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Optimized nitrogen fertilizer application improves yield, water and nitrogen use efficiencies of winter rapeseed cultivated under continuous ridges with film mulching
Industrial Crops & Products 109 (2017) 233–240
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Optimized nitrogen fertilizer application improves yield, water and nitrogen use efficiencies of winter rapeseed cultivated under continuous ridges with film mulching
MARK
⁎
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
A B S T R A C T
Keywords: Continuous ridges with film mulching Nitrogen fertilizer Seed yield Water use efficiency Nitrogen use efficiency Winter rapeseed
The continuous ridges with film mulching (CRFM) cultivation pattern has been rapidly adopted for production of winter rapeseed (Brassica napus L.) in northwest China due to significant improvements in soil moisture, water use efficiency (WUE) and yield. However, in many cases, the crop yield, WUE, and nitrogen (N) use efficiency (NUE) were still very low under CRFM cultivation due to the deficiency of N nutrients. The objective of this study was to investigate the response of winter rapeseed to six N application amounts: 0 (N0), 60 (N60), 120 (N120), 180 (N180), 240 (N240), and 300 (N300) kg N ha−1. Aboveground dry matter and shoot N uptake at flowering and harvest, yield, oil yield, ET, WUEY, and WUEOY were all significantly higher in N180, N240, and N300 than in N0, N60, and N120. Average WUEY, WUEOY, N partial factor productivity and N recovery efficiency did not differ markedly between N180 and N240, but were all significantly higher than in N300. However, average seed yield and oil yield in N240 were 11.9% (427 kg ha−1) and 9.7% (144 kg ha−1) significantly higher than in N180. In addition, seed oil and protein content in N240 did not differ significantly from N180 and N300. These results suggest that the optimal N application amount for winter rapeseed under CRFM cultivation pattern is 240 kg N ha−1. This rate simultaneously improves seed yield, oil yield, WUEY, WUEOY and NUE.
1. Introduction Rapeseed (Brassica napus L.) produces a kind of vegetable oil that is used for human consumption, and is a source for biodiesel (Zhang et al., 2012). Because of this, rapeseed is grown around the world, and the global planting area has remained stable or increased in some areas in recent years (FAOSTAT, 2016). In 2014, Canada, China, and India had the largest rapeseed planting areas globally, with about 8.1, 7.6, and 6.6 million hectares, respectively (FAOSTAT, 2016). However, the average rapeseed yields in China, Canada, and India were as low as 1947, 1926, and 1185 kg ha−1, respectively (FAOSTAT, 2016), which might be due to low water and nitrogen use efficiencies, especially in arid and semi-arid regions (Jing and Dong, 2004; Gu et al., 2016a). Mulching is an important cultivation method to improve yield, soil moisture, and water use efficiency (WUE) in rapeseed cultivation (Su et al., 2014; Gu et al., 2016a). Su et al. (2014) reported that straw mulching increased soil moisture at 0–30 cm depths by about 8.4% throughout the growth stages of rapeseed, and ultimately improved seed yield by 25.6%. Gu et al. (2016a) found that values for soil water content, rapeseed yield, and WUE in film mulching treatments were ⁎
3.1–7.2%, 20.4–70.7%, and 34.9–122.0% higher than in the conventional cultivation pattern. Rapeseed yield is also heavily dependent on nitrogen (N) availability. In order to produce 0.1 t of seeds, rapeseed crops need to accumulate 6 kg N (Rathke et al., 2006), meaning that farmers apply large amounts of N fertilizer to produce high rapeseed yields. Adding N fertilizer can increase rapeseed yields by 1.1–2.4 t per hectare (Rathke et al., 2005; Zou et al., 2011). However, N fertilization is inefficient, and excess N in the soil is lost through leaching, gasification, and runoff (Zhu and Chen, 2002), which cause serious environmental problems. Thus, determining the optimal application rate for N fertilizer is critical for rapeseed production. Many researchers found that application of 150–180 kg N ha−1 could significantly increase yield and oil production, as well as maintain a high NUE of rapeseed under the conventional cultivation pattern (Barlóg and Grzebisz, 2004; Li et al., 2011; Schuster and Rathke, 2001; Zou et al., 2011). When applied at 210 kg N ha−1, straw mulching significantly increased yield, N uptake, and N use efficiency (NUE) of rapeseed though more N was lost due to ammonia volatilization because of topdressing (Su et al., 2014). Previous studies only investigated the application rate of N fertilizer
Corresponding author at: No.23 Weihui Road, Yangling, Shaanxi Province, 712100, China. E-mail addresses: [email protected] (X.-B. Gu), [email protected] (Y.-N. Li).
http://dx.doi.org/10.1016/j.indcrop.2017.08.036 Received 15 June 2017; Received in revised form 9 August 2017; Accepted 18 August 2017 0926-6690/ © 2017 Published by Elsevier B.V.
Industrial Crops & Products 109 (2017) 233–240
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Each plot received 60 mm (at each irrigation) of irrigation water in the first season on 15 January and 5 April 2013, because of severe drought; 30 mm in the second season on 15 September 2013 to ensure seedling emergence, and none in the third and fourth seasons. Weed control was also performed in order to reduce yield loss. Plants were harvested on 20 May 2013, 22 May 2014, 23 May 2015, and 20 May 2016, and the plastic film was recycled.
in rapeseed cultivated under straw mulching and conventional patterns (Fismes et al., 2000; Hocking, 2001; Rathke et al., 2005; Su et al., 2014; Zou et al., 2011). However, little is known about N uptake, NUE, and how different N rates affect yield and oil production of rapeseed under the film mulching planting pattern, especially under the continuous ridges with film mulching (CRFM) cultivation method, which has been proven to be appropriate for winter rapeseed in arid and semi-arid areas (Gu et al., 2016a). The goal of the present study was to determine how N fertilization affects yield, WUE, and NUE of rapeseed grown using CRFM cultivation. Our results will be used to manage N fertilization and to improve production of winter rapeseed.
2.3. Measurements and methods 2.3.1. Weather conditions Daily rainfall and air temperatures during the winter rapeseed growing seasons were measured at Yangling National Meteorological Observing Station, which is located 50 m away from the experimental field. The monthly total rainfall and monthly mean air temperatures were calculated using these data.
2. Materials and methods 2.1. Experimental site A field experiment was conducted over four years (September 2012 to May 2016) at the Key Laboratory of Agricultural Soil and Water Engineering in Arid and Semiarid Areas of the Ministry of Education (34°18′N, 108°24′E; 521 m a.s.l.), Yangling, Shaanxi, China. Mean annual precipitation in this region is 632 mm, with 60–70% falling from July to September, making this a typical rainfed region. Per year in this region, soil evaporation has a mean of 1500 mm; mean air temperature is 12.9 °C; and mean sunshine duration is 2164 h. Loamy soil is present at this site, and it has a filled capacity of 24% with a dry bulk density of 1.40 g cm−3. Top-soil (0–20 cm) nutrient properties at the start of each growing season are in Table 1.
2.3.2. Aboveground dry matter and shoot N uptake Ten representative plants from each plot were cut at ground level at three growth stages: seedling (78 DAS in 2013–2014, 75 DAS in all other seasons); flowering (215 DAS); and harvest (247, 252, 244, and 246 DAS in 2012–2013, 2013–2014, 2014–2015, and 2015–2016, respectively). Plants were separated into leaves, stems, pod walls, and seeds. Plant tissues were first oven-dried to deactivate enzymes (30 min at 105 °C), and then dried to a constant weight (75 °C). The weights of dry leaves, stems, pod walls, and seeds were added together to obtain aboveground dry matter, and then these plant tissues were ground and digested with H2SO4-H2O2 (Bao, 2000). We used an automated continuous flow analyser (AA3, Seal, Norderstedt, Germany) to determine the N concentration in different tissues. Finally, we calculated shoot N uptake by multiplying the dry weight by the N concentration in different tissues.
2.2. Experimental design Six application rates of N (as urea) were used in this experiment: 0 (N0), 60 (N60), 120 (N120), 180 (N180), 240 (N240), and 300 (N300) kg N ha−1. The N fertilizer was applied as a basal dressing to all plots. Four replicates of each rate were used (24 total plots), and the experiment was designed as a randomized block. Plots were 4 m × 5 m in size, and were spaced 1 m apart. Calcium superphosphate (P2O5 = 16%), potassium sulphate (K2O = 51%), and borax (B = 11%) at rates of 90 kg P2O5 ha−1, 120 kg K2O ha−1, and 15 kg B ha−1 were also used as basal fertilizers in each plot. No additional fertilization was used during the growth period. The continuous ridges with film mulching (CRFM) method was used to plant winter rapeseed. Ridges were 20 cm high and 50 cm wide (Fig. 1). In each growing season, we ploughed the field and separated it into plots; applied fertilizers; and formed ridges. After these steps, a transparent plastic film (0.8 m wide and 0.008 mm thick) containing small holes every 0.3 m for rainwater infiltration, was laid manually over the ridge layer at the soil surface (Fig. 1). Shaanyou No. 107 seeds were planted by hand in plot furrows on 15 September 2012, 12 September 2013, 21 September 2014, and 16 September 2015. At the three leaves stage, seedlings were thinned manually, and at the five leaves stage, we determined that the plant density was 120 000 plants ha−1.
