Introduction
Wheat (Triticum aestivum L.) as the principal food crops accounts for 29.8 and
25.9% of the harvested area and production worldwide (FAO 2019). The wheat production should be increased by approximately 70–100% over
its present levels to meet the future consumption needs (Chen et al.
2014). Wheat acreage has decreased from 1997 to 2017 (FAO 2019; NBSC 2019); thus, meeting the increased food demand will depend on the ability to
achieve higher average yield of wheat. Therefore, efforts on agronomic
innovation should be made.
Irrigation
and application of fertilizers, especially nitrogen (N), are important
agronomic practices in crop production and contribute significantly to the
increase in wheat production (Mueller et al. 2012; Thapa et al. 2019). However, excessive N application and over-exploitation of
groundwater for irrigation not only decrease NUE and WUE but also cause adverse
environmental impacts (Zhu and Chen 2002; Behera and Panda 2009; Qi et al. 2019). Moreover, water scarcity is causing severe
drought stress for plant growth (Farooq et al.
2009, 2014). Supplemental irrigation (SI) is one of the key agronomic
practices for stabilizing and improving crop yield and WUE in semi-arid and
arid regions. SI increases wheat roots length
density in deeper soil and enhances availability of soil water; consequently,
higher WUE and grain yield are obtained (Xu et al. 2016). Tavakkoli and Oweis (2004) confirmed that SI significantly increased yield
and maximises WUE. A specific SI method has been developed in North China in
which soil water content is recharged to 70–75% field capacity in 0–140 cm
layers at jointing and anthesis stages of wheat by SI. This method can increase
flag leaf area and photosynthesis rate, delay leaf senescence, and improve yield
as compared with conventional flood irrigation practice (Lin et al. 2016). Nitrogen (N) is the most required nutrient for crops amongst the
main influential factors of plant growth (Halitligil et al. 2000), as it affects cell
building, photosynthetic activity, and protein assimilation rates (King et al. 2003; Sadras and Lawson 2013). Hence, N
application optimization is essential for crops. Despite much has been
investigated regarding N management, the optimum N application under the new SI
regime in wheat needs attention in order to evaluate if grain yield, WUE and
NUE can be simultaneously increased.
Annual precipitation cannot satisfy the wheat demand
in major wheat production regions. Thus, irrigation is necessary for
maintaining high wheat production. Moreover, shortage of water resources and
over-exploitation of groundwater for irrigation threaten the winter wheat
production (Yang et al. 2019).
Therefore, the new SI method with limited irrigation at key wheat growing
stages that substantially increases wheat production should be adopted.
Nevertheless, the effects of N rates on WUE and NUE and grain yield in this new
SI regime have been rarely explored through field experimentation. Therefore,
the present study aimed to evaluate various nitrogen rates under SI regime for
(1) post-anthesis dry matter translocation and allocation, (2) soil water use
and (3) wheat yield, NUE and WUE.
Materials and Methods
Experimental site
This 2-year field experiment was conducted at
Shandong Agricultural University (36°18' N, 117°16' E, 128 m asl). The
average annual precipitation in study area is 683.2 mm with 195 frost-free days
and 2627 sunshine hours. As pre-sowing soil analysis, the content of soil
organic matter was 13.7 g kg−1 with available N, K and P were
respectively 102.1, 88.4, 39.4 mg kg−1. Corresponding values for 0–140 cm deep soil profile (20 cm increment) were 28.83, 26.70, 26.43,
22.91, 23.66, 24.11 and 26.33% for average field capacity (FC) and 1.45, 1.51,
1.54, 1.56, 1.58, 1.58, and 1.58 g cm-3 for bulk density.
Experimental design and treatments
The experimental design was a split-plot with
three replications. Main plots consisted of SI regime and conventional flood
irrigation treatments, whereas sub-plots consisted of four nitrogen
levels i.e., 0, 180, 210 and 240 kg N ha−1.
