Effects of ridge-furrow film mulching and nitrogen fertilization on growth, seed yield and water productivity of winter oilseed rape (Brassica napus L.) in Northwestern China

Agricultural Water Management 200 (2018) 60–70

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Agricultural Water Management journal homepage: www.elsevier.com/locate/agwat

Effects of ridge-furrow film mulching and nitrogen fertilization on growth, seed yield and water productivity of winter oilseed rape (Brassica napus L.) in Northwestern China Xiao-Bo Gu, Yuan-Nong Li ∗ , Ya-Dan Du College of Water Resources and Architectural Engineering, Key Laboratory of Agricultural Soil and Water Engineering in Arid and Semiarid Areas of Ministry of Education, Northwest A&F University, Yangling, Shaanxi, 712100, China

a r t i c l e

i n f o

Article history: Received 23 April 2017 Received in revised form 1 January 2018 Accepted 2 January 2018 Keywords: Cultivation pattern Nitrogen fertilization Dryland winter oilseed rape Water productivity Economic benefit

a b s t r a c t Poor soil conditions and drought stress are two main factors restricting the agriculture production in arid and semiarid areas of China. The ridge-furrow film mulching (RFFM) cultivation pattern has been shown to have the ability of improving yield and water productivity (WP) of maize, wheat and potato. However, its effect on winter oilseed rape is not clear. A two-year (2014–2016) field experiment was conducted to determine whether the RFFM cultivation pattern has the potential of improving winter oilseed rape productivity under dryland conditions. The optimal nitrogen (N) application rate for winter oilseed rape maximum yield under the RFFM cultivation pattern was also measured. Winter oilseed rape was planted in RFFM and flat cultivation patterns, both with six nitrogen (N) application rates (0, 60, 120, 180, 240 and 300 kg ha−1 ). The results showed that compared to the flat cultivation pattern, the RFFM cultivation pattern greatly increased leaf area index (LAI) by 18.7% on average, aboveground dry matter (ADM) by 25.6% at harvest, seed yield by 23.8% and WP by 32.7%, and decreased evapotranspiration (ET) by 7.2%. Application of N fertilizer remarkably increased LAI, ADM, ET, seed yield and WP of winter oilseed rape under both cultivation patterns. Under the RFFM cultivation pattern, average seed yield, WP, and economic benefit in 240 kg N ha−1 were 2904 kg ha−1 , 8.8 kg ha−1 mm−1 , and 1259.6 $ ha−1 , respectively, and were significantly higher than the other five N rates. The optimal N-application amount for maximum winter oilseed rape productivity under the RFFM cultivation pattern was found to be 240 kg N ha−1 . In conclusion, the RFFM cultivation pattern has the potential of improving the seed yield and WP of winter oilseed rape in northwest China. © 2018 Elsevier B.V. All rights reserved.

1. Introduction Droughts majorly limit crop production in arid and semiarid regions of northwest China (Huang et al., 2005; Wang et al., 2009; Zhang et al., 2009). Low yields have been reported in spring wheat (about 1500–3000 kg ha−1 ) and maize (2500–3500 kg ha−1 ) crops in areas where heat leads to high evaporation and rainfall is sparse and unevenly distributed (Hu et al., 2009; Huang et al., 2005; Wang et al., 2008). Film mulching is an important agricultural technique for improving soil moisture and crop yields (Gan et al., 2013). The ridge-furrow planting pattern has also been widely applied to

∗ Corresponding author at: No.23 Weihui Road, Yangling, Shaanxi Province, 712100, PR China. E-mail addresses: xiaobo [email protected] (X.-B. Gu), [email protected] (Y.-N. Li). https://doi.org/10.1016/j.agwat.2018.01.001 0378-3774/© 2018 Elsevier B.V. All rights reserved.

conserve soil water during crop production (Li et al., 2007). The combination of the two techniques has been termed the ridgefurrow film mulching (RFFM) planting pattern, which employs ridges mulched with plastic film to serve as the runoff area and furrows used as the planting area (Li et al., 2001; Li and Gong, 2002). Numerous studies have demonstrated that the RFFM planting pattern significantly improves soil water availability, crop yield, and water productivity (WP) in maize (Wang et al., 2009; Wang et al., 2015), wheat (Li et al., 2017; Zhang et al., 2007), and potato (Qin et al., 2014; Zhao et al., 2012). However, the RFFM planting pattern has rarely been tested in oilseed rape (Brassica napus L.) for yield improvements in areas where soil evaporation is high. Oilseed rape is one of the most widely cultivated oil crops throughout the world. As one of the leading rapeseed producing countries, China generated an annual average of 12.6 million tons of seeds from 2001 to 2014 (FAOSTAT, 2016). Chinese rapeseed

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Fig 1. Monthly total rainfall and monthly mean temperature during the winter oilseed rape season in 2014–2015, 2015–2016, and 2006–2014 (mean value) at the experimental site.

yields have steadily increased over the last five decades not only due to the introduction of high-yield potential cultivars and the improved agronomic practices, but also the higher nitrogen-based fertilizer inputs (Hamzei and Soltani, 2012; Rathke et al., 2006). However, excessive use of N fertilizers not only causes a huge waste of resources and economic losses, but also adversely impacts the environment (Godfray et al., 2010), thereby affecting the safety of human beings (Hvistendahl, 2010). Oilseed rape response to N fertilizers is dependent upon many environmental factors including water availability, ambient temperature and soil properties (Rathke et al., 2006). RFFM planting pattern has been suggested to have an effect on soil N-transport, N mineralization and plant N uptake through its effect on soil temperature and moisture (Wang et al., 2015). All of these factors may alter the responses of oilseed rape to N fertilization, affecting seed yield. The objectives of the present study were to examine the coupling effects of the RFFM planting pattern and N fertilizer on leaf area index, aboveground dry matter, evapotranspiration, seed yield and WP of winter oilseed rape. Results from this study may provide information that can be used to (1) determine whether the RFFM planting pattern has the potential to improve winter oilseed rape productivity and (2) offer insight into optimum N application rates under the RFFM system for high oilseed rape yields and WP. 2. Materials and methods 2.1. Experimental site Field experiments were conducted at the Key Laboratory of Agricultural Soil and Water Engineering in arid and semiarid areas at the Ministry of Education (34◦ 18N, 108◦ 24E, 521 m ASL), Northwest A&F University, Yangling, Shaanxi, China from September 2014 to May 2016. The average annual precipitation and pan evaporation were approximately 632 mm and 1500 mm, respectively. The mean temperature was 12.9 ◦ C, the duration of sunlight was 2164 h, and the frost-free period was more than 210 d. The experimental field soil was a loam with a field capacity of 24.0%, dry bulk density of 1.40 g cm−3 . The nutrient properties of the 0–20 cm soil layer were as follows: soil organic matter 12.18 g kg−1 , nitrate nitrogen 76.01 mg kg−1 , Olsen phosphorus 25.22 mg kg−1 , NH4 OAc-extracted potassium 132.97 mg kg−1 , pH (water) 8.14 at the beginning of 2014–2015; and the corresponding data were 12.57 g kg−1 , 73.93 mg kg−1 , 24.80 mg kg−1 , 133.62 mg kg−1 , and 8.13, respectively, at the beginning of 2015–2016.

