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It has been an extremely dry and warm start to the 2020-21 irrigation season. If the La Niña weather pattern continues as predicted, Canterbury irrigators will need to keep a careful watch on their seasonal allocation limits and make tactical decisions around their irrigation. If you have used over 60% of your allocation by the end of December, you will need to think about how to reduce your irrigated area so you can get through. It is better to irrigate a smaller area well than do a bad job everywhere! Options to consider include focusing irrigation to areas with more efficient irrigation systems, to more productive areas of the farm, or to higher value crops. So why are we saying this?
The Lincoln weather station data shows there was 32mm of rain during September and up until the 25 October there had only been 4mm of rain. Potential Evapotranspiration (PET) was 83mm and 91mm respectively, an average of 2.6mm and 3.6mm per day. These rates are 30% and 18% higher than the 10-year average and are also the highest recorded for this period. For a soil with 100mm Plant Available Water (PAW) an efficient irrigator would have applied approximately 150mm of irrigation. This means over 20% of the seasonal allocation limit has been used.
The Winchmore weather station shows there was 56mm of rain during September and up until the 25 October there had only been 23mm of rain. Potential Evaporation was 86mm and 85mm respectively, an average of 2.9mm and 3.4mm per day. For a soil with 100mm Plant Available Water (PAW) an efficient irrigator would have applied approximately 120mm of irrigation. Again, this means over 20% of the seasonal allocation limit has been used.
The Timaru Airport weather station shows there was 37mm of rain during September and up until the 24 October there had only been 15mm of rain. Potential Evapotranspiration was 67mm and 60mm respectively, an average of 2.2mm and 2.0mm per day. For a soil with 100mm Plant Available Water (PAW) an efficient irrigator would have applied approximately 80mm of irrigation. This means 10% of the seasonal allocation limit has been used. However, of more concern for South Canterbury is the record low rainfall, only 235mm since 1 January. The 30-year annual average for Timaru Airport is 565mm.
To help irrigators through what is shaping up to be a challenging irrigation season, Water Strategies will be running more irrigator workshops in November. They will be held in Geraldine and Rakaia; the dates, times and venues for these are on our website www.waterstrategies.co.nz. Alternatively, if you would like a hand with making sense of your soil moisture sensors (we can do this over the phone if you provide us with your log-in), working out how best to deal with restrictions, or you are experiencing issues with your irrigation system and would like experienced independent support to resolve these, give the team at Water Strategies a call.

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