Soil Structural Properties under Four Different Cultivars of Switchgrass.

This study was conducted to assess the impact of switchgrass on soil structural properties. Analysis of seasonal changes in structural properties was done under four switchgrass cultivars (i.e., Alamo, GA-992, GA-993, and SL-93-2) in Milan, TN. Soil bulk density and total porosity did not differ among cultivars, but bulk density of the 0-5 cm depth was significantly lower than that of 5-10 and 10-15 cm depths in spring and fall. Root densities also did not differ among cultivars but were three times higher in surface soils (19.3 and 13.1 mg/cm³ in April and October, respectively) than in sub-surface soils (6.9 and 5.0 mg/cm³ in April and October, respectively). The ratio of mean weight diameter (MWD) for post:pre wet-sieving (post:pre MWD) was significantly higher in July (0.61) compared with April (0.52) and October (0.54) among months, and also significantly decreased with depth (i.e., 0.83 in 0-5 cm, 0.58 in 5-10 cm 0.26 in 10-15 cm). Although there was no significant difference among cultivars, post:pre sieving ratio of MWD of SL-93-2 was the highest (0.58). The log-transformed tensile strength (TS) of wet-sieved aggregates was the highest in 1.0-2.0 mm aggregate size (log TS = 2.51 kPa) among three aggregate size fractions (4.75-8.0, 2.0-4.75, 1.0-2.0 mm), in 0-5 cm in depth (log TS = 2.21 kPa) among three different depths (0-5, 5-10, 10-15 cm), and in July (log TS = 2.24 kPa) among three months (Apr, July, Oct). The log TS of wet-sieved aggregates in GA-993 and SL-93-2 (2.14 and 2.12 kPa, respectively) were higher than in GA-992 (2.06 kPa). Pore size distribution with intact core samples were measured in October. There was a general trend of a higher ratio of pores which were bigger than 4 μm in diameter. under same soil volume, and was higher in GA-993 (9.5%) and SL-93-2 (9.0%) than other cultivars.