Soll organic matter and nitrogen contents of saga polder rice fields: Changes with depth and time

Effect of long-term application of organic residues on the distribution of organic matter and nitrogen in some rice soil profiles

“…This finding is in opposition to the usual observations that organic C/total N ratios decrease with depth (10). The decrease at the lower depth horizon reflects the fact that the organic C content of the soil was reduced slightly faster than that of total N. a Calculated on the basis of the assumption made in the text.…”

“…Organic N was obtained by calculating the difference between total Nand total inorganic N (extractable inorganic N fraction+fixed NH,+-N). The amounts of NH, + -N present in the sample before and after incubation under anaerobic conditions for a period of 4 weeks at 30°C were determined, and mineralized N was calculated from the difference (10). All values reported here are averages of triplicate determinations expressed on a moisture-free basis, the moisture being determined from the loss in weight after drying at !05°C for 24 h.…”

“…According to our previous report (10), this evidence probably suggests that the mineralization process is affected by the interaction of some organic N compounds with clay minerals which may thus be protected against microbial attack in the soil. Indeed, the relation for the mineralized N did not constrain the regression line to pass an origin (Fig.…”