Characteristics Of Nitrogen Supply On Paddy-upland Rotation Soil And The Effects On Accumulation And Distribution Of Nitrogen In Flue-cured Tobacco

High quality flue-cured tobacco requires an adequate supply of nitrogen before flowering, and a less supply after removal of the shoot apex to avoid darkening and too high nicotine concentration. The process of soil nitrogen mineralization and the interactive effects with the rule of nitrogen accumulation in tobacco plant are the key problems urgently needed to be solved in tobacco production. In situ incubation experiment and 15N-labelled experiment were designed to study the characteristics of soil nitrogen mineralization and its effects on nitrogen accumulation and distribution of flue-cured tobacco and yield and quality of tobacco leaves under the condition of nitrogen fertilizer application and rice straw incorporation on paddy-upland rotation soil. The experiments were carried out at Zhaowei Village Group 6 and Zhaowei Experiment Base in Hongta District, Yuxi City, Yunnan Province. The main results were as the following:The in situ incubation experiment showed that the accumulation quantities of mineralized nitrogen were 164 kg·ha^-1 and 112 kg·ha^-1 at nitrogen rates of 0 and 90 kg·ha^-1 in the field of Group 6, and the numbers were 122 kg·ha^-1 and 101 kg·ha^-1 at Experiment Base during the tobacco growth period. The abilities of soil nitrogen mineralization were great in the fields of Group 6 and Experiment Base. The percentages of nitrogen mineralized after removal of the shoot apex occupied the total nitrogen mineralized in the whole growth period approximated to 50 in two fields.Different application amounts of nitrogen fertilizer had different effects on nitrogen absorption, accumulation and distribution of nitrogen derived from soil and fertilizer in tobacco plants and yield and quality of leaves. Nitrogen absorption were 70.9 kg·ha^-1 and 115 kg·ha^-1 at nitrogen rates of 0 and 90 kg·ha^-1 in the field of Group 6 in the whole tobacco growth period, and the numbers were 89.7 kg·ha^-1 and 140 kg·ha^-1 at Experiment Base. Using nitrogen fertilizer remarkably increased nitrogen content of flue-cured tobacco. The 15N-labelled experiment indicated that most nitrogen in tobacco plants derived from soil, and the nitrogen derived from soil and its ratio to total nitrogen markedly increased with growth period extending and stalk position ascending under the condition of applying nitrogen 90 kg·ha^-1. The percentages of nitrogen derived from soil were respectively up to 69.1 and 73.5 at the end of growth period in Group 6 field and Experiment Base field. Application of nitrogen fertilizer increased yield, but the effect was not significant in Group 6 field. Using nitrogen fertilizer remarkably increased nitrogen and nicotine content, and improved the quality of tobacco leaves both in Group 6 field and Experiment Base field. However, the nicotine concentrations of upper leaves were too high because of the excessive supply of soil nitrogen. Our study suggests controlling the supply amount of soil nitrogen in latter period of tobacco growth is important to improve the quality of tobacco leaves, especially to upper leaves.The effects on soil nitrogen mineralization and quality of tobacco leaves were different under different straw incorporation manners. Rice straw mulching remarkably accelerated soil nitrogen mineralization in vigorous growing period, but plowing rice straw into soil had better promotion effects on nitrogen mineralization during maturation. While both straw mulching and plowing increased soil nitrogen mineralization, nitrogen and nicotine content evidently reduced and total sugar and reductive sugar remarkably increased of upper leaves. The experiments indicated that rice straw incorporation improved the quality and usability of upper leaves.