Introduction
Tobacco (Nicotiana tobacum
L.) the most important economic crop in southwest regions of China, reached a
cultivated area of 53, 0000 ha in 2019 (Zhang and Ma 2020). To achieve higher
economic benefits and yield, tobacco growers usually apply large amounts of
chemical fertilizer and practice continual tobacco monocropping. This causes
constant loss of soil nutrients and deterioration of soil physical and chemical
properties, leading to soil compaction, soil nutrient imbalance, soil
microflora change, and frequent occurrence of soil-borne diseases (Cheng et
al. 2013; Qin et al. 2015; Ma et al. 2017).
Tobacco stalks after leaf harvest are agricultural waste, with a biomass
of 2250 ~ 3000 kg ha-1. There are about 3 million metric tons of
tobacco stalks in China's tobacco areas (Han and Wang 2016). In traditional management, most of these stalks
are burned and returned to the field as ash because fresh stalks and roots left
in field could cause disease for the next tobacco growing season (Zou et al.
2017). However, this management is resource wasteful and pollutes the
environment. Balancing waste tobacco stalk production and use with continually
decreased soil quality is a challenge and opportunity for sustainable tobacco
production.
Biochar is a term for the solid material formed by pyrolysis or
carbonization of biomass such as plant tissue, agricultural, and forestry
residues, plant straw, etc. (El-Naggar et al. 2019). The typical carbon content of
biochar is 65–90%, and it contains 3–20% of potassium, phosphorus, calcium, magnesium, silicon, manganese, zinc and other oxides and nitrogen
compounds (Emma 2006; Yuan et al. 2016; Li et al. 2017). Biochar
has good water absorption and adsorption capacity because of its large
intermolecular distance (Wang and Sun 2016; Hussain et al. 2017; Farooq et al.
2020a). After application, biochar can loosen the soil increase the number of
aggregates in soil, and increase the soil pH (Lin et al. 2018; Li et
al. 2019; Farooq et al. 2020b).
The nutrient elements in biochar could increase the content of organic matter
in soil and reduce nitrogen leaching (Sarma et al. 2018; Zhang et al.
2018; Wei et al. 2019; Baruah et al. 2020; Liu et al. 2020).
Biochar can reduce or inhibit soil borne diseases, promote carbon and nitrogen
metabolism, and improve crop yield and quality even under less than optimum
conditions (Wang et al. 2015; Farooq et
al. 2020c).
Reports on biochar have mainly focused on reducing heavy metals in soil,
remediation of soil pollution, soil nutrients, and the microbial community.
There are few reports about using tobacco stalk biochar to influence soil
aggregate structure and soil organic carbon
and nitrogen stocks during tobacco growth. Three tobacco growing sites with
different nutrient status were selected to explore the proportion of different particle size aggregates, the
changes of organic carbon and soil nitrogen stocks, and tobacco yield and
quality. Exploring the influence of tobacco stalk biochar on soil nutrients and
plant growth would support sustainable and recyclable agricultural management
in tobacco growing regions.
General situation of test sites
This study was conducted at
three sites: Midu, Eryuan and Jianchuan, Dali City, Yunnan Province, China. The
basic geographical conditions and soil physical and
chemical properties in the three sites are in Tables 1 and 2. Sampling and
measurement in this study occurred from April to
September 2017.
Experiment design
Six different biochar levels were used at each site: 0,
3,000, 4,500, 6,000, 9,000, and 12,000 kg ha-1. Biochar was produced
from tobacco stalks by combustion in an open-top carbonization device under
hypoxic condition at about 450°C for 30 min. The basic physico-chemical
properties of tobacco stalk biochar are in Table 3.
The study sites were
initially established in 2016, and sampling started in 2017. The experiment
followed a randomized complete block design with factorial arrangement and was
replicated three times with plot size of 14 m × 2 m. The biochar was scattered
onto the soil surface by hand and then ploughed to achieve mixing to 40 cm
depth soil. A flue-cured tobacco variety, ‘K326,’ was used as plant material.
The planting density was 16,500 plants ha-1, and plant spacing was
50 cm × 120 cm. A compound fertilizer (N: P2O5: K2O
= 1: 2: 2.5) amounting 75 kg ha-1 was strip-applied, with one third
applied as a base fertilizer before transplanting and the remaining two thirds
applied 30 days after transplanting.