Each sub-plot was 20 m2 in size. In SI regime treatment, two supplemental irrigations brought the soil
water content in 0–140 cm
soil profile to 70% of field capacity
at jointing
and anthesis stages. In conventional flood irrigation treatment,
two 60-mm irrigations were applied at jointing and anthesis stages.
Soil water contents were measured to
calculate the supplemental irrigation amount for treatment SI regime (Wang et al. 2013):
%201135-1141_files/image002.png){kind=small}
%201135-1141_files/image004.png){kind=small}
Where I (mm) is SI amount; B (g cm–3) is soil bulk density; D (cm) is soil layer depth (140 cm for
this experiment); α (%) is the target soil water content after SI, and β (%) is the
soil water content before irrigation; FC (%) is field capacity, and θ (%) is the target
relative soil water content at jointing and anthesis stages. At jointing stage,
the average SI amounts for 0, 180, 210 and 240 kg N
ha−1 treatments were respectively 80.7,
58.3, 52.0 and 69.6 mm in 2012–2013 growth season and 84.9, 72.4, 53.9 and 81.1
mm in 2013–2014 growth season. At anthesis stage, the average SI amounts for 0, 180, 210 and 240 kg N
ha−1 treatments were respectively 55.7,
61.9, 48.8 and 59.5 mm in 2012–2013 growth season and 40.4, 32.9, 38.3 and 43.9
mm in 2013–2014 growth season. Water was evenly sprayed onto the plots with a
flow meter measured the irrigation amount.
Crop management
The wheat variety used in this
experiment was Jimai22, which was sown in 20-cm apart rows on 7 October 2012 and harvested on 8
June 2013 for the first growth season. Similarly, sowing and harvesting was
done on 7 October 2013 and 4 June 2014, respectively, for the second growth
season. The P2O5 and K2O rate were 120 kg ha-1
and 100 kg ha-1 for each treatment. All P and K fertilizers and 50%
of N were applied as basal dressing. At jointing stage, the remaining N
fertilizer was used as side dressing.
Measurement
Crop
evapo-transpiration: For the entire growth period, soil
samples were collected from 0–200 cm depth (20 cm increment) in each plot. Crop
evapo-transpiration (ET) was calculated as follows (Wang et al. 2013):
ET=△W+ P + I
Where ET (mm) is crop evapo-transpiration; △W (mm) is soil water storage at sowing stage minus
soil water storage at maturity stage; P (mm) is precipitation amount and I (mm)
is irrigation amount.
Water use
efficiency
WUE=Y/ET
Where WUE (kg ha-1 mm-1) is
water use efficiency; and Y (kg ha-1) is grain yield.
Nitrogen
use efficiency
Nitrogen use efficiency (NUE) was calculated by Cassman et al. (2002) and Du et al. (2017):
NUE=Y/Nr
Where NUE (kg kg-1) is nitrogen use
efficiency; and Nr (kg ha-1) is nitrogen applied rate.
Plant determinations
Plants were harvested from 1 m row
length for determination of dry matter production at anthesis and maturity
phase. The plant samples were separated into three parts (spike, leaves, and
stem + sheaths) at anthesis and four parts (grains, spike axis + glume, leaves,
and stem + sheaths) at maturity. Dry matter allocation and translocation were
calculated using formulas described by Jiang et al. (2004) and Masoni et
al. (2007).
Statistical analysis
ANOVA was used to determine effects of irrigation,
nitrogen and their interaction. Significant differences among treatments were
identified with Duncan’s test at P <
0.05. Data were analyzed with S.P.S.S. 13.0 statistical software.
%201135-1141_files/image006.png)
Fig. 1: Effect of nitrogen application and irrigation
regime on soil water consumption in the 0-200 cm soil layers in 2012-2013 (a,
b) and 2013-2014 (c, d)
Results
Soil water consumption
Nitrogen
management significantly affected soil water consumption of 0–200 cm layers,
but there was no difference between SI regime and conventional flood irrigation treatments (Fig. 1).
