Delaying Irrigation Until Leaf Drop Boosts Lucerne Seed Yield

More water does not always produce more lucerne (also called alfalfa) seed. A five-year trial near Keith, South Australia, found that delaying irrigation until early leaf drop generally increased seed yield and consistently delivered the highest gross margin — the income left after variable costs. The AgriFutures Australia trial shows controlled moisture stress can lift seed production and cut irrigation costs, while variety choice still matters.

Established at Warrawee Park near Keith in June 2018, the trial compared 31 proprietary and benchmark lucerne varieties over five seed harvests. Each variety grew under three flood irrigation strategies, where water flows across the field rather than sprayed or dripped. Standard irrigation followed current practice; moderate stress delayed watering until plants wilted; high stress delayed watering until plants showed early leaf drop, guided by soil moisture and weather data.

After the establishment year, the high-stress strategy generally produced higher seed yields than standard irrigation, averaging about 0.6 to 0.7 metric tons per hectare. The exception was 2021-22, when seasonal rainfall disrupted the planned treatments and the difference was not significant. Moderate stress gave less consistent results, showing a small irrigation delay did not reliably improve performance. The high-stress treatment was carefully managed, stopping at early leaf drop rather than allowing severe or prolonged stress. Varieties SW18NPK91, SARDI (South Australian Research and Development Institute) 10 Series II (the second series), Heritage 10 and SARDI 7 Series II were consistently among the highest yielding across treatments and seasons.

The high-stress strategy delivered the highest gross margin in each of the four years analyzed — $3,064 to $4,210 per hectare, versus $2,071 to $3,074 under standard irrigation. The gain came from higher yields and lower irrigation costs, with high seed prices boosting returns in the final year. These are comparative gross margins, not complete production costs.

The Keith trial was conducted on sandy loam soil under flood irrigation, with findings reported by K. Copping and B. Close (2025) in the AGA Seeds of Change Proceedings.