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Improved soil characteristics in the deeper plough layer can increase grain yield of winter wheat
Journal of Integrative Agriculture 2020, 19(5): 1215–1226 Available online at www.sciencedirect.com
ScienceDirect
RESEARCH ARTICLE
Improved soil characteristics in the deeper plough layer can increase grain yield of winter wheat CHEN Jin1, 3*, PANG Dang-wei1, 3*, JIN Min2, 3*, LUO Yong-li1, 3, LI Hao-yu2, 3, LI Yong2, 3, WANG Zhen-lin2, 3 1 2 3
College of Life Sciences, Shandong Agricultural University, Tai’an 271018, P.R.China College of Agronomy, Shandong Agricultural University, Tai’an 271018, P.R.China State Key Laboratory of Crop Biology, Shandong Agricultural University, Tai’an 271018, P.R.China
Abstract In the North China Plain (NCP), soil deterioration threatens winter wheat (Triticum aestivum L.) production. Although rotary tillage or plowing tillage are two methods commonly used in this region, research characterizing the effects of mixed tillage on soil characteristics and wheat yield has been limited. A fixed-site field trial was carried out during 2011–2016 to examine the impacts of three tillage practices (5-year rotary tillage with maize straw removal (RT); 5-year rotary tillage with maize straw return (RS); and annual RS and with a deep plowing interval of 2 years (RS/DS)) on soil characteristics and root distribution in the plough layer. Straw return significantly decreased soil bulk density, increased soil organic carbon (SOC) storage and SOC content, macro-aggregate proportion (R0.25) and its stability in the plough layer. The RS/DS treatment significantly increased the SOC content, total nitrogen (TN), and root length density (RLD) in the 10–40 cm layer, and enhanced the proportion of RLD in the 20–30 and 30–40 cm layers. In the 20–30 and 30–40 cm layers, an increase in SOC and TN could lead to higher grain production than commensurate increases in the surface layer, resulting in a sustainable increase in grain yield from the RS/DS treatment. Thus, the RS/DS treatment could lead to high productivity of winter wheat by improving soil characteristics and root distribution at the deeper plough layer in the NCP. Keywords: soil characteristics, root length density, tillage practice, straw return, winter wheat
production (Chen et al. 2014). Traditional agricultural
1. Introduction The North China Plain (NCP) plays a vital role in ensuring China’s food security, especially through winter wheat
practices, characterized with high rates of fossil fuel energy use and lavish nutrient inputs, have been used to maximize crop productivity in this region (Jin et al. 2012). Chronic over-fertilization and a lack of adequate soil conservation techniques have led to such negative impacts as water pollution, soil deterioration, and loss of soil fertility (Liu et al.
Received 21 January, 2019 Accepted 18 March, 2019 Correspondence LI Yong, E-mail: [email protected]; WANG Zhen-lin, E-mail: [email protected] * These authors contributed equally to this study. © 2020 CAAS. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/). doi: 10.1016/S2095-3119(19)62679-1
2018). Therefore, agricultural methods that both promote soil quality and maintain high grain yield are urgently needed (Zhu et al. 2010; Zhang et al. 2013; Parihar et al. 2018). Incorporating crop straw is a known technique to prevent soil degradation (Xu et al. 2019). In the production process, straw is often tilled into the soil. Compared with straw removal, returning maize straw through plowing tillage
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improves soil aggregation and other properties in the plough layer, and enhances wheat productivity (Zhang et al. 2014). Similar effects on the soil plough layer have also been reported under different tillage practices, e.g., straw mulching with no-till farming (Lenka and Lal 2013) and straw incorporation with rotary tillage (Tao et al. 2019). Also, in one 17-year study, soil organic carbon (SOC) and total nitrogen (TN) contents were enhanced with straw return (He et al. 2015). Therefore, incorporating crop straw into farmland can help prevent the loss of soil nutrients. Plowing and rotary tillage have been generally adopted by smallholder farmers in the NCP (Wang et al. 2006). Over the last 10 years, rotary tillage has been widely applied due to associated lower costs in fuel oil and equipment (Shi et al. 2016). However, intensive rotary tillage has led to deteriorating soil conditions in the deeper plough layer, ultimately decreasing soil productivity (Václav et al. 2013). Fertile soil in agriculture as we consider, should be equipped with thick, fertile, and well-structured plough layer. Deep plowing creates a richer soil for roots, but costs more than rotary tillage (Hou et al. 2012; Xie et al. 2015). Therefore, soil tillage techniques characterized by high productivity and low consumption are urgently needed. Previous studies have mainly considered the plough layer as a whole, as well as the effects of no-till, rotary and plowing tillage on the physical characteristics and nutrient content of soils. However, studies of the effects of mixed tillage regimes on the vertical distribution of soil characteristics and root systems, and their relationship with the grain yield of winter wheat, are still limited. With the common cultivation equipment in mind, we hypothesized that deep plowing after rotary tillage at 2-year intervals would lead to significant changes in soil characteristics and root distribution in the plough layer, increasing grain yield over levels found in traditional farming practices. Accordingly, we assessed the effect of tillage practices on: (1) characteristics of the vertical soil column and root systems within the plough layer, and (2) changes in grain yield and SOC storage over 5 years. We also sought to verify whether the hypothetical tillage practice can simultaneously enhance both soil quality and wheat production.
2. Materials and methods 2.1. Research site description A 5-year field trial was performed from October 2011 to June 2016 in a winter wheat-summer maize cropping system at the Research Station of Zibo Academy of Agricultural Sciences, Shandong, China (36°90´N, 118°01´E). The soil was a sandy loam (Typic Cambisols; FAO/EC/ISRIC, 2003)
with a pH of 7.87 (water:soil=5:1). Prior to the experiment, winter wheat and summer maize were cultivated for 3 years using locally recommended chemical fertilizers rates and conventional plowing tillage without crop straw return, and the average wheat yield was 7.09 Mg ha–1.
2.2. Experimental design and management The experimental treatments included: 5-year rotary tillage without maize straw applied (RT); 5-year rotary tillage with maize straw applied (RS); annual RS with additional deep plowing at a 2-year interval (RS/DS). We used a randomized complete block design with three replicates (nine plots). Each plot was 30.0 m×4.0 m (16 rows of winter wheat spaced 25 cm apart). Winter wheat cultivar Jimai 22 (broadly planted in this region) was used. In each growing season of winter wheat, 112.5 kg ha–1 N (as urea), 105 kg ha–1 P2O5 (as calcium superphosphate), and 75 kg ha–1 K2O (potassium chloride) were applied to each plot as basal fertilization. Land preparation procedures and machinery used for the different treatments are shown in Table 1. At the jointing stage, 112.5 kg ha–1 N (as urea) was furrow-applied as topdressing. Seeds were sown on October 10 each year. The treatments were arranged to the same experimental plot and wheat straw was removed from the field at harvesting over the 5-year period. Harvest was done on 8 June 2012, 13 June 2013, 11 June 2014, 10 June 2015, and 12 June 2016.
2.3. Sampling and measurement At the end of the experiment, and 1 day before harvest (11 June 2016), soil was collected using a separated soil column sampler (AMS-ETC-300E, USA) from the three treatments at four layers (0–10, 10–20, 20–30, and 30–40 cm). Soil was collected from five points of each plot and well-mixed to produce a composite sample. Composite samples were passed through a 7-mm sieve without soil compaction and deformation. Pebbles and plant residues were discarded, and the samples were placed under shade to air dry. Roots of winter wheat were sampled at depths of 0–10, 10–20, 20–30, and 30–40 cm at the flowering stage (2 May 2016) of the 2015–2016 growing season. Prior to root sampling, plants in the sampling area were cut off at the soil surface. Wheat roots were collected from an area which was 0.75 m long (three rows) and 0.40 m wide. Each soil cuboid was put into a nylon net bag and washed with tap water. Roots were then removed from the mixture (including organic debris) and were floated in shallow water in a transparent tray (0.20 m×0.30 m), scanned with a flatbed scanner (Epson Perfection V700 Photo, Seiko Epson Corp,
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Table 1 Operation procedures and the equipment used of different tillage practices Tillage1) RT
RS
RS/DS
1)
2)
Operation procedure2) Total maize straw removed from the field → Base fertilizer spreading → Rotary cultivating two times with IGQN200K-QY rotary cultivator (working depth was about 10–12 cm)→ Forming the border-check → Seeding with common seeder Total maize straw returned to the field → Base fertilizer spreading → Rotary cultivating two times with IGQN-200KQY rotary cultivator (working depth was about 10–12 cm) → Forming the border-check → Seeding with common seeder The same to RS in the first two seasons. In the 3rd year: Total maize straw returned to the field → Base fertilizer spreading → Mouldboard plowing once with ILFQ330 turnover plough (working depth was about 28–30 cm) → Rotary cultivating two times with IGQN-200K-QY rotary cultivator → Forming the border-check → Seeding with common seeder→ The same to RS in the last 2 years
RT, 5-year rotary tillage without maize straw applied; RS, 5-year rotary tillage with maize straw applied; RS/DS, annual RS with additional deep plowing at a 2-year interval. The manufacturers of IGQN-200K-QY rotary cultivator and ILFQ330 turnover plough are YTO Group Corporation and Runlian Scientific and Technological Development Co., Ltd., respectively.
