Weather conditions
There was a large variation in rainfall between the two years, with more than half of the annual rainfall from July to September (Fig. 1A), the maximum monthly mean rainfall occurred in July 2017 and August 2018, respectively. Compared with the long-term average of 377 mm (1981-2010), the annual rainfall was higher in 2017 (407.4 mm) and 2018 (481.1 mm). Compared with the yearly average fallow rainfall (99.1 mm), the fallow rainfall was higher in 2017 (109.9 mm) and 2018 (120.2 mm). The seasonal rainfall in 2017 was similar to the yearly average, but it was higher in 2018 (360.9 mm). The annual rainfall during the wetter growing season (2018) was higher by 23% than the long-term average (1981-2010). Minimum temperatures occurred in January each year during the growing season while maximum temperatures occurred at the young fruit stage in each growing season (Fig. 1B).
Soil water storage
There was no significant difference in soil water storage (SWS) among the N0, N60 and N120 treatments before sowing in 2017 (Figure 2a,c), but they were significantly varied by nitrogen (N) and irrigation treatments (Figure 2b,d) before sowing and after harvest in 2018. The SWS of treatment I0 was significantly lower than that of treatment I1200 and I1800 after harvest in 2017 (Figure 2c). The SWS of N60 treatment was significantly increased by 10.26% and 17.83%, respectively, compared to N0 and N120 treatments after harvest in 2018. In addition, SWS was increased with increas of irrigation rate. Compared with I0 treatment, SWS was increased by 14.32% and 19.23% in I1200 and I1800 treatments, respectively, before oilseed flax sowing. SWS was affected by interaction between irrigation and nitrogen levels, significantly, at the postharvest stage in 2018 (Figure 2d). There was highest SWS in I1800N60 treatment and lowest SWS in I0N120 treatment.
Evapotranspiration, soil water depletion and soil water balance
Precipitation storage efficiency (PSE) was significantly varied by irrigation and nitrogen levels (Figure 3). Compared with N0 treatment in 2017, the PSE in N60 and N120 treatment was increased by 12.85% and 26.86%, respectively. In 2018, PSE of different irrigation treatments was showed I1800>I0>I1200, while under different nitrogen treatments was showed N120>N60>N0. The I1800N120 treatment had the highest PSE, followed by the I1800N60, I0N60 and I1800N0 treatments. The PSE in I1800N120 treatment was increased by 13.55% compared to the I0N0 treatment in 2018.
The soil water components in the 0-160 cm soil depth was significantly influenced by irrigation and nitrogen levels (Table 1). The SWCs, SWCh, ΔSWCg, ETg and ΔSWCy were increased with the increasing of irrigation amount, and the ETf was reduced. Averaged across the 2 yrs., compared with the I0 treatment, the SWCs, SWCh, ETg, and ΔSWCy was increased by 9.36%, 17.02%, 56.46%, and 58.81% respectively, in I1800 treatment. However, compared with I0 treatment, the ETf of I1800 treatment was decreased by 45.05% in 2018. ΔSWCf, ETf, ΔSWCg, ETg, and ΔSWCy were significantly affected by nitrogen rate. Averaged across the 2 yrs., the SWCs, ΔSWCf and ETg in the N120 treatment was 4.43%, 16.42%, and 2.14%higher than that in N0 treatment, respectively. Conversely, the N120 treatment was decreased SWCh, ΔSWCg and ΔSWCy by 0.74%, 55.12% and 12.83%, respectively, compared with N0 treatment on an average of two years. The interaction effect of irrigation and nitrogen levels significantly affected SWCh, ETf, ΔSWCg, ETg and ΔSWCy in 0-160 cm soil depth (Table 1). Compared with the I0N0 treatment, the SWCs, SWCh, ΔSWCf, ETg and ΔSWCy was increased by 18.74%, 15.37%, 18.76%, 42.73% and 7.88%, respectively, under I1800N60 treatment in 2018.
