Available Organic Carbon Controls Nitrification and Immobilization of Ammonium in an Acid Loam-Textured Soil

Abstract

Effect of organic-C on immobilization and nitrification patterns in acidic soil was examined during 20 weeks incubation period to verify if organic amendments such as composted material can increase soil retention of N by stimulating microbial immobilization of . Four treatments were laid out: control without fertilizer N and glucose (treatment code: S), ammonium sulfate (SN), ammonium sulfate with single glucose at the commencement (0 week) of incubation (SNG), and ammonium sulfate with double glucose at 0 and 4 weeks of incubation (SNGG). Glucose application (SNG) significantly increased microbial immobilization of within 1 week of incubation over SN. Immobilization was followed by remineralization thereafter; however, second-application of glucose (SNGG) restored immobilization. At the same time, nitrification was significantly inhibited by glucose application as indicated by consistently low concentration in SNG and SNGG soils, suggesting that microbial assimilation of is predominant compared to nitrification when available C-source is abundant. These results suggest application of chemical fertilizer-N with organic amendment would have beneficial effect on soil-N retention and environmental conservation by reducing production of which is likely to be lost through leaching or denitrification.