Fertilizer N use efficiency

In general, the N use efficiency in paddy rice cultivation is low mainly due to denitrification and volatilization. Denitrification takes place in the reduced soil layer. After flooding, microorganisms are able to use NO3- as an electron acceptor. Thereby, NO3- is reduced to gaseous N2O or N2 resulting in losses of N to the atmosphere. Denitrification occurs after NO3- application, since only low amounts of NO3- are naturally present in submerged soils. Volatilization is a chemical process (not involving microorganisms) that occurs in floodwater at high pH. Thereby the ammonium nitrogen (NH4+) is converted to gaseous NH3 resulting in losses of N to the atmosphere. A high pH in floodwater can be found because of algae growth.

Additional reasons for a low N use efficiency: 

• No split application 
• Bad timing 
• Unbalanced nutrient supply 
• Micro nutrient deficiency 
• Other growth limiting factors