Effects of fertilizer and manure application on L-glutaminase and L-asparaginase activities on volcanic ash soil and gray lowland soil were examined. The activities were estimated by using the indophenol method. This involved the colorimetric estimation of NH4+ released from L-glutamine or L-asparagine catalyzed by the enzymes, when the soils were incubated with 0.25 M L-glutamine or L-asparagine in 0.1 M phosphate buffer (pH 7.6) and toluene used as a germicide. Both L-glutaminase and L-asparagine activities were the largest in the farmyard manure plot (OM), followed by the chemical fertilizer plot (CF) and the plot without fertilizer application, hereafter referred to as “no fertilizer plot” (NF).
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