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The compaction risk: rain close to picking
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With recent rainfall in several valleys and picking on the horizon, now is a good time to remind ourselves of the potential for compaction to occur. By way of a reminder as to the scale of this issue, compaction is thought to affect about half of our crops with some fields losing over a bale per hectare.
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What can you do?
The best approach to managing soil compaction is to avoid it. This can be best achieved with Controlled Traffic Farming (CTF), but where CTF is not practised, compaction can be minimised by ensuring field traffic only occurs when the soil is well below its plastic limit.
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Determining the plastic limit
The simplest way to determine if a soil is below its plastic limit is to take soil samples and squeeze it between thumb and forefinger. If it feels like plasticine, then the soil is above its plastic limit and so should not be driven on and given more time to dry out.
Soil will lose a few mm of moisture every day, but may take several days to a week for even the surface 10cm of the soil to dry out. Deeper soil will still be wet and compact under traffic, even when we don’t see wheel ruts on the surface, so remember to consider testing deeper soil’s plastic limit and try to dry out as much of the profile as possible before picking.
The crop will help with the speed of the drying process, but only if it has not been defoliated, because once the leaves are off the plants they are no longer sucking moisture out of the soil.
So if you've had rain, try to dry your soil out before you defoliate/harvest. If you're worried about compaction in the future then start to think about how you might move to a CTF system on your fields.
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For more information, see the soil compaction section within chapter 6 of the CRDC/CottonInfo Australian Cotton Production Manual.
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