Abstract: By incubation experiment with luvisol,the influences of rare earths on the trans formations of simultaneously applied urea in the soil were studied.When the dosa ge of applied rare earths was more than 10mg穔g^-1 oven dried soil,the co ncentration of urea derived exchangeable NH₄⁺-N in the soil significantly increased and the increase appeared the dose dependent relationship.During diff erent periods of soil incubation,the concentration of soil urea derived (NO₃++NO₂+) N decreased with increasing dosage of applied rare earths.In addi tion,at the dosages more than 50mg穔g^-1 oven dried soil,a significant r ed uction of this N form in the soil appeared.Applying rare earths could cause an i ncrease in the concentration of soil available nitrogen,mainly due to a substant ial NH₄⁺ N pool available in the soil. Considering the variation of pH valu es in the soil,it is concluded that the application of rare earths at a dosage h igher than 10mg穔g^-1 oven dried soil,can retard the hydrolysis of simult aneously applied urea in the soil and inhibit the oxidation of its hydrolyzed NH₄⁺-N.This indicates that a joint application of urea and rare earths can be beneficial to the retention of applied urea in soil.

Key words: Rare earths, Urea, Mineral N, Nitrification, Lu visol