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Lime-nitrogen (calcium cyanamide, CaCN 2 ) is used as a nitrogenous fertilizer, pesticide, and herbicide. During the process of decomposition of lime-nitrogen in the soil, dicyandiamide (DCD), a nitrification inhibitor, is formed. Therefore, lime-nitrogen application may mitigate nitrous oxide (N 2 O) emission from the soil. We conducted a field experiment to investigate the effect of lime-nitrogen on nitrification and N 2 O emission in fertilized soils, and a soil incubation experiment for further analysis of the effect of the limenitrogen. In a field experiment we compared four nitrogen (N) fertilizer treatments: CF (chemical fertilizer), LN100 (application of all N fertilizer as lime-nitrogen), LN50 (application of 50% of N as lime nitrogen and the remainder as chemical fertilizer), and CFD (chemical fertilizer with DCD). In a soil incubation experiment, we also studied two nitrogen treatments: CF and lime-nitrogen. Soil nitrification activity was lower in the LN100, LN50, and CFD plots than in the CF plot. The duration of this reduction in soil nitrification activity was longer in the LN100 plot than in the other plots. We found an apparent decrease in the N 2 O emission rate between 7 and 14 days after fertilization in the LN100, LN50, and CFD plots compared with that in the CF plot. This period of decreased N 2 O emission paralleled that when DCD was detected in the topsoil layers of the former three plots. Moreover, in the soil incubation experiment, cumulative N 2 O emission was significantly lower in the lime-nitrogen treatment than in the CF treatment, although the difference in cumulative N 2 O emission among the plots was not significant in the field experiment. Correlation analysis suggested that application of lime-nitrogen affects N 2 O emission by controlling both the first (ammonium to nitrite) and the second (nitrite to nitrate) soil nitrification reactions, whereas DCD blocks only the first nitrification reaction.

Melamine belongs to the s-triazine family, and industrially used as raw product in many ways all over the world. Melamine has been reported for human harmful effects and detected from some crops, soil and water. To remove melamine from the polluted environment, the efficient melamine-mineralizing microorganisms have been needed. We newly isolated three melamine-degrading bacteria from the same upland soil sample using soil-charcoal perfusion method. These bacteria were classified as Arthrobacter sp. MCO, Arthrobacter sp. CSP and Microbacterium sp. ZEL by 16S rRNA genes sequencing analysis. Both Arthrobacter species completely degraded melamine within 2 days, and consumed melamine as a sole nitrogen source. Both strains also grew in cyanuric acid as sole nitrogen source, and released small quantities of ammonium ions. These strains are the first identified bacteria that can mineralize both melamine and cyanuric acid as sole initial nitrogen source in Arthrobacter sp. Although ammeline and ammelide intermediates were detected, these strains possess none of the known genes encoding melamine degrading enzymes. Since the Arthrobacter strains also degraded melamine in a high pH liquid medium, they present as potential bioremediation agents in melamine-polluted environments.

We studied the effect of lime-nitrogen (calcium cyanamide, CaCN 2 ) application on the emission of nitrous oxide (N 2 O) from a vegetable field with imperfectly-drained sandy clay-loam soil. Lime-nitrogen acts as both a pesticide and a fertilizer. During the decomposition of lime-nitrogen in the soil, dicyandiamide (DCD), a nitrification inhibitor, is formed, and as a result lime-nitrogen application may mitigate N 2 O emission from the soil. The study design consisted of three different nitrogen-application treatments in field plots with a randomized block design. The nitrogen application treatments were: CF (chemical fertilizer), LN (all nitrogen fertilizer applied as lime-nitrogen), and CFD (chemical fertilizer containing DCD). Soil nitrification activity was lower in the LN and CFD plots than in the CF plots, and nitrification was inhibited for a longer period in the LN plots than in the CFD plots. In the LN plots, N 2 O emission was lower than those of other treatments from 20 to 40 days after fertilization, a period when large peaks of N 2 O emission were observed after rainfall in the CF and CFD plots. ; P < 0.05). Our results suggested that lime-nitrogen application decreased N 2 O emission by inhibiting both nitrification and denitrification.