2.3.3. Seed yield and oil and protein contents To determine seed yield, plants at a size of 1 m2 (1 × 1 m) from the middle of each plot were chosen at harvest, and were then sun-dried and threshed. Then, near-infrared reflectance spectroscopy (NIR System 5000, Foss, Denmark) was used to measure seed oil and protein content. Oil yield was calculated by seed yield × oil content. 2.3.4. Evapotranspiration (ET) and WUE Soil moisture contents at depths between 0 and 200 cm were determined before planting and after harvest in order to calculate changes in soil water storage during the winter rapeseed growth period. Coring at 10 cm depth intervals was done manually between two plants in the same row. Soil moisture content was then calculated using the oven dry weight method (samples were dried at 105 °C). Soil water storage was calculated using Eq. (1): SWS = 10Σgi × hi × ωi
Where SWS (mm) is soil water storage, γi (g cm ) is soil dry bulk density in each different soil layer, hi (cm) is the soil thickness, ωi (%) is gravimetric water content in each different soil layer, and i = 10, 20, 30,…, 200. The soil water balance equation (Eq. (2)) was used to calculate the evapotranspiration of winter rapeseed (Heerman, 1985):
Table 1 Nutrient properties in the 0–20 cm soil layer at the start of each growing season at the experimental site. Soil property
pH (water) Organic matter (g kg−1) Total N (g kg−1) Alkali hydrolysable N (mg kg−1) Available P (mg kg−1) Available K (mg kg−1)
Growing season 2012–2013
2013–2013
2014–2015
2015–2016
8.12 12.35 0.95 75.31
8.14 12.78 0.98 72.54
8.14 12.18 0.94 76.01
8.13 12.57 0.97 73.93
25.34 131.92
24.26 135.32
25.22 132.97
24.8 133.62
(1) −3
ET = I + P − D + SWS0–SWS1
(2)
Where ET (mm) is the evapotranspiration of winter rapeseed; I (mm) is the amount of irrigation; P (mm) is precipitation; D (mm) is deep drainage into the lower boundary of 200 cm (which was assumed to be negligible in this study because no heavy rains or irrigation occurred during the rapeseed growing seasons); and SWS0 and SWS1 (mm) are the soil water storages before sowing and after harvesting, respectively. 234
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Fig. 1. Schematic diagram of the continuous ridges with film mulching.
the four growing seasons: the maximum temperature in February 2014 was 1.5–2.4 °C lower than the other three seasons; and the maximum, mean, and minimum temperatures in January 2016 were 2.0–3.6 °C, 1.2–2.1 °C, and 1.2–1.8 °C lower than the other three seasons. Total rainfall during the growing seasons of winter rapeseed were 120 mm, 330 mm, 264 mm, and 184 mm, in 2012–2013, 2013–2014, 2014–2015, and 2015–2016, respectively. The growing seasons in 2012–2013 and 2015–2016 were much drier than in 2013–2014 and 2014–2015.
WUEY and WUEOY of the winter rapeseed were calculated using Eqs. (3) and (4): WUEY = Y/ET
(3)
WUEOY = OY/ET
(4)
Where WUEY and WUEOY (kg ha−1 mm−1) is yield water use efficiency and oil yield water use efficiency, Y and OY (kg ha−1) is yield and oil yield of winter rapeseed, and ET (mm) is evapotranspiration. 2.3.5. NUE Two indicators were used to evaluate nitrogen use efficiency (NUE): nitrogen recovery efficiency (NRE), and nitrogen partial factor productivity (NPFP). Eqs. (5) to (6) were used as follows: NRE (%) = (UN–U0)/TN NPFP (kg kg
−1
) = YN/TN
3.2. Aboveground dry matter Aboveground dry matter in N0 was always significantly lower than in the other five N application treatments in 2012–2013, 2013–2014, 2014–2015, and 2015–2016 (Table 2). At seedling stage, there were no significant differences of aboveground dry matter among N60, N120, N180, N240, and N300 treatments across the four growing seasons. At flowering stage, aboveground dry matter in N120 was significantly higher than that in N60, and was significantly lower than that in N180, N240, and N300. There were no significant differences among the N180, N240, and N300 treatments across the four growing seasons. At harvest, aboveground dry matter in N240 was significantly higher than in N0, N60, N120, and N180, at 128.9–139.3%, 82.8–101.4%, 37.3–46.3%, and 13.4–16.1% respectively. At harvest, no significant differences were found between the aboveground dry matter of N240 and N300 across the four growing seasons except for 2014–2015, in which the aboveground dry matter of N240 was significantly higher than N300 at 8.4%.
(5) (6)
−1
Where YN (kg ha ) is the seed yield with N fertilization; UN and U0 (kg N ha−1) are the shoot N uptakes with and without N fertilization, respectively; and TN is the total input of N fertilizer (kg N ha−1). 2.4. Data analysis Data were compiled and analysed using Excel 2010. Analysis of variance was used to test for significant differences between treatments of seed yield, aboveground dry matter, shoot N uptake, seed oil, seed protein content, and NUE. Least significant difference tests were used to compare means (P < 0.05). SPSS 18.0 was used for statistical analyses. AutoCAD 2007 was used to create Fig. 1, and Origin 8.0 was used to create other four figures.
3.3. Shoot N uptake Shoot N uptake of winter rapeseed was markedly influenced by the N application rate (P < 0.05) (Table 3). At seedling stage, shoot N uptake increased significantly from N0 to N60, and was then stable until N300. Compared to shoot N uptake at seedling stage, shoot N uptake at flowering stage increased by 25.7–46.7, 37.7–63.2, 27.6–59.4, and 25.3–47.2 kg N ha−1 in the 2012–2013, 2013–2014, 2014–2015, and 2015–2016 growing seasons, respectively. At flowering stage, shoot N uptake increased significantly from N0 to N180, and then did not vary from N180 to N300. At harvest, there were no
3. Results 3.1. Weather conditions Maximum, mean, and minimum air temperatures in the four growing seasons almost followed the same trend: they decreased from September to December or January, and then increased until May (Fig. 2). However, slight differences in temperature were found among
Fig. 2. Monthly maximum, mean, and minimum temperatures and monthly total rainfall during the 2012–2013, 2013–2014, 2014–2015, and 2015–2016 winter rapeseed growing seasons at the experimental site.
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Table 2 Aboveground dry matter (kg ha−1) of winter rapeseed for the six treatments at the seedling, flowering, and harvest stages in the four growing seasons. Treatment
N0 N60 N120 N180 N240 N300
2012–2013
2013–2014
2014–2015
2015–2016
Seedling
Flowering
Harvest
Seedling
Flowering
Harvest
Seedling
Flowering
Harvest
Seedling
Flowering
Harvest
2572 3063 3101 3267 3304 3358
3524 4547 5436 6072 6125 6098
5172 e 6148 d 8507 c 10801 b 12379 a 11527 ab
2326 2828 2931 3052 3108 3096
5013 6049 7261 7977 8106 8168
6870 e 8196 d 11024 c 13626 b 15728 a 14986 a
2795 3352 3487 3513 3582 3576
4627 5536 7668 8534 8614 8639
6157 e 7358 d 10036 c 12654 b 14685 a 13549 b
2608 3298 3381 3428 3492 3506
3815 5036 6652 7319 7503 7489
5413 e 6851 d 9124 c 11048 b 12526 a 12357 a
b a a a a a
d c b a a a
Analysis of variance (LSD0.05) Seedling Flowering N rate (N) 326∗ 582∗ ∗ Year (Y) 483 783∗ Y×N 889∗ 1201∗
b a a a a a
d c b a a a
b a a a a a
d c b a a a
b a a a a a
d c b a a a
Harvest 945∗ 959∗ 2102∗
N0, N60, N120, N180, N240, and N300 represent nitrogen application rate at 0, 60, 120, 180, 240, and 300 kg N ha−1. Different letters within a column indicate significant differences among treatments within a season at P < 0.05. * means significant at P = 0.05 level.
N60, N120, N180, and N300, respectively. The relationship between seed yield and N application rate was: Y = 1409.665 + 18.444 x − 0.035 x2. Oil yield consistently and significantly increased from N0 to N240, and then decreased significantly at N300 across the four growing seasons (Fig. 3b). No significant differences in oil yield were found between N180 and N300 across the four growing seasons. Average oil yield in N240 was significantly higher by 129.2%, 82.8%, 33.6%, 9.1%, and 13.5% compared to N0, N60, N120, N180, and N300, respectively. The relationship between seed yield and N application rate was: OY = 629.971 + 7.602 x − 0.016 x2 (Fig. 4).
significant differences between the shoot N uptake in N240 and N300, and the average shoot N uptake in N240 was significantly higher than in N0, N60, N120, and N180, at 107.4%, 53.2%, 29.5%, and 11.9%, respectively. 3.4. Seed oil and protein contents Seed oil content decreased as N application amount increased, and the seed oil content in N0 was significantly higher than the other five N application treatments across the four growing seasons (Table 4). Average seed oil content in N240 was significantly lower than that in N0, N60, N120, and N180 at 9.7%, 6.7%, 4.7%, and 2.5%, respectively; and was 1.5% slightly higher than that in N300. Seed protein content increased as N application amount increased, and seed protein content in N fertilizer treatments was consistently and significantly higher than that in the N0 treatment across the four growing seasons (Table 4). Average seed protein content in N240 did not differ significantly from N180 and N300; however, it was significantly higher than average seed protein content in N0, N60, and N120 at 23.6%, 14.6%, and 10.2%, respectively.
3.6. ET and WUE ET of winter rapeseed was significantly affected by the N application amount (P < 0.05) and ranged from 205.8 mm to 340.6 mm under the six N application rates across the four growing seasons (Table 5). ET in N0 was significantly lower than in the other five N treatment rates except in the 2013–2014 growing season, and increased as N application amount increased. ET did not differ significantly between N180 and N240 except in 2014–2015, and the ET in N240 was significantly lower than that in N300 at 6.8-9.6% across the four growing seasons. WUEY of winter rapeseed was consistently highest in N240 and lowest in N0 across the four growing seasons (Table 5). WUEY in N0 was significantly lower than that in other five N application treatments across the four growing seasons except for non-significant differences between N0 and N60 in 2014–2015 and 2015–2016. WUEY in N240
3.5. Seed yield and oil yield Seed yield in N240 was consistently and significantly higher than the other five N application treatments across the four growing seasons except for non-significant differences between N240 and N300 in 2012–2013 (Fig. 3a). Average seed yield in N240 was significantly higher by 153.8%, 96.0%, 40.3%, 11.9%, and 11.8% compared to N0,
Table 3 Shoot N uptake (kg ha−1) of winter rapeseed for the six treatments at the seedling, flowering, and harvest stages in the four growing seasons. Treatment
N0 N60 N120 N180 N240 N300
2012–2013
2013–2014
2014–2015
2015–2016
Seedling
Flowering
Harvest
Seedling
Flowering
Harvest
Seedling
Flowering
Harvest
Seedling
Flowering
Harvest
19.0 29.6 32.3 32.9 32.6 33.4
44.7 55.6 69.4 78.1 79.3 78.7
53.5 e 73.4 d 86.9 c 100.3 b 114.7 a 110.2 a
18.2 28.5 31.8 32.1 32.7 32.3
55.9 72.4 85.2 94.6 95.9 95.2
69.8 e 90.2 d 103.7 c 120.5 b 133.6 a 134.3 a
20.6 30.2 33.0 33.6 34.1 34.8
48.2 65.8 84.7 93.0 93.5 92.3
58.3 e 81.2 d 98.5 c 112.9 b 125.6 a 130.8 a
19.8 29.4 32.8 33.3 33.6 34.0
45.1 57.6 69.9 80.3 80.6 81.2
55.2 e 75.8 d 90.1 c 105.4 b 117.3 a 114.6 a
b a a a a a
d c b a a a
Analysis of variance (LSD0.05) Seedling Flowering N rate (N) 4.7∗ 8.1∗ ns Year (Y) 1.8 10.3∗ Y×N 5.1∗ 18.2∗
b a a a a a
d c b a a a
b a a a a a
d c b a a a
b a a a a a
d c b a a a
Harvest 11.6∗ 11.2∗ 26.5∗
N0, N60, N120, N180, N240, and N300 represent nitrogen application rate at 0, 60, 120, 180, 240, and 300 kg N ha−1. Different letters within a column indicate significant differences among treatments within a season at P < 0.05. * and ns mean significant and non-significant at P = 0.05 level, respectively.
