Introduction
Songliao Plain is an
important grain production region and export base in China. It is known as one
of the three golden corn belts in the world along with those in the United
States and Ukraine at the same latitude (Zhang et al. 2011). Over the past several decades, the maize (Zea mays L.) planting pattern in this area has improved yearly, and
the yield has greatly increased (Li et al. 2016). Increased
planting density plays a key role in improving maize yield (Yang et al. 2013). However, in
recent years, production density has reached the upper limit under the
traditional sole-cropping mode and is often accompanied by the occurrence of
field lodging. Therefore, lodging has become the primary factor limiting the
increase of planting density and maize yield in Songliao Plain. Many studies
have shown that a reasonable increase in density is still an important way to
improve maize yield. Historically, records of high maize yield competitions at
nationally and abroad were set under the conditions of high density (79500109500 plants ha-1) (Tollenaar and Lee
2002; Li et al. 2016). However, with increased density, the internal structure
of the population changes, the development space of a sole plant becomes
limited, and the probability of lodging increases. Thus, solving the lodging
problem under high-density conditions is a difficult problem in the production of maize. Therefore, many studies have
been carried out to determine the causes of maize lodging, regulation measures,
selection of lodging resistance indexes, and improvement of maize varieties (Peng et al. 2010).
Lodging
is considered the main limiting factor for high yield, stable yield, and high
quality of maize and the main quantitative traits controlling maize yield (Bai et
al. 2010). It is estimated
that yield loss due to the lodging of maize can be around 525% or even higher (Tollenaar and Lee 2002). Lodging can be divided into stem lodging and root lodging
based on the organ parts where it occurs. Of these, the harm caused by stem
folding is more severe (Wilkinson
and Davies 2002). Lodging is
closely related to crop varieties, climate, soil conditions, and cultivation
measures (Novacek et al. 2013). First, plant morphological characteristics have a
significant effect on the lodging resistance performance. Under adverse
conditions, such as low light, plant height increases, while internode
elongation, and stem diameter and
dry matter accumulation decreases, which increase the lodging risk (Wang et
al. 2019). Lodging is
negatively correlated with aboveground parts such as ear height and center of
gravity height and underground traits, such as root weight, root length, and
root number (Liu
et al. 2012). Among them, stem strength contributes the most to
lodging followed by root weight (Han 1990). The coordinated growth of stems and roots within the
plant population is the primary way to alleviate lodging (Takayuki and Ken 2004). Secondly, the
chemical composition and related enzyme activity of the stems are also closely
related to lodging (Zhou et al. 2007). Studies have shown that the increase of lignin,
cellulose and auxin content in maize stalks and the expression of related
enzyme genes can enhance the anti-inversion ability of maize stalks (Ma et al. 2019). A study on the mechanical properties and anatomical structure of maize
stems revealed that the crushing strength, puncture strength and bending
strength of the stem are negatively correlated with the lodging rate (Jampatong et al. 2000; Robertson et al. 2014). Moreover, the
anatomical structure of stems, such as the epidermal mechanical cells,
mechanical tissues, and vascular bundles, directly affected the mechanical
properties of the stems (Xue et
al. 2016). Additionally,
quantitative trait loci analysis revealed that the key genes affecting lodging
are located on chromosome 3 (Teng et al. 2013; Li et al. 2014).
Currently,
the methods to improve maize lodging resistance mainly include the selection of
lodging-resistant varieties, reasonable planting densities, scientific fertilization,
strengthening the prevention and control of disease grass, and spraying plant
growth regulators (Liu et al. 2012). Although these methods effectively reduce the lodging
rate, lodging still cannot be effectively resolved under high-density
cultivation conditions. In this study, it was tested that whether strip
intercropping pattern of maize and soybean (Glycine max L.) can influence lodging resistance of maize, even if the
maize is grown at high densities under this cropping pattern. Current studies
on this cropping model focus on the efficient utilization of photothermal
responses and water resources; the prevention and control of diseases, insect
pests, and weeds; and the regulation of nutrient elements in the root system. The effect of strip intercropping on the lodging resistance
ability of maize has not been investigated. Therefore, this two-year field
study was designed to evaluate the effects of maize-soybean strip intercropping
on lodging resistance, productivity and LER of maize crop. This study may provide
a theoretical basis and technical support for achieving high-density lodging
resistance during maize production in Songliao Plain.
Materials and Methods
Experimental site description
The experiment was conducted in 2016 and 2017 at the
agricultural college experiment base of Jilin Agricultural University. The soil
was a typical black with an excellent fertility level, rich in organic matter
content of 26.9 g kg-1, alkali-hydrolyzed nitrogen of 120 mg kg-1,
available phosphorus of 16.5 mg kg-1, available potassium of 122 mg
kg-1, total nitrogen of 1.65 g kg-1,
total phosphorus of 0.85 g kg-1, and pH of 6.8. The maize variety
xianyu 335 provided by Denghai pioneer company and soybean variety jinong
40 provided by Department of Agriculture, Jilin Agricultural University was
used as testing material.
