Table 1 The details of irrigation in maize field from 2014 to 2018
Date
|
Irrigation
(mm)
|
Date
|
Irrigation
(mm)
|
Date
|
Irrigation
(mm)
|
Date
|
Irrigation
(mm)
|
Date
|
Irrigation
(mm)
|
2014/6/6
|
50.00
|
2015/6/1
|
50.00
|
2016/4/24
|
51.00
|
2017/4/23
|
35.10
|
2018/5/1
|
50.77
|
2014/6/23
|
50.00
|
2015/6/13
|
50.00
|
2016/6/10
|
45.47
|
2017/6/14
|
68.02
|
2018/6/7
|
53.08
|
2014/6/28
|
50.00
|
2015/6/26
|
50.00
|
2016/6/25
|
49.82
|
2017/6/25
|
64.79
|
2018/6/18
|
40.58
|
2014/7/7
|
50.00
|
2015/7/10
|
50.00
|
2016/7/3
|
54.26
|
2017/7/10
|
62.07
|
2018/6/30
|
49.62
|
2014/7/18
|
50.00
|
2015/7/24
|
50.00
|
2016/7/15
|
65.09
|
2017/7/22
|
57.45
|
2018/7/11
|
55.38
|
2014/7/28
|
50.00
|
2015/8/7
|
50.00
|
2016/7/27
|
54.45
|
2017/8/8
|
53.76
|
2018/7/22
|
50.96
|
2014/8/22
|
50.00
|
2015/8/20
|
50.00
|
2016/8/7
|
53.53
|
2017/8/22
|
27.09
|
2018/8/1
|
68.27
|
|
|
2015/8/31
|
50.00
|
2016/8/22
|
53.19
|
|
|
2018/8/14
|
53.27
|
Table 2 The details of fertilization in maize field from 2014 to 2018
Year
|
Date
|
(NH4)2HPO4
(kg hm-1)
|
Urea
(kg hm-1)
|
Compound fertilizer
(kg hm-1)
|
2014
|
10-Apr (base fertilizer)
|
275.00
|
42.00
|
|
8-Jun
|
|
150.00
|
|
5-Jul
|
|
120.00
|
|
2015
|
12-Apr (base fertilizer)
|
262.50
|
37.50
|
|
30-May
|
63.00
|
9.00
|
|
11-Jun
|
78.75
|
11.25
|
|
25-Jun
|
168.00
|
24.00
|
|
9-Jul
|
126.00
|
18.00
|
|
27-Jul
|
105.00
|
15.00
|
|
2016
|
5-Apr (base fertilizer)
|
300.00
|
225.00
|
|
27-Jun
|
|
300.00
|
|
15-Jul
|
|
150.00
|
|
2017
|
26-Mar (base fertilizer)
|
375.00
|
|
375.00
|
15-Jun
|
|
270.00
|
|
30-Jun
|
|
180.00
|
|
2018
|
26-Mar (base fertilizer)
|
375.00
|
|
375.00
|
7-Jun
|
|
225.00
|
|
18-Jun
|
|
150.00
|
|
30-Jun
|
|
75.00
|
|
Table 3 Dry grain (Dg), dry cob (Dc), dry leaf (Dl), dry stem (Ds) and exported carbon (Ce) in the spring maize field during 2014-2018
Year
|
Dg
(g m-2)
|
Dc
(g m-2)
|
Dl
(g m-2)
|
Ds
(g m-2)
|
Ce
(g C m-2)
|
2014
|
904
|
126.43
|
314.70
|
502.63
|
795.75
|
2015
|
997
|
139.44
|
310.42
|
724.63
|
931.98
|
2016
|
1095
|
153.15
|
432.91
|
596.09
|
979.73
|
2017
|
529
|
73.99
|
192.40
|
614.35
|
599.27
|
2018
|
792
|
110.77
|
372.28
|
492.23
|
757.55
|
AVG
|
863.40
|
120.76
|
324.54
|
585.99
|
812.86
|
Table 4 Growing season sums of net ecosystem exchange (NEE), ecosystem respiration (ER) and gross primary productivity (GPP),NEEmax is the peak of NEE in the growing season, ERmax is the maximum value of ecosystem respiration in the growing season, GPPmax is the maximum value of GPP in the growing seasons
Year
|
Growing days
|
NEE
|
ER
|
GPP
|
NEEmax
|
ERmax
|
GPPmax
|
(Day)
|
(g C m-2)
|
(g C m-2)
|
(g C m-2)
|
(g C m-2)
|
(g C m-2)
|
(g C m-2)
|
2014
|
134
|
-630.13
|
485.46
|
1115.54
|
-14.32
|
7.6
|
20.83
|
2015
|
132
|
-729.89
|
975.46
|
1705.3
|
-18.69
|
14.67
|
26.79
|
2016
|
144
|
-601.18
|
825.81
|
1427.05
|
-13.67
|
9.98
|
21.31
|
2017
|
142
|
-406.76
|
661.84
|
1068.63
|
-10.98
|
8.77
|
18.99
|
2018
|
146
|
-527.47
|
724.94
|
1252.35
|
-11.42
|
9.14
|
17.94
|
Mean
|
139.6
|
-579.09
|
734.7
|
1313.77
|
-13.82
|
10.03
|
21.17
|
SD
|
5.57
|
107.89
|
163.58
|
232.07
|
2.75
|
2.44
|
3.06
|
CV
|
0.04
|
-0.19
|
0.22
|
0.18
|
-0.20
|
0.24
|
0.14
|
SD is the standard deviation.
