بخش بندي فيزيكي كربن آلي در خاك هاي شني و رسي تيمار شده با كود جانوري و زئوليت

Physical fractionation of organic carbon in clay and sandy soils treated with zeolite and manure

نگهداشت كربن در خاك از راه افزودن كودهاي جانوري به خاك و كاربرد زئوليت مي تواند افزون بر بهبود ويژگي هاي خاك، به كااهش گازهاي گلخانه اي كمك كند. هدف از اين پژوهش، بررسي پيامدكاربرد زئوليت و كودهاي جانوري بر ريخت هاي كربن آلي خاك بود. دو نمونه خاك شني و رسي از لايه 30 سانيي متري رويين دو زمين كشاورزي در همدان برداشت شد. اين خااك ها در لوله هاي پي وي سي با قطر 20 سانتي مت كه به دو بخش جداگانه برش داده شده بود، ريخته و ذرت كشت شد. هنگامي كه گياه ذرت به گام گلدهي از رشد خود رسيد، از دو جايگاه ريز وسفر ر و ناريزوسفري خاك ها نمونه برداري گرديد و بخش هاي فيزيكي كربن آلي خاك اندازه گيري شد. اين پژوهش نشان داد كه كاربرد زئوليت در خاك شني پيامد چشم گيري بر همه كربن آلي بخش سبك و كربن آلي بخش هم اندازه شن نداشت؛ ولي كربن آلي بخش هم اندازه سيلت و رس را به اندازه چشم گيري افزايش داد. كربن آلي بخش سنگين با افزودن زئوليت افزايش يافت؛ ولي اين افزايش از ديدگاه آماري چشم گير نبود. در خاك رسي، همه كربن آلي خااك،بخش هم اندازه شن، كربن آلي بخش هم اندازه سيلت و رس و كربن آلي بخش سنگين با افزودن زئوليت كاهش چشم گيري يافت ؛ ولي كربن آلي بخش سبك دگرگوني چشم گيري نداشت. افزودن كودهاي جانوري و به ويژه كود گاوي مايه افزايش ماده آلي بخش هاي گوناكون به ويژه بخش سبك در هر دو خاك شني و رسي شد. كربن آلي خاك بويژه بخش سنگين و بخش هم اندازه سيلت و رس در خاك هاي ريز و سفري بيش از ناريز و سفري بود.

Introduction Carbon sequestration by addition of organic manures and zeolite can improve soil properties and reduce greenhouse gases. There are many reports on the suitable effect of zeolite on soil physical, chemical and biological properties. The study of the effects of zeolite application on rice yield, nitrogen recovery and nitrogen use efficiency showed that it was a good treat for infertile soil. The effect of zeolite on soil biological properties was more obvious in sandy soil compared to clay soil. It can increase or decrease soil carbon degradation in sand and clay soils. The objective of this study was to evaluate the influence of addition of natural zeolite and organic manures on different forms of soil organic carbon. Materials and Methods Soils were sampled from the top 30-cm layer of two agricultural lands in Hamadan, Iran with a semiarid climate. Corn was planted in two parts PVC cylinder containing sand and clay soils. Two separate experiments were conducted, one with a loamy sand and the other with a clay soil. Each experiment was conducted under a complete randomized factorial design in three replicates. The studied factors were zeolite (at three levels of 0%, 10% and 20%, fertilizer at a rate of 20 g kg-1 of dry weight basis ( at three levels including no manure, poultry manure and cow manure) and soil sampling zone at two levels including rhizosphere and nonrhizosphere. A modified thin-slicing technique was used for sampling from rhizosphere zone. The experimental setup included plant growth con¬tainers and an automatic drainage system. Each plant growth container comprised a two-compartment PVC cylinder. The compartments were separated by 25 µm galvanized-iron mesh. The upper part was 20 cm high with an internal diameter of 20 cm, while the lower part was one PVC cylinder of the same diameter (20 cm) with heights of 50 mm with 100 µm nylon mesh in the bottom which separates it from silicon powder base. Plant root hairs and fungal hyphae (but not plant roots) were able to penetrate the 25 µm mesh and enter the soil in the lower part and thus create the rhizosphere. Soil sampled from the top10 mm of the lower part was taken as rhizosphere soil and that sampled from bottom 40 mm was taken as nonrhizosphere soil. At the flowering stage of plant maize growth, each treated soil was sampled from the rhizosphere and nonrhizosphere zones. Physical SOC fractions were determined by density fractionation and particle size fractionation and statistically were analyzed. Results and Discussion Soil OC especially in heavy fraction and silt+clay size fractions were relatively higher in rhizosphere soils compared to those in non-rhizosphere soils. The effect of zeolite application on total organic carbon and organic carbon in sand size fraction in sandy soil was not significant. However, organic carbon in the silt+clay size fraction increased by addition of zeolite. The OC in light fraction increased significantly by application of manures (especially cow manure), however, the effect of zeolite addition on this fraction was not significant in loamy sand soil. Although soil OC in heavy fraction increased by addition of zeolite, this effect was not significant. Total organic carbon in the clay soil samples decreased significantly by addition of zeolite; however, soil organic carbon in the sand size fraction did not change significantly. Soil organic carbon in the heavy fraction and silt+clay size fraction also decreased in zeolite treatment of the clay soil. This effect was against that obtained in the sandy loam soil. Soil organic carbon in light fraction in the clay soil similar to that in sandy loam soil was increased by the addition of manures (especially cow manure). Zeolite application, however, did not show significant influence on organic carbon in light fraction in clay soil. Conclusion This study showed that the effect of zeolite application on soil organic carbon sequestration in clay was more obvious than on that in sandy soil. This shows physical protection of organic carbon by soil clay mineral and complexation of heavy fraction in carbon sequestration are very important. The size of zeolite applied in this study was between 0.1 and 0.4 mm. The size was equal to fine thne to medium sand particles which can lower the relative importance of organo-mineral complexation and clay protection of organic matter in the clay soil.