Lanthanum uptake from soil and nutrient solution and its effects on plant growth

In view of restrictions in the application of antibiotics in animal production, Lanthanum (La) is intended to be introduced as a new growth promoter for pigs. Because most of the supplied La is subsequently excreted, it will be found in organic fertilizers which are applied to agricultural land. Thus, we examined the effect of lanthanum on the growth and La contents of plants in nutrient solution and in soils as well as its extractability from different soils. In nutrient solutions with concentrations of available La of up to 20 μmol L^-1, shoot growth of bush bean was markedly reduced by up to 60% of the control at 20 μM La. By contrast, growth was not affected in maize. Lanthanum was mainly accumulated in the roots, but maize shoot contained considerable amounts of La as well. In contrast to nutrient solution, shoot growth of bush bean and spinach in soils supplemented with La up to 360 μmol kg^-1 (50 mg kg^-1) was not decreased. In contrast to spinach, bush bean shoots showed an increased La content at the highest La level. Extractability of La with 0.1 mol L^-1 acetic acid from 12 different soils previously spiked with La was related mainly to soil pH, CEC, and C_org. We therefore conclude that except of strongly acidic conditions, the application of La-containing organic fertilizers does not represent a risk for plant growth for the next over 100 years, provided that the recommended doses of feed supplementation is not increased.