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Effects of subsoiling before winter wheat on water consumption characteristics and yield of summer maize on the North China Plain
Agricultural Water Management 227 (2020) 105786
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Effects of subsoiling before winter wheat on water consumption characteristics and yield of summer maize on the North China Plain
T
Naikun Kuanga, Dechong Tana, Haojie Lia, Qishu Goua, Quanqi Lia,⁎, Huifang Hanb,⁎ a b
College of Water Conservancy and Civil Engineering, Shandong Agricultural University, Tai’an, 271018, China College of Agronomy, State Key Laboratory of Crop Biology, Shandong Agricultural University, Tai’an, 271018, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Subsoiling Soil stable infiltration rate Soil moisture Water–saving agriculture Soil water consumption
As an important industry for national development, summer maize production occupies a key position in China and globally. However, agricultural water consumption is becoming increasingly problematic, and global climate change and long-term traditional rotary tillage have negative effects on the soil surface layer. Subsoiling has been an effective measure to improve soil surface-layer structure and increase yield. In the present study, field experiments were conducted to compare the effects of subsoiling and rotary tillage in winter wheat and summer maize double cropping systems. Subsoiling treatments at a depth of 40 cm (S40) and 35 cm (S35), and rotary tillage at a depth of 15 cm (R15) before winter wheat planting were used, and the effects of tillage methods on soil stable infiltration rate, soil water consumption, evapotranspiration, grain yield, and crop water productivity (CWP) in summer maize growing seasons were determined. The results showed that subsoiling significantly improved soil infiltration rate. Water consumption in the subsoiling treatments increased significantly, and especially promoted the crops to utilize soil water at depths below 60 cm in the soil profile. As a result, compared with R15, kernel numbers per row and 1000–grain weight in S35 were significantly increased; therefore, both grain yield and CWP were significantly improved. Our results indicate that the S35 treatment is a reasonable subsoiling measure on the North China Plain, which can increase both summer maize grain yield and CWP in double cropping systems.
1. Introduction Summer maize production occupies an important position in China and globally. The North China Plain (NCP) is an important grain production region, and a large proportion of the sown area consists of summer maize. However, there is an increasingly prominent discrepancy between supply and demand. The implementation of water resource allocations for agricultural production in the region increases tensions (Leng et al., 2015). Global climate change leads to increased occurrence of extreme droughts, and many crops, including summer maize, are facing problems with stagnant or decreasing yields (Ren et al., 2018b). In recent years, the development of water–saving agricultural production methods has attracted much attention. Conservation tillage strategies (e.g., no–tillage, low–tillage, and subsoiling) have been developed that are more beneficial in terms of regulating soil water transport and consumption than rotary tillage methods, resulting in increased yield (Qin et al., 2008; Bogunovic et al., 2018). Implementing conservation tillage is important to achieve efficient water use and sustainable development of agriculture.
⁎
The main cropping system on the NCP consists of wheat–maize continuous cropping. In this cropping system, different tillage methods are usually applied before winter wheat planting, and the traditional method involves rotary tillage (farming depth about 15 cm). Guan et al. (2014) showed that short-term rotary tillage can improve soil moisture content and crop yield. However, long-term rotary tillage will lead to the formation of the bottom layer of the plough, which is often obstructed by the crop root system (Moreira, 2016; Yu et al., 2016). Longterm single rotary tillage and the movement of agricultural machinery aggravate the surface structure of the soil, and the average surface depth becomes shallow (16.5 cm) (Zhang and Li, 2010). As a result, the ability of water and fertilizer conservation decrease significantly, which has an adverse effect on the growth of summer maize. Optimizing farming methods can improve the surface layer structure and increase crop yield. Currently, the main problem on the NCP concerns the formation of a reasonable tillage layer to form a solid bottom using perennial rotary tillage. Subsoiling is an effective measure to break the plow sole. Previous studies have shown that subsoiling under stable soil conditions
Corresponding authors. E-mail addresses: [email protected] (Q. Li), [email protected] (H. Han).
https://doi.org/10.1016/j.agwat.2019.105786 Received 7 May 2019; Received in revised form 3 September 2019; Accepted 9 September 2019 0378-3774/ © 2019 Elsevier B.V. All rights reserved.
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2.2. Experimental design
can alleviate the effects of drought stress on crops, improve soil production potential, and increase yield by about 20% (Schneider et al., 2017). More specifically, studies have shown that subsoiling can improve soil properties, nutrient-use efficiency and crop water productivity (CWP), and promote crop growth and development, compared with conventional tillage methods. Subsoiling (at a depth of 35–40 cm) can effectively increase water infiltration, by removing the resistance from the solid bottom layer (Kaur and Arora, 2019; Varsa et al., 1997; Bogunovic et al., 2018). In addition, Tao et al. (2015) showed that subsoiling can effectively decrease the bulk density of the surface layers, alleviating soil compaction. Zhang et al. (2017) also showed that subsoiling can increase the connectivity of soil pores, especially that of large soil pores. Meanwhile, studies have shown that subsoiling increases nutrient accumulation and soil water content, which serves to both reduce drought stress and provide a more favorable soil environment for root system growth and yield increase (Cai et al., 2014; Zhai et al., 2017). Furthermore, Yu et al. (2016) and Sun et al. (2017) showed that subsoiling promoted the growth of crop roots, which utilized the nutrients and water in the deeper soil layers, increasing the nutrient -use efficiency and CWP. Most previous studies selected the appropriate depth for subsoiling according to the conditions of the site under investigation (e.g., soil type, cultivation mode, and rainfall); this depth was usually from 30 to 50 cm (Cai et al., 2014; Jabro et al., 2016; Sun et al., 2018). Previous studies have mostly focused on depths of 30–40 cm (Mu et al., 2016; Shao et al., 2016). However, to our knowledge, there has been no research on the suitable subsoiling depth on the NCP. As the depth of cultivation increases, so does the cost of production, which is not conducive to environmental protection and the increase of farmers' output and income. Therefore, two subsoiling treatments (at 40 cm and 35 cm) were set in the present study, and the traditional rotary tillage method was used as the control. We measured the dynamic changes in soil moisture, crop water consumption, and CWP to find the optimal depth for subsoiling in this area. We hypothesized that subsoiling could increase water infiltration rate and soil water content, and thus increase grain yield and CWP compared with rotary tillage. Therefore, in this experiment, our goal was to determine the following: (1) soil infiltration rate after subsoiling treatments on continuous rotary tillage test plots; (2) water use of summer maize under different topsoil structure conditions; and (3) which of the two depths tested (40 cm or 35 cm) performs better in terms of grain yield and CWP for subsoiling. Answering the above questions can provide choice space and practical experience for optimizing farming mode and constructing reasonable surface layer structure in rain–fed agriculture mode on the NCP.
