有机质对红壤烤烟氮素累积分配特征的影响

利用15N示踪技术，研究了有机质含量对红壤烤烟氮累积分配特征的影响。结果表明，随着土壤有机质含量增加，烤烟氮素累积时期延长，且累积量增加。烤烟后期吸收的氮素，在低有机质含量红壤上来自土壤供氮，中有机质含量来自肥料供氮，高有机质含量来自肥料供氮与土壤供氮。烤烟吸收总氮量中29.07%~40.26%来自肥料供氮，59.74%~70.93%来自土壤供氮，表明烤烟吸收氮素大部分来自土壤供氮。氮素在烟株不同部位分配量表现为:烟叶烟茎烟根；烟叶各部位中的分配量为:在低有机质含量的红壤，下、中、上3个部位分配量相等，中有机质含量和高有机质含量上则为上部叶中部叶下部叶。有机质含量对下部叶氮素分配量影响不大，其它部位均表现为有机质含量越高，氮素分配量越大。烤烟不同部位中肥料氮比例表现为下部叶中部叶烟根烟茎上部叶，土壤氮比例表现为上部叶烟茎烟根中部叶下部叶；并且土壤有机含量越高，各部位中土壤氮的比例越高，肥料氮的比例越低，上部叶受土壤供氮影响最大。红壤上烤烟氮肥利用率在25.42%~30.61%之间，低有机质含量土壤氮肥利用率较低，中、高有机质含量利用率相对较高。在施肥过程中，低有机质红壤上应在N 90 kg/hm2基础上适当增加氮肥施用量，中等有机质含量上保持不变，高有机质含量上应适当降低氮肥用量。

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 othertwo 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.