Japan) at a resolution of 600 dots per inch (dpi), and then analyzed with an image analyzer (WinRHIZO, Regent Instruments Canada Inc.) to measure their lengths (Dai et al. 2014). The root length density (RLD; mm cm–3) was defined as follows: RLD (mm cm–3)=TL/VS where TL (mm) was the total root length, and VS (cm3) was the volume of soil cuboid. The cutting ring (100 cm3) method was used to determine soil bulk density (SBD, g cm–3) in the 0–40 cm layer, as described by Cheng et al. (2015). A core sample was collected at random in each plot before harvest in 2015– 2016. At the time of the final harvest, all plants covering a 10-m2 area from each experimental plot were used to measure grain yield. The soil aggregates were measured by placing a soil sample (50 g) on a stack of sieves (5, 2, 1, 0.5, and 0.25 mm, respectively) fitted to a soil aggregate analyzer (TTF-100, China). The stacked sieves were immersed in water and moved up and down by 3.5 cm at a frequency of 30 cycles min–1 for 15 min. The mass proportion of aggregates that analyzed >5, 5–2, 2–1, 1–0.5, and 0.5–0.25 mm were calculated by drying and weighing the soil samples remaining on these sieves. The macro-aggregate proportion (R0.25), the mean weight diameter (MWD), and the geometric mean diameter (GMD) were calculated using standard methods, as described by Zhang et al. (2014). R0.25 (%)=
MR>0.25 MT
∑ xiw MWD (mm)= i =n1 ∑ i =1 wi n
i
∑ i =1 wilnxi n ∑ i =1 wi n
GMD (mm)=exp
where R 0.25 represents the mass percentage of soil aggregate with a diameter>0.25 mm, MR>0.25 is the weight
of aggregates>0.25 mm, MT is the weight of the soil sample (50 g), wi (%) is the weight of the aggregates in a specific size range as a fraction of the total mass of the sample analyzed, n is the number of sieves, and xi (mm) is the mean diameter of aggregates for each sieve. The wet oxidation-redox titration method was used to determine samples’ SOC content (Kou et al. 2012). An automatic Kjeldahl distillation-titration unit (Foss, Sweden) was used to determine the soil total N (TN) concentration. The carbon preservation capacity of the macro-aggregate (CPC) was then calculated as follows: n CPC (g kg–1)=∑i =1 SOCi ×wi where wi (%) is the weight proportion of soil aggregates in a specific size range relative to the total dry weight of the sample analyzed, and SOCi (g kg–1) is the SOC content for a given size of soil aggregate. The SOC storage in each soil layer of thickness (d, 10 cm in this study) was calculated as follows: SOC storage (Mg ha–1)=SOC×SBD×d×10 The SOC stocks of macro-aggregate and microaggregate (Mg ha–1) were calculated as follows: SOC stocks of macro-aggregate=C concentraton×SBD× d×fraction weight SOC stocks of micro-aggregate=SOC storage–SOC stocks of macro-aggregate where C concentration (g kg–1) refers to the SOC content in each fraction size and fraction weight is weight proportion of the fraction in the whole soil. Before treatment, we calculated the soil factors mentioned above (Table 2). The increased grain yield per unit SOC (or TN) was calculated as follows: Increased grain yield SOC TN)= Increased grain yield perper unitunit SOC (or (or TN)=
ΔGYΔGY×1 ΔGY×1 ΔGY 000000 ( ( ) ) ΔSOC ΔTN ΔTN ΔSOC where ΔGY (Mg ha–1) is the average change in grain yield relative to the level before the experiment, and ΔSOC (g kg–1) and ΔTN (mg kg–1) are changes of SOC and TN
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Table 2 The values of basic soil factors before treatment1) Depth (cm) 0–10 10–20 20–30 30–40 1)
SBD (g cm–3) 1.30 1.39 1.50 1.53
R0.25 (%) 77.24 76.02 70.44 63.72
WMD (mm) 1.21 1.15 1.09 0.93
GMD (mm) 0.82 0.79 0.72 0.63
SOC (g kg–1) 8.53 7.45 6.32 5.23
TN (g kg–1) 0.76 0.72 0.63 0.57
C/N 11.28 10.42 10.05 9.15
CPC (g kg–1) 6.41 5.40 4.21 3.23
SOC storage (Mg ha–1) 11.11 10.35 9.49 8.00
Macro-AC (Mg ha–1) 8.35 7.50 6.31 4.93
Micro-AC (Mg ha–1) 2.76 2.85 3.17 3.06
SBD, soil bulk density; R0.25, macro-aggregate proportion; WMD, mean weight diameter; GMD, geometric mean diameter; SOC, soil organic carbon; TN, total nitrogen; C/N, soil C:N ratio; CPC, carbon preservation capacity of macro-aggregate; AC, SOC stock of aggregate.
content, respectively.
1.6 1.5
2.4. Statistical analysis
3. Results 3.1. Soil bulk density Fig. 1 shows differences in SBD among the treatments in the 0–40 cm soil layers. Straw return significantly decreased SBD by 1.22–8.74% relative to pre-treatment levels, with the opposite being true for the RT treatment. Compared to RT, RS, and RS/DS significantly decreased SBD by 11.07 and 8.15% in the 0–10 cm layer; by 4.20 and 9.19% in the 10–20 cm layer; by 2.03 and 7.38% in the 20–30 cm layer; and by 2.73 and 4.16% in the 30–40 cm layer, respectively.
1.4 Soil bulk density (g cm–3)
The effects of different treatments on soil properties were tested with one-way ANOVA. All the statistical analyses were conducted using SPSS 19.0 (IBM Corp., Chicago, IL, USA). Comparisons between the treatments were conducted using the LSD method.
0–10 cm
A
b
1.3
1.1 1.6 1.5
d
C
a
a
1.4
10–20 cm b
a
1.2
B a
d
c
20–30 cm b c
c
D a
a
30–40 cm b b
1.3 1.2 1.1
PR RT RS RS/DS PR RT RS RS/DS Tillage practices
Fig. 1 The effects of different tillage practices on soil bulk density in the 0–40 cm soil layers. PR, pre-treatment level; RT, 5-year rotary tillage without maize straw applied; RS, 5-year rotary tillage with maize straw applied; RS/DS, annual RS with additional deep plowing at a 2-year interval. Vertical bars represent SE (n=3), and different letters indicate significant differences as determined by LSD method (P<0.05).
3.2. Soil aggregate
3.3. SOC and TN
The RS and RS/DS treatments significantly increased R0.25 by 3.33–8.56% and 4.09–9.88% in the 0–40 cm layer relative to pre-treatment levels, respectively (Fig. 2). The greatest increase in R0.25 was observed in the RS plots in the 0–10 cm layer; the RS/DS treatment had the highest R0.25 in the 10–40 cm layer. Compared with pre-treatment levels, the RT treatment decreased R0.25 by an average of 5.76% in the 0–40 cm layer. Straw return significantly increased MWD and GMD by 5.99 and 6.80% in the 0–40 cm layer, while RT decreased MWD and GMD by 9.63 and 7.87%, relative to pre-treatment levels. The MWD and GMD of the different tillage practices ranked as RS>RS/DS>RT in the 0–10 cm layer (Fig. 2-E and I), and RS/DS>RS>RT in the remaining layers, respectively. Meanwhile, both MWD and GMD decreased gradually with the soil depth (Fig. 2).