In the 2017 and 2018 summer maize growing seasons, three treatments were applied: rotary tillage (15 cm, R15), subsoiling (40 cm, S40), and subsoiling (35 cm, S35). Subsoiling treatment was applied once every two years. In this experiment, subsoiling was treated before winter wheat was planted in 2016. The subsoiling procedure was: before sowing winter wheat, subsoiling (40 and 35 cm) was applied, then rotary tillage was applied (15 cm). After the winter wheat was harvested, winter wheat straw was crushed and returned to the field. Before sowing summer maize, fertilizer (effective N content of urea was 46.6%) was applied and the whole plot was rotated again (depth of rotation was 15 cm). Finally, a spoon-wheel maize precision seeder was used for sowing. Summer maize was planted with row spacing of 60 cm, plant spacing of 22.5 cm, and planting density of 7.5 × 104 plants/hm2. Three replicates were set for each treatment, with a total of nine plots. Before sowing, urea was applied as a base fertilizer with a dosage of 280 kg/hm2, and the same amount of urea was applied at the jointing stage. Summer maize was planted on June 9, 2017 and June 13, 2018, and was harvested on October 5, 2017 and October 7, 2018, respectively. No irrigation was applied during both summer maize growing seasons. The summer maize variety for the experiment was “Zhengdan 958,” which has been widely planted on the NCP. 2.3. Measurements 2.3.1. Soil stable infiltration rate At the summer maize maturity stage, the stable infiltration rate of soil water in each plot was measured with the single-ring soil water infiltration meter. In each plot, soil that had not been damaged by human activity was selected, then the infiltration ring was inserted into the soil, stopping at the mark on the outer edge of the ring. There was 4 cm of water maintained in the ring using a variable flow bottle, and the calibration of the bottle was recorded at regular intervals, until the water level in the bottle no longer changed. The amount of infiltration water was considered to be the amount of water used in the bottle minus the residual water above the soil. Soil infiltration rate i was calculated as follows:
i=
ΔL × AM ÷δ AH × Δt
where, i is soil water infiltration rate (cm/h); Δ L is the variable flow bottle water level change (cm); AM is the cross–sectional area of the variable flow bottle (cm2); AH is the cross–sectional area of infiltrated soil (cm2); Δ t is the infiltration time (h); δ is the error rate of a single ring soil water infiltration meter (1.84).
2. Material and methods 2.1. Experimental site
2.3.2. Soil moisture content The volumetric moisture content of soil in the 0–130 cm layer was measured using Time Domain Reflectometry (IMKO company, Germany) with a depth interval of 10 cm. The soil volume water content was corrected in the 0–10 cm layer using a W.E.T sensor kit soil temperature and humidity meter (Delta–t Company, UK). In the summer maize growing seasons, average soil moisture content was measured every 10 days, and additional measurements were conducted before and after rainfall. Soil water consumption in maize seasons was calculated as the soil moisture content in 0–130 cm on harvesting day deducted from the initial soil moisture content on the sowing day (Li et al., 2012).
The study was carried out in the summer maize growing season of 2017 and 2018, in the agriculture experimental station of Shandong Agricultural University (36°10′19″ N, 117°9′03″ E), which is on the NCP. Since 2004, the experimental field has been continuously rotated before sowing. The bottom soil layer was solid and impermeable, and the surface layer becomes shallower year by year. The experimental site has a temperate continental monsoon climate. The average precipitation from June to September is 453.7 mm, which can basically meet the water consumption of summer maize. The area receives 2461 h of accumulated annual sunshine. In the 2017 and 2018 summer maize growth seasons, total rainfall was 389.5 mm and 447.0 mm, respectively (Fig. 1). The soil in the experimental field is loam, the basic properties of the surface soil under each treatment are shown in Table 1. Soil mechanical compositions at the experimental site are shown in Table 2. In the experimental field, the 0–30 cm soil layer was loam, and the 30–120 cm layer was silty sandy loam.
2.3.3. Evapotranspiration ET in the summer maize growing seasons was calculated using water balance equation (Li et al., 2010): ET = P + I – D – R + W + ΔSWC 2
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Fig. 1. Rainfall and average temperature in 2017 and 2018 summer maize growing seasons.
where, ET is evapotranspiration (mm); P is precipitation (mm), provided by weather stations near the field; I is irrigation water (mm), and no irrigation was applied during both growing seasons, so I was zero; D is soil water drainage (mm); R is surface runoff (mm), but there were beds around each plot, so there was no surface runoff in the experiment; W is groundwater recharge in the experimental site (mm), but underground water level was more than 5 m in our study, so W was ignored; and ΔSWC was the change in soil water storage capacity in 0–130 cm soil profiles during the summer maize growing seasons (mm). In 2018, owing to the occurrence of heavy rain during the growing season of the summer maize, soil water drainage was measured using the water balance method (Gong and Li, 1995; Tracy et al., 1997). When the soil moisture content at 1.3 m was equal to or less than the field moisture capacity, the soil water drainage was zero (the field moisture capacity of the 0–40-cm layer was calculated according to Table 1, and that below 40 cm was calculated according to 25.73%). However, when the soil water content at 1.3 m was more than the field moisture capacity, soil water drainage was calculated as the difference between the soil moisture content and field moisture capacity.
Table 2 Soil mechanical compositions at the experimental site. Soil depth (cm)
0–10 10–20 20–30 30–40 40–60 60–80 80–100 100–120
Percentage of particle content (%)
Soil texture classification
< 0.002 mm
0.02–0.002 mm
2–0.02 mm
4.50 4.57 4.85 5.49 6.10 6.34 6.40 6.64
40.51 43.17 42.57 46.81 48.83 48.74 50.22 53.01
54.99 52.26 52.58 47.70 45.07 44.92 43.38 40.34
loam loam loam silty sandy silty sandy silty sandy silty sandy silty sandy
loam loam loam loam loam
the whole summer maize growing seasons (mm). 2.4. Statistical analysis Microsoft Excel 2010 and SPSS Statistics 18.0 were used for statistical analysis. When significance was observed, the least significant difference (LSD) was used to conduct comparisons at a significance level of α = 0.05.
2.3.4. Grain yield and yield compositions When the plants reached maturity, spike numbers in each plot were counted. Then, spikes in 1.5 m × 1.5 m were hand collected, and the row numbers per spike and kernel numbers per row were counted. After air drying, the 1000–kernel weight and grain yield were recorded.
