Direct Evidence of Foliar-absorption of Urea : Synthesis and Utilization of N-15 Rich Urea

Abstract

In this paper, a preparatory method of synthesizing N-15 rich urea and the mechanism of foliar absorption and translocation of this heavy urea in wheat plant are released. 1. Synthesis of N-15 rich urea Aiming at an economical use of ammonia and concentrating N-15 at the sametime, by letting N-15 in both-NH_2 groups of urea as much as possible, the authors adopted a wet method in which N-15 rich ammonia passes through the aqueous or alcoholic solution of diphenyl-carbonate. At the first step, diphenyl-carbonate was prepared from Na-phenolate aq. and phosgen, then recrystalized from alcohol. The yield was nearly quantitative. M. p. 80°. To synthesize urea from diphenyl-carbonate and ammonia, an apparatus was set as shown in Fig. N^*H_4NO_3(N-15 atom : excess 1.75%) in a three-necked flask was decomposed with NaOH aq., which was led through a separatory funnel fitted to one of the side necks. Evolved ammonia passed through the reaction tube containing calculated quantity of diphenyl carbonate in aqueous or alcoholic cold solution. When ammonia had been absorbed thoroughly, the reaction tube was removed, then stoppered tightly or fused, left it overnight, then shaken for a whole day at room temperature. After 48 hours, the contents separated in two layers of liquid. Then the reaction tube was opened and the products were separated and washed with ether and water. The aqueous solution and washings were collected, washed with ether and benzol to remove phenol, phenyl-carbamate, and diphenyl-carbonate, then evaporated to dryness under a reduced pressure. Obtained crude urea was recrystalized from absolute alcohol and dry acetone. By this procedure ammonium-carbonate were removed. Recrystalized heavy urea melt at 133°; did not show any depression in mixed sample and it was ascertained that its N-15 content was 2.13% of the total nitrogen, The yield was 72% on the basis of ammonia from ammoniumnitrate employed. 2. Foliar absorption and translocation of urea in wheat plants There are yet some doubt in the practical use of foliar application of urea to gramineae, but some research workers have reported fairly good results in wheat experiments about the application during late stage of growth or after the head sprouting period. As a preliminary work studying the assimilation mechanism of foliar absorbed urea, the authors cultivated wheat plants with nonnitrogen nutrient solution and applied the above heavy urea in 2% solution for 5 days just before the head sprouting. Two weeks later, plants were harvested and analized for their nitrogen contents by GANNING'S alteration; and atomic ratio of N-15 in N_2 gas which was prepared from this ammonia, was determined by mass spectroscope. Obtained results are shown in Table. From this, it has been revealed that the following percentage of the applied nitrogen in urea, was absorbed and translocated to each part of plant respectively : 8.6 % to the ear, 2.7% to the boot-leaf, 8.5% to the stem and root, 21.5% to the leaf-sheath of the applied leaf. Under this experimental conditions, the ratio of translocated urea-origin nitrogen to the total nitrogen was about 20% in the stem and root, ear, and boot-leaf.