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Table 4 Oil and protein contents of winter rapeseed for the six treatments in the four growing seasons. Treatment
N0 N60 N120 N180 N240 N300
Oil content (%)
Protein content (%)
2012–2013
2013–2014
2014–2015
2015–2016
Average
2012–2013
2013–2014
2014–2015
2015–2016
Average
44.93 43.35 42.92 41.23 41.04 40.35
44.01 42.48 41.96 41.48 40.69 39.20
44.14 42.83 41.67 41.30 40.18 39.37
45.46 44.17 42.65 41.34 40.30 39.82
44.64 43.21 42.30 41.34 40.30 39.69
20.12 21.58 22.46 24.98 25.22 25.95
20.74 22.29 23.13 25.14 26.19 26.58
20.40 22.44 23.36 25.08 25.81 26.17
21.48 22.94 23.88 24.93 25.05 26.73
20.69 22.31 23.21 25.03 25.57 26.36
a b b c c d
Analysis of variance (LSD0.05) Oil content N rate (N) 0.87∗ Year (Y) 0.73 ns Y×N 1.69∗
a b bc c d e
a b c c d e
a b c d e e
a b c d e e
c b b a a a
d c bc b a a
d c c b ab a
d c bc b b a
d c c b ab a
Protein content 1.02∗ 0.84 ns 2.26∗
N0, N60, N120, N180, N240, and N300 represent nitrogen application rate at 0, 60, 120, 180, 240, and 300 kg N ha−1. Different letters within a column indicate significant differences among treatments within a season at P < 0.05. * and ns mean significant and non-significant at P = 0.05 level, respectively.
correlation between WUEOY and N application WUEOY = 2.977 + 0.021 x − 4.291E–5 x2 (Fig. 5).
was significantly higher than that in N0, N60, and N120 at 85.1–118.5%, 62.6–84.4%, and 24.8–44.3%, respectively across the four growing seasons. There were no significant differences between the WUEY in N180 and N240 except in 2012–2013, where the WUEY in N240 was significantly higher than that in N180 at 12.0%. WUEY in N300 was significantly lower than WUEY in N240 in 2012–2013, 2013–2014, and 2014–2015, however, significant differences were not found between the two treatments in 2015–2016. The correlation between WUEY and N application amount was: WUEY = 6.628 + 0.053 x − 1.011E–4 x2. N240 consistently had the highest WUEOY across the four growing seasons, followed by N180 and N300; N0 had the lowest WUEOY (Table 5). WUEOY in N240 did not differ significantly from N180; however, it was significantly higher than the other four N application treatments across the four growing seasons except in 2015–2016. Average WUEOY in N240 was 78.8%, 62.8%, 30.4%, 5.4%, and 18.6% higher than in N0, N60, N120, N180, and N300, respectively. The
amount
was:
3.7. NUE NPFP of winter rapeseed decreased as the N application amount increased, and NPFP in N60 was consistently and significantly higher than in N120, N180, N240, and N300 across the four growing seasons (Table 6). Average NPFP in N240 did not differ significantly from N180, but it was significantly lower than average NPFP in N60 and N120 at 48.5% and 24.6%, respectively, and was 32.4% significantly higher than average NPFP in N300. The correlation between NPFP and N application amount was: NPFP = 34.425–0.075 x. NRE of winter rapeseed decreased with the increase of N application amount, and NPFP in N60 was consistently and significantly higher than NRE in the other four N application treatments across the four growing seasons (Table 6). Average NRE in N240 did not differ
Fig. 3. Yield (a) and oil yield (b) of winter rapeseed for the six treatments in the 2012–2013, 2013–2014, 2014–2015, and 2015–2016 growing seasons. Bars represent standard deviations. N0, N60, N120, N180, N240, and N300 represent nitrogen application rate at 0, 60, 120, 180, 240, and 300 kg N ha−1. Different letters above the bars indicate significant differences among treatments within a season at P < 0.05. * means significant at P = 0.05 level.
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Fig. 4. Relationship between the rate of N application and average yield and oil yield of the winter rapeseed. ** means significant at the P = 0.01 level.
Fig. 5. Relationship between the rate of N application and average water use efficiencies of the winter rapeseed. WUEY and WUEOY mean water use efficiencies for yield and oil yield, respectively. * means significant at the P = 0.05 level.
significantly from N120 and N180; however, it was reduced significantly by 24.1% in comparison to N60, and was increased significantly by 25.7% in comparison to N300. The correlation between NRE and N application amount was: NRE = 37.305–0.051 x (Fig. 6).
4. Discussion 4.1. Aboveground dry matter and shoot N uptake Under CRFM cultivation, both dry matter accumulation and N uptake increased significantly in winter rapeseed when N fertilizers were applied. Previous studies in maize (Li et al., 2015), tomato (Badr et al.,
Table 5 Evapotranspiration (ET) and water use efficiency (WUE) of the winter rapeseed for the six treatments in the four growing seasons. Soil water storage before sowing (mm)
Soil water storage after harvesting (mm)
Rainfall (mm)
Irrigation (mm)
ET (mm)
WUEY (kg ha−1 mm−1)
WUEOY (kg ha−1 mm−1)
2012–2013 N0 N60 N120 N180 N240 N300
500.6 500.6 500.6 500.6 500.6 500.6
534.8 515.7 497.7 484.4 478.0 455.2
120 120 120 120 120 120
120 120 120 120 120 120
205.8 224.9 242.9 256.2 262.6 285.4
e d c bc b a
6.9 d 7.8 d 9.7 c 12.5 b 14.0 a 12.2 b
3.1 3.4 4.1 5.2 5.8 4.9
d d c ab a b
2013–2014 N0 N60 N120 N180 N240 N300
457.5 457.5 457.5 457.5 457.5 457.5
605.1 593.4 574.8 551.1 540.3 516.2
330 330 330 330 330 330
30 30 30 30 30 30
212.4 224.1 242.7 266.4 277.2 301.3
d d c b b a
8.5 e 9.9 d 12.9 c 15.1 ab 16.1 a 14.1 b
3.8 4.2 5.4 6.3 6.5 5.5
c c b a a b
2014–2015 N0 N60 N120 N180 N240 N300
533.7 533.7 533.7 533.7 533.7 533.7
604.6 585.8 570.5 554.0 535.5 507.6
264 264 264 264 264 264
0 0 0 0 0 0
193.1 211.9 227.2 243.7 262.2 290.1
f e d c b a
8.7 d 9.6 d 12.1 c 15.6 a 16.1 a 13.5 b
3.8 4.1 5.0 6.4 6.5 5.3
c c b a a b
2015–2016 N0 N60 N120 N180 N240 N300
559.3 559.3 559.3 559.3 559.3 559.3
479.1 461.6 450.9 434.2 425.8 402.7
184 184 184 184 184 184
0 0 0 0 0 0
264.2 281.7 292.4 309.1 317.5 340.6
d c c b b a
5.4 c 6.4 c 8.4 b 10.9 a 11.8 a 10.5 a
2.5 2.8 3.6 4.5 4.8 4.2
c c b a a a
1.4∗ 1.6∗ 3.1∗
0.7∗ 0.6∗ 1.7∗
Treatment
Analysis of variance (LSD0.05) N rate (N) Year (Y) Y×N
14.7∗ 25.6∗ 30.9∗
N0, N60, N120, N180, N240, and N300 represent nitrogen application rate at 0, 60, 120, 180, 240, and 300 kg N ha−1. Different letters within a column indicate significant differences among treatments within a season at P < 0.05. *Means significant at P = 0.05 level.
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Table 6 Nitrogen (N) partial factor productivity (NPFP), N agronomic efficiency (NAE), N physiological efficiency (NPE), and N recovery efficiency (NRE) of the winter rapeseed for the six treatments in the four growing seasons. Indicator
Treatment
2012–2013
2013–2014
2014–2015
2015–2016
Average
NPFP (kg kg−1)
N0 N60 N120 N180 N240 N300
– 29.22 19.57 17.86 15.34 11.64
a b bc c d
– 36.88 26.05 22.40 18.55 14.14
a b c d e
– 34.05 22.86 21.07 17.54 13.03
a b b c d
– 30.10 20.53 18.65 15.67 11.87
a b bc c d
– 32.56 22.25 19.99 16.78 12.67
a b bc c d
N0 N60 N120 N180 N240 N300
– 33.17 27.83 26.00 25.50 18.90
a b b b c
– 34.00 28.25 28.17 26.58 21.50
a b b b c
– 38.17 33.50 30.33 28.04 24.17
a b bc c c
– 34.33 29.08 27.89 25.88 19.80
a b bc c d
– 34.92 29.67 28.10 26.50 21.09
a b b b c
NPFP 3.5∗ 2.3∗ 5.7∗
NRE 3.2∗ 3.1∗ 6.5∗
NRE (%)
Analysis of variance (LSD0.05) N rate (N) Year (Y) Y×N
N0, N60, N120, N180, N240, and N300 represent nitrogen application rate at 0, 60, 120, 180, 240, and 300 kg N ha−1. Different letters within a column indicate significant differences among treatments within a season at P < 0.05. *Means significant at P = 0.05 level.
