1 2 Supporting information 3 4 5 6 Supplementary Table 1. Plant type of the tested maize hybrids Cultivars Plant type References ZD 2 H 417 DY 13 ND 60 YD 13 ND108 ZD 958 XD20 XY335 Spreading leaves Semi-upright leaves Spreading leaves Upright leaves Upright leaves Semi-upright leaves Upright eaves Upright leaves Upright leaves Xing YW, Shi XH, Wang KL et al., 2005 Zhang JP, Zhang YP, Cao HW et al., 2010 Xing YW, Shi XH, Wang KL et al., 2005 Feng HM, 1992 Guo YQ, Dong ST, Wang KJ et al., 2003 Guo J, Guo XY, Wang JH et al., 2005 Wang CH, Ou XQ, Wang H, 2009 Zhang SL, Chang JZ, Cheng XJ et al., 2007 Xu MJ, Liu J, Dong QT et al., 2009 Feng HM (1992) Preliminary study on the cultivation of maize hybrid ND60. Applied Techniques and Development. 7, 31-32 (In Chinese). 7 Guo J, Guo XY, Wang JH et al. (2005) Characteristics parameters of light responses of corn 8 varieties with different plant shapes. Acta Botanica Boreali-Occidentalia Sinica, 25, 1612-1617 9 (In Chinese). 10 Guo YQ, Dong ST, Wang KJ et al. (2003) Adjustment of colony kernel and leaf physiological 11 characteristics of different spike type maize (Zea Mays L.). Acta Agronomica Sinica, 29, 626- 12 632 (In Chinese). 13 14 15 16 17 18 Wang CH, Ou XQ, Wang H (2009) Studies on physiology and ecology of zhengdan 958 etc. High Yield Varieties. Seed, 28, 41-44 (In Chinese). Xing YW, Shi XH, Wang KL et al. (2005) Studies on the production and agronomic traits of different pant type maize hybrids. Journal of Maize Sciences, 13, 92-94 (In Chinese). Xu MJ, Liu J, Dong QT et al. (2009) Preliminary study on proper cultivation density and character index of Xianyu 335. Journal of Anhui Agricultural Sciences, 37, 8928-8930 (In Chinese) 19 Zhang JP, Zhang YP, Cao HW et al. (2010) Preliminary Analysis of the breeding strategy for 20 summer maize in Huang-Huai-Hai Plain. Journal of Henan Agricultural Sciences, 9, 151-153 21 (In Chinese). 22 23 Zhang SL, Chang JZ, Cheng XJ et al. (2007) Characteristics of New Maize Varieties Xundan No. 20 and Its High Yield Cultivation Technology. Seed, 26, 98-99 (In Chinese). 24 1 25 26 Supplementary Table 2. Nitrogen remobilization efficiency and N harvest index of nine maize hybrids under different N supplies N remobilization efficiency (%) N0 N harvest index (%) N240 N0 N120 N240 ZD2 H417 34.6 73.8 d a 42.8 60.0 cd ab 42.6 53.5 de ab 64.6 70.0 bcd ab 66.4 70.1 bc ab 63.5 64.9 b b DY13 ND60 62.6 50.4 ab abcd 49.4 62.3 cd ab 48.8 61.3 bcd a 63.1 65.4 cd cd 60.6 69.6 d b 60.0 67.8 c b YD13 ND108 55.6 39.2 abc bcd 47.5 38.8 bcd d 40.2 47.4 e bcd 62.9 60.4 cd d 64.4 61.4 cd d 60.9 59.9 c c ZD958 XD20 XY335 37.0 58.1 cd ab 51.0 53.6 cd abc 51.5 46.8 bc cd 65.1 66.6 72.3 bcd abc a 67.2 70.2 74.2 bc b a 64.7 64.7 69.3 b b a CV% 27 N120 51.3 bcd 25.1 68.0 a 18.0 54.1 ab 12.9 5.58 6.59 Note: Different letters in the same column denote significant difference at p<0.05 probability level between two maize hybrids 28 2 5.16 30 31 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 135 140 145 150 155 29 Precipitation (mm) 90 45 80 40 70 35 60 30 50 40 30 Precipitation (mm) 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 135 140 145 150 155 Growing degree days (℃) 12 10 8 6 4 Growing degree days (℃) 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 135 140 145 150 155 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 120 125 130 Sunshine hours (h) 10 8 6 Sunshine hours (h) 16 14 14 12 12 10 4 16 14 32 3 8 6 4 2 2 0 0 20 Days after sowing 18 Days after sowing 18 16 14 12 10 8 6 2 4 2 0 0 Days after sowing Days after sowing 25 20 20 15 10 10 5 0 0 Days after sowing Days after sowing Supplementary Figure 1. Weather data in the experimental location Siping in 2010 and 2011 16000 Potential yield (kg ha -1 ) 14000 12000 10000 8000 6000 4000 2000 y = 107.9x - 20574 r = 0.60** 0 1970 1980 1990 2000 2010 2020 Year 33 34 Supplementary Figure 2. Potential yield of each year × hybrid combination from 1973 to 2011. 35 Yield potential was simulated by matching each maize hybrid to the climatic conditions of the 36 year(s) in which it was grown, e.g. ZD2 was used to simulate the yield potential from 1973 to 37 1977 and H417 was used to simulate the yield potential for 1978. This method indicated that 38 modern breeding increased yield potential by 108 kg ha−1 yr−1 on average. In 1973 the yield 39 potential simulated with the hybrid ZD2 was 7314 kg ha−1, whereas in 2011 the yield potential 40 rose to 11,430 kg ha−1 as simulated with the hybrid XY335. 41 4 65 Harvest index (%) 60 y = 0.185x - 315.0 r = 0.63 NS 55 50 45 40 35 y = 0.285x - 517.5 r = 0.72* A LN HN 30 1970 1975 1980 1985 1990 1995 2000 2005 Year of hybrid release Ear numbers per unit area (plant ha -1 ) 42 60000 y = 281.8x - 50759 r = 0.68* 55000 50000 45000 y = 508.4x - 96114 r = 0.94** 40000 B LN HN 35000 1970 1975 1980 1985 1990 1995 2000 2005 Year of hybrid release 43 44 Supplementary Figure 3. Relationship between the year of hybrid release and harvest index 45 (A), and ear numbers per unit area (B). 46 5 14 Yield / sunshine hours during growth period (kg ha -1 h -1 ) 12 10 8 6 4 2 y = 0.169x - 328.6 r = 0.85** 0 1970 1980 1990 Yield / growing degree days during growth period (kg ha -1 ℃-1 ) 47 2020 10 8 6 4 2 1970 y = 0.062x - 118.8 r = 0.56** 1980 1990 48 Yield / precipitation during growth period (kg ha -1 mm -1 ) 2010 12 0 2000 Year 2010 2020 60 50 40 30 20 10 y = 0.436x - 849.4 r = 0.54** 0 1970 49 50 51 52 2000 Year 1980 1990 2000 Year 2010 2020 Supplementary Figure 4. Sunshine hours, Thermal time, and Water use efficiency in maize hybrids released since 1973. Maize yields of different eras were simulated using Maize-Hybrid model. 53 6 Type I: Early-senescent Type II: late-senescent 54 55 56 Supplementary Figure 5. Cluster analysis of 9 maize hybrids based on leaf senescence traits. 57 58 7