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Influence of different nitrogen (N) application rates on SPAD values at flowering stage in winter wheat during 2018 and 2019. Above bars, different small letters show significant differences among N treatments. N0: unfertilized control; N75: N application at 75 kg N⋅ha– 1; N150: N application at 150 kg N⋅ha– 1; N225: N application at 225 kg N⋅ha– 1; N300: traditional N application rate of 300 kg N⋅ha– 1.