Monthly mean temperatures during the two experimental seasons followed a similar trend and were close to the mean value of 2006–2014, while the temperature in January 2015 was higher than the mean value of 2006–2014 (Fig. 1). Total rainfall during the growing period was 264.3 mm and 183.9 mm for 2014–2015 and 2015–2016, respectively, and the mean rainfall during the growing period in 2006–2014 was about 263 mm at the experimental site. March to May is the stem elongation, flowering, and pod-filling stages of winter oilseed rape occurring in northwest China. Rainfall from March to May in 2014–2015 and 2015–2016 was 178.7 and 48.1 mm, which was 33.4% more and 64.1% lower than the mean value of 2006–2014 (134 mm), respectively.

2.2. Experimental design Field experiments for each season were arranged on a split plot design with the cultivation pattern as the main plot and the N levels as the subplot. Each plot was 20 m2 (4 m × 5 m) in size and three replicates were conducted in each season. Two cultivation patterns were involved in the experiment: ridge-furrow film mulching (Fig. 2a) and flat planting (Fig. 2b) methods. Each cultivation pattern had six N levels: 0 (N0), 60 (N60), 120 (N120), 180 (N180), 240 (N240) and 300 (N300) kg N ha−1 , in the form of urea (N = 46%) and were all applied as basal fertilizer. In addition, calcium superphosphate (P2 O5 = 16%), potassium sulphate (K2 O = 51%), and borax (B = 11%) were applied at rates of 90 kg P2 O5 ha−1 , 120 kg K2 O ha−1 , and 15 kg B ha−1 in each plot before oilseed rape was sown. No additional fertilizer was applied during the growth of the oilseed rape. After ploughing and leveling the experimental field, dividing the experimental plots, and applying all basal fertilizers in each plot, the ridges and furrows as shown in Fig. 2a were formed. Seeds of winter rape ‘Shaanyou No. 107 were manually sown on 21 September 2014, and 16 September 2015. Transparent plastic film, 0.8 m wide and 0.008 mm thick, was laid over the soil surface layer of ridges immediately after emergence for the RFFM treatments (Fig. 2a). Plant density was determined as 120 000 plants ha−1 at the fifth-leaf stage by manually thinning seedlings. Other field production practices such as weed and pest control were conducted to minimise yield loss. The plastic film was gathered and recycled after the crop was harvested on 23 May 2015, and 20 May 2016. No irrigation was applied during the growth of winter oilseed rape for both seasons.

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Fig. 2. Schematic diagram of the cultivation patterns of winter oilseed rape.

2.3. Measurements and methods 2.3.1. Leaf area index (LAI) and aboveground dry matter (ADM) A total of 12 plants in each plot were cut at ground level about every 30 days to determine leaf area index (LAI) and aboveground dry matter (ADM). The plants were separated into stems, leaves, pods, and seeds. Leaf area was measured using a leaf area-meter (Li3100c, Li-COR Inc., USA). LAI was defined as the ratio of total onesided leaf area to ground surface area (Behrens and Diepenbrock, 2006). After the leaf area was measured, each separated organ was dried in an oven for 30 min at 105 ◦ C to deactivate enzymes, then dried at 75 ◦ C to a constant weight, and weighed. ADM was the sum of the weights of the dry stem, leaf, pod, and seed. 2.3.2. Soil moisture Before sowing, after harvesting, and at each plant sampling time, soil moisture to a depth of 200 cm was determined for calculating soil water storage in the soil profiles in each growing season. Three soil cores per plot were manually sampled at 10-cm intervals between adjacent plants within a row, and the gravimetric water content of the soil samples was calculated on the basis of oven-dried weights (dried at 105 ◦ C). Soil water storage was defined as: SWS = 10hω

(1)

where SWS is soil water storage (mm),  is soil dry bulk density (g cm−3 ), h is soil thickness (cm), and ω is gravimetric water content (%). Evapotranspiration was calculated using the equation for the soil-water balance: ET = I + P + R − D + W 0 –W 1

(2)

where ET is evapotranspiration (mm), I is irrigation amount (mm), which equalled to zero in each treatment because no irrigation was

applied in this study, P is precipitation (mm), R is runoff (mm), which was assumed to be zero as no heavy rain occurred and the experimental soil had a good infiltration rate, and also each plot was protected by a 50 cm bund in this study, D is deep drainage into the lower boundary of 200 cm (mm), which was assumed to be negligible in this study because no heavy rains appeared during the rapeseed growing seasons, and W0 and W1 are the SWSs before sowing and after harvesting (mm), respectively. 2.3.3. Seed yield and water productivity (WP) Plants were manually harvested from an area of 1 m2 in the middle of each plot, and were threshed after being sun-dried to determine seed yield. Water productivity was calculated as: WP = Y/ET

(3) (kg ha−1

where WP and Y are the water productivity seed yield (kg ha−1 ) of winter rape, respectively.

mm−1 )

and

2.4. Data analysis All data were presented as the mean value of three replicates. The analysis of variance was conducted by SPSS 18.0, and the significant differences between the treatments were compared by the least significant differences test at 5% probability. Origin 8.0 was used to make graphics. 3. Results 3.1. Leaf area index (LAI) As shown in Tables 1 and 2, LAI varied at different growth stages and constantly changed overtime. LAI had no significant response to N fertilizer at the first two and the last samplings

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Table 1 Leaf area index (LAI) of winter oilseed rape under ridge-furrow film mulching (RFFM) and flat cultivation treatments in 2014–2015 growing season. Date of determination

N rates (kg ha−1 )

