Dilnee Suraweera1, Fiona Robertson1, Malcolm McCaskill1, Brendan Christy2, Roger Armstrong3, Debra Partington1, Reto Zollinger1, John Byron1, Steve Clark1
1Agriculture Victoria Research, 915 Mt Napier Rd, Hamilton Victoria 3300, Australia
2Agriculture Victoria Research, 124 Chiltern Valley Rd, Rutherglen Victoria 3685, Australia
3Agriculture Victoria Research, 110 Natimuk Rd, Horsham Victoria 340, Australia
Waterlogging is a major constraint for wheat production in the high-rainfall zone (HRZ) of south-eastern Australia. During waterlogging, significant quantities of nitrogen (N) derived from fertilisers can be lost, reducing potential supply to the crop. A field experiment was conducted to quantify the effectiveness of different in-crop N application rates in reducing the effects of pre-anthesis waterlogging on wheat grain yield. The experiment was designed with two water regimes (waterlogged and rainfed) and four rates of in-crop N (urea) fertiliser (nil N, 70,140 and 210 kg N ha-1). The waterlogged regime was irrigated from mid-tillering (GS23) to flag-leaf emergence (GS39). In-crop N fertiliser rates were split; 70% at early-tillering (GS21) and 30% at flag-leaf emergence. At grain maturity, tiller number, ear number, above-ground biomass, grain yield and harvest index were determined. Results demonstrated that tiller numbers, ear numbers, above-ground biomass, grain number and grain yield significantly increased with increasing rates of N applied compared to nil N under both water regimes. Pre-anthesis waterlogging significantly delayed heading, anthesis and maturity (3-5 days) and significantly reduced tiller numbers (21%), ear numbers (11%) and above-ground biomass at anthesis (15%). This reduction was less under high N rates. Adequate soil moisture availability for grain filling in a dry spring followed by pre-anthesis waterlogging significantly increased grains per ear (24%) and this increase was greater at high rates of N application. Grain yield and above-ground biomass at maturity were not significantly affected by waterlogging at low N rates but increased 8-17% at high N rates. Pre-anthesis waterlogging significantly reduced grain protein content at low N rates but there was no significant effect of waterlogging on grain protein content at high N rates due to increased N uptake. Overall, adequate supply of N fertilizer before and after waterlogging can alleviate the detrimental effect of pre-anthesis waterlogging on wheat grain production.