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Intensive rice cultivation for a long time resulted in increasing soil degradation and less yield. This study aimed to evaluate effects of the combining reducing nitrogen fertilizer (N) with biochar amendment on soil chemical properties, rice growth parameters, and grain yield in the rice cultivation system in the Mekong Delta region, Vietnam (VMD). Field experiment was designed in the split-plot design with two factors, including N fertilizer (main plot) and biochar (sub-plot). Two N fertilizer rates were: (N50)—50 kg N ha–1 and (N100)—100 kg N ha–1, which is the farmer's practice. Biochar was amended with three rates: no applied biochar (B0), 5 t ha–1 (B5), and 10 t ha–1 (B10). The results indicated that reducing N fertilizer by 50% combined 5–10 t biochar ha–1 resulted in maintaining soil pH, soil electrical conductivity, soil organic carbon, cation exchange capacity, and rice biomass. Applying biochar at a rate of 5–10 t ha–1 significantly increased the available N, available P, and rice height compared to the treatment with no applied biochar (B0). Rice yield in the treatments applied with 5–10 t ha–1 was significantly higher than the treatment without the use of biochar by 11.6–14.7%. The findings of this study confirmed that reducing 50% N fertilizer combined with 5 t ha–1 or 10 t ha–1 of biochar could improve soil available N, available P, rice growth, and grain yield in intensive rice cultivation systems in the VMD region. [ABSTRACT FROM AUTHOR]

Given that rice husk biochar has been shown to modulate salinity in salt-affected acid soils, the objective of this study was to investigate the effects of organic amendment of salinized acid soils on P fractions, enzyme activities, and associated rice yield. Four treatments, viz. Rice–Rice–Rice, [RRR]; Fallow–Rice–Rice, [FRR]; Fallow–Rice–Rice + 3 Mg ha−1 of compost [FRR + Comp]; and Fallow–Rice–Rice + 10 Mg ha−1 of biochar [FRR + BC] were established at Ben Tre and Kien Giang sites, Viet Nam, over six consecutive crops. Soil properties at harvest of the sixth crop showed that there were diverse patterns of fractionation between P forms with respect to treatment. Overarchingly, biochar increased labile and moderately labile inorganic P and organic P by 30% to 70%, respectively, whilst compost had a relatively modest effect on these pools. Soil phosphatase activities at crop tillering increased following the FRR + Comp and FRR + BC treatments compared with those in RRR, except for acid phosphatase at Ben Tre. At harvest, there were no significant differences between the enzyme activities among the treatments. Rice yield was positively correlated with the more labile forms of P, soil C, and acid phosphatase activity. In the absence of organic amendments, there was no effect of triple versus double rice crops being grown in one-year cycle. Repeated application of biochar (10 Mg ha−1 × 5 times) showed potential to increase grain yields and total soil C in salt-affected acid soils, via modulation of P transformations to more plant-available forms. [ABSTRACT FROM AUTHOR]

Heavy metal contamination in agricultural land is an alarming issue in Vietnam. It is necessary to develop suitable remediation methods for environmental and farming purposes. The present study investigated the effectiveness of using peanut shell-derived biochar to remediate the two heavy metals Zn and Pb in laboratory soil assays following Tessier's sequential extraction procedure. The concentration of heavy metals was analyzed using Inductively coupled plasma mass spectrometry (ICP-MS). This study also compared the effectiveness of the blend of biochar and apatite applied and the mere biochar amendment on the chemical fractions of Pb and Zn in the contaminated agricultural soil. Results have shown that the investigated soil was extremely polluted by Pb (3047.8 mg kg−1) and Zn (2034.3 mg kg−1). In addition, the pH, organic carbon, and electrical conductivity values of amended soil samples increased with the increase in the amendment's ratios. The distribution of heavy metals in soil samples was in the descending order of carbonate fraction (F2) > residue fraction (F5) > exchangeable fraction (F1) > Fe/Mn oxide fraction (F3) > organic fraction (F4) for Pb and F5   ≈   F2 > F1 > F3 > F4 for Zn. The peanut shell-derived biochar produced at 400 °C and 600 °C amended at a 10% ratio (PB4:10 and PB6:10) could significantly reduce the exchangeable fraction Zn from 424.82 mg kg−1 to 277.69 mg kg−1 and 302.89 mg kg−1, respectively, and Pb from 495.77 mg kg−1 to 234.55 mg kg−1 and 275.15 mg kg−1, respectively, and immobilize them in soil. Amending the biochar and apatite combination increased the soil pH, then produced a highly negative charge on the soil surface and facilitated Pb and Zn adsorption. This study shows that the amendment of biochar and biochar blended with apatite could stabilize Pb and Zn fractions, indicating the potential of these amendments to remediate Pb and Zn in contaminated soil. [ABSTRACT FROM AUTHOR]