In SI regime treatment, the soil water
consumption rates of 60–120 cm were higher by 58.0, 21.2 and 9.5% in the 210 kg
N ha−1 treatment than in the 0, 180 and 240 kg N ha−1
treatments, respectively (P < 0.05).
In conventional flood irrigation
treatment, the soil
water consumption rates under 210 kg N ha−1 were 38.9, 23.2 and
13.8% higher than in 0, 180 and 240 kg N ha−1 in 80–120 cm for
the first season. For the second season, it was 39.2, 21.2 and 13.7% higher in
60–100 cm, respectively. There were no significant differences in 0–40 and
160–200 cm.
Crop evapo-transpiration
and proportional contributions
Crop evapo-transpiration and proportional
contributions of soil water consumption, precipitation and irrigation, towards
crop evapo-transpiration were significantly affected by nitrogen levels (Table
1). In SI regime treatment, 210 kg N ha−1
decreased evapo-transpiration on average by 4.8% (P < 0.05) as compared with 240 kg N ha−1 but
had no significant difference with 0 and 180 kg N ha−1. In conventional flood irrigation treatment, 210 kg N ha−1
increased evapo-transpiration by 9.2 and 4.9% as compared with 0 and 180 kg N
ha−1, respectively. As compared with N application rates
of 0, 180 and 240 kg ha−1, 210 kg N ha−1 increased
soil water consumption by 33.6, 18.0 and 6.3% in SI regime, and by 29.0, 15.7 and 6.4% in conventional flood
irrigation treatment, respectively. The lowest irrigation amount and its
proportional contributions to evapo-transpiration were found in SI regime with 210 kg N ha−1 whereas the
highest values for same occurred in SI regime with 0 kg N ha−1.
Water potential, ΦPSII and Fv/Fm of flag
leaves
The water
potential (Ψw) after
anthesis was significantly influenced by irrigation and nitrogen management
(Fig. 2). In both years, there was no significant difference for Ψw amongst treatments at 7 days after
anthesis. However, from day 14 to 28 after anthesis, high Ψw values in flag leaves were found in 210 kg N ha−1.
In particular, at 28 days after anthesis, the Ψw values in 210 kg N ha−1 were higher than
those in 0 and 180 kg N ha−1 by respectively 25.0 and 16.8%
under SI regime treatment
and 29.1 and 16.7% under conventional flood irrigation treatment.
During 2012–2013, similar trends
of ΦPSII and Fv/Fm were observed after anthesis across all treatments
(Fig. 3). In both SI regime and conventional flood irrigation treatments,
ΦPSII and Fv/Fm values were significantly affected by nitrogen management.
In SI regime treatment,
210 kg N ha−1 increased ΦPSII after anthesis. Compared
180 and 240 kg N ha−1 treatments, ΦPSII values
in 210 kg N ha−1 treatment were higher by respectively 16.7
and 8.3% at 14 days after anthesis and 19.7 and 6.2% at 21 days after anthesis.
In conventional flood irrigation treatment,
higher ΦPSII values were found in 210 and 240 kg N ha−1
than in 180 kg N ha−1. Fv/Fm values in 0 kg N ha−1
were the lowest during 7–28 days after anthesis. At 14 days after anthesis, and
afterwards, 210 and 240 kg N ha−1 increased the Fv/Fm.
Particularly in conventional flood irrigation treatment, the Fv/Fm
values in 210 and 240 kg N ha−1 were higher than in 180 kg N
ha−1 by respectively 5.9 and 4.8% at 21 days after anthesis
and 8.4 and 9.7% at 28 days after anthesis.