Mean of LAI for N rate

LSD0.05 for N rate

0.22 0.81 1.42 1.32 1.43 3.20 3.31 0.26 1.50 0.046

0.21 0.78 1.29 1.19 1.30 2.65 2.82 0.24

0.034 0.082 0.088 0.079 0.130 0.201 0.226 0.035

0.18 0.68 1.09 1.07 1.22 2.81 2.84 0.15 1.26 0.052

0.17 0.65 0.99 0.97 1.10 2.33 2.42 0.13

0.024 0.072 0.084 0.086 0.103 0.137 0.134 0.031

0

60

120

180

240

300

RFFM cultivation treatment 20-Oct 20-Nov 20-Dec 20-Jan 21-Feb 21-Mar 17-Apr 23-May Mean of LAI for date LSD0.05 for date

0.20 0.73 0.91 0.83 0.89 1.41 1.62 0.23 0.85 0.035

0.21 0.76 1.14 1.07 1.15 1.96 2.07 0.20 1.07 0.049

0.21 0.78 1.26 1.19 1.25 2.76 2.98 0.22 1.33 0.040

0.22 0.80 1.48 1.34 1.52 3.24 3.44 0.25 1.54 0.048

0.22 0.81 1.50 1.39 1.55 3.31 3.51 0.25 1.57 0.051

Flat cultivation treatment 20-Oct 20-Nov 20-Dec 20-Jan 21-Feb 21-Mar 17-Apr 23-May Mean of LAI for date LSD0.05 for date

0.16 0.61 0.70 0.68 0.76 1.24 1.39 0.11 0.71 0.022

0.16 0.63 0.88 0.87 0.96 1.72 1.78 0.12 0.89 0.042

0.16 0.65 0.97 0.97 1.06 2.43 2.56 0.13 1.12 0.053

0.17 0.67 1.14 1.09 1.29 2.85 2.95 0.14 1.29 0.048

0.18 0.68 1.16 1.13 1.32 2.91 3.01 0.14 1.32 0.056

Table 2 Leaf area index (LAI) of winter oilseed rape under ridge-furrow film mulching (RFFM) and flat cultivation treatments in 2015–2016 growing season. Date of determination

N rates (kg ha−1 )

Mean of LAI for N rate

LSD0.05 for N rate

0.27 0.96 1.19 1.15 1.32 2.91 3.13 0.22 1.39 0.042

0.26 0.94 1.08 1.04 1.20 2.41 2.67 0.21

0.038 0.086 0.079 0.080 0.115 0.136 0.149 0.025

0.24 0.74 1.05 1.01 1.06 2.57 2.68 0.22 1.20 0.064

0.23 0.71 0.94 0.91 0.96 2.12 2.28 0.21

0.039 0.078 0.076 0.081 0.097 0.203 0.126 0.032

0

60

120

180

240

300

RFFM cultivation treatment 15-Oct 15-Nov 15-Dec 15-Jan 15-Feb 15-Mar 18-Apr 20-May Mean of LAI for date LSD0.05 for date

0.25 0.88 0.76 0.72 0.82 1.28 1.53 0.20 0.81 0.025

0.25 0.92 0.96 0.93 1.06 1.78 1.96 0.20 1.00 0.032

0.26 0.94 1.06 1.04 1.15 2.51 2.82 0.20 1.25 0.064

0.26 0.95 1.24 1.17 1.40 2.95 3.25 0.20 1.43 0.049

0.27 0.96 1.26 1.21 1.43 3.01 3.32 0.21 1.46 0.051

Flat cultivation treatment 15-Oct 15-Nov 15-Dec 15-Jan 15-Feb 15-Mar 18-Apr 20-May Mean of LAI for date LSD0.05 for date

0.22 0.67 0.66 0.63 0.66 1.13 1.31 0.19 0.68 0.019

0.22 0.69 0.83 0.81 0.85 1.57 1.67 0.20 0.86 0.035

0.23 0.70 0.92 0.91 0.93 2.21 2.40 0.20 1.06 0.033

0.23 0.71 1.08 1.02 1.13 2.60 2.77 0.21 1.22 0.065

0.24 0.74 1.09 1.06 1.15 2.62 2.83 0.22 1.24 0.068

under the RFFM cultivation condition or the flat cultivation condition. However, LAI was significantly influenced by N levels at the other five time points in both cultivation patterns and growth seasons (Tables 1 and 2). From the third to seventh determination, the N240 treatment resulted in the largest LAI, followed by N180 and N300, however, no significant differences were found among the three N levels, in both cultivation patterns and growth seasons. The N0 treatment always produced the lowest LAI, and was always significantly lower than the other five N levels. The RFFM cultivation pattern increased LAI throughout the entire growth stages of winter oilseed rape in comparison to flat cultivation pattern (Tables 1 and 2). For flat cultivation treatments, the average LAI of the six N levels was around 0.68 by midNovember, around 0.94 by mid-January, increased to larger than 2.30 by mid-April, and then sharply declined to about 0.17. The corresponding LAI for the RFFM cultivation treatments was much

larger than non-film mulching. The LAI was around 0.85 by midNovember, around 1.12 by mid-January, increased to larger than 2.65 by mid-April, and then sharply reduced to about 0.23. 3.2. Aboveground dry matter (ADM) At any time of determinations, the ADM in the RFFM cultivation treatment was significantly higher than that in flat cultivation treatment (Tables 3 and 4). At maturity, the average ADM of the six N levels was 9268 kg ha−1 in 2014–2015 and 7957 kg ha−1 in 2015–2016 for RFFM cultivation treatment, while was 7518 kg ha−1 in 2014–2015 and 6195 kg ha−1 in 2015–2016 for flat cultivation treatment, the former being 23.3% higher in 2014–2015 and 28.4% higher in 2015–2016 than the latter. ADM of winter oilseed rape had no significant response to N fertilizer under either the RFFM cultivation or flat cultivation

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Table 3 Aboveground dry matter (ADM) (kg ha−1 ) of winter oilseed rape under ridge-furrow film mulching (RFFM) and flat cultivation treatments in 2014–2015 growing season. Date of determination

N rates (kg ha−1 )

