Application of humic acid increases the economic value and yield of superior tobacco as well as improves the chemical and processing quality

Abstract

The overuse of nitrogen (N) fertilizer in the vegetable growing season leads to a high amount of soil residual N and a decrease of resistance to tobacco disease in the vegetable–tobacco continuous cultivation system, which will seriously threaten the sustainable development of tobacco production. Humic acid (HA) rich in bioactive substances and microelements may enhance leaf growth rate and improve the quality of tobacco. A two‐factor randomized block experiment was carried out over 2 years to evaluate the effects of additional applying HA (0 and 150 L ha−1) combined with three N rates (0, 60, and 90 kg N ha−1) on tobacco growth, economic value, chemical, and processing quality. Applying HA significantly increased the tobacco economic value by 5%–28%. The superior tobacco yields positively correlated with the economic value (R2 = 0.88), which was the key factor determining the increase of the economic value. The application of HA decreased the disease severity and increased the microelement uptake and the daily leaf growth rate in the prosperous growing stage which was positively correlated with the superior tobacco yield. Applying HA significantly improved the chemical quality and reduced the leaf midrib proportion. At the N rate of 60 kg N ha−1, HA showed the best effect of improving quality and increasing income. Our results demonstrated that the addition of HA can significantly improve the economic value and the chemical and processing quality of tobacco. The best effect can be achieved by adjusting the N rate appropriately according to the amount of soil residual N before transplanting tobacco seedlings.