PJB-2009-151
EFFECT OF DICYANDIAMIDE ON MICROBIAL ACTIVITY IN THE RHIZOSPHERE AND BULK SOILS UNDER COTTON
REHMAT ALI1, JAVED IQBAL2, UM-E-ROBAB1 AND TARIQ MAHMOOD1*
Abstract
Study was conducted under greenhouse conditions to elucidate the effects of dicyandiamide (DCD, a nitrification inhibitor) on microbial activity in the root-zone and bulk soils under cotton fertilized with two levels (60 and 120 mg kg–1) of urea-N. Dicyandiamide applied @ 15–30 mg kg–1 effectively inhibited nitrification at relatively high soil temperatures (19.5–33°C) prevailing during the four-week experiment period by the end of which 25–46% of the mineral N was found in NH4+ form in DCD-treated pots. Application of DCD caused a minor leaf tip necrosis but without negative effects on the biomass and N yields. Averaged across treatments, microbial activity (aerobic and anaerobic soil respiration, denitrification potential, microbial biomass carrying capacity and dehydrogenase activity) was highest in the root-zone soil followed by planted-bulk and unplanted soils. Averaged across soil types, microbial activity parameters generally showed higher values in the DCD-treated soil. The stimulatory effect of DCD was more pronounced at lower N application rate, and was consistently observed in the root-zone, planted bulk and unplanted soils. At higher N application rate, however, DCD had no effect on the microbial activity of the unplanted soil. Results suggested that relatively high concentrations of DCD required to inhibit nitrification under warm climates may not be phytotoxic but may have significant implications in soil microbial processes.
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