Hello Meng, The horse power is for the engine that's used to drive the pump. For sprinkler pump selection, you will need the pump specifications mostly in terms of pump head and discharge. For this sprinkler (Yuzuak JET35) - One piece, you will need a pump with a discharge 6,500 to 32,000 litres per hour and a pressure head of 2 to 6 bars. For more than one sprinkler head, you will need to multiply the flow but the pressure for the sprinkler excluding other head losses will remain constant. One engine can be mounted on sevaral pumping units of different outputs.
Yes, you need a different pump with lower pressure/lift(depending on your site slope from water source to delivery longest and highest point) and discharge required.