fertilization levels, some researchers have found that rapeseed yields are stagnant or reduced under conventional flat cultivation pattern (Li et al., 2015). Present study obtained similar results under CRFM pattern. However, some differences in rapeseed yield occurred between previous studies and the present study. Most previous studies found that the highest rapeseed yield was obtained at 150–180 kg N ha−1 under conventional flat cultivation (Barlóg and Grzebisz, 2004; Li et al., 2011; Schuster and Rathke, 2001; Zou et al., 2011). The highest rapeseed yield occurred at 240 kg N ha−1 under CRFM cultivation in the present study. In the 2014–2015 and 2015–2016 growing seasons, we also conducted experiments with different N amounts (0, 60, 120, 180, 240 and 300 kg N ha−1) under the conventional flat cultivation pattern, and the highest rapeseed yield (2499 kg ha−1 in average) was observed at 180 kg N ha−1. The differences in rapeseed yield under CRFM and conventional flat cultivation patterns might be because the CRFM cultivation pattern lowers soil evaporation, increases the infiltration of rainwater into the soil, and enhances the retention of soil water (Ramakrishna et al., 2006). Typically, as the N application rate increases, the efficiency of N fertilization decreases (Zhang et al., 2008; Zhang et al., 2015), which is consistent with the linear decreases we observed in NPFP and NRE as the N application rate increased (Table 6 and Fig. 6). In our previous study (Gu et al., 2016b), we found that NPFP values of rapeseed cultivated under the conventional flat pattern were 10.9 and 17.7 kg kg−1 at 180 kg N ha−1 in 2012–2013 and 2013–2014 seasons, respectively; these values were much lower than NPFP of rapeseed cultivated under the CRFM pattern at 180 kg N ha−1 in 2012–2013 (17.86 kg kg−1) and 2013–2014 (22.40 kg kg−1) seasons. This result may be caused by higher soil water content in the root zone under the CRFM pattern, which could make an important contribution to N uptake and utilization (Gu et al., 2016a). In the present study, we found that increasing N fertilizer rate led to a decrease in seed oil content, but an increase in seed protein content (Table 4). Rathke et al. (2005) and Zhao et al. (2007) reported similar findings. Seed yield increased by applying more N fertilizer at the expense of seed oil content; however, oil yield was also the highest at N240 (1623 kg ha−1) because this treatment led to a much higher seed yield compared to other treatments.
Fig. 6. Relationships between the rate of N application and average nitrogen partial factor productivity (NPFP), and N recovery efficiency (NRE) of the winter rapeseed. * and ** mean significant at the P = 0.05 and P = 0.01 levels, respectively.
2016), and potato (Zotarelli et al., 2015) had similar results. At harvest, aboveground dry matter and shoot N uptake significantly increased from N0 to N240, then kept stable until N300 (Tables 2 and 3). This result indicates that dry matter accumulation and N uptake are not promoted by excessive application of N fertilizer in winter rapeseed. Crops including castor (Xue et al., 2017), maize (Bu et al., 2014), and potato (Kamiji et al., 2014) had similar results. Values of aboveground dry matter and shoot N uptake under CRFM cultivation were all significantly higher than under non-film mulching cultivation (data not shown). This result might be due to the improvement in soil water content and the decrease in the soil temperature fluctuation by film mulching (Su et al., 2014). The higher soil water content and stable soil temperature are conducive to development of the root system, and thus improve the ability of roots to absorb more soil water and nutrients (Barber et al., 1988; Kang et al., 1999).
4.2. Seed yield, oil yield, and NUE 4.3. ET and WUEY Increasing N fertilization has a positive impact on rapeseed yield (Barlóg and Grzebisz, 2004; Rathke et al., 2005), but at excessive N
Increasing the amount of applied N has been demonstrated to 239
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China, pp. 264–267. Barber, S.A., Mackay, A.D., Kuchenbuch, R.O., Barraclough, P.B., 1988. Effects of soil temperature and water on maize root growth. Plant Soil 111, 267–269. Barlóg, P., Grzebisz, W., 2004. Effect of timing and nitrogen fertilizer application on winter oilseed rape (Brassica napus L.). I. Growth dynamics and seed yield. J. Agron. Crop Sci. 190, 305–313. Bu, L.D., Liu, J.L., Zhu, L., Luo, S.S., Chen, X.P., Li, S.Q., 2014. Attainable yield achieved for plastic film-mulched maize in response to nitrogen deficit. Eur. J. Agron. 55, 53–62. FAOSTAT, 2016. FAO Statistics Division (Available from: http://faostat3.fao.org./faostatgateway/go/to/download/Q/*/E). Fismes, J., Vong, P.C., Guckert, A., Frossard, E., 2000. Influence of sulfur on apparent Nuse efficiency: yield and quality of oilseed rape (Brassica napus L.) grown on a calcareous soil. Eur. J. Agron. 12, 127–141. 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. Mach. 47, 122–132. Heerman, D.F., 1985. ET in irrigation management. In: Proceedings of the National Conference on Advances in Evapotranspiration. December 16–17, 1985, Chicago, IL., USA. pp. 323–334. Hocking, P.J., 2001. Effects of sowing time on nitrate and total nitrogen concentrations in field-grown canola (Brassica napus L.) and implications for plant analysis. J. Plant Nutr. 24, 43–59. Jing, J.S., Dong, Z.S., 2004. Development status and prospects of film mulching rapeseed cultivation technology. Crops 1, 40–42. Kamiji, Y., Pang, J.Y., Milroy, S.P., Palta, J.A., 2014. Shoot biomass in wheat is the driver for nitrogen uptake under low nitrogen supply: but not under high nitrogen supply. Field Crops Res. 165, 92–98. Kang, S.Z., Zhang, J.H., Liang, J.S., 1999. Combined effects of soil water content and temperature on plant root hydraulic conductivity. Acta Phytophysiol. Sin. 23, 211–219. Li, Y.B., Lu, J.W., Liao, X., Zou, J., Li, X.K., Yu, C.B., Ma, C.B., Gao, X.Z., 2011. Effect of nitrogen application rate on yield and nitrogen fertilization efficiency in rapeseed. Chin. J. Oil Crop Sci. 33, 379–383. Li, H., Cong, R.H., Ren, T., Li, X.K., Ma, C.B., Zheng, L., Zhang, Z., Lu, J.W., 2015. Yield response to N fertilizer and optimum N rate of winter oilseed rape under different soil indigenous N supplies. Field Crops Res. 181, 52–59. Liu, C.A., Zhou, L.M., Jia, J.J., Wang, L.J., Si, J.T., Li, X., Pan, C.C., Siddique, K.H.M., Li, F.M., 2014. Maize yield and water balance is affected by nitrogen application in a film?mulching ridge?furrow system in a semiarid region of China. Europ. J. Agron. 52, 103–111. Norse, D., Ju, X.T., 2015. Environmental costs of China’s food security. Agric. Ecosyst. Environ. 209, 5–14. Qi, L.H., Dang, T.H., Chen, L., 2009. The water use characteristics of winter wheat and response to fertilization on dryland of Loess Plateau. Res. Soil Water Conserv. 16, 105–109. Ramakrishna, A., Tam, H.M., Wani, S.P., Long, T.D., 2006. Effect of mulch on soil temperature moisture, weed infestation and yield of groundnut in northernVietnam. Field Crops Res. 95, 115–125. Rathke, G.W., Christen, O., Diepenbrock, W., 2005. Effects of nitrogen source and rate on productivity and quality of winter oilseed rape (Brassica napus L.) grown in different crop rotations. Field Crops Res. 94, 103–113. Rathke, G.W., Behrens, T., Diepenbrock, W., 2006. Integrated nitrogen management strategies to improve seed yield, oil content and nitrogen efficiency of winter oilseed rape (Brassica napus L.): a review. Agric. Ecosyst. Environ. 117, 80–108. Schuster, C., Rathke, G.W., et al., 2001. Nitrogen fertilization of transgenic winter oilseed rape. In: Horst, W.J. (Ed.), Plant Nutrition: Food Security and Sustainability of AgroEcosystems Through Basic and Applied Research. Kluwer Academic Publishers, Dordrecht, pp. 336–337. Su, W., Lu, J.W., Wang, W.N., Li, X.K., Ren, T., Cong, R.H., 2014. Influence of rice straw mulching on seed yield and nitrogen use efficiency of winter oilseed rape (Brassica napus L.) in intensive rice?oilseed rape cropping system. Field Crops Res. 159, 53–61. Xue, X.R., Mai, W.X., Zhao, Z.Y., Zhang, K., Tian, C.Y., 2017. Optimized nitrogen fertilizer application enhances absorption of soil nitrogen and yield of castor with drip irrigation under mulch film. Ind. Crops Prod. 95, 156–162. Zhang, F.S., Wang, J.Q., Zhang, W.F., Cui, Z.L., Ma, W.Q., Chen, Q.P., Jiang, R.F., 2008. Nutrient use efficiencies of major cereal crops in china and measures for improvement. Acta Pedol. Sin. 45, 915–924. Zhang, S.J., Liao, X., Zhang, C.L., Xu, H.J., 2012. Influences of plant density on the seed yield and oil content of winter oilseed rape (Brassica napus L.). Ind. Crops Prod. 40, 27–32. Zhang, X., Davidson, E.A., Mauzerall, D.L., Searchinger, T.D., Dumas, P., Shen, Y., 2015. Managing nitrogen for sustainable development. Nature 528, 51–59. Zhao, J.X., Cheng, G.P., Ren, T.B., Gao, Z.H., 2007. Effect of different nitrogen rates on yield and quality parameters of high grade yellow seed hybrid rape. Plant Nutr. Fert. Sci. 13, 882–889. Zhu, Z.L., Chen, D.L., 2002. Nitrogen fertilizer use in China-Contributions to food production, impacts on the environment and best management strategies. Nutr. Cycling Agroecosyst. 63, 117–127. Zotarelli, L., Rens, L.R., Cantliffe, D.J., Stoffella, P.J., Gergela, D., Burhans, D., 2015. Rate and timing of nitrogen fertilizer application on potato ‘FL1867’. Part I: Plant nitrogen uptake and soil nitrogen availability. Field Crops Res. 183, 246–256. Zou, J., Lu, J.W., Chen, F., Li, Y.S., Li, X.K., 2011. Study on yield increasing and nutrient uptake effect by nitrogen application and nitrogen use efficiency for winter rapeseed. Sci. Agric. Sin. 44, 745–752.