Dry matter allocation and translocation
Table 1: Evapo-transpiration and
proportional contributions of water sources to evapo-transpiration of winter
wheat
|
Season |
Treatments |
Evapo-transpiration |
Amount of water consumption sources |
Proportional contributions of water sources to evapo-transpiration |
|||||
|
Irrigation type |
N levels |
(mm) |
Irrigation |
Soil water consumption (mm) |
Precipitation |
Irrigation |
Soil water consumption (%) |
Precipitation |
|
|
(kg ha−1) |
(mm) |
(mm) |
(%) |
(%) |
|||||
|
2012-2013 |
SI regime |
0 |
399.60d |
136.32a |
67.48e |
195.8 |
34.11a |
16.89e |
49.00a |
|
180 |
402.51cd |
120.24b |
86.47cd |
195.8 |
29.87b |
21.48cd |
48.65ab |
||
|
210 |
411.44bcd |
100.78c |
114.86a |
195.8 |
24.49d |
27.92a |
47.59abc |
||
|
240 |
434.08a |
129.05a |
109.23ab |
195.8 |
29.73b |
25.16ab |
45.11d |
||
|
Conventional flood irrigation |
0 |
392.13d |
120 |
76.33de |
195.8 |
30.60b |
19.47de |
49.93a |
|
|
180 |
409.92bcd |
120 |
94.12bc |
195.8 |
29.27b |
22.96bc |
47.77abc |
||
|
210 |
432.22ab |
120 |
116.42a |
195.8 |
27.76c |
26.93a |
45.30cd |
||
|
240 |
424.92abc |
120 |
109.12ab |
195.8 |
28.24c |
25.68ab |
46.08bcd |
||
|
2013-2014 |
SI regime |
0 |
430.70cd |
125.27a |
139.93d |
165.5 |
29.08a |
32.49c |
38.43ab |
|
180 |
438.40bcd |
105.33b |
167.56bc |
165.5 |
24.03b |
38.22b |
37.75abc |
||
|
210 |
446.61bc |
92.14c |
188.97a |
165.5 |
20.63c |
42.31a |
37.06bcd |
||
|
240 |
464.88a |
125.02a |
174.36ab |
165.5 |
26.89ab |
37.51b |
35.60d |
||
|
Conventional flood irrigation |
0 |
421.93d |
120 |
136.43d |
165.5 |
28.44a |
32.33c |
39.22a |
|
|
180 |
442.24bcd |
120 |
156.74c |
165.5 |
27.13ab |
35.44bc |
37.42bcd |
||
|
210 |
463.93a |
120 |
178.43ab |
165.5 |
25.87b |
38.46b |
35.67d |
||
|
240 |
452.27ab |
120 |
166.77bc |
165.5 |
26.53ab |
36.87b |
36.59cd |
||
|
Significance based on a repeated-measures ANOVA (P value) |
|||||||||
|
Y (year) |
< 0.001 |
- |
< 0.001 |
- |
< 0.001 |
< 0.001 |
< 0.001 |
||
|
I (irrigation) |
0.677 |
- |
0.497 |
- |
0.191 |
0.315 |
0.679 |
||
|
N (nitrogen) |
< 0.001 |
- |
< 0.001 |
- |
< 0.001 |
< 0.001 |
< 0.001 |
||
|
Y × I |
0.665 |
- |
0.023 |
- |
0.022 |
0.012 |
0.642 |
||
|
Y × N |
0.941 |
- |
0.576 |
- |
0.643 |
0.228 |
0.63 |
||
|
I × N |
0.012 |
- |
0.771 |
- |
0.001 |
0.127 |
0.022 |
||
|
Y × I × N |
0.999 |
- |
0.907 |
- |
0.813 |
0.757 |
0.952 |
||
Note: Mean values within columns at
the same growth season of wheat followed by the different letters differ
