Provided summer weeds have largely been eliminated via fallow or summer crop management in the previous two or three summers and there is good stored soil water, the probability of summer grass pasture sowing success is greatest from early sowing.
Date for early sowing is environment and season dependent with most species needing a soil temperature of about 16 degrees Celsius or higher, much the same as is needed for sorghum. For our area, and for many others, that’s around early November onwards, but in some years can be earlier.
This past season well below average summer rainfall occurred. Premier digit grass was sown on our property on November 2 by Rob Williams from Coona Valley Contracting. His zero-till Seed Hawk seeder accurately places seed from the surface to no deeper than 10mm, generally ideal placement depth, followed by a press wheel.
Being mainly lighter soil, germination and establishment occurred on a scattering of rainfall events less than 20mm through the summer. Staged germinations resulted in some plants fully developed three months after sowing, while others germinated on later showers, as late as late January and are still to reach flowering. New stands should not be first grazed until flowering.
A friend reckoned it was best not to sow tropical grasses until February (gives him more weed control options). However the probability of receiving good germinating rain reduces the longer sowing is delayed. On our property, typical for many districts, the App ClimMate, using past rainfall records for most parts of Australia, alerts us the chance of receiving 20mm of rain, within three days, between early November and mid-March is 99 percent. That’s generally sufficient rain on light country for good establishment.
If we delay sowing to early February, the probability of a good establishment reduces. CliMate for our district indicates probability of receiving 20mm (in a three or less day period) for the reduced sowing window reduces by 10 per cent and by mid-February receival of 20mm reduced to more than one quarter of years receiving sufficient rain.
Light soils have an advantage over heavier ones for new tropical grass establishment. Commonly heavy soils require double or more rain for an establishment event, especially after it has been dry for some time. And heavy soils need more rain to fill soil profiles so establishing pastures can tap quickly into subsoil moisture. Back to my February sowing advocate. This past summer he missed germinating events that occasionally fell through late spring to the end of January. Even if he gets a good late summer/early autumn germination rain he will have a new pasture that will require greater grazing management going into winter as plants will commonly be poorly anchored and vulnerable to over-grazing even through the following spring early summer, especially if spring summer is below par for rainfall.
In contrast early sown and more than often early established stands can be fully productive within three to five months of sowing. Commonly they have built a good body of feed that provides valuable late summer autumn feed, much appreciated from a new pasture. Their normal management such as introducing annual legumes into them in autumn (generally a one-off operation) can routinely proceed.
A major part of early sowing success is that the soil weed seed bank is largely depleted over the preceding two and preferably three summers. Commonly these fallows are part of a winter cropping phase. In the last year leading into pasture sowing, the winter crop (commonly an early sown grazing one) can be terminated early to preserve good sub-soil moisture.
Next week. New wheat varieties out-yield old.
- Bob Freebairn is an agricultural consultant based at Coonabarabran. Email robert.freebairn@bigpond.com or contact (0428) 752 149.
