Abstract
Nitrogen-absorbing activity of Crotalaria juncea L. and Zea mays L. grown as a cleaning crop in nitrogen-accumulated soil was evaluated in an experiment conducted with 200 L-volume containers filled with volcanic ash soil using the 15N dilution technique. At 60 days after sowing, the dry weight and total nitrogen content of the tops in both plant species under an excess nitrogen condition (70 g N/m2) were significantly higher than those under a low nitrogen condition (3 g N/m2). Under the excess nitrogen condition, the dry weight and total nitrogen content in the tops of C. juncea were 28% and 55% of those in Z. mays, respectively. The proportion of the fixed nitrogen to total nitrogen was approximately 75% in C. juncea under the low nitrogen condition, whereas it was less than 1% and nodulation was negligible under the excess nitrogen condition. The amount of nitrogen absorbed by C. juncea under the excess nitrogen condition was approximately 35g/m2. The C-N ratio, which is one of the parameters of the decomposition rate of organic matter, was approximately 15 for the tops of C. juncea under the excess nitrogen condition. The results showed that C. juncea absorbed a large amount of nitrogen derived from soil and fertilizer under an excess nitrogen condition, and also suggested that yielded foliage would be useful as incorporating material.
