Spray fast to capture soil moisture, farmers urged

North Canterbury farmers keen to hoard every drop of soil moisture after the first proper rain in 18 months should spray run out paddocks with herbicide as soon they get a weed strike.


That will stop weeds growing and effectively pumping what moisture is available straight back out of the ground as they grow, according to a local pasture specialist.


Spraying will allow farmers to ‘bank’ the rain for autumn sowing.


“Some existing crops and pastures will recover after the rain, and that’s fantastic news for anyone affected by the drought,” explains Craig Weir, upper South Island area manager for Agriseeds.


“But in paddocks which have been damaged past the point of recovery, the only thing that is likely to respond to the rain after months of drought is weeds.


“If they get away, they will just suck the soil dry again by pumping up moisture and losing it to the air through evapotranspiration. Effectively you end up with hundreds of little pumps per hectare.”


Weed seedlings treated with glyphosate herbicide will stop removing water from the soil as soon as they are sprayed, conserving moisture for autumn sown pasture or crops. This is particularly important in case conditions do remain dry.


Craig says farmers may not be able to spray off all their drought-ravaged paddocks, nor may they want to.


By prioritising their better soils and country first, however, they can use this method to get the best returns from sowing new pasture or crops into these paddocks in the next month or two.


“What you plan to sow will influence your timing. And if the weather stays dry, February is probably the earliest many farmers would want to sow a new crop, once we are past the heat of summer and nights are getting longer,” he says.


Direct-drilling goes hand in hand with spraying to conserve soil moisture.


“Cultivation is a great way to establish crop or pastures, but the process of cultivating means sacrificing a lot of soil moisture, as it brings the wetter soil to the surface of the paddock to dry.


“Direct-drilling is a proven soil moisture conservation technique, and is more appropriate in these situations.”


Craig Weir says when it does come time to re-sow paddocks and get farms growing again, several options are available, depending on when feed is required.


“For winter feed, crops like Interval rape are a great option for sowing from late January on, depending on conditions.


“For a multi-graze 12-18 month pasture an Italian ryegrass like Tabu is ideal, but should not be sown before late February at the earliest. We advise similar timing with perennial options like Bareno pasture brome or Rohan SPR ryegrass.”