Soil replacement for lawn

Hi all,

4 years ago I replaced the top 150mm of clay soil for my lawn with a loamy sand in order to improve drainage. At the same time 400mm deep drainage trenches were dug into the clay below at 2m intervals.

This totally sorted the drainage issue, but its gone too far the other way and now struggles to retain sufficient moisture or nutrients for healthy growth due to the low levels of silt and clay (I’ve had structural soil analysis carried out). The soil provided is actually a loamy sand, rather than the desired sandy clay loam, meaning it is very sandy indeed!

To remedy the situation I’m looking to replace the soil and am wondering whether I can get away with a 50/50 mix of new and existing by replacing just half of the loamy sand (75mm) with a more general purpose soil with higher levels of clay silt.

Or, whether I’m best off replacing the full 150mm with a soil that is already confirmed as having the desired proportions of sand / clay / silt.

My concern with a 50/50 mix is whether I’d be able to effectively combine the two to create a homogenous mix throughout the lawn. I don’t have any experience of rotivators, so not sure how effective they are in this respect.

Would love to hear if anyone has any experience of using a rotivator for this type of job.

Thanks