Effects and Mechanism of Continuous Liming on Cadmium Immobilization and Uptake by Rice Grown on Acid Paddy Soils

Abstract

Lime application is the most effective agricultural practice for the reduction of cadmium (Cd) bioavailability in acid soils. This study was conducted to investigate the impact of continuous liming across five consecutive growing seasons on the remediation of Cd in acid paddy soils, as well as rice yield. Two rice cultivars, i.e., Zhuliangyou 819 and Xiangwanxian 12, were cultivated in Cd-contaminated paddy soil for five consecutive growing seasons from 2014 to 2018. The investigated lime levels were 0, 450, 900, 1350, 1800, 2250, 3000, and 3750 kg ha −1. Lime application significantly increased rice yield, soil pH, exchangeable soil Ca 2+ , and rice calcium (Ca) contents; besides, it reduced soil and rice Cd contents. The application of lime at the rate of 1350-2250 kg ha −1 significantly increased rice yield. Under continuous liming, rice yield obviously increased first and then decreased with the cumulative application of lime. The application of a cumulative lime amount of 18,000 kg ha −1 was identified as the critical transition point of soil pH, soil Cd, and rice Cd content. Application of lime up to or above 3000 kg ha −1 per season reduced Cd content in brown rice below 0.20 mg kg −1. The results suggest that the reduction in effective Cd content might be a result of the combined action of exchangeable soil Ca 2+ and soil pH rather than being a direct effect of Ca 2+. Therefore, acid Cdcontaminated paddy fields can realize the safe production of rice by the continuous application of an appropriate amount of lime.

Slaked lime improves growth, antioxidant capacity and reduces Cd accumulation of peanut (Arachis hypogaea L.) under Cd stress

“…Among the soil characteristics, soil pH is considered as an important index that impact Cd uptake by crops, since pH can obviously affect the speciation and solubility of Cd in soil liquids 15 . The use of slaked lime can neutralize excessive H + concentrations in soil solutions and decrease Cd solubility 33 , but there were no observable differences among the different growth stages.

Figure 1 Effects of slaked lime application on soil pH values.

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“…Cd toxicity directly affects net CO 2 assimilation and the transportation of photosynthetic electrons and indirectly reduces chlorophyll concentrations (by indirectly inhibiting chlorophyll biosynthesis) or by preventing the photosynthetic process at different levels of its tissues, the lipid and protein ingredients of thylakoid membranes, and chloroplast fine structure 39 . It has been widely demonstrated that addition of slaked lime to acidic soils very strongly and directly enhances crop productivity by improving the soil physical–chemical and biological characteristics, which ultimately boost the mobility and availability of essential crop nutrients 33 .…”

“…Due to the competition between Ca and Cd for uptake by crop roots, the higher Ca concentrations in lime strongly reduced Cd adsorption by farmland crops. It has been accepted that competition between Ca 2+ and Cd 2+ is one of the crucial influences for suppressing Cd mobility and therefore remarkably enhanced Ca concentrations and decreased Cd accumulations in crops 33 . In addition, increasing soil pH usually results in the formation of more negatively charged sorption sites, hydroxyl species of positive metal ions, and sedimentation of Cd 2+ as Cd(OH) 2 and leads to a reduction in soil Cd availability 12 .…”

“…Higher Ca content in lime reduces crop uptake of accumulated Cd due to competing Ca and Cd uptake in plant roots 56 . Previous studies have indicated that the competition between Ca 2+ and Cd 2+ was one of the crucial reasons for the inhibition of Cd migration, thereby significantly enhancing the Ca content in plants and decreasing the accumulation of Cd in plants 33 , 56 , 57 . Besides, too high soil pH can lead to the dissolution of heavy metals.…”

Effects of water-fertilizer coupling on immobilization remediation technology using sepiolite

“…Numerous soil amendments, i.e., alkaline compounds (Liu et al, 2020), clay minerals (Xie et al, 2018), metal oxides (Lin et al, 2021), organic scraps (Jin et al, 2020) and phosphate sul des (Song et al, 2021) have been proposed and evaluated for their ability to immobilize heavy metals in soil environment. The mechanism involved in Cd adsorption of natural clay mineral containing redox potential (Fulda et al 2013), soil pH (Yin et al, 2017), ion-exchange (Bolan et al, 2013;Luo et al, 2013), surface complexation (Liang et al, 2017) and precipitation reactions (Khaokaew et al, 2011;Agrawal and Sahu, 2006).…”