Effect of NH~4~+ to NO_3~- ratio(NH_4~+/NO~3~-)on biological characteristics of rice with different nitrogen use efficiency

As the rice plant is increasingly cultivated in the soil intermittently irrigated or even in aerobic soil in which nitrate nutrition of rice is more important than ever before,there are many evidences of enhanced effect by nitrate(NO3-)on rice crop although it prefers the ammonium(NH4+)nutrition to nitrate.Solution culture experiment were carried out to study the effects of different ratios of NH4+/NO3-(NH4+/NO3-as 100/0,75/25,50/50 and 25/75)on the biological characteristics of eight genotypes of rice with different nitrogen(N)efficiency at the seedling stage.The results obtained were as follows.Different rice genotypes had different responses to NO3-.Among the eight rice genotypes,the improvement of growth by NO3-to the rice genotypes with higher N use efficiency was greater than that with lower N use efficiency.Furthermore,we compared the growth of Nanguang(higher N efficiency),Yunjing 38(higher N efficiency)and ELIO(lower N efficiency)at the ratio of NH4+/NO3-as 75/25 and 100/0.The tillers and photosynthetic rate in the leaves of Nanguang and Yunjing 38 were averagely increased by 35% and 24%,respectively,while those of ELIO had no significant difference,between the treatments of 75/25 and 100/0.It was not the N content but the increased dry matter that partial replacement of NH4+ by NO3-contributed to N accumulation in rice plants.NO3-could improve the accumulation of dry matter in the roots of Nanguang and Yunjing 38 and increase the volume of roots of Nanguang,Yunjing 38 and ELIO.