Mean of ADM for N rate

LSD0.05 for N rate

452 747 1256 1215 2286 5615 7522 10496 3699 538.5

437 733 1202 1147 2122 4753 6858 9268

115.8 132.7 205.2 174.5 302.1 669.8 753.6 751.4

380 691 1023 984 1923 3856 5361 8425 2830 613.7

374 672 978 934 1766 3264 4888 7518

103.4 107.0 114.6 105.2 216.0 234.6 745.8 886.2

0

60

120

180

240

300

RFFM cultivation treatment 20-Oct 20-Nov 20-Dec 20-Jan 21-Feb 21-Mar 17-Apr 23-May Mean of ADM for date LSD0.05 for date

370 683 925 904 1515 3035 5115 6789 2417 256.1

406 711 1158 1082 1852 3864 6346 7565 2873 308.1

455 734 1235 1205 2184 4593 6936 9332 3334 498.9

469 745 1277 1218 2395 5671 7461 10357 3699 522.0

467 776 1360 1256 2501 5742 7765 11069 3867 604.2

Flat cultivation treatment 20-Oct 20-Nov 20-Dec 20-Jan 21-Feb 21-Mar 17-Apr 23-May Mean of ADM for date LSD0.05 for date

316 603 827 784 1275 2084 3646 5675 1901 322.0

346 652 946 901 1527 2653 4523 6622 2271 342.7

388 680 975 938 1753 3154 4944 7602 2554 478.2

417 696 1037 989 2015 3894 5318 8147 2814 604.8

398 708 1058 1005 2104 3942 5538 8639 2924 756.3

Table 4 Aboveground dry matter (ADM) (kg ha−1 ) of winter oilseed rape under ridge-furrow film mulching (RFFM) and flat cultivation treatments in 2015–2016 growing season. Date of determination

N rates (kg ha−1 )

Mean of ADM for N rate

LSD0.05 for N rate

518 839 996 932 2003 4312 5676 9281 3070 642.8

499 811 947 898 1840 3650 5175 7957

98.3 106.9 110.2 93.6 198.5 236.1 749.2 735.6

491 758 997 970 1836 3467 4355 7165 2505 642.5

460 743 910 890 1685 2927 3974 6196

94.3 105.7 136.7 151.8 187.2 203.5 726.1 621.4

0

60

120

180

240

300

RFFM cultivation treatment 15-Oct 15-Nov 15-Dec 15-Jan 15-Feb 15-Mar 18-Apr 20-May Mean of ADM for date LSD0.05 for date

420 738 807 774 1328 2331 3859 5803 2008 259.6

460 808 923 871 1591 2967 4789 6795 2401 320.5

514 811 950 916 1826 3527 5234 7875 2707 541.3

552 825 978 936 2099 4355 5630 8475 2981 549.8

528 844 1030 960 2192 4410 5859 9513 3167 651.2

Flat cultivation treatment 15-Oct 15-Nov 15-Dec 15-Jan 15-Feb 15-Mar 18-Apr 20-May Mean of ADM for date LSD0.05 for date

385 671 731 708 1215 1873 2964 4317 1608 219.3

421 734 876 867 1456 2338 3677 5354 1965 350.7

471 758 898 879 1678 2836 4017 6062 2200 533.0

505 766 949 921 1920 3498 4324 6960 2480 563.4

487 771 1008 993 2007 3549 4508 7317 2580 685.7

patterns at the first two determinations (Tables 3 and 4). After the first two sampling times, ADM in N application treatments was markedly higher than that without N application, and ADM was almost increased until N rate reaching 240 kg ha−1 , and then slightly decreased when N rate was 300 kg ha−1 . At oilseed rape maturity, the ADM in N240 was significantly higher than in N60 and N120 treatments, and had no marked differences with N180 and N300 treatments in both cultivation patterns and growing seasons. 3.3. Evapotranspiration (ET) As shown in Tables 5, 6, 7 and 8, ET of winter oilseed rape was affected by both cultivation patterns and N levels in 2014–2015 and 2015–2016. Throughout the experiment, ET was low at early growth stages and high at vigorous growth stages, especially in March, April and May.

ET at each determination was always higher in flat cultivation treatments than in RFFM cultivation treatments at the same N levels (Tables 5, 6, 7 and 8). RFFM cultivation treatments substantially decreased total ET of winter oilseed rape. On average, RFFM cultivation treatments consumed 324.0 mm ha−1 and 312.0 mm ha−1 water in 2014–2015 and 2015–2016, respectively, and the corresponding data in flat cultivation treatments were 354.5 mm ha−1 and 331.0 mm ha−1 , respectively. In addition, some other differences were also found between RFFM cultivation and flat cultivation conditions. ET under RFFM cultivation treatments was lower at early growth stages and was higher at vigorous growth stages than ET under flat cultivation treatments. Application of N fertilizer increased the ET of winter oilseed rape. The ET continually increased from N0 to N300 at each determination in both cultivation patterns and growth seasons (Tables 5, 6, 7 and 8). Using the average of total ET to make

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Table 5 Soil water storage (SWS) in 0–200 cm layer, rainfall and evapotranspiration (ET) with six N rates under ridge-furrow film mulching (RFFM) cultivation pattern in 2014–2015 growing season. Date of determination

Treatment and indicators

21-Sep

Rainfall (mm) N rate at 0 kg ha−1 SWS (mm) ET (mm)

534.3

N rate at 60 kg ha−1 SWS (mm) ET (mm)

534.3

N rate at 120 kg ha−1 SWS (mm) ET (mm)

534.3

20-Oct

20-Nov

20-Dec

20-Jan

21-Feb

21-Mar

17-Apr

23-May

Total

50.6

5.6

21.1

0

8.1

44.2

82.9

51.8

264.3

572.1 12.8

544.6 33.1

539.4 26.3

524.9 14.5

504.2 28.8

493.7 54.7

500.5 76.1

508.3 44.0

290.3

570.6 14.3

541.3 34.9

535.4 27.0

520.2 15.2

498.8 29.5

484.9 58.1

482.7 85.1

487.9 46.6

310.7

569.2 15.7

538.8 36.0

531.4 28.5

514.6 16.8

491.8 30.9

476.9 59.1

473.4 86.4

475.1 50.1

323.5

567.1 17.8

536.1 36.6

528.2 29.0

510.9 17.3

487.6 31.4

471.2 60.6

466.4 87.7

465.9 52.3

332.7

566.4 18.5

534.7 37.3

526.3 29.5

508.2 18.1

484.1 32.2

466.8 61.5

460.9 88.8

460.2 52.5

338.4

565.7 19.2

533.8 37.5

524.9 30.0

506.6 18.3

481.9 32.8

463.4 62.7

455.3 91.0

450.1 57.0

348.5

−1

N rate at 180 kg ha SWS (mm) ET (mm)

