| چکیده انگلیسی مقاله |
Introduction: Use of organic fertilizers such as vermicompost in agricultural soils with low organic matter content is almost considered as a one way for adding nutrients in these soils. However, application of these fertilizers may affect micronutrient release characteristics. Micronutrient release Kinetics in soils especially in amended soils give information about potential of amended soils to release these elements into solution. Although it is important to study kinetics of micronutrient release from soils to identify soil micronutrients buffering capacity, little attention has been paid to micronutrients desorption rate studies especially in amended soils. The rate of release micronutrients from soil solid phase by considering micronutrients as adsorbed ions or in mineral forms is an important parameter in nutrition of plants by microelements and a dynamic factor that regulates its continuous supply to growing plants; nonetheless, little attention has been paid to micronutrients kinetics inrelease studies. Material and Methods: In this study, kinetics of zinc (Zn) and copper (Cu) were compared in one calcareous soil amended with 0, 0.5, and 1% (w/w) of manure and vermicompost in a completely randomized design and then amended and un-amended soils were incubated at field capacity, for 30 days. After incubation period, amended and un-amended soils were air-dried and were prepared to kinetics study. Kinetics of Zn and Cu release were studied by successive extraction with DTPA-TEA solution. Two grams of the amended and un-amended soils, in triplicate, suspended in 20 ml DTPA-TEA solution were equilibrated at 25±10C for 1, 8, 24, 48, 72, 96, 120, 144, 168, 336 and 504 h by shaking for 15 min. before incubation and 15 min. before the suspensions were centrifuged. Seven drops of toluene were added to each 1000 ml of extractant to inhibit microbial activity. Zinc and copper desorption with time was fitted by using different equations (Zero-order, First-order, Parabolic diffusion, Simplified Elovich, and Power function). Results and Discussion: Results showed that released Zn in soils amended with manure and vermicompost compared to control soil significantly increased (p 0.05) and released Cu in soil amended with vermicompost decreased significantly (p< 0.05) with respect to control soil. Released Zn and Cu in soils amended with vermicompost decreased significantly (p< 0.05) compared to soils amended with manure. The amount of released Zn in reclaimed soil with 0.5 and 1% manure and vermicompost was 2.54, 2.98, 2.14, and 2.61 mg kg-1, respectively. In addition, the amount of released Cu in amended soil with 0.5 and 1% manure and vermicompost was 2.92, 2.72, 2.41, and 2.40 mg kg-1, respectively. Different mathematical models were tested for their suitability to describe desorption of Zn and Cu from the amended and un-amended soils. Comparisons of R2 and SE values indicated that the power function equation described the reaction rates fairy well, as evidenced by the high coefficients of determination and low standard error of the estimate. The constant a in the power function may be indicated the number of surface sites available for desorption. In addition, the constant b is a measure of the affinity of elements for these sites with increasing affinity of sites being indicated by the value of 1/b. In the other words, an increase in the value of a decrease in the value of b probably indicates an increase in the rate of metal desorption from the soils with DTPA. The results showed that rate constant of released Zn, a constant in amended soils with 0.5 and 1 % manure were 0.882 and 1.097 mg kg-1, respectively. This constant in amended soils with 0.5 and 1 % vermicompost were 0.659 and 0.825 mg kg-1, respectively. Also, the b constant, ranged from 0.231 (soil amended with 0.5% manure) to 0.267 (soil amended with 0.5% vermicompost) (mg kg-1h-1). Rate constant of released Cu, a constant in amended soils with 0.5 and 1 % manure were 0.916 and 0.834 mg kg-1, respectively. This constant in amended soils with 0.5 and 1 % vermicompost were 0.745 and 0.787 mg kg-1, respectively. Also, the b constant, ranged from 0.231 (soil amended with 0.5% manure) to 0.267 (soil amended with 0.5% vermicompost) (mg kg-1h-1). Rate constant (a*b) of released Zn in the amended soils with 0.5 and 1 % vermicompost were 0.216 and 0.176, respectively. While this constant in the amended soils with 0.5 and 1 % manure were 0.214 and 0.254 respectively. Moreover, rate constant (a*b) of released Cu in the amended soils with 0.5 and 1 % vermicompost were 0.197 and 0.199, respectively. While this constant in the amended soils with 0.5 and 1 % manure were 0.242 and 0.222, respectively. Conclusion: Our results revealed that the rate of released Zn and Cu in soils amended with vermicompost was lower than the soils amended with manure. In the other words the difference between rates of release constants indicated that Zn and Cu supplying power of the amended soils with manure was higher than amended soils with vermicompost |