Integrated Effects of Reducing N Application and Cutting-Roots with K Top-Dressing on N, K Uptake, and Yield, Quality of Flue-Cured Tobacco

Abstract

Cutting-roots with K top-dressing at topping of flue-cured tobacco plant, which was supplied with nitrogen fertilizer at the conventional rate, had been considered having positive effect on potassium uptake and leaf quality in flue-cured tobacco, due to the improvement of lateral roots’ development and activity. However, it could be inferred that nitrogen uptake of plant be im-proved simultaneously, which may result in higher concentration of nicotine and undesired quality of leaves. Therefore, we hypothesized that nitrogen fertilization rate during the whole growth period should be reduced in the case that the practice cutting roots with K top-dressing be adopted at the stage of decapitation of flue-cured tobacco, in order to get superior flue-cured leaves. Field experiments were conducted to compare dry matter accumulation (DMA), N and K uptake as well as leaf yield and eco-nomic returns for (a) normal fertilization at recommended N rate without cutting-roots and K top-dressing at decapitation (CK), (b) normal fertilization at recommended N rate coupled with cutting-roots and K top-dressing at decapitation (CK+C+K) and (c) reducing nitrogen fertilization rate up to 80% coupled with cutting-roots and K top-dressing at decapitation (RN+C+K). The re-sults showed that the practice cutting roots with K top-dressing enhanced growth in later growth stage of tobacco, with RN+C+K and CK+C+K both showing significant advantages in terms of leaf area and SPAD value on upper and middle position of the stalk, DMA, N and K uptake, leaf yield and economic returns as well as leaf quality compared with CK. In addition, DMA, N and K uptake, leaf yield and economic value in RN+C+K were recorded 97.2%, 97.8%, 98.9%, 98.6%, and 102.0% of those in CK+C+K respectively, while nicotine concentration in upper leaves in RN+C+K were 6.7% and 4.5% less than CK and CK+C+K, and po-tassium concentration in upper leaves in RN+C+K 18.9% and 5.6% higher than CK and CK+C+K respectively. It suggested that nitrogen rate applied to tobacco plant should be reduced in the case of coupling with the practice cutting roots with K top-dressing atstage of decapitation, in order to obtain more desirable leaf quality, higher economic value and higher nitrogen fertilizer utilization efficiency.