How permanent water timing can influence crop development, water use, yield and grain quality
Published: October 2026
The timing of permanent water (PW) in drill-sown rice can influence crop development, weed control, nitrogen-use efficiency, water use, yield potential, harvest timing and grain quality. This fact sheet outlines the key factors to consider when deciding when to apply PW in CY27.
Best practice PW timing
The aim is to time PW so that panicle initiation (PI) and microspore occur within the recommended window for the variety, while also considering potential water savings and the operational needs of your farming system.
Four factors to consider when timing PW
Timing: Use the updated PI Predictor to compare how different PW dates may affect PI timing for your variety. Aim for PI to occur in the first week of January. Later-sown crops may need to go to PW at an earlier crop stage than earlier-sown crops to achieve this target.
Weed control: Going to PW earlier can be a useful tool in paddocks with high weed pressure. Understand the weed seedbank before sowing and prioritise early management in these paddocks. However, applying PW too early may bring PI forward of the recommended window.
Water use: Delaying PW can deliver significant water savings, but the crop must be carefully managed. Avoid early-season moisture or nutrient stress and maintain effective weed control so that yield is not compromised.
Harvest: Timing PW to achieve PI in the recommended early-January window can help place the crop in the optimum harvest window for dry-down and grain quality. Crops with an early PI can lose grain moisture quickly, reducing the time available to harvest within the 18–22% moisture window. Later PI crops may have a wider harvest window for achieving high-quality scores, but generally have lower yield potential and a greater risk of wet ground at harvest. A later harvest may also delay sowing of the following winter cereal crop.
Benchmarking results
Benchmarking across the past three seasons has shown a consistent decline in yield when PI occurs later than the optimum timing for the season.
In CY25, Matilda yields declined by around 90 kg/ha for each day PI occurred later than the optimum date. While the optimum timing varies between seasons, targeting PI in the first week of January generally provides the best balance between yield potential, exposure to cold and heat at sensitive crop stages and grain quality at harvest.
Key takeaways
PW timing can directly influence crop development, weed control, water use, yield and grain quality.
Use the PI Predictor to compare likely PI dates under different PW timings and historical seasonal conditions.
Aim for PI in the first week of January, while considering the recommended window for the variety.
Balance water-saving opportunities with the need to avoid crop stress and maintain effective weed control.
Consider the flow-on effects of PW timing on harvest and the following winter crop.
Key takeaways
CY26 Annual Summary (Pages 34,35)
Rice variety guide 2025–26 (Page 6)