Cadmium Immobilization in the Rice - Paddy Soil with Biochar Additive

Abstract

Cadmium (Cd) is toxic for humans, but its effects on the yield and quality of rice under contaminated irrigation conditions remain uncertain. In this study, paddy soils in the Red River Delta (Vietnam) were selected for experiments with the purpose of understanding the effects of Cd contaminated irrigation water on growth, yields, and grain Cd accumulation. In addition, biochar was produced from rice husk (BRH) and rice straw for preventing Cd infiltration into rice was also studied in this experiment. A field experiment was established with applicated BRH and straw into polluted paddy soil, as a result the Cd content in grains reduced significantly. The Cd contaminated soil was added to the BRH and rice straw (RS) with six ratios, including: (1) RS 2.5%, (2) BRH 2.5%, (3) RS-BRH: 1.25-1.25%, (4) RS 5.0%, (5) BRH 5.0%, (6) RS-BRH: 2.5-2.5%, (w:w). Besides, three content levels 0.01-0.05-0.5 mg/L of Cd in irrigation water were applied throughout crop season. The results showed that the Cd accumulation in rice was in the following order: roots > stems > seeds. With 3 contaminated irrigation levels which were applied, the Cd concentrations of 0.05 mg/L and 0.5 mg/L affected plant height and yield. However, the Cd content in grains under contaminated soil condition can be controlled from 82.47-83.94% by applying a BRH ratio from 2.5-5% (w:w).

Potential of Irrigation and Biochar on Reduction Methane Emission and Leaching Nitrate into Groundwater

“…Soil samples were air dried before passing through a 2-mm sieve, and about 10 kg of soil was transferred into a pot with a 30 cm diameter and higher of 40 cm with one rice plant/pot. The biochar ratio was chosen from our previous study of biochar application in the paddy field (1, 2.5, 5%, w:w) (Vu et al, 2022) and based on many tests before designing the experiment. The treatment with a biochar under 1% ratio was not significantly changed and a biochar over 5% ratio reduced grain yield.…”

“…Furthermore, some irrigation systems without water resources must receive contaminated domestic and livestock wastewater to provide for paddy systems. Many irrigation systems polluted nitrogen (N) with content over standard of 2.48-4.15 times such as Bac Hung Hai, Bac Duong and Cau Bay rivers (Vu et al, 2022). Besides growing rice is a major contributor to human-made greenhouse gases, releasing 6 to 11% of all methane emissions from our activities globally (Smith et al, 2021).…”

“…Biochar from agricultural by-products with high porosity and good water-holding capacity was widely used to treat N in wastewater and improve soil moisture and nutrition (Diep et al, 2020). Biochar from rice husk with low-cost was produced from the pyrolysis of rice husk under limited or no oxygen (Vu et al, 2022) to evaporate organic substances to keep on the porous surface with components K + , Na + , Ca 2+ , Mg 2+ carry a positive charge (Konneh et al, 2021). The NO 3 adsorption process occurs by electrostatic attraction including negatively charged NO 3 attracted to the surface of biochar (Vo et al, 2021;Gai et al, 2014).…”