Experimental
details
Maize
and soybean were sown in strips intercropping as: M2S2 (maize-soybean intercropping with 2 row strips of each), M4S2 (maize-soybean intercropping with 4
row strips of maize and 2 row strips of soybean), M4S4
(maize-soybean intercropping with 4 row strips of maize and soybean) and M6S6 (maize-soybean intercropping with 6 row
strips of maize and soybean) taking sole maize (M) and sole soybean (S) as control (Table 1).
The
experiment was laid out following randomized complete block design with 3
replicates of each treatment and net plot size of 65 m2 (M and S),
52 m2 (M2S2),
78 m2 (M4S2),
104 m2 (M4S4)
and 156 m2 (M6S6).
Crop husbandry
Maize and soybean crops were sown
on April 28 and 29 during 2016 and 2017, respectively on well prepared seedbed.
April 29. After the emergence of seedlings, the seedlings were fixed according
to the plant to plant distance of maize (19.23 cm) and soybean (7.6 cm) under
sole cropping and strip intercropping condition. Row
spacing of maize and soybean all were 65 cm and row spacing of adjacent maize
and soybean was 65 cm in strip intercropping. The quantity of fertilizer
applied to maize strip was 90 kg nitrogen (N) ha-1, 120 kg
phosphorus (P2O5) ha-1 and 160 kg potassium (K2O)
ha-1 before sowing. Additional N fertilizer was applied with a
quantity of 140 kg N ha-1 for each treatment on 16 June 2016 and 22
July 2017.
The
quantity of fertilizer applied to soybean strip was 60 kg P2O5 ha-1
and 25 kg K2O ha-1 before
sowing. The
plants were not irrigated during the whole experimental period, because there
was enough rainfall during the growing season. After maize and soybean were
sown and before emergence, the plots were sprayed with a pre-emergence
herbicide common to maize and soybean for closed soil weeding. The harvest dates were September 28, 2016 and September
30, 2017.
Determination of items and methods
Determination of plant morphological index: The
morphological indexes of plants were investigated at the filling period and five successive plants were
chosen to measure plant
height, ear height, stem diameter (measured at the first internode near the
surface), internode length and diameter of 110 internodes above ground were
measured by tape and Vernier caliper. The height of the center of gravity is
the distance from the base of the stem to the equilibrium fulcrum of the stalk
(ear, leaf and sheath). The units are in centimeters. Internode fresh weight
(110 internodes) is weighed using a scale. Internode length/diameter, fresh
weight to length of internode (FWLI) was calculated. The calculation formula is
as follows:
FWLI (g/cm) = IFW / IL
Here IFW is internode fresh weight and IL is internode length.
Root bleeding quantity and root index investigation
During the filling period, five
successive plants were chosen, the main stem was cut off from the basic
stem node, and a wound bag filled with absorbent cotton was put on, and
collected and weighed for 12 h from 18:00 to 6:00 a.m. the next day. Meanwhile,
the number and diameter of aerial roots in soil were investigated. After that, the underground roots were dug out according to
the soil volume of 30 cm in length, 30 cm in width and 40 cm in depth. Then,
the root related indexes were investigated by washing clean, including the root
fresh weight, root diameter, number of root layers, number of nodal roots, and
the fresh weight of aerial roots into the soil.
Stalk crushing strength
During the fulling period, five
successive plants were chosen, YYD-1 digital dynamometer produced by
Aili instrument co., LTD was used to measure the crushing strength of stalk.
The measurement method is to place the two ends of each node at the base of
110 internodes in the groove of a fixed width support frame, and then slowly
press down until the stem is crushed. At this time, the value read is the
crushing strength of the node. The formula is as follows:
LRI = CS / HCG
Here LRI is lodging resistance index,
CS is crushing strength and HCG is height of center of gravity.
IUBRS = ICS / IL
Here IUBRS is internode unit
breaking-resistant strength, ICS is internode crushing strength and IL is
internode length.
Lodging rate
In the tasseling stage and the mature stage, the
percentage of lodging rate of each treatment was investigated. The number of
maize plants with stem lodging and root lodging and number of maize plants in
the whole plot were recorded. The calculation formula is as follows:
LR = NLP / NWP
Here LR is lodging rate, NLP is number
of lodging plants and NWP is number of whole plants.
Crop
yield and Land equivalent ratio
At mature stage, maize and soybean
soles were harvested in the middle 2 rows of their plots. The yield of
different strip intercropping treatments were calculated in the maize strip by
harvesting all the maize in the maize sowing strip and in the soybean strip by
harvesting all soybean in the soybean sowing strip. After which, the compound
yield of strip intercropping was calculated according to the proportion of
maize and soybean area by different treatments and the yield in each strip.
Land equivalent ratio (LER) is used to calculate the land use advantage
provided by intercropping (Mao et al. 2012), as follows:
LER = Yim / Ymm+ Yis / Yms (5)
Here Yim and Yis are yields of intercropped
maize and soybean, and Ymm and Yms are yields in soled maize and soybean, respectively. They
express for each crop species the area of land that would be needed in sole
cropping to achieve the same yield as one-unit area of intercrop. When the LER
is greater than 1, there is a land use advantage of intercropping.
Statistical
analysis
All statistical analyses of the data
were done with the (Microsoft Excel 2007 and S.P.S.S. 13.0) after verifying the homogeneity of error variances
following one-way ANOVA. Multiple comparisons among the treatments were
analyzed with least-significant difference (LSD) test at the 0.05 level of
probability.
