Investigating the agronomic traits of winter canola in seeding and transplanting systems with different plant densities under delayed cultivation conditions

Oilseed rape (Brassica napus L.) is a traditional oil crop in Iran. Conventional oilseed rape production during the past decades has been performed through manual sowing, transplanting, and harvesting. In cold and temperate regions of the Iran in the Karaj region, due to delays in harvesting the previous crop such as corn, canola planting date is delay and it is not possible to planting oilseed rape seeds directly. Problems such as supplying primary soil water for crop establishment of canola fields, possibility of damage from cold and frost stress and late season drought due to delayed planting are the main problems of canola cultivation in Karaj region (Jabbari et al., 2022). Because of this, canola transplanting can solve the problems and be a good choice in these kinds of situations (Zeinalzadeh-Tabrizi et al., 2022). Although there have been many seeding rate studies done for canola, the optimum seeding rate and plant population for canola is not known. Optimum density for canola depends on both biological and economic factors. verall economic optimum plant density for canola was 30 to 40 plants m-2 (French et al., 2016). On the other hand, the transplanting method (bare-root or potted-root transplant), transplanting density and the number of seedlings per hole one seedling or two seedlings are very important to achieve the highest seed yield.

In order to agronomic evaluation of winter canola in seeding and transplanting systems with different plant densities under delayed cultivation conditions in the Karaj region, an experiment was conducted as a randomized complete block design with three replications in two cropping years, 2019-2020 and 2020-2021. Experimental treatments included direct sowing of seeds as a control at a rate of 6 kg/ha; transplanting with densities of 20, 30, and 40 plants per square meter, each density with both bare-root transplant and potted-root transplant; and also with one seedling or two seedlings in the planting hole. During the experiment, traits including Days to flowering time, flowering duration, growth period, plant height, stem diameter, branch number, silique length and diameter, silique per plant, seed number per silique, 1000-seed weight and seed yield were recorded. Combined analysis of variance carried out by SAS statistical analysis software and the least significant difference (LSD) test was used to compare treatment means with a probability threshold of 0.05.

The results of combined analysis showed that seed yield in the treatments of potted-root and bare-root seedling was between 686 and 1142 kg.ha-1 more than seeding cultivation. Yield reduction in seeding cultivation was due to the reduction of yield components, especially the number of silique per plant. Also, among all the investigated treatments, the highest seed yield (4395 kg.ha-1) was observed in the treatment of bare-root seedlings with a density of 40 plants with one seedling in the hole, which this issue was related to the relatively long flowering duration, noticeable superiority for silique per plant and high 1000 seeds weight. An independent comparison of bare-root and potted-root transplant treatments showed that in the total of two experimental years, bare-root treatments caused a significant decrease of 7.3% in days to beginning of flowering and 13.3% increase in the length of the flowering period, 7.2% in plant height, 42.7% in siliques per plant and 17.1% in the seed yield. Early maturity and higher of siliques number and number of seeds in siliques led to the superiority of seed yield in the bare-root treatment compared to the potted-root treatment. Mentioned issue was related to more competition between seedlings in the pot at the the potted-root treatment and the greater use of soil space for root development and less competition between seedlings in bare-root treatment.

Generally, results showed that bare-root transplant treatments were superior to potted-root transplant treatments for yield components and seed yield. Therefore, in the conditions of delayed cultivation of canola, it is recommended to bare-root transplanting with a density of 40 plants per square meter and one seedling in the planting hole, especially in the Karaj region.