چكيده لاتين :
Introduction
In general, canola is a salt sensitive crop especially at germination and seedling establishment stages. Hence, saline soil or saline water can affect canola yield potential through salt stress induction (Francois 1994; Hashemi et al. 2010). Soil and water salinity are two of the major problems of agriculture in the arid and semi-arid regions of the world, especially in Iran (Ashraf and McNeilly 2004; Rameeh et al. 2004). On the other hand, reasonable canola production depends on nutrient supply and any increase in quantitative and qualitative yields is highly correlated with the availability of nutrients, especially nitrogen and Zinc (Chamorro et al. 2002; Bahmanyar and Kazemi Poshtmasari 2010).
Since Zn deficiency is one of the most widespread micronutrient deficiencies in Iran as a result of calcareous soil, it is important to apply zinc fertilizers to increase crop yield and improve crop quality in such conditions (Hacisalihoglu and Kochian 2003; Khoshgoftar et al. 2006). On the other hand, N and Zn fertilization differ from normal to saline soils. Therefore, the objective of this study was to investigate the effects of different rates of N and Zn on quantitative and qualitative traits of canola irrigated with saline and ultra saline water.
Materials and methods
In order to investigate the effects of nitrogen and zinc levels and water salinity on yield quality characteristics and nutrient uptake in canola (Brassica napus L. cv. Okapi), a field experiment was conducted in the Agriculture Research Center of East Azerbaijan, Iran from 2009 to 2010. The experiment was arranged by using a completely randomized block design based on factorial fashion with three replications. The experimental treatments included different nitrogen levels (0, 50 and 100 kg. ha-1), different zinc levels (0, 5 and 10 kg. ha-1) and different irrigation salinity levels (8 and 16 dS.m-1), respectively.
Each plot was 8 m long and consisted of six rows, 0.5 m apart. Between the blocks and the plots, a 1 m wide alley was kept to eliminate all influences of the treatments on each other. Full amounts of potassium and phosphorus fertilizers and one third of the N fertilizer were applied at seed sowing time. The rest of the N fertilizers were used at the rosette and flowering stages.
At the physiological maturity stage, seed yield and yield components in each plot were estimated by harvesting 8 plants at random. The oil percentage and glucosinolate content were measured using succulent and HPLC methods, respectively. In addition, N, phosphorous, potassium, calcium, magnesium, sodium and chlorine were measured in the canola seeds.
The results were subjected to statistical analysis using the SAS software. The analysis of variance (ANOVA) was carried out as a combined analysis. Mean values were compared by using Duncan’s multiple range test.
Results and discussion
Based on the results, nitrogen and zinc applications showed a significant influence on increasing plant height, number of pods per plant and seed yield of canola. However, such traits of canola decreased as a result of increasing water salinity levels (from 8 to 16 dS.m-1). Irrigation salinity at rate of 16 dS.m-1 showed a significant effect on increasing glucosinolate percentage in seeds up to 9.5% (from 27.49% to 30.11%).
Glucosinolate which is a toxic organic component is considered as an undesirable qualitative trait in canola seeds (Francois, 1994; Kim et al., 2002; Bybordi & Malakouti, 2003), although the mechanism by which salinity affects glucosinolate content is not clearly known. It seems that water or temperature stresses during crop growth cause glucosinolate accumulation in seeds and consequently affect meal quality. Soil or water salinity is not an exception and can decrease oil or meal quality during the process.
Increasing salinity levels caused a decrease in N, P, K and Ca uptake and caused a significant enhancement of Na and Cl accumulation in the seeds. Totally, it seems that nutrient supply, especially nitrogen, can be considered as an effective approach to diminish the negative effects of salinity stress.
References
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