Submitted to: Plant and Soil
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/21/2010
Publication Date: 7/1/2011
Citation: Khoshgoftarmanesh, A.H., Taheri, S., Shariatmadari, H., Chaney, R.L. 2011. Kinetics of zinc release from ground tire rubber and rubber ash in a calcareous soil as alternatives to Zn fertilizers. Soil Science and Plant Nutrition (SSPN). 341:89-97. Interpretive Summary: Zinc deficiency is the most common microelement deficiency and growers have to purchase expensive zinc fertilizers to obtain full soil productivity. Zinc deficiency of humans is a significant global problem, so maintaining soil zinc status is important in public health. At the same time, rubber tire wastes are generated in every nation and the rubber contains high levels of zinc used to vulcanize the rubber. Improper disposal of rubber can cause zinc contamination and potential phytotoxicity in acidic soils. This manuscript considers beneficially using ground rubber as a zinc fertilizer where such fertilizer is needed. In contrast with some other byproduct zinc sources, the zinc in rubber is highly purified and as free of cadmium and lead as the highest quality commercial zinc fertilizers. The reported research evaluated the release of zinc from rubber, rubber ash, commercial zinc fertilizer and lab grade zinc sulfate; because rubber zinc is within the matrix of the rubber, the zinc is released as the rubber is biodegraded over time. Kinetic analysis of the release of zinc to the DTPA-extraction soil test reagent showed that rubber ash was similar to zinc fertilizer in release of zinc, but the ground rubber was a slow release source which maintained plant available zinc for a longer period in the soil. Taken together, these findings indicate that waste ground rubber could be recycled as an agricultural zinc fertilizer source, providing slow release and more persistent plant available zinc than common fertilizers used today. Ground rubber or rubber ash used as zinc fertilizers could be mixed in bulk mix fertilizers while recycling waste rubber for societal benefit and considerable savings to growers. In another manuscript, these researchers confirmed that ground rubber and rubber ash were very effective zinc fertilizers for wheat in zinc deficient fields in Iran.
Technical Abstract: Ground rubber contains 15-20 g Zn/kg but very low levels of Cd and could serve as an inexpensive byproduct Zn fertilizer. The aim of this investigation was to test the kinetics of Zn release in a soil treated with ground tire rubber and rubber ash compared with commercial Zn fertilizer and a laboratory grade zinc sulfate. A Zn-deficient soil was chosen from wheat fields in Isfahan province, central Iran, and the ground rubber, rubber ash, fertilizer-Zn and laboratory ZnSO4 were added at 1 and 4 kg Zn/ha; 1 kg/ha would usually correct Zn deficiency in such pot tests. The soil incubated at field capacity moisture content and room temperature and sub samples were taken 1, 3, 5, 10, 15, 20, and 25 weeks after mixing with the Zn amendments. The soil DTPA-extractable Zn was then measured using atomic absorption spectroscopy (AAS) and the results were described examining first order, Elovich, power function and parabolic diffusion kinetic models. Results showed that ground rubber and rubber ash significantly increased the concentration of DTPA-Zn in the soil and this increase was higher than achieved with the commercial Zn fertilizer. At a lower Zn application rate, Zn release followed parabolic diffusion, while at the higher rate, the kinetics of release followed power function and Elovich models. Comparison of the rate constant indicates that the rate of Zn release in soil was greater at the higher Zn concentration. In addition, the ground rubber and rubber ash had a higher rate of Zn release than the commercial Zn fertilizer. Thus, ground rubber and rubber ash offer strong value as Zn fertilizer for Zn deficient soils.