بررسی اثر کود سوپرفسفات تریپل و شوری آب آبیاری بر تحرک و جذب کادمیم خاک

تحرک کادمیم در خاک تحت تاثیر عوامل مختلفی است و جذب آن توسط توتون بیشتر از سایر گیاهان زراعی است. این آزمایش با هدف بررسی برهمکنش سه عامل شوری آب آبیاری (صفر، 20 و 40 میلی‌مولار nacl)، کود سوپر فسفات تریپل (صفر و 1/5 گرم بر کیلوگرم خاک) و آلودگی کادمیم خاک ( صفر و 12 میلی‌گرم بر کیلوگرم خاک) به صورت فاکتوریل در قالب طرح کاملا تصادفی با چهار تکرار بر غلظت کادمیم بخش هوایی، غلظت کادمیم دود توتون، درصد استخراج dtpa، غلظت کادمیم خاکستر توتون، فاکتور تحرک کادمیم و درصد توزیع شکل‌های شیمیایی کادمیم خاک، انجام شد. نتایج نشان داد که فاکتور تحرک کادمیم در خاک آلوده شده به کادمیم نسبت به خاک غیر آلوده در شوری صفر، 20 و 40 میلی‌مولار به طور میانگین و به‌ترتیب 25/6، 32/4 و 36/2 درصد افزایش نشان داد. کاربرد کود فسفاته، سبب کاهش معنی‌دار فاکتور تحرک کادمیم در خاک های غیر آلوده به کادمیم شد. در خاک‌های آلوده به کادمیم، درصد استخراج dtpa با افزایش سطوح شوری آب آبیاری از صفر به 20 و 40 میلی‌مولار به‌ترتیب به مقدار 5/26 و 4/56 درصد افزایش نشان داد. در خاک‌های غیر آلوده به کادمیم، کاربرد کود سوپر فسفات تریپل در شوری‌های صفر، 20 و 40 میلی‌مولار آب آبیاری به‌ترتیب سبب کاهش درصد استخراج dtpa به میزان 20/2، 28/4 و 24/6 درصد نسبت به عدم کاربرد کود شد. با افزایش سطوح آلودگی کادمیم خاک، درصد غلظت کادمیم بخش‌های اکسیدی خاک کاهش و درصد غلظت کادمیم بخش کربناتی، آلی و باقی‌مانده افزایش نشان داد. کاربرد کود فسفاته سبب افزایش غلظت کادمیم باقی مانده خاک شد. با افزایش سطوح آلودگی کادمیم خاک، درصد کادمیم بخش کربناتی و ماده آلی خاک نسبت به خاک غیر آلوده به کادمیم افزایش معنی‌داری نشان داد. نتایج هم چنین نشان داد که کاربرد کود سوپرفسفات تریپل در خاک آلوده به کادمیم و در شوری صفر، 20 و 40 میلی‌مولار به‌ترتیب سبب افزایش غلظت کادمیم خاکستر توتون به مقدار 1/47، 15/89 و 29/80 درصد و غلظت کادمیم دود توتون به میزان 23/2، 23/3 و 18 درصد گردید. عامل شوری و کود فسفاته روند معکوسی بر کادمیم بخش محلول+تبادلی و کادمیم فراهم با dtpa خاک داشتند به طوری‌که با افزایش شوری، این غلظت‌ها افزایش و با افزایش کود سوپر فسفات تریپل، کاهش نشان داد.

