[Effects of selenium fertilization on selenium availability in rice soil.]

Selenium (Se) is easy to be fixed in acidic rice soil of South China, and thus its availability is low. The aim of this study was to investigate the influence of Se fertilizer on Se availability in rice rhizosphere and non-rhizosphere soils. The results showed that Se application increased yield and rice Se concentration. The water soluble, exchangeable, Fe/Mn oxide-bound, organic matter/sulfide-bound, and residual Se contents of the rhizosphere soil were lower than those of the non-rhizosphere soil. There was no significant difference in the migration coefficient of Se between the rhizosphere and non-rhizosphere soils. Se application had no significant effect on the migration coefficient of Se between roots and leaves but improved its migration coefficient between leaves and grains. The secretion of organic acids was increased by the application of 0.5 mg·kg-1 and decreased by the application of 1.0 and 5.0 mg·kg-1 Se. The secretion of organic acids had no significant effect on the rhizosphere soil pH. The pH of rhizosphere soil was higher than that of the non-rhizosphere soil, while the application of Se decreased the pH of the rhizosphere soil. With the increases of Se application, the intensity of the infrared absorption of clay mineral (kaolinite) in the rhizosphere soil showed an increasing trend. In this study, most of the Se was transformed into forms that were difficult to be absorbed and utilized by rice and difficult to move to rhizosphere soil. The enhancement of soil Se availability following the secretion of organic acids was not due to its effects on soil pH.硒在华南稻区酸性土壤中极易被固定使其有效性较低.本研究旨在通过盆栽试验,探明施用硒肥对水稻根际和非根际土壤硒有效性的影响.结果表明: 施硒能提高水稻产量,增加籽粒硒含量;水稻根际土壤中水溶态硒、交换态硒、铁锰氧化物结合态硒、有机物-硫化物结合态硒和残渣态硒含量均低于非根际土壤.各施硒处理之间,根际和非根际土壤中硒的迁移系数没有显著差异;施硒对根和叶片之间硒的迁移系数也没有显著影响,但是施硒提高了叶片和籽粒之间硒的迁移系数.施用0.5 mg·kg-1硒增加了水稻根系有机酸的分泌,而施用1.0、5.0 mg·kg-1硒则降低了有机酸的分泌.根系有机酸的分泌对根际土壤pH值影响不大,根际土壤pH值反而高于非根际土壤,但施硒显著降低了根际土壤pH值.随着施硒水平的提高,根际土壤黏土矿物(高岭石)的红外吸收光谱不断增强.施入土壤中的硒多转化为水稻难以吸收利用的形态,且不易向根际移动.根系分泌的有机酸也并不是通过影响土壤pH值来提高土壤硒的有效性.