Results
Yield and land equivalent ratio (LER) comparison
The yield of maize strip under strip intercropping was
significantly higher than sole maize (Table 2). In two years, the maize yield
in the maize strip intercropping was in order of M2S2 >
M4S4 >
M4S2 >
M6S6 >
M; however, compared with sole maize the yield
increased by 69.2, 64.8, 54.5 and 47.4%, respectively. By comparing the
compound yield of crops under intercropping and sole cropping, the compound
yield of M4S2 was
higher than that of maize sole cropping. The composite
yield of crops under different treatments from high to low was M4S2 > M > M4S4 > M6S6 > M2S2, sole maize between other treatments reached a
significant level. The LER of strip intercropping treatments were more than
1.000, the LER value of M4S4
treatment was the highest, the two-year average was 1.23. The LER of different
strip intercropping treatment was in order: M4S4> M4S2> M6S6> M2S2
(Table 2).
Table 1: Experiment treatment
|
Treatment |
Maize seeding strip |
Soybean seeding strip |
Maize and soybean composite area (m2) |
||||||
|
Strip width (m) |
Rows in strip |
Plant to plant distance (cm) |
Strip area (m2) |
Strip width (m) |
Rows in strip |
Plant to plant distance (cm) |
Strip area (m2) |
||
|
M |
6.5 |
10 |
19.23 |
65 |
-- |
-- |
-- |
-- |
65 |
|
S |
-- |
-- |
-- |
-- |
6.5 |
10 |
7.6 |
65 |
65 |
|
M2S2 |
1.3 |
2 |
19.23 |
13 |
1.3 |
2 |
7.6 |
13 |
26 |
|
M4S2 |
2.6 |
4 |
19.23 |
26 |
1.3 |
2 |
7.6 |
13 |
39 |
|
M4S4 |
2.6 |
4 |
19.23 |
26 |
2.6 |
4 |
7.6 |
26 |
52 |
|
M6S6 |
3.9 |
6 |
19.23 |
39 |
3.9 |
6 |
7.6 |
39 |
78 |
Row
spacing of maize and soybean all were 0.65 m, and row spacing of adjacent maize
and soybean was 0.65 m in strip intercropping
M= Maize sole cropping; M2S2= Maize-soybean 2:2 intercropping; M4S2= Maize-soybean 4:2 intercropping; M4S4= Maize-soybean 4:4 intercropping; M6S6= Maize-soybean 6:6 intercropping
Table 2: Comparison of yield and
land equivalent ratio (LER) between strip intercropping and sole
cropping of maize and soybean
|
Year |
Treatment |
Yield of maize seeding strip (kg ha-1) |
Yield of soybean seeding strip (kg ha-1) |
Maize and soybean composite yield (kg ha-1) |
LER |
||
|
Maize |
Soybean |
Composite yield |
|||||
|
2016 |
S |
-- |
2948.5a |
-- |
2948.5a |
2948.5e |
1.000c |
|
M |
11578.5e |
-- |
11578.5ab |
-- |
11578.5b |
1.000c |
|
|
M2S2 |
19208.3a |
1684.6d |
9604.1c |
842.3c |
10446.4c |
1.115b |
|
|
M4S2 |
17485.2c |
1572.2d |
11656.8a |
524.1d |
12180.9a |
1.184ab |
|
|
M4S4 |
18746.3b |
2393.4c |
9373.2c |
1196.7b |
10569.9c |
1.215a |
|
|
M6S6 |
16827.6d |
2685.1b |
8413.8d |
1342.6b |
9756.3d |
1.182ab |
|
|
2017 |
S |
-- |
2764.6a |
-- |
2764.6a |
2764.6e |
1.000c |
|
M |
10680.9e |
-- |
10680.9b |
-- |
10680.9b |
1.000c |
|
|
M2S2 |
18432.8a |
1482.9d |
9216.4c |
741.5d |
9957.8c |
1.131b |
|
|
M4S2 |
16883.7c |
1343.6d |
11255.8a |
447.9e |
11703.7a |
1.216a |
|
|
M4S4 |
17919.0a |
2198.6c |
8959.5c |
1099.3c |
10058.8c |
1.236a |
|
|
M6S6 |
15970.8d |
2469.7b |
7985.4d |
1234.9b |
9220.2d |
1.194ab |
|
Means with same letters differ non-significantly
at P ≤ 0.05
M= Maize sole cropping; M2S2= Maize-soybean 2:2 intercropping; M4S2= Maize-soybean 4:2 intercropping; M4S4= Maize-soybean 4:4 intercropping; M6S6= Maize-soybean 6:6 intercropping
Effects
of strip intercropping on plant characteristics and lodging
After strip intercropping, the plant height, ear height,
and center of gravity height of the aboveground parts and lodging rate were
significantly lower (ranging from large to small were M > M6S6
> M4S2 > M4S4 > M2S2),
while the lodging resistance index, the stem diameter and stalk crushing
strength were significantly higher than those of sole cropping (Table 3). The
maximum resistance index of strip intercropping was 3.02, while that of sole
cropping was only 1.58. From the tasseling to maturity stage, the average
lodging rate of the sole cropping increased rapidly from 6.0 to 34.5%, while
that of the strip intercropping increased from 0.2 to 1.5 (Table 3). Strip
intercropping significantly improved the lodging resistance ability of maize
through these stages. All the indexes under strip intercropping were
significantly higher than sole cropping. The
comparison of four intercropping treatments showed that all the indexes of M2S2, M4S2, and M6S6
treatments reached to a significant level.
