The turnover of 15N labelled straw and FYM in a rice-rice rotation under flooded condition at two locations

The combined recovery of N from straw by two crops without application of fertilizer N was 20.6% at Cuttack and 7.2% at Hyderabad. The total recovery increased nearly two-fold when fertilizer N was applied to both crop seasons. On an average, about 57 to 62% of the straw N was left behind in the root zone at the end of the experiment at Hyderabad. The highest recovery (i.e. 82%) of N from farm yard manure (FYM) at Cuttack occurred when N fertilization was delayed until the second season. Under submerged conditions, addition of straw immobilized about 4% of the fertilizer N at Hyderabad and increased its incorporation in the hexosamine fraction of the soil N. The mineralization of straw N and immohilization of fertilizer N by added straw in this field investigation employing normal application rate and physical condition of the straw were not comparable with those reported from greenhouse experiments elsewhere. (author)