Abstract
The loss of nitrogen by direct volatilisation of ammonia transformed from urea was studied in relation to the amount of urea applied, the method of urea application and to the amount of lime applied under upland and waterlogged soil conditions. lOO g. of air dried alluvial soil in an Erlenmeyer flask was added with 15 or 60 mg N as urea, from O to 180 mg of calcium oxide and was incubated at 30℃ for three weeks as shown in Fig. 1. Ammonia free air was passed through the flask and the ammonia volatilised was collected by standard acid. The results are shown in Table 1 and 2. The loss amounted to 2.2〜0.0 mg N per 100 g. air dry soil under the upland soil condition, whereas under the waterlogged it increased to 5.3〜0.1mg. For the increase by waterlogging is primarily responsible the higher soil pH on waterlogging as compared to upland. In general, the loss increased as the amount of nitrogen and lime applied increased respectively and was more pronounced in the surface application of urea than in the total layer application. The loss appears to be primarily dependent on the concentration of the ammoniacal nitrogen transformed from urea and soil pH. In view of the recent increase of the use of urea fertiliser in Japan, discussion on its practcial application particularly as top dressing was made on the basis of the laboratory results obtained. Even in extreme cases, it is supposed that only a few percents of the applied nitrogen will be lost by direct volatilisation provided that the soil is not too alkaline.
