Timing fallow weed hit critical for soil moisture

Because fallow weeds use water so very quickly, their timely control by farmers is therefore one of the most critical parts of maximising crop yields.

At and soon after harvest there are a multitude of farm aspects that require urgent attention.

These include flies in sheep, other delayed operations, and "agreed" plans for a family break.

While this holiday period has well passed its worth reinforcing the well-established importance of efficient fallow management.

Dry periods are common in the coming crop and also common is lack of "in-crop" rainfall to achieve consistent good to high crop yields.

There are many urgent time requirements on any farm but the need for urgent attention to fallow weeds to ensure effective weed kills and resultant efficient capture of soil water is a dominant one.

Using livestock to control fallow weeds, while common, is compounded with less efficient capture and storage of fallow moisture.

Many weeds are able to set seed while grazed low to the ground, set seed quickly after rain and leave little residue if grazed hard (which is necessary for most effective rainfall capture).

Weeds, and self-sown crop resulting from normal harvest losses (pinched grain etc) can lead to soil water loss of round 6.0 mm per day.

It doesn't take many days to lose over 50mm of stored soil water.

Also importantly where weeds are allowed to grow to some size in a fallow considerable quantities of soil nitrogen are tied up in them.

This can be 40 kg/ha less available nitrogen to the following crop.

So much has recently been written and spoken about anti herbicides and other modern farm practices (generally without and querying of facts to support such statements), commentary similar to anti modern agriculture promoted by some for decades.

For example cultivation as a main weed control system, has been well proven to commonly be ineffective at controlling weeds (except when part of a well-integrated program), and is nowhere near as effective at conserving fallow moisture compared to herbicide fallow management.

More importantly cultivation badly impacts on soil structure destroying soil pores and reduces water infiltration rates.

Soil erosion risk is greatly increased.

And ploughing as the main weed control and fallow moisture capture approach results in progressive substantial loss of soil organic matter, and therefore carbon.

Related: Smart knowledge needed for dual cropping

Fallow herbicide application timing is critical in many respects.

Especially critical is weed stage and soil moisture content.

Delayed spraying resulting in larger weeds, often less soil moisture, and commonly hotter temperatures, reduces weed kill efficiency.

This can occur especially if weeds have developed some level of resistance to given herbicide products over time.

As part of avoiding herbicide resistance developing in certain weeds, for example fleabane and windmill grass, "double knock" for many farmers, including ourselves, is part of effective integrated fallow weed control.

Glyphosate plus 2,4-D ester has not controlled these weeds, even when sprayed early in mild moist conditions.

A follow up gramoxone spray, a research has indicated, has resulted in good control.

Other "second knock" treatments are also working well on fleabane.

Good crop weed control options, as part of what is generally described as "integrated" control, include where possible use the most vigorous variety, barley generally more weed competitive than wheat, but with big variety differences, closer row spacing (a return to 7 inch or 18cm), high soil fertility, and for some weeds sowing early prior to the weeds normal germination period.

Next week: Meat quality award linked to top pastures.

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