Ability of sulfur-oxidising bacteria to hasten degradation of ground rubber particles in soil for release of zinc as a fertiliser to correct deficiency in wheat

Abstract

Previous research has shown that ground rubber from tyres can be used to supply fertiliser zinc (Zn) for prevention of Zn-deficiency in crops, and that inoculation of the ground rubber with several bacterial species hastens the release of Zn to the soil. We evaluated the ability of several microbial combinations to speed the release of Zn from ground rubber and to decrease soil pH to favour phytoavailability of Zn to crops. In a batch experiment, treatment combinations of two rates of ground crumb rubber (nil or 300mg kg–1, equal to 0 or 3.4mg Zn kg–1) and 24 bacterial inoculants were incorporated into a Zn-deficient calcareous soil. In a pot experiment, two wheat cultivars were grown on the soil without or with ground rubber amendment or with equivalent Zn from ZnSO4 (15mg kg–1) in combination with two selected microbial treatments. All microbial treatments significantly decreased soil pH at week 3, most notably the inoculant comprising Rhodococcus erythropolis and Acinetobacter calcoaceticus (RA)+Pseudomonas putida P41 (P1)+mixed Thiobacillus spp. (Mt). In the presence of tyre rubber, soil pH at week 10 was still significantly lower than the initial value, and soil DTPA-extractable Zn concentration increased until week 6 and then remained unchanged or slightly reduced at week 10. The greatest increase in DTPA-Zn concentration occurred with the RA inoculation. Microbial inoculation treatments were classified by cluster analysis into eight groups based on soil pH and concentrations of iron (Fe) and Zn. Group 8 produced the lowest pH and highest concentrations of DTPA-Fe ( average 6.92mg kg–1) and DTPA-Zn (average 2.67mg kg–1). Inoculations with RA and with RA+P1+T. thioparus were the most effective in hastening an increase in DTPA-extractable Zn and significantly enhanced Zn uptake by wheat plants, whereas inoculations with P. putida P168 and with RA+P2+Mt were most effective in decreasing soil pH and increasing plant Fe concentration.

Zinc-solubilizing Pseudomonas strains accelerate the release of zinc from tire waste powder and improve maize growth and zinc nutrition

“…The increase in plant growth in the TWP and Pseudomonas strains treatments can be attributed to the effects of TWP (as a source of Zn and Fe) and the diverse plant growth-promoting properties of Pseudomonas strains such as nutrient solubilization (via exudation of organic acid anions), producing indole-3-acetic acid (IAA), as well as improving plant stress tolerance by exuding ACC deaminase (Azarmi et al 2016). These ndings are in accordance with the results of Asadollahzadeh et al (2019) who reported that the application of sulfuroxidizing bacteria was effective in increasing wheat biomass in a TWP-treated soil.…”

“…Thiobacillus ferrooxidans and T. thioparus were shown to break the S-S bonds at the surface of rubber particles (Chritiansson et al 1998;Li et al 2011). Asadollahzadeh et al (2019) demonstrated that inoculation of TWP with some PGPR strains (Rhodococcus erythropolis, Acinetobacter calcoaceticus, Pseudomonas putida P41, Thiobacillus spp) led to a signi cant decrease in soil pH and therefore increased Zn bioavailability.…”

“…Beside pH reduction, exudation of chelating agents such as siderophore and low molecular weight organic acid anions is suggested to be related to the micronutrient-solubilizing capability of PGPR (Sha gh et al 2019b; Asadollahzadeh et al 2019). The microbial siderophores can form stable complexes with Zn and other micronutrients and increase the solubility of metals in soils (Hamidpour et al 2019;Asadollahzadeh et al 2019).…”