Table 1
Effects of different irrigation levels and nitrogen levels on soil water balance components (soil-water storage at previous harvest - SWCph, soil-water storage at harvest - SWCh, soil-water storage at sowing - SWCs, the change in soil-water storage during the fallow period - ΔSWCf, the change in soil-water storage during the growing season - ΔSWCg, the change in soil-water storage during the whole year - ΔSWCy, the evapotranspiration during the fallow period - ETf, the evapotranspiration during the growing season - ETg) in the 0 - 160 cm soil depth at Dingxi station, China.
Growing seasons
|
I
|
N
|
SWCph
|
SWCs
|
SWCh
|
Fallow period
|
Growing period
|
ΔSWCy
|
mm
|
mm
|
mm
|
ΔSWCf (mm)
|
ETf (mm)
|
ΔSWCg (mm)
|
ETg (mm)
|
(mm)
|
2017
|
I0
|
N0
|
202.81
|
234.66a
|
182.13c
|
31.85b
|
78.05a
|
-52.54d
|
350.04c
|
-20.68f
|
N60
|
238.75a
|
188.20c
|
35.94ab
|
73.96a
|
-46.47c
|
343.97c
|
-14.61e
|
N120
|
243.22a
|
195.13c
|
40.41a
|
69.49ab
|
-39.53c
|
337.03c
|
-7.68d
|
I1200
|
N0
|
234.66
|
225.22ab
|
31.85
|
78.05
|
-13.54ab
|
431.04b
|
22.41b
|
N60
|
238.75
|
229.94a
|
35.94
|
73.96
|
-8.82a
|
426.32b
|
27.13a
|
N120
|
243.22
|
228.61a
|
40.41
|
69.49
|
-10.14a
|
427.64b
|
25.80a
|
I1800
|
N0
|
234.66
|
217.46b
|
31.85
|
78.05
|
-25.76b
|
503.26a
|
14.65c
|
N60
|
238.75
|
224.11ab
|
35.94
|
73.96
|
-19.11b
|
496.61a
|
21.30b
|
N120
|
243.22
|
228.91a
|
40.41
|
69.49
|
-14.31ab
|
491.81a
|
26.10a
|
2018
|
I0
|
N0
|
182.13
|
219.54e
|
274.85d
|
37.41bc
|
103.47a
|
55.31b
|
242.19g
|
92.72d
|
N60
|
188.20
|
229.54d
|
303.05c
|
41.34b
|
93.47b
|
73.51a
|
223.99h
|
114.85a
|
N120
|
195.13
|
230.08d
|
257.19e
|
34.94c
|
92.93b
|
27.11d
|
270.39f
|
62.06g
|
I1200
|
N0
|
225.22
|
255.06c
|
313.79b
|
29.84c
|
67.95c
|
58.73b
|
358.77e
|
88.57d
|
N60
|
229.94
|
261.66c
|
313.44b
|
31.72c
|
61.35d
|
51.78b
|
365.72de
|
83.50e
|
N120
|
228.61
|
259.70c
|
300.06c
|
31.08c
|
63.31cd
|
40.37c
|
377.13d
|
71.45f
|
I1800
|
N0
|
217.46
|
258.39c
|
325.75a
|
40.93b
|
64.62cd
|
67.35a
|
410.15c
|
108.29b
|
N60
|
224.11
|
270.16b
|
324.76a
|
46.05ab
|
52.85e
|
54.60b
|
422.90b
|
100.65c
|
N120
|
228.91
|
281.20a
|
317.89 ab
|
52.29a
|
41.81e
|
36.69c
|
440.81a
|
88.98d
|
F-Values
|
I
|
-
|
*
|
ns
|
*
|
*
|
*
|
**
|
**
|
N
|
-
|
ns
|
ns
|
*
|
**
|
*
|
*
|
**
|
I×N
|
-
|
ns
|
*
|
ns
|
*
|
*
|
*
|
**
|
Y
|
-
|
ns
|
**
|
ns
|
ns
|
**
|
**
|
**
|
Y×I
|
-
|
-
|
*
|
-
|
-
|
*
|
*
|
**
|
Y×N
|
-
|
ns
|
ns
|
ns
|
*
|
*
|
*
|
*
|
Y×I×N
|
-
|
-
|
ns
|
-
|
-
|
*
|
*
|
*
|
Note: I0, no irrigation; I1200, irrigation 1200 m3 ha−1; I1800, irrigation 1800 m3 ha−1; N0, no nitrogen; N60, 60 kg N ha−1; N120, 120 kg N ha−1. I, irrigation; N, nitrogen; Y, year. * means a significant difference at 0.05 probability level; ** means significant difference at 0.01 probability level; ns means no significant difference at 0.05 probability level. Mean values with different letters within column under the same growing season are significantly different from each other at 0.05 probabily level.
