Effects of site-specific nitrogen management on morphology and physiology of roots and yield of rice

Two rice cultivars of Shanyou 63(indica)and Lianjing 6(japonica)were grown in field experiments with two nitrogen(N)managements,site-specific N management(SSNM,N application according to soil fertility,leaf color and growth status,and cultivar types)and farmers' fertilizer practice(FFP).Present investigation was aimed to determine the effect of SSNM on roots growth and yield of rice.Results showed that the root dry weight in the FFP was higher as compared to that in the SSNM before heading,whereas it was lower at and after heading.During the whole growing season,SSNM significantly increased the root-shoot ratio.Compared with FFP,SSNM increased root oxidation activity(ROA)at and after panicle initiation,especially ROA per stem.SSNM also increased the photosynthetic rate of the flag leaves after heading.Compared with FFP,SSNM increased grain yield by 7.2%-9.4%,N partial-factor productivity(grain yield/amount of N applied)by 38%-46%,and N agronomic efficiency by 56%-77%.The enhancement of root growth at the latter growing stage would account for the increase in grain yield and N use efficiency under SSNM.