The Effect of Withholding Irrigation and Foliar Application of Zn and Mn on Yield and Eco-physiological Characteristics of Rapeseed (Brassica napus L.)

Development of new canola (Brassica napus L.) varieties need effective tools to monitor characterizes association in yield and its components. Although, determination of the response of oil seeds cultivars to environmental variables is one of the principal of agriculture planning to achieve maximum qualitative and quantitative yield. Water deficit stress and sufficient nutrition are the most important factors limiting yield production by changing the physiological processes of the plant. Iran is considered as the arid and semi-arid with average rainfall of 250 mm. On the other hand, 33% of agriculture land is devoted to dry cultivation. Water deficit by affecting on vegetative and reproductive growth period and balance between them will change yield and product quality.

In order to study the responses of three winter canola cultivars to late season drought stress and foliar application of Mn and Zinc sulfate fertilizer on physiological, morphology characteristics and yield, a split factorial experiment was carried out based on randomized complete block design with three replications in 2017-2018 at the Karaj province. Irrigation in two levels, normal and water holding at flowering stage to next, foliar application in four levels, sprayed with water (control), foliar application with zinc sulfate, foliar application with Mn sulfate, foliar application composition with zinc sulfate and Mn sulfate (each of them was with concentration of four per thousand) both in main plot and three cultivars included Nima (control) and two new lines KS7 and R15 in sob plot. Foliar application was applied during the stem elongation stage. When the 50% of pod appeared total chlorophyll and leaves carbohydrate solution content was measured as index of drought stress damage. Eight traits were measured on 10 random plants per plot. The traits were plant height, number of pods /plant, number of seeds/pod, 1000 seed weight, seed yield, biomass yield, oil percentage and oil yield.

The results showed all characteristics significantly were influenced by water holding and foliar application. Interaction of water holding and foliar application was significant in attributes of plant height and oil content. Main effect of cultivar and interaction of water holding and cultivar were significant in all treatment except oil content. Due to water holding increasing in soluble carbohydrates and reducing the concentration of chlorophyll was occurred. The yield components of canola because of irrigation disruption decreased which leads to lower grain and rapeseed oil yield. The results showed that in normal irrigation, the highest seed yield (5168 kg.ha-1) oil yield (2244 kg.ha-1) and water use efficiency (0.99 %) were related to R15 line but in water holding condition the Nima cultivar obtained the highest achievements. In complete irrigation, foliar application of the two micro elements increased the traits studied. Most of the seed oil yield (1728 kg.ha-1), the weight of one thousand seeds (3.21 g), biological yield (15675 kg.ha-1) and water use efficiency were related to the main effect of zinc sulfate and Mn sulfate combination. Spraying plants with zinc sulfate and Mn sulfate improved plant height and increased oil content in drought stress condition in relation to spray by water (control). Among cultivars, Nima cv. had better outperformed relative to KS7 and R15 in normal irrigation. In water holding treatment, two cultivars R15 and Nima narrowly to each other had better outperformed relative to KS7. Non significant interaction effects of foliar application and cultivars for seed and oil yield indicated that all cultivars had similar trend. Drought not only causes dramatic loss of pigments but also leads to disorganization of thylakoid membrane, therefore reduction in chlorophyll contents is expected. The water holding condition in late season may influence plant growth that can be attributed to the lose yield components.

Correlation between drought situation and yield components in all cultivars, identify the most suitable indicators for monitoring drought tolerance cultivars. According to these results, R15 can be recommended for semiarid regions due to maximum seed and oil yield among and non stress condition. In water deficit condition R15 can be recommended for semiarid regions due to maximum seed and oil yield among and non stress condition.