Assessment of Triple Super Phosphate Fertilizer and Irrigation Salinity Effects on Soil Cadmium Mobility and Absorption

IntroductionCadmium (Cd) mobility in soil is affected by various factors and its absorption from soil by tobacco is higher than other crops. Application of phosphate fertilizers in agricultural lands is an essential step to increase the yield of tobacco plants. Since most phosphate fertilizers contain small amounts of Cd, the uptake of Cd by tobacco plant in its cultivated areas due to the application of triple superphosphate fertilizer (TSP) is not unexpected. In many tobacco growing areas, the water or soil used is between low and medium salinity in terms of salinity, which can also influence the solubility of cadmium and, consequently, its uptake by tobacco plant. Cadmium can be absorbed through food, drink and respiration. This metal not only is absorbed by the digestive organs, but also is absorbed by the respiratory organs through airborne particles and cigarette smoke. Tobacco is resistant to high concentrations of Cd in soil and can absorb it from Cdcontaminated soil. The aim of this study is to investigate the effect of P fertilizer and salinity on Cd mobility in soil and tobacco plant.Materials and MethodsThis experiment was conducted with the aim of investigating the interaction of three factors of irrigation salinity (0, 20 and 40 mM NaCl), triple tuper phosphate fertilizer (TSP) (0 and 1.5 g kg1 soil) and soil Cd contamination level (0 and 12 mg kg1 soil) in a completely randomized design with four replications on shoot Cd concentration, smoke Cd concentration, extraction percentage of DTPA, tobacco ash Cd concentration, Cd mobility factor and Cd fractions in soil. To homogenize the samples, they were thoroughly mixed together and the resulting composite samples were passed through a 2 mm sieve to incubate the samples and then implant. Cadmium contamination levels (0 and 12 mg kg1) were prepared from Cd(NO3)2.4H2O source. Prior to planting, the relevant levels of contamination were added by spraying on the entire soil surface and mixed thoroughly. Soil samples were transferred to plastic storage containers and incubated for four months in a controlled greenhouse within a temperature range of 2530 °C and 70% water holding capacity of the soil measured by the weighing method. Cultivation was carried out under controlled conditions in a greenhouse environment located in Bardaskan city. Two 60dayold tobacco seedlings (Nicotiana tabacum L.) of Cocker 347 cultivar, which were previously seeded in noncontaminated cadmium soil and grown with nonsaline water, were transferred to each pot and planted. The cultivar used in this experiment was a greenhouse tobacco cultivar used in the cigarette industry. Immediately after transferring the seedlings to pots, irrigation was performed with salinefree water (distilled water), salinity of 20 or 40 mM NaCl salt for 75 days according to the required treatment. Up to the fourth week, the amount of 400 ml per pot in each irrigation cycle, and after that until the end of the experiment, the amount of 800 ml per pot in each irrigation cycle was applied.  Results and DiscussionThe results showed that Cd mobility factor in Cdcontaminated soil increased on average by 25.6%, 32.4% and 36.2% compared to noncontaminated soil at 0, 20 and 40 mM salinity, respectively. Application of phosphate fertilizer significantly reduced the mobility factor of cadmium in noncadmiumcontaminated soils. In Cdcontaminated soil, the extraction percentage of DTPA increased 26.5% and 56.4% with increasing irrigation salinity levels from 020 and 040, respectively. In nonCd contaminated soil, TSP application reduced extraction percentage of DTPA 20.2%, 28.4% and 24.6% in 0, 20 and 40 irrigation salinity levels, respectively in compared to nonTSP application. With increasing the levels of soil Cd contamination, the percentage Cd concentration in oxide fraction of soil decreased and the percentage of Cd concentration in carbonate, organic and residual fractions increased. Application of TSP increased the concentration of residual Cd fraction in the soil.ConclusionWith increasing the level of Cd contamination in soil, the percentage of Cd in carbonate and organic fractions increased compared to nonCd contaminated soil. The results showed that TSP application in Cd contaminated soil in salinitylevels of 0, 20, and 40 mM increased Cd concentration of tobacco ash by 1.47%, 15.89% and 29.80% and increased Cd concentration of tobacco smoke by 23.20%, 23.30% and 18%, respectively. Salinity factor and phosphate fertilizer showed the reverse effect on soluble + exchangeable cadmium and DTPA available Cd in soil, so with increasing salinity, these concentrations increased and with increasing triple superphosphate fertilizer decreased.