Soil fixing ability of flue-cured tobacco roots at different growth stages

Flue-cured tobacco (Nicotiana tabacum) is the main crop in Yunnan Province. The characteristics of soil fixing ability of flue-cured tobacco roots at different growth stages (rosette stage, budding stage and maturity stage) were measured in situ with the anchor-shank tensiometer and self-designed shearing box at soil depths of 0 10 cm and 0 20 cm. The results showed that the order of the root density of flue-cured tobacco for different depths during the same stage were 0 10 cm > 0 20 cm. The order of the root densities of different growth stages for the same depth were maturity stage > budding stage > rosette stage. The soil fixing abilities of flue-cured tobacco roots for the same soil depth were in sequence of maturity stage > budding stage > rosette stage. Then the soil fixing abilities of roots for different soil depths during the budding stage and maturity stage were 0 10 cm > 0 20 cm. The soil fixing abilities of roots during rosette stage of sampled squares was 0 10 cm > 0 20 cm as roots hardly reached 0 20 cm of soil depth. For the same growth stage and soil depth, the load and displacement of sampled soil squares were in significant liner correlation (P < 0.01). With increasing load, three critical load points appeared: tensile proportional limit (F1), tensile yield strength (F2) and tensile strength limit (F3). For the same soil depth, no significant correlation was noted between F1 and the density of flue-cured tobacco roots. However, the correlations between F2 and root density and between F3 and root density were that of power regression. For the of 0 10 cm soil depth, the correlations between F2 and root density and between F3 and root density were as follows: y=1.313x^0.042 and y=1.379x^0.084, respectively. For the 0 20 cm soil depth, the correlation equations for F2 and root density and for F3 and root density were y=1.389x^0.048 and y=1.638x^0.077, respectively. It was proposed that anchor-shank tensiometer and self-designed shearing box were effective in analyzing the characteristics of soil fixing ability of flue-cured tobacco roots at different growth stages.