3. Results 3.1. Soil stable infiltration rate
2.3.5. Crop water productivity (CWP) CWP was calculated as follows (Faramarzi et al., 2010):
At the summer maize maturity stage in 2017, the soil stable infiltration rate in the S40 and S35 treatments was significantly higher than that in R15 by 89.1% and 58.1%. In 2018, the soil stable infiltration rate in S40 and S35 was significantly higher than that in R15
CWP = Y/ET where, Y is grain yield (kg/m2) and ET is the evapotranspiration over Table 1 Basic properties of soil in experiment plots under different treatments. Treatment
Available P (mg/kg)
Available K (mg/kg)
Alkaline hydrolysis nitrogen (mg/kg)
Soil origin carbon (mg/g)
Field Capacity (%)
R15 S40 S35
91.7 82.4 86.1
91.5 84.5 80.1
238.2 226.9 244.2
7.4 7.4 6.6
29.0 30.0 28.0
R15 represents rotation tillage of 15 cm, S40 represents subsoiling of 40 cm, and S35 represents subsoiling of 35 cm, respectively. 3
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Fig. 2. Soil stable infiltration rate at summer maize maturity stages in 2017 and 2018. R15 represents rotation tillage of 15 cm, S40 represents subsoiling of 40 cm, and S35 represents subsoiling of 35 cm, respectively. Vertical bars are standard errors.
treatment increases the soil water consumption in maize seasons in the deeper soil layers. This means that crops can utilize deep soil water for their growth and development.
by 89.9% and 63.3%, respectively (Fig. 2). The soil stable infiltration rate in 2018 was higher than that in 2017. The soil stable infiltration rate in R15, S40, and S35 in 2018 was higher than in 2017 by 3.6%, 4.0%, and 7.0%, respectively.
3.3. Grain yield and yield compositions 3.2. Soil water consumption in maize seasons Table 3 shows grain yield and yield compositions in the 2017 and 2018 summer maize growing seasons. During the two–year experiment, the experimental results showed that the subsoiling treatment improved kernel number per row, 1000–grain weight, and grain yield of summer maize. However, the treatment had no significant effect on row numbers per spike. In both growing seasons, the highest kernel numbers per row was obtained in the S35 treatment, followed by that under S40 treatment, and the lowest was found in the R15 treatment. The 1000–grain weight for S35 was significantly higher than that of R15 by
Fig. 3 shows the soil water consumption through 0–130 cm of the soil profile in the 2017 and 2018 summer maize growing seasons. In both growing seasons, the change in soil water consumption in the 0–50 cm soil layer was similar, with no significant difference being found among treatments. With the deepening of soil layer, the soil water consumption in maize seasons, when treated with subsoiling, significantly increased at 50–90 cm and 90–130 cm in the following order: S40 > S35 > R15. These results indicate that subsoiling
Fig. 3. Soil water consumption in 2017 and 2018 summer maize growing seasons. R15 represents rotation tillage of 15 cm, S40 represents subsoiling of 40 cm, and S35 represents subsoiling of 35 cm, respectively. Horizonal bars are standard errors. 4
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Table 3 Grain yield and yield compositions in 2017 and 2018 summer maize growing seasons. Treatments
Row numbers per spike (rows/spike)
Kernel numbers per row (kernels/row)
Spike numbers (Spikes × 104/ha)
1000-kernel weight (g)
Grain yield (g/m2)
2017 R15 S40 S35
15.7a 14.5b 14.8b
35.4b 36.9a 37.3a
7.6a 7.7a 7.6a
329.0b 339.7ab 342.7a
830.6b 911.9ab 939.8a
2018 R15 S40 S35
14.1a 14.2a 14.6a
24.7b 24.5b 24.9a
7.1a 7.2a 7.2a
388.9b 399.1a 399.8a
822.3b 857.4ab 889.5a
In each growing season, in the same column, values followed by different letters differ significantly (P < 0.05) among treatments. R15 represents rotation tillage of 15 cm, S40 represents subsoiling of 40 cm, and S35 represents subsoiling of 35 cm, respectively.
maize growth. In this experiment, the results showed that the S35 treatment had the best performance, with a balanced relationship between water consumption and grain yield. As a result, the highest CWP was observed under this treatment. There is a plow sole in the tillage layer, which hinders the infiltration of water. Drought stress caused by a lack of soil water has a major limiting effect on crop growth. It has been reported that different tillage methods have significant effects on soil water status, crop growth, and the regulation of the soil-crop system (Mosaddeghi et al., 2009; Ren et al., 2018a). Compared with rotary tillage, subsoiling broke down the plow sole and made the surface soil more porous, so that the root system could grow earlier and extend into the deeper soil layers, which was beneficial for summer maize CWP (Yan et al., 2017). Previous studies have shown that the distribution of soil water infiltration was related to the distribution pattern of the maize fiber root system, and that the connectivity between macropores plays a key role in soil water migration (Wu et al., 2009). Thus, while subsoiling created preferred paths for the flow of water, the preferred flow created by fibrous roots also guided and facilitated water infiltration into deeper soil layers (Jiang et al., 2018). In this experiment, the soil stable infiltration rate in S40 and S35 was significantly higher than that in R15, which created an effective water transport channel for timely rainfall infiltration, even to the deeper soil layers. Wang et al. (2012) and Bogunovic et al. (2018) showed that subsoiling treatment enhanced the capacity of soil water and increased maize yield. In our experiment, the stable infiltration rate under the subsoiling treatment was higher than that under the rotary tillage treatment, which allowed the water to infiltrate the deep soil (below 60 cm) and increased the water utilization in the later stage of summer maize growth. Tillage methods significantly changed the topsoil environment and greatly affected maize yield (Tao et al., 2015). Under more adequate water conditions, subsoiling delayed summer maize leaf senescence and maintained a higher leaf area index and photosynthetic rate, laying a solid physiological foundation for the final yield increase (Sun et al., 2017). In terms of water consumption, the results of this experiment showed that the evapotranspiration of subsoiling treatment was significantly higher than that of rotary tillage treatment. Subsoiling machinery works effectively to break the plow sole and better tillage layer structure is beneficial to the downward growth of summer maize root systems. Yu et al. (2016) showed that subsoiling at 38 cm significantly increased water consumption. In our study, the results were similar, more soil water was consumed under the subsoiling treatments compared with that under the rotary tillage, especially soil water below 50 cm. Hsiao (2000) indicated that maize root system under the condition of drought response mechanism, water transport is a process of absorption, root in the soil played a vital role in the extraction of moisture. Root systems absorb the deep soil water after hydraulic promotion functions and balances the water levels in the plants, providing resistance to drought stress (Cai et al., 1993). At the same time, another important reason for the significant increase in water consumption in the subsoiling treatment is that this
