Long-Term (35 years) No-till System Caused a Major Shift in Weed Community Structure in a Continuous Sorghum Cropping System.

The impact of long-term tillage practices on weed population dynamics was studied in two different tillage systems [no-till (NT) and conventional till (CT)] in a 35-year old continuous sorghum experiment. Further, soil physiochemical properties were also documented to understand the impact of these factors on weed communities. Preliminary results have revealed that the NT system had greater water holding capacity (11% greater), bulk density (1.39 g cm^-3) and soil porosity (52%) compared to CT. Soil organic carbon, organic matter and carbon mineralization were also greater in the NT system compared to CT (0.45%, 0.73% and 50 g kg^-1 of soil greater, respectively at 0-5 cm). Weed community composition was drastically different between the two systems. The NT system had greater weed diversity (Shannon-Weiner index) and dominance (Simpson index). However, species evenness (Shannon-Weiner index) was greater in the CT system. Moreover, only 59% of the weed species were common between the two production systems (Steinhaus index) though the plots were in close proximity, indicating a significant weed species shift when adopting continuous NT system. About 60% of the species in NT system were small-seeded annuals, compared to only about 25% in CT. Further, the NT system had greater densities of Johnsongrass (Sorghum halepense) (21 seedlings m^-2 greater than that of CT), which is the predominant perennial species found in the plots. This might be due to the absence of soil inversion in the NT system which would otherwise deplete underground rhizomes. Results indicate that a shift to conservation tillage practices will require a significant change in weed management considerations.