Compared to pre-treatment levels, SOC and TN contents significantly increased in the 0–40 cm soil layer with straw return. Conversely, SOC and TN contents decreased significantly in the RT treatment. The RS treatment had significantly higher SOC and TN contents than RS/DS in the 0–10 cm layer (Fig. 3-A and E), but notably lower contents at the remaining layers. The RT treatment decreased the soil C/N ratio in the 0–40 cm layer compared to pre-treatment levels, and soil C/N tended to decline with soil depth (Fig. 3). Compared with the RT treatment, the soil C/N increased with the RS and RS/DS treatments by 3.09 and 3.14% in the 0–10 cm layer (Fig. 3-I), by 8.06 and 8.19% in the 10–20 cm layer (Fig. 3-J), by 9.13 and 9.10% in the 20–30 cm layer (Fig. 3-K), and by 4.75 and 9.25% in the 30–40 cm layer (Fig. 3-L), respectively. Comparable values were observed between
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R0.25 (%)
90
A
80
a c
0–10 cm b
b
c
d
C
10–20 cm
B
a b
c
d
70
20–30 cm
30–40 cm
D
a a
d
c
60
MWD (mm)
1.3 E 1.2
b
c
a
0–10 cm b
F c
10–20 cm a b
G
20–30 cm a b
c
1.1
30–40 cm a c
d
0.9
d
H
d
1.0
b
b d
0.8
GMD (mm)
0.9
I
0–10 cm b
0.8
b
a
b
J
10–20 cm
a
20–30 cm
b
c
c
0.6 RT
RS RS/DS
PR
RT
30–40 cm
b
RS RS/DS
PR
RT
a c
d PR
L
a
d
0.7
K
RS RS/DS
PR
b d RT
RS RS/DS
Tillage practices
Fig. 2 Effects of different tillage practices on macro-aggregate proportion (R0.25), mean weight diameter (WMD), and geometric mean diameter (GMD) in the 0–40 cm soil layers. PR, pre-treatment level; RT, 5-year rotary tillage without maize straw applied; RS, 5-year rotary tillage with maize straw applied; RS/DS, annual RS with additional deep plowing at a 2-year interval. Vertical bars represent SE (n=3), and different letters indicate significant differences (P<0.05).
RS and RS/DS in the 0–30 cm layer, but significantly higher value was found in RS/DS in the 30–40 cm layer. SOC content had a significant and negative correlation with SBD. Conversely, a significant positive correlation was observed between SOC content and R0.25 (Fig. 4).
3.4. Carbon preservation capacity of macro-aggregate The CPC increased in the RS and RS/DS treatments compared to pre-treatment levels by 22.46 and 12.35% in the 0–10 cm layer (Fig. 5-A); by 10.49 and 22.49% in the 10–20 cm layer (Fig. 5-B); by 8.34 and 23.13% in the 20– 30 cm layer (Fig. 5-C); and by 6.64 and 26.83% in the 30–40 cm layer (Fig. 5-D), respectively. Conversely, CPC significantly decreased in the RT treatment by 9.79–17.09% in the four layers, respectively (Fig. 5).
3.5. Changes of SOC storage The SOC storage significantly changed with different tillage practices relative to pre-treatment levels (Fig. 6). SOC
storage decreased by 1.84 Mg ha–1 in the 0–40 cm soil layer in the RT treatment. The RS and RS/DS treatments significantly enhanced SOC storage by between 0.22–0.74 and 0.48–0.85 Mg ha–1 at the four soil layers, respectively (Fig. 6-A–D). These increments can mainly be credited to the increases of macro-aggregate SOC stock (Fig. 6-E–H). Conversely, the RS and RS/DS treatments reduced microaggregate SOC stock over the RT treatment in the 0–40 cm soil layer (Fig. 6-I–L).
3.6. Root length density Compared with RT (Fig. 7-A), both RS and RS/DS significantly increased RLD in the 0–40 cm layer, but the effects of the RS and RS/DS treatments on RLD varied with soil depths (Fig. 7-B and C). The RS treatment enhanced RLD compared to the RS/DS treatment in the 0–10 cm layer, but significantly reduced RLD by 6.18–26.01% in the deeper layers (Table 3). Compared with the RT and RS treatments, the RS/DS treatment significantly decreased the RLD proportion in the 0–10 cm layer by 7.88 and 13.53%, respectively. Conversely, the RS/DS treatment significantly
Soil C/N ratio
Soil TN content (g kg–1)
SOC content (g kg–1)
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10
0–10 cm c
8
a
b
B 20–30 cm
A 10–20 cm
d
c
b
0.8
a
0–10 cm c
b
d
c
E 10–20 cm
d
c
0.7
a
d
11
a
a
I
c
d
a
J a
ab
d
b bc
20–30 cm
c
a
a
RS RS/DS
PR
RT
a
RS RS/DS PR RT Tillage practices
L
a
b
RT
b
K 30–40 cm
a
b
PR
a
H
a bc
c
9 8
b
b
10–20 cm
10
a
G 30–40 cm
d c
0–10 cm a a
b
F 20–30 cm
0.6 0.5 12
D
a
6 4 0.9
C 30–40 cm
RS RS/DS
PR
RT
b
RS RS/DS
Fig. 3 Effects of different tillage practices on soil organic carbon (SOC), total nitrogen (TN) contents, and soil C/N ratio in the 0–40 cm soil layers. PR, pre-treatment level; RT, 5-year rotary tillage without maize straw applied; RS, 5-year rotary tillage with maize straw applied; RS/DS, annual RS with additional deep plowing at a 2-year interval. Vertical bars are SE (n=3), and different letters indicate significant differences (P<0.05). 1.6
A
90
B
85 80
1.4
75 70
1.3
1.1
y=3.84x+45.36 R2=0.86**
y=–0.07x+1.91 R2= 0.96**
1.2
4
6 8 10 SOC content (g kg–1)
12 4
6 8 10 SOC content (g kg–1)
R0.25 (%)
SBD (g cm–3)
1.5
65 60 55 12
Fig. 4 Correlation between soil organic carbon (SOC) content and soil bulk density (SBD, A) and macro-aggregate proportion (R0.25, B) in the 0–40 cm soil layer. **, P<0.01.
increased the RLD proportion in the 20–30 and 30–40 cm layers. Significant differences were not observed among tillage treatments in the 10–20 cm layer (Table 3). The SBD in the 0–10, 10–20, and 20–30 cm layers negatively correlated with RLD in the soil layers immediately below (i.e., 10–20, 20–30, 30–40 cm) (Table 4). Meanwhile, TN contents of 0–10, 10–20, 20–30, and 30–40 cm soil
layers positively correlated with RLD in the same soil layer (Table 4).
3.7. Grain yield The RT treatment reduced grain yield throughout the 5-year study period by 0.11, 0.37, 0.58, 0.85, and 1.07 Mg ha–1
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CPC of macro-aggregate (g kg–1)
8
c
6
d
compared the pre-treatment level (7.09 Mg ha–1) (Fig. 8). In 2011–2012 and 2012–2013, the RS treatment increased grain yield by 3.59 and 6.64% relative to the pre-treatment level, respectively. However, the grain yield increments became lower after 2013–2014. Compared with the RS treatment, the RS/DS treatment significantly increased grain yield by 5.89, 11.81, and 20.21% in 2013–2014, 2014–2015, and 2015–2016, respectively (Fig. 8). Grain yield was enhanced with increasing SOC (g kg–1) and TN (mg kg–1) contents in the four layers. Increasing SOC content in the 20–30 and 30–40 cm layers could lead to significantly higher grain yields than commensurate increases in the 0–10 and 10–20 cm layers (Fig. 9-A). A similar tendency was observed for TN content in the 0–40 cm layer, but there were no significant differences between the 20–30 and 30–40 cm layers (Fig. 9-B).
10–20 cm
a 0–10 cm B b
A
a
b
c d
4 2 20–30 cm
8 C 6 c
4 2
d
PR
RT
b
30–40 cm
D
a c
a
b
d
RS RS/DS PR RT Tillage practices
RS RS/DS
SOC storage of macroaggregate (Mg ha–1)
SOC storage of bulk soil (Mg ha–1)
Fig. 5 Effects of different tillage practices on the carbon preservation capacity of macro-aggregate (CPC) in the 0–40 cm soil layers. PR, pre-treatment level; RT, 5-year rotary tillage without maize straw applied; RS, 5-year rotary tillage with maize straw applied; RS/DS, annual RS with additional deep plowing at a 2-year interval. Vertical bars are SE (n=3), and different letters indicate significant differences (P<0.05).
13 12
b
11
b
4.1. Soil properties affected by tillage This study shows straw return significantly reduces the SBD
10–20 cm
B b
10
a
20–30 cm
C
c
c
b
a
d
c
8 7 10 9
a 0–10 cm b
E c
8
F
d
10–20 cm a b
c
7
G
d
6
20–30 cm
c
b
3.0
I
0–10 cm
a b
a
J
a b
b
b
2.5
10–20 cm
a
b
30–40 cm
a c
20–30 cm a
b
a
a
d
K
d
b
H
5
3.5
30–40 cm
D
a
9
4 4.0
SOC storage of microaggregate (Mg ha–1)
cm a 0–10 a
A
4. Discussion
L
b d
a
a
PR
RT
c
30–40 cm a
b
2.0 1.5 1.0
PR
RT
RS RS/DS
PR
RT
RS RS/DS PR Tillage practices
RT
RS RS/DS
RS RS/DS
Fig. 6 Effects of different tillage practices on total soil organic carbon (SOC) storage and aggregate SOC stock in the 0–40 cm soil layers. PR, pre-treatment level; RT, 5-year rotary tillage without maize straw applied; RS, 5-year rotary tillage with maize straw applied; RS/DS, annual RS with additional deep plowing at a 2-year interval. Vertical bars are SE (n=3), and different letters indicate significant differences (P<0.05).