4.2% in 2017, and the 1000–grain weight for S35 and S40 was significantly higher than that of R15 by 2.6% and 2.8% in 2018, respectively. In 2017, grain yield in S35 increased by 13.1% and 3.0% compared with R15 and S40, respectively. In 2018, gain yield in S35 increased by 8.3% and 3.7% compared with R15 and S40, respectively. However, owing to precipitation, grain yield in R15, S40, and S35 was lower in 2018 than in 2017 by 1.1%, 6.0%, and 5.3%, respectively. 3.4. ET and crop water productivity Table 4 shows ET and CWP in 2017 and 2018 summer maize growing seasons. There was no significant difference in soil water consumption between R15 and S35 in these growing seasons; however, soil water consumption in S40 was significantly higher than that in R15 in the first and second growing seasons. The two–year experiment showed that subsoiling treatment significantly increased ET in the following order: S40 > S35. In both growing seasons, CWP was significantly higher in S35 than that in S40 and R15. In 2017, CWP in S35 was significantly higher than in R15 and S40 by 10.2% and 9.1%, respectively. In 2018, CWP in S35 was significantly higher than in R15 and S40 by 7.5% and 7.5%, respectively. In addition, CWP in R15, S40, and S35 was much lower in 2018 than that in 2017 by 1.9%, 2.3%, and 4.2%, respectively. 4. Discussion Many previous studies have shown that subsoiling improved the physical properties of continuous no-tillage or rotary tillage soils and increased the yield of food crops (Putte et al., 2012; Cai et al., 2014). In the present study, subsoiling at depths of 35 cm and 40 cm were tested. Compared with rotary tillage, the subsoiling treatments promoted the absorption and use of water from the deeper soil layers during summer Table 4 ET and crop water productivity in 2017 and 2018 summer maize growing seasons. Treatments
Soil water consumption (mm)
Soil water drainage (mm)
ET (mm)
CWP (kg/ m³)
2017 R15 S40 S35
–96.4b –70.2a –90.3b
– – –
293.1b 319.3a 299.3b
2.8b 2.9b 3.1a
2018 R15 S40 S35
–36.7b 7.8a –13.8ab
22.2b 46.5a 44.3a
387.1b 404.4a 388.5b
2.1b 2.1b 2.3a
In each growing season, in the same column, values followed by different letters differ significantly (P < 0.05) among treatments. R15 represents rotation tillage of 15 cm, S40 represents subsoiling of 40 cm, and S35 represents subsoiling of 35 cm, respectively. 5
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treatment can improve the photosynthetic performance and transpiration rate of summer maize (Xu et al., 2017). As we all know, summer maize transpiration plays a leading role in farmland evapotranspiration, which increases soil water consumption. In general, the evapotranspiration of the subsoiling treatment was significantly higher than that of the rotary tillage treatment. On this physical basis, it is possible for crop growth to increase and to achieve increased yield and ultimately improve CWP. Tian et al. (2016) pointed out that the conditions of their study area were under the influence of many factors such as rainfall and farming methods, and the changes in yield and CWP were similar to our results. In our experiment, summer maize grain yield in 2018 showed a different degree of decrease compared with that in 2017. The main reason may be related to heavy rainfall, which was concentrated during the flowering stage, resulting in decreased quality of pollination and spike numbers (Shao et al., 2016; Gao et al., 2018). In view of the deterioration of soil structure caused by continuous rotary tillage on the NCP, subsoiling at 35 cm and 40 cm could provide improvements, by increasing soil stable infiltration rate, water consumption, and grain yield. In our experiment, the subsoiling treatment S35 balanced the relationship between water content and grain yield and reached the highest CWP. Therefore, the results suggest that subsoiling at 35 cm before winter wheat (once every two years) should be taken as the preferred tillage method for promoting increased crop yields on the NCP. This experiment mainly studied soil water dynamics and crop water consumption characteristics, but the response of photosynthesis and fluorescence of summer maize to subsoiling at different depths remains unclear. At the same time, the study of soil infiltration mechanisms is also of great significance.
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Tillage and crop residue effects on rainfed wheat and maize production in Northern China. Field Crops Res. 132, 106–116. Wu, J.Q., Zhang, J.F., Gao, R., 2009. Physical simulation experiments of effects of macropores on soil water infiltration characteristics. Tran. Chin. Soc. Agric. Eng. 25, 13–18. Xu, J., He, Z.K., Feng, Q.Q., Zhang, Y.Y., Li, X.S., Xu, J.J., Lin, X., Han, H.F., Ning, T.Y., Li, Z.J., 2017. Effect of tillage method on photosynthetic characteristics and annual yield formation of winter wheat–summer maize cropping system. Plant Nutr. Fert. Sci. 23, 10–109. Yan, Z.X., Gao, C., Ren, Y.J., Zong, R., Ma, Y.Z., Li, Q.Q., 2017. Effects of pre–sowing irrigation and straw mulching on the grain yield and water use efficiency of summer maize in the North China Plain. Agric. Water Manage. 186, 21–28. Zhai, L.C., Xu, P., Zhang, Z.B., Li, S.K., Xie, R.Z., Zhai, L.F., Wei, B.H., 2017. Effects of deep vertical rotary tillage on dry matter accumulation and grain yield of summer maize in the Huang–Huai–Hai Plain of China. Soil Till. Res. 170, 167–174. Zhang, S.H., Li, S.K., 2010. Domestic and Foreign Corn Industrial Technology Development Report. China Agricultural Science and Technology Press, Beijing. Zhang, Y.J., Wang, R., Wang, S.L., Wang, H., Xu, Z.G., Jia, G.C., Wang, X.L., Jun, Li, 2017. Effects of different subsoiling frequencies incorporated into no–tillage systems on soil properties and crop yield in dryland wheat–maize rotation system. Field Crops Res. 209, 151–158.