Soil sampling and sample preparation
Soil samples were
collected from April to September. Soil bulk density (BD) was measured with a
cutting ring with a volume of 100 cm3. The particle size
distribution of aggregates in soil, soil organic carbon stocks (SOCs), and
total soil nitrogen stocks (TSNs) were determined by separate random sampling
to obtain 54 soil samples from depths of 0~20 cm and 20~40 cm in each block.
After removing roots and pebbles, the soil was placed in self-sealing plastic
bags, and stored in a refrigerator at 4°C. Within a week, the soil aggregates
were screened by wet sieving method.
Sieving of
wet aggregates
To avoid disruption during rewetting of dried soil
field-moist soil was used to size grades within the aggregate samples (Zou
et al. 2015).
The mean weight diameter (MWD) and the geometric mean diameter (GMD) of
the aggregates, the SOC or TSN stock in each aggregate size fraction and whole
soil were computed using Equation (1), (2), (3), and (4), respectively (Zou
et al. 2015).
%20632-638_files/image002.png){kind=small}
(1)
%20632-638_files/image004.png){kind=small}
(2)
%20632-638_files/image006.png){kind=small}
(3)
%20632-638_files/image008.png){kind=small}
(4)
Agronomic traits were determined according to the
Investigating and Measuring Methods of Agronomical Character of Tobacco in Tobacco
Industry Standard of the People’s Republic of China YC/T142-2010. Fifteen
flue-cured tobacco plants from each plot were evaluated in the rosette stage.
Yield refers to the
total yield of tobacco leaves per unit area. The 5~8th leaves (lower
leaves), 10~13th leaves (middle leaves), and 14~17th
leaves (upper leaves) were collected from the bottom to the top of tobacco
stalk position when the tobacco leaves were mature. After flue-curing, the
tobacco samples were graded and measured according to Chinese Standard GB
2635-1992, and indices, such as proportions (%) of top and middle-grade tobacco
were obtained. The output was calculated according to the purchase price for
that year (2017).
Data analysis
Data were analyzed
with the General Linear Model (GLM) procedure of the S.A.S. 9.3 computer
package (S.A.S. Institute Inc., Cary, NC). This study used by factor design including
study sites and biochar application rates. There were significant treatment
effects if the probability (P) was
< 0.05. Sigma Plot 14.0 (Systat Software Inc., Chicago, IL, USA) was used to
produce all associated output plots.
Results
Effects of
biochar on soil physical properties
Table 1: Basic geographical
conditions of different test sites
|
|
Longitude
and latitude |
Altitude (m) |
Annual
average temperature (℃) |
Annual
rainfall (mm) |
Annual
sunshine hours (h) |
|
Jianchuan |
N
24°47′，E
100°19′ |
1780 |
18.3 |
824.4 |
2750 |
|
Midu |
N 25°23′，E 100°16′ |
1980 |
16.3 |
665.6 |
2740 |
|
Eryuan |
N 28°56′，E 99°13′ |
1590 |
20.0 |
559.4 |
2720 |
Table 2: Physical and
chemical properties of soil foundation
|
Sites |
pH (2.5:1) |
Soil organic matter (g/kg) |
Total nitrogen (g/kg) |
Total phosphorus (g/kg) |
Total potassium (g/kg) |
Hydrolyzable nitrogen (g/kg) |
Available phosphorus (g/kg) |
Available potassium (g/kg) |
|
Midu |
6.5 |
56.2 |
2.8 |
1.1 |
17.6 |
210.8 |
91.3 |
285.5 |
|
Eryuan |
6.7 |
27.4 |
1.3 |
0.9 |
10.4 |
154.3 |
36.7 |
62.4 |
|
Jianchuan |
6.5 |
41.6 |
2.2 |
0.9 |
15.9 |
143.8 |
60.4 |
142.7 |
