What is Reddit's opinion of Auger Drill Bit for Planting, Spiral Hole Drill Planter Hex Shaft Auger, Post or Umbrella Hole Digger Auger Garden Spiral Drill Bits for Earth Garden Plant Flower Bulb (1.6 x 9 Inch)?

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You should avoid having different layers of soil, when there is a sudden change in soil particle size you get impeded drainage and roots tend to struggle to grow deep.

It's possible that the developer already put 'topsoil' on top of the native soil, if that is the case then you will end up with grass that has very short roots and turns brown in dry periods. You can correct this by tilling the two layers together until the change is turned into a gradient.

If you still have the native soil then you are good to go, to add amendments to the soil without destroying the lawn you can use a bulb planter drill attachment to drill holes which can be filled with amendments like biochar or compost. Fine compost can be used as a top dressing for the lawn.