Changes
in maize stalk internode length under
strip intercropping
The internode length of
each internode from 2 to 10 was smaller in intercropping than in sole cropping
and showed the following pattern: M2S2 < M4S4
< M4S2 < M6S6 < M (Fig.
1A). The average length of each internode from 2 to 10 of the
four intercropping treatments respectively decreased by 28.63, 14.76, 12.42,
17.77 and 14.75% as compared to the corresponding internodes in sole cropping.
The plant height, ear height, and center of gravity height of maize were
significantly lower in the intercropping than in the sole cropping, mainly
owing to the shortening of each internode length after intercropping.
The
maximum internode length was usually located at the 4th node.
The LSD (P＜0.05) of the low nodes (4th: 2.1393) was generally
greater than that of the high node (10th: 0.80). This indicates that
the effect of strip intercropping was greater on the length of the
lower nodes than on the higher nodes.
Changes to the internode diameter of the stalk under strip
intercropping
Table 3: Maize plant characteristics
and lodging rate under different strip intercropping treatments with soybean
|
Year |
Treatment |
Plant height(cm) |
Ear height (cm) |
Centre of gravity
height (cm) |
Stem diameter (cm) |
SCS(N) |
Lodging resistance
index |
Lodging rate (%) |
|
|
Tasseling stage |
Maturity stage |
||||||||
|
2016 |
M |
332.53a |
160.23a |
127.07a |
2.21e |
200.61e |
1.58e |
5.67a |
32.67a |
|
M2S2 |
307.57c |
121.20d |
112.44d |
2.76a |
339.66a |
3.02a |
0.00b |
0.00c |
|
|
M4S2 |
321.30b |
135.60c |
120.60b |
2.60c |
279.19c |
2.31c |
0.00b |
1.33c |
|
|
M4S4 |
312.20c |
122.87d |
116.93bc |
2.69b |
304.29b |
2.60b |
0.00b |
0.67c |
|
|
M6S6 |
325.25b |
151.10b |
122.83b |
2.34d |
240.43d |
1.96d |
0.67b |
3.00b |
|
|
|
LSD(P ≤ 0.05) |
2.85 |
2.14 |
1.69 |
0.05 |
41.82 |
0.18 |
0.07 |
1.42 |
|
2017 |
M |
328.50a |
151.40a |
125.10a |
2.00d |
165.48e |
1.32e |
6.33a |
36.33a |
|
M2S2 |
300.83d |
118.67e |
107.83e |
2.44a |
321.40a |
2.98a |
0.00b |
0.33d |
|
|
M4S2 |
313.87bc |
131.60c |
114.20c |
2.19c |
244.42c |
2.14c |
0.00b |
1.67c |
|
|
M4S4 |
309.57cd |
123.63d |
110.83d |
2.27b |
302.94b |
2.73b |
0.00b |
0.66cd |
|
|
M6S6 |
320.90b |
138.20b |
117.36b |
2.16c |
215.48d |
1.84d |
1.00b |
4.33b |
|
|
|
LSD(P ≤ 0.05) |
4.40 |
4.40 |
1.87 |
0.04 |
40.02 |
0.16 |
0.07 |
1.54 |
Means with same letter differ non-significantly at
P ≤ 0.05
M= Maize sole cropping; M2S2= Maize-soybean 2:2 intercropping; M4S2= Maize-soybean 4:2 intercropping; M4S4= Maize-soybean 4:4 intercropping; M6S6= Maize-soybean 6:6 intercropping; SCS= Stalk crushing strength (average of basal 2-10 internodes); LSD= Least
significant difference
%201383-1392_files/image002.png)
Fig. 1: The change of internode length (A), internode diameter (B) and internode length /diameter (C) under different treatments
2nd= Basal second internode; 4th, 6th, 8th
and 10th= fourth, sixth, eighth and tenth internode; M= Maize sole
cropping; M2S2= Maize-soybean
2:2 intercropping; M4S2= Maize-soybean
4:2 intercropping; M4S4= Maize-soybean
4:4 intercropping; M6S6= Maize-soybean
6:6 intercropping
The internode diameters of
nodes 210 were greater in intercropping than sole cropping (Fig. 1B). In
contrast to the pattern observed for the internode lengths, the specific order
of the internode diameters for the various treatments, from the largest to
smallest, was M2S2 > M4S4 > M4S2
> M6S6 > M. The average diameters of internodes
210 of the four intercropping treatments were increased respectively by 9.9,
13.3, 16.5, 16.4 and 19.9%, respectively, relative to those of the
corresponding internodes in the sole cropping treatment. By comparing the
different strip widths of the intercropping treatments, it was found that the
average internode diameter of M2S2
increased by 3.87, 5.93, and 12.98% as compared to M4S4,
M4S2, and M6S6, respectively. The
average internode diameter of M4S4 was increased by 2.2
and 9.0% as compared to M4S2 and M6S6,
respectively. The diameters of internodes 210 increased with both the decrease
of the intercropping maize strip width and the increase of the adjacent soybean
strip width.
