Characteristics of Three Organic Fertilizers and Their Influence on the Mobility of Cadmium and Arsenic in a Soil-Rice (Oryza Sativa L.) System

Overview

Tan and colleagues compared human-manure, mushroom-residue, and soybean-meal organic fertilizers as amendments for low-level cadmium (Cd)/As-contaminated paddy soil planted with rice. The source is mitigation evidence: it reports how amendment choice changed soil leachability and rice root/shoot uptake, but it does not report consumer rice grain concentrations and should not be pooled as rice occurrence data.

Key numbers

Amendment design

The pot experiment used 1 kg soil per pot and three replicate pots per treatment. Each fertilizer type was applied at 0.50%, 1.00%, and 2.00% addition rates; the untreated control received 0%. The rice plants were grown from May 22 to July 12 and harvested at the tillering stage, so the plant measurements are roots and shoots rather than harvested grain.

Organic fertilizer characteristics

Table 2 reports elemental content of the three organic fertilizers. Mushroom-residue organic fertilizer (MO) had the highest carbon, hydrogen, and oxygen content: C 37.03%, H 4.76%, and O 50.73%, compared with C 16.77%, H 1.96%, O 20.52% for human-manure fertilizer and C 10.05%, H 1.27%, O 20.58% for soybean-meal fertilizer. MO also had the largest BET surface area, 14.60 m2/g, compared with 1.10 m2/g for human-manure fertilizer and 0.87 m2/g for soybean-meal fertilizer.

Soil leachability

Figure 4 reports TCLP-extractable Cd and As in soil. The untreated control TCLP-Cd concentration was 513.67 ug/kg. The lowest TCLP-Cd values were under medium-rate and high-rate mushroom-residue fertilizer: 425.33 ug/kg and 389.33 ug/kg, reductions of 17.20% and 24.21% from the control. For TCLP-As, mushroom-residue and soybean-meal fertilizers significantly reduced leaching concentrations; MO reductions ranged from 9.10% to 19.04%, while soybean-meal reductions ranged from 9.82% to 36.93%. Human-manure fertilizer increased TCLP-As in soil.

Rice uptake

Figure 5 reports Cd and arsenic (As) concentrations in rice roots and shoots. Compared with the untreated control, mushroom-residue fertilizer reduced rice-shoot Cd by 23.35%, 34.24%, and 44.36% at the low, medium, and high application rates. The same MO treatments reduced rice-shoot As by 11.30%, 16.19%, and 17.61%. Soybean-meal fertilizer reduced shoot As by 17.75%, 15.97%, and 18.24% across low, medium, and high rates, but the authors did not report the same simultaneous Cd benefit for soybean meal.

Accumulation factors

The authors calculated bioaccumulation factors and transport factors from soil, root, and shoot concentrations. They report that mushroom-residue fertilizer reduced both BCF and TF values for Cd and As relative to the untreated control, while human-manure fertilizer mainly reduced Cd indices and soybean-meal fertilizer mainly reduced As indices.

Methods (brief)

The soil came from the paddy-soil cultivation layer in Liuyang City, Hunan Province, China. Organic fertilizers were prepared from human manure, mushroom waste, and soybean meal. Soil total Cd/As and fertilizer metal concentrations were measured after HNO3/HF digestion in a closed high-pressure reactor at 160 degrees C for 10 h. TCLP-Cd and TCLP-As followed the USEPA TCLP method, and concentrations were measured by ICP-OES. Rice plants were separated into roots and shoots after harvest; the paper reports total Cd and total arsenic, not inorganic arsenic speciation.

Related evidence

• Agronomic mitigation
• Remediation evidence — drivers and interventions
• Arsenic
• Cadmium
• Rice
• Testing

Update history

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