significantly (P < 0.05)
%201135-1141_files/image008.png)
Fig. 2: Effect of nitrogen application and irrigation
regime on water potential (Ψw) of flag leaf after anthesis in the
2012-2013 (a) and 2013-2014 (b) growth season
%201135-1141_files/image010.png)
Fig. 3: Effect of nitrogen application and irrigation
regime on ΦPSII (a)
and Fv/Fm (b) of flag leaf after anthesis in 2012-2013
Table 2: Dry matter allocation and translocation before
and after anthesis of winter wheat
|
Season |
Treatments |
Dry matter accumulation at maturity (kg ha-1) |
Pre-anthesis reserves |
Post-anthesis dry matter |
|||
|
Irrigation type |
N levels (kg ha−1) |
Translocated into grain (kg ha-1) |
Contribution to grain (%) |
Allocation to grain (kg ha-1) |
Contribution to grain (%) |
||
|
2012-2013 |
SI regime |
0 |
13860.99e |
2763.19ab |
36.29b |
4851.90e |
63.71d |
|
180 |
17135.79d |
2755.66a |
32.33c |
5768.71d |
67.67c |
||
|
210 |
21018.33a |
2387.29d |
25.12e |
7116.15a |
74.88a |
||
|
240 |
19051.13b |
2669.57bc |
29.41d |
6406.07b |
70.59b |
||
|
Conventional flood irrigation |
0 |
13553.19e |
2777.08ab |
37.48a |
4633.28e |
62.52c |
|
|
180 |
17258.43d |
2726.79abc |
32.53c |
5656.68d |
67.47b |
||
|
210 |
19423.61b |
2624.36c |
29.47d |
6279.37bc |
70.53a |
||
|
240 |
18179.86c |
2820.69a |
32.05c |
5980.00cd |
67.95b |
||
|
2013-2014 |
SI regime |
0 |
13913.17e |
2781.75c |
36.60b |
4818.38d |
63.40c |
|
180 |
17522.88d |
2862.41b |
32.86cd |
5847.95b |
67.14b |
||
|
210 |
21005.16a |
2620.17d |
27.25e |
6994.52a |
72.75a |
||
|
240 |
18842.22c |
2779.00c |
31.21d |
6125.97b |
68.79b |
||
|
Conventional flood irrigation |
0 |
13508.51e |
2859.22b |
39.09a |
4456.02d |
60.91d |
|
|
180 |
17362.13d |
3083.55a |
36.57b |
5348.06c |
63.43c |
||
|
210 |
19812.87b |
2883.67b |
31.37d |
6308.37b |
68.63a |
||
|
240 |
18229.12c |
3020.91a |
33.96c |
5873.41b |
66.04b |
||
|
Significance based on a repeated-measures
ANOVA (P value) |
|||||||
|
Y (year) |
0.479 |
< 0.001 |
< 0.001 |
0.082 |
< 0.001 |
||
|
I (irrigation) |
< 0.001 |
< 0.001 |
< 0.001 |
< 0.001 |
< 0.001 |
||
|
N (nitrogen) |
< 0.001 |
< 0.001 |
< 0.001 |
< 0.001 |
< 0.001 |
||
|
Y × I |
0.781 |
0.001 |
0.050 |
0.619 |
0.050 |
||
|
Y × N |
0.772 |
< 0.001 |
0.414 |
0.816 |
0.414 |
||
|
I × N |
0.003 |
< 0.001 |
0.030 |
0.084 |
0.030 |
||
|
Y × I × N |
0.754 |
0.075 |
0.140 |
0.466 |
0.140 |
||
Note: Mean values within columns at the same growth season of wheat
followed by the different letters differ significantly (P < 0.05).
