Answer #1: Ref. 0916 Soil. Sounds as though your soil is very compacted or you have lost a lot of your
top soil when they installed the yard. Adding lime (preferable in the
fall) will sweeten the soil. You need to incorporate any type of humus
whether it is rotting leaves, manure, etc. into the soil. If you do not
want to tear up the yard to incorporate humus, you can go to a local store
and purchase manure and compost in a bag. Hand broad cast it over the lawn. It is a slow process. What you are
doing is slowly building up the topsoil, this in turn goes through the
deeper layers of your soil. It may take a complete summer but you do not
want to put so much on that it kills your grass. -- Janice Murphy Comment
Answer #2: Clay Soil Problem. The previous answer is correct regarding the humus, but you should check the acidity/alkalinity of the soil before adding lime as it could already be alkaline. You can buy a pH test kit from your local garden centre. If it is more than slightly acid then you should add lime, if it is already alkaline then add sulphur.
Aeriate the soil by using a garden fork; using your body weight force the fork into the ground every few inches or so, this let the water drain away quicker and allow the organic matter to be pulled down into the soil. Feeding with organic fertilisers such as fish, bone and blood will speed up the absorption of the compost or humus.
Of the measures I have advocated, the adding humus is the really important one, but you will have to be patient as it takes several years to improve your topsoil.
For really marshy areas you can also add broken up walnut husks or pistachio shells -- Ed qznaz Comment