Improving wheat growth and nitrogen-use efficiency under waterlogged conditions

Soil moisture content has a significant impact on nutrient availability in wheat. Excessive soil moisture due to waterlogging can severely reduce nutrient availability through substantial dilution of nutrient concentrations and leaching of mobile nutrients like nitrogen (N). Nitrogen-use efficiency (NUE) may be improved by using controlled-release fertilisers (CRFs) and appropriate timing of N fertiliser application. This study investigated whether timing of N application and source of applied N can alleviate the adverse effects of waterlogging on wheat growth and improve NUE. The experiment was designed as a split-plot with irrigation regime and N fertiliser application as main-plot and subplot factors and three replicates. The irrigation regime included: rainfed, irrigated and waterlogged while N fertiliser application had nil N, single-applied urea, split-applied urea and CRF treatments. At harvest, tiller number, ear number, grain yield and harvest index were determined. Nitrogen-use efficiency, its components and grain protein content were also determined. The results showed that waterlogging and N fertiliser application had a significant effect (P < 0.05) on tiller number, ear number, grain yield and NUE. The CRF had the highest grain yield for all irrigation regimes, with 9.2 t/ha, 9.4 t/ha and 6.8 t/ha for the rainfed, irrigated and waterlogged respectively. There were significant variations (P < 0.05) in NUE between different irrigation regimes and N fertiliser treatments. The CRF had the highest NUE for all irrigation regimes. Under waterlogged conditions, the CRF improved NUE by 17% and 27% more than single- and split- applied urea respectively.