The dry summer is turning into a dry autumn with many areas of Canterbury, particularly central and north, receiving very little rainfall since mid-December. Despite the dry, for autumn irrigation you need to closely follow the weather forecast to get your irrigation right as daily plant water use (ET) is much less than at peak. Through February, Lincoln and Winchmore climate station data shows ET rates averaged 3.2 mm/day and the effective rainfall was 15 mm and 55 mm respectively. During March, Lincoln and Winchmore ET rates have been averaging 2.2 mm/day and 2.3 mm/day with the effective rainfall 0 mm and 10 mm.

Using a pivot irrigator applying 15 mm as an example, for Lincoln during February you should have been irrigating every 5 – 6 days (adjusting for the two small rainfall events) and for Winchmore there were only two irrigation applications required due to the 30 mm of rainfall in early February followed by the 23 mm on February 23. During March irrigation applications have extended out to every 7 – 9 days (accounting for the small amount of effective rainfall that has occurred at Winchmore).

Water Strategies have run many irrigation management training days this season, our last being in the Culverden Basin. At this we had a great conversation around the importance of developing an irrigation strategy for your farm – understanding the factors that drive your irrigation, any limitations and risks around these, and then setting your irrigation trigger points and application depths across the season accordingly. The Culverden conversation also discussed considerations for the autumn – how to manage for lower ET rates, potential rainfall, water supply restrictions and soil limitations.

Culverden soils range from shallow Balmoral silt loams over stones with very low water holding, these require a little (5 – 8 mm) and often (every 2 – 4 days) approach for the autumn, through to heavy Ayreburn clays. Clay soils can be particularly challenging to manage in the autumn. When it’s dry you don’t want to let them dry-out too far otherwise they crack and any irrigation applied (or rainfall) doesn’t stay in the rooting zone until they are re-wetted, but at the same time you need to avoid running them too wet otherwise you risk compaction and pugging when grazing or cultivating. Careful timing of grazing rotations in relation to irrigation applications is key for successful management of clay or clay loam soils year-round, but particularly during the autumn.

If you would like specific support or advice for: your irrigation scheduling – setting trigger points and applications depths over the season or help ‘making sense of your sensor’; an assessment of this seasons scheduling practice – including practical suggestions as to how it could be improved; issues with your irrigation equipment; or are looking at redeveloping your farm irrigation system; call the Water Strategies team today. We specialise in solving your issues and saving you money!


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