The maturity group ranking is based on the flowering date of oats when sown in late May and early June. Figure 2 shows the change in duration to watery ripe as the date of seeding is delayed for representatives from each of the maturity groups in( Table 1.can be found in post Determining the cutting date for oat hay).
As oat varieties modify their flowering date in response to changes in day length (due to location) and temperature (due to season and sowing date), some varieties may be more sensitive to some sowing dates than others.
Needilup, Possum , Swan and Winjardie are four varieties that are more sensitive to day length than other varieties. As a consequence, they are able to contract the period from sowing to watery ripe as seeding is delayed into late June and July or delay it if seeding begins in late April.
That means those varieties may flower at a different time relative to other varieties in their same maturity group when sown in early May or late June. For example, Winjardie sown in late April may reach the watery ripe stage some 14 days later than Carrolup, only 7 days when sown in late May and 3 days when sown in late June.
Most other varieties, however, follow the patterns exhibited by varieties representing their maturity group in Table 1 and Figure 2, as presented in Tables 2 and 3. It should be noted that a three week delay in sowing date results in only an approximate 7 to 10 day delay in cutting date for most varieties, particularly in May and June sowing months (Figure 2).
For example, we would expect Carrolup to be ready for hay cutting (watery ripe) at Katanning around 11 October when sown on 28 May and ready around 20 October if seeding was delayed three weeks until 18 June.
When choosing varieties to sow it is therefore important to take into account their maturity group and likely differences in duration to reach watery ripe. Then, depending on which varieties are chosen, sow them at appropriate times to spread the risk (so they are ready for cutting at staggered times).
Impact of season on cutting date:
Average daily temperature influences the duration to watery ripe. In seasons or locations where there is a higher than average temperature during winter, an earlier duration to watery ripe (up to one week earlier than the predicted date) will result. Seasons with a lower than average temperature may result in a later duration to watery ripe (up to one week later than the predicted date).
Impact of location on cutting date:
Our experience from flowering date trials conducted at Katanning and Northam show large differences in the predicted date at which oat varieties will reach the watery ripe stage due to location. This is due to differences in daylength and temperature between locations. During winter, for example, Katanning has slightly shorter days and slightly lower average temperatures.
It therefore takes an oat crop sown at Katanning around 14 days longer to reach the watery ripe stage than an oat crop sown on the same day in May at Northam. When seeding is delayed to June, the Katanning crop will reach watery ripe around 10 days later than an oat crop sown at Northam.
Expected date to reach watery ripe for May, June and early July sowing:
Tables 2 and 3 present predicted data for each of the 24 oat varieties studied in the flowering date trials. The data presented in Tables 2 and 3 gives an indication of when these varieties are expected to reach the watery ripe stage (optimum hay cutting stage) based on five seeding dates - early May, late May, early June, late June and early July at two different locations – Katanning (Table 2) and Northam (Table 3).
It is important to note that the data presented is predicted data, not actual data, and will vary with season, location and sowing date.
Tables 2 and 3 can be used as indicators of when to start monitoring crops. Monitoring of crops should commence at least one week prior to the date indicated and build up around the predicted date. Growers who farm between Northam and Katanning should start monitoring their crops about the date suggested for Northam in Table 3. Growers north of Northam may wish to start monitoring their crops at least one week earlier than the date suggested in Table 3.
Despite having these tables, growers need to actually squeeze a representative number of florets in order to determine if the crop is ready for cutting. The colour of the crop is not always an accurate guide as some of the newer varieties such as Wintaroo maintain green leaf colour. In the event of rain occurring at the cutting stage, it is often better to delay cutting as the impact of rain on cut hay can often reduce hay quality more than a seven day delay in cutting date.
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