EFFECT OF ORGANIC RESIDUE AMENDMENT ON MINERALIZATION OF NITROGEN IN FLOODED RICE SOILS UNDER LABORATORY CONDITIONS

This study was undertaken to assess the mineralization of nitrogen (N) in rice soils amended with organic residues under flooded condition. A lab incubation study with a 3x3 factorial design (two replications) was conducted with three rice soils (Joydebpur, Faridpur, and Thakurga on) receiving the following treatments: 1) control, 2) rice straw (Ory za sativa L.), or 3) pea vine (Pisum sativum L.). The organic residue (25 mg straw g(-1) soil) was mixed with soil and glass beads (1:1, soi l to beads ratio), and transferred into a Pyrex leaching tube, flooded and then incubated at 35 degrees C for up to 12 weeks. The soils in t he leaching tubes were leached (while maintaining flooded condition) a t 1, 2, 4, 8, and 12 weeks with deionized water for determination of N H4-N, NO3-N, pH, and Eh. Nitrogen mineralization in soils amended with rice straw was somewhat different than that of soils treated with pea vine. Soil treated with rice straw had a higher N mineralization rate than soils treated with pea vine, which was due to a lower carbon (C) :N ratio for rice straw. The potentially mineralizable N pool (N,) in soils amended with rice straw and pea vine under flooded conditions, e stimated using a Ist order exponential equation, were 7 to 15 times, a nd 3 to 9 times greater for rice straw N,values and pea vine, respecti vely, than the control. The M, values for unamended soils ranged from 0.35 to 0.52 mg N kg(-1) wk(-1) and rice straw and pea vine treated so ils were from 0.75 to 1.22 and 0.46 to 0.58 mg N kg(-1) wk(-1). The lo wer N-o and K-N values in pea vine treatments suggested there was grea ter immobilization of N than in rice straw treatments.