greatly increase ET of crops (Gu et al., 2016b; Li et al., 2015). We got similar results in the present study. The reason for this increase in ET might be due to increased leaf area and biomass under N application treatments (Qi et al., 2009). WUE of crops can be increased with application of N fertilizer, even when the crops are grown using film mulching conditions (Li et al., 2015). Our study gained a similar result. In addition, we found a significant negative quadratic correlation between the N application amount and WUEY. Our result is consistent with the findings of Liu et al. (2014) for maize planted under plastic film. In our previous studies (Gu et al., 2016a), ET and WUEY of rapeseed cultivated under the flat pattern without film mulching ranged from 298.3–331.1 mm and 5.23–8.46 kg ha−1 mm−1, respectively, at 180 kg N ha−1. The ET was much higher and the WUEY was much lower than under the CRFM pattern in the present study. The most probable reason for this difference was that CRFM significantly decreased soil evaporation, increased soil water content in the root zone, and thereby improved rapeseed yield (Gu et al., 2016a). 4.4. Determining an optimal rate of N application Sustainable agriculture is implemented to meet increasing demands for food, while maintaining high crop productivity as well as high WUE and NUE, but also reducing environmental costs (Norse and Ju, 2015). According to the correlations between yield, oil yield, WUEY, WUEOY, and N application rate (Figs. 4 and 5), the highest values of yield, oil yield, WUEY, and WUEOY of winter rapeseed were obtained at 264, 238, 262, and 244 kg N ha−1, respectively. These N rates are all around 240 kg N ha−1. In addition, N240 did not decrease NPFP and NRE much in comparison to N120 and N180. Therefore, we determined that 240 kg N ha−1 was the optimal amount of N for winter rapeseed under the CRFM cultivation pattern to obtain high seed yield and oil yield, and also high WUE and NUE. In addition, under conventional flat cultivation, the highest rapeseed yield, oil yield, WUEY, and WUEOY were all obtained at 180 kg N ha−1 in 2014–2015 and 2015–2016 seasons (data not shown). The optimal N application rate of rapeseed under CRFM cultivation pattern was 60 kg N ha−1 higher than under conventional flat cultivation. This result proved that film mulching could improve the nitrogen absorption capacity of rapeseed. 5. Conclusions Application of N fertilizer greatly increased aboveground dry matter, shoot N uptake, seed yield, oil yield, seed protein content, ET, WUEY, and WUEOY, but decreased seed oil content, NPFP, and NRE. N240 consistently resulted in the highest seed yield, oil yield, WUEY, and WUEOY, without much reduction of NPFP and NRE across the four growing seasons. Therefore, 240 kg N ha−1 is recommended as the optimal N application amount for winter rapeseed under the CRFM cultivation pattern in arid and semiarid areas. Acknowledgments This research was supported by the Special Fund for Agro-scientific Research in the Public Interest, China (grant numbers: 201503125 and 201503105) and the National High Technology Research and Development Program of China (National 863 Program, grant number: 2011AA100504). References Badr, M.A., Abou-Hussein, S.D., El-Tohamy, W.A., 2016. Tomato yield, nitrogen uptake and water use efficiency as affected by planting geometry and level of nitrogen in an arid region. Agric. Water Manag. 169, 90–97. Bao, S.D., 2000. Soil Agricultural-Chemical Analysis. China Agricultural Press, Beijing,
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Optimized nitrogen fertilizer application improves yield, water and nitrogen use efficiencies of winter rapeseed cultivated under continuous ridges with film mulching
MARK
⁎
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
A B S T R A C T
Keywords: Continuous ridges with film mulching Nitrogen fertilizer Seed yield Water use efficiency Nitrogen use efficiency Winter rapeseed
The continuous ridges with film mulching (CRFM) cultivation pattern has been rapidly adopted for production of winter rapeseed (Brassica napus L.) in northwest China due to significant improvements in soil moisture, water use efficiency (WUE) and yield. However, in many cases, the crop yield, WUE, and nitrogen (N) use efficiency (NUE) were still very low under CRFM cultivation due to the deficiency of N nutrients. The objective of this study was to investigate the response of winter rapeseed to six N application amounts: 0 (N0), 60 (N60), 120 (N120), 180 (N180), 240 (N240), and 300 (N300) kg N ha−1. Aboveground dry matter and shoot N uptake at flowering and harvest, yield, oil yield, ET, WUEY, and WUEOY were all significantly higher in N180, N240, and N300 than in N0, N60, and N120. Average WUEY, WUEOY, N partial factor productivity and N recovery efficiency did not differ markedly between N180 and N240, but were all significantly higher than in N300. However, average seed yield and oil yield in N240 were 11.9% (427 kg ha−1) and 9.7% (144 kg ha−1) significantly higher than in N180. In addition, seed oil and protein content in N240 did not differ significantly from N180 and N300. These results suggest that the optimal N application amount for winter rapeseed under CRFM cultivation pattern is 240 kg N ha−1. This rate simultaneously improves seed yield, oil yield, WUEY, WUEOY and NUE.
1. Introduction Rapeseed (Brassica napus L.) produces a kind of vegetable oil that is used for human consumption, and is a source for biodiesel (Zhang et al., 2012). Because of this, rapeseed is grown around the world, and the global planting area has remained stable or increased in some areas in recent years (FAOSTAT, 2016). In 2014, Canada, China, and India had the largest rapeseed planting areas globally, with about 8.1, 7.6, and 6.6 million hectares, respectively (FAOSTAT, 2016). However, the average rapeseed yields in China, Canada, and India were as low as 1947, 1926, and 1185 kg ha−1, respectively (FAOSTAT, 2016), which might be due to low water and nitrogen use efficiencies, especially in arid and semi-arid regions (Jing and Dong, 2004; Gu et al., 2016a). Mulching is an important cultivation method to improve yield, soil moisture, and water use efficiency (WUE) in rapeseed cultivation (Su et al., 2014; Gu et al., 2016a). Su et al. (2014) reported that straw mulching increased soil moisture at 0–30 cm depths by about 8.4% throughout the growth stages of rapeseed, and ultimately improved seed yield by 25.6%. Gu et al. (2016a) found that values for soil water content, rapeseed yield, and WUE in film mulching treatments were ⁎
3.1–7.2%, 20.4–70.7%, and 34.9–122.0% higher than in the conventional cultivation pattern. Rapeseed yield is also heavily dependent on nitrogen (N) availability. In order to produce 0.1 t of seeds, rapeseed crops need to accumulate 6 kg N (Rathke et al., 2006), meaning that farmers apply large amounts of N fertilizer to produce high rapeseed yields. Adding N fertilizer can increase rapeseed yields by 1.1–2.4 t per hectare (Rathke et al., 2005; Zou et al., 2011). However, N fertilization is inefficient, and excess N in the soil is lost through leaching, gasification, and runoff (Zhu and Chen, 2002), which cause serious environmental problems. Thus, determining the optimal application rate for N fertilizer is critical for rapeseed production. Many researchers found that application of 150–180 kg N ha−1 could significantly increase yield and oil production, as well as maintain a high NUE of rapeseed under the conventional cultivation pattern (Barlóg and Grzebisz, 2004; Li et al., 2011; Schuster and Rathke, 2001; Zou et al., 2011). When applied at 210 kg N ha−1, straw mulching significantly increased yield, N uptake, and N use efficiency (NUE) of rapeseed though more N was lost due to ammonia volatilization because of topdressing (Su et al., 2014). Previous studies only investigated the application rate of N fertilizer
Corresponding author at: No.23 Weihui Road, Yangling, Shaanxi Province, 712100, China. E-mail addresses: [email protected] (X.-B. Gu), [email protected] (Y.-N. Li).
http://dx.doi.org/10.1016/j.indcrop.2017.08.036 Received 15 June 2017; Received in revised form 9 August 2017; Accepted 18 August 2017 0926-6690/ © 2017 Published by Elsevier B.V.
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Each plot received 60 mm (at each irrigation) of irrigation water in the first season on 15 January and 5 April 2013, because of severe drought; 30 mm in the second season on 15 September 2013 to ensure seedling emergence, and none in the third and fourth seasons. Weed control was also performed in order to reduce yield loss. Plants were harvested on 20 May 2013, 22 May 2014, 23 May 2015, and 20 May 2016, and the plastic film was recycled.
in rapeseed cultivated under straw mulching and conventional patterns (Fismes et al., 2000; Hocking, 2001; Rathke et al., 2005; Su et al., 2014; Zou et al., 2011). However, little is known about N uptake, NUE, and how different N rates affect yield and oil production of rapeseed under the film mulching planting pattern, especially under the continuous ridges with film mulching (CRFM) cultivation method, which has been proven to be appropriate for winter rapeseed in arid and semi-arid areas (Gu et al., 2016a). The goal of the present study was to determine how N fertilization affects yield, WUE, and NUE of rapeseed grown using CRFM cultivation. Our results will be used to manage N fertilization and to improve production of winter rapeseed.
2.3. Measurements and methods 2.3.1. Weather conditions Daily rainfall and air temperatures during the winter rapeseed growing seasons were measured at Yangling National Meteorological Observing Station, which is located 50 m away from the experimental field. The monthly total rainfall and monthly mean air temperatures were calculated using these data.
2. Materials and methods 2.1. Experimental site A field experiment was conducted over four years (September 2012 to May 2016) at the Key Laboratory of Agricultural Soil and Water Engineering in Arid and Semiarid Areas of the Ministry of Education (34°18′N, 108°24′E; 521 m a.s.l.), Yangling, Shaanxi, China. Mean annual precipitation in this region is 632 mm, with 60–70% falling from July to September, making this a typical rainfed region. Per year in this region, soil evaporation has a mean of 1500 mm; mean air temperature is 12.9 °C; and mean sunshine duration is 2164 h. Loamy soil is present at this site, and it has a filled capacity of 24% with a dry bulk density of 1.40 g cm−3. Top-soil (0–20 cm) nutrient properties at the start of each growing season are in Table 1.
