Effects of row spacing, seeding rate and seed-placed phosphorus on root diseases of spring wheat and barley under zero tillage.
The effects of row spacing (10, 20, 30 cm), sowing rate (54, 108, 161 kg/ha for barley; 67, 134, 202 kg/ha for spring wheat) and seed-placed phosphorus (0, 8, 16 kg/ha) on root diseases in spring wheat and barley were studied using a zero-tillage production system at Indian Head, Saskatchewan (heavy clay) and Rapid City, Manitoba (clay loam) in 1993 and 1994. Root rot severity was assessed by visual ratings and the causal agents were identified. Analyses of variance indicated significant differences in root rot severity and the incidence of some causal agents for the main treatment effects (i.e. row spacing, sowing rate, seed-placed P) and no significant interactions between locations, years, and cultural practices. Contrasts of treatment means showed that higher rates of sowing decreased root rot severity and the incidence of Fusarium (F. culmorum, F. graminearum [Gibberella zeae] and F. avenaceum [G. avenacea) in wheat but these effects were small (<6%). The higher rates of monoammonium phosphate fertilizer reduced root rot severity in barley by 7% and the incidence of Gaeumannomyces graminis var. tritici in wheat by >40%. Wider row spacings showed a small reduction of 6% in root rot severity in wheat but mostly had no effect on root diseases. Wheat yields were negatively associated with root rot severity in three of four environments. Fertility, root rot severity, and sowing rate had the greatest impact on wheat yield. Root diseases did not affect barley yields. It is concluded that the use of wider row spacings and higher sowing rates with zero tillage practices will not lead to adverse effects on root diseases in wheat and barley. P fertilizer use was recommended to reduce losses resulting from take-all diseases in wheat.