ABSTRACT
An incubation study investigated the effects of nitrification inhibitors (NIs), dicyandiamide (DCD), and neem oil on the nitrification process in loamy sand soil under different temperatures and fertilizer rates. Results showed that NIs decreased soil nitrification by slowing the conversion of soil ammonium (NH4+)-nitrogen (N) and maintaining soil NH4+-N and nitrate (NO3−)-N throughout the incubation time. DCD and neem oil decreased soil nitrous oxide (N2O) emission by up to 30.9 and 18.8%, respectively. The effectiveness of DCD on reducing cumulative soil N2O emission and retaining soil NH4+-N was inconsistently greater than that of neem oil, but the NI rate was less obvious than temperature. Fertilizer rate had a stronger positive effect on soil nitrification than temperature, indicating that adding N into low-fertility soil had a greater influence on soil nitrification. DCD and neem oil would be a potential tool for slowing N fertilizer loss in a low-fertility soil under warm to hot climatic conditions.
Acknowledgments
We are very thankful for the instrumental support provided by the Department of Biology, Chulalongkorn University. Additional assistance was also provided by Tassanee Prueksasit, Nipawan Sananwai, and Punlop Wimolsoponkitti.
Funding
We acknowledge funding by the Academic Position Stimulus Policy (APSP) of the Faculty of Science, Kasetsart University, and Kasetsart University Research and Development Institute (KURDI) for supporting this research.