5. Conclusions Subsoiling significantly improved soil stable infiltration rate, summer maize water consumption, and grain yield. Subsoiling S35 balanced the relationship between soil water content and grain yield, and achieved the highest CWP. Therefore, our results suggest that 35 cm can be used as a reasonable subsoiling depth to improve summer maize grain yield and CWP on the NCP. Acknowledgements This work was financially supported in part by the National Nature Science Foundation of China (31771737), by the Key Research and Development Plan in Shandong Province, China (2019GSF109054), and by the Funds of Shandong “Double Tops” Program (SYL2017YSTD02). References Bogunovic, I., Pereira, P., Kisic, I., Sajko, K., Sraka, M., 2018. Tillage management impacts on soil compaction, erosion and crop yield in Stagnosols (Croatia). Catena 160, 376–384. Cai, H.G., Ma, W., Zhang, X.Z., Ping, J.Q., Yan, X.G., Liu, J.Z., Yuan, J.C., Wang, L.C., Dawson, T.E., 1993. Hydraulic lift and water use by plants: implications for water balance, performance and plant–plant interactions. Oecologia 95, 565–574. Cai, H.G., Ma, W., Zhang, X.Z., Ping, J.Q., Yan, X.G., Liu, J.Z., Yuan, J.C., Wang, L.C., Ren, J., 2014. Effect of subsoil tillage depth on nutrient accumulation, root distribution, and grain yield in spring maize. Acta Agron. Sin. 2, 297–307. Faramarzi, M., Yang, H., Schulin, R., Abbaspour, K.C., 2010. Modeling wheat yield and crop water productivity in Iran: implications of agricultural water management for wheat production. Agric. Water Manage. 97, 1861–1875. Gao, Z., Feng, H.Y., Liang, X.G., Zhang, L., 2018. Limits to maize productivity in the North China Plain: a comparison analysis for spring and summer maize. Field Crops Res. 228, 39–47. Gong, Y.S., Li, B.G., 1995. Using field water balance model to estimate the percolation of soil water. Adv. Water Sci. 6, 16–21. Guan, D.H., Mahdi, M.A., Zhang, Y.S., Duan, L.S., Tan, W.M., Zhang, M.C., Li, Z.H., 2014. Tillage practices affect biomass and grain yield through regulating root growth, root–bleeding sap and nutrients uptake in summer maize. Field Crops Res. 157, 89–97. Hsiao, T.C., 2000. Sensitivity of growth of roots versus leaves to water stress: biophysical
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Effects of subsoiling before winter wheat on water consumption characteristics and yield of summer maize on the North China Plain
T
Naikun Kuanga, Dechong Tana, Haojie Lia, Qishu Goua, Quanqi Lia,⁎, Huifang Hanb,⁎ a b
College of Water Conservancy and Civil Engineering, Shandong Agricultural University, Tai’an, 271018, China College of Agronomy, State Key Laboratory of Crop Biology, Shandong Agricultural University, Tai’an, 271018, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Subsoiling Soil stable infiltration rate Soil moisture Water–saving agriculture Soil water consumption
As an important industry for national development, summer maize production occupies a key position in China and globally. However, agricultural water consumption is becoming increasingly problematic, and global climate change and long-term traditional rotary tillage have negative effects on the soil surface layer. Subsoiling has been an effective measure to improve soil surface-layer structure and increase yield. In the present study, field experiments were conducted to compare the effects of subsoiling and rotary tillage in winter wheat and summer maize double cropping systems. Subsoiling treatments at a depth of 40 cm (S40) and 35 cm (S35), and rotary tillage at a depth of 15 cm (R15) before winter wheat planting were used, and the effects of tillage methods on soil stable infiltration rate, soil water consumption, evapotranspiration, grain yield, and crop water productivity (CWP) in summer maize growing seasons were determined. The results showed that subsoiling significantly improved soil infiltration rate. Water consumption in the subsoiling treatments increased significantly, and especially promoted the crops to utilize soil water at depths below 60 cm in the soil profile. As a result, compared with R15, kernel numbers per row and 1000–grain weight in S35 were significantly increased; therefore, both grain yield and CWP were significantly improved. Our results indicate that the S35 treatment is a reasonable subsoiling measure on the North China Plain, which can increase both summer maize grain yield and CWP in double cropping systems.
1. Introduction Summer maize production occupies an important position in China and globally. The North China Plain (NCP) is an important grain production region, and a large proportion of the sown area consists of summer maize. However, there is an increasingly prominent discrepancy between supply and demand. The implementation of water resource allocations for agricultural production in the region increases tensions (Leng et al., 2015). Global climate change leads to increased occurrence of extreme droughts, and many crops, including summer maize, are facing problems with stagnant or decreasing yields (Ren et al., 2018b). In recent years, the development of water–saving agricultural production methods has attracted much attention. Conservation tillage strategies (e.g., no–tillage, low–tillage, and subsoiling) have been developed that are more beneficial in terms of regulating soil water transport and consumption than rotary tillage methods, resulting in increased yield (Qin et al., 2008; Bogunovic et al., 2018). Implementing conservation tillage is important to achieve efficient water use and sustainable development of agriculture.
⁎
The main cropping system on the NCP consists of wheat–maize continuous cropping. In this cropping system, different tillage methods are usually applied before winter wheat planting, and the traditional method involves rotary tillage (farming depth about 15 cm). Guan et al. (2014) showed that short-term rotary tillage can improve soil moisture content and crop yield. However, long-term rotary tillage will lead to the formation of the bottom layer of the plough, which is often obstructed by the crop root system (Moreira, 2016; Yu et al., 2016). Longterm single rotary tillage and the movement of agricultural machinery aggravate the surface structure of the soil, and the average surface depth becomes shallow (16.5 cm) (Zhang and Li, 2010). As a result, the ability of water and fertilizer conservation decrease significantly, which has an adverse effect on the growth of summer maize. Optimizing farming methods can improve the surface layer structure and increase crop yield. Currently, the main problem on the NCP concerns the formation of a reasonable tillage layer to form a solid bottom using perennial rotary tillage. Subsoiling is an effective measure to break the plow sole. Previous studies have shown that subsoiling under stable soil conditions
Corresponding authors. E-mail addresses: [email protected] (Q. Li), [email protected] (H. Han).
https://doi.org/10.1016/j.agwat.2019.105786 Received 7 May 2019; Received in revised form 3 September 2019; Accepted 9 September 2019 0378-3774/ © 2019 Elsevier B.V. All rights reserved.
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2.2. Experimental design
can alleviate the effects of drought stress on crops, improve soil production potential, and increase yield by about 20% (Schneider et al., 2017). More specifically, studies have shown that subsoiling can improve soil properties, nutrient-use efficiency and crop water productivity (CWP), and promote crop growth and development, compared with conventional tillage methods. Subsoiling (at a depth of 35–40 cm) can effectively increase water infiltration, by removing the resistance from the solid bottom layer (Kaur and Arora, 2019; Varsa et al., 1997; Bogunovic et al., 2018). In addition, Tao et al. (2015) showed that subsoiling can effectively decrease the bulk density of the surface layers, alleviating soil compaction. Zhang et al. (2017) also showed that subsoiling can increase the connectivity of soil pores, especially that of large soil pores. Meanwhile, studies have shown that subsoiling increases nutrient accumulation and soil water content, which serves to both reduce drought stress and provide a more favorable soil environment for root system growth and yield increase (Cai et al., 2014; Zhai et al., 2017). Furthermore, Yu et al. (2016) and Sun et al. (2017) showed that subsoiling promoted the growth of crop roots, which utilized the nutrients and water in the deeper soil layers, increasing the nutrient -use efficiency and CWP. Most previous studies selected the appropriate depth for subsoiling according to the conditions of the site under investigation (e.g., soil type, cultivation mode, and rainfall); this depth was usually from 30 to 50 cm (Cai et al., 2014; Jabro et al., 2016; Sun et al., 2018). Previous studies have mostly focused on depths of 30–40 cm (Mu et al., 2016; Shao et al., 2016). However, to our knowledge, there has been no research on the suitable subsoiling depth on the NCP. As the depth of cultivation increases, so does the cost of production, which is not conducive to environmental protection and the increase of farmers' output and income. Therefore, two subsoiling treatments (at 40 cm and 35 cm) were set in the present study, and the traditional rotary tillage method was used as the control. We measured the dynamic changes in soil moisture, crop water consumption, and CWP to find the optimal depth for subsoiling in this area. We hypothesized that subsoiling could increase water infiltration rate and soil water content, and thus increase grain yield and CWP compared with rotary tillage. Therefore, in this experiment, our goal was to determine the following: (1) soil infiltration rate after subsoiling treatments on continuous rotary tillage test plots; (2) water use of summer maize under different topsoil structure conditions; and (3) which of the two depths tested (40 cm or 35 cm) performs better in terms of grain yield and CWP for subsoiling. Answering the above questions can provide choice space and practical experience for optimizing farming mode and constructing reasonable surface layer structure in rain–fed agriculture mode on the NCP.
