Figure.5b showed the average soil moisture of three points 0, 25, and 50 cm from the lateral pipes and two profiles 0–20, 20–40 cm for two years 2007 and 2008
under different nitrogen application amount. All average soil moisture from 0 to 40 cm depth in whole growth period were maintained at above 50 available soil moisture
except SDI N
75
under SDI and DI irrigation method.
3.2. Seasonal patterns of soil moisture
A. 2007 0-20cm
0.0 0.1
0.2 0.3
0.4
30 M
ay 14
Jun 29
Jun 14
Jul 29
Jul 13
A ug
28 A
ug 12
S ep
S o
il w ate
r c o
n te
n t c
m
3
c m
3
40 80
120 160
Ir rig
atio n
, r ain
fa ll m
m
R I
FC SDI N150
DI N150 WP
B. 2007 20-40cm 0.0
0.1 0.2
0.3 0.4
30 M
ay 14
Jun 29
Jun 14
Jul 29
Jul 13
A ug
28 A
ug 12
S ep
S o
il w ate
r c o
n te
n t
cm
3
c m
3
40 80
120 160
Ir rig
atio n
, r ain
fa ll m
m
R I
FC SDI N150
DI N150 WP
C. 2007 40-60cm 0.0
0.1 0.2
0.3 0.4
30 M
ay 14
Jun 29
Jun 14
Jul 29
Jul 13
A ug
28 A
ug 12
S ep
S o
il w
at er
c o
n te
n t c
m
3
c m
3
40 80
120 160
Irri g
at io
n , ra
in fa
ll m
m
R I
FC SDI N150
DI N150 WP
D. 2008 0-20cm
0.0 0.1
0.2 0.3
0.4
2 Ju
n 17
J un
2 Jul
17 J
u l
1 A
ug 16
A ug
31 A
ug 15
S ep
S o
il w ate
r c o
n te
n t c
m
3
c m
3
40 80
120 160
Ir rig
atio n
, r ai
n fa
ll m
m
R I
FC SDI N150
DI N150 WP
Figure 5
. Soil mois
ture at different layers a. Soil moistu
re in 0-20, 20
-40, 40 -60
cm depth und
er N
150
.
E . 200
8 2 0-
40c m
0. 0.
1 0.
2 0.
3 0.
4 2Jun
17Jun 2Jul
17Jul 1Aug
16Aug 31Aug
15Sep Soil water content cm
3
cm
3
40 80
12 16
Irrigation, rainfall mm
R
I
FC SD
I N 1
5 D
I N 150
WP
F . 2
008 40-
60cm 0.0
0.1 0.2
0.3 0.4
2Jun 17Jun
2Jul 17Jul
1Aug 16Aug
31Aug 15Sep
Soil water content cm
3
cm
3
40 80
120 160
Irrigation, rainfall mm
R
I
FC SD
I N 1
5 DI N
1 5
WP A
. 200 7 S
D I
0. 0.
1 0.
2 0.
3 0.
4 30May
14Jun 29Jun
14Jul 29Jul
13Aug 28Aug
12Sep Soil water content cm
3
cm
3
40 80
12 16
Irrigation, rainfall mm
R I
FC WP
N0 N7
5 N1
50 N3
00
B . 20
07 D
I 0.0
0.1 0.2
0.3 0.4
30May 14Jun
29Jun 14Jul
29Jul 13Aug
28Aug 12Sep
Soil water content cm
3
cm
3
40 80
12 16
Irrigation, rainfall mm
R I
FC WP
N0 N7
5 N150
N300
b. Average soil moisture of 0-40 cm depth under different nitrogen treatment.
3.3. Root distribution Table 5. Root length density RLD of bell pepper as influenced by irrigation method
and N application levels Treatment
RLDcmcm
3
2007 2008 Nitrogen
N 0.42c
0.18d N
75
0.51b 0.30b
N
150
0.61a 0.33a
N
300
0.39c 0.22c
Irrigation SDI
0.51a 0.27a
DI 0.45b
0.24b Average of two irrigation methods.
Average of four different nitrogen levels. Table 5 shows a significant difference in RLD between SDI and DI and among the
different nitrogen levels. RLD obviously increased with increasing nitrogen levels until the nitrogen level reached 150 kgha in both years, and then it sharply decreased.
The effect of irrigation methods on RLD was apparent; the RLD of SDI was obviously higher than that of DI.
