Replacing Gardena Automatic 6000/5 with IB0 H-SWQ 1800 Pump: Pressure Loss & Sprinkler Efficiency

Please help. I need to replace the submersible pump used for watering the garden-lawn (I currently have Gardena automatic 6000/5 with the parameters max. Pressure 5 bar, max. Water flow 100 ml / min), because it turns out that the pressure received on sprinklers (1bar to 1, 5 bar depending on the section) is too low than assumed in the design (min. 2 bar, water demand is about 80 ml / min) and irrigation does not work properly (grass that dries nicely in places)
My question is as follows (I found an IB0 H-SWQ 1800 submersible pump on the internet with parameters max. Lifting 53 m, max water flow 270 l / min) unfortunately there is a 2-inch diameter connector at the outlet and I can connect it to my installation I have to reduce it to 1 inch. Is it possible to calculate roughly the pressure loss caused by the reduced pipe diameter and whether this new pump is able to provide pressure at the sprinkler of 2.5 bar.
I would like to inform you immediately that reducing the number of sprinklers per section (increasing the number of irrigation sections) is not an option.

Hello. Why do you want to use a pump that has a different use?
You should think about a pressure booster pump with a tank and a pressure switch, where you will be able to set the pressure that is suitable for your sprinklers.

Unfortunately, I have to redo something that has been incorrectly designed and already done. For personal reasons, I can not enforce a correction from the designer and contractor (which is a pity!) Replacing the submersible pump with a pump with a hydrophore would be the most sensible but would involve major alterations and devastation of a very nice (in my opinion) lawn by having to build a pump with a hydrophore. The water tank, in which there is a pump, is a tank for rainwater replenished when the water level drops through the tap water (a solenoid valve and float switch is used) and is dug in the middle of the lawn. Irrigation has been in operation for 3 years and has been doing well for 2 years (it was clear that the grass grows less well in some places, but it did not dry out completely). Only last year it dried up in undersized areas for very hot summer. I would like to avoid a similar situation this year. I have a very large lawn - over 20 ares watered by over 100 sprinklers. At the moment (after reading into it) I know that it is poorly designed (unnecessarily so many sprinklers and unchecked pressure drop when the water demand is 4 m3) / hour - just look at the Gardeny's table.) Unfortunately, a wise Pole after injury.
Greetings Marcin