|
Biomass accumulation and grain yield The interaction of irrigation and nitrogen levels significantly affected the dry matter accumulation (DMA) of oilseed flax from budding stage to maturity (Figure 4). DMA increased linearly from seedling stage to maturity stage. The DMA under different irrigation treatments was showed that I1800> I1200> I0, while under different nitrogen levels was showed that N60> N120> N0 during the growth stage of oilseed flax. Compared to the I0N0 treatment, the I1800N60 treatment improved DMA of oilseed flax 36.96% and 38.68% at budding, 52.25% and 82.78% at anthesis, 50.07% and 37.39% at kernel stage, 79.73% and 77.58% at maturity in 2017 and 2018, respectively.
The interaction of irrigation and nitrogen significantly affected the number of effective capsules per plant (EC), number of seeds per pod (SN) and seed yield (Table 2). In 2017, EC varied from 17.9 to 25.6 per plant, SN per pod from 6.7 to 8.0 and grain yield from 913.8 to 1535.8 kg ha−1, while in 2018, EC varied from from 9.1 to 13.8 per plant, SN per pod from 6.5 to 7.5 and grain yield from 1044.0 to 1203.0 kg ha−1. EC, SN and grain yield in 2017 were increased by 45.0%, 2.2% and 13.7%, respectively, compared to 2018. Grain yield increased with increasing irrigation in both season. The N120 treatment had the highest grain yield in 2017, while the N60 treatment produced the optimum grain yield in 2018. The N0 treatment had the least grain yield in both seasons. Compared to the control (I0N0), the I1800N60 treatment increased EC (29.9%), SN (6.3%), and grain yield (40.9%) in 2017. However, 1000-grain weight was not significantly varied under different irrigation and nitrogen treatments in both seasons (Table 2).
Table 2
Effects of irrigation and nitrogen levels on yield and yield components of oilseed flax
Treatment
|
2017
|
2018
|
Effective capsule number plant−1
|
Grain number pod−1
|
1000 grain weight (g)
|
Grain yield
( kg ha−1)
|
Effective capsule number plant−1
|
Grain number pod−1
|
1000 grain weight (g)
|
Grain yield
( kg ha−1)
|
I0
|
N0
|
17.93d
|
7.40b
|
5.58b
|
913.79f
|
9.13f
|
7.10ab
|
7.88ab
|
1044.00c
|
N60
|
19.67c
|
6.73e
|
5.77ab
|
1006.50e
|
12.27c
|
7.10ab
|
7.45b
|
1069.67c
|
N120
|
22.33b
|
6.80 de
|
5.57 b
|
1224.61d
|
12.20c
|
7.30a
|
7.97a
|
1097.00c
|
I1200
|
N0
|
20.57c
|
7.27bc
|
5.40b
|
1339.17c
|
13.13b
|
6.53c
|
8.00a
|
1087.67c
|
N60
|
22.17b
|
8.03a
|
6.28a
|
1424.71b
|
10.43e
|
7.10ab
|
7.53ab
|
1165.67 b
|
N120
|
23.03b
|
7.00bcde
|
5.98ab
|
1467.07b
|
11.63d
|
7.53a
|
7.43b
|
1153.33b
|
I1800
|
N0
|
16.87d
|
6.87cde
|
