Question
We are trying to irrigate an mx track. Our power is by generator, so we are trying to use the smallest pump possible. Track surface is approx 3.4 acres. We are having a 100' deep, 4" well drilled. What is the smallest hp pump you would recommend to effectively water this area. Thanks.

Answer
Thanks for the question.
I may not be able to give you an exact HP of the pump, that's more of a question for the well driller. I can give you some guidelines for water requirements. With this you can tell the well driller how much water you need per minute and they can size the motor.
First you will have to decide how long you can water. How much water you want to apply and how often. To apply 1/4" of water to the 3.4 acres you will need 22200 gallons of water. If you want to do this in a 12 hour period, it requires 1853 gal/ hour. So your gallon per minute will be (1853 divided by 60 minutes) = 31 gpm well.
If you want to change the hours divide 22200 by ___hours, then divide that number by 60 minutes.
The reason I can't give you a HP is until the well is drilled we don't know how high the water will rise in the well pipe. The water may be 80' down or rise all the way to the surface. The HP difference is large between the two.
Hope this helps, if you need further help just reply back.

Matt