Correlation of soil nutrients with total and reducing sugars of flue-cured tobacco in southwestern Guizhou, China

Objectives High reducing sugar (RS) and total sugar (TS) contents are two important factors that reduce the quality of tobacco leaves in southeastern Guizhou. Here, we studied the contribution of soil nutrient contents to the accumulation of total and reducing sugars in tobacco leaves to provide a theoretical base for improving tobacco quality through fertilization.

Methods Soil and tobacco leaf samples were collected from tobacco fields in Qinglong, Puan, Xingren, Xingyi, Zhenfeng, and Anlong of Guizhou Province to measure soil available nutrient and the total and reducing sugar contents in tobacco leaves. Stepwise regression and path analysis were used to estimate the relationship between soil available nutrients and sugar contents in tobacco leaves.

Results The total and reducing sugar contents of tobacco leaves were 18%–24% and 16%–22%. The pH of the tobacco-growing soils ranged from neutral to weakly alkaline, the soil organic matter, available N, Ca, Mg, Fe, and Mn were abundant, the K, P, Cu, Zn, B, and Mo were adequate, despite uneven spatial distribution. Soil nutrients (P < 0.05) correlated with the contents of TS and RS in tobacco leaves. The leaf TS was negatively correlated with soil K, Zn, and B, and positively correlated with Mo. There was a (P<0.05) negative correlation between RS and soil K, Zn, B. The regression equations of TS and RS with soil available nutrients were TS=31.69−1.78Zn+17.05Mo+1.09Cu+0.003Mg−0.01AK, and RS=25.12−0.01AK+1.39Cu+6.91Mo. Soil K, Cu, and Mo were important indexes affecting reducing sugars in tobacco leaves. Path analysis also showed that soil nutrients indirectly affect tobacco sugar contents positively (promoting) or negatively (restricting).

Conclusions The soil nutrients with higher contribution to the sugar content of tobacco in southwest Guizhou are soil available K, Mg, Cu, Zn, and Mo. High soil available K and Zn contents would inhibit total and reducing sugars accumulation in tobacco leaves after curing. Conversely, available Mg, Cu and Mo have the potential to increase total and reducing sugars in tobacco leaves.