After a cold and damp start, the 2019-20 irrigation season has finally begun. In the last post we predicted it would be early November before irrigation needed to start-up. This prediction turned out to be on the money. It was informed through running a water budget using Winchmore and Lincoln climate data, 2-day and 10-day weather forecasts, and based on a typical Canterbury soil with 80 mm of Profile Available Water. For irrigation systems such as pivots, using the Lincoln data irrigation should have started on the 31st of October and using Winchmore data 4 days later.
For irrigators, this shows the value of keeping an eye on the 10-day weather forecast alongside the detailed predictions for the next 48 hours. It also demonstrates that running a simple water budget and applying a weather forecast to these is a robust and cost-effective way of knowing when to start and stop irrigating for many irrigators. You don’t need to spend thousands of dollars on soil moisture sensors if you’re prepared to take an hour or two a couple of times a week and collate the following information in a spreadsheet. Site specific daily rainfall data; Irrigation application depths; and Daily PET data from your local climate station.
Looking forward, despite the mini heatwave in early November irrigation should have stopped on the 11th November due to the rainfall. Based upon the subsequent rainfall, current 48-hour and 10-day forecasts and noting ET levels typically average between 3.5 and 4.0 mm/ day during mid to late November, irrigation will need to start again in late November.
For this season if you’ve applied more than 60 mm of irrigation before the end of November you need to be asking yourself questions around whether you need help getting your irrigation right. For those of you that have applied between 30 and 40 mm you’re spot on and the Farm Environment Plan auditor should be giving you top marks for your excellent irrigation scheduling practice!
I thought it would be useful to share an observation from the Water Strategies Irrigation WOF scheduling assessments we’ve undertaken this spring. Through these we’ve looked at a range of different soil moisture traces and we’re concerned with the service some companies are providing. Many have no field capacity or irrigation trigger points set and where set some are incorrect – generic settings have been applied. We’ve also noted certain interfaces that provide multiple traces at multiple depths have little or no explanation around how to read them. The above can make life very frustrating and confusing for the end-user.
For soil moisture sensors to be useful both field capacity and irrigation trigger points must be set. It’s also prudent to calibrate the sensors from time to time as sensor traces, when the current season is compared to the previous, often show a declining trend in their readings overtime.
The other point of note that we continue to find, particularly on older irrigation equipment, is the application depth on the controller is frequently different from the actual application depth. Flow rates and machine speed need testing to check this annually.
If you would like an assessment of your scheduling practice, including suggestions around how your irrigation practice could be improved, or you’ve issues with your irrigation equipment call us today to book in your Water Strategies Irrigation WOF.