EFFECTS OF ROW SPACING, SEEDING RATE AND SEED-PLACED PHOSPHORUS ON ROOT DISEASES OF SPRING WHEAT AND BARLEY UNDER ZERO-TILLAGE

Changes in tillage and other agronomic practices have shown benefits o f increased grain yield for many crops, but these changes may alter th e micro-environment resulting in changes to populations of disease-cau sing agents and other micro-organisms. This study examined the effects of row spacing (10, 20, 30 cm), seeding rate (54, 108, 161 kg ha(-1) for barley; 67, 134, 202 kg ha(-1) for spring wheat) and seed-placed p hosphorus (0, 8, 16 kg ha(-1)) on root diseases in spring wheat and ba rley using a zero-tillage production system in four environments. Root rot severity was assessed by visual ratings and the causal agents wer e identified. Analyses of variance indicated significant differences i n root rot severity and the incidence of some causal agents for the ma in treatment effects (i.e. row spacing, seeding rate, seed-placed phos phorus) and no significant interactions between locations, years, and cultural practices. Contrasts of treatment means showed that higher ra tes of seeding decreased root rot severity and the incidence of Fusari um in wheat but these effects were small (less than 6%). The higher ra tes of monoammonium phosphate fertilizer reduced root rot severity in barley by 7% and the incidence of Gaeumannomyces graminis var. tritici in wheat by greater than 40%. Wider row spacings showed a small reduc tion of 6% in root rot severity in wheat but mostly had no effect on r oot diseases. Wheat yields were negatively associated with root rot se verity in three of four environments. Fertility, root rot severity, an d seeding rate had the greatest impact on wheat yield. Root diseases d id not affect barley yields. Therefore, the use of wider row spacings and higher seeding rates with zero tillage practices will not lead to adverse effects on root diseases in wheat and barley. Phosphorus ferti lizer should be used to reduce losses resulting from take-all disease in wheat.