Huang Daoyou

A three-season field study on the in-situ remediation of Cd-contaminated paddy soil using lime, two industrial by-products, and a low-Cd-accumulation rice cultivar

To mitigate the serious problem of Cd-contaminated paddy soil, we investigated the remediation potential of combining in-situ immobilization with a low-Cd-accumulation rice cultivar. A three-season field experiment compared the soil pH, available Cd and absorption of Cd by three rice cultivars with different Cd accumulation abilities grown in Cd-contaminated paddy soil amended with lime (L), slag (S), and bagasse (B) alone or in combination. The three amendments applied alone and in combination significantly increased soil pH, reduced available Cd and absorption of Cd by rice with no effect on grain yield. Among these, the LS and LSB treatments reduced the brown rice Cd content by 38.3-69.1% and 58.3-70.9%, respectively, during the three seasons. Combined with planting of a low-Cd-accumulation rice cultivar (Xiang Zaoxian 32) resulted in a Cd content in brown rice that met the contaminant limit (≤0.2mgkg-1). However, the grain yield of the low-Cd-accumulation rice cultivar was approximately 30% lower than the other two rice cultivars. Applying LS or LSB as amendments combined with planting a low-Cd-accumulation rice cultivar is recommended for the remediation of Cd-contaminated paddy soil. The selection and breeding of low-Cd-accumulation rice cultivars with high grain production requires further research.

Spatial variation in organic carbon, nutrients and microbial biomass contents of paddy soils in a hilly red soil region

The contents of soil organic C (SOC), total N (TN), total P (TP), dissolved N (DN), Olsen-P, and microbial biomass C, N, P (BC, BN, BP) of 254 paddy soils (0–18 cm in depth) in a hilly red soil region of subtropical zone of China were studied. The results showed that the contents of SOC, TN, BC, BN and DN of paddy soils at the bottom of hills were 14.6%, 13.6%, 24.6%, 20.4% and 95.8% higher than those at the foothill, respectively. The Olsen-P content of paddy soils at the foothill was 33.3% higher than that at the bottom of hills. However, the differences in TP, BP and available P (the sum of BP and Olsen-P) contents were not significant between the two positions. In addition, the ratios of soil C/P, BC/BP and BC/SOC of paddy soils at the bottom of hills were 12.7%, 28.5% and 8.2% higher than those at the foothill, respectively, but the differences in ratios of soil C/N, BC/BN, BN/TN and BP/TP were not statistically significant between various positions.

Effect of biochar from peanut shell on speciation and availability of lead and zinc in an acidic paddy soil

Biochar has been used to reduce the mobility and availability of heavy metals in contaminated paddy soils. A pot experiment was carried out to analyze the effects of peanut shell biochar (PBC) on the speciation and phytoavailability of Pb and Zn in contaminated acidic paddy soil using rice (Oryza sativa L.) as an indicator plant. Peanut shell biochar was applied to an acidic paddy soil contaminated with Pb and Zn at four rates (0%, 1%, 2%, and 5% w/w), and rice plants were grown in this soil. The soil pH, cation exchange capacity (CEC), water-soluble SO42-, dissolved organic carbon (DOC), CaCl2-extractable heavy metals, and speciation of heavy metals were determined. Additionally, biomass and concentrations of heavy metals in rice tissues were determined. The application of PBC significantly increased the pH, CEC, water-soluble SO42-, and DOC in the paddy soil, but decreased the content of CaCl2-extractable Pb and Zn. The CaCl2-extractable Pb and Zn showed significant negative correlations with the pH, CEC, water-soluble SO42-, and DOC (p < 0.05). Following the application of biochar to the contaminated paddy soil, the Pb and Zn concentrations in the CaCl2 extracts were reduced by 41.04-98.66% and 17.78-96.87% (p < 0.05), respectively. Sequential chemical extractions showed a reduction in the acid-soluble Pb and Zn fraction and an increase in the reducible fraction following the addition of biochars. PBC obviously inhibited the uptake and accumulation of Pb and Zn in the rice plants. The Pb concentrations in the rice grain were significantly reduced by 60.32%, with the addition of 5% PBC. Neither of the biochars significantly changed the Zn concentrations in the rice grain. The influence of biochar on Pb and Zn phytoavailability varied not only with the application rate of biochar, but also with the kind of metals. Overall, the use of peanut shell biochar at a high application rate is more effective in immobilizing Pb and Zn in the acidic paddy soil contaminated with heavy metals, especially in reducing the phytoavailability of Pb to the rice plants.