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Plant Form Control of Bedding Plants by Irrigation and Fertilizer Application
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Release of nutrients from resin-coated fertilizers was studied in atmospheres of different water vapor pressures. The coated fertilizers tested were : urea coated with thermoplastic resin or thermosetting resin ; and a NK mixed fertilizer coated with thermosetting resin. The water vapor pressures were adjusted by placing the coated fertilizers in bottles containing saturated solutions of different salts. The rates of nutrient release were simulated with the kinetic method proposed by SUGIHARA et al. (1986) and with the model proposed by KOCHBA et al. (1990). 1) The nutrient release from the resin-coated fertilizers was proportional to the differences in water vapor pressures between the inside and outside of the coated fertilizers, regardless of the different coating materials. 2) The release of nutrients fitted well either to the model by KOCHBA et al. or to the curves simulated with the method by SUGIHARA and KONNO. We did not find and conceptual differences between these two methods, and concluded that the temperatures firstly affected the vapor pressures, and the latter then directly controlled the release of nutrients from the coated fertilizers.
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_ ) and TAU_2(E_ ). 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_ ) was 69,900-98,000 (J mol^<-1>), and apparent activation energy for TAU_2(E_ ) 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.