534.3

N rate at 240 kg ha−1 SWS (mm) ET (mm)

534.3

N rate at 300 kg ha−1 SWS (mm) ET (mm)

534.3

Table 6 Soil water storage (SWS) in 0–200 cm layer, rainfall and evapotranspiration (ET) with six N rates under flat cultivation pattern in 2014–2015 growing season. Date of determination

Treatment and indicators

21-Sep

Rainfall (mm) N rate at 0 kg ha−1 SWS (mm) ET (mm)

534.3

N rate at 60 kg ha−1 SWS (mm) ET (mm)

534.3

20-Oct

20-Nov

20-Dec

20-Jan

21-Feb

21-Mar

17-Apr

23-May

Total

50.6

5.6

21.1

0

8.1

44.2

82.9

51.8

264.3

555.2 29.7

519.7 41.1

506.1 34.7

489.2 16.9

460.2 37.1

453.9 50.5

470.1 66.7

479.5 42.4

319.1

548.6 36.3

512.1 42.1

497.4 35.8

478.8 18.6

442.6 44.3

430.9 55.9

446.5 67.3

453.8 44.5

344.8

547.9 37.0

509.7 43.8

494.4 36.4

474.8 19.6

437.2 45.7

425.1 56.3

439.2 68.8

445.6 45.4

353.0

547.0 37.9

508.1 44.5

491.4 37.8

470.8 20.6

432.8 46.1

420.2 56.8

433.9 69.2

439.3 46.4

359.3

546.2 38.7

504.9 46.9

487.7 38.3

465.1 22.6

425.6 47.6

411.8 58.0

423.2 71.5

427.8 47.2

370.8

545.5 39.4

503.1 48.0

484.6 39.6

461.3 23.3

420.6 48.8

405.1 59.7

415.2 72.8

418.6 48.4

380.0

−1

N rate at 120 kg ha SWS (mm) ET (mm)

534.3

N rate at 180 kg ha−1 SWS (mm) ET (mm)

534.3

N rate at 240 kg ha−1 SWS (mm) ET (mm)

534.3

−1

N rate at 300 kg ha SWS (mm) ET (mm)

534.3

comparisons, under the RFFM cultivation conditions the N fertilized treatments consumed 330.8 mm ha−1 and 319.5 mm ha−1 water on average and the control (N0) 290.3 mm ha−1 and 274.5 mm ha−1 water in 2014–2015 and 2015–2016, respectively. Under the flat cultivation conditions, the N fertilized treatments consumed 361.6 mm ha−1 and 337.0 mm ha−1 water on average and N0 319.1 mm ha−1 and 298.3 mm ha−1 water in 2014–2015 and 2015–2016, respectively. 3.4. Seed yield and water productivity (WP) Seed yield initially increased and then decreased with the increase of N levels in both seasons and cultivation patterns (Table 9). In the flat cultivation condition treatment, seed yield significantly increased among the N0 to N180 treatments in both seasons. Seed yield began to reduce when N levels rose to

240 kg ha−1 , however, no significant difference was found between N180 and N240, while seed yield was markedly decreased when N level rose to 300 kg ha−1 . In the RFFM cultivation condition treatment, N240 obtained a significantly higher seed yield than other N levels in both seasons, and the average seed yield in N240 was 8.0% (215.0 kg ha−1 ) and 11.2% (292.5 kg ha−1 ) greater than in N180 and N300, respectively. The effect of cultivation patterns on seed yield was consistent in both seasons. Seed yield in the RFFM cultivation treatments was consecutively higher than in flat cultivation treatments by 22.0% (438 kg ha−1 ) in 2014–2015, and by 26.0% (414 kg ha−1 ) in 2015–2016 (Table 9). Applying N fertilizer significantly improved WP of winter oilseed rape, regardless of growth seasons and cultivation patterns (Table 9). Compared to N0, average WP of the other five N levels was improved by 55.0% (2.6 kg ha−1 mm−1 ) in the RFFM cultiva-

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Table 7 Soil water storage (SWS) in 0–200 cm layer, rainfall and evapotranspiration (ET) with six N rates under ridge-furrow film mulching (RFFM) cultivation pattern in 2015–2016 growing season. Date of determination

Treatment and indicators

16-Sep

Rainfall (mm) N rate at 0 kg ha−1 SWS (mm) ET (mm)

559.3

N rate at 60 kg ha−1 SWS (mm) ET (mm)

559.3

N rate at 120 kg ha−1 SWS (mm) ET (mm)

559.3

15-Oct

15-Nov

15-Dec

15-Jan

15-Feb

15-Mar

18-Apr

20-May

Total

27.5

74.6

26.9

1.0

5.4

1.6

22.2

24.7

183.9

573.9 12.9

614.5 34.0

619.1 22.3

605.1 15.0

583.7 26.8

535.2 50.1

487.1 70.3

468.7 43.1

274.5

571.2 15.6

610.5 35.3

612.9 24.5

596.4 17.5

573.4 28.4

520.1 54.9

467.3 75.0

442.3 49.7

300.9

569.7 17.1

608.1 36.2

609.2 25.8

591.8 18.4

567.9 29.3

511.5 58.0

455.4 78.3

428.4 51.7

314.8

568.9 17.9

606.8 36.7

607.5 26.2

588.6 19.9

564.1 29.9

507.2 58.5

450.7 78.7

423.4 52.0

319.8

568.1 18.7

605.4 37.3

605.8 26.5

585.9 20.9

560.7 30.6

502.3 60.0

444.8 79.7

416.1 53.4

327.1

567.2 19.6

604.0 37.8

603.9 27.0

582.6 22.3

556.5 31.5

497.0 61.1

438.2 81.0

408.2 54.7

335.0

−1

N rate at 180 kg ha SWS (mm) ET (mm)

559.3

N rate at 240 kg ha−1 SWS (mm) ET (mm)

559.3

N rate at 300 kg ha−1 SWS (mm) ET (mm)

559.3

Table 8 Soil water storage (SWS) in 0–200 cm layer, rainfall and evapotranspiration (ET) with six N rates under flat cultivation pattern in 2015–2016 growing season. Date of determination

Treatment and indicators

16-Sep

Rainfall (mm) N rate at 0 kg ha−1 SWS (mm) ET (mm)

