Study on fertilizer N leaching, accumulation, and balance in tobacco fields with 15 N tracing technique

To reveal the amount and distribution of fertilizer N, a self-made observation device was developed, and the 15 N tracing technique was adopted. Leaching of N accounted a fairly small part for the fertilizer N gross during the growth period of tobacco, while a considerable large proportion of fertilizer N remained in soil, forming a potential threat to the surrounding environment. It was also found that 26.43% of the leaching of N was brought by runoffs, 38.12% infiltrated with the seepage water and 35.46% was in the sediment brought by seepages. The amount of N leaching had significant difference (p≤0.05) among treatments, proving that there was marked interrelationship between N leaching and N application. The analysis of fertilizer N accumulation in tobacco plants confirmed the average proportion of fertilizer N in leaf, lateral bud+ blossom, stem and root: 45.37%, 22.26%, 22.19% and 10.18%, respectively. The absorption of fertilizer N among treatments was significantly different (p≤0.05). Moreover, to select a preferable fertilizer regime and ensure the practicality of the experimental results, the tobacco was treated by five different fertilizer regimes, and the projection pursuit model was built for the selection. Based on the model calculations, 90 kg hm -2 of fertilizer was appropriate, it would brought both economic and environmental benefits for the tobacco cultivation in Hunan province.