DUAL purpose oats sown mid-March and coming out into head mid May is not an uncommon situation, particularly this year, when many crops were sown on March rains.
Grazing these before they get to early heading is often not possible, especially if a common prolonged dry period follows sowing (as it did this year with no follow-up rain until May 19 or 20 for many areas).
Secondary roots to anchor plants usually need follow up rain after sowing for their development to prevent plants being pulled out by grazing.
Crops that run prematurely to head from early sowing have no or insufficient “winter habit” or other features that restrict the rate of head movement up the tiller.
These are in contrast to “spring habit” types.
When conditions are warm, as they generally are for extended periods following early sowing, heads of “spring habit” types quickly move up the stem and commonly head in late autumn or early winter. The unfortunate aspect of heads moving up the stem prematurely is that when grazed below head height, tillers die.
New tillers can reform, but a time lag occurs for leaf regrowth and if conditions are dry, new tiller formation can commonly be quite poor.
In contrast varieties of all species (oats, wheat, barley, triticale and brassica species such as canola) with “winter habit” or similar attributes, means the growing point or head remains at ground level until sufficient cold or other vernalisation requirements are met.
Until “winter habit” is satisfied, regrowth continues from existing leaves and no damage is done to tillers and regrowth occurs relatively unhindered. Several genetic factors can provide early sown varieties with the ability to develop slower than “spring habit” types, so as to avoid heading too early and being severely frosted or more prone to grazing damage. “Winter habit” or “vernalisation requirement” is a main genetic attribute that results in plants not developing head movement up the stem until after sufficient cold temperatures (zero to 12 degrees Celsius) have occurred.
There are other genes that affect the amount of “cold requirement” needed in a variety to trigger head development. For examples colder areas often favour varieties with a long “cold requirement” but warmer areas best suit varieties with a short “cold requirement”, otherwise they develop heads too late for grain production after grazing. Examples of varieties with a lower cold requirement are Wedgetail and KittyHawk wheat, Eurabbie, Bimbil and Mannus oats, Urambie barley, Cartwheel triticale and various brassica options. If a crop is mainly for early sowing and for long grazing time but no grain recovery a variety with high level “winter habit” may suit best. For example there are a number of longer season “winter habit” wheats.
Photoperiod sensitive (plants develop slowly until exposed to a given duration of day length) and thermal time responsiveness (plants speed up development as temperature increases) are other features in some varieties suited to earlier sowing and grazing.
“Spring habit” grazing types tend to suit later sowing, shorter grazing periods followed by closing for grain. Oner such variety is Yarran oats. Slow maturing “spring habit” varieties have the advantage of remaining green, although stalky, well after quicker lines have hayed off. But they also have their heads move up the stem from early sowing, although at a slower pace than quick maturing “spring habit” types. Other factors need to be considered for choosing grazing or dual-purpose crops, such as rust resistance and barley yellow dwarf virus tolerance. Regardless of variety choice agronomy aspects like soil fertility and stored fallow moisture are critical.
Next week. A host of new winter crop varieties.
- Bob Freebairn is an agricultural consultant based at Coonabarabran. Email robert.freebairn@bigpond.com or contact (0428) 752 149.