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A
B
C
0–10 cm 10–20 cm 20–30 cm 30–40 cm
Fig. 7 Contrast diagram of spatial heterogeneity of root length density distribution affected by different tillage practices, representing the 5-year rotary tillage without maize straw applied (RT, A), 5-year rotary tillage with maize straw applied (RS, B), and annual RS with additional deep plowing at a 2-year interval (RS/DS, C) treatments. Table 3 Effects of tillage practices on root length density in 0–40 cm soil layer1) Treatment2) RT RS RS/DS
0–10 cm 16.06 c/35.82 b 20.04 a/38.16 a 18.43 b/33.03 c
10–20 cm 13.69 c/30.55 a 15.17 b/28.89 a 16.17 a/28.98 a
20–30 cm 8.95 c/19.96 b 10.50 b/20.00 b 12.01 a/21.53 a
30–40 cm 6.13 c/13.67 b 6.80 b/12.95 b 9.19 a/16.46 a
1)
Red and blue figures indicate root length density and its proportion in different soil layers, respectively. RT, 5-year rotary tillage without maize straw applied; RS, 5-year rotary tillage with maize straw applied; RS/DS, annual RS with additional deep plowing at a 2-year interval. Different lowercase letters indicate significant differences (P<0.05). 2)
Table 4 Correlation analysis (r) between soil bulk density and root length density (RLD), and soil total nitrogen content and root length density in different soil layers RLD 0–10 cm 10–20 cm 20–30 cm 30–40 cm *
, P<0.05; **, P<0.01.
Grain yield (Mg ha–1)
9
Soil bulk density (g cm–3) 10–20 cm 20–30 cm –0.46 –0.29 –0.83** –0.77** –0.81** –0.74* –0.77** –0.75**
0–10 cm –0.87** –0.68* –0.58 –0.33
2012–2013 C
2013–2014 D
a
b
2014–2015 E a
a b
Soil total nitrogen (g kg–1) 10–20 cm 20–30 cm 0.58 0.4 0.96** 0.83** 0.94** 0.90** 0.87** 0.93**
a
a
a
b
c
c
RT
RS RS/DS
RT
RS RS/DS
RT RS RS/DS Tillage practices
RT
1
2015–2016 a
b
b
c
6 5
30–40 cm 0.45 0.78** 0.86** 0.79**
–1
8 7
0–10 cm 0.90** 0.74* 0.67* 0.44
2011–2012 B
A
30–40 cm –0.52 –0.73* –0.63* –0.52
RS RS/DS
RT
RS RS/DS
Fig. 8 Effects of different tillage practices on grain yield during the study period. PR, pre-treatment level; RT, 5-year rotary tillage without maize straw applied; RS, 5-year rotary tillage with maize straw applied; RS/DS, annual RS with additional deep plowing at a 2-year interval. Vertical bars are SE (n=3), different letters indicate significant differences (P<0.05).
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2.0
A
0.08
B
a
1.5
1.0
a b
c c
a
0.5
0
b
0–10
0.06
10–20 20–30 30–40
0–10
b
10–20 20–30 30–40
0.04
0.02
0
Grain yield increment per unit TN (Mg ha–1)
Grain yield increment per unit SOC (Mg ha–1)
CHEN Jin et al. Journal of Integrative Agriculture 2020, 19(5): 1215–1226
Soil layers (cm)
Fig. 9 Effects of different tillage practices on grain yield rate caused by soil organic carbon (SOC) and total nitrogen (TN) changes. Vertical bars are SE (n=3), different letters indicate significant differences (P<0.05).
in the 0–40 cm soil layer compared with straw removal, in accord with previous findings (Rawls et al. 1998). The increase in SOC content could account for this improvement, as SBD has been found to be negatively correlated with SOC content (Wang et al. 2018), consistent with our observation (Fig. 4). Higher SOC and TN contents associated with straw return are generally considered important factors for aggregation (Six et al. 2002; Tong et al. 2009; Li et al. 2010, 2017; Karami et al. 2012; Zhao H L et al. 2018). SOC accumulation in cropland was mostly determined by the balance between the crop residue inputs and the export of new and old soil organic matter decomposition (Kou et al. 2012; Zhang et al. 2012). Incorporating straw significantly increased C inputs into soil (Liu et al. 2019) and promoted soil aggregation (Huang et al. 2018), which could reduce or offset the loss of SOC (Laird and Chang 2013; Li et al. 2016). Meanwhile, straw return significantly improved the mass proportion, stability, and CPC of macro-aggregate, which indicates a synergistic relationship between soil aggregation and SOC accumulation. Previous studies have shown straw incorporation contributes more to C/N than root inputs alone (Puget and Lal 2005; Tan et al. 2007), consistent with our findings (Fig. 3). Our experiment indicates that conversion from rotary tillage to deep plowing changed the vertical distribution of soil factors (SBD, aggregate, SOC storage, soil N, etc.) in the soil profile, improving soil factors in the deeper plough layer, especially in the 20–30 and 30–40 cm layers. Continuous rotary tillage tended to shallow plough layer, and thicken and harden the plough pan upward to the topsoil, which critically limited the subsoil’s capacity to preserve SOC (Zhao Y C et al. 2018). That deep plowing induced changes in soil factor distribution with depth was likely a result of two
causes: redistribution of topsoil nutrients and root growth promotion. First, the topsoil has most of the nutrients, and deep plowing can move maize straw and surface nutrients into the subsoil. Second, deep plowing thickens the plough layer down to the 20–40 cm layers, changes the soil’s physical condition, and promotes more wheat root growth in those loose soil layers (Luo et al. 2010), thereby enhancing carbon input.
4.2. Root distribution affected by tillage Root systems depend on the soil, and changes in soil properties have significant impacts on root action (Curaqueo et al. 2011; Xu et al. 2018). Our findings demonstrated that straw return significantly increased RLD in the 0–40 cm soil layers (Table 3). Straw return enables the soil to create a complex decomposition sub-system, and it could buffer the impact of external forces, and accumulate nutrients and energy, both of which are beneficial for growing roots (Song et al. 2016). Tillage-induced various distribution of nutrient and physical conditions, which led to spatial heterogeneity of RLD in the plough layer (Fig. 7). Rotary tillage reduced nutrient concentration, decreased soil disturbance, and increased soil compaction in the 20–40 cm layers. It not only inhibit root growth into the deeper layers (Benjamin and Nielsen 2006; Bengough et al. 2011; Mu et al. 2016), but also limited the downwards movement of topsoil nutrients.
4.3. Wheat grain yield affected by tillage Straw removal resulted in soil compaction within the topsoil layers, which produced soil factors detrimental for crop growth and a consequent reduction in yield (Mele and Crowley 2008). Similarly, in our experiment,
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the RT treatment significantly decreased grain yield over the duration of the study. The RS treatment significantly increased grain yield during the first 2 years (Fig. 8), as reported by others (Wang et al. 2015; Zhang et al. 2016). However, grain yield reduction was observed in the following two seasons, and grain yield in the final year of the study was comparable to the pre-treatment level (Fig. 8). This suggests straw return could not maintain high and stable production when inappropriate tillage was applied (Chen et al. 2017; Li et al. 2018). Continuous rotary tillage would induce an adverse soil structure, poor nutrient density in the deeper plough layer, and ultimately reduced wheat production (Kong 2014; He et al. 2019). Compared with the RS treatment, the RS/DS treatment significantly increased grain yield after deep plowing was applied (Fig. 8), which could be explained by higher root length density (Fig. 7), and increased SOC and TN contents in the 20–40 cm soil layers (Fig. 9). With improved soil conditions in the 0–20 cm layer over the pre-treatment level, the RS/DS treatment led to a harvest of more grain, which suggests appropriately improving soil quality in topsoil was indispensable.
5. Conclusion Straw return decreased SBD, facilitated soil aggregation and SOC preservation, and increased RLD in each soil layer. The improved soil factors and increased RLD in the subsoil had greater effects on grain yield than similar changes in the topsoil. A significant improvement of soil properties and increased RLD in the subsoil were observed in the RS/ DS treatment, which also had the highest grain yield. The above results demonstrated that RS/DS could be a more efficient and operable approach to improve both soil quality and wheat production in the NCP.
Acknowledgements The research was supported by the National Basic Research Program of China (973 Program; 2015CB150404), the National Key Research and Development Program of China (2017YFD0301001 and 2016YFD0300403), and the Shandong Province Mount Tai Industrial Talents Program, China.
