EFFECTS OF FLOODING AND LIMING ON THE PROMOTION OF MINERALIZATION OF SOIL ORGANIC NITROGEN

Incubation and pot experiments were carried out for investigating the effects of flooding and limiting (CaCO3) on the mineralization of soil organic N. The pH values of the flooded soil were hardly affected by liming, while those of the nonflooded soil increased with the amount of applied CaCO3. Flooding alone increased the soil pH to a value above 6 and promoted the mineralization of soil organic N. Nitrogen mineralization in the nonflooded soil was also promoted when the soil pH was brought to a value above 6 by liming. Rice grown in the flooded soil absorbed a larger quantity of soil N than Job's tears (an upland crop) grown in the same nonflooded soil when the amount of applied CaCO3 was below 0.2%. However, the absorption of soil N by Job's tears was enhanced when the amount of applied CaCO3 exceeded 0.4%, and thus, Job's tears absorbed a larger quantity of soil N than rice at 0.6% CaCO3 application. These results indicate that either flooding alone or liming of nonflooded soil enable to increase the soil pH as well as promote the mineralization of soil organic N and the plant uptake of soil N.