dm,

Do some experiments with your system. The important thing is water getting to the roots at various stages of growth and weather. Usually the movement of soil is based on soil type. You can change the basic structure of your soil but not by much. So run the system for varying lengths of time and see how far and deep the soil moves in the soil for varying times after you finish irrigating. You are mapping your soil profile with the depth of your plants as they age (root growth). Do this for Spring Summer and Fall for different season maps. When you have done this you can give expert opinions on GardenWeb. Or go by the "rule of thumb" of about an inch of water a week Spring and Fall and an inch and a half for summer. Or "Rule of thumb" part 2 with about 1/2 to 1 gallon of water per plants every three days. With the rule of thumbs you still have to check if this is too much or too little over time (depends on soil). Gardeners check their plants somewhat frequently that the plants are getting what it needs. JMHO Aloha

Excellent advice, lehua!

I had read the first rule of thumb of acre-inches and was looking for an easy way to calculate that. But then I have to concern myself with water pressure and area and drip heads and, well, that's a lot of factors.

Your second rule of thumb sounds pretty easy to use. I can calculate the per-plant watering fairly simply, however, and change watering times based on weather and plant condition.

Don't need to calcualte anythingg.

Run the system for an hour.
Turn it off.
Wait an hour, then probe the soil to see how deep the water went.
- If sufficent to moisten the entire rotzone, you have now "calculated" the run time for your soil and the plants you will grow. Repeat as needed.
-If too brief to moisten entire rootzone, run another trial, but 2 hours long. Stop. Wait an hour Probe again. Do your need to run longer? Or is it okay?