CV is coefficient of variation.
Table 5 Partial correlation coefficients between environmental variables and net ecosystem exchange (NEE), ecosystem respiration (ER) and gross primary productivity (GPP)
Carbon flux
|
Year
|
Rn
|
Ta
|
VPD
|
SWC
|
IP
|
LAI
|
NEE
|
2014
|
-0.47**
|
-0.320**
|
0.153
|
-0.303**
|
-0.176*
|
-0.817**
|
2015
|
-0.390**
|
-0.470**
|
0.044
|
-0.148
|
-0.146
|
-0.806**
|
2016
|
-0.625**
|
-0.666**
|
-0.407**
|
-0.266**
|
-0.175*
|
-0.497**
|
2017
|
-0.581**
|
-0.638**
|
-0.449**
|
-0.148
|
-0.109
|
-0.749**
|
2018
|
-0.480**
|
-0.666**
|
-0.11
|
-0.293**
|
-0.188*
|
-0.765**
|
ER
|
2014
|
0.448**
|
0.395**
|
-0.037
|
0.231**
|
-0.013
|
0.775**
|
2015
|
0.258**
|
0.733**
|
0.350**
|
0.339**
|
0.034
|
0.742**
|
2016
|
0.313**
|
0.675**
|
0.217**
|
0.111
|
0.05
|
0.471**
|
2017
|
0.329**
|
0.770**
|
0.432**
|
0.272**
|
0.114
|
0.878**
|
2018
|
0.338**
|
0.618**
|
-0.202*
|
0.384**
|
0.154
|
0.929**
|
GPP
|
2014
|
0.499**
|
0.365**
|
-0.132
|
0.303**
|
0.137
|
0.859**
|
2015
|
0.376**
|
0.619**
|
0.106
|
0.237**
|
0.117
|
0.858**
|
2016
|
0.596**
|
0.748**
|
0.393**
|
0.247**
|
0.154
|
0.547**
|
2017
|
0.523**
|
0.727**
|
0.470**
|
0.204*
|
0.118
|
0.845**
|
2018
|
0.455**
|
0.687**
|
0.001
|
0.344**
|
0.186*
|
0.892**
|
** Significantly correlated at the 0.01 level (bilateral) and * significantly correlated at the 0.05 level (bilateral).
ER: ecosystem respiration; NEE: net ecosystem exchange; GPP: gross primary productivity; Rn: net radiation; Ta: air temperature; VPD:vapor pressure deficit; SWC: soil water content; IP: the sum of precipitation and irrigation and LAI: leaf area index.
Table 6 Regression results of multi-factor liner model between daily carbon flux (NEE, ER and GPP) and environmental variables and LAI, selected according to significant level p<0.01
Carbon flux
|
Year
|
Multi-factor liner model
|
R2
|
p
|
NEE
|
2014
|
NEE=-0.02Rn-0.05Ta-24.87SWC-1.50LAI+8.03
|
0.73
|
<0.01
|
2015
|
NEE=-0.04Rn-0.05Ta-1.83LAI+7.29
|
0.78
|
<0.01
|
2016
|
NEE=-0.03Rn-0.30Ta-1.17VPD-10.19SWC-0.41LAI+10.22
|
0.72
|
<0.01
|
2017
|
NEE=-0.03Rn-0.07Ta-0.44VPD-1.42LAI+5.07
|
0.74
|
<0.01
|
2018
|
NEE=-0.01Rn-0.24Ta+3.44SWC-1.22LAI+5.59
|
0.76
|
<0.01
|
|
Total
|
NEE=-1.03LAI-0.029Rn-1.67Ta-0.03IP+5.72SWC
|
0..79
|
<0.01
|
ER
|
2014
|
ER=0.01Rn+0.06Ta+10.06SWC+0.54LAI-1.50
|
0.79
|
<0.01
|
2015
|
ER=0.004Rn+0.27Ta+1.60VPD+3.36SWC+0.85LAI-4.38
|
0.78
|
<0.01
|
2016
|
ER=0.003Rn+0.47Ta-2.09VPD-0.09LAI-1.16
|
0.76
|
<0.01
|
2017
|
ER=-0.002Rn+0.23Ta+0.03VPD+1.15SWC+0.83LAI-1.32
|
0.90
|
<0.01
|
2018
|
ER=0.002Rn+0.09Ta-0.74SWC+0.87LAI+0.77
|
0.89
|
<0.01
|
Total
|
ER=0.52LAI+0.17Ta+0.01Rn+5.04SWC
|
0.71
|
<0.01
|
GPP
|
2014
|
GPP=-0.01Rn+0.04Ta+17.39SWC+2.69LAI-3.36
|
0.85
|
<0.01
|
2015
|
GPP=0.05Rn+0.53Ta-34.61SWC+2.70LAI-6.04
|
0.90
|
<0.01
|
2016
|
GPP=0.04Rn+0.77Ta-1.91VPD+8.70SWC+0.33LAI-11.09
|
0.70
|
<0.01
|
2017
|
GPP=0.02Rn+0.29Ta+0.45VPD+2.26LAI-6.10
|
0.86
|
<0.01
|
2018
|
GPP=0.02Rn+0.33Ta-4.17SWC+2.09LAI-4.82
|
0.89
|
<0.01
|
Total
|
GPP=1.54LAI+0.03Rn+0.34Ta+0.02IP
|
0.89
|
<0.01
|