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Executive Editor-in-Chief LI Shao-kun Managing editor WANG Ning
ScienceDirect
RESEARCH ARTICLE
Improved soil characteristics in the deeper plough layer can increase grain yield of winter wheat CHEN Jin1, 3*, PANG Dang-wei1, 3*, JIN Min2, 3*, LUO Yong-li1, 3, LI Hao-yu2, 3, LI Yong2, 3, WANG Zhen-lin2, 3 1 2 3
College of Life Sciences, Shandong Agricultural University, Tai’an 271018, P.R.China College of Agronomy, Shandong Agricultural University, Tai’an 271018, P.R.China State Key Laboratory of Crop Biology, Shandong Agricultural University, Tai’an 271018, P.R.China
Abstract In the North China Plain (NCP), soil deterioration threatens winter wheat (Triticum aestivum L.) production. Although rotary tillage or plowing tillage are two methods commonly used in this region, research characterizing the effects of mixed tillage on soil characteristics and wheat yield has been limited. A fixed-site field trial was carried out during 2011–2016 to examine the impacts of three tillage practices (5-year rotary tillage with maize straw removal (RT); 5-year rotary tillage with maize straw return (RS); and annual RS and with a deep plowing interval of 2 years (RS/DS)) on soil characteristics and root distribution in the plough layer. Straw return significantly decreased soil bulk density, increased soil organic carbon (SOC) storage and SOC content, macro-aggregate proportion (R0.25) and its stability in the plough layer. The RS/DS treatment significantly increased the SOC content, total nitrogen (TN), and root length density (RLD) in the 10–40 cm layer, and enhanced the proportion of RLD in the 20–30 and 30–40 cm layers. In the 20–30 and 30–40 cm layers, an increase in SOC and TN could lead to higher grain production than commensurate increases in the surface layer, resulting in a sustainable increase in grain yield from the RS/DS treatment. Thus, the RS/DS treatment could lead to high productivity of winter wheat by improving soil characteristics and root distribution at the deeper plough layer in the NCP. Keywords: soil characteristics, root length density, tillage practice, straw return, winter wheat
production (Chen et al. 2014). Traditional agricultural
1. Introduction The North China Plain (NCP) plays a vital role in ensuring China’s food security, especially through winter wheat
practices, characterized with high rates of fossil fuel energy use and lavish nutrient inputs, have been used to maximize crop productivity in this region (Jin et al. 2012). Chronic over-fertilization and a lack of adequate soil conservation techniques have led to such negative impacts as water pollution, soil deterioration, and loss of soil fertility (Liu et al.
Received 21 January, 2019 Accepted 18 March, 2019 Correspondence LI Yong, E-mail: [email protected]; WANG Zhen-lin, E-mail: [email protected] * These authors contributed equally to this study. © 2020 CAAS. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/). doi: 10.1016/S2095-3119(19)62679-1
2018). Therefore, agricultural methods that both promote soil quality and maintain high grain yield are urgently needed (Zhu et al. 2010; Zhang et al. 2013; Parihar et al. 2018). Incorporating crop straw is a known technique to prevent soil degradation (Xu et al. 2019). In the production process, straw is often tilled into the soil. Compared with straw removal, returning maize straw through plowing tillage
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improves soil aggregation and other properties in the plough layer, and enhances wheat productivity (Zhang et al. 2014). Similar effects on the soil plough layer have also been reported under different tillage practices, e.g., straw mulching with no-till farming (Lenka and Lal 2013) and straw incorporation with rotary tillage (Tao et al. 2019). Also, in one 17-year study, soil organic carbon (SOC) and total nitrogen (TN) contents were enhanced with straw return (He et al. 2015). Therefore, incorporating crop straw into farmland can help prevent the loss of soil nutrients. Plowing and rotary tillage have been generally adopted by smallholder farmers in the NCP (Wang et al. 2006). Over the last 10 years, rotary tillage has been widely applied due to associated lower costs in fuel oil and equipment (Shi et al. 2016). However, intensive rotary tillage has led to deteriorating soil conditions in the deeper plough layer, ultimately decreasing soil productivity (Václav et al. 2013). Fertile soil in agriculture as we consider, should be equipped with thick, fertile, and well-structured plough layer. Deep plowing creates a richer soil for roots, but costs more than rotary tillage (Hou et al. 2012; Xie et al. 2015). Therefore, soil tillage techniques characterized by high productivity and low consumption are urgently needed. Previous studies have mainly considered the plough layer as a whole, as well as the effects of no-till, rotary and plowing tillage on the physical characteristics and nutrient content of soils. However, studies of the effects of mixed tillage regimes on the vertical distribution of soil characteristics and root systems, and their relationship with the grain yield of winter wheat, are still limited. With the common cultivation equipment in mind, we hypothesized that deep plowing after rotary tillage at 2-year intervals would lead to significant changes in soil characteristics and root distribution in the plough layer, increasing grain yield over levels found in traditional farming practices. Accordingly, we assessed the effect of tillage practices on: (1) characteristics of the vertical soil column and root systems within the plough layer, and (2) changes in grain yield and SOC storage over 5 years. We also sought to verify whether the hypothetical tillage practice can simultaneously enhance both soil quality and wheat production.
2. Materials and methods 2.1. Research site description A 5-year field trial was performed from October 2011 to June 2016 in a winter wheat-summer maize cropping system at the Research Station of Zibo Academy of Agricultural Sciences, Shandong, China (36°90´N, 118°01´E). The soil was a sandy loam (Typic Cambisols; FAO/EC/ISRIC, 2003)
with a pH of 7.87 (water:soil=5:1). Prior to the experiment, winter wheat and summer maize were cultivated for 3 years using locally recommended chemical fertilizers rates and conventional plowing tillage without crop straw return, and the average wheat yield was 7.09 Mg ha–1.
2.2. Experimental design and management The experimental treatments included: 5-year rotary tillage without maize straw applied (RT); 5-year rotary tillage with maize straw applied (RS); annual RS with additional deep plowing at a 2-year interval (RS/DS). We used a randomized complete block design with three replicates (nine plots). Each plot was 30.0 m×4.0 m (16 rows of winter wheat spaced 25 cm apart). Winter wheat cultivar Jimai 22 (broadly planted in this region) was used. In each growing season of winter wheat, 112.5 kg ha–1 N (as urea), 105 kg ha–1 P2O5 (as calcium superphosphate), and 75 kg ha–1 K2O (potassium chloride) were applied to each plot as basal fertilization. Land preparation procedures and machinery used for the different treatments are shown in Table 1. At the jointing stage, 112.5 kg ha–1 N (as urea) was furrow-applied as topdressing. Seeds were sown on October 10 each year. The treatments were arranged to the same experimental plot and wheat straw was removed from the field at harvesting over the 5-year period. Harvest was done on 8 June 2012, 13 June 2013, 11 June 2014, 10 June 2015, and 12 June 2016.
2.3. Sampling and measurement At the end of the experiment, and 1 day before harvest (11 June 2016), soil was collected using a separated soil column sampler (AMS-ETC-300E, USA) from the three treatments at four layers (0–10, 10–20, 20–30, and 30–40 cm). Soil was collected from five points of each plot and well-mixed to produce a composite sample. Composite samples were passed through a 7-mm sieve without soil compaction and deformation. Pebbles and plant residues were discarded, and the samples were placed under shade to air dry. Roots of winter wheat were sampled at depths of 0–10, 10–20, 20–30, and 30–40 cm at the flowering stage (2 May 2016) of the 2015–2016 growing season. Prior to root sampling, plants in the sampling area were cut off at the soil surface. Wheat roots were collected from an area which was 0.75 m long (three rows) and 0.40 m wide. Each soil cuboid was put into a nylon net bag and washed with tap water. Roots were then removed from the mixture (including organic debris) and were floated in shallow water in a transparent tray (0.20 m×0.30 m), scanned with a flatbed scanner (Epson Perfection V700 Photo, Seiko Epson Corp,
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Table 1 Operation procedures and the equipment used of different tillage practices Tillage1) RT
RS
RS/DS
1)
2)
Operation procedure2) Total maize straw removed from the field → Base fertilizer spreading → Rotary cultivating two times with IGQN200K-QY rotary cultivator (working depth was about 10–12 cm)→ Forming the border-check → Seeding with common seeder Total maize straw returned to the field → Base fertilizer spreading → Rotary cultivating two times with IGQN-200KQY rotary cultivator (working depth was about 10–12 cm) → Forming the border-check → Seeding with common seeder The same to RS in the first two seasons. In the 3rd year: Total maize straw returned to the field → Base fertilizer spreading → Mouldboard plowing once with ILFQ330 turnover plough (working depth was about 28–30 cm) → Rotary cultivating two times with IGQN-200K-QY rotary cultivator → Forming the border-check → Seeding with common seeder→ The same to RS in the last 2 years
RT, 5-year rotary tillage without maize straw applied; RS, 5-year rotary tillage with maize straw applied; RS/DS, annual RS with additional deep plowing at a 2-year interval. The manufacturers of IGQN-200K-QY rotary cultivator and ILFQ330 turnover plough are YTO Group Corporation and Runlian Scientific and Technological Development Co., Ltd., respectively.