In the 2017 and 2018 summer maize growing seasons, three treatments were applied: rotary tillage (15 cm, R15), subsoiling (40 cm, S40), and subsoiling (35 cm, S35). Subsoiling treatment was applied once every two years. In this experiment, subsoiling was treated before winter wheat was planted in 2016. The subsoiling procedure was: before sowing winter wheat, subsoiling (40 and 35 cm) was applied, then rotary tillage was applied (15 cm). After the winter wheat was harvested, winter wheat straw was crushed and returned to the field. Before sowing summer maize, fertilizer (effective N content of urea was 46.6%) was applied and the whole plot was rotated again (depth of rotation was 15 cm). Finally, a spoon-wheel maize precision seeder was used for sowing. Summer maize was planted with row spacing of 60 cm, plant spacing of 22.5 cm, and planting density of 7.5 × 104 plants/hm2. Three replicates were set for each treatment, with a total of nine plots. Before sowing, urea was applied as a base fertilizer with a dosage of 280 kg/hm2, and the same amount of urea was applied at the jointing stage. Summer maize was planted on June 9, 2017 and June 13, 2018, and was harvested on October 5, 2017 and October 7, 2018, respectively. No irrigation was applied during both summer maize growing seasons. The summer maize variety for the experiment was “Zhengdan 958,” which has been widely planted on the NCP. 2.3. Measurements 2.3.1. Soil stable infiltration rate At the summer maize maturity stage, the stable infiltration rate of soil water in each plot was measured with the single-ring soil water infiltration meter. In each plot, soil that had not been damaged by human activity was selected, then the infiltration ring was inserted into the soil, stopping at the mark on the outer edge of the ring. There was 4 cm of water maintained in the ring using a variable flow bottle, and the calibration of the bottle was recorded at regular intervals, until the water level in the bottle no longer changed. The amount of infiltration water was considered to be the amount of water used in the bottle minus the residual water above the soil. Soil infiltration rate i was calculated as follows:
i=
ΔL × AM ÷δ AH × Δt
where, i is soil water infiltration rate (cm/h); Δ L is the variable flow bottle water level change (cm); AM is the cross–sectional area of the variable flow bottle (cm2); AH is the cross–sectional area of infiltrated soil (cm2); Δ t is the infiltration time (h); δ is the error rate of a single ring soil water infiltration meter (1.84).
2. Material and methods 2.1. Experimental site
2.3.2. Soil moisture content The volumetric moisture content of soil in the 0–130 cm layer was measured using Time Domain Reflectometry (IMKO company, Germany) with a depth interval of 10 cm. The soil volume water content was corrected in the 0–10 cm layer using a W.E.T sensor kit soil temperature and humidity meter (Delta–t Company, UK). In the summer maize growing seasons, average soil moisture content was measured every 10 days, and additional measurements were conducted before and after rainfall. Soil water consumption in maize seasons was calculated as the soil moisture content in 0–130 cm on harvesting day deducted from the initial soil moisture content on the sowing day (Li et al., 2012).
The study was carried out in the summer maize growing season of 2017 and 2018, in the agriculture experimental station of Shandong Agricultural University (36°10′19″ N, 117°9′03″ E), which is on the NCP. Since 2004, the experimental field has been continuously rotated before sowing. The bottom soil layer was solid and impermeable, and the surface layer becomes shallower year by year. The experimental site has a temperate continental monsoon climate. The average precipitation from June to September is 453.7 mm, which can basically meet the water consumption of summer maize. The area receives 2461 h of accumulated annual sunshine. In the 2017 and 2018 summer maize growth seasons, total rainfall was 389.5 mm and 447.0 mm, respectively (Fig. 1). The soil in the experimental field is loam, the basic properties of the surface soil under each treatment are shown in Table 1. Soil mechanical compositions at the experimental site are shown in Table 2. In the experimental field, the 0–30 cm soil layer was loam, and the 30–120 cm layer was silty sandy loam.
2.3.3. Evapotranspiration ET in the summer maize growing seasons was calculated using water balance equation (Li et al., 2010): ET = P + I – D – R + W + ΔSWC 2
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Fig. 1. Rainfall and average temperature in 2017 and 2018 summer maize growing seasons.
where, ET is evapotranspiration (mm); P is precipitation (mm), provided by weather stations near the field; I is irrigation water (mm), and no irrigation was applied during both growing seasons, so I was zero; D is soil water drainage (mm); R is surface runoff (mm), but there were beds around each plot, so there was no surface runoff in the experiment; W is groundwater recharge in the experimental site (mm), but underground water level was more than 5 m in our study, so W was ignored; and ΔSWC was the change in soil water storage capacity in 0–130 cm soil profiles during the summer maize growing seasons (mm). In 2018, owing to the occurrence of heavy rain during the growing season of the summer maize, soil water drainage was measured using the water balance method (Gong and Li, 1995; Tracy et al., 1997). When the soil moisture content at 1.3 m was equal to or less than the field moisture capacity, the soil water drainage was zero (the field moisture capacity of the 0–40-cm layer was calculated according to Table 1, and that below 40 cm was calculated according to 25.73%). However, when the soil water content at 1.3 m was more than the field moisture capacity, soil water drainage was calculated as the difference between the soil moisture content and field moisture capacity.
Table 2 Soil mechanical compositions at the experimental site. Soil depth (cm)
0–10 10–20 20–30 30–40 40–60 60–80 80–100 100–120
Percentage of particle content (%)
Soil texture classification
< 0.002 mm
0.02–0.002 mm
2–0.02 mm
4.50 4.57 4.85 5.49 6.10 6.34 6.40 6.64
40.51 43.17 42.57 46.81 48.83 48.74 50.22 53.01
54.99 52.26 52.58 47.70 45.07 44.92 43.38 40.34
loam loam loam silty sandy silty sandy silty sandy silty sandy silty sandy
loam loam loam loam loam
the whole summer maize growing seasons (mm). 2.4. Statistical analysis Microsoft Excel 2010 and SPSS Statistics 18.0 were used for statistical analysis. When significance was observed, the least significant difference (LSD) was used to conduct comparisons at a significance level of α = 0.05.