Table 3: The physical and
chemical characteristics of tobacco stalk biochar in this study
|
Gravimetric Water content (%) |
Carbon content (%) |
Ash content (%) |
Specific surface area (m2·g-1) |
pH |
Total nitrogen (%) |
Mineralizable nitrogen (mg kg-1) |
Available phosphorus (mg kg-1) |
Available potassium (%) |
Chloride content (%) |
|
6.5 |
66.7 |
18.3 |
6.0 |
7.3 |
3.4 |
42.5 |
227 |
1.3 |
0.1 |
Table 4: The effect of
biochar application on soil bulk density (BD), the mean weight diameter (MWD),
and the geometric mean diameter (GMD) in 0-20 cm and 20-40 cm
|
Depth (cm) |
Biochar levels (kg ha-1) |
Bulk density
(BD) (g/cm3) |
MWD (mm) |
GMD (mm) |
||||||
|
Midu |
Eryuan |
Jianchuan |
Midu |
Eryuan |
Jianchuan |
Midu |
Eryuan |
Jianchuan |
||
|
0-20 |
0 |
1.2 b |
1.2 b |
1.3 a |
1.7 i |
1.8 hi |
1.8 g-i |
0.5 j |
0.5 j |
0.5 j |
|
3000 |
1.2 b |
1.2 b |
1.2 b |
1.8 f-i |
2.0 d-h |
2.0 d-g |
0.6 h-j |
0.7 g-i |
0.6 h-j |
|
|
4500 |
1.2 b |
1.3 a |
1.2 b |
1.9 e-h |
2.1 c-e |
2.1 b-e |
0.7 f-h |
0.8 d-g |
0.7 e-h |
|
|
6000 |
1.2 b |
1.2 b |
1.2 b |
2.0 c-f |
2.1 c-e |
2.3 ab |
0.8 c-f |
0.8 c-f |
0.9 b-d |
|
|
9000 |
1.2 b |
1.2 b |
1.2 b |
2.1 c-e |
2.2 a-c |
2.4 a |
0.9 c-e |
0.9 a-c |
1.1 ab |
|
|
12000 |
1.2 b |
1.2 b |
1.2 b |
2.1 b-d |
2.3 a |
2.4 a |
0.9 b-d |
1.1 a |
1.1 a |
|
|
20-40 |
0 |
1.2 b |
1.3 a |
1.2 b |
2.0 h-j |
1.6 k |
1.9 ij |
0.6 gh |
0.4 i |
0.4 hi |
|
3000 |
1.2 b |
1.3 a |
1.2 b |
2.2 ef |
1.8 ij |
2.2 e-g |
0.7 ef |
0.5 g-i |
0.6 gh |
|
|
4500 |
1.2 b |
1.2 b |
1.2 b |
2.4 c-e |
1.9 ij |
2.3 c-f |
0.9 cd |
0.6 gh |
0.7 ef |
|
|
6000 |
1.2 b |
1.2 b |
1.2 b |
2.4 b-d |
2.0 g-i |
2.4 b-d |
1.0 bc |
0.6 fg |
0.8 d-f |
|
|
9000 |
1.2 b |
1.2 b |
1.2 b |
2.5 a-c |
2.2 f-h |
2.6 ab |
1.1 ab |
0.8 de |
0.9 cd |
|
|
12000 |
1.2 b |
1.2 b |
1.2 b |
2.6 ab |
2.3 d-f |
2.7 a |
1.2 a |
0.9 cd |
1.2 a |
|
Means with different lowercase letters, within a column
and rows for each trait, are statistically different from each other at P < 0.05 according to DNMR test
When tobacco stalk biochar application rates
were more than 4500 kg ha-1, there were significant decreases in
soil bulk density (BD) depending on site and depth (Table 4). At 0–20 cm depth,
when biochar application rate reached 4500 kg ha-1, the MWD and GMD in each site were significantly higher than
the control. At 6000 kg ha-1, the MWD became significantly different
between sites (Table 4). At 20–40 cm depth, the effect of biochar on increasing
MWD and GMD was more obvious than at 0–20 cm depth (Table 4).
Biochar to 4,500 or
6,000 kg ha-1 significantly increased the large macroaggregate
proportion (LMP) and small macroaggregate proportion (SMP) in each site
relative to the control and this trend at 20–40 cm depth was more obvious than
that at 0–20 cm depth (Table 5). The SMP of each site increased significantly
at 4,500 kg ha-1 biochar
application with site specific differences at 20–40 cm depth. Biochar
application reduced soil MIP and SCP in each site. At 0–20 cm depth, when the
biochar rate was 4500 kg ha-1,
the soil MIP began to be significantly lower than the control. In the 20–40 cm
depth, there were significant site differences in MIP. The SCP in soil was
significantly reduced relative to the control when the biochar application rate
was 3,000 kg ha-1. At
20–40 cm soil depth, there were significant site differences in SCP.