Japan) at a resolution of 600 dots per inch (dpi), and then analyzed with an image analyzer (WinRHIZO, Regent Instruments Canada Inc.) to measure their lengths (Dai et al. 2014). The root length density (RLD; mm cm–3) was defined as follows: RLD (mm cm–3)=TL/VS where TL (mm) was the total root length, and VS (cm3) was the volume of soil cuboid. The cutting ring (100 cm3) method was used to determine soil bulk density (SBD, g cm–3) in the 0–40 cm layer, as described by Cheng et al. (2015). A core sample was collected at random in each plot before harvest in 2015– 2016. At the time of the final harvest, all plants covering a 10-m2 area from each experimental plot were used to measure grain yield. The soil aggregates were measured by placing a soil sample (50 g) on a stack of sieves (5, 2, 1, 0.5, and 0.25 mm, respectively) fitted to a soil aggregate analyzer (TTF-100, China). The stacked sieves were immersed in water and moved up and down by 3.5 cm at a frequency of 30 cycles min–1 for 15 min. The mass proportion of aggregates that analyzed >5, 5–2, 2–1, 1–0.5, and 0.5–0.25 mm were calculated by drying and weighing the soil samples remaining on these sieves. The macro-aggregate proportion (R0.25), the mean weight diameter (MWD), and the geometric mean diameter (GMD) were calculated using standard methods, as described by Zhang et al. (2014). R0.25 (%)=
MR>0.25 MT
∑ xiw MWD (mm)= i =n1 ∑ i =1 wi n
i
∑ i =1 wilnxi n ∑ i =1 wi n
GMD (mm)=exp
where R 0.25 represents the mass percentage of soil aggregate with a diameter>0.25 mm, MR>0.25 is the weight
of aggregates>0.25 mm, MT is the weight of the soil sample (50 g), wi (%) is the weight of the aggregates in a specific size range as a fraction of the total mass of the sample analyzed, n is the number of sieves, and xi (mm) is the mean diameter of aggregates for each sieve. The wet oxidation-redox titration method was used to determine samples’ SOC content (Kou et al. 2012). An automatic Kjeldahl distillation-titration unit (Foss, Sweden) was used to determine the soil total N (TN) concentration. The carbon preservation capacity of the macro-aggregate (CPC) was then calculated as follows: n CPC (g kg–1)=∑i =1 SOCi ×wi where wi (%) is the weight proportion of soil aggregates in a specific size range relative to the total dry weight of the sample analyzed, and SOCi (g kg–1) is the SOC content for a given size of soil aggregate. The SOC storage in each soil layer of thickness (d, 10 cm in this study) was calculated as follows: SOC storage (Mg ha–1)=SOC×SBD×d×10 The SOC stocks of macro-aggregate and microaggregate (Mg ha–1) were calculated as follows: SOC stocks of macro-aggregate=C concentraton×SBD× d×fraction weight SOC stocks of micro-aggregate=SOC storage–SOC stocks of macro-aggregate where C concentration (g kg–1) refers to the SOC content in each fraction size and fraction weight is weight proportion of the fraction in the whole soil. Before treatment, we calculated the soil factors mentioned above (Table 2). The increased grain yield per unit SOC (or TN) was calculated as follows: Increased grain yield SOC TN)= Increased grain yield perper unitunit SOC (or (or TN)=
ΔGYΔGY×1 ΔGY×1 ΔGY 000000 ( ( ) ) ΔSOC ΔTN ΔTN ΔSOC where ΔGY (Mg ha–1) is the average change in grain yield relative to the level before the experiment, and ΔSOC (g kg–1) and ΔTN (mg kg–1) are changes of SOC and TN
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Table 2 The values of basic soil factors before treatment1) Depth (cm) 0–10 10–20 20–30 30–40 1)
SBD (g cm–3) 1.30 1.39 1.50 1.53
R0.25 (%) 77.24 76.02 70.44 63.72
WMD (mm) 1.21 1.15 1.09 0.93
GMD (mm) 0.82 0.79 0.72 0.63
SOC (g kg–1) 8.53 7.45 6.32 5.23
TN (g kg–1) 0.76 0.72 0.63 0.57
C/N 11.28 10.42 10.05 9.15
CPC (g kg–1) 6.41 5.40 4.21 3.23
SOC storage (Mg ha–1) 11.11 10.35 9.49 8.00
Macro-AC (Mg ha–1) 8.35 7.50 6.31 4.93
Micro-AC (Mg ha–1) 2.76 2.85 3.17 3.06
SBD, soil bulk density; R0.25, macro-aggregate proportion; WMD, mean weight diameter; GMD, geometric mean diameter; SOC, soil organic carbon; TN, total nitrogen; C/N, soil C:N ratio; CPC, carbon preservation capacity of macro-aggregate; AC, SOC stock of aggregate.
content, respectively.
1.6 1.5
2.4. Statistical analysis
3. Results 3.1. Soil bulk density Fig. 1 shows differences in SBD among the treatments in the 0–40 cm soil layers. Straw return significantly decreased SBD by 1.22–8.74% relative to pre-treatment levels, with the opposite being true for the RT treatment. Compared to RT, RS, and RS/DS significantly decreased SBD by 11.07 and 8.15% in the 0–10 cm layer; by 4.20 and 9.19% in the 10–20 cm layer; by 2.03 and 7.38% in the 20–30 cm layer; and by 2.73 and 4.16% in the 30–40 cm layer, respectively.
1.4 Soil bulk density (g cm–3)
The effects of different treatments on soil properties were tested with one-way ANOVA. All the statistical analyses were conducted using SPSS 19.0 (IBM Corp., Chicago, IL, USA). Comparisons between the treatments were conducted using the LSD method.
0–10 cm
A
b
1.3
1.1 1.6 1.5
d
C
a
a
1.4
10–20 cm b
a
1.2
B a
d
c
20–30 cm b c
c
D a
a
30–40 cm b b
1.3 1.2 1.1
PR RT RS RS/DS PR RT RS RS/DS Tillage practices
Fig. 1 The effects of different tillage practices on soil bulk density in the 0–40 cm soil layers. PR, pre-treatment level; RT, 5-year rotary tillage without maize straw applied; RS, 5-year rotary tillage with maize straw applied; RS/DS, annual RS with additional deep plowing at a 2-year interval. Vertical bars represent SE (n=3), and different letters indicate significant differences as determined by LSD method (P<0.05).
3.2. Soil aggregate
3.3. SOC and TN
The RS and RS/DS treatments significantly increased R0.25 by 3.33–8.56% and 4.09–9.88% in the 0–40 cm layer relative to pre-treatment levels, respectively (Fig. 2). The greatest increase in R0.25 was observed in the RS plots in the 0–10 cm layer; the RS/DS treatment had the highest R0.25 in the 10–40 cm layer. Compared with pre-treatment levels, the RT treatment decreased R0.25 by an average of 5.76% in the 0–40 cm layer. Straw return significantly increased MWD and GMD by 5.99 and 6.80% in the 0–40 cm layer, while RT decreased MWD and GMD by 9.63 and 7.87%, relative to pre-treatment levels. The MWD and GMD of the different tillage practices ranked as RS>RS/DS>RT in the 0–10 cm layer (Fig. 2-E and I), and RS/DS>RS>RT in the remaining layers, respectively. Meanwhile, both MWD and GMD decreased gradually with the soil depth (Fig. 2).
