5Albrecht K A. Selection reversal in strains of cron previously longsterm selected for chemical conposition[J]. Crop sci , 1986,26 (5) : 1051-1055.
6Shaohua W, Yan Zh, Haidong J,et al. Posititional differences in nitrogen and sugar concentrations of upper leaves relate to plant N status in rice under different N rates [J]. Field Crop Research, 2006,96 : 224-234.