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Studies ranked according to location and soil type, with growth stage at sidedressing. Medium soils are numbered from 1 to 36 and fine soils from 37 to 51.

 
Study no. Study Surface soil texture Growth stage at sidedressing
1 Missouri, Clarkton, 2006 (irrigated) loamy fine sand V6
2 Oklahoma, Stillwater, 2006 fine sandy loam V8
3 Oklahoma, Stillwater, 2008 fine sandy loam V8
4 Illinois, Dixon Springs 2006 silt loam V5
5 Illinois, Dixon Springs, 2007 silt loam V8
6 Kansas, Manhattan, 2006 silt loam V9
7 Kansas, Manhattan, 2008 silt loam V9
8 Missouri, Centralia, 2006 (irrigated) silt loam V10
9 Missouri, Miami, 2006 silt loam V9
10 Missouri, Portageville, 2006 (irrigated) silt loam V6
11 Missouri, Centralia, 2007 silt loam V9
12 Missouri, Portageville, 2008 (irrigated) silt loam V8
13 Nebraska, Shelton, 2006 (irrigated) silt loam V8
14 Ohio, Wooster 1, 2006 silt loam V4
15 Ohio, Wooster 2, 2006 silt loam V8
16 Ohio, Wooster 1, 2007 silt loam V4
17 Ohio, Wooster 2, 2007 silt loam V8
18 Ohio, Wooster 1, 2008 silt loam V4
19 Ohio, Wooster 2, 2008 silt loam V8
20 Ohio, Wooster 1, 2009 silt loam V4
21 Ohio, Wooster 2, 2009 silt loam V8
22 Ohio, Western 1, 2006 sandy loam/sandy clay loam V4
23 Ohio, Western 2, 2006 sandy loam/sandy clay loam V8
24 Ohio, Western 1, 2007 sandy loam/sandy clay loam V4
25 Ohio, Western 2, 2007 sandy loam/sandy clay loam V8
26 Ohio, Western 1, 2008 sandy loam/sandy clay loam V4
27 Ohio, Western 2, 2008 sandy loam/sandy clay loam V8
28 Ohio, Western 1, 2009 sandy loam/sandy clay loam V4
29 Ohio, Western 2, 2009 sandy loam/sandy clay loam V8
30 Virginia, Blacksburg, 2006 loam V6
31 Virginia, ATD, 2007 loam V6
32 Virginia, BHD, 2007 loam V6
33 Virginia, MCD, 2007 loam V6
34 Virginia, Varina, 2007 loam V4
35 Quebec, L’Acadie, 2007 loam V8
36 Quebec, L’Acadie 2007 (irrigated) loam V8
37 Quebec, L’Acadie, 2006 clay loam V6
38 Quebec, L’Acadie, 2008 clay loam V7
39 Quebec, L’Acadie, 2009 clay loam V6
40 Ohio, Northwest 1, 2006 silty clay loam V8
41 Ohio, Northwest 1, 2007 silty clay loam V4
42 Ohio, Northwest 2, 2007 silty clay loam V8
43 Ohio, Northwest 1, 2009 silty clay loam V4
44 Ohio, Northwest 2, 2009 silty clay loam V8
45 Missouri, Wilton, 2006 silty clay V10
46 Missouri, Rocheport, 2007 silty clay V9
47 Mexico, Cd Obregón, 2007 clay V7
48 Mexico, MC, 2007 clay V7
49 Mexico, MP, 2007 clay V7
50 Mexico, MC, 2008 clay V7
51 Mexico, MP, 2008 clay V7



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Weather parameters used in the meta-analysis. The sum was taken over daily data during a given time period.

