Fertilizer Rate and Urease and Nitrification Inhibitors Effects on Soil Inorganic Nitrogen and Sugarcane Yields in Central Thailand

Improving nitrogen fertilizer use by plants and reducing N losses through applying the appropriate nitrogen (N) fertilizer rate with urease inhibitors (UIs) and nitrification inhibitors (NIs) may enhance crop production and the efficiency of N use. Sugarcane and unplanted plots were established in Central Thailand to investigate the effects of fertilizer application based on soil analysis and UIs, NIs and their combination (UINIs) on soil inorganic N, sugarcane productivity and N uptake. Both synthetic and natural inhibitors were investigated: UIs from N-(n-butyl) thiophosphoric triamide (NBPT) and garlic (Allium sativum L.) and NIs from dimethylpyrazole phosphate (DMPP), ground neem seed (Azadirachta indica A. Juss.) and praxelis (Praxelis clematidea (Griseb.) R.M. King & H. Rob). The results indicated the potential of applying UIs, NIs and UINIs along with N fertilizer to obtain a slower decrease in soil NH4+ and improve sugar products. The results indicated enhanced sugarcane growth and an apparent increase (up to 31%) in the cane and sugar yields in all the inhibitory treatments. Notably, despite the synthetic NIs and NIs from plants having similar effects on soil inorganic N, the natural NIs tended to enhance sugarcane yields and N uptake. These findings supported the application of UIs and NIs as a potential solution to reduce N fertilizer rates and N losses from soil, while increasing crop productivity. In addition, NIs from plants might be of interest for further investigation and for promotion to farmers.