Table 3: Grain yield, water use efficiency and N use
efficiency of winter wheat
|
Season |
Treatments |
Grain yield (kg ha-1) |
Water use efficiency (kg ha-1
mm-1) |
N use efficiency (kg kg-1) |
|
|
Irrigation type |
N levels (kg ha−1) |
||||
|
2012-2013 |
SI regime |
0 |
7608.05e |
19.04d |
—— |
|
180 |
8519.45cd |
21.17b |
47.33a |
||
|
210 |
9400.38a |
22.85a |
44.76b |
||
|
240 |
9047.45ab |
20.84bc |
37.70d |
||
|
Conventional flood irrigation |
0 |
7391.40e |
18.85d |
—— |
|
|
180 |
8368.68d |
20.42c |
46.49ab |
||
|
210 |
8893.15bc |
20.58bc |
42.35c |
||
|
240 |
8761.23bcd |
20.62bc |
36.51d |
||
|
2013-2014 |
SI regime |
0 |
7576.50e |
17.59d |
—— |
|
180 |
8673.57cd |
19.78b |
48.19a |
||
|
210 |
9587.30a |
21.47a |
45.65b |
||
|
240 |
8867.63bc |
19.08bc |
36.95d |
||
|
Conventional flood irrigation |
0 |
7298.70e |
17.30d |
—— |
|
|
180 |
8396.85d |
18.99c |
46.65ab |
||
|
210 |
9156.77b |
19.74b |
43.60c |
||
|
240 |
8860.45bc |
19.59bc |
36.92d |
||
|
Significance based on a
repeated-measures ANOVA (P value) |
|||||
|
Y (year) |
0.443 |
< 0.001 |
0.168 |
||
|
I (irrigation) |
< 0.001 |
< 0.001 |
< 0.001 |
||
|
N (nitrogen) |
< 0.001 |
< 0.001 |
< 0.001 |
||
|
Y × I |
0.762 |
0.204 |
0.680 |
||
|
Y × N |
0.437 |
0.618 |
0.326 |
||
|
I × N |
0.395 |
< 0.001 |
0.150 |
||
|
Y × I × N |
0.739 |
0.448 |
0.524 |
||
Note: Mean values within columns at the same growth
season of wheat followed by the different letters differ significantly (P <
0.05)
Irrigation
and nitrogen management significantly affected total dry matter accumulation,
allocation and translocation to grains of assimilated dry matter after anthesis
(Table 2). In both growth seasons, the highest dry matter accumulation amounts
at maturity and dry matter allocation to grain of post-anthesis were found in SI regime with 210 kg N ha−1. On the contrary, the dry matter translocation and its
contribution to grain dry matter were lowest in SI regime with 210
kg N ha−1 amongst all treatments.
Yield, WUE and NUE
Wheat yield, WUE, and NUE were significantly affected by nitrogen levels
and irrigation regimes (Table 3). The grain yields were higher in 210 kg N ha−1
than those in 180 and 240 kg N ha−1 by respectively 9.5 and
5.6% under SI regime treatment and 7.1 and 2.4% under conventional flood irrigation treatment.
The highest WUE was found in SI regime with 210 kg N ha−1, which was
7.6 and 10.0% higher than those in SI regime with 180 kg N ha−1
and SI regime with 240 kg
N ha−1, respectively. The NUE in 210 kg N ha−1 was
lower than in 180 kg N ha−1 under both irrigation treatments;
however, 210 kg N ha−1 recorded higher NUE than 240 kg N ha−1
by 17.4 and 14.6% under SI regime and conventional flood irrigation treatments,
respectively (P < 0.05).
Discussion
There are three
contributors to the total crop evapo-transpiration i.e. soil water
supply, irrigation, and precipitation. Various evidences showed that optimum
fertilization and irrigation significantly affect crop evapo-transpiration and
WUE (Duncan et al. 2018; Yang et al.
2019). As mentioned
earlier, limited irrigation is beneficial in decreasing crop water consumption
and, thus, improving WUE (Panda et al.
2003; Yang et al.
2019). In this study, a new supplemental irrigation
(SI) regime was adopted in which calculated irrigation amounts were applied to
recharge the soil water content to the target soil relative water content. It
appeared that the new SI regime increased the soil water supply from deeper
soil layers (80–100 cm). A previous study showed that crop evapo-transpiration
under N rate of 80 kg ha−1 was lower by 5.8 and 8.3 mm, on
average, than under N rate of 120 and 160 kg ha−1 treatments,
respectively (Behera and Panda 2009). The present study also showed that crop
evapo-transpiration increased with the increase in N rate under the new SI
regime. However, there was no significant difference in crop
evapo-transpiration between N rate of 210 and 180 kg ha−1.
Moreover, the highest WUE was obtained under the SI regime at 210 kg N ha−1,
which might be ascribed to the highest proportion of soil water usage under
this treatment combination. It seems that increasing the use of stored water
from deeper soil layers by optimizing N and water management can decrease
irrigation amount and, thus, achieve higher WUE (Man et al. 2014; Rathore et al.
