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 N fertilizer in vegetable growing season leads to the high amount of soil residual N and the decrease of resistance to tobacco disease in 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 two years to evaluate the effects of additional applying HA (0, 150 L ha⁻¹) combining 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. Application of HA decreased the disease severity and increased the microelement uptake and the daily leaf growth rate in prosperous growing stage which positive 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 addition of humic acid can significantly improve the economic value, the chemical and processing quality of tobacco. The best effect can be achieved by adjusting N rate appropriately according to the amount of soil residual N before transplanting of tobacco seedling.

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