Phytotron studies to compare nitrogen losses from corn-planted soil by the 15-N balance or direct dinitrogen and nitrous oxide measurements

摘要

Containers filled with soil mixed with potassium nitrate highly enriched in15N were planted with corn (Zea maysL.) and kept in a phytotron under controlled conditions for 79 days. Soil water content was normally maintained at exactly 60 water-holding capacity (−33 kPa), but it was increased several times to 85 (−5 kPa) for short periods to favour denitrification. The soil headspace was sealed from the phytotron atmosphere and aerated by a continuous stream of air. Nitrous oxide emission was measured by estimating the N2O concentration differences in the air entering and leaving the containers. Emission of N2was estimated by mass spectroscopy from changes in the N2composition in the temporarily enclosed soil headspace. Both methods were carefully checked for accuracy by different tests. At specific times during the experiment the distribution of15N between plants and soil was determined and a15N balance established. Emission of N gases peaked at times of increased water content and reached maxima of 149 and 142 μg N pot−1day−1for N2O and N2, respectively. While N losses of 5 ± 2 were indicated by the15N balance, only 1.1 ± 0.3 loss from 2.7 g applied N was estimated from the N2O and N2measurements after 79 days. Possible reasons for these differences are