Combining Azolla and urease inhibitor to reduce ammonia volatilization and increase nitrogen use efficiency and grain yield of rice

Abstract

Paddy Azolla is considered as a promising technical approach to reduce ammonia (NH3) volatilization and increase nitrogen use efficiency (NUE). However, it is not effective in highly fertilized paddy fields as the high ammonium N (NH4+-N) concentrations adversely inhibit the growth and N uptake of Azolla. Urease inhibitors could effectively decrease NH4+-N concentrations in surface water and NH3 volatilization. However, a lack of information still exists regarding the combined effects of Azolla and urease inhibitors on NH3 volatilization, NUE, and grain yield (GY) of rice. A two-year field experiment was conducted including five treatments (no urea application (control), urea (N), urea + Azolla (NA), urea + urease inhibitor (NUI), and urea + Azolla + urease inhibitor (NAUI)). Results showed that NA treatment (−25.2%) was not effective in reducing NH3 volatilization compared with NUI treatment (−43.3%). The NAUI treatment substantially reduced NH3 volatilization (−54.6%) more than that by NA and NUI treatments, primarily because of the lower NH4+-N concentrations, pH, and temperature in surface water. Furthermore, NAUI treatments significantly increased the grain yield (GY) and the apparent N recovery efficiency (ANRE) of rice by 9.0–9.7% and 66.0–71.3%, respectively. The significant increase in GY was mainly from the increased panicle number (4.0%), spikelet number per panicle (15.9%), and total biomass (22.9%), which caused by the enhanced total N uptake (35.8%). NAUI treatment also decreased the yield-scaled NH3 volatilization by 61.1–63.6%. Overall, the co-application of Azolla and urease inhibitor in the rice field substantially decreased NH3 volatilization, and increased NUE and rice yield.