Estimation of the Nitrogen Liquation of Coated Urea by Kinetic Method

Abstract

The nitrogen liquation of coated ureas (LP 140, LP 100, LPS 140, U-L) were estimated by the kinetic method under the condition of paddy soil The results obtained are summarized as follows : 1) It was found that the nitrogen liquation patterns of coated urea can be obeyed approximately to the first-order reaction model. And five parameters (liquation rate, apparent activation energy for liquation rate, lag-time, apparent activation energy for a lag-time which is dependent on temperature, nitrogen liquation potential) were obtained on the four kinds of coated urea. N=A{1-exp[k(t-TAU)]}, TAU=TAU_1+TAU_2, where N(%) is amounts of liquated nitrogen, A(%) is nitrogen liquation potential, k(d^<-1>) is liquation rate constant, TAU_1 is a lag-time which is independent to temperature, and TAU_2 is a lag-time which is dependent on temperature. Apparent activation energy (E_a) was determined separately for k(E_<a1>) and TAU_2(E_<a2>). 2) The following values were obtained for the characteristic parameters. Liquation rate constant (k) is 0.0177-0.0326 (25℃, d^<-1>), Apparent activation energy for k(E_<a1>) was 69,900-98,000 (J mol^<-1>), and apparent activation energy for TAU_2(E_<a2>) was 114,300-126,800 (J mol^<-1>). 3) There was a lag-time which is dependent on temperature in two kinds of coated urea (LPS 140 and U-L). By the way, LP 100 and LP 140 had only a lag-time which was independent on temperature.