Key Points
- The economic applied optimum N inputs are generally lower than the rates used by many ryegrass seed growers (48–190kg N/ha - perennial ryegrass or 0–120kg N/ha Italian ryegrass, results from 2005/06 season).
- Excess N (beyond the optimum response) often depressed seed yield; and certainly depressed economic return by up to $500/ha.
- A reasonable relationship exists between late winter soil mineral N (0-30 cm) and the amount of applied N to achieve an optimum seed yield for Italian ryegrass. However the relationship in perennial ryegrass is only a weak predicator.
- Italian ryegrass appears to require less N to achieve optimum yields than perennial ryegrass.
- Colour scores and secondary growth during seed fill are inversely related to seed yield; meaning that higher yielding crops appear to be “under-done” or short of N and that high N increases secondary growth, suggesting a possible cause of declining seed yield at high N rates.
- Slow release N gave similar results to urea, but not consistently better results.