Sowing rice on time in wet conditions

The topic of greatest interest at recent rice grower discussion groups in the Deniliquin district was how to sow crops on time. It’s been many years since wet paddock conditions throughout September have delayed ground preparation like they have this season.

Why sow on time?

There are two main recommended sowing windows for aerially sown crops in the Murray Valley – they are 10-25 October for longer-seasoned varieties (i.e. Reiziq, Koshi and Illabong) and 15 October- 5 November for other main varieties (i.e. Sherpa and Opus). YRK 5 and YRM70 are later again, but these varieties are more suited to drill sowing.

These sowing windows are designed to have the most cold-sensitive growth stage, young microspore, occur in late January to early February, when we are least likely to encounter cold nights. Sowing early or later than recommended will normally lead to young microspore occurring at a time when cold nights are more common.

We need to remember, however, that each year is different. Just because late January to early February has historically been the time when cold nights are less likely to occur, there is no guarantee that it will be the safest time for young microspore this coming season. While later-sown crops are more likely to encounter cold conditions than those sown on time, there have been some years when they were less impacted. All we can say with some certainty is that if you always sow on time, you will be less affected by cold weather more often than not.

Preparing wet paddocks for timely sowing

Rice growers are fearful that they will not have time to both adequately prepare paddocks and sow on time. This leaves them with the choice of either:

  • preparing paddocks as they normally would and sowing later than optimum, or
  • taking some ‘shortcuts’ with preparation to achieve timely sowing.

Growers are trying to decide which option is likely to produce the best outcome at harvest.

My approach is to undertake a type of ‘cost benefit analysis’ on paddock preparation shortcuts. Some things are essential to achieve, even if they delay sowing, while other things are desirable but could be dispensed with in order to assist timely sowing.

The essential objectives are:

  • Establishment - achieving an adequate plant stand. Even plant stands can be as low as 50 plants/m2 without any loss of yield potential.
  • Water control – the ability to have shallow water early (while still covering the clods for weed control); deep water later is essential.
  • Timeliness – the more sowing is delayed beyond the recommended period, the greater the risk of failure.

The desirable objective that can be varied or delayed

  • Weed control method - good weed control is essential, but if your desired technique delays sowing beyond the recommended window, find an alternative (even if it’s more expensive).
  • Trash levels – minimal trash is desirable at sowing. But it takes time to achieve. Be prepared to tolerate more trash, and its associated problems, than normal (see following comments).
  • Nitrogen management – pre-drilling urea into soil prior to permanent water is the best and most efficient nitrogen management approach. However, extra nitrogen can be bought if a less efficient application method is required in order to sow on time (whereas extra ‘time’ cannot be bought if you delay sowing beyond the recommended window).
  • Dry seeding – while I do not consider dry seeding a ‘desirable’ management option, I do acknowledge it is the practice of many growers. However this is not the year to dry sow – either into water or prior to flooding, as pre-germinated seed will give quicker and better establishment.

Managing trash levels at sowing

The main way to shorten paddock preparation time is to be willing to tolerate more trash at sowing. If you don’t have time to get rid of the plant material currently on your paddocks, then manage it in order to minimise its negative impacts on crop establishment.

One of the main problems with trash is its potential to produce large and damaging amounts of slime. However, in my experience, this problem is minimised (but not eliminated) if the plant material is dead before the field is flooded. Living or green material, especially legumes such as medics and trefoils, is likely to cause greater concerns than dead plant material. Therefore, knockdown herbicides that produce good brown outs are required.

If sheep are to be used to help remove plant material after spraying, then be sure to adhere to label directives. This may mean that only a high rate of glyphosate can be used, as additional chemicals are likely to have extended stock withholding periods (e.g. seven days for 2,4-D, 14 days for Hammer®).

If grazing is not following herbicide application, then use other herbicides in addition to glyphosate to achieve a quick brown out. Phenoxy herbicides are good at controlling thistles (but have a 7-14 day rice plantback), Group G (e.g. Hammer®, Goal®) help gain a quicker and better brownout and Lontrel® is good at controlling trefoils and medics. All of these products have formulations that are compatible with glyphosate formulations, but are not necessarily compatible with each other, so talk to your commercial agronomist before deciding which best suits your paddock situation.

John Fowler, Extension Agronomist, Murray Local Land Services, Rice Extension Newsletter, October 2016