Changes to the
internode length/diameter of the stalk under strip intercropping
The internode length/diameter value of M treatment was
the highest, followed by the ratio of M6S6, with the
ratio of M2S2 being the lowest, the specific expression
was M > M6S6 > M4S2 > M4S4
> M2S2 (Fig. 1C). The length/diameter values of
internodes 210 in M treatment increased by 51.9, 32.1, 31.9, 41.9 and 40.6%
relative to the average values of corresponding internodes in strip
intercropping. The average internode length/diameter value of M2S2
decreased by 12.5, 20.7 and 27.1% compared to M4S4, M4S2,
and M6S6, respectively, and the average internode length/diameter value of M4S4
decreased by 9.4 and 16.7% compared to M4S2 and M6S6,
respectively.
Changes
to internode fresh weight under strip intercropping
For all treatments, the maximum value of internode fresh
weight was usually located at the 4th internode (Table 4).
The average internode fresh weight followed the order of M2S2
> M4S4 > M4S2 > M6S6
> M. The fresh weight of internodes 210 of M stalk reached significance
with the corresponding internodes of M2S2, M4S2,
and M4S4. Compared with the four
intercropping treatments, the fresh weight of internodes 210 of the M2S2
stalk reached significance with those of M4S2 and M6S6.
The LSD (P＜0.05) values
of internode fresh weight at the low internodes (2nd, 4th)
were greater than that at the high internodes (8th, 10th).
Strip intercropping had a more significant effect on the internode fresh weight
at the low internode.
Comparison of fresh weight per unit
internode length under strip intercropping
Table 4 shows that the fresh
material weight per unit internode length from internodes 210 of
intercropping was greater than that of sole cropping (M2S2
> M4S4 > M4S2 > M6S6
> M). The difference of the 2nd10th internodes
between M and strip intercropping treatments were reached significance. The comparison of four intercropping treatments showed that,
the difference of the
2nd10th internodes between M2S2 and M4S2
and M6S6 reached significance.
The LSD value shows that strip intercropping had a more significant effect on
the fresh material weight per unit internode length at the low internode.
Changes
in the internode crushing strength under strip intercropping
Comparing the overall average of the 2nd10th
internodes of the four intercropping treatments over two years with the sole
cropping showed that the internode crushing strengths
of M2S2, M4S2
and M4S4 were significantly higher than M,
respectively (Table 4). The
overall performance was M2S2 > M4S4
> M4S2 > M6S6 > M. The comparison of four intercropping treatments showed that,
the difference of the 2nd6th internodes between M2S2
and M4S2 and M6S6 reached
significance. Strip intercropping had a greater influence on the crushing
strength of maize stalks at the low internodes.
Comparison
of internode unit breaking resistance strength under strip intercropping
The internode unit breaking
resistance strength from internodes 210 of intercropping were all greater
than sole cropping (M2S2 > M4S4 >
M4S2 > M6S6 > M) (Table 4). M2S2,
M4S2 and M4S4 were significantly
different from M, respectively. The internode of M4S2 and
M6S6 were significantly different from M2S2,
respectively. Strip intercropping had a greater influence on the internode unit
breaking resistance strength at the low internodes.
Comparison
of the root traits of maize under strip intercropping
After strip intercropping, the root fresh weight, root
diameter, diameter of aerial roots in soil, fresh weight of aerial roots in
soil and root bleeding quantity were significantly greater than those of sole
cropping (M2S2 > M4S4 > M4S2
> M6S6 > M) (Table 5). And the treatment of M4S2,
M4S4 and M6S6
were significantly different from M2S2, respectively. The
fresh weight of aerial roots in soil of M2S2 was 66.72%
higher than M4S4, M4S4 was 13.54%
higher than M4S2, M4S2 was 30.76%
higher than M6S6 and M6S6 was
19.46% higher than M. The root traits of maize increased with both the decrease
of the intercropping maize strip width and the increase of the adjacent soybean
strip width.
