Overview
This greenhouse pot experiment from Qingdao Agricultural University (China) investigated the combined effects of foliar selenium application and biochar soil amendment on cadmium accumulation and selenium enrichment in two peanut cultivars (Huayu 23, low cadmium (Cd) accumulator; Huayu 20, high Cd accumulator). The soil used had a background cadmium of 0.85 mg/kg and was spiked to either 5 mg/kg (low, 8 times the third-level soil Cd pollution standard) or 20 mg/kg (high) to simulate cadmium-contaminated farmland.
These grain Cd values reflect artificially contaminated soil conditions and are not representative of market-level peanut cadmium concentrations. The study’s value to the peanuts literature is mechanistic and agronomic.
Key numbers
Control group grain cadmium concentrations (CK, no treatment; Table 2, mg/kg dry weight):
- Huayu 23, high Cd (20 mg/kg soil): grain Cd 13.83 mg/kg
- Huayu 23, low Cd (5 mg/kg soil): grain Cd 8.19 mg/kg
- Huayu 20, high Cd: grain Cd 14.76 mg/kg
- Huayu 20, low Cd: grain Cd 10.20 mg/kg
These values are 2 to 3 orders of magnitude above typical market peanut Cd concentrations because the soil Cd loading was 8 to 160 times the third-level soil Cd pollution standard.
Intervention effects on grain Cd (best treatment, T5: foliar Se plus biochar vs CK):
- Huayu 23, high Cd: grain Cd reduced from 13.83 to 7.21 mg/kg (47.9% reduction)
- Huayu 23, low Cd: grain Cd reduced from 8.19 to 5.27 mg/kg (35.7% reduction)
- Huayu 20, high Cd: grain Cd reduced from 14.76 to 7.37 mg/kg (50.1% reduction)
- Huayu 20, low Cd: grain Cd reduced from 10.20 to 5.53 mg/kg (45.8% reduction)
Cd distribution order in plant tissues under all treatments: leaf > root > stem > grain. Combined foliar Se and biochar increased peanut biomass by 73.44 to 132.41% and grain yield by 0.60 to 3.48 fold, while decreasing grain Cd by 32.81 to 50.07% and increasing grain Se content by 31.57 to 99.75 fold.
Background soil characteristics: pH 8.66, Cd 0.85 mg/kg, Se 0.0025 mg/kg, alkaline hydrolysis nitrogen 67.50 mg/kg, available phosphorus 4.19 mg/kg, available potassium 161.90 mg/kg, organic matter 15.90 mg/kg.
Mechanistic findings
The biochar amendment reduced soil available Cd by adsorption, complexation, and precipitation. Selenium spraying increased glutathione and phytochelatin levels in plant cells, which sequester Cd in vacuoles and reduce its transport to grains. The combination of both amendments had synergistic effects larger than either alone. The study distinguishes two peanut cultivar types: low-Cd-accumulating (Huayu 23) and high-Cd-accumulating (Huayu 20), confirming that cultivar selection is an agronomic lever for reducing grain Cd.
Methods (brief)
Greenhouse pot experiment (polyethylene pots, 18 cm high, 28 cm inner diameter, 6.3 kg soil per pot). CdCl2 added to achieve target soil Cd levels. Base fertilizer: N, P2O5, K2O at 0.15 g/kg soil each; biochar at 1% (w/w) corn stover biochar pyrolyzed at 550 C. Selenium applied as sodium selenite (Na2SeO3) at 0.5 mg/kg soil (soil Se) or equivalent foliar dose (foliar Se). Plants harvested after 5 months; fresh samples dried at 80 C to constant weight. Cd and Se quantified by ICP-MS after acid digestion. Statistical analysis: ANOVA with LSD multiple comparison test (p 0.05), n=3 replicates per treatment.
Implications
This paper documents that peanut grain Cd is reducible through soil amendment and foliar intervention, with the combined foliar Se plus biochar treatment achieving 32 to 50% reductions across cultivars and Cd stress levels. The cultivar difference (Huayu 20 grain Cd consistently 10 to 20% higher than Huayu 23 at the same Cd stress level) confirms that cultivar selection is a viable strategy for reducing Cd in the peanut supply chain. These findings are agronomically relevant for farmers in cadmium-impacted agricultural zones, particularly in parts of China where soil Cd is elevated from industrial or mining sources.
Provenance notes
Open access under CC BY 4.0 (MDPI). Published 16 March 2022. DOI 10.3390/ijerph19063542. Authors are affiliated with Shandong Peanut Research Institute and College of Resources and Environment, Qingdao Agricultural University, China.
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