At the same fertilization level, the root length and percentage of root length in each layer to total root length decreased with soil depths Table 6. The percentages of root
length at 30-40 cm soil depth to total root length under DI and SDI were 1.25 DI N
150
and 2.81 SDI N
150
, respectively, indicating that there were almost no bell pepper roots below 40 cm soil depth. Root lengths under SDI N
, SDI N
75
, SDI N
150
, and SDI N
300
were 1.06, 1.06, 1.46, and 1.07 times longer than those under DI N , DI
N
75
, DI N
150
, and DI N
300
, respectively. The percentage of root length below 10 cm soil depth under SDI N
150
was higher than that under DI N
150
by 7. Hence, SDI does not
C. 2008 SDI
0.0 0.1
0.2 0.3
0.4
2 Jun
17 J
u n
2 Ju
l 17
J ul
1 A
ug 16
A u
g 31
A u
g 15
S ep
S o
il w ate
r c o
n te
n t
c m
3
c m
3
40 80
120 160
Ir rig
ati o
n , ra
in fa
ll m
m
R I
FC WP
N0 N75
N150 N300
D. 2008 DI
0.0 0.1
0.2 0.3
0.4
2 Jun
17 J
u n
2 Jul
17 J
u l
1 A
ug 16
A u
g 31
A u
g 15
S ep
S o
il w ate
r co
n te
n t c
m
3
c m
3
40 80
120 160
Ir rig
atio n
, r ain
fa ll
m m
R I
FC WP
N0 N75
N150 N300
only promote root growth but also results in deeper root development.
Table 6. Bell pepper root length at different soil depths
Depth cm 0–10
10–20 20–30
30–40 0–40 DI N
Root lengthcm 7431 3772
719 431
12354 Proportion 53.47
27.14 5.18
3.10 100
SDI N Root lengthcm 6038
4976 1370
750 13135
Proportion 45.97 37.88
10.43 5.71
100 DI N
75
Root lengthcm 8263 6917
1922 937
18038 Proportion
45.81 38.34
10.65 5.19
100 SDI N
75
Root lengthcm 6923 8017
3035 1255
19231 Proportion 36.00
41.69 15.78
6.53 100
DI N
150
Root lengthcm 11582 4588
1089 219
17479 Proportion 66.26
26.25 6.23
1.25 100
SDI N
150
Root lengthcm 15235 7353
2319 719
25625 Proportion
59.45 28.69
9.05 2.81
100 DI N
300
Root lengthcm 8555 4076
919 827
14377 Proportion 59.51
28.35 6.39
5.75 100
SDI N
300
Root lengthcm 7199 6419
951 820
15390 Proportion 46.78
41.71 6.18
5.33 100
Under the same irrigation methods, the impact of different nitrogen levels on RLD at harvest is shown in Fig.6. At 0–10 cm soil depth, RLD gradually increased with
increasing nitrogen levels. However, at 10–20 cm soil depth, RLD declined sharply when the nitrogen level exceeded 150 kgha. These findings imply that too much
nitrogen application inhibits root growth in deeper soil layers.
Figure.6 RLD distribution during the 2007 growing season in all treatments
3.4. NO
3 -
-N distribution in soils Figure.7 shows NO
3 -
-N concentrations in soil 2 d before fertilization Aug 14, 2 d after fertilization Aug 18, and 22 d after fertilization Sep 7.
Before fertilization, there was no significant difference in NO
3 -
-N distribution between SDI and DI. However, 2 d after fertilization, NO
3 -
-N concentrations under SDI treatment were distributed with a parabolic curve; the maximum value 14.2 mgkg
was found at 20–40 cm soil depth. In contrast, NO
3 -
-N concentrations under DI treatment declined with increasing soil depth, and a maximum concentration 15.7
mgkg was obtained at the top soil 0–20 cm. Furthermore, 22 d after the fertilization, NO
3 -
-N gradually moved downward due to water movement, crop growth, and root activities. The maximum NO
3 -
-N concentration 22 d after fertilization under SDI and DI occurred at 40–60 cm and 60–80 cm, respectively.
SDI 10
20
30 0.0
0.2 0.4
0.6 0.8
1.0 RLD cm•cm
-3
D ept
h cm
N0 N75
N150 N300
DI 10
20
30 0.0
0.2 0.4
0.6 0.8
1.0 RLD cm•cm
-3
D ept
h cm
N0 N75
N150 N300
Figure 7. Vertical distribution of NO
3 -
-N concentration in soil profiles As mentioned above, bell pepper roots were concentrated at 0–40 cm soil depth.
