بررسی اثر کاربرد زئولیت بر شاخصهای پایداری خاکدانهها

Abstract

Introduction: Soil structural stability affects the profitability and sustainability of agricultural systems. Particle size distribution (PSD) and aggregate stability are the important characteristics of soil. Aggregate stability has a significant impact on the development of the root system, water and carbon cycle and soil resistance against soil erosion. Soil aggregate stability, defined as the ability of the aggregates to remain intact when subject to a given stress, is an important soil property that affects the movement and storage of water, aeration, erosion, biological activity and growth of crops. Dry soil aggregate stability (Mean Weight Diameter (MWD), Geometric Mean Diameter (GMD)) and Wet Aggregate Stability (WAS) are important indices for evaluating soil aggregate stability.To improve soil physical properties, including modifying aggregate, using various additives (organic, inorganic and chemicals), zeolites are among what has been studied.According to traditional definition, zeolites are hydratealuminosilicates of alkaline and alkaline-earth minerals. Their structure is made up of a framework of[SiO4]−4 and [AlO4]−5 tetrahedron linked to each other's cornersby sharing oxygen atoms. The substitution of Si+4 by Al+3 intetrahedral sites results inmore negative charges and a high cation exchange capacity.Zeolites, as natural cation exchangers, are suitable substitutes to remove toxic cations. Among the natural zeolites,Clinoptilolite seems to be the most efficient ion exchanger and ion-selective material forremoving and stabilizing heavy metals.Due to theexisting insufficient technical information on the effects of using different levels of zeolite on physical properties of different types of soils in Iran, the aim of this research was to assess the effects of two different types of zeolite (Clinoptilolite natural zeolite, Z4, and Synthetic zeolite, A4) on aggregate stability indicesof soil. Materials and Methods: In this study at first, after preparation of two different types of soil with light and medium texture and doing identification tests such as determination of gradation and hydrometer tests and Atterberg limits, zeolite in four levels, 0 (control), 1%, 5%, and 10%w/w, was mixed with two soil textures (sandy loam and silty loam) in three replications. Then, each treatment was saturated for 48 hours in each month, during 6 months. Dry soil aggregate stability (Mean Weight Diameter (MWD), Geometric Mean Diameter (GMD), and Wet Aggregate Stability (WAS)), were determined. The experiment was carried out using factorial method in a randomized complete design. Results and Discussion:The results showed that, in sandy loam texture, there was no significant difference between two types of zeolites, their level of using and their interaction on MWD (p<0.01). Nevertheless, using zeolite had a significant effect on GMD in this soil texture and it was increased to 2.1 and 3.8% by using 10 and 1% w/w zeolite, respectively. In silty loam texture, although using two types of zeolite had a significant effect on both MWD and GMD, the aggregate stability indices were decreased by increasing the level of zeolite comparing to control. According to critical levels of dry soil aggregate stability based on mean weight diameter (MWD), in two soil textures MWD was low and adding zeolite and increasing their levels did not have a significant effect on these indices. The results also indicated that in two soil textures, using two types of zeolite had no considerable effect on WAS.The erosion rate depends on surface particle sizedistribution.Wind erosion is one of the phenomena which causes land degradation in arid and semi-arid regions. Due to impact of dry soil aggregate stability on soil resistance against soil erosion, and although using a high level of zeolite could improve aggregates stability indices, it was concluded that zeolite is not a proper additive for improving aggregates stability indices of soils to reduce wind and water erosion. Conclusion: In general, although based on statistical analyses, using zeolite has a significant effect on soil aggregate stability at a high level of zeolite application, using it was not an effective factor in improving this index of soil in this research.