Biochar could
significantly increase SOCs and TSNs (Table 6). The SOCs in 0–20 cm depth at
Midu increased most obviously (40–50%), followed by Eryuan and Jianchuan. Among
three sites, the SOCs in Jianchuan were significantly less than in Midu and
Eryuan. At 20–40 cm depth, the SOCs in Midu was significantly higher than in
Eryuan and Jianchuan. Unlike SOCs, biochar addition most increased TSNs in
Jianchuan at 0–20 cm depth (41–110%), followed by Midu and Eryuan. The TSNs in
Midu were also significantly higher than in Jianchuan after biochar
application.
Effects of biochar on agronomic traits of tobacco
Table 5: The effect of biochar application on the large
macroaggregate proportion, small macroaggregate proportion, microaggregate
proportion and Silt-clay proportion in 0-20 and 20-40 cm depth
|
Depth (cm) |
Biochar levels (kg ha-1) |
Large macroaggregate proportion (LMP) (%) |
Small macroaggregate proportion (SMP) (%) |
Microaggregates proportion (MIP) (%) |
Silt-clay proportion (SCP) (%) |
||||||||
|
Midu |
Eryuan |
Jianchuan |
Midu |
Eryuan |
Jianchuan |
Midu |
Eryuan |
Jianchuan |
Midu |
Eryuan |
Jianchuan |
||
|
0-20 |
0 |
24.9 i |
26.7 hi |
28.5 f-i |
40.1 d-f |
37.2 fg |
33.0 h |
9.1 b-d |
11.1 a |
10.5 ab |
26.0 ab |
25.1 ab |
28.1 a |
|
3000 |
26.5 hi |
30.0 e-h |
31.2 e-g |
43.0 b-d |
39.6 d-g |
35.8 gh |
8.1 c-f |
9.9 a-c |
9.5 a-d |
22.4 b-d |
20.5 c-e |
23.6 bc |
|
|
4500 |
27.8 g-i |
31.7 e-g |
32.6 c-f |
45.2 ab |
41.6 b-e |
38.4 e-g |
7.9 d-f |
8.8 b-d |
8.5 c-e |
19.2 d-f |
17.9 e-g |
20.4 c-e |
|
|
6000 |
29.3 f-h |
31.9 d-g |
36.0 a-d |
47.4 a |
43.2 b-d |
40.8 c-f |
6.9 e-g |
8.2 c-f |
6.9 e-g |
16.4 f-h |
16.7 e-h |
16.3 f-h |
|
|
9000 |
30.2 e-h |
33.7 b-e |
37.5 ab |
48.0 a |
44.9 a-c |
41.9 b-e |
5.7 g |
6.8 e-g |
6.5 fg |
16.1 f-h |
14.7 gh |
14.1 gh |
|
|
12000 |
31.0 e-g |
36.2 a-c |
38.0 a |
48.5 a |
45.3 ab |
42.5 b-d |
5.4 g |
5.9 g |
6.5 fg |
15.1 gh |
12.6 h |
13.0 h |
|
|
20-40 |
0 |
31.8 gh |
25.1 i |
33.4 fg |
31.8 e-g |
27.2 hi |
20.7 j |
10.0 cd |
16.8 a |
14.4 b |
26.5 bc |
31.0 a |
31.5 a |
|
3000 |
36.5 ef |
27.9 hi |
37.5 d-f |
32.9 d-f |
31.9 e-g |
23.3 ij |
8.4 d-f |
13.7 b |
10.9 c |
22.2 d-f |
26.6 bc |
28.3 ab |
|
|
4500 |
38.9 c-e |
29.1 hi |
40.0 b-e |
35.0 b-e |
34.8 c-e |
28.2 gh |
7.9 e-g |
11.0 c |
7.6 fg |
18.2 gh |
25.1 b-d |
24.0 cd |
|
|
6000 |
40.2 b-e |
30.9 gh |
41.9 bc |
37.3 a-c |
36.5 a-d |
28.5 gh |
6.3 g-i |
9.8 c-e |
6.5 gh |
16.2 g-i |
22.8 c-e |
23.5 c-e |
|
|
9000 |
41.4 b-d |
33.9 fg |
44.0 ab |
39.1 ab |
39.6 a |
29.8 f-h |
5.1 hi |
7.9 e-g |
6.5 g-i |
14.3 h-j |
18.5 fg |
19.8 e-g |
|
|
12000 |
43.0 a-c |
36.4 ef |
46.3 a |
40.2 a |
40.5 a |
33.9 c-e |
4.6 i |
6.3 g-i |
6.3 f-h |
12.2 j |
16.9 g-i |
13.2 ij |
|
Means with different
lowercase letters, within a column and rows for each trait, are statistically
different from each other at P < 0.05
according to DNMR test
Table 6: Effects of biochar application rates on soil organic
carbon stock (SOC) and total soil nitrogen stock (STNs) in 0-20 and 20-40cm
depth
|
Depth (cm) |
Biochar levels (kg ha-1) |
SOCs (g C/m2) |
TSNs (g N/m2) |
||||
|
Midu |
Eryuan |
Jianchuan |
Midu |
Eryuan |
Jianchuan |
||
|
0-20 |
0 |
3628.9 i |
4194.4 h |
