enhanced irrigated canola seedling emergence with longitudinal cracks along seed rows from a furrow opener and press wheel

poor stand establishment of canola (brassica napus l.) under flatland mechanized planting and crust-forming soil is a major problem for farmers in central iran. previous research there showed that irrigated cotton emergence on crust-forming soils under flatland planting can be significantly improved using a double-disk planter with zero-pressure press wheel tires and no crust-breaking. in that research, it was not clear whether the furrow opener or the press wheel caused the development of the crack line along the seed rows. in the present study, field testing was conducted in loamy soil to study the effects of two furrow openers (runner, double-disk) and four press wheels (zero-pressure pneumatic, v-shaped edge, single conical rib, open-center concave steel press wheels) on canola emergence using a randomized complete block design in a factorial arrangement (2×4) with four replications. effective crack (crack line developed along emerging seedlings) percentage, stand establishment uniformity, percentage of emergence, and plant density before onset of winter were measured. the results showed that, for all parameters, the double-disk opener had significantly higher values compared with the runner opener. the press wheel had a significant effect on the effective crack percentage and the stand establishment uniformity index before the onset of winter. however, the other parameters were not significantly affected. planters with a single-conical rib and open-center press wheels had the best effective crack percentage and lowest index of stand establishment uniformity. based on the results from this study, the best planter for canola production for the soil and climate of central iran is a double-disk planter with a single conical rib and open-center concave steel press wheels. the single conical rib creates a v-shaped depression and the steel press wheels stabilize the depression. this creates a crack along the deepest line of the depression after flood irrigation and during soil shrinkage, causes creation of crack along the deepest line of depression.