2.3.2. Aboveground dry matter and shoot N uptake Ten representative plants from each plot were cut at ground level at three growth stages: seedling (78 DAS in 2013–2014, 75 DAS in all other seasons); flowering (215 DAS); and harvest (247, 252, 244, and 246 DAS in 2012–2013, 2013–2014, 2014–2015, and 2015–2016, respectively). Plants were separated into leaves, stems, pod walls, and seeds. Plant tissues were first oven-dried to deactivate enzymes (30 min at 105 °C), and then dried to a constant weight (75 °C). The weights of dry leaves, stems, pod walls, and seeds were added together to obtain aboveground dry matter, and then these plant tissues were ground and digested with H2SO4-H2O2 (Bao, 2000). We used an automated continuous flow analyser (AA3, Seal, Norderstedt, Germany) to determine the N concentration in different tissues. Finally, we calculated shoot N uptake by multiplying the dry weight by the N concentration in different tissues.
2.2. Experimental design Six application rates of N (as urea) were used in this experiment: 0 (N0), 60 (N60), 120 (N120), 180 (N180), 240 (N240), and 300 (N300) kg N ha−1. The N fertilizer was applied as a basal dressing to all plots. Four replicates of each rate were used (24 total plots), and the experiment was designed as a randomized block. Plots were 4 m × 5 m in size, and were spaced 1 m apart. Calcium superphosphate (P2O5 = 16%), potassium sulphate (K2O = 51%), and borax (B = 11%) at rates of 90 kg P2O5 ha−1, 120 kg K2O ha−1, and 15 kg B ha−1 were also used as basal fertilizers in each plot. No additional fertilization was used during the growth period. The continuous ridges with film mulching (CRFM) method was used to plant winter rapeseed. Ridges were 20 cm high and 50 cm wide (Fig. 1). In each growing season, we ploughed the field and separated it into plots; applied fertilizers; and formed ridges. After these steps, a transparent plastic film (0.8 m wide and 0.008 mm thick) containing small holes every 0.3 m for rainwater infiltration, was laid manually over the ridge layer at the soil surface (Fig. 1). Shaanyou No. 107 seeds were planted by hand in plot furrows on 15 September 2012, 12 September 2013, 21 September 2014, and 16 September 2015. At the three leaves stage, seedlings were thinned manually, and at the five leaves stage, we determined that the plant density was 120 000 plants ha−1.
2.3.3. Seed yield and oil and protein contents To determine seed yield, plants at a size of 1 m2 (1 × 1 m) from the middle of each plot were chosen at harvest, and were then sun-dried and threshed. Then, near-infrared reflectance spectroscopy (NIR System 5000, Foss, Denmark) was used to measure seed oil and protein content. Oil yield was calculated by seed yield × oil content. 2.3.4. Evapotranspiration (ET) and WUE Soil moisture contents at depths between 0 and 200 cm were determined before planting and after harvest in order to calculate changes in soil water storage during the winter rapeseed growth period. Coring at 10 cm depth intervals was done manually between two plants in the same row. Soil moisture content was then calculated using the oven dry weight method (samples were dried at 105 °C). Soil water storage was calculated using Eq. (1): SWS = 10Σgi × hi × ωi
Where SWS (mm) is soil water storage, γi (g cm ) is soil dry bulk density in each different soil layer, hi (cm) is the soil thickness, ωi (%) is gravimetric water content in each different soil layer, and i = 10, 20, 30,…, 200. The soil water balance equation (Eq. (2)) was used to calculate the evapotranspiration of winter rapeseed (Heerman, 1985):
Table 1 Nutrient properties in the 0–20 cm soil layer at the start of each growing season at the experimental site. Soil property
pH (water) Organic matter (g kg−1) Total N (g kg−1) Alkali hydrolysable N (mg kg−1) Available P (mg kg−1) Available K (mg kg−1)
Growing season 2012–2013
2013–2013
2014–2015
2015–2016
8.12 12.35 0.95 75.31
8.14 12.78 0.98 72.54
8.14 12.18 0.94 76.01
8.13 12.57 0.97 73.93
25.34 131.92
24.26 135.32
25.22 132.97
24.8 133.62
(1) −3
ET = I + P − D + SWS0–SWS1
(2)
Where ET (mm) is the evapotranspiration of winter rapeseed; I (mm) is the amount of irrigation; P (mm) is precipitation; D (mm) is deep drainage into the lower boundary of 200 cm (which was assumed to be negligible in this study because no heavy rains or irrigation occurred during the rapeseed growing seasons); and SWS0 and SWS1 (mm) are the soil water storages before sowing and after harvesting, respectively. 234
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Fig. 1. Schematic diagram of the continuous ridges with film mulching.
the four growing seasons: the maximum temperature in February 2014 was 1.5–2.4 °C lower than the other three seasons; and the maximum, mean, and minimum temperatures in January 2016 were 2.0–3.6 °C, 1.2–2.1 °C, and 1.2–1.8 °C lower than the other three seasons. Total rainfall during the growing seasons of winter rapeseed were 120 mm, 330 mm, 264 mm, and 184 mm, in 2012–2013, 2013–2014, 2014–2015, and 2015–2016, respectively. The growing seasons in 2012–2013 and 2015–2016 were much drier than in 2013–2014 and 2014–2015.
WUEY and WUEOY of the winter rapeseed were calculated using Eqs. (3) and (4): WUEY = Y/ET
(3)
WUEOY = OY/ET
(4)
Where WUEY and WUEOY (kg ha−1 mm−1) is yield water use efficiency and oil yield water use efficiency, Y and OY (kg ha−1) is yield and oil yield of winter rapeseed, and ET (mm) is evapotranspiration. 2.3.5. NUE Two indicators were used to evaluate nitrogen use efficiency (NUE): nitrogen recovery efficiency (NRE), and nitrogen partial factor productivity (NPFP). Eqs. (5) to (6) were used as follows: NRE (%) = (UN–U0)/TN NPFP (kg kg
−1
) = YN/TN
3.2. Aboveground dry matter Aboveground dry matter in N0 was always significantly lower than in the other five N application treatments in 2012–2013, 2013–2014, 2014–2015, and 2015–2016 (Table 2). At seedling stage, there were no significant differences of aboveground dry matter among N60, N120, N180, N240, and N300 treatments across the four growing seasons. At flowering stage, aboveground dry matter in N120 was significantly higher than that in N60, and was significantly lower than that in N180, N240, and N300. There were no significant differences among the N180, N240, and N300 treatments across the four growing seasons. At harvest, aboveground dry matter in N240 was significantly higher than in N0, N60, N120, and N180, at 128.9–139.3%, 82.8–101.4%, 37.3–46.3%, and 13.4–16.1% respectively. At harvest, no significant differences were found between the aboveground dry matter of N240 and N300 across the four growing seasons except for 2014–2015, in which the aboveground dry matter of N240 was significantly higher than N300 at 8.4%.
(5) (6)
−1
Where YN (kg ha ) is the seed yield with N fertilization; UN and U0 (kg N ha−1) are the shoot N uptakes with and without N fertilization, respectively; and TN is the total input of N fertilizer (kg N ha−1). 2.4. Data analysis Data were compiled and analysed using Excel 2010. Analysis of variance was used to test for significant differences between treatments of seed yield, aboveground dry matter, shoot N uptake, seed oil, seed protein content, and NUE. Least significant difference tests were used to compare means (P < 0.05). SPSS 18.0 was used for statistical analyses. AutoCAD 2007 was used to create Fig. 1, and Origin 8.0 was used to create other four figures.
3.3. Shoot N uptake Shoot N uptake of winter rapeseed was markedly influenced by the N application rate (P < 0.05) (Table 3). At seedling stage, shoot N uptake increased significantly from N0 to N60, and was then stable until N300. Compared to shoot N uptake at seedling stage, shoot N uptake at flowering stage increased by 25.7–46.7, 37.7–63.2, 27.6–59.4, and 25.3–47.2 kg N ha−1 in the 2012–2013, 2013–2014, 2014–2015, and 2015–2016 growing seasons, respectively. At flowering stage, shoot N uptake increased significantly from N0 to N180, and then did not vary from N180 to N300. At harvest, there were no
3. Results 3.1. Weather conditions Maximum, mean, and minimum air temperatures in the four growing seasons almost followed the same trend: they decreased from September to December or January, and then increased until May (Fig. 2). However, slight differences in temperature were found among
Fig. 2. Monthly maximum, mean, and minimum temperatures and monthly total rainfall during the 2012–2013, 2013–2014, 2014–2015, and 2015–2016 winter rapeseed growing seasons at the experimental site.
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Table 2 Aboveground dry matter (kg ha−1) of winter rapeseed for the six treatments at the seedling, flowering, and harvest stages in the four growing seasons. Treatment
N0 N60 N120 N180 N240 N300
2012–2013
2013–2014
2014–2015
2015–2016
Seedling
Flowering
Harvest
Seedling
Flowering
Harvest
Seedling
Flowering
Harvest
Seedling
Flowering
Harvest
2572 3063 3101 3267 3304 3358
3524 4547 5436 6072 6125 6098
5172 e 6148 d 8507 c 10801 b 12379 a 11527 ab
2326 2828 2931 3052 3108 3096
5013 6049 7261 7977 8106 8168
6870 e 8196 d 11024 c 13626 b 15728 a 14986 a
2795 3352 3487 3513 3582 3576
4627 5536 7668 8534 8614 8639
6157 e 7358 d 10036 c 12654 b 14685 a 13549 b
2608 3298 3381 3428 3492 3506
3815 5036 6652 7319 7503 7489
5413 e 6851 d 9124 c 11048 b 12526 a 12357 a
b a a a a a
d c b a a a
Analysis of variance (LSD0.05) Seedling Flowering N rate (N) 326∗ 582∗ ∗ Year (Y) 483 783∗ Y×N 889∗ 1201∗
b a a a a a
d c b a a a
b a a a a a
d c b a a a
b a a a a a
d c b a a a
Harvest 945∗ 959∗ 2102∗
N0, N60, N120, N180, N240, and N300 represent nitrogen application rate at 0, 60, 120, 180, 240, and 300 kg N ha−1. Different letters within a column indicate significant differences among treatments within a season at P < 0.05. * means significant at P = 0.05 level.