559.3

N rate at 60 kg ha−1 SWS (mm) ET (mm)

559.3

N rate at 120 kg ha−1 SWS (mm) ET (mm)

559.3

15-Oct

15-Nov

15-Dec

15-Jan

15-Feb

15-Mar

18-Apr

20-May

Total

27.5

74.6

26.9

1.0

5.4

1.6

22.2

24.7

183.9

555.2 31.6

591.2 38.6

585.6 32.5

569.2 17.4

539.1 35.5

494.0 46.7

460.7 55.5

444.9 40.5

298.3

554.6 32.2

589.2 40.0

582.5 33.6

564.5 19.0

533.0 36.9

484.7 49.9

448.4 58.5

429.2 43.9

314.0

552.8 34.0

585.5 41.9

577.4 35.0

558.1 20.3

525.1 38.4

475.7 51.0

435.7 62.2

415.8 44.6

327.4

551.7 35.1

583.2 43.1

572.9 37.2

552.4 21.5

518.6 39.2

466.0 54.2

424.8 63.4

403.6 45.9

339.6

550.6 36.2

581.1 44.1

570.2 37.8

549.0 22.2

513.3 41.1

459.4 55.5

417.2 64.4

395.2 46.7

348

549.5 37.3

579.3 44.8

567.2 39.0

544.7 23.5

508.0 42.1

453.4 56.2

410.1 65.5

387.0 47.8

356.2

−1

N rate at 180 kg ha SWS (mm) ET (mm)

559.3

N rate at 240 kg ha−1 SWS (mm) ET (mm)

559.3

N rate at 300 kg ha−1 SWS (mm) ET (mm)

559.3

tion condition, and 56.1% (2.1 kg ha−1 mm−1 ) in the flat cultivation condition. In the RFFM cultivation condition, N240 produced a significantly higher WP than in the other five N levels in both seasons. In the flat cultivation condition, N180 achieved the highest WP among the six N levels, however, no significant differences were found between N180 and N240, and the WP of these two nitrogen treatments in both seasons were significantly higher than the other N levels. The RFFM cultivation pattern greatly increased seed yield and reduced ET, thus improving WP (Table 9). RFFM cultivation substantially improved WP by 32.1% (1.8 kg ha−1 mm−1 ) in 2014–2015, and 33.3% (1.6 kg ha−1 mm−1 ) in 2015–2016, respectively, when compared to the flat cultivation treatments. In addition, seed yield and WP in 2014–2015 were 21.1% and 15.6% higher in film mulching conditions, and 25.0% and 16.7% higher in non-film mulching conditions than in 2015–2016.

3.5. Relationship among seed yield, ET, and WP Relationships between seed yield and ET, and WP and ET under the RFFM cultivation and flat cultivation conditions are shown in Fig. 3. The slopes of correlation between seed yield and ET, and WP and ET in RFFM cultivation condition were 27.676 and 0.068, respectively, and were much higher than the corresponding data (19.835 and 0.044) in the flat cultivation condition treatment. These results confirmed that seed yield and WP are much higher in RFFM cultivation condition than in flat cultivation condition when the plants of winter rapeseed consumed same amount of water. 3.6. Economic benefit Economic benefit was assessed from five aspects: rapeseed yield, establishment for cultivation pattern, fertilizer, weed con-

X.-B. Gu et al. / Agricultural Water Management 200 (2018) 60–70

67

Table 9 Seed yield and water productivity (WP) of winter oilseed rape under ridge-furrow film mulching (RFFM) and flat cultivation patterns in 2014–2015 and 2015–2016 growing seasons. Determination items

N rate (kg ha−1 )

Mean

LSD0.05

2843 348.5 8.2

2430 324.0 7.4

175.9 7.5 0.43

2498 370.8 6.7

2321 380.0 6.1

1992 354.5 5.6

128.7 11.9 0.35

2391 319.8 7.5

2606 327.1 8.0

2380 335.0 7.1

2007 312.0 6.4

154.3 7.8 0.48

2010 339.6 5.9

2007 348.0 5.8

1862 356.2 5.2

1593 331.0 4.8

112.6 9.1 0.31

0

60

120

180

240

300

2014–2015 RFFM cultivation treatment Seed yield (kg ha−1 ) Evapotranspiration (mm) WP (kg ha−1 mm−1 )

1442 290.3 5.0

1742 310.7 5.6

2364 323.5 7.3

2987 332.7 9.0

3202 338.4 9.5

Flat cultivation treatment Seed yield (kg ha−1 ) Evapotranspiration (mm) WP (kg ha−1 mm−1 )

1180 319.1 3.7

1458 344.8 4.2

1994 353.0 5.6

2503 359.3 7.0

2015–2016 RFFM cultivation treatment Seed yield (kg ha−1 ) Evapotranspiration (mm) WP (kg ha−1 mm−1 )

1229 274.5 4.5

1579 300.9 5.2

1855 314.8 5.9

Flat cultivation treatment Seed yield (kg ha−1 ) Evapotranspiration (mm) WP (kg ha−1 mm−1 )

995 298.3 3.3

1147 314.0 3.7

1537 327.4 4.7

Fig. 3. Correlations between seed yield, evapotranspiration, and water productivity of winter oilseed rape under film mulched and non-film mulched conditions in 2014–2015 and 2015–2016 seasons. RFFM was the abbreviation of ridge-furrow film mulching. ∗∗ denotes significant at P ≤ 0.01 level.

trol, and harvest (Table 10). The highest economic benefit in both seasons was found in N240 (averaged 1259.6 $ ha−1 ) for RFFM cultivation pattern and N180 (averaged 1010.9 $ ha−1 ) for flat cul-

tivation pattern, respectively. The economic benefit was lower in RFFM cultivation pattern than in flat cultivation pattern in both seasons when N rate was 0 kg ha−1 . While when N rate was up to

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Table 10 Economic return of winter oilseed rape with six N rates under ridge-furrow film mulching (RFFM) and flat cultivation patterns in 2014–2015 and 2015–2016 growing seasons. Planting pattern

2014–2015 RFFM cultivation

Flat cultivation

2015–2016 RFFM cultivation

Flat cultivation

N rate (kg ha−1 )

Income ($ ha−1 )

Outcome ($ ha−1 ) Establishment for cultivation pattern

Fertilizer

Weed control

Harvest

Economic benefit ($ ha−1 )

