Gupta et al. 2023 — Household ash as rice fertiliser in Bangladesh: effects on grain iAs and Cd
This field trial from the Meharg group at Queen’s University Belfast investigates whether recycling household biomass ash as a fertiliser in Bangladeshi rice paddies can improve soil fertility and rice yield without increasing accumulation of inorganic arsenic (iAs) or cadmium (Cd) in grain. Large-scale trials across two geographically distinct regions (Barind and Madhupur Tracts), two growing seasons (dry/Boro and wet/Amon), and three fertiliser treatments found that ash application boosted rice yield by approximately 20 percent relative to conventional NPKS without altering grain iAs, dimethylarsonic acid (DMA), or Cd. The study also characterises rhizosphere microbial communities and demonstrates that region, season, and soil microbial composition are the dominant drivers of elemental accumulation in rice grain, outweighing the treatment effect on iAs and Cd. This is a practically significant null finding from a high-quality research group: a low-cost agronomic intervention that improves yield does not worsen grain arsenic or cadmium in this context.
Key numbers
Ash application boosted rice yield by approximately 20 percent in both regions and both seasons. No statistically significant effect of ash treatment on grain iAs, DMA, or Cd (three-way ANOVA with region × season × treatment). Grain arsenic speciation by IC-ICP-MS (iAs and DMA measured separately); Cd, Zn, Cu, Mn, P, Rb by ICP-MS. CRMs: ISE921, NCS 73007 (soil); NIST 1568b (rice). Soil Al, As, Cu, Fe, and Ni were significantly higher in Madhupur than Barind (p ≤ 0.001); soil pH and K, P, Si higher in Barind (p less than 0.001). Ash from Barind tract: 0.83 t/ha/year median; Madhupur: 0.56 t/ha/year. Ash treatments applied at 1 t/ha in experimental plots. Cultivars: BRRI dhan28 (dry season) and BRRI dhan49 (wet season).
Methods (brief)
Field trials on 5 m × 5 m subplots with 3 treatments × 3 replicates per village, 18 villages (9 Barind, 9 Madhupur). Grain and soil collected at harvest; rhizosphere soil collected at grain-filling stage. Grain arsenic speciation by IC-ICP-MS; grain Cd by ICP-MS; soil elements by XRF. Microbial community composition by 16S rRNA amplicon sequencing (Illumina MiSeq, 250 bp paired-end). CAP ordination and Spearman correlation used to link microbial genus-level ASVs to grain elemental concentrations. Statistical analysis: three-way ANOVA, PERMANOVA, FDR correction. Limitation: single application rate for ash treatment; long-term soil accumulation effects not assessed.
Implications
Certification: Directly relevant to rice iAs and Cd risk characterisation for Bangladeshi-origin rice. Documents that household ash use — a widespread agronomic practice — does not elevate grain iAs or Cd above what region and season effects already produce, which is an important mitigation finding.
Courses: Core reference for modules on rice arsenic and cadmium, agronomic mitigation strategies, and the interaction between flooded-paddy redox chemistry and As versus Cd bioavailability.
App: Supports the rice ingredient iAs and Cd profile; the null treatment finding simplifies risk attribution to region and season, consistent with the geographic variance framing in the ingredient-page schema.
Microbiome: Contains 16S rRNA microbial community data from rice rhizosphere; documents significant region × season effects on microbial composition and Spearman correlations between microbial genera and grain iAs, DMA, Cd, and Zn. Relevant as supply-chain context (soil microbiome influences rice grain arsenic); not directly relevant to human gut microbiome.