Effect of water availability and nitrogen source on wheat growth and nitrogen-use efficiency

Soil moisture content has a significant impact on soil nutrient availability. Excessive soil moisture due to waterlogging can severely reduce nutrient availability through denitrification, leaching and restricted root growth, which impairs nutrient uptake by plants. This reduces nitrogen (N) uptake and utilization by plants thereby decreasing nitrogen-use efficiency (NUE). Controlled-release fertilizers (CRFs) can improve NUE through synchronisation between N supply and crop demand. A study was conducted to investigate whether timing of N application and source of applied N can alleviate the adverse effects of waterlogging on wheat growth and improve NUE. A split-plot design experiment with irrigation regime as main-plot factor and nitrogen application sub-plot factor was setup. Irrigation regimes included waterlogged and rainfed; nitrogen treatments included: nil N, single-and split-applied urea and CRF. Wheat growth and yield attributes were monitored during stem elongation and anthesis. Grain yield and NUE were determined at harvest. The study findings showed that waterlogging significantly (P<0.05) decreased tiller number, ear number and NUE for all nitrogen treatments. Although split-applied urea had a higher number of tillers and ears than single-applied urea under waterlogged conditions at harvest, there was no significant yield advantage under both irrigation regimes. The CRF increased grain yield by 1t/ha compared to both single- and split- applied urea of the waterlogged treatment. CRF also improved wheat NUE by 7% and 10% under rainfed and waterlogged conditions respectively.