0 60 120 180 240 300

1118.3 1350.9 1833.3 2316.4 2483.2 2204.7

378.1 378.1 378.1 378.1 378.1 378.1

221.6 251.9 282.3 312.6 343.0 373.3

155.1 155.1 155.1 155.1 155.1 155.1

116.3 116.3 116.3 116.3 116.3 116.3

247.2 449.5 901.5 1354.3 1490.7 1181.9

0 60 120 180 240 300

915.1 1130.7 1546.3 1941.1 1937.2 1799.9

155.1 155.1 155.1 155.1 155.1 155.1

221.6 251.9 282.3 312.6 343.0 373.3

155.1 155.1 155.1 155.1 155.1 155.1

116.3 116.3 116.3 116.3 116.3 116.3

267.0 452.3 837.5 1202.0 1167.7 1000.1

0 60 120 180 240 300

953.1 1224.5 1438.6 1854.2 2021.0 1845.7

378.1 378.1 378.1 378.1 378.1 378.1

221.6 251.9 282.3 312.6 343.0 373.3

155.1 155.1 155.1 155.1 155.1 155.1

116.3 116.3 116.3 116.3 116.3 116.3

82.0 323.1 506.8 892.1 1028.5 822.9

0 60 120 180 240 300

771.6 889.5 1191.9 1558.8 1556.4 1444.0

155.1 155.1 155.1 155.1 155.1 155.1

221.6 251.9 282.3 312.6 343.0 373.3

155.1 155.1 155.1 155.1 155.1 155.1

116.3 116.3 116.3 116.3 116.3 116.3

123.5 211.1 483.1 819.7 786.9 644.2

Seed of winter oilseed rape is sold about 775.5 $ per ton; establishment for cultivation pattern included plastic film (67.9 $ ha−1 ) under RFFM pattern, plough (155.1 $ ha−1 ) under both patterns, and the form of the ridges and furrows under RFFM pattern (155.1 $ ha−1 ).

120 kg ha−1 , the economic benefit in RFFM cultivation pattern was 43.9 $ ha−1 higher than in flat cultivation pattern. The gap between the economic benefit of RFFM and flat cultivation pattern reached its peak at 240 kg N ha−1 (averaged 282.3 $ ha−1 ). 4. Discussion 4.1. Growth characteristics The RFFM planting system more efficiently uses sparse precipitation by harvesting and retaining rainwater from the ridges and offering water to crop plants in the furrows compared with flatfarming practices (Zhou et al., 2009). It has been reported that the RFFM planting pattern exhibits rainwater harvesting efficiency as high as 87% due to better use of light rainfalls <5 mm (Li et al., 2000). Additionally, studies have shown that film mulching effectively increases the temperature of topsoil (Ramakrishna et al., 2006; Wang et al., 2015). Increased soil temperature and higher volumes of retained water as a consequence of RFFM conditions have resulted in boosted plant vigor and enhanced canopy size (Li et al., 2015; Qin et al., 2014). In the present study, results showed that LAI and ADM were always higher under RFFM treatments than under flat cultivation treatments at same N application rates (Tables 1, 2, 3 and 4). Adequate levels of N fertilization have been shown to accelerate crop growth, increase dry matter accumulation and expand leaf area (Rossini et al., 2011). However, in the current study LAI and ADM had no significant response to N fertilizer under either the RFFM cultivation conditions or the flat cultivation conditions at first two determinations. This was a result of the indigenous soil N being adequate for plant nutrient requirement. As N application rates increased, both LAI and ADM began to show an escalated response until the N rate reached 240 kg ha−1 . The decrease in LAI

and ADM at nitrogen rates of 300 kg N ha−1 suggests that excessive use of N would not promote winter oilseed rape growth. Corroborating reports have shown that the growth of winter oilseed rape is very poor with low N supply and ADM in lower N input treatments is only 21.9–60.0% of the ADM in the high N input treatments (Ren et al., 2017). However, in our study, ADM in N0 and N60 treatments accounted for 52.8–66.1% and 65.9–84.1% of the ADM in other four N application rates, respectively. The differences might be caused by the different climates, varieties, and cultivation patterns. 4.2. ET Understanding the ET rates of a cropping system helps improve water management and efficiency. Other studies have shown that compared to the flat cultivation pattern, the RFFM cultivation pattern significantly decreases the ET of maize by 6.0–31.0 mm (Zhou et al., 2009), wheat by about 50 mm (Zhang et al., 2007), and potato by 9.9–12.6 mm (Qin et al., 2014). In our study, the RFFM cultivation pattern decreased the ET of winter oilseed rape by 12.6–34.1 mm compared to the flat cultivation pattern. Plastic mulches on the soil surface have been shown to conserve water by suppressing soil evaporation, especially early in the crop season when the crop canopy is small (Bond and Willis, 1969). At the seedling stage of winter oilseed rape (from September to February), ET under the RFFM treatment was 40.4–61.3 mm lower than ET under the flat cultivation treatment. The main reasons might be due to RFFM could make better use of light rains collected by mulching ridges, and retained more water in the soil (Li et al., 2000). In addition, the plastic film can intercept the moisture and heat exchange between ground and atmosphere, and then decreased the soil evaporation (Jalota and Prihar, 1990); larger canopies under RFFM treatments will shade the soil surface and also reduce the soil evaporation (Li et al., 2015). By reducing soil

X.-B. Gu et al. / Agricultural Water Management 200 (2018) 60–70

evaporation when the canopy is small during the early growth period, maintained soil water will be used for plant transpiration and increase water productivity later in the season (Li et al., 2008). In our study, from winter oilseed rape stem elongation to the maturity stage, the RFFM cultivation pattern increased ET by 15.2–29.8 mm compared to the flat cultivation pattern. The application of N fertilizers plays a very important role to increase plant transpiration, in turn increasing crop ET. Reports have shown that compared to no N addition, the ET of maize in N fertilized plots increased by 44.9–120.9 mm under plastic film mulching conditions (Li et al., 2015). Additionally, even in flat cultivation conditions, the ET of winter oilseed rape in N fertilized plots was 16.0–68.0 mm higher than when no nitrogen was amended to the soils (Gu et al., 2016b). In our study, the ET of winter oilseed rape increased with rising N application, and the N fertilized plots increased ET by 20.4–60.5 mm and 15.7–60.9 mm in comparison to the N0 under the RFFM and flat cultivation patterns, respectively.