3803.7 i |
324.8 g |
382.2 e |
212.3 i |
|
3000 |
5070.1 d-f |
4963.1 d-f |
4250.6 h |
451.0 cd |
411.0 d |
300.4 h |
|
|
4500 |
5091.4 c-e |
5078.6 de |
4349.6 h |
478.8 b |
422.6 d |
340.9 f |
|
|
6000 |
5266.1 b-d |
5283.6 b-d |
4399.1 gh |
510.9 b |
479.2 b |
378.1 ef |
|
|
9000 |
5290.3 b-d |
5540.8 ab |
4769.0 ef |
551.7 b |
529.3 b |
433.8 cd |
|
|
12000 |
5440.7 a-c |
5715.6 a |
4712.5 fg |
532.8 b |
572.8 a |
457.7 c |
|
|
20-40 |
0 |
3466.7 f-h |
2892.3 i |
2891.5 i |
304.3 de |
212.0 f |
101.6 h |
|
3000 |
4249.4 cd |
3316.1 h |
3317.1 h |
400.8 c |
257.6 e |
145.7 h |
|
|
4500 |
4461.2 bc |
3388.5 h |
3425.1 gh |
457.6 bc |
269.0 e |
191.8 g |
|
|
6000 |
4522.6 a-c |
3411.2 h |
3207.1 hi |
441.2 bc |
269.5 e |
160.9 gh |
|
|
9000 |
4793.9 ab |
3770.5 e-g |
3517.4 f-h |
480.4 ab |
341.2 d |
261.4 e |
|
|
12000 |
4836.0 a |
3816.7 ef |
3940.1 de |
482.0 a |
349.9 d |
333.8 d |
|
Means with different
lowercase letters, within a column and rows for each trait, are statistically
different from each other at P < 0.05
according to DNMR test
Table 7: Effects of different biochar application rates on plant
height, stem circumference, maximum leaf length, and maximum leaf width at
rosette stage of flue-cured tobacco grown at different sites
|
Biochar levels (kg ha-1) |
Plant height (cm) |
Stalk girth (cm) |
Maximum leaf length
(cm) |
Maximum leaf width (cm) |
||||||||
|
Midu |
Eryuan |
Jianchuan |
Midu |
Eryuan |
Jianchuan |
Midu |
Eryuan |
Jianchuan |
Midu |
Eryuan |
Jianchuan |
|
|
0 |
7.0 e |
7.0 e |
7.1 e |
4.3 d |
4.1 e |
3.1 g |
26.0 g |
30.8 b |
21.5 k |
12.4 h |
14.5 ef |
10.7 j |
|
3000 |
7.0 e |
7.5 d |
7.0 e |
4.3 c |
4.3 d |
3.0 h |
26.2 g |
31.7 a |
21.9 jk |
12.8 g |
16.3 b |
10.1 k |
|
4500 |
7.0 e |
7.5 d |
7.0 e |
2.7 i |
4.4 bc |
3.0 h |
26.0 g |
30.7 b |
23.9 h |
11.3 i |
15.2 d |
12.1 h |
|
6000 |
10.0 b |
11.5 a |
10.0 b |
4.8 a |
3.2 g |
3.0 h |
30.0 c |
28.0 ef |
22.2 ij |
15.9 c |
17.0 a |
11.5 i |
|
9000 |
5.5 g |
6.5 f |
5.6 g |
4.0 e |
4.4 c |
2.7 i |
29.0 d |
27.5 f |
20.9 l |
14.6 e |
14.2 f |
11.2 i |
|
12000 |
8.5 c |
8.5 c |
8.5 c |
3.8 f |
4.5 b |
3.2 g |
28.1 e |
30.8 b |
22.6 i |
14.7 e |
15.5 d |
11.3 i |
Means with different
lowercase letters, within a column and rows for each trait, are statistically
different from each other at P < 0.05
according to DNMR test
Compared
with the control, when the biochar application rate was 6,000 and 12,000 kg ha-1,
plant height of flue-cured tobacco significantly increased. When the biochar
rate was 9,000 kg ha-1, plant height was significantly lower than
the control (Table 7). After applying biochar, plant height of flue-cured
tobacco in Eryuan was significantly higher than in Midu and Jianchuan. The
difference of stem girth among the three sites was significant, with the order
of Midu > Eryuan > Jianchuan. The stem girth (SG) decreased significantly
compared to the control in each site when the biochar rate was 4,500 (Midu),
6,000 (Eruyuan), and 9, 000 (Jianchuan) kg ha-1 respectively. The
maximum leaf length and maximum leaf width of flue-cured tobacco in Midu
decreased significantly at the 4,500 kg ha-1 biochar rate, while in
the Eryuan and Jianchuan sites they began to decrease at rates of 9,000 kg ha-1.