N60, N120, N180, and N300, respectively. The relationship between seed yield and N application rate was: Y = 1409.665 + 18.444 x − 0.035 x2. Oil yield consistently and significantly increased from N0 to N240, and then decreased significantly at N300 across the four growing seasons (Fig. 3b). No significant differences in oil yield were found between N180 and N300 across the four growing seasons. Average oil yield in N240 was significantly higher by 129.2%, 82.8%, 33.6%, 9.1%, and 13.5% compared to N0, N60, N120, N180, and N300, respectively. The relationship between seed yield and N application rate was: OY = 629.971 + 7.602 x − 0.016 x2 (Fig. 4).
significant differences between the shoot N uptake in N240 and N300, and the average shoot N uptake in N240 was significantly higher than in N0, N60, N120, and N180, at 107.4%, 53.2%, 29.5%, and 11.9%, respectively. 3.4. Seed oil and protein contents Seed oil content decreased as N application amount increased, and the seed oil content in N0 was significantly higher than the other five N application treatments across the four growing seasons (Table 4). Average seed oil content in N240 was significantly lower than that in N0, N60, N120, and N180 at 9.7%, 6.7%, 4.7%, and 2.5%, respectively; and was 1.5% slightly higher than that in N300. Seed protein content increased as N application amount increased, and seed protein content in N fertilizer treatments was consistently and significantly higher than that in the N0 treatment across the four growing seasons (Table 4). Average seed protein content in N240 did not differ significantly from N180 and N300; however, it was significantly higher than average seed protein content in N0, N60, and N120 at 23.6%, 14.6%, and 10.2%, respectively.
3.6. ET and WUE ET of winter rapeseed was significantly affected by the N application amount (P < 0.05) and ranged from 205.8 mm to 340.6 mm under the six N application rates across the four growing seasons (Table 5). ET in N0 was significantly lower than in the other five N treatment rates except in the 2013–2014 growing season, and increased as N application amount increased. ET did not differ significantly between N180 and N240 except in 2014–2015, and the ET in N240 was significantly lower than that in N300 at 6.8-9.6% across the four growing seasons. WUEY of winter rapeseed was consistently highest in N240 and lowest in N0 across the four growing seasons (Table 5). WUEY in N0 was significantly lower than that in other five N application treatments across the four growing seasons except for non-significant differences between N0 and N60 in 2014–2015 and 2015–2016. WUEY in N240
3.5. Seed yield and oil yield Seed yield in N240 was consistently and significantly higher than the other five N application treatments across the four growing seasons except for non-significant differences between N240 and N300 in 2012–2013 (Fig. 3a). Average seed yield in N240 was significantly higher by 153.8%, 96.0%, 40.3%, 11.9%, and 11.8% compared to N0,
Table 3 Shoot N uptake (kg ha−1) of winter rapeseed for the six treatments at the seedling, flowering, and harvest stages in the four growing seasons. Treatment
N0 N60 N120 N180 N240 N300
2012–2013
2013–2014
2014–2015
2015–2016
Seedling
Flowering
Harvest
Seedling
Flowering
Harvest
Seedling
Flowering
Harvest
Seedling
Flowering
Harvest
19.0 29.6 32.3 32.9 32.6 33.4
44.7 55.6 69.4 78.1 79.3 78.7
53.5 e 73.4 d 86.9 c 100.3 b 114.7 a 110.2 a
18.2 28.5 31.8 32.1 32.7 32.3
55.9 72.4 85.2 94.6 95.9 95.2
69.8 e 90.2 d 103.7 c 120.5 b 133.6 a 134.3 a
20.6 30.2 33.0 33.6 34.1 34.8
48.2 65.8 84.7 93.0 93.5 92.3
58.3 e 81.2 d 98.5 c 112.9 b 125.6 a 130.8 a
19.8 29.4 32.8 33.3 33.6 34.0
45.1 57.6 69.9 80.3 80.6 81.2
55.2 e 75.8 d 90.1 c 105.4 b 117.3 a 114.6 a
b a a a a a
d c b a a a
Analysis of variance (LSD0.05) Seedling Flowering N rate (N) 4.7∗ 8.1∗ ns Year (Y) 1.8 10.3∗ Y×N 5.1∗ 18.2∗
b a a a a a
d c b a a a
b a a a a a
d c b a a a
b a a a a a
d c b a a a
Harvest 11.6∗ 11.2∗ 26.5∗
N0, N60, N120, N180, N240, and N300 represent nitrogen application rate at 0, 60, 120, 180, 240, and 300 kg N ha−1. Different letters within a column indicate significant differences among treatments within a season at P < 0.05. * and ns mean significant and non-significant at P = 0.05 level, respectively.
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Table 4 Oil and protein contents of winter rapeseed for the six treatments in the four growing seasons. Treatment
N0 N60 N120 N180 N240 N300
Oil content (%)
Protein content (%)
2012–2013
2013–2014
2014–2015
2015–2016
Average
2012–2013
2013–2014
2014–2015
2015–2016
Average
44.93 43.35 42.92 41.23 41.04 40.35
44.01 42.48 41.96 41.48 40.69 39.20
44.14 42.83 41.67 41.30 40.18 39.37
45.46 44.17 42.65 41.34 40.30 39.82
44.64 43.21 42.30 41.34 40.30 39.69
20.12 21.58 22.46 24.98 25.22 25.95
20.74 22.29 23.13 25.14 26.19 26.58
20.40 22.44 23.36 25.08 25.81 26.17
21.48 22.94 23.88 24.93 25.05 26.73
20.69 22.31 23.21 25.03 25.57 26.36
a b b c c d
Analysis of variance (LSD0.05) Oil content N rate (N) 0.87∗ Year (Y) 0.73 ns Y×N 1.69∗
a b bc c d e
a b c c d e
a b c d e e
a b c d e e
c b b a a a
d c bc b a a
d c c b ab a
d c bc b b a
d c c b ab a
Protein content 1.02∗ 0.84 ns 2.26∗
N0, N60, N120, N180, N240, and N300 represent nitrogen application rate at 0, 60, 120, 180, 240, and 300 kg N ha−1. Different letters within a column indicate significant differences among treatments within a season at P < 0.05. * and ns mean significant and non-significant at P = 0.05 level, respectively.
correlation between WUEOY and N application WUEOY = 2.977 + 0.021 x − 4.291E–5 x2 (Fig. 5).
was significantly higher than that in N0, N60, and N120 at 85.1–118.5%, 62.6–84.4%, and 24.8–44.3%, respectively across the four growing seasons. There were no significant differences between the WUEY in N180 and N240 except in 2012–2013, where the WUEY in N240 was significantly higher than that in N180 at 12.0%. WUEY in N300 was significantly lower than WUEY in N240 in 2012–2013, 2013–2014, and 2014–2015, however, significant differences were not found between the two treatments in 2015–2016. The correlation between WUEY and N application amount was: WUEY = 6.628 + 0.053 x − 1.011E–4 x2. N240 consistently had the highest WUEOY across the four growing seasons, followed by N180 and N300; N0 had the lowest WUEOY (Table 5). WUEOY in N240 did not differ significantly from N180; however, it was significantly higher than the other four N application treatments across the four growing seasons except in 2015–2016. Average WUEOY in N240 was 78.8%, 62.8%, 30.4%, 5.4%, and 18.6% higher than in N0, N60, N120, N180, and N300, respectively. The
amount
was:
3.7. NUE NPFP of winter rapeseed decreased as the N application amount increased, and NPFP in N60 was consistently and significantly higher than in N120, N180, N240, and N300 across the four growing seasons (Table 6). Average NPFP in N240 did not differ significantly from N180, but it was significantly lower than average NPFP in N60 and N120 at 48.5% and 24.6%, respectively, and was 32.4% significantly higher than average NPFP in N300. The correlation between NPFP and N application amount was: NPFP = 34.425–0.075 x. NRE of winter rapeseed decreased with the increase of N application amount, and NPFP in N60 was consistently and significantly higher than NRE in the other four N application treatments across the four growing seasons (Table 6). Average NRE in N240 did not differ
Fig. 3. Yield (a) and oil yield (b) of winter rapeseed for the six treatments in the 2012–2013, 2013–2014, 2014–2015, and 2015–2016 growing seasons. Bars represent standard deviations. N0, N60, N120, N180, N240, and N300 represent nitrogen application rate at 0, 60, 120, 180, 240, and 300 kg N ha−1. Different letters above the bars indicate significant differences among treatments within a season at P < 0.05. * means significant at P = 0.05 level.
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Fig. 4. Relationship between the rate of N application and average yield and oil yield of the winter rapeseed. ** means significant at the P = 0.01 level.
Fig. 5. Relationship between the rate of N application and average water use efficiencies of the winter rapeseed. WUEY and WUEOY mean water use efficiencies for yield and oil yield, respectively. * means significant at the P = 0.05 level.
significantly from N120 and N180; however, it was reduced significantly by 24.1% in comparison to N60, and was increased significantly by 25.7% in comparison to N300. The correlation between NRE and N application amount was: NRE = 37.305–0.051 x (Fig. 6).