4.3. Yield and WP In the present study, the RFFM cultivation pattern significantly improved yield and WP of winter oilseed rape compared to the flat cultivation pattern over both growing seasons. This result was consistent with previous studies in maize (Gao et al., 2014) and potato (Qin et al., 2014). The differences in yields and WP found in the two cultivation conditions may be due to: (1) higher LAI and ADM in the RFFM cultivation treatments than in the flat cultivation pattern was consistent throughout the crop growth periods; (2) the RFFM cultivation pattern lowers soil evaporation, increases the infiltration of rainwater into the soil, and enhances the retention of soil water (Ramakrishna et al., 2006); and (3) the RFFM cultivation pattern increases the diameter and weight of taproots, and significantly induced the proliferation of lateral roots (Gu et al., 2016a). Higher taproot diameter and weight can improve the lodging resistance of oilseed rape (Ma et al., 2010); and higher lateral root proliferation can increase nutrient and water uptake by oilseed rape (Hammer et al., 2009), the two of which could make an important contribution to the rapeseed yield. N fertilizers are very important for significantly increasing WP and crop yield (Liu, 2000; Li et al., 2009). In many cases, even when film mulching is properly conducted, the crop yield and WP are still very low because N nutrients were deficient in the soils (Li et al., 2009). Yield and WP of winter oilseed rape have increased by 22.0–37.1% and 7.5–18.1%, respectively, when 100–260 kg N ha−1 are applied (Gu et al., 2016b). Zou et al. (2011) reported that seed yield is improved by 200–2850 kg ha−1 under N application treatments in most regions of China. The present study showed that when the N application rate was 0 or 60 kg ha−1 , the seed yield and WP of winter oilseed rape under the RFFM cultivation pattern ranged from 1229 to 1742 kg ha−1 and from 4.5 to 5.6 kg ha−1 mm−1 , respectively. When the N application rate reached 240 kg ha−1 , seed yield and WP were increased by 112.0–122.1% and 77.8–90.0% in comparison to the N0 treatment, and by 65.0-83.8% and 53.8-69.6% in comparison to N60 in both growth seasons. Seed yield and WP of winter oilseed rape in 2014–2015 were higher than in 2015–2016. This may be because there was 130.6 mm more rainfall during 2014–2015 in March, April and May when the flowering and pod-filling stages of winter oilseed rape in northwestern China occur. This demonstrates that irrigation should be carefully monitored and only applied at the flowering and podfilling stages. This is especially dire for regions where irrigation water is scarce and efficiency is the key to achieve a higher seed yield.

69

4.4. Finding an optimal N-application rate It is well documented that N fertilizer applications increase crop yields significantly, however, excess N has been shown to hinder yields (Hu et al., 2013; Kirda et al., 2005). In addition, N fertilization must be monitored and modulated as excessive N fertilization poses a real danger to environmental safety (Morell et al., 2011). Understanding optimal N application rates for different crop systems is the key to maximize yields, profits and environmental security. In the present study, seed yield, WP, and economic benefit of winter oilseed rape significantly increased from N0 to N240 application rates, then significantly decreased at the N300 rate under the RFFM cultivation pattern. However, in the flat cultivation pattern, the seed yield, WP, and economic benefit significantly increased from N0 to N180 application rates, and remained stable up to a rate of N240, followed by a significant reduction at N300 application rate. These results showed that the optimal N application rates for winter oilseed rape are 240 and 180 kg ha−1 under the RFFM and flat cultivation patterns, respectively, in northwest China. 5. Conclusions RFFM cultivation pattern significantly improved LAI, ADM, rapeseed yield and WP, meanwhile significantly decreased ET of winter oilseed rape in comparison to flat cultivation without mulching. In addition, N240 treatment obtained the significantly higher seed yield and WP than the other five N levels under RFFM cultivation pattern. Present study indicated that RFFM cultivation pattern has the potential of improving winter oilseed rape productivity in arid and semiarid regions, with the optimal N-application rate of 240 kg ha−1 . Further study is mainly needed to evaluate (1) the optimal N application level of winter oilseed rape under ridgefurrow planting pattern covered by biodegradable film (ridges) or straw (furrows); and (2) the soil nutrient condition (microorganism, enzymatic activity, especially the distribution and leaching of nitrate N) under different cultivation patterns and N levels. Acknowledgements This research was supported by the Special Fund for Agroscientific Research in the Public Interest, China (201503125 and 201503105) and the National High Technology Research and Development Program of China (2011AA100504). References Behrens, T., Diepenbrock, W., 2006. Using hemispherical radiation measurements to predict weight-related growth traits in oilseed rape (Brassica napus L.) and barley (Hordeum vulgare L.) canopies. J. Agron. Crop Sci. 192, 465–474. Bond, J.J., Willis, W.O., 1969. Soil water evaporation: surface residue rate and placement effects. Soil Sci. Soc. Am. J. 33, 445–448. FAOSTAT, 2016. FAO Statistics Division (Available from: http://faostat3.fao.org./faostat-gateway/go/to/download/Q/*/E). Gan, Y.T., Siddique, K.H.M., Turner, N.C., Li, X.G., Niu, J.Y., Yang, C., Liu, L.P., Chai, Q., 2013. Chapter Seven–Ridge-furrow mulching systems–an innovative technique for boosting crop productivity in semiarid rain-fed environments. Adv. Agron. 118, 429–476. Gao, Y.H., Xie, Y.P., Jiang, H.Y., Wu, B., Niu, J.Y., 2014. Soil water status and root distribution across the rooting zone in maize with plastic film mulching. Field Crops Res. 156, 40–47. Godfray, H.C., Beddington, J.R., Crute, I.R., Haddad, L., Lawrence, D., Muir, J.F., Pretty, J., Robinson, S., Thomas, S.M., Toulmin, C., 2010. Food security: the challenge of feeding 9 billion people. Science 12, 812–818. Gu, X.B., Li, Y.N., Du, Y.D., 2016a. Continuous ridges with film mulching improve soil water content, root growth, seed yield and water use efficiency of winter oilseed rape. Ind. Crops Prod. 85, 139–148. Gu, X.B., Li, Y.N., Du, Y.D., Zhou, C.M., Yin, M.H., Yang, D., 2016b. Effects of water and nitrogen coupling on nitrogen nutrition index and radiation use efficiency of winter oilseed rape (Brassica napus L.). Trans. Chin. Soc. Agric. Machin. 47, 122–132 (in Chinese with English abstract).

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