2.3.4. Grain yield and yield compositions When the plants reached maturity, spike numbers in each plot were counted. Then, spikes in 1.5 m × 1.5 m were hand collected, and the row numbers per spike and kernel numbers per row were counted. After air drying, the 1000–kernel weight and grain yield were recorded.
3. Results 3.1. Soil stable infiltration rate
2.3.5. Crop water productivity (CWP) CWP was calculated as follows (Faramarzi et al., 2010):
At the summer maize maturity stage in 2017, the soil stable infiltration rate in the S40 and S35 treatments was significantly higher than that in R15 by 89.1% and 58.1%. In 2018, the soil stable infiltration rate in S40 and S35 was significantly higher than that in R15
CWP = Y/ET where, Y is grain yield (kg/m2) and ET is the evapotranspiration over Table 1 Basic properties of soil in experiment plots under different treatments. Treatment
Available P (mg/kg)
Available K (mg/kg)
Alkaline hydrolysis nitrogen (mg/kg)
Soil origin carbon (mg/g)
Field Capacity (%)
R15 S40 S35
91.7 82.4 86.1
91.5 84.5 80.1
238.2 226.9 244.2
7.4 7.4 6.6
29.0 30.0 28.0
R15 represents rotation tillage of 15 cm, S40 represents subsoiling of 40 cm, and S35 represents subsoiling of 35 cm, respectively. 3
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Fig. 2. Soil stable infiltration rate at summer maize maturity stages in 2017 and 2018. R15 represents rotation tillage of 15 cm, S40 represents subsoiling of 40 cm, and S35 represents subsoiling of 35 cm, respectively. Vertical bars are standard errors.
treatment increases the soil water consumption in maize seasons in the deeper soil layers. This means that crops can utilize deep soil water for their growth and development.
by 89.9% and 63.3%, respectively (Fig. 2). The soil stable infiltration rate in 2018 was higher than that in 2017. The soil stable infiltration rate in R15, S40, and S35 in 2018 was higher than in 2017 by 3.6%, 4.0%, and 7.0%, respectively.
3.3. Grain yield and yield compositions 3.2. Soil water consumption in maize seasons Table 3 shows grain yield and yield compositions in the 2017 and 2018 summer maize growing seasons. During the two–year experiment, the experimental results showed that the subsoiling treatment improved kernel number per row, 1000–grain weight, and grain yield of summer maize. However, the treatment had no significant effect on row numbers per spike. In both growing seasons, the highest kernel numbers per row was obtained in the S35 treatment, followed by that under S40 treatment, and the lowest was found in the R15 treatment. The 1000–grain weight for S35 was significantly higher than that of R15 by
Fig. 3 shows the soil water consumption through 0–130 cm of the soil profile in the 2017 and 2018 summer maize growing seasons. In both growing seasons, the change in soil water consumption in the 0–50 cm soil layer was similar, with no significant difference being found among treatments. With the deepening of soil layer, the soil water consumption in maize seasons, when treated with subsoiling, significantly increased at 50–90 cm and 90–130 cm in the following order: S40 > S35 > R15. These results indicate that subsoiling
Fig. 3. Soil water consumption in 2017 and 2018 summer maize growing seasons. R15 represents rotation tillage of 15 cm, S40 represents subsoiling of 40 cm, and S35 represents subsoiling of 35 cm, respectively. Horizonal bars are standard errors. 4
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Table 3 Grain yield and yield compositions in 2017 and 2018 summer maize growing seasons. Treatments
Row numbers per spike (rows/spike)
Kernel numbers per row (kernels/row)
Spike numbers (Spikes × 104/ha)
1000-kernel weight (g)
Grain yield (g/m2)
2017 R15 S40 S35
15.7a 14.5b 14.8b
35.4b 36.9a 37.3a
7.6a 7.7a 7.6a
329.0b 339.7ab 342.7a
830.6b 911.9ab 939.8a
2018 R15 S40 S35
14.1a 14.2a 14.6a
24.7b 24.5b 24.9a
7.1a 7.2a 7.2a
388.9b 399.1a 399.8a
822.3b 857.4ab 889.5a
In each growing season, in the same column, values followed by different letters differ significantly (P < 0.05) among treatments. R15 represents rotation tillage of 15 cm, S40 represents subsoiling of 40 cm, and S35 represents subsoiling of 35 cm, respectively.
maize growth. In this experiment, the results showed that the S35 treatment had the best performance, with a balanced relationship between water consumption and grain yield. As a result, the highest CWP was observed under this treatment. There is a plow sole in the tillage layer, which hinders the infiltration of water. Drought stress caused by a lack of soil water has a major limiting effect on crop growth. It has been reported that different tillage methods have significant effects on soil water status, crop growth, and the regulation of the soil-crop system (Mosaddeghi et al., 2009; Ren et al., 2018a). Compared with rotary tillage, subsoiling broke down the plow sole and made the surface soil more porous, so that the root system could grow earlier and extend into the deeper soil layers, which was beneficial for summer maize CWP (Yan et al., 2017). Previous studies have shown that the distribution of soil water infiltration was related to the distribution pattern of the maize fiber root system, and that the connectivity between macropores plays a key role in soil water migration (Wu et al., 2009). Thus, while subsoiling created preferred paths for the flow of water, the preferred flow created by fibrous roots also guided and facilitated water infiltration into deeper soil layers (Jiang et al., 2018). In this experiment, the soil stable infiltration rate in S40 and S35 was significantly higher than that in R15, which created an effective water transport channel for timely rainfall infiltration, even to the deeper soil layers. Wang et al. (2012) and Bogunovic et al. (2018) showed that subsoiling treatment enhanced the capacity of soil water and increased maize yield. In our experiment, the stable infiltration rate under the subsoiling treatment was higher than that under the rotary tillage treatment, which allowed the water to infiltrate the deep soil (below 60 cm) and increased the water utilization in the later stage of summer maize growth. Tillage methods significantly changed the topsoil environment and greatly affected maize yield (Tao et al., 2015). Under more adequate water conditions, subsoiling delayed summer maize leaf senescence and maintained a higher leaf area index and photosynthetic rate, laying a solid physiological foundation for the final yield increase (Sun et al., 2017). In terms of water consumption, the results of this experiment showed that the evapotranspiration of subsoiling treatment was significantly higher than that of rotary tillage treatment. Subsoiling machinery works effectively to break the plow sole and better tillage layer structure is beneficial to the downward growth of summer maize root systems. Yu et al. (2016) showed that subsoiling at 38 cm significantly increased water consumption. In our study, the results were similar, more soil water was consumed under the subsoiling treatments compared with that under the rotary tillage, especially soil water below 50 cm. Hsiao (2000) indicated that maize root system under the condition of drought response mechanism, water transport is a process of absorption, root in the soil played a vital role in the extraction of moisture. Root systems absorb the deep soil water after hydraulic promotion functions and balances the water levels in the plants, providing resistance to drought stress (Cai et al., 1993). At the same time, another important reason for the significant increase in water consumption in the subsoiling treatment is that this