 
Weather parameter Definition
Corn heat units (CHU) CHU = Σ(Ymax + Ymin)/2, where Ymax and Ymin are the contributions to CHU from daily maximum (Tmax, up to 30°C) and minimum (Tmin) air temperatures, respectively: Ymax = 3.33(Tmax – 10.0) – 0.084(Tmax – 10.0)2, if Tmax < 10.0, Ymax = 0.0; Ymin = 1.8(Tmin – 4.44), if Tmin < 4.44, Ymin = 0.0
Cumulative precipitation (PPT) PPT = Σ(Rain), where Rain is the daily rainfall (mm)
Precipitation evenness: Shannon diversity index (SDI) SDI = [–Σpi ln(pi)]/ln(n), where pi = Rain/PPT is the fraction of daily rainfall relative to the total rainfall in a given time period and n is the number of days in that period. SDI = 1 implies complete evenness (i.e., equal amounts of rainfall in each day of the period); SDI = 0 implies complete unevenness (i.e., all rain in 1 d)



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Ratio of between-studies variance to total variance (I2) for N rates used in the studies (N rate = starter + in-season N rate [kg ha−1] or the N-rich rate, which was 178 kg ha−1 applied at sowing with no N fertilizer at sidedressing).

 
I2
Subgroup† Nb‡ 36 + 0 36 + 27 36 + 54 36 + 80 36 + 107 36 + 134 36 + 161 N rich
All studies together
All textures, all weather 51 –0.26 0.20 0.28 0.21 0.26 0.27 0.31 0.34
Subgroups for texture properties
Fine texture 15 –0.02 0.29 0.46 0.26 0.38 0.33 0.54 0.49
Medium texture 36 –0.43 0.07 0.01 –0.32 –0.07 0.11 0.03 0.08
Subgroups for weather properties
Low CHU 28 –0.02 0.31 0.40 0.33 0.39 0.37 0.42 0.49
High CHU 23 0.01 0.18 0.32 –0.02 0.22 0.36 0.21 0.26
Low PPT 28 –0.37 0.15 0.31 0.30 0.27 0.30 0.28 0.31
High PPT 23 –0.62 –0.12 –0.11 –0.61 0.02 0.09 0.07 0.23
Low SDI 30 –0.50 0.15 0.24 0.26 0.13 0.43 0.38 0.24
High SDI 21 –0.33 0.03 0.03 –0.26 0.25 0.03 0.13 0.26
Low AWDR 29 –0.50 0.01 0.13 0.07 0.11 0.25 0.15 0.16
High AWDR 22 –0.59 –0.09 –0.27 –0.68 0.09 –0.09 –0.03 0.17
Subgroups for combined texture and weather properties
Fine texture–low CHU 12 0.07 0.43 0.42 0.40 0.29 0.44 0.51 0.56
Fine texture–high CHU 3 –0.12 0.16 –0.11 –0.46 0.44 –0.34 –0.16 –0.40
Medium texture–low CHU 16 –0.13 –0.01 0.09 –0.13 0.06 –0.06 0.04 0.13
Medium texture–high CHU 20 0.39 0.18 0.19 0.14 0.04 0.40 0.07 0.17
Fine texture–low AWDR 8 –0.16 0.08 0.26 0.28 0.10 0.25 0.43 0.47
Fine texture–high AWDR 7 –0.07 0.09 0.09 0.10 0.11 0.26 0.25 0.16
Medium texture–low AWDR 21 –0.66 –0.07 –0.04 –0.10 –0.01 0.14 –0.06 –0.10
Medium texture–high AWDR 15 –0.45 0.03 –0.37 –0.91 –0.27 –0.13 –0.09 0.17
Subgroups for rainfall and CHU for fine soil textures combined
Low AWDR–low CHU 5 –0.22 –0.06 0.26 0.03 0.19 0.11 0.17 0.28
Low AWDR–high CHU 2 –0.02 –0.11 0.00 –0.01 0.07 –0.01 0.01 –0.02
High AWDR–low CHU 7 –0.15 0.09 0.07 0.14 0.25 0.27 0.30 0.06
High AWDR–high CHU 1
CHU, corn heat units; PPT, cumulative precipitation; SDI, Shannon’s diversity index, a measure of precipitation evenness; AWDR, abundant and well-distributed rainfall, representing optimal water availability and determined as PPT × SDI.
Nb, number of studies in each subgroup.