Efficiency evaluation for remediating paddy soil contaminated with cadmium and arsenic using water management, variety screening and foliage dressing technologies.

Paddy soils in many regions of China have been seriously polluted by multiple heavy metals or metalloids, such as arsenic (As), cadmium (Cd) and lead (Pb). In order to ensure the safety of food and take full advantage of the limited farmland resources of China, exploring an effective technology to repair contaminated soils is urgent and necessary. In this study, three technologies were employed, including variety screening, water management and foliage dressing, to assess their abilities to reduce the accumulation of Cd and As in the grains of different rice varieties, and meanwhile monitor the related yields. The results of variety screening under insufficient field drying condition showed that the As and Cd contents in the grains of only four varieties [Fengliangyouxiang 1 (P6), Zhongzheyou 8 (P7), Guangliangyou 1128 (P10), Y-liangyou 696 (P11)] did not exceed their individual national standard. P6 gained a relatively high grain yield but accumulated less As and Cd in the grains despite of the relatively high As and Cd concentrations in the rhizosphere soil. However, long-playing field drying in water management trial significantly increased Cd but decreased As content in the grains of all tested three varieties including P6, suggesting an important role of water supply in controlling the accumulation of grain As and Cd. Selenium (Se) showed a stronger ability than silicon (Si) to reduce As and Cd accumulation in the grains of Fengliangyou 4 (P2) and Teyou 524 (P13), and keep the yields. The results of this study suggest that combined application of water management and foliage dressing may be an efficient way to control As and Cd accumulation in the grains of paddy rice exposing to As- and Cd-contaminated soils.

Root application of selenite can simultaneously reduce arsenic and cadmium accumulation and maintain grain yields, but show negative effects on the grain quality of paddy rice.

Most current technologies can hardly simultaneously reduce the accumulation of arsenic (As) and cadmium (Cd) in crops. In this study, root application of selenite [Se (IV)] and selenate [Se (VI)] was used to assess their abilities to reduce the accumulation of As and Cd, and maintain the yields and quality of rice grains. The results show that Se (IV) showed a weaker ability than Se (VI) to maintain the grain contents of many essential elements, but a stronger ability to decrease As and Cd contents in rice grains, and maintain the yields, photosynthesis rate and stomatal conductance, and increase the grain contents of several amino acids (AAs), total Se, selenomethionine (SeMet) and selenocysteine (SeCys). The best outcomes resulted at a relatively high application of 5 mg kg-1 Se (IV), reflecting in the highest total Se, SeCys and SeMet content (14.95, 118.70 and 864.73 µg kg-1, respectively) in the grains, highest grain yield, and lowest grain As and Cd content (0.36 and 0.07 mg kg-1, respectively). In addition, the application of 1-5 mg kg-1 Se (IV) seemed to facilitate the formation of SeMet in the grains, but most inorganic Se in the grains were transformed into SeCys and SeMet under Se (VI) treatments. This study provides a new idea to resolve the problems of high accumulation of As and Cd in rice grains and insufficiency of Se intake in China.

[Effects of amino acid-N and ammonium-N on wheat seedlings under sterile culture].

The dry weight, total N, and glutamate-oxaloacetate transaminase(GOT) and glutamate-pyruvate transaminase (GPT) activities in roots and leaves of wheat seedlings (Triticum aestivum) grown with ammonium sulfate or amino acids (glycine, glutamate or lysine) were studied under sterile sand culture. The results showed that both NH4(+)-N and amino acid-N could be absorbed by wheat. The total N of plant fed with NH4(+)-N was similar to that fed with amino acid-N. The dry weight of plants grown 30 days with glycine or glutamate was significantly higher than that of plants grown with NH4(+)-N or free N. The dry weight of ammonium treatment was similar to that of lysine treatment or free N. NH4(+)-N in concentration of 0.7 mmol.L-1 significantly increased GPT activity of roots, but had no significant effects on leaves or roots treated 6 h in concentration of 35.7 mmol.L-1. Different species or concentrations of amino acids had different abilities to increase the GOT or GPT activity in leaves or roots.

[Effect of phosphorus on arsenic adorption by three different soils].

The effect of phosphorus on arsenic adsorption by yellow soil, red soil and brown soil was studied using batch experiment. The results indicated that the arsenic without P amendment adsorption capacity of three tested soils was yellow soil > red soil > brown soil. The maximal adsorption capacity of yellow soil and red soil was decreased with 60 mg.kg-1 phosphorus added, and that of brown soil was increased with 20 mg.kg-1 phosphorus added. The arsenic adsorption capacity of three soils was greater when P: As = 1:2 than that when P: As = 1:1 and P: As = 2:1, and the differences between P: As = 1:1 and P: As = 2:1 treatments were not significant. Observations could be better fitted by Langmuir equations.