Effect of Zeolite, Selenium and Silicon on Yield, Yield Components and Some Physiological Traits of Canola under Salt Stress Conditions

Canola can be cultivated in large areas of the country due to its specific characteristics such as suitable composition of the fatty acids, its germination ability under low temperature, as well as its good compatibility with different climates. Canola is a high demanding crop in terms of fertilizers so that it uptakes considerable amount of nutrients from the soil during the growing season. Canola cultivation in poor soils or application of imbalanced fertilizers, especially nitrogen, can reduce qualitaty and quantity of final yield. On the other hand, salinity is known as one of the major limiting factors in canola production. Therefore, the aim of this study is the application of zeolite, selenium and silicon treatments to amend soil and increasing salinity tolerance in canola.
In order to study the effect of soil applied zeolite and foliar application of selenium and silicon on yield, yield components and some physiological traits of canola grown under salinity stress, a factorial experiment in randomized complete block design was conducted in Agriculture and Natural Resource Research Center in East Azerbaijan during 2011-2013 cropping seasons. Zeolite was applied at three levels (0, 5 and 10 ton ha-1) and foliar selenium and silicon were applied at three levels as well (each one zero, 2 and 4 g l-1). For this purpose, seedbed was prepared using plow and disk and then plot were designed. Canola seeds, cultivar Okapi, were sown in sandy loam soil with 4 dS.m-1 salinity at the depth of 2-3 cm. Irrigation was performed using local well based on 60% field capacity using the closed irrigation system. Potassium selentae and potassium silicate were used for selenium and silicon treatments. Treatments at rosette and stem elongation stages were sprayed on plants using a calibrated pressurized backpack sprayer. At flowering stage, photosynthesis rate was recorded. Then leaf samples were randomly collected to assay chlorophyll, relative water content, catalase, peroxidase and superoxide dismutase activity, as well as malondialdehyde, sodium and potassium content in the leaves. The samples were immediately frozen in liquid nitrogen and kept in -80° C freezer. At the end of the growing season, agronomic traits such as silique number, seed number on silique, 1000- grain weight, grain yield, biological yield and harvest index were recorded. Total oil percentage and fatty acids (oleic, linolenic and linoleic) percentage were measured.
The combined analysis of variance indicated that the effect of year was significant on all studied traits, except for silique number, grain number in silique, linoleic acid, chlorophyll content and peroxidase activity. In addition, the results showed that the main effect of zeolite, selenium and silicon were significant on all canola studied traits. However, relative water content and peroxidase activity were not affected by silicon application. Comparison of means indicated that triple interaction was significant at 1000- grain weight, grain yield, biological yield, chlorophyll content, photosynthesis rate, relative water content and antioxidant enzyme activity. Some traits such as 1000- grain weight, grain yield, biological yield, harvest index, oil percentage, linolenic percentage and superoxide dismutase activity as well as sodium content in leaves were found to be higher in the second year compared with the first year. Zeolite significantly increased silique number and grain number in silique. Furthermore, harvest index increased with the increase of zeolite level. According to the results, selenium increased silique number, grain number in silique and harvest index in canola plants. Silicon foliar application also significantly increased silique number, grain number in silique and harvest index. The highest chlorophyll contents, photosynthesis rate and relative water content were registered when zeolite was applied at 10% w: w and silicon and selenium were applied at 4 g per litter. Similarly, the highest peroxidase and superoxide dismutase activity was observed in this treatment. Finally, the highest grain yield (3009.92 kg ha-1) and biological yield (108778 kg ha-1) were obtained when 10% w: w zeolite was applied along with 4 g per liter selenium and 4 g per liter silicon In general, we concluded that application of zeolite, selenium and silicon could reduce adverse effects of salt stress and improve canola tolerance against salinity stress.
Among the applied treatments 10% w: w zeolite along with 4 g per liter selenium and 4 g per l liter silicon caused the best results in terms of canola grain yield.