Nitrogen leaching below 40 cm, which was hardly useful to the plants, was of residual value. The maximum residual NO
3 -
-N concentration at 40-60 cm under SDI 8.4 mgkg was far lower than that under DI treatment 13.8 mgkg at 60–80 cm.
Residual NO
3 -
-N concentrations in soil profiles increased with increasing levels of nitrogen fertilizers Fig. 8, but the residual of N
150
was only slightly higher than N
75
. The NO
3 -
-N residual concentration for N
300
treatment was sharply higher than that for N
150
treatment 22 d after fertilization. This tend was found in all nitrogen treatments. The data above show that SDI promoted the development of bell pepper roots and
favored the establishment of intensive root layers, which can prevent nitrate leaching. At nitrogen level lower than 150 kgha, fertigation produced lesser residues.
SDI N
150
20 40
60 80
100 10
20 30
40 N0
3 -
-N distribution mg.kg
-1
dept h
cm 14-Aug
18-Aug 7-Sep
DI N
150
20 40
60 80
100 10
20 30
40 N0
3 -
-N distribution mg.kg
-1
d ept
h cm
14-Aug 18-Aug
7-Sep
18-Aug-2007 SDI
20 40
60 80
100 10
20 30
40 NO
3 -
-N distribution mg.kg
-1
de p
th cm
N75 N150
N300 18-Aug-2007
DI 20
40 60
80 100
10 20
30 40
NO
3 -
-N distribution mg.kg
-1
de pt
h cm
N75 N150
N300
Figure 8. Vertical distribution of NO
3 -
-N as influenced by different nitrogen levels 3.5. ET
c
Bell pepper plants were transplanted at May 20 in 2007 and May 21 in 2008. The growth seasons last 118 d and 115 d separately in 2007 and 2008.
Bell pepper ET
c
was calculated by formula 1. D in formula 1, the amounts of drainage water collected from the lysimeter are shown in Table.7.
Table.8 shows the cumulative water consumption of bell pepper and ET calculated
by Penman-Monteith’s formula during the two growing seasons. The ET
c
and ET of
all treatments in 2008 were lower than those in 2007 due to the lower monthly average temperature in 2008. as compared with 2007. A very low temperature 2.4
°C in May 30, 2008 inhibited seedling establishment.
Table 7. Drainage water amounts mm
a. 2007 SDI N
SDI N
75
SDI N
150
SDI N
300
DI N DI N
75
DI N
150
DI N
300
16-Jul 5.2 2.4
20-Jul 5.6 4.9
24-Jul 6.0 2.9
27-Jul 8.5 6.9
5-Aug 5.7 7-Aug
3.9 13-Aug 4.9
5.3 16-Aug 5.0
17-Aug 13.9 5.9
21-Aug 11.4 5.7
5.5 25-Aug 11.8
5.6 3.5
26-Aug 8.2 6.5
14.7 7.8
22.7 10.7
10.8 2-Sep 2.1
5-Sep 3.4 9-Sep 1.8
10-Sep 11.5 6.3
8.3 Total 105
47.5 19.6
11.7 22.7
28 10.8
7-Sep-2007 SDI
20 40
60 80
100 10
20 30
40 NO
3 -
-N distribution mg.kg
-1
dept h
cm N0
N75 N150
N300 7-Sep-2007
DI 20
40 60
80 100
10 20
30 40
NO
3 -
-N distribution mg.kg
-1
de pt
h cm
N0 N75
N150 N300
b. 2008 SDI N
SDI N
75
SDI N
150
SDI N
300
DI N DI N
75
DI N
150
DI N
300
9-Jul 3.6
16-Jul 9.8 5.3
5.4 7.5
20-Jul 16.7 15.3
12.2 18.2
3.1 24-Jul 19.2
12.3 10.6
16.6 2.2
2.4 25-Jul
2.3 2.1
2.6 1.2 29-Jul 2.9
5.3 2.7
5.4 4.6
5.4 5.4
5-Aug 10 8.4
3.5 7.2
9 7.0
10-Aug 3.5 7.5
3.8 8.5
2.7 Total 62.1
33.2 31.8
42.7 25
25.4 2.6
9.3
Table 8. Cumulative water consumption under different irrigation
and fertilization practices ET
mm ET
c
mm N
N
75
N
150
N
300
2007 508 DI 407
426 451 404
SDI 301
405 438 432
2008 406 DI 362
387 382 382
SDI 334
357 377 359
The maximum and minimum water consumption were recorded for DI N
150
treatment 451 mm and SDI N
treatment 301 mm, respectively, in 2007. In 2008, the maximum water consumption was recorded for DI N
75
387 mm, followed by DI N
150
and DI N
300
382 mm. The minimum value was at 334 mm for SDI N . Except for N
300
treatment in 2007, all cumulative water consumptions under SDI were lower than under DI.