The maximum leaf length and maximum leaf width of the three sites were also
significant in the order of Eryuan > Midu > Jianchuan.
Effects of biochar on flue-cured tobacco yield
When the biochar rate was 6,000 and 12,000 kg ha-1,
the yield of flue-cured tobacco in Midu significantly increased, by 280–300 kg
ha-1 compared to the control (Table 8). Under the same biochar
application rate, the yield in Jianchuan was significantly less than in Midu
and Eryuan. Similar to the yield, there was a maximum value of the proportion
of superior leaves at 6,000 and 3,000 kg ha-1 biochar application
rates in Midu and Eryuan, respectively. In Jianchuan, the maximum value of the
superior leaves appeared when the biochar application rate was 4,500 kg ha-1.
Except for the application rate of 6,000 and 9,000 kg ha-1, the proportion
of superior leaves in each site was significant with the order: Midu > Eryuan
> Jianchuan. The trend in the average price was the same as that of the
proportions of superior leaves.
Table 8: Effects of different biochar rates yield, proportion of
superior leaves and average leaves price of tobacco grown at different
locations
|
Biochar levels (kg ha-1) |
Yield (kg ha-1) |
Proportions of superior leaves (%) |
Average price (dollar kg-1) |
||||||
|
Midu |
Eryuan |
Jianchuan |
Midu |
Eryuan |
Jianchuan |
Midu |
Eryuan |
Jianchuan |
|
|
0 |
2892 b-d |
2853 c-e |
2533 gh |
58.6 d |
53.7 g |
49.8 k |
4.3 d |
3.7 i |
3.6 j |
|
3000 |
2890 b-d |
2923 bc |
2781 de |
59.0 cd |
58.8 d |
49.3 k |
4.5 b |
4.3 d |
4.0 g |
|
4500 |
2988 b |
2859 b-e |
2745 ef |
60.0 bc |
55.1 f |
52.1 h |
4.5 bc |
4.0 g |
3.9 h |
|
6000 |
3174 a |
2910 b-d |
2533 gh |
61.8 a |
58.5d |
50.0 jk |
4.5 c |
4.3 e |
3.6 j |
|
9000 |
2750 ef |
2922 bc |
2488 h |
57.2 e |
56.4 e |
51.2 hi |
4.2 f |
4.2 e |
3.5 k |
|
12000 |
3193 a |
2780 de |
2635 fg |
61.0 ab |
54.7 fg |
50.9 ij |
4.6 a |
3.9 h |
3.7 i |
Means with different
lowercase letters, within a column and rows for each trait, are statistically
different from each other at P < 0.05
according to DNMR test
Table 8: Effects of different biochar rates yield, proportion of
superior leaves and average leaves price of tobacco grown at different
locations
|
Biochar levels (kg ha-1) |
Yield (kg ha-1) |
Proportions of superior leaves (%) |
Average price (dollar kg-1) |
||||||
|
Midu |
Eryuan |
Jianchuan |
Midu |
Eryuan |
Jianchuan |
Midu |
Eryuan |
Jianchuan |
|
|
0 |
2892 b-d |
2853 c-e |
2533 gh |
58.6 d |
53.7 g |
49.8 k |
4.3 d |
3.7 i |
3.6 j |
|
3000 |
2890 b-d |
2923 bc |
2781 de |
59.0 cd |
58.8 d |
49.3 k |
4.5 b |
4.3 d |
4.0 g |
|
4500 |
2988 b |
2859 b-e |
2745 ef |
60.0 bc |
55.1 f |
52.1 h |
4.5 bc |
4.0 g |
3.9 h |
|
6000 |
3174 a |
2910 b-d |
2533 gh |
61.8 a |
58.5d |
50.0 jk |
4.5 c |
4.3 e |
3.6 j |
|
9000 |
2750 ef |
2922 bc |
2488 h |
57.2 e |
56.4 e |
51.2 hi |
4.2 f |
4.2 e |
3.5 k |
|
12000 |
3193 a |
2780 de |
2635 fg |
61.0 ab |
54.7 fg |
50.9 ij |
4.6 a |
3.9 h |
3.7 i |
Means with different
lowercase letters, within a column and rows for each trait, are statistically
different from each other at P < 0.05
according to DNMR test
Discussion
%20632-638_files/image010.png)
