Geochemical Characteristics of Soil Selenium and Influencing Factors of Selenium Bioavailability in Rice Root Soils in Qingxi Area, Ganxian County, Jiangxi Province

BACKGROUND The south of Jiangxi Province is a typical geographical distribution area of selenium deficiency. However, some research results in recent years indicate that the rice has high selenium content. The reasons for inconsistency about selenium enrichment between soil and rice is still not clear. It is important to discuss the characteristics of selenium content in soil and crops for the utilization of selenium-enriched land resources and the development of selenium-enriched agricultural products. OBJECTIVES To understand the reasons of inconsistency about selenium content between soil and crops in Qingxi area, Ganxian County. METHODS Samples of 1734 topsoil, 57 sets of rice and corresponding root soil were collected from Qingxi area. The content of selenium and its speciation geochemistry in these samples were determined by inductively coupled plasma-mass spectrometry and inductively coupled plasma-optical emission spectrometry. The selenium content and distribution characteristics in soil and rice were systematically analyzed, and the influencing factors of selenium bioavailability in root soil were discussed. RESULTS The topsoil in the area was dominated by selenium-enriched soil and selenium-sufficient soil. The selenium content in soil were closely related to soil parent rocks. The rules of soil selenium content in different parent-rock areas were as follows: Paleozoic metamorphic rocks>Mesozoic granite>Neoproterozoic metamorphic rocks>Mesozoic terrigenous clastic rocks>Cenozoic quaternary. The selenium content in root soil were lower than 0.4mg/kg, and selenium-enrichment rate of rice was 64.91%, indicating that it had a high capacity to enrich selenium in the soil (enrichment coefficient was 20.05%). When the selenium content in root soil was more than 0.25mg/kg, the rate of selenium-enrichment reached up to 70.83%, and would produce high-quality selenium-enriched rice stably. The form of selenium was the main factor to influence selenium bioavailability in soil. When the content of total selenium in soil was low, water-soluble, ion-exchangeable and carbonate-bound selenium accounted for a high proportion, which enhanced the bioavailability of selenium. The weak ability of selenium adsorption by low content organic matter was also an important factor for the high bioavailability of selenium. CONCLUSIONS Selenium content in soil, soil physical and chemical index and the influence of selenium form on bioavailability of selenium in soil should be comprehensively considered when exploiting selenium-enriched soil and selenium-sufficient soil in Qingxi area, Ganxian County. It is beneficial to scientifically guide the delimitation of natural selenium-enriched land and develop selenium-enriched rice.