Effect of organic matter on accumulation and distribution of nitrogen of the flue-cured tobacco in red soil

Effect of organic matter content on accumulation and distribution of nitrogen of the flue-cured tobacco was investigated by using 15N isotopic tracer technique in red soils with three different levels of OM contents in order to provide decision making information to rational utilization of nitrogen fertilizers. The results show that the period of nitrogen accumulation of flue-cured tobacco is extended, and the amount of nitrogen accumulation is increased with the increase of soil organic matter content. Nitrogen absorbed by flue-cured tobacco in red soils with low, middle, high organic matter contents at the late growth stages of tobacco is from soil, fertilizer, soil and fertilizer, respectively. About 29.07%~40.26% of total nitrogen absorbed by flue-cured tobacco is from fertilizer, and 59.74%~70.93% from soil, these indicate that most of nitrogen absorption is from soil. The amounts of total nitrogen in different parts of tobacco are in the order of leaves stems roots. For the amounts of nitrogen in tobacco leaves at different high levels, the amounts are equal in each level of leaves in red soils with a low organic matter content, while for soils with middle and high organic matter contents, the order is leaves in the top leaves in the medium leaves in the bottom. Distribution of total nitrogen in the bottom leaves is not significantly influenced by organic contents, while in the other two levels, the higher the organic matter content, the larger the amount. The percentages of nitrogen from fertilizer in the different parts and leaf levels of the plant are arranged by the order of bottom leaves medium leaves roots stems top leaves, while the percentages of nitrogen from soils are top leaves stems roots medium leaves bottom leaves. Furthermore the higher the content of soil organic matter, the higher the percentage of nitrogen from soil, and the lower percentage from fertilizer. These indicate nitrogen accumulation in the top leaves is significantly influenced by the supplication of nitrogen from soils. The utilization of nitrogen from fertilizer is low in soils with low organic matter content, and is relatively high in soils with middle and high organic matter contents. The utilization is from 25.42% to 30.61% in red soil. Taking the application of 90 kg/ha nitrogen as a base, the application amount of N fertilizer should be raised up for soils with low OM content, not changed for soils with middle OM content, and decreased for soils with high OM content.