Fig. 1: The average monthly temperature and monthly accumulated
precipitation at Midu, Eryuan and Jianchuan
Soil structure plays an important role in plant growth
and soil water movement, but also has a vital role in improving soil physical
and chemical properties, and biological processes (Wei et al. 2006; An et al. 2008). In this experiment, biochar application decreased the soil bulk
density (Table 4), was due to the porous structure of biochar, which
effectively increase soil porosity and improve soil aeration. This result is
similar to the results of Meng et al. (2020). The mean weight
diameter and geometric mean diameter of soil aggregates increased with the
biochar application rate in each site, indicating that biochar application
could improve soil aggregate stability; these results are consistent with Zhu et
al. (2018). The MWD and GMD at Eryuan were significantly lower than at Midu and
Jianchuan for the 20–40 cm depth (Table 4). We believe the main reason for this
difference among the three sites was the variation of soil nutrients (Shinjo et
al. 2000). Compared with Midu and Jianchuan, the soil organic matter and
total nitrogen content in Eryuan were significantly less than in the other two
sites. This limited the availability of nutrients to microorganisms in soil,
and because the secretion of microbial products and the production of hyphae
are the core of soil aggregation, this limited the increase of aggregate mean
weight diameter and geometric mean diameter (Wang et al. 2020).
Many studies show
that the quantity and distribution of water stable aggregates determine the
stability of soil structure and its resistance to erosion, especially the
number of aggregates with particle size > 0.25 mm, which is one of the
important indexes to determine the quality of soil (Li et al. 2014;
Amundson et al. 2015). Applying biochar significantly increased the
proportion of large and small aggregates and decreased the proportion of
microaggregates and silty clay -sized aggregates. This result was similar with
previous studies (Chen et al. 2008). The main reason for the change in aggregate proportion was that the
biochar having a nutrient holding capacity effect, offering sufficient nutrient
for the growth and reproduction of microorganisms. The hyphae of fungi and
actinomycetes can mechanically entangle particles in the soil to form
aggregates, thus increasing the proportion of large and small aggregates.
However, the proportion of large aggregates in Jianchuan was significantly
higher than the other two sites (Table 5). This may be related to the
difference of precipitation and temperature in three
sites (Fig. 1). Previous studies showed that soil aggregate stability
was negatively correlated with temperature and soil moisture. High temperature
and high humidity will reduce soil aggregate stability (Ye et al. 2013;
Xu et al. 2019). In this study, the temperature and precipitation in
Jianchuan during soil sampling period (Apr. to Sep.) were
lower than in Midu and Eryuan (Fig. 1), which was conducive
to maintaining the activity of soil microorganisms and the stability of soil
structure. It was beneficial to the formation of large aggregates.