Table 4: Comparative of different treatments on the fresh
weight, fresh weight to length, stalk crushing strength and unit internode
fracture resistance of maize internode
|
Trait |
Year |
Treatment |
Internode |
||||
|
2nd |
4th |
6th |
8th |
10th |
|||
|
Fresh weight of internode (g) |
2016 |
M |
43.27c |
44.43c |
27.10d |
15.83c |
10.57d |
|
M2S2 |
58.06a |
54.08a |
41.30a |
22.74a |
15.03a |
||
|
M4S2 |
50.93b |
53.4ab |
34.37c |
19.41b |
12.06c |
||
|
M4S4 |
55.15a |
54.18a |
36.62b |
20.30b |
12.83b |
||
|
M6S6 |
45.65c |
49.34b |
33.47c |
19.76b |
11.83c |
||
|
LSD (P ＜ 0.05) |
3.21 |
4.43 |
2.12 |
1.72 |
0.51 |
||
|
2017 |
M |
39.99c |
35.96e |
20.54d |
9.36d |
5.09c |
|
|
M2S2 |
42.93a |
51.09a |
37.35a |
18.63a |
10.05a |
||
|
M4S2 |
41.50b |
42.81c |
28.85b |
16.19b |
7.08b |
||
|
M4S4 |
42.53ab |
50.29b |
30.73b |
16.58b |
9.37a |
||
|
M6S6 |
39.79c |
38.82d |
25.67c |
12.70c |
5.94bc |
||
|
LSD (P ＜ 0.05) |
2.13 |
2.61 |
2.13 |
1.35 |
0.78 |
||
|
Fresh
weight per unit internode length (g/cm) |
2016 |
M |
2.83d |
1.71c |
1.00c |
0.78c |
0.52c |
|
M2S2 |
6.31a |
2.82a |
2.09a |
1.55a |
0.95a |
||
|
M4S2 |
4.32b |
2.42b |
1.31b |
1.15b |
0.69b |
||
|
M4S4 |
4.60b |
2.63ab |
1.82a |
1.30b |
0.74b |
||
|
M6S6 |
3.43c |
1.98c |
1.40b |
1.22b |
0.64b |
||
|
LSD (P ＜ 0.05) |
0.33 |
0.16 |
0.22 |
0.13 |
0.04 |
||
|
2017 |
M |
1.91c |
1.47c |
0.90d |
0.43d |
0.26c |
|
|
M2S2 |
3.58a |
2.58a |
1.88a |
1.14a |
0.64a |
||
|
M4S2 |
2.71b |
1.94b |
1.32bc |
0.79bc |
0.40b |
||
|
M4S4 |
2.92b |
2.39a |
1.46b |
0.90b |
0.58a |
||
|
M6S6 |
2.62b |
1.71b |
1.17cd |
0.62c |
0.34bc |
||
|
LSD (P ＜ 0.05) |
0.18 |
0.13 |
0.11 |
0.06 |
0.05 |
||
|
Internodecrushing strength (N) |
2016 |
M |
214.30d |
181.47c |
141.07c |
127.63c |
85.67d |
|
M2S2 |
399.17a |
321.13a |
230.50a |
203.17a |
117.70a |
||
|
M4S2 |
331.07b |
265.07b |
183.23b |
146.83b |
100.53c |
||
|
M4S4 |
356.20b |
289.70a |
223.47a |
174.47b |
106.33b |
||
|
M6S6 |
273.12c |
205.80bc |
181.63b |
141.02bc |
93.92cd |
||
|
LSD (P ≤
0.05) |
37.14 |
27.19 |
26.67 |
31.79 |
14.64 |
||
|
2017 |
M |
216.43d |
139.23c |
93.00c |
72.37bc |
45.03c |
|
|
M2S2 |
443.43a |
272.67a |
200.50a |
101.30a |
65.87a |
||
|
M4S2 |
360.00b |
194.10b |
153.33b |
97.83ab |
64.30ab |
||
|
M4S4 |
423.00b |
266.37a |
163.93a |
98.67ab |
62.73ab |
||
|
M6S6 |
289.17c |
166.97bc |
115.10c |
88.53b |
51.17bc |
||
|
LSD (P ≤
0.05) |
15.69 |
11.07 |
17.16 |
9.13 |
7.58 |
||
|
Unit
internode fracture resistance (N/cm) |
2016 |
M |
14.06d |
6.98d |
5.19c |
6.34d |
4.22e |
|
M2S2 |
43.42a |
16.79a |
11.68a |
13.81a |
7.43a |
||
|
M4S2 |
28.11c |
12.00c |
6.96b |
8.73c |
5.77c |
||
|
M4S4 |
29.86b |
14.11b |
11.10a |
11.17b |
6.58b |
||
|
M6S6 |
20.58c |
8.25d |
7.63b |
8.65c |
5.08d |
||
|
LSD (P ≤
0.05) |
3.11 |
1.64 |
1.08 |
1.52 |
0.58 |
||
|
2017 |
M |
10.36d |
5.68c |
4.08c |
3.31c |
2.29d |
|
|
M2S2 |
36.95a |
13.77a |
10.08a |
6.20a |
4.19a |
||
|
M4S2 |
23.48c |
8.81b |
7.03b |
4.80b |
3.62b |
||
|
M4S4 |
29.04b |
12.66a |
7.78b |
5.33a |
3.87ab |
||
|
M6S6 |
19.02c |
7.33b |
5.24c |
4.34b |
2.93c |
||
|
LSD (P ≤
0.05) |
1.89 |
1.45 |
1.08 |
0.56 |
0.42 |
||
Means with same letters differ non-significantly
at P ≤ 0.05
2nd= Basal second internode; 4th, 6th, 8th
and 10th= fourth, sixth, eighth and tenth internode; M= Maize sole
cropping; M2S2= Maize-soybean
2:2 intercropping; M4S2= Maize-soybean
4:2 intercropping; M4S4= Maize-soybean
4:4 intercropping; M6S6= Maize-soybean
6:6 intercropping; LSD= Least significant
difference
Correlation between lodging and plant traits
The lodging rate was significant negatively correlated with
the stalk crushing strength (-0.79**), the lodging resistance index (-0.78**), internode diameter (-0.70*) and internode fresh weight (-0.62*) (Table 6). The lodging
rate was positively correlated with the internode length (0.80**), internode length/diameter (0.79**), ear height (0.77**), and
the center of gravity height (0.74**).
