اثر تلقیح باکتری ریزوبیوم و قارچ میکوریزی گونه گلوموس موسه آ با نخود بر پایداری ساختمان خاک و توزیع اندازه خاکدانه ها در دو شرایط گلخانه ای و مزرعه ای

علی‌رغم تاثیر قابل توجه قار‌چ ها و باکتری‌ها بر پایداری ساختمان خاک، تاثیر قارچ مایکوریزا گونه گلوموس موسه آ و باکتری ریزوبیوم بر ساختمان خاک، به‌ندرت مورد بررسی قرار گرفته است. آزمایش در قالب طرح بلوک‌های کامل تصادفی با سه تکرار در دو مرحله گلخانه‌ای و مزرعه‌‌ای با کشت نخود اجرا شد. در شرایط مزرعه تیمارهای آزمایشی شامل قارچ مایکوریزا گونه گلوموس موسه آ، باکتری ریزوبیوم، ترکیب تیمار اول و دوم (مایکوریزاباکتری ریزوبیوم) و شاهد (بدون تلقیح) و در شرایط گلخانه علاوه بر چهار تیمار فوق تیمار ماده زمینه سترون شده قارچ مایکوریزا و تیمار بدون گیاه، تیمارهای آزمایشی بودند. مقدار کربن آلی و پایداری خاکدانه‌ها در حالت تر مورد بررسی قرار گرفت. نتایج گلخانه ای نشان داد که تیمار مایکوریزا نسبت به تیمار شاهد و شاهد بدون گیاه باعث افزایش معنی دار میانگین وزنی قطر خاکدانه ها (به‌ترتیب 51.6 و 189.1 درصد) شد. در شرایط گلخانه مقدار کربن آلی دارای همبستگی بالا با میانگین وزنی قطر خاکدانه‌ها (0.53=r^2) بود و تیمار حاوی مایکوریزا باعث افزایش کربن آلی از 0.73 درصد در شاهد بدون گیاه به 1.02 درصد شد. در شرایط گلخانه تیمارمایکوریزا باعث افزایش خاکدانه‌های درشت و کاهش خاکدانه‌های ریز شد. همچنین استفاده همزمان باکتری و قارچ تاثیر کمتری بر پایداری خاکدانه ها نسبت به اثرات جداگانه آن ها داشت، زیرا استفاده همزمان، تاثیری بر رشد گیاه نداشت. در شرایط مزرعه تیمارها تاثیر معنی داری بر سایر کلاس اندازه خاکدانه ها نداشتند. نتایج نشان داد که همزیستی میکوریزی و باکتری ریزوبیوم به‌عنوان یک روش بیولوژیک و پایدار باعث ارتقای کیفیت ساختمان خاک شد.

Effects of Chickpea Inoculation with Rhizobium (Mesorhizobium caesar) and Mycorrhizae (Glomus mosseae) on Soil Structural Stability and Aggregates Size Distribution under both Greenhouse and Field Conditions

Introduction: Stability of soil aggregates is a result of complex physical, chemical and biological processes in the soil. In many studies, organic matter has been studied as a major factor in formation of aggregates and the effects of symbiosis between mycorrhizal fungi and bacteria largely ignored, however these microorganisms have a great effect in the formation of the aggregates. Plant roots provide a suitable habitat for the activity of many soil microorganisms. In this regard, the symbiosis of plant roots with fungi is one of the most common and longlived symbiotic relationships that are found in most ecosystems. On the other hand, biological fertilizers can improve soil aggregation through influence the growth of root and plant. Despite the significant effect of fungi and bacteria on the stability of the soil structure, the effect of arbuscular mycorrhizal fungi species Glomus mosseae and Rhizobium species Mesorhizobiumon caesar on the soil structure has been rarely investigated. Therefore, the aim of this study was to evaluate the effect of chickpea inoculation with Rhizobium (Mesorhizobium caesar) and mycorrhizae (Glomus mosseae) on soil structural stability and aggregates size distribution under both greenhouse and field conditions.;Materials and Methods: The present study was conducted as a randomized completeblock design with three replications in both greenhouse and field conditions. The treatments under field condition were mycorrhizal fungus (Glomus mosseae), Rhizobium (Mesorhizobium caesar), mycorrhizae – rhizobium combined treatment and a control (no inoculation). In the greenhouse condition, sterilized mycorrhiza background material and without plant (without inoculation) treatments were also added. Chickpea was planted at both conditions. Soil sampling was carried out after harvesting. The stability of aggregates using wet sieving method and soil organic carbon content were investigated.;Results and Discussion: Greenhouse study results showed that mycorrhizae treatment significantly increased the mean weight diameter of the aggregates by 51.6% and 189.1%, in comparison with the control (without inoculation) and control without plant (without inoculation), respectively. This treatment increased macro aggregates and decreased the fine aggregates. In the greenhouse condition, soil organic carbon content had a high correlation with the mean weight diameter of the aggregates (R2 = 0.53) and mycorrhizal treatment increased organic carbon content from 0.73% in the control (without plant) to 1.02%. However, the mycorrhizae – rhizobium combined treatment had less effect on the stability of the aggregates than their single effects. The mass of aggregates of 1–2 mm are more sensitive to shortterm management. In the greenhouse condition all the three biofertilizer treatments significantly increased the mass of the aggregates of 12 mm in comparison with the control treatment without plant (without inoculation). On the other hand, the mean comparison results showed that there was no significant difference between the sterilized mycorrhizal background and the control without plant (without inoculation). This may be due to the lower organic matter content in these two treatments compared to others. In the greenhouse condition, increasing the mass of coarse aggregates of 48 mm in diameter indicates the suitability of soil structure. On the other hand, aggregates coarser than 0.25 mm are considered as coarse and stable aggregates. It can be concluded that the application of mycorrhiza and rhizobium increased soil structural stability through the increase of the mass of these classes of the aggregates (24 and 48 mm), probably by affecting the length and volume of the root and plant yield. Under the field condition, the treatments had no impact on the mass of the aggregates in different size classes.;Conclusion: Bacteria and fungi can be effective factors in improving soil structure through increasing organic carbon in soil. The results of the present study indicated that aggregate stability was affected by biological fertilizer treatments under greenhouse condition so that the treatments containing biofertilizers increased soil aggregate stability and improved the soil structure that was probably due to increasing plant yield and root. Also, the less effect of biofertilizers on the stability of the aggregates and the increase of coarse aggregates under the field condition can be due to the uncontrolled climatic conditions compared to the greenhouse and the short duration of the study. In recent decades, the physical and chemical properties of soils have changed due to the use of chemical inputs in agricultural lands.The use of biological and organic fertilizers is an appropriate solution to these problems. It is recommended further study on the efficacy of other species of mycorrhizal fungi and rhizobium bacteria in improving soil physical and chemical quality, especially at the field scale. Also, considering the implementation of this project in the field condition, it is suggested to study the physical, mechanical and chemical properties of soil in the long term.