Compared to pre-treatment levels, SOC and TN contents significantly increased in the 0–40 cm soil layer with straw return. Conversely, SOC and TN contents decreased significantly in the RT treatment. The RS treatment had significantly higher SOC and TN contents than RS/DS in the 0–10 cm layer (Fig. 3-A and E), but notably lower contents at the remaining layers. The RT treatment decreased the soil C/N ratio in the 0–40 cm layer compared to pre-treatment levels, and soil C/N tended to decline with soil depth (Fig. 3). Compared with the RT treatment, the soil C/N increased with the RS and RS/DS treatments by 3.09 and 3.14% in the 0–10 cm layer (Fig. 3-I), by 8.06 and 8.19% in the 10–20 cm layer (Fig. 3-J), by 9.13 and 9.10% in the 20–30 cm layer (Fig. 3-K), and by 4.75 and 9.25% in the 30–40 cm layer (Fig. 3-L), respectively. Comparable values were observed between
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R0.25 (%)
90
A
80
a c
0–10 cm b
b
c
d
C
10–20 cm
B
a b
c
d
70
20–30 cm
30–40 cm
D
a a
d
c
60
MWD (mm)
1.3 E 1.2
b
c
a
0–10 cm b
F c
10–20 cm a b
G
20–30 cm a b
c
1.1
30–40 cm a c
d
0.9
d
H
d
1.0
b
b d
0.8
GMD (mm)
0.9
I
0–10 cm b
0.8
b
a
b
J
10–20 cm
a
20–30 cm
b
c
c
0.6 RT
RS RS/DS
PR
RT
30–40 cm
b
RS RS/DS
PR
RT
a c
d PR
L
a
d
0.7
K
RS RS/DS
PR
b d RT
RS RS/DS
Tillage practices
Fig. 2 Effects of different tillage practices on macro-aggregate proportion (R0.25), mean weight diameter (WMD), and geometric mean diameter (GMD) in the 0–40 cm soil layers. PR, pre-treatment level; RT, 5-year rotary tillage without maize straw applied; RS, 5-year rotary tillage with maize straw applied; RS/DS, annual RS with additional deep plowing at a 2-year interval. Vertical bars represent SE (n=3), and different letters indicate significant differences (P<0.05).
RS and RS/DS in the 0–30 cm layer, but significantly higher value was found in RS/DS in the 30–40 cm layer. SOC content had a significant and negative correlation with SBD. Conversely, a significant positive correlation was observed between SOC content and R0.25 (Fig. 4).
3.4. Carbon preservation capacity of macro-aggregate The CPC increased in the RS and RS/DS treatments compared to pre-treatment levels by 22.46 and 12.35% in the 0–10 cm layer (Fig. 5-A); by 10.49 and 22.49% in the 10–20 cm layer (Fig. 5-B); by 8.34 and 23.13% in the 20– 30 cm layer (Fig. 5-C); and by 6.64 and 26.83% in the 30–40 cm layer (Fig. 5-D), respectively. Conversely, CPC significantly decreased in the RT treatment by 9.79–17.09% in the four layers, respectively (Fig. 5).
3.5. Changes of SOC storage The SOC storage significantly changed with different tillage practices relative to pre-treatment levels (Fig. 6). SOC
storage decreased by 1.84 Mg ha–1 in the 0–40 cm soil layer in the RT treatment. The RS and RS/DS treatments significantly enhanced SOC storage by between 0.22–0.74 and 0.48–0.85 Mg ha–1 at the four soil layers, respectively (Fig. 6-A–D). These increments can mainly be credited to the increases of macro-aggregate SOC stock (Fig. 6-E–H). Conversely, the RS and RS/DS treatments reduced microaggregate SOC stock over the RT treatment in the 0–40 cm soil layer (Fig. 6-I–L).
3.6. Root length density Compared with RT (Fig. 7-A), both RS and RS/DS significantly increased RLD in the 0–40 cm layer, but the effects of the RS and RS/DS treatments on RLD varied with soil depths (Fig. 7-B and C). The RS treatment enhanced RLD compared to the RS/DS treatment in the 0–10 cm layer, but significantly reduced RLD by 6.18–26.01% in the deeper layers (Table 3). Compared with the RT and RS treatments, the RS/DS treatment significantly decreased the RLD proportion in the 0–10 cm layer by 7.88 and 13.53%, respectively. Conversely, the RS/DS treatment significantly
Soil C/N ratio
Soil TN content (g kg–1)
SOC content (g kg–1)
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10
0–10 cm c
8
a
b
B 20–30 cm
A 10–20 cm
d
c
b
0.8
a
0–10 cm c
b
d
c
E 10–20 cm
d
c
0.7
a
d
11
a
a
I
c
d
a
J a
ab
d
b bc
20–30 cm
c
a
a
RS RS/DS
PR
RT
a
RS RS/DS PR RT Tillage practices
L
a
b
RT
b
K 30–40 cm
a
b
PR
a
H
a bc
c
9 8
b
b
10–20 cm
10
a
G 30–40 cm
d c
0–10 cm a a
b
F 20–30 cm
0.6 0.5 12
D
a
6 4 0.9
C 30–40 cm
RS RS/DS
PR
RT
b
RS RS/DS
Fig. 3 Effects of different tillage practices on soil organic carbon (SOC), total nitrogen (TN) contents, and soil C/N ratio in the 0–40 cm soil layers. PR, pre-treatment level; RT, 5-year rotary tillage without maize straw applied; RS, 5-year rotary tillage with maize straw applied; RS/DS, annual RS with additional deep plowing at a 2-year interval. Vertical bars are SE (n=3), and different letters indicate significant differences (P<0.05). 1.6
A
90
B
85 80
1.4
75 70
1.3
1.1
y=3.84x+45.36 R2=0.86**
y=–0.07x+1.91 R2= 0.96**
1.2
4
6 8 10 SOC content (g kg–1)
12 4
6 8 10 SOC content (g kg–1)
R0.25 (%)
SBD (g cm–3)
1.5
65 60 55 12
Fig. 4 Correlation between soil organic carbon (SOC) content and soil bulk density (SBD, A) and macro-aggregate proportion (R0.25, B) in the 0–40 cm soil layer. **, P<0.01.
increased the RLD proportion in the 20–30 and 30–40 cm layers. Significant differences were not observed among tillage treatments in the 10–20 cm layer (Table 3). The SBD in the 0–10, 10–20, and 20–30 cm layers negatively correlated with RLD in the soil layers immediately below (i.e., 10–20, 20–30, 30–40 cm) (Table 4). Meanwhile, TN contents of 0–10, 10–20, 20–30, and 30–40 cm soil
layers positively correlated with RLD in the same soil layer (Table 4).
3.7. Grain yield The RT treatment reduced grain yield throughout the 5-year study period by 0.11, 0.37, 0.58, 0.85, and 1.07 Mg ha–1
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CPC of macro-aggregate (g kg–1)
8
c
6
d
compared the pre-treatment level (7.09 Mg ha–1) (Fig. 8). In 2011–2012 and 2012–2013, the RS treatment increased grain yield by 3.59 and 6.64% relative to the pre-treatment level, respectively. However, the grain yield increments became lower after 2013–2014. Compared with the RS treatment, the RS/DS treatment significantly increased grain yield by 5.89, 11.81, and 20.21% in 2013–2014, 2014–2015, and 2015–2016, respectively (Fig. 8). Grain yield was enhanced with increasing SOC (g kg–1) and TN (mg kg–1) contents in the four layers. Increasing SOC content in the 20–30 and 30–40 cm layers could lead to significantly higher grain yields than commensurate increases in the 0–10 and 10–20 cm layers (Fig. 9-A). A similar tendency was observed for TN content in the 0–40 cm layer, but there were no significant differences between the 20–30 and 30–40 cm layers (Fig. 9-B).
10–20 cm
a 0–10 cm B b
A
a
b
c d
4 2 20–30 cm
8 C 6 c
4 2
d
PR
RT
b
30–40 cm
D
a c
a
b
d
RS RS/DS PR RT Tillage practices
RS RS/DS
SOC storage of macroaggregate (Mg ha–1)
SOC storage of bulk soil (Mg ha–1)
Fig. 5 Effects of different tillage practices on the carbon preservation capacity of macro-aggregate (CPC) in the 0–40 cm soil layers. PR, pre-treatment level; RT, 5-year rotary tillage without maize straw applied; RS, 5-year rotary tillage with maize straw applied; RS/DS, annual RS with additional deep plowing at a 2-year interval. Vertical bars are SE (n=3), and different letters indicate significant differences (P<0.05).
13 12
b
11
b
4.1. Soil properties affected by tillage This study shows straw return significantly reduces the SBD
10–20 cm
B b
10
a
20–30 cm
C
c
c
b
a
d
c
8 7 10 9
a 0–10 cm b
E c
8
F
d
10–20 cm a b
c
7
G
d
6
20–30 cm
c
b
3.0
I
0–10 cm
a b
a
J
a b
b
b
2.5
10–20 cm
a
b
30–40 cm
a c
20–30 cm a
b
a
a
d
K
d
b
H
5
3.5
30–40 cm
D
a
9
4 4.0
SOC storage of microaggregate (Mg ha–1)
cm a 0–10 a
A
4. Discussion
L
b d
a
a
PR
RT
c
30–40 cm a
b
2.0 1.5 1.0
PR
RT
RS RS/DS
PR
RT
RS RS/DS PR Tillage practices
RT
RS RS/DS
RS RS/DS
Fig. 6 Effects of different tillage practices on total soil organic carbon (SOC) storage and aggregate SOC stock in the 0–40 cm soil layers. PR, pre-treatment level; RT, 5-year rotary tillage without maize straw applied; RS, 5-year rotary tillage with maize straw applied; RS/DS, annual RS with additional deep plowing at a 2-year interval. Vertical bars are SE (n=3), and different letters indicate significant differences (P<0.05).