2007
1 2
3 4
5 6
7
seedling stage blossom and fruit
set period full bearing period the late stages of
development dai
ly w at
er cons
u m
pt ion
m m
·d
-1
DI N150 SDI N150
Figure 9. Daily averaged water consumption at different growth stages
Daily average water consumptions at different growth stage under different irrigation techniques N
150
treatment are shown in Fig.9. During the seedling establishment period, the DI method resulted in higher daily averaged water consumption compared
with SDI because of higher evaporation under DI. After entering the blossom and fruit- set period, the daily average water consumption under SDI became higher than that
under DI. This result may be attributed to faster root growth under SDI than under DI. At full bearing period, the plants grew vigorously, leading water consumption to reach
its maximum. Water consumption under SDI was lower than that under DI, contributing to low plant height and leaf area Fig. 10. However, daily average water
consumption under DI was slightly lower than that under SDI at the late crop growth stages.
2008
1 2
3 4
5 6
7
seedling stage blossom and fruit
set period full bearing period the late stages of
development d
ai ly w
at er
co ns
u m
pt io
n m
m ·d
-1
DI N150 SDI N150
10 20
30 40
50
19Jun 1Jul
13Jul 25Jul
6Aug 18Aug
30Aug 11Sep
Hei g
h t
c m
SDI N0 SDI N75
SDI N150 SDI N300
DI N0 DI N75
DI N150 DI N300
Figue 10. Plant height and LAI for different treatments 2007
There was a polynomial correlation between crop water consumption and nitrogen levels Fig.11. ET
c
increased with increasing nitrogen levels, reaching a maximum value at 150 kgha nitrogen level. Thereafter, ET
c
again declined. Nitrogen became excessive after 150 kgha and too much nitrogen restricts bell pepper growth leading
to lower ET
c.
Figure 11. Relationship between ET
c
and nitrogen levels
2 4
6 8
10 12
19Jun 1Jul
13Jul 25Jul
6Aug 18Aug
30Aug 11Sep
LA I
SDI N0 SDI N75
SDI N150 SDI N300
DI N0 DI N75
DI N150 DI N300
2007
y
SDI
= -0.0035x
2
+ 1.4546x + 305.09 R
2
= 0.9838 y
DI
= -0.0018x
2
+ 0.5418x + 403.82 R
2
= 0.9204
250 300
350 400
450 500
50 100
150 200
250 300
Nitrogen applied amount kg N·ha
-1
ET
c
m m
DI SDI
2008
y
SDI
= -0.0013x
2
+ 0.4679x + 332.57 R
2
= 0.9743 y
DI
= -0.0007x
2
+ 0.251x + 364.92 R
2
= 0.7637
300 325
350 375
400
50 100
150 200
250 300
Nitrogen applied amount kg N·ha
-1
ET
c
mm DI
SDI
Table 9. Calculated k
c
at each growth stage a. SDI N
150
, 2007 ET
ET
c
Calculated k
c
k
c
recommended by FAO- Seedling establishment
167 115 0.69
0.6 Blossom and fruit-set period
120 101 0.84
1.05 Full bearing period
160 191 1.19
1.05 Late crop growth stages
60 44
0.74 0.9
Whole growing season 508 451
0.89 b. SDI N
150
, 2008 ET
ET
c
Calculated k
c
k
c
recommended by FAO- Seedling establishment
115 76 0.66
0.6 Blossom and fruit-set period
107 87
0.82 1.05
Full bearing period 115 149
1.30 1.05
Late crop growth stages 69
65 0.93
0.9 Whole growing season
406 377 0.93
Crop coefficient k
c
for bell pepper at different growth stages for the experimental site under SDI N
150
is shown in Table 9. At the seedling establishment and full bearing periods, k
c
values were higher than the values recommended by FAO-56. On the contrary, k
c
at the blossom and fruit-set period was higher than that recommended by FAO-56. Meanwhile, k
c
at the late crop growth stages was not stable.
3.5. Yield and water use efficiency