Analysis of yield-formation processes under no-till and conventional tillage for soft red winter wheat in the South-Central Region

Production of winter wheat (Triticum aestivum L.) under no-till (NT) can have economic and edaphic benefits over conventional tillage (CT) systems, although in some years it can result in lower yields. Analysis of yield-formation processes of wheat grown under NT and CT systems may elucidate why yields are sometimes lower under NT. The objective of this study was to determine the effects of tillage systems on yield-formation processes of soft red winter wheat. Two experiments were conducted at two locations in Kentucky using randomized complete block split-plot designs. Main plots in both experiments were two tillage systems (NT and CT). In Exp. 1, which was conducted in 2004, split plots were four cultivars with different heading dates. In Exp. 2, which was conducted in 2005 and 2006, the split and split-split plots were two cultivars and three seeding rates, respectively. Total plant biomass, grain yield, yield components, and harvest index (HI) were measured at maturity. Grain yield was lower under NT than under CT in two of the five location/years. Neither cultivar differences in days to heading nor seeding rates altered the impact of NT on grain yield. The dominant response of soft red winter wheat to NT in this study was to increase tillering and reduce HI. The increased tillering growth habit due to NT could increase internal competition for assimilates, thereby diverting assimilates away from grain production to vegetative growth and reducing HI. The reduction in HI led in some years to a reduction in yield.