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A
B
C
0–10 cm 10–20 cm 20–30 cm 30–40 cm
Fig. 7 Contrast diagram of spatial heterogeneity of root length density distribution affected by different tillage practices, representing the 5-year rotary tillage without maize straw applied (RT, A), 5-year rotary tillage with maize straw applied (RS, B), and annual RS with additional deep plowing at a 2-year interval (RS/DS, C) treatments. Table 3 Effects of tillage practices on root length density in 0–40 cm soil layer1) Treatment2) RT RS RS/DS
0–10 cm 16.06 c/35.82 b 20.04 a/38.16 a 18.43 b/33.03 c
10–20 cm 13.69 c/30.55 a 15.17 b/28.89 a 16.17 a/28.98 a
20–30 cm 8.95 c/19.96 b 10.50 b/20.00 b 12.01 a/21.53 a
30–40 cm 6.13 c/13.67 b 6.80 b/12.95 b 9.19 a/16.46 a
1)
Red and blue figures indicate root length density and its proportion in different soil layers, respectively. RT, 5-year rotary tillage without maize straw applied; RS, 5-year rotary tillage with maize straw applied; RS/DS, annual RS with additional deep plowing at a 2-year interval. Different lowercase letters indicate significant differences (P<0.05). 2)
Table 4 Correlation analysis (r) between soil bulk density and root length density (RLD), and soil total nitrogen content and root length density in different soil layers RLD 0–10 cm 10–20 cm 20–30 cm 30–40 cm *
, P<0.05; **, P<0.01.
Grain yield (Mg ha–1)
9
Soil bulk density (g cm–3) 10–20 cm 20–30 cm –0.46 –0.29 –0.83** –0.77** –0.81** –0.74* –0.77** –0.75**
0–10 cm –0.87** –0.68* –0.58 –0.33
2012–2013 C
2013–2014 D
a
b
2014–2015 E a
a b
Soil total nitrogen (g kg–1) 10–20 cm 20–30 cm 0.58 0.4 0.96** 0.83** 0.94** 0.90** 0.87** 0.93**
a
a
a
b
c
c
RT
RS RS/DS
RT
RS RS/DS
RT RS RS/DS Tillage practices
RT
1
2015–2016 a
b
b
c
6 5
30–40 cm 0.45 0.78** 0.86** 0.79**
–1
8 7
0–10 cm 0.90** 0.74* 0.67* 0.44
2011–2012 B
A
30–40 cm –0.52 –0.73* –0.63* –0.52
RS RS/DS
RT
RS RS/DS
Fig. 8 Effects of different tillage practices on grain yield during the study period. PR, pre-treatment level; RT, 5-year rotary tillage without maize straw applied; RS, 5-year rotary tillage with maize straw applied; RS/DS, annual RS with additional deep plowing at a 2-year interval. Vertical bars are SE (n=3), different letters indicate significant differences (P<0.05).
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2.0
A
0.08
B
a
1.5
1.0
a b
c c
a
0.5
0
b
0–10
0.06
10–20 20–30 30–40
0–10
b
10–20 20–30 30–40
0.04
0.02
0
Grain yield increment per unit TN (Mg ha–1)
Grain yield increment per unit SOC (Mg ha–1)
CHEN Jin et al. Journal of Integrative Agriculture 2020, 19(5): 1215–1226
Soil layers (cm)
Fig. 9 Effects of different tillage practices on grain yield rate caused by soil organic carbon (SOC) and total nitrogen (TN) changes. Vertical bars are SE (n=3), different letters indicate significant differences (P<0.05).
in the 0–40 cm soil layer compared with straw removal, in accord with previous findings (Rawls et al. 1998). The increase in SOC content could account for this improvement, as SBD has been found to be negatively correlated with SOC content (Wang et al. 2018), consistent with our observation (Fig. 4). Higher SOC and TN contents associated with straw return are generally considered important factors for aggregation (Six et al. 2002; Tong et al. 2009; Li et al. 2010, 2017; Karami et al. 2012; Zhao H L et al. 2018). SOC accumulation in cropland was mostly determined by the balance between the crop residue inputs and the export of new and old soil organic matter decomposition (Kou et al. 2012; Zhang et al. 2012). Incorporating straw significantly increased C inputs into soil (Liu et al. 2019) and promoted soil aggregation (Huang et al. 2018), which could reduce or offset the loss of SOC (Laird and Chang 2013; Li et al. 2016). Meanwhile, straw return significantly improved the mass proportion, stability, and CPC of macro-aggregate, which indicates a synergistic relationship between soil aggregation and SOC accumulation. Previous studies have shown straw incorporation contributes more to C/N than root inputs alone (Puget and Lal 2005; Tan et al. 2007), consistent with our findings (Fig. 3). Our experiment indicates that conversion from rotary tillage to deep plowing changed the vertical distribution of soil factors (SBD, aggregate, SOC storage, soil N, etc.) in the soil profile, improving soil factors in the deeper plough layer, especially in the 20–30 and 30–40 cm layers. Continuous rotary tillage tended to shallow plough layer, and thicken and harden the plough pan upward to the topsoil, which critically limited the subsoil’s capacity to preserve SOC (Zhao Y C et al. 2018). That deep plowing induced changes in soil factor distribution with depth was likely a result of two
causes: redistribution of topsoil nutrients and root growth promotion. First, the topsoil has most of the nutrients, and deep plowing can move maize straw and surface nutrients into the subsoil. Second, deep plowing thickens the plough layer down to the 20–40 cm layers, changes the soil’s physical condition, and promotes more wheat root growth in those loose soil layers (Luo et al. 2010), thereby enhancing carbon input.
4.2. Root distribution affected by tillage Root systems depend on the soil, and changes in soil properties have significant impacts on root action (Curaqueo et al. 2011; Xu et al. 2018). Our findings demonstrated that straw return significantly increased RLD in the 0–40 cm soil layers (Table 3). Straw return enables the soil to create a complex decomposition sub-system, and it could buffer the impact of external forces, and accumulate nutrients and energy, both of which are beneficial for growing roots (Song et al. 2016). Tillage-induced various distribution of nutrient and physical conditions, which led to spatial heterogeneity of RLD in the plough layer (Fig. 7). Rotary tillage reduced nutrient concentration, decreased soil disturbance, and increased soil compaction in the 20–40 cm layers. It not only inhibit root growth into the deeper layers (Benjamin and Nielsen 2006; Bengough et al. 2011; Mu et al. 2016), but also limited the downwards movement of topsoil nutrients.
4.3. Wheat grain yield affected by tillage Straw removal resulted in soil compaction within the topsoil layers, which produced soil factors detrimental for crop growth and a consequent reduction in yield (Mele and Crowley 2008). Similarly, in our experiment,
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the RT treatment significantly decreased grain yield over the duration of the study. The RS treatment significantly increased grain yield during the first 2 years (Fig. 8), as reported by others (Wang et al. 2015; Zhang et al. 2016). However, grain yield reduction was observed in the following two seasons, and grain yield in the final year of the study was comparable to the pre-treatment level (Fig. 8). This suggests straw return could not maintain high and stable production when inappropriate tillage was applied (Chen et al. 2017; Li et al. 2018). Continuous rotary tillage would induce an adverse soil structure, poor nutrient density in the deeper plough layer, and ultimately reduced wheat production (Kong 2014; He et al. 2019). Compared with the RS treatment, the RS/DS treatment significantly increased grain yield after deep plowing was applied (Fig. 8), which could be explained by higher root length density (Fig. 7), and increased SOC and TN contents in the 20–40 cm soil layers (Fig. 9). With improved soil conditions in the 0–20 cm layer over the pre-treatment level, the RS/DS treatment led to a harvest of more grain, which suggests appropriately improving soil quality in topsoil was indispensable.
5. Conclusion Straw return decreased SBD, facilitated soil aggregation and SOC preservation, and increased RLD in each soil layer. The improved soil factors and increased RLD in the subsoil had greater effects on grain yield than similar changes in the topsoil. A significant improvement of soil properties and increased RLD in the subsoil were observed in the RS/ DS treatment, which also had the highest grain yield. The above results demonstrated that RS/DS could be a more efficient and operable approach to improve both soil quality and wheat production in the NCP.
Acknowledgements The research was supported by the National Basic Research Program of China (973 Program; 2015CB150404), the National Key Research and Development Program of China (2017YFD0301001 and 2016YFD0300403), and the Shandong Province Mount Tai Industrial Talents Program, China.
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