Mg content of soil
|
Treatments |
Exchangeable
Ca content (mg kg–1) |
Exchangeable Mg content (mg kg–1) |
||||||
|
2015 |
2016 |
2017 |
2018 |
2015 |
2016 |
2017 |
2018 |
|
|
CK |
956.7 a |
996.6 b |
1039.9 b |
1099.3 c |
137.7 a |
127.0 b |
141.2 b |
150.1 b |
|
St |
971.5 a |
1030.2 b |
1112.3 b |
1154.3 c |
143.8 a |
138.7 b |
149.5 b |
167.1 b |
|
St + D |
1077.4 a |
1087.9 ab |
1235.4 b |
1388.7 b |
159.1 a |
196.7 a |
217.3 a |
310.9 a |
|
St + L |
1098.7 a |
1283.7 a |
1540.1 a |
1813.4 a |
132.3 a |
144.0 b |
144.1 b |
169.8 b |
Means sharing different
letters, within a column, differ significantly from each other at P < 0.05
Here CK, St, St + D
and St + L are respectively tobacco
straw removed, tobacco straw return, tobacco straw return with dolomite, tobacco
straw return with lime
%20291-297_files/image006.png)
Fig. 3: Effect of liming and straw return on soil pH (mean ± SD)
Here CK, St, St + D
and St + L are respectively tobacco
straw removed, tobacco straw return, tobacco straw return with dolomite, tobacco
straw return with lime
Columns with different lowercase letters indicate a significant
difference for different year (P <
0.05)
In this study, liming
significantly enhanced leaves yield of flue-cured tobacco on an acidic soil also reported in previous studies (Karaivazoglou
et al. 2007; Jiang et al. 2015; Pang et al. 2019). The improvement in soil pH of lime and dolomite treatment probably increased the growth, yield and
quality of tobacco. Karaivazoglou et al. (2007) also found an increase in yield of tobacco leaves in a field experiment limed with
0 to 3 t Ca(OH)2 ha-1. Similarly, in our previous study found
significant yield increases of flue-cured tobacco on acidic soil, after the application of 1.5 t (Ca(OH)2 ha-1, which resulted in a pH increase from 5.3 to 5.8 (Jiang et al.
2015).
Liming and dolomite also improved the smoking quality of cured tobacco leaf.
Karaivazoglou et al. (2007) found that the quality of cured
leaf was significantly increased from 6.7
to 7.2 by grade indices the application of hydrated lime (Ca(OH)2).
Jiang et al. (2015) found that N from tobacco straw is released during
tobacco season, and its supply for high quality tobacco leaves was excessive.
It was also reported that straw retention improved soil N supply, stimulated
the growth of tobacco and increased the yield of cured leaf (Zhou et al. 2016; Tan et al. 2018; Wang et al.
2018).
Straw return increased leaf K concentration on
average from 18.2to 20.9 g kg-1 (14% increase). Wang et al. (2018) found that wheat straw return significantly increased K
concentration of middle and upper leaves by 8.39 and 22.63%, respectively. The
increase of leaf K concentration under straw retention is primarily due to
straw return significantly increased soil available K content (Li et al. 2014; Jiang et al. 2015) and enhanced the total amount of K uptake by plant (Bai et al. 2015). Moreover, previous research also showed that straw
returned to the field can partially counterbalance the total K2O
consumption (Jiang et al. 2015; Yin et al. 2018a). Therefore, straw return has a great potential to reduce the use of chemical
potassium fertilizer in China (Yin et al.
2018b). Liming increased 13–25% leaf Ca concentration of flue-cured tobacco after 4 years. The lower K content of leaves in limed
treatments maybe due to the competition between K and Ca in their uptake by
tobacco plants (Karaivazoglou et al.
2007; Duan et al. 2010). We found
that the exchangeable Ca concentration of soil was significantly increased by 29 and 65% in
lime application for 2 and 4 consecutive years. The exchangeable Ca of soil is an important source of calcium in tobacco,
which also increased tobacco leaves Ca (Liu et
al. 2017). In the study, the available potassium content was slightly
decreased by the liming for two consecutive years even though there was no statistically significant
difference. Karaivazoglou et al. (2007) reported that leaf K concentration was significantly
decreased by 10 and 12% under the application of 1.5 and 3.0 t ha-1
Ca(OH)2 in flue-cured tobacco. However, Wei et al. (2011) reported that calcium application improved the
potassium uptake and increased the potassium content in flue-cured tobacco
leaves. Therefore, liming may intensify K deficiency if low or no K fertilizer
is applied. In general, high quality tobacco leaves require K concentration greater than 20 g kg−1. Therefore, to
increase the K concentration
of tobacco leaves, more potassium fertilizer may need to
be applied in this
study area.