Many studies have shown
that biochar can significantly enlarge the SOCs and TSNs in topsoil (Shinjo et
al. 2000; Mao et al. 2008). As an exogenous organic matter, biochar
can directly increase the soil organic matter content and maintain the relative
stability of soil organic carbon stocks (Wang and Sun 2016). The present study
showed that biochar application could significantly enlarge soil SOCs (Midu)
and TSNs (Jianchuan). It is consistent with the results of previous studies
(Wang and Sun 2016). Ji et al. (2018) hold the opinion that adding high
C/N ratio biochar into low organic matter soil or adding low activity biochar
in high organic matter soil could inhibit the mineralization of soil organic
matter. In this study, the soil organic matter content in Midu was highest.
Adding biochar could inhibit organic matter mineralization in soil, thus
contributing to the stability of SOCs. However, the
content of soil organic matter, animal, plant, and microbial residues in 20–40
cm depth are less than topsoil, which makes its storage capacity smaller.
Plants growth
depends on good soil environment. The plant height increased significantly when
the biochar rate was 6000 kg ha-1. This result is consistent with
previous studies (Chen and Du 2015; Minhas et
al. 2020). However, when the biochar rate was 9000 kg ha-1, the plant height decreased significantly
compared with no biochar application. That is because biochar has a threshold
effect (Zhang et al. 2015). When the biochar application rate was low,
it provided tobacco with nutrients for the growth; when the rate was high, the
soil structure was destroyed, and the crop growth affected negatively (Wei
et al. 2019). Excessive carbon accumulated in the soil will affect the
absorption of water and nutrients by plant roots, resulting in the decrease of
yield and its components (Liang et al. 2006;
Qiu et al. 2020). The stalk girth at a certain biochar concentration
decreased compared with the control (Table 7), which may be related to nitrogen
leaching caused by biochar. With benefits from the improvement of soil physical
and chemical properties, the yield of tobacco leaves and the proportion of
upper leaves also increased, which contributed to the increase of average
price.
Previous research
showed that after applying biochar, the availability of soil nutrients and the
efficiency of plant nutrient absorption were improved (Jeffery et al. 2011). In this study, the effects of biochar on yield and quality of
flue-cured tobacco in different locations were in the order of Midu > Eryuan
> Jianchuan. This is mainly because at the rosette stage (late May to early
June), the Midu site had the highest SOM, total nitrogen content and total soil
nitrogen stock among three sites, which provided sufficient nutrition for the
tobacco roots growth. Moreover, the precipitation in Midu area is less than
that in Eryuan site, which reduces the nitrogen leaching in topsoil (Table 6).
Conclusion
Tobacco stalk
biochar improved soil physical structure. Biochar decreased soil bulk density,
increased the proportion and diameter of large and small soil aggregates, and
increased soil organic carbon and nitrogen stocks. Biochar addition also
improved the yield and quality of tobacco leaves. However, if the biochar
application rate exceeded 9,000 kg ha-1, it deteriorated conditions
conducive to plant growth. The optimum biochar application rates for better
plant height, stem diameter, maximum leaf length and leaf width, yield, and
average price differed by site. These rates were: 6,000 kg ha-1 (Midu),
3,000 kg ha-1(Eryuan) and 4,500 kg ha-1 (Jianchuan),
respectively.
Acknowledgements
The authors are thankful to Mark S. Coyne for his
valuable assistance and advice in the preparation of this paper. This work was
financially supported in part by the Yunnan Fundamental Research Project (grant
NO. 2017FB074, 202001AT070013) and the National Natural Science Foundation of
China Grant (41601330), and the Yunnan Provincial Tobacco Monopoly Bureau
Grants (2017YN10, 2017YN09, 2017YN07, 2018530000241017, 2020530000241025 and
2019530000241019). Authors thank to Yunnan Technology Innovation Program
(2019HB068) and Yunnan Ten Thousand People Program (YNWR-QNBJ-2018-400) for
supporting Congming Zou.
Author Contributions
Y Li and CM Zou designed the study and collected the data; X
He and MY Hu conceived the idea; JE Su, TY Xu and R Liu carried out the field
experiment; TX Liu and KY Gu analyzed the data; all authors contributed to the
writing and revisions.
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