2017).
Generally, irrigation and N
application rate affect wheat physiology and growth (Wang et al. 2013: Deng et al. 2014). For example, Guo et al. (2014) found that SI
regime increases flag leaf area and ETR at anthesis stage and delays
leaf senescence, thereby increasing dry matter accumulation amounts at maturity
phase and wheat yield. In the present study, the SI regime also increased
ΦPSII and Fv/Fm after anthesis as compared with conventional flood
irrigation regime. In addition, the higher dry matter allocation of
post-anthesis assimilated dry matter to grains was obtained under SI regime.
Nitrogen significantly affects crop growth of wheat. In current study, the flag
leaf Ψw of post-anthesis
increased with the increase in N application rate, thereby enhancing ΦPSII
and Fv/Fm of the flag leaf. The higher ΦPSII and Fv/Fm might be the reason
for the higher dry matter accumulation under the treatment of 210 kg N ha−1
(Table 2). Furthermore, application of excess N fertilizer resulted in a
diminution of post-anthesis dry matter assimilation into grains and its
relative contribution to total grain dry matter, which was consistent with
previous findings (Deng et al. 2014; Dai et al.
2017). It is believed that the increase in carbon
remobilisation from vegetative tissues to grains is conducive to high grain
yield (Yang and Zhang 2006; Rivera-Amado et al. 2019). In summary, the
treatment of 210 kg N ha−1 in the SI regime promoted dry
matter assimilation into grains and resulted in the highest grain yield in the
current study.
The main challenge in crop production is to
simultaneously increase resource use efficiency and grain yield. Optimum
nitrogen and water management are crucial to enhance the grain yield (Chen et al. 2014; Rathore et
al. 2017; Thapa et al. 2019). The N input for wheat production in this study
area is approximately 220–325 kg N ha−1 (Ju et al. 2009; Lu et al. 2015) and the irrigation amount is approximately 300 mm
(Zhang et al. 2006). Although such
high nitrogen and irrigation amounts can maintain high wheat yields, the NUE
and WUE are merely about 20 kg kg-1 (Ju et al. 2009) and 13.5 kg ha-1 mm-1 (Wang 2010), respectively, which are correspondingly
1.5 (Zhang et al. 2008) and 1 times
lower than in the developed countries (Wang 2010). In the present study, the
highest WUE of 22.85 kg ha−1 mm−1 in 2013 and
21.47 kg ha−1 mm−1 in 2014 were obtained when
received 100.78 and 92.14 mm irrigation and N application rate of 210 kg ha−1.
The lower crop evapo-transpiration and the highest wheat yield were the reasons
for higher WUE. Moreover, the NUE under N rate of 210 kg ha−1 was lower than that under 180 kg ha−1,
but higher than 240 kg ha−1. It was showed that nitrogen application rate
of 210 kg ha–1 in SI regime was a desirable practice for
simultaneously enhancing yield, WUE and NUE.
Conclusion
The SI regime with N application of 210 kg ha−1 reduced the irrigation amount and increased
the use of stored water from deeper soil layers, resulting in lower crop
evapo-transpiration and higher WUE. Moreover, the highest total dry matter
accumulation amounts at maturity phase and dry matter allocation to grain of
post-anthesis led to highest grain yield. Meanwhile, NUE under nitrogen
application rate of 210 kg ha−1 were higher. Taken together, it appeared that nitrogen application
rate of 210 kg ha−1 in SI regime can maintain sustainable
winter wheat production in semi-arid regions.
Acknowledgements
The study was funded by Nature Science Foundation
of China (31771715); the China Agriculture Research System-Wheat (CARS-3-1-19).
Author
Contributions
Xin Wang,
Zhenwen Yu and Chengyan Zheng designed the research. Xin Wang, Yu Shi and
Chengyan Zheng conducted the experiments and collected data. Xin Wang and
Chengyan Zheng contributed to data analysis and wrote the manuscript. All
authors approved the final manuscript.
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