In addition, liming significantly decreased leaf Mg
concentration from 2.36 to 2.02 g kg-1 in 2017 and from 2.21 to 1.76
g kg-1 in 2018. The
lower leaf Mg concentration in limed treatments was probably due to the
competition between Ca and Mg in their uptake.
Previous study also showed that increasing Ca application caused a gradual
decline in Mg concentration in cured tobacco leaves (López-Lefebre et al. 2001). Duan et al. (2010) reported that reduced Ca2+/Mg2+ resulted
in the improvement of Mg uptake and increased leaf Mg concentration. The lower
leaf Mg concentration in limed treatments was probably due to the competition between
Ca and Mg in their uptake (Liu et al.
2017), which found that Mg concentration
in leaf was decreased with the increase of soil exchangeable Ca. In
contrast, the dolomite significantly
increased leaf Mg concentration by 18% after 2
years compared with the straw retention. The increase of leaf Mg concentration
could be explained by the dolomite powder containing a lot of Mg (124.3 g kg−1) in this study. Dolomite powder has significantly
effect on increasing the Mg concentration in tobacco leaves, and improved
the smoking quality of cured tobacco leaf.
Moreover, straw return significantly increased the concentration of K but
hardly significantly changed the concentrations of Ca and Mg in cured leaf.
Moreover, the soil exchangeable Ca and Mg content was slightly affected by the
straw retention. Therefore, more attention should be paid to investigate how
long-term straw retention influences soil exchangeable Ca and Mg content and
their concentration in plant tissue. And further research is needed to
illuminate the Ca and Mg release and adsorption on tobacco straw residue.
Tobacco quality is a complex combination of visual,
physical and chemical characteristics of cured leaves (Bilalis et al. 2015; Lin and Zhang 2016). Among
them, traits including nicotine content, reducing sugars
concentration and their ratio substantially affect the quality of tobacco leaf (Bilalis et al. 2015). The present study results
showed that nicotine content was significantly increased by 13% for three years
of straw retention (Table 1). The percentage of nicotine is one of the most
important traits of tobacco (Çakir and Çebi 2010; Yin et al. 2018). It has
been established that nicotine content of flue-cured tobacco leaf should be
0.3–3%, preferably around 2.95%, though nowadays taking into account the
harmful effects of nicotine on the health of smokers, great attention is given
to searching ways to decrease nicotine content to around 1% (Çakir and Çebi
2010; Shi et al. 2018). Reducing sugars concentration is also an indicator of
smoking quality (Shao et al. 2011; Bilalis et al.
2015). Among other factors, cultivar may dramatically affect
the levels of sugars in tobacco leaf (Bilalis et al. 2015; Gao et al. 2019). In this study, dolomite
significantly increased the reducing sugar content of tobacco leaf after two
years continuous cropping (Table 1). However, the straw return had no significant effect on reducing sugar, confirming
the important role of dolomite on the quality parameters of tobacco content of tobacco
leaf.
Conclusion
In a four-year experiment, it was
determined the effects of straw return and liming on soil pH, flue-cured
tobacco yield and quality. Both liming and straw return significantly increased
the trade yield and market value of cured tobacco leaves. Dolomite application
increased K concentration and smoking quality of tobacco leaves. Furthermore,
dolomite increased reducing sugars content and Mg concentration of tobacco
leaves. Therefore, it was suggested that dolomite should be applied with straw
return to enhanced tobacco leaf quality, particularly for Mg concentration
and reducing sugars content in tobacco-rice cropping system in southern China.
Acknowledgements
This
work was jointly supported by Science and Technology Project of Anhui Province
Tobacco Company (20170551022 and
20180551009) and the Discipline Team Project of Anhui Academy of Agricultural
Sciences (2020YL059).
Author Contributions
CQ
Jiang and CL Zu designed the study; CQ Jiang, J Shen and YF Yang performed the
experiments, collected and analyzed data; CQ Jiang and CL Zu wrote the and
revised the manuscript." add after the Acknowledgments
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