5.50b
|
1424.71 b
|
11.90cd
|
7.37a
|
7.75ab
|
1152.33b
|
N60
|
25.57a
|
7.90a
|
5.83ab
|
1545.42a
|
13.77a
|
7.07abc
|
7.83ab
|
1281.67a
|
N120
|
22.50b
|
7.20bcd
|
5.72ab
|
1535.77a
|
10.37e
|
6.67bc
|
7.88ab
|
1203.00ab
|
I
|
*
|
**
|
ns
|
***
|
*
|
*
|
ns
|
***
|
N
|
***
|
*
|
ns
|
**
|
*
|
*
|
ns
|
**
|
I×N
|
**
|
*
|
ns
|
*
|
***
|
*
|
ns
|
*
|
Note: I0, no irrigation; I1200, irrigation 1200 m3 ha−1; I1800, irrigation 1800 m3 ha−1; N0, no nitrogen; N60, 60 kg N ha−1; N120, 120 kg N ha−1. I, irrigation; N, nitrogen. * means a significant difference at 0.05 probability level; ** means significant difference at 0.01 probability level; ns means no significant difference at 0.05 probability level. Mean values with different letters within column are significantly different from each other at 0.05 probabily level . |
HI, WUE, ANUE and NPFP
Water use efficiency (WUE), irrigation use efficiency (WUEI), agronomic nitrogen use efficiency (ANUE) and nitrogen partial factor productivity (NPFP) were significantly varied under the different interaction of irrigation and nitrogen levels (Table 3). The main effect of irrigation levels did not significantly affect ANUE and NPFP, while nitrogen levels had an insignificant effect on WUEI. The WUE varied from 4.52 to 6.12, WUEI from 7.92 to 12.23, ANUE from 0.93 to 2.59 and NPFP from12.80 to 25.76 in 2017, while WUE varied from 4.57 to 22.91, WUEI from 6.40 to 9.71, ANUE from 0.42 to 2.16 and NPFP from 9.14 to 21.36 in 2018. The content of WUEI, ANUE, and NPFP were increased by 19.44%, 44.68%, and 13.92% in 2017, respectively, compared to those in 2018. The WUE in 2018 was higher by 38.74% than in 2017. I0N120 and I0N60 treatments had the highest WUE in 2 growth seasons of oilseed flax. The highest WUEI was recorded under the I1200N120 treatment (12.23) in 2017 and under the I1200N60 treatment (9.71) in 2018. The I1800N60 treatment had the highest ANUE and NPFP values in both seasons, while the I1800N120 and I0N120 treatments had the lowest ANUE and NPFP values, respectively. Only the main effect of nitrogen levels significantly affected the harvest index (HI). HI varied from 0.36 to 0.59 in 2017 and 0.36 to 0.51 in 2018. HI followed the trend of N0>N120>N60. Compared to the N0 treatment, the N60 treatment reduced HI by 18.80% in 2017 and 21.21% in 2018, respecitivily.
Table 3
Effects of irrigation and nitrogen levels on harvest index (HI), water use efficiency (WUE), irrigation use efficiency (WUEI), nitrogen agronomy use efficiency (ANUE) and nitrogen partial factor productivity (NPFP) of oilseed flax.