Therefore, the two indexes of stalk crushing strength and internode length
could be used to measure the lodging-resistance ability of plants. The lodging
rate was significant negatively correlated with the diameter of aerial
roots in the soil (-0.74**), fresh weight of aerial roots in the soil (-0.65*)
and the root bleeding quantity (-0.61*). The key root traits
affecting the lodging rate included diameter of aerial roots and fresh weight
of aerial roots in the soil.
Table 5: Comparison of root-related traits under different
maize-soybean intercropping systems
|
Years |
Treatments |
Root fresh weight (g) |
Root diameter (cm) |
The root layer (layer) |
Number of nodal root (loaf) |
Number of aerial roots in soil (loaf) |
Diameter of aerial roots in soil (cm) |
Fresh weight of aerial roots in soil (g) |
Root bleeding quantity (g) |
|
2016 |
M |
91.53e |
2.21d |
6.00b |
44.67c |
15.33c |
0.47c |
14.30e |
35.48e |
|
M2S2 |
206.99a |
2.80a |
7.33a |
58.00a |
23.00a |
0.61 |
41.02a |
68.27a |
|
|
M4S2 |
127.60c |
2.61b |
6.67ab |
48.33b |
18.00b |
0.53c |
21.91c |
46.37c |
|
|
M4S4 |
145.84b |
2.70ab |
6.67ab |
50.33b |
18.67b |
0.57b |
25.03b |
52.00b |
|
|
M6S6 |
109.09d |
2.34c |
6.00b |
45.67c |
15.67c |
0.49d |
17.054d |
40.15d |
|
|
LSD (P ≤ 0.05) |
16.32 |
0.12 |
0.10 |
1.77 |
1.50 |
0.03 |
0.56 |
2.64 |
|
|
2017 |
M |
80.45e |
2.07d |
6.00b |
43.33d |
14.67c |
0.46e |
12.60e |
32.32e |
|
M2S2 |
190.94a |
2.45a |
7.00a |
56.67a |
22.00a |
0.60a |
38.50a |
60.60a |
|
|
M4S2 |
115.04c |
2.19bc |
6.33ab |
45.67c |
17.67b |
0.54c |
20.10c |
40.92c |
|
|
M4S4 |
135.37b |
2.28b |
6.67ab |
48.6Bb |
18.33b |
0.57b |
22.67b |
45.69b |
|
|
M6S6 |
92.94d |
2.17c |
6.00b |
44.33cd |
15.33c |
0.49d |
15.08d |
36.76d |
|
|
LSD (P ≤ 0.05) |
18.65 |
0.12 |
0.10 |
1.88 |
0.91 |
0.02 |
0.74 |
4.74 |
Means
with same letters differ non-significantly at P ≤ 0.05
2nd= Basal second internode; 4th,
6th, 8th and 10th= fourth, sixth, eighth and tenth internode; M= Maize sole cropping; M2S2= Maize-soybean 2:2 intercropping; M4S2= Maize-soybean 4:2 intercropping; M4S4= Maize-soybean 4:4 intercropping; M6S6= Maize-soybean 6:6 intercropping; LSD= Least significant difference
Table 6: Correlation between lodging rate and plant traits (degree of freedom=
9)
|
Crop traits |
Lodging rate (%) |
|
|
Stem |
Plant height (cm) |
0.74** |
|
Ear height (cm) |
0.77** |
|
|
Centre of gravity height (cm) |
0.74** |
|
|
Stem diameter (cm) |
-0.62* |
|
|
Length of internode (cm) |
0.80** |
|
|
Internode diameter (cm) |
-0.70* |
|
|
Internode length /diameter |
0.79** |
|
|
Internode fresh weight (g) |
-0.62* |
|
|
SCS (N) |
-0.79** |
|
|
LRI |
-0.78** |
|
|
Root |
Fresh root weight (g) |
-0.61* |
|
Diameter of aerial roots in soil (cm) |
-0.74** |
|
|
Weight of aerial roots in soil (g) |
-0.65* |
|
|
Root bleeding quantity (g) |
-0.61* |
|
*and** denote significance
at 5% and 1% probability levels, respectively
SCS= Stalk crushing strength; LRI= Lodging
resistance index
Discussion
Many
studies have shown that the lodging rate is positively correlated with plant
height, ear height, center of gravity height, and basal
internode length (Sangoi
et al.
2002; Fallah
2012). Conversely, the lodging rate is
negatively correlated with the stem thickness, internode cross-sectional area,
basal internode weight, and other morphological traits (Zhang et al. 2018). Usually, with increased plant density, the stem
internode length increases, and the stem thickness significantly decreases,
which results in the decline of the stems lodging resistance (Zhao et al. 2009; Ignacio and Tony 2011). Presently, plant growth regulators are widely used in
maize production to improving the stem lodging resistance (Zhang et al. 2014; Xu et al. 2017). In this study adopted the
planting mode of maize-soybean strip intercropping was
used to significantly improve the lodging resistance of maize. Strip
intercropping to make the plant height, ear height, the center of gravity
height, the internode length and the internode length/diameter of maize plants
significantly lower than those of sole cropping. Strip intercropping could
reduce plant height, ear height, and height of center of gravity height by
shortening the length of internodes 210. The internode diameter, fresh weight, and unit fresh
matter weight of internodes were all greater in the intercropping than in the
sole cropping. Ma et al.