4.2% in 2017, and the 1000–grain weight for S35 and S40 was significantly higher than that of R15 by 2.6% and 2.8% in 2018, respectively. In 2017, grain yield in S35 increased by 13.1% and 3.0% compared with R15 and S40, respectively. In 2018, gain yield in S35 increased by 8.3% and 3.7% compared with R15 and S40, respectively. However, owing to precipitation, grain yield in R15, S40, and S35 was lower in 2018 than in 2017 by 1.1%, 6.0%, and 5.3%, respectively. 3.4. ET and crop water productivity Table 4 shows ET and CWP in 2017 and 2018 summer maize growing seasons. There was no significant difference in soil water consumption between R15 and S35 in these growing seasons; however, soil water consumption in S40 was significantly higher than that in R15 in the first and second growing seasons. The two–year experiment showed that subsoiling treatment significantly increased ET in the following order: S40 > S35. In both growing seasons, CWP was significantly higher in S35 than that in S40 and R15. In 2017, CWP in S35 was significantly higher than in R15 and S40 by 10.2% and 9.1%, respectively. In 2018, CWP in S35 was significantly higher than in R15 and S40 by 7.5% and 7.5%, respectively. In addition, CWP in R15, S40, and S35 was much lower in 2018 than that in 2017 by 1.9%, 2.3%, and 4.2%, respectively. 4. Discussion Many previous studies have shown that subsoiling improved the physical properties of continuous no-tillage or rotary tillage soils and increased the yield of food crops (Putte et al., 2012; Cai et al., 2014). In the present study, subsoiling at depths of 35 cm and 40 cm were tested. Compared with rotary tillage, the subsoiling treatments promoted the absorption and use of water from the deeper soil layers during summer Table 4 ET and crop water productivity in 2017 and 2018 summer maize growing seasons. Treatments
Soil water consumption (mm)
Soil water drainage (mm)
ET (mm)
CWP (kg/ m³)
2017 R15 S40 S35
–96.4b –70.2a –90.3b
– – –
293.1b 319.3a 299.3b
2.8b 2.9b 3.1a
2018 R15 S40 S35
–36.7b 7.8a –13.8ab
22.2b 46.5a 44.3a
387.1b 404.4a 388.5b
2.1b 2.1b 2.3a
In each growing season, in the same column, values followed by different letters differ significantly (P < 0.05) among treatments. R15 represents rotation tillage of 15 cm, S40 represents subsoiling of 40 cm, and S35 represents subsoiling of 35 cm, respectively. 5
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treatment can improve the photosynthetic performance and transpiration rate of summer maize (Xu et al., 2017). As we all know, summer maize transpiration plays a leading role in farmland evapotranspiration, which increases soil water consumption. In general, the evapotranspiration of the subsoiling treatment was significantly higher than that of the rotary tillage treatment. On this physical basis, it is possible for crop growth to increase and to achieve increased yield and ultimately improve CWP. Tian et al. (2016) pointed out that the conditions of their study area were under the influence of many factors such as rainfall and farming methods, and the changes in yield and CWP were similar to our results. In our experiment, summer maize grain yield in 2018 showed a different degree of decrease compared with that in 2017. The main reason may be related to heavy rainfall, which was concentrated during the flowering stage, resulting in decreased quality of pollination and spike numbers (Shao et al., 2016; Gao et al., 2018). In view of the deterioration of soil structure caused by continuous rotary tillage on the NCP, subsoiling at 35 cm and 40 cm could provide improvements, by increasing soil stable infiltration rate, water consumption, and grain yield. In our experiment, the subsoiling treatment S35 balanced the relationship between water content and grain yield and reached the highest CWP. Therefore, the results suggest that subsoiling at 35 cm before winter wheat (once every two years) should be taken as the preferred tillage method for promoting increased crop yields on the NCP. This experiment mainly studied soil water dynamics and crop water consumption characteristics, but the response of photosynthesis and fluorescence of summer maize to subsoiling at different depths remains unclear. At the same time, the study of soil infiltration mechanisms is also of great significance.
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5. Conclusions Subsoiling significantly improved soil stable infiltration rate, summer maize water consumption, and grain yield. Subsoiling S35 balanced the relationship between soil water content and grain yield, and achieved the highest CWP. Therefore, our results suggest that 35 cm can be used as a reasonable subsoiling depth to improve summer maize grain yield and CWP on the NCP. Acknowledgements This work was financially supported in part by the National Nature Science Foundation of China (31771737), by the Key Research and Development Plan in Shandong Province, China (2019GSF109054), and by the Funds of Shandong “Double Tops” Program (SYL2017YSTD02). References Bogunovic, I., Pereira, P., Kisic, I., Sajko, K., Sraka, M., 2018. Tillage management impacts on soil compaction, erosion and crop yield in Stagnosols (Croatia). Catena 160, 376–384. Cai, H.G., Ma, W., Zhang, X.Z., Ping, J.Q., Yan, X.G., Liu, J.Z., Yuan, J.C., Wang, L.C., Dawson, T.E., 1993. Hydraulic lift and water use by plants: implications for water balance, performance and plant–plant interactions. Oecologia 95, 565–574. Cai, H.G., Ma, W., Zhang, X.Z., Ping, J.Q., Yan, X.G., Liu, J.Z., Yuan, J.C., Wang, L.C., Ren, J., 2014. Effect of subsoil tillage depth on nutrient accumulation, root distribution, and grain yield in spring maize. Acta Agron. Sin. 2, 297–307. Faramarzi, M., Yang, H., Schulin, R., Abbaspour, K.C., 2010. Modeling wheat yield and crop water productivity in Iran: implications of agricultural water management for wheat production. Agric. Water Manage. 97, 1861–1875. Gao, Z., Feng, H.Y., Liang, X.G., Zhang, L., 2018. Limits to maize productivity in the North China Plain: a comparison analysis for spring and summer maize. Field Crops Res. 228, 39–47. Gong, Y.S., Li, B.G., 1995. Using field water balance model to estimate the percolation of soil water. Adv. Water Sci. 6, 16–21. Guan, D.H., Mahdi, M.A., Zhang, Y.S., Duan, L.S., Tan, W.M., Zhang, M.C., Li, Z.H., 2014. Tillage practices affect biomass and grain yield through regulating root growth, root–bleeding sap and nutrients uptake in summer maize. Field Crops Res. 157, 89–97. Hsiao, T.C., 2000. Sensitivity of growth of roots versus leaves to water stress: biophysical
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