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.
The excessive amounts of cadmium and lead in food chain can cause health problems for humans and ecosystem. Rice is an important food in human diet. Therefore this study was conducted in order to investigate cadmium and Lead concentrations in seed rice (Oryza saliva) of paddy fields in southwest of Iran. A total of 70 rice seed samples were collected from paddy fields in five regions of Khuzestan province, Southwest Iran, during harvesting time. In the samples cadmium and Lead concentrations were measured. To assess the daily intake of Cadmium and Lead by rice, daily consumption of rice was calculated. The results showed that average concentrations of Cadmium and Lead in rice seeds were 273.6 and 121.8 μg/kg, respectively. Less than 72% of rice seed samples had Cadmium concentrations above 200 μg/kg (i.e. Guide value for cadmium); and less than 3% had Lead concentrations above 150 μg/kg (i.e. Guide value for Lead). The estimated daily intakes of cadmium by the local population was calculated to 0.59 μg/day kg bw, which corresponds to 59% of the tolerable daily intakes (i.e. 1 μg/day kg bw). Eleven out of 70 samples (15.71%) exceed the tolerable daily intakes. The dietary intakes for Lead in the local population ranged from 0.22 to 0.47 μg/day kg bw. Tolerable daily intakes for Lead is 3.6 μg/day kg bw. As a whole, long term consumption of the local rice may bear high risk of heavy metal exposure to the consumer in the study region.
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.
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