(2016) found that the stem diameter had
the greatest influence
on the lodging-resistance ability of plants. Kaack et
al. (2003) believed that lodging was
not significantly correlated with plant height and that the ear height
coefficient is an important index to evaluate the lodging resistance of plants.
Thus, the evaluation index of stem lodging resistance of maize is still
controversial. In this study, the internode length of 3rd6th internodes of maize were considered an
important index to evaluate lodging resistance. Chen et al. (2011)
suggested that with the decrease of the longest internode and the substantial
increase of each internode length, plants were prone to lodging. Similar results were observed in the current study;
after intercropping, the shortening of the internode length and an increase of
the internode fresh weight and crushing strength of maize were more obvious at
the lower internodes (2nd4th internodes) than at the
higher internodes (6th10th). These effects on the
morphology of different nodes, mechanical properties, and assimilate partition
enhanced the lodging-resistance ability of plants under strip intercropping.
Stem mechanical properties were significant
negatively correlated with the lodging rate (Robertson et al. 2014), which is usually measured by the puncture strength of
hard skin, crushing strength, and bending resistance strength (Dudley 1994; Kang et al. 1999).
Maize densification increased the competitive pressure among the individual
plants and affecting the anatomical structure and mechanical strength of the
stems (Han
1990; Novacek
et al. 2013). Thomison et al. (2011) believed that at higher the densities there is a greater
decrease of stem crushing strength and the more obvious colony lodging was. In
the current study, intercropping maize with soybean improved the stem
mechanical properties and significantly increased the internode crushing
strength, internode unit bending force, and comprehensive lodging-resistance
index of internodes 210. The increased mechanical resistance was owing to the
increase of the internode diameter and the internode unit fresh weight. Feng et al. (2008) also believed that stalk
thickness below the ear level was significantly correlated with stalk strength,
in which the 3rd internode was the most closely correlated with
lodging (Gaarcia et al. 2003).
Other studies have shown that the lodging rate can be effectively reduced by
spraying plant growth control agents, mainly by significantly increasing the
stem folding resistance and stem skin puncture strength in sections 3, 4, and 5
aboveground (Xu
et al. 2019). In the current study, the mechanical resistance indexes
of the 3rd6th stem internodes significantly improved
after intercropping, which contributed the most to improving the plants
comprehensive lodging resistance. Therefore, in this study considered the 3rd6th internodes to be the key nodes affecting
lodging. In future cultivation and breeding research, the crushing strength,
resistance index, and internode length of the 3rd6th internodes of the aboveground stem can be
used to measure the lodging-resistance ability of a plant.
The traits of the aboveground
stems and belowground roots were the two major factors affecting lodging (Fan et al. 2012).
The number of aerial roots, the number of layers, and root quality were
important indicators of the root resistance to lodging (Liu et al. 2011).
Spraying plant growth regulators could increase the number of aerial rooting
layers and strips, improve the quality of dry matter and root activity, and
thus, improve the lodging-resistance ability of spring maize (Lan et al. 2011; Xu et al. 2014). In the current study, the
adoption of strip intercropping had significantly increasing indexes such as
the root fresh weight, traits of aerial roots in the soil, and root bleeding
quantity relative to those in sole cropping. All root traits were significantly
negatively correlated with the lodging rate. Some researchers have suggested
that the number of aerial roots in the soil had the most
significant effect on lodging (Feng et al. 2008). In the current
study, the diameter and fresh weight of aerial roots in the
soil had the most significant effect on lodging. There were also differences in the ability to resistance
lodging under different intercropping treatments, mainly caused by the action
of the stem and root traits resistance to lodging. With the increase of in the
width of the maize sowing band, the lodging-resistance ability of the maize plants decreased
gradually and became similar to that in the sole cropping. When the width of
the maize strip was fixed, the lodging-resistance ability of maize increased with
the increasing width of the adjacent soybean bands. In the cultivation of
maize, we can reasonably adjust the width of the two crops according to this
concept and seek the best lodging-resistance model. The overall
lodging-resistance ability of plants under the different treatments was M2S2
> M4S4 > M4S2 > M6S6
> M. The land equivalent ratios of maize-soybean strip intercropping were
all greater than 1, which had the advantage of intercropping.
Conclusion
Results revealed that lodging
resistance of maize plants was increased by strip intercropping relative to its
sole cropping. Under high-density conditions, maize-soybean strip
intercropping seemed an effective and novel way to resolve sole crop lodging
and to increase the green yield in Songliao Plain. Moreover, the lodging
resistance ability of maize differed between different strip widths; therefore,
appropriate density and ratio of strip widths in intercropping should be
studied further to maximize densification resistance along with higher yield.
Acknowledgements
This research was supported by Project of Education
Department in Jilin (No. JJKH20190934KJ), by China
national key research and development plan (No.2017YFD0300607), by the
innovation and entrepreneur ship project for college students of Jilin
Agricultural University (No.201810193022).
Author Contributions
X Chen, Y Gu and C Wu planned the
experiments, Y Gu and Z Wang interpreted the results, X Chen, N Sun and Y Gu
made the write up, Y Liu and J Li statistically analyzed the data and made
illustrations.
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