Microbial distribution and function across wheat rhizosphere with oxamide and ammonium sulfate as N sources

Analysis of the effect of slow-releasing N fertilizers on microbial paramet ers of the rhizosphere soil is essential for their effective use. This inve stigation revealed the comparative effects of oxamide and ammonium sulfate as different N sources on some selected microbial parameters as well as the pH in the rhizosphere of wheat (Triticum aestivum cv. Nourin No. 61). The study was conducted on a Japanese upland alluvial soil using a rhizobox sys tem. In the central compartment (CC) of the rhizoboxes treated with oxamide and ammonium sulfate, four wheat seedlings were grown for 53 d. In either of the treatments, the pH of the rhizosphere soil increased with the increa se in the distance from the CC. In contrast, nitrate production, bacterial and fungal numbers, microbial biomass nitrogen, and beta -acetylglucosamini dase activity decreased with the increase in the distance, with the highest values of the respective parameters being recorded in the CC. However, rem arkable changes of these microbial parameters were found within a distance of 1-2 mm from the CC to the distant compartments. Thus the results indicat ed that pH, bacterial number, and nitrate production were high in the oxami de treatment. In contrast, higher fungal number, microbial biomass N, and b eta -acetylglucosaminidase activity were associated with the ammonium sulfa te treatment. It was assumed that the significant (p<0.05) effect of the rh izosphere on microbial activities varied with the treatments.