The Ecological Effect Of Rare Earth Elements And Available State Of Rare Earth Elements In Soil

Soil pot experiments were carried out to study the ecological effect of rare earth elements(REs) on rice in yellow brown earth. The ryegrass was used as an indicator plant to study the relationship between chemical available REs and REs absorbed by plant in four different soils and to study the concentrations threshold in soils. Some useful data were provided in this paper for clarifying the mechanism of transference, transformation and enrichment of REs in the ecosystem of farmland, for prevention of environment pollution by REs and for the application of RE in agriculture. The results are presented as follows: The REs application within a proper range of concentration was favourable for plant growth but under too high concentration it was harmful. The growth effect curves differ obviously with the growth and development status of plant, plant species and soil types. The REs concentrations in rice and ryegrass growing in yellow brown soil were at a similar level. The REs concentration in ryegrass growing in four soils differed from each other. The REs absorbed by plant were mainly maintained in roots. The concentrations in the underground part rised with increment of applied RE. The concentration threshold in plant were varied with the soil types. For ryegrass, it was 127.10 Li g/g in yellow brown earth, 10.82 Li gig in yellow fluvo- aquic earth , 13.46 ii g/g in luvic chernozem soil and 232.62 ii g/g in red earth respectively. For rice, it was 173.20 ii g/g in paddy soil(yellow brown earth). The concentration of the light REs in plant was much higher than that of heavy REs. In the transferring process from roots to upper parts the transfer-capacity of heavy REs was larger than light ones. Differentiation of single REs in soils occurred during the process of being available in soil. Differentiation of single REs also occurred in the process of 125 plant uptake and transference toward aboveground parts. 1 molIL NH4NO3(pH 7.0) was used as chemical extractant for determining the content of available REs in acidic, neutral and limestone soils. The concentration threshold of available REs favourable for ryegrass growth was 1.41 Sug/g in yellow brown soil, O.249ug/g in yellow fluvo-aquic soil, 0. lé©©ug/g in luvic chemozem soil and 75.494 ug/g in red soil. The concentration threshold of available REs favourable for rice is 7.786ug1g in paddy soil(yellow brown soil).