Good irrigation is a struggle. In our praxis as consultant we seldom see the irrigation just done good. We see the following main issues:
- From late starts to early stops – causing a big drydown overnight
- Early starts to late stops – causing too wet substrate overnight
- High joules between the irrigations – causing dry substrate
- Set minimum times between the irrigations to big, causing dry substrates on sunny days
- Set maximum times between the irrigations to low, causing too wet substrates on dark cloudy days
Sub optimal irrigation causes a lot of problems. From bad quality fruits (soft, sensitive skin) to low yields, bad shelf life. It is one of the main issues if we talk about fruit quality.
So far we assumed that there is a linear relation between radiation (Watt) and evaporation. Thus irrigation on joules is one of the most reliable ways of irrigation. Still I think it is one of the better ways of setting up your irrigation. But in hot summers, or circumstances with a lot of sun, we always see dry substrates, increasing EC etc.
A small modification of your settings may help. Adding an influence of radiation on shotsize: for example in the range 500-1000 Watt: add 10-20% on your shotsize. This will increase the shots in the hot of the day, but decrease it again at the beginning and ends of the day.
Sub optimal system
In quite a lot of cases we see that the system is not capable of optimum irrigation. In case of sunny weather the min time between the irrigations is 45 minutes for example or better 300-400 joules. That means yield and quality issues are already build in the system. For a good system you need to be able to irrigate at least every 150 joules at 400 ml/lm
A standard setting might then look the following (take care, climate, LAI, subtrate etc will define your definite optimum settings).
Beginning irrigation: 2 hours after sunrise (or better 50-75 Joules after sunrise)
Interval between irrigations: 200 joule
Shotsize 100 ml/dripper (or better 400 ml/linear meter) – 5 drippers/lm is optimal
Correction on radiation: 500-1000 Watt: + 10-20%
Last irrigation: 2-3 hours before sunset
Minimum time between irrigations: 10 minutes
Maximum time between irrigations: 4 hours
[with the last two point be sure your settings are correct for your climate and crop development stage]
But the most important is always check what you are doing. How much water do you give, what percentage of drain do you get, what is the sum EC, feed EC, drain EC etc.
Based on that decide changes in your settings.