ارتباط عناصر کم‌مصرف با برخی خصوصیات خاک و لندفرم در اراضی آهکی دشت گلپایگان

خاک مهم‌ترین منبع تغذیه گیاه است و هر گونه کمبود یا بیش بود عناصر غذایی در خاک، رشد گیاه را محدود خواهد کرد. بنا بر این درک عوامل موثر بر توزیع عناصر غذایی، برای مدیریت خاک و کاربرد صحیح کودها ضروری است. به منظور بررسی و تعیین فراهمی آهن، منگنز، روی و مس در 98 نمونه از خاک‌های آهکی دشت گلپایگان و ارتباط آن با ویژگیهای اصلی خاک و لندفرم این پژوهش انجام شد. بر اساس نتایج دامنه تغییرات میزان عناصر آهن، منگنز، روی و مس قابل عصاره گیری با dtpa به ترتیب 46/6 04/1، 82/19 82/1، 24/2 – 02/0 و 38/2 16/0 میلیگرم در کیلوگرم بود. کمبود آهن بیشترین گسترش را در منطقه مطالعاتی داشت. سمیت عناصر در هیچیک از نمونه ها مشاهده نگردید. همبستگی معنی داری بین میزان قابل جذب عناصر و برخی ویژگی‌های اندازه گیری شده خاک از قبیل بافت، میزان مواد آلی و آهک وجود داشت. آهکی بودن خاک‌ها و پائین بودن ماده آلی از مهم‌ترین عوامل موثر بر کمبود عناصر کم مصرف در منطقه است. بین مقدار قابل جذب آهن و منگنز و مس همبستگی مثبت مشاهده شد که می تواند به دلیل منشا زمین شناسی یکسان این عناصر در خاک‌ها باشد. به رغم شباهت مواد مادری روند متفاوت فرایندهای خاکساز و هوازدگی بر میزان، گسترش و فراهم بودن عناصر کم مصرف تاثیر گذار بوده و واحدهای مختلف اراضی از نظر برخی عناصر تفاوت معنی دار نشان دادند. بیشترین مقدار عناصر ریز مغذی به جز در مورد منگنز در خاک‌های torrifluvents وجود داشت. کمترین میزان روی و مس به ترتیب در واحدهای اراضی فلات و واریزه های بادبزنی مشاهده و تفاوت آن با دشت‌های سیلابی و دامنه ای (entisols) معنی دار گردید. می توان گفت درجه متفاوت تکامل خاک از طریق تاثیر بر ویژگی‌های خاک چرخه عناصر ریزمغذی را تحت تاثیر قرار می دهد.

Micronutrient Availability in Relation to Selected Soil Properties and landscape Position in Calcareous Soils of Golpayegan

Introduction: Variety of soil reactions govern the distribution of metal micronutrients that includes complexation with organic and inorganic ligands, ion exchange, adsorption and desorption processes, precipitation and dissolution of solids and acidbased equilibria. The relative importance of these reactions depends on many factors such as soil physical, chemical, and mineralogical properties and the nature of metal ions. Environmental factors such as climate, physiographic position, and soil development may affect variability of some soil properties and thereby nutrient availability. The present research was conducted to find relationships between Iron, manganese, zinc, and copper availability and some major soil properties, physiographic condition and soil development. Materials and Methods: Golpayegan region is located in northwest of Isfahan province in central Iran. The mean elevation of the studied area is 1790 above sea level. Annual precipitation was about 244mm and mean monthly temperature ranges from 6 in January to 34°C in August. The soils were developed on different physiographic conditions including piedmont plains, alluvialfan, plateaus, and flood plains belonging to Entisols and Aridisols. Soil samples (0–60 cm) were collected from 98 grid points with 2000m distance in the agricultural area of Golpayegan. Particle size distribution, calcium carbonate, organic carbon, available potassium and phosphorus of the soils were measured by SWRI standard methods. Available Zn, Cu, Mn, and Fe were determined by addition of 10 g soil to 20mL 0.005M diethylentriaminepentacetic‏. The solutions were shaken for 2 h at 25°C, centrifuged, filtered, and Fe, Mn, Zn, and Cu concentrations were measured by an atomic absorption spectrophotometer. Results Discussion: Studied soils were developed on calcareous material and about 60% of samples have more than 20% of calcium carbonate. Available Fe ranged from 1.4 to 6.5 mg kg1 (mean 15.8 mg kg1). Significant relationships were also found between DTPAextractable Fe, organic matter (OM) and calcium carbonate. The results indicated that organic matter (OM) is the most influential soil characteristics that predict Fe availability. DTPAextractable Mn in the soils ranged from 1.8 to 19.8 mg kg1 (mean 7 mg kg1). There were also no relationship between available Mn and soil properties. It has been reported that Mn availability in soils is mainly influenced by oxidationreduction rather than other factors. Available Zn in the studied soils ranged from 0 to 2.4 mg kg1 (mean 0.8 mg kg1) and had significant correlations with particle size and OM contents. This result showed the importance of soil exchanger phase (clay and OM) in Zn availability in calcareous soils, and was in agreement with the findings of Wu et al. (2006) in soils of North Dakota. DTPAextractable Cu ranged from 0.2 to 2.4 mg kg1 (mean 0.9 mg kg1). According to the report of Lindsay and Norvell (1978), 90% of soils had sufficient Cu. However, there were variations among soils in available Cu as a function of physiographic position. The highest values were found in the soils developed on piedmont plains. Significant relationships between available Cu and some major soils properties such as sand, clay, OM, and calcium carbonate were also found. This result was in agreement with findings of Wu et al. (2010) who concluded that soil properties influencing the spatial distribution of Cu availability. Conclusions: Nutrient availability is one of the most critical concerns of plant production in calcareous soils of Golpayegan . Different pedogenic processes, variable deposition and transport, and different weathering regimes affect micronutrient content, distribution, and availability. Results indicated that Fe deficiencies followed by Mn and Zn in the studied soils are more critical than Cu deficiencies. In fact, 90% of soils had sufficient Cu. Mainly micronutrient availability in the studied soils was related to soil texture and organic matter, although Mn availability showed no relationships with major soil properties. It was concluded that the availability of Fe, Zn, and Cu may be predicted to some extent using some factors such as soil properties and physiographic condition. Availability of Fe, Zn, and Cu in Torrifluvents developed on piedmont plain was higher than in other soils and this may be due to the high amounts of OM and clay, whereas Haplocalcids developed on plateaus had the lowest content. Generally, it was concluded that the mentioned factors affect metal distribution and cycling in the soils and thereby metal availability for plants. On the other hand, prediction of micronutrient availability using these factors can be taken into consideration for better management.