Low nutrient availability and biological activity are the main challenges in calcareous soils with low organic matter (OM) content. The purpose of the present study was to evaluate the responses of soil nutrient status and biological traits to addition of corn residue biochar produced at different pyrolysis temperature in a calcareous soil. Biochars were made at 200 (BC200), 350 (BC350), and 500°C (BC500), added to a calcareous soil at 1 and 2% (w/w) and were incubated for 90 days. The application of biochars increased soil organic carbon (SOC), electrical conductivity (EC), cation exchange capacity (CEC), total N [1.21-to 1.41-fold], available P [1.71-to 2.65-fold], K [1.53-to 2.60-fold], Mn [1.14-to 1.21-fold], microbial respiration [1.21-to 2.23fold], substrate-induced respiration [1.22-to 2.63-fold], microbial biomass carbon [1.20-to 2.24-fold], the activity of catalase [1.80-to 2.93-fold], and dehydrogenase [1.47-to 2.30-fold], which varied with the pyrolysis temperature and application rate. Generally, all the measured biological attributes were higher in BC200 than the other treatments. The BC200 biochar increased soil inorganic nitrogen [1.14-to 1.21-fold] and available Fe [1.12-to 1.17-fold], Zn [1.32-to 1.42-fold], and Cu [1.06-to 1.10fold]. In contrast, the BC500 at 2% rate decreased available Fe, Zn, and Cu. The findings revealed that the application of corn biochar obtained at 200°C to calcareous soil was more efficient for improving the nutrient availability and microbial activity.

Ligninolytic enzyme complexes are involved in lignin degradation. Among them laccases are outstanding because they use molecular oxygen as a co-substrate instead of hydrogen peroxide as used by peroxidases. Bacterial laccase of Bacillus genus was first reported in Claus and Filip (Microbiol Res 152:209-216, 1997), since then more bacterial laccases have been found. In this research, laccase-producing bacteria were screened from pulp and paper industry wastewater, bagass and sugarcane rhizosphere. Nutrient agar medium containing 0.5 mM of guaiacol was used. It was observed that the laccase-producing strains developed brown colour from which 16 strains of Bacillus were identified. One of the isolated strains was identified as Bacillus subtilis WPI based on the results of biochemical tests and 16S rDNA sequence analysis. This strain showed laccase-like activity towards the oxidizing substrates ABTS and guaiacol. In this study guaiacol was used as the substrate of laccase activity assay. For determination of laccase activity of this isolate guaiacol was used as a substrate of assay for the first time in this study. SDS-PAGE and Native-PAGE confirmed the presence of laccase.

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Soil salinity is one of the limiting factors of agricultural production in arid and semi-arid areas that reduces yields and optimal crop production. Awareness of rhizosphere bacterial diversity and use of salinity-resistant bacteria is considered as a critical strategy to increase plant growth in these areas. This study aimed to determine the population diversity of sugarcane rhizosphere bacteria in saline and non-saline soil and survey some growth-promoting properties. For this purpose, random sampling from the rhizosphere of sugarcane was performed. Bacteria were isolated by culturing serial on nutrient agar medium and were identified based on biochemical assays. The ability of isolates to fix nitrogen, dissolute phosphate and potassium and auxin production was investigated. Finally, the best growthpromoting isolates were identified based on 16S rRNA sequences. Generally, 40 bacteria were isolated from saline and non-saline soil that these strains were mainly from Bacillus, Paenibacillus and Pseudomonas. Salinity had the highest effect on bacterial community structure with the higher diversity of microorganisms in saline soils. Four strains were selected as growth-promoting strains which based on biochemical and phylogenetic analysis were identified asEnterobacter cloacae R13, Enterobacter cloacae R33, Paenibacillus lactis and Pseudomonas sp.

Availability of Zinc (Zn) is very low in calcareous soils and hence, an amendment must be used to increase Zn availability to plants. The main objective of this study was to assess the changes in chemical fractions and availability of Zn in a calcareous soil amended with corn residue biochar. Three corn residue biochars were produced at 200 (B200), 350 (B350), and 500°C (B500) and applied at 1 and 2% w/w to a calcareous soil with low organic C content (4.1 g kg −1) and high pH (7.7). The mixtures were incubated for 90 days in the laboratory (25 ± 2°C and 80% of soil field capacity). The application of biochar increased soil total organic carbon (TOC) (1.81-to 3.27-fold), cation exchange capacity (CEC) (1.03-to 1.14-fold) and Zn bound to organic matter (1.34-to 2.15-fold). Relative to untreated soil, the B200 biochar (1) decreased soil pH (0.22-0.30 unit); (2) increased dissolved organic carbon (DOC) (1.34-to 1.59-fold), microbial biomass carbon (MBC) (1.56-to 1.67-fold) and DTPA-extractable Zn (1.32-to 1.42-fold); and (3) maximized Zn content in 3 out of 5 soil pools, i.e., exchangeable Zn; organically bounded Zn; and Fe/ Mn-oxide-bounded Zn. In contrast, the B500 biochar (1) increased soil pH; (2) did not affect DOC or DTPA-extractable Zn quantities in soil extracts; and (3) maximized Zn content in carbonate-Zn and residual-Zn soil fractions. The B350 biochar (1) did not affect soil DOC and DTPA-extractable Zn and (2) slightly increased carbonate-Zn fractions. The effects of biochar addition on soil properties and chemical fractions of Zn were greater at 2% than 1% application rates. Results suggest that corn residue biochar produced at 200°C and applied to calcareous soils at a 2% rate may effectively increase Zn availability by increasing the amount of Zn held in the more labile Zn soil fractions.