Growing Seasons
|
Irrigation Rate
|
Nitrogen
Rate
|
HI
|
WUE
|
WUEI
|
ANUE
|
NPFP
|
2017
|
I0
|
N0
|
0.49c
|
5.36cd
|
—
|
—
|
—
|
N60
|
0.36d
|
6.12b
|
—
|
1.55c
|
16.78bc
|
N120
|
0.51bc
|
7.77a
|
—
|
2.59a
|
10.21c
|
I1200
|
N0
|
0.57ab
|
5.41bcd
|
11.16a
|
|
|
N60
|
0.48c
|
5.87bc
|
11.87a
|
1.43c
|
23.75a
|
N120
|
0.49c
|
6.01bc
|
12.23a
|
1.07d
|
12.23c
|
I1800
|
N0
|
0.59a
|
4.52e
|
7.92b
|
—
|
—
|
N60
|
0.46c
|
5.01de
|
8.59b
|
2.01b
|
25.76a
|
N120
|
0.51bc
|
5.06de
|
8.53b
|
0.93d
|
12.80c
|
2018
|
I0
|
N0
|
0.51a
|
16.09b
|
—
|
—
|
—
|
N60
|
0.36b
|
22.91a
|
—
|
0.43c
|
17.83a
|
N120
|
0.39ab
|
11.78c
|
—
|
0.44c
|
9.14b
|
I1200
|
N0
|
0.40ab
|
5.99de
|
9.06a
|
—
|
—
|
N60
|
0.37b
|
6.19d
|
9.71a
|
1.30b
|
19.43a
|
N120
|
0.40ab
|
5.77de
|
9.61a
|
0.55c
|
9.61b
|
I1800
|
N0
|
0.42ab
|
4.95f
|
6.40b
|
—
|
—
|
N60
|
0.35b
|
5.22ef
|
7.12b
|
2.16a
|
21.36a
|
N120
|
0.40ab
|
4.57f
|
6.68b
|
0.42c
|
10.03b
|
I
|
ns
|
**
|
**
|
ns
|
ns
|
N
|
**
|
**
|
ns
|
**
|
**
|
I×N
|
ns
|
**
|
*
|
*
|
*
|
Y
|
**
|
**
|
*
|
*
|
ns
|
Y×I
|
*
|
**
|
ns
|
ns
|
ns
|
Y×N
|
ns
|
**
|
ns
|
*
|
*
|
Y×I×N
|
ns
|
**
|
ns
|
ns
|
ns
|
Note: I0, no irrigation; I1200, irrigation 1200 m3 ha−1; I1800, irrigation 1800 m3 ha−1; N0, no nitrogen; N60, 60 kg N ha−1; N120, 120 kg N ha−1. I, irrigation; N, nitrogen; Y, year. * means a significant difference at 0.05 probability level; ** means significant difference at 0.01 probability level; ns means no significant difference at 0.05 probability level. |
Correlation analysis
The relationship between grain yield and soil water balance components of oilseed flax was showed in Table 4. Grain yield showed positive and highly significant correlation with PSE (r = 0.856), SWCs (r = 0.935), Etg (r = 0.853) and SWCy (r = 0.935) in 2017; however, grain yield correlated negatively and non-significantly with ETf (r = -0.348), WUE (r = -0.322) and ANUE (r = -0.345). In 2018, grain yield showed positive and significant correlation with ANUE (r = 0.834); however, it was negatively correlated with ETf (r = 0.527), WUE (r = -0.535), HI (r = -0.515) and SWCh (r = -0.048).
Table 4
Correlation analysis between grain yeild and soil water balance components( precipitation storage efficiency - PSE, the soil water content at harvest - SWCh, the change in soil-water storage during the fallow season - SWCf, the amount of evapotranspiration at fallow season - ETf, the change in soil-water storage during the growing season - SWCg, the amount of evapotranspiration during the growing season - ETg, the change in soil-water storage during the whole year - ΔSWCy, harvest index – HI and water use efficiency - WUE) measured in 2017 and 2018 for oilseed flax grown in various irrigation and nitrogen levels systems at Dingxi station, China.
Year
|
PSE
|
SWCs
|
SWCh
|
SWCf
|
ETf
|
SWCg
|
ETg
|
ΔSWCy
|
HI
|
WUE
|
ANUE
|
2017
|
0.856**
|
0.348
|
0.935**
|
0.348
|
-0.348
|
0.443
|
0.853**
|
0.935**
|
0.394
|
-0.322
|
-0.345
|
2018
|
0.16
|
0.167
|
-0.048
|
0.214
|
-0.527
|
-0.001
|
0.493
|
0.287
|
-0.515
|
-0.535
|
0.834*
|
*, significant at P <0.05; **, significant at P <0.01. |