4. Discussion 4.1. Aboveground dry matter and shoot N uptake Under CRFM cultivation, both dry matter accumulation and N uptake increased significantly in winter rapeseed when N fertilizers were applied. Previous studies in maize (Li et al., 2015), tomato (Badr et al.,
Table 5 Evapotranspiration (ET) and water use efficiency (WUE) of the winter rapeseed for the six treatments in the four growing seasons. Soil water storage before sowing (mm)
Soil water storage after harvesting (mm)
Rainfall (mm)
Irrigation (mm)
ET (mm)
WUEY (kg ha−1 mm−1)
WUEOY (kg ha−1 mm−1)
2012–2013 N0 N60 N120 N180 N240 N300
500.6 500.6 500.6 500.6 500.6 500.6
534.8 515.7 497.7 484.4 478.0 455.2
120 120 120 120 120 120
120 120 120 120 120 120
205.8 224.9 242.9 256.2 262.6 285.4
e d c bc b a
6.9 d 7.8 d 9.7 c 12.5 b 14.0 a 12.2 b
3.1 3.4 4.1 5.2 5.8 4.9
d d c ab a b
2013–2014 N0 N60 N120 N180 N240 N300
457.5 457.5 457.5 457.5 457.5 457.5
605.1 593.4 574.8 551.1 540.3 516.2
330 330 330 330 330 330
30 30 30 30 30 30
212.4 224.1 242.7 266.4 277.2 301.3
d d c b b a
8.5 e 9.9 d 12.9 c 15.1 ab 16.1 a 14.1 b
3.8 4.2 5.4 6.3 6.5 5.5
c c b a a b
2014–2015 N0 N60 N120 N180 N240 N300
533.7 533.7 533.7 533.7 533.7 533.7
604.6 585.8 570.5 554.0 535.5 507.6
264 264 264 264 264 264
0 0 0 0 0 0
193.1 211.9 227.2 243.7 262.2 290.1
f e d c b a
8.7 d 9.6 d 12.1 c 15.6 a 16.1 a 13.5 b
3.8 4.1 5.0 6.4 6.5 5.3
c c b a a b
2015–2016 N0 N60 N120 N180 N240 N300
559.3 559.3 559.3 559.3 559.3 559.3
479.1 461.6 450.9 434.2 425.8 402.7
184 184 184 184 184 184
0 0 0 0 0 0
264.2 281.7 292.4 309.1 317.5 340.6
d c c b b a
5.4 c 6.4 c 8.4 b 10.9 a 11.8 a 10.5 a
2.5 2.8 3.6 4.5 4.8 4.2
c c b a a a
1.4∗ 1.6∗ 3.1∗
0.7∗ 0.6∗ 1.7∗
Treatment
Analysis of variance (LSD0.05) N rate (N) Year (Y) Y×N
14.7∗ 25.6∗ 30.9∗
N0, N60, N120, N180, N240, and N300 represent nitrogen application rate at 0, 60, 120, 180, 240, and 300 kg N ha−1. Different letters within a column indicate significant differences among treatments within a season at P < 0.05. *Means significant at P = 0.05 level.
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Table 6 Nitrogen (N) partial factor productivity (NPFP), N agronomic efficiency (NAE), N physiological efficiency (NPE), and N recovery efficiency (NRE) of the winter rapeseed for the six treatments in the four growing seasons. Indicator
Treatment
2012–2013
2013–2014
2014–2015
2015–2016
Average
NPFP (kg kg−1)
N0 N60 N120 N180 N240 N300
– 29.22 19.57 17.86 15.34 11.64
a b bc c d
– 36.88 26.05 22.40 18.55 14.14
a b c d e
– 34.05 22.86 21.07 17.54 13.03
a b b c d
– 30.10 20.53 18.65 15.67 11.87
a b bc c d
– 32.56 22.25 19.99 16.78 12.67
a b bc c d
N0 N60 N120 N180 N240 N300
– 33.17 27.83 26.00 25.50 18.90
a b b b c
– 34.00 28.25 28.17 26.58 21.50
a b b b c
– 38.17 33.50 30.33 28.04 24.17
a b bc c c
– 34.33 29.08 27.89 25.88 19.80
a b bc c d
– 34.92 29.67 28.10 26.50 21.09
a b b b c
NPFP 3.5∗ 2.3∗ 5.7∗
NRE 3.2∗ 3.1∗ 6.5∗
NRE (%)
Analysis of variance (LSD0.05) N rate (N) Year (Y) Y×N
N0, N60, N120, N180, N240, and N300 represent nitrogen application rate at 0, 60, 120, 180, 240, and 300 kg N ha−1. Different letters within a column indicate significant differences among treatments within a season at P < 0.05. *Means significant at P = 0.05 level.
fertilization levels, some researchers have found that rapeseed yields are stagnant or reduced under conventional flat cultivation pattern (Li et al., 2015). Present study obtained similar results under CRFM pattern. However, some differences in rapeseed yield occurred between previous studies and the present study. Most previous studies found that the highest rapeseed yield was obtained at 150–180 kg N ha−1 under conventional flat cultivation (Barlóg and Grzebisz, 2004; Li et al., 2011; Schuster and Rathke, 2001; Zou et al., 2011). The highest rapeseed yield occurred at 240 kg N ha−1 under CRFM cultivation in the present study. In the 2014–2015 and 2015–2016 growing seasons, we also conducted experiments with different N amounts (0, 60, 120, 180, 240 and 300 kg N ha−1) under the conventional flat cultivation pattern, and the highest rapeseed yield (2499 kg ha−1 in average) was observed at 180 kg N ha−1. The differences in rapeseed yield under CRFM and conventional flat cultivation patterns might be because the CRFM cultivation pattern lowers soil evaporation, increases the infiltration of rainwater into the soil, and enhances the retention of soil water (Ramakrishna et al., 2006). Typically, as the N application rate increases, the efficiency of N fertilization decreases (Zhang et al., 2008; Zhang et al., 2015), which is consistent with the linear decreases we observed in NPFP and NRE as the N application rate increased (Table 6 and Fig. 6). In our previous study (Gu et al., 2016b), we found that NPFP values of rapeseed cultivated under the conventional flat pattern were 10.9 and 17.7 kg kg−1 at 180 kg N ha−1 in 2012–2013 and 2013–2014 seasons, respectively; these values were much lower than NPFP of rapeseed cultivated under the CRFM pattern at 180 kg N ha−1 in 2012–2013 (17.86 kg kg−1) and 2013–2014 (22.40 kg kg−1) seasons. This result may be caused by higher soil water content in the root zone under the CRFM pattern, which could make an important contribution to N uptake and utilization (Gu et al., 2016a). In the present study, we found that increasing N fertilizer rate led to a decrease in seed oil content, but an increase in seed protein content (Table 4). Rathke et al. (2005) and Zhao et al. (2007) reported similar findings. Seed yield increased by applying more N fertilizer at the expense of seed oil content; however, oil yield was also the highest at N240 (1623 kg ha−1) because this treatment led to a much higher seed yield compared to other treatments.
Fig. 6. Relationships between the rate of N application and average nitrogen partial factor productivity (NPFP), and N recovery efficiency (NRE) of the winter rapeseed. * and ** mean significant at the P = 0.05 and P = 0.01 levels, respectively.
2016), and potato (Zotarelli et al., 2015) had similar results. At harvest, aboveground dry matter and shoot N uptake significantly increased from N0 to N240, then kept stable until N300 (Tables 2 and 3). This result indicates that dry matter accumulation and N uptake are not promoted by excessive application of N fertilizer in winter rapeseed. Crops including castor (Xue et al., 2017), maize (Bu et al., 2014), and potato (Kamiji et al., 2014) had similar results. Values of aboveground dry matter and shoot N uptake under CRFM cultivation were all significantly higher than under non-film mulching cultivation (data not shown). This result might be due to the improvement in soil water content and the decrease in the soil temperature fluctuation by film mulching (Su et al., 2014). The higher soil water content and stable soil temperature are conducive to development of the root system, and thus improve the ability of roots to absorb more soil water and nutrients (Barber et al., 1988; Kang et al., 1999).
4.2. Seed yield, oil yield, and NUE 4.3. ET and WUEY Increasing N fertilization has a positive impact on rapeseed yield (Barlóg and Grzebisz, 2004; Rathke et al., 2005), but at excessive N
Increasing the amount of applied N has been demonstrated to 239
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greatly increase ET of crops (Gu et al., 2016b; Li et al., 2015). We got similar results in the present study. The reason for this increase in ET might be due to increased leaf area and biomass under N application treatments (Qi et al., 2009). WUE of crops can be increased with application of N fertilizer, even when the crops are grown using film mulching conditions (Li et al., 2015). Our study gained a similar result. In addition, we found a significant negative quadratic correlation between the N application amount and WUEY. Our result is consistent with the findings of Liu et al. (2014) for maize planted under plastic film. In our previous studies (Gu et al., 2016a), ET and WUEY of rapeseed cultivated under the flat pattern without film mulching ranged from 298.3–331.1 mm and 5.23–8.46 kg ha−1 mm−1, respectively, at 180 kg N ha−1. The ET was much higher and the WUEY was much lower than under the CRFM pattern in the present study. The most probable reason for this difference was that CRFM significantly decreased soil evaporation, increased soil water content in the root zone, and thereby improved rapeseed yield (Gu et al., 2016a). 4.4. Determining an optimal rate of N application Sustainable agriculture is implemented to meet increasing demands for food, while maintaining high crop productivity as well as high WUE and NUE, but also reducing environmental costs (Norse and Ju, 2015). According to the correlations between yield, oil yield, WUEY, WUEOY, and N application rate (Figs. 4 and 5), the highest values of yield, oil yield, WUEY, and WUEOY of winter rapeseed were obtained at 264, 238, 262, and 244 kg N ha−1, respectively. These N rates are all around 240 kg N ha−1. In addition, N240 did not decrease NPFP and NRE much in comparison to N120 and N180. Therefore, we determined that 240 kg N ha−1 was the optimal amount of N for winter rapeseed under the CRFM cultivation pattern to obtain high seed yield and oil yield, and also high WUE and NUE. In addition, under conventional flat cultivation, the highest rapeseed yield, oil yield, WUEY, and WUEOY were all obtained at 180 kg N ha−1 in 2014–2015 and 2015–2016 seasons (data not shown). The optimal N application rate of rapeseed under CRFM cultivation pattern was 60 kg N ha−1 higher than under conventional flat cultivation. This result proved that film mulching could improve the nitrogen absorption capacity of rapeseed. 5. Conclusions Application of N fertilizer greatly increased aboveground dry matter, shoot N uptake, seed yield, oil yield, seed protein content, ET, WUEY, and WUEOY, but decreased seed oil content, NPFP, and NRE. N240 consistently resulted in the highest seed yield, oil yield, WUEY, and WUEOY, without much reduction of NPFP and NRE across the four growing seasons. Therefore, 240 kg N ha−1 is recommended as the optimal N application amount for winter rapeseed under the CRFM cultivation pattern in arid and semiarid areas. Acknowledgments This research was supported by the Special Fund for Agro-scientific Research in the Public Interest, China (grant numbers: 201503125 and 201503105) and the National High Technology Research and Development Program of China (National 863 Program, grant number: 2011AA100504). References Badr, M.A., Abou-Hussein, S.D., El-Tohamy, W.A., 2016. Tomato yield, nitrogen uptake and water use efficiency as affected by planting geometry and level of nitrogen in an arid region. Agric. Water Manag. 169, 90–97. Bao, S.D., 